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1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
4 *
5 * Copyright IBM Corporation, 2008
6 *
7 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
8 * Manfred Spraul <manfred@colorfullife.com>
9 * Paul E. McKenney <paulmck@linux.ibm.com>
10 *
11 * Based on the original work by Paul McKenney <paulmck@linux.ibm.com>
12 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
13 *
14 * For detailed explanation of Read-Copy Update mechanism see -
15 * Documentation/RCU
16 */
17
18#define pr_fmt(fmt) "rcu: " fmt
19
20#include <linux/types.h>
21#include <linux/kernel.h>
22#include <linux/init.h>
23#include <linux/spinlock.h>
24#include <linux/smp.h>
25#include <linux/rcupdate_wait.h>
26#include <linux/interrupt.h>
27#include <linux/sched.h>
28#include <linux/sched/debug.h>
29#include <linux/nmi.h>
30#include <linux/atomic.h>
31#include <linux/bitops.h>
32#include <linux/export.h>
33#include <linux/completion.h>
34#include <linux/kmemleak.h>
35#include <linux/moduleparam.h>
36#include <linux/panic.h>
37#include <linux/panic_notifier.h>
38#include <linux/percpu.h>
39#include <linux/notifier.h>
40#include <linux/cpu.h>
41#include <linux/mutex.h>
42#include <linux/time.h>
43#include <linux/kernel_stat.h>
44#include <linux/wait.h>
45#include <linux/kthread.h>
46#include <uapi/linux/sched/types.h>
47#include <linux/prefetch.h>
48#include <linux/delay.h>
49#include <linux/random.h>
50#include <linux/trace_events.h>
51#include <linux/suspend.h>
52#include <linux/ftrace.h>
53#include <linux/tick.h>
54#include <linux/sysrq.h>
55#include <linux/kprobes.h>
56#include <linux/gfp.h>
57#include <linux/oom.h>
58#include <linux/smpboot.h>
59#include <linux/jiffies.h>
60#include <linux/slab.h>
61#include <linux/sched/isolation.h>
62#include <linux/sched/clock.h>
63#include <linux/vmalloc.h>
64#include <linux/mm.h>
65#include <linux/kasan.h>
66#include <linux/context_tracking.h>
67#include "../time/tick-internal.h"
68
69#include "tree.h"
70#include "rcu.h"
71
72#ifdef MODULE_PARAM_PREFIX
73#undef MODULE_PARAM_PREFIX
74#endif
75#define MODULE_PARAM_PREFIX "rcutree."
76
77/* Data structures. */
78
79static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
80 .gpwrap = true,
81#ifdef CONFIG_RCU_NOCB_CPU
82 .cblist.flags = SEGCBLIST_RCU_CORE,
83#endif
84};
85static struct rcu_state rcu_state = {
86 .level = { &rcu_state.node[0] },
87 .gp_state = RCU_GP_IDLE,
88 .gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT,
89 .barrier_mutex = __MUTEX_INITIALIZER(rcu_state.barrier_mutex),
90 .barrier_lock = __RAW_SPIN_LOCK_UNLOCKED(rcu_state.barrier_lock),
91 .name = RCU_NAME,
92 .abbr = RCU_ABBR,
93 .exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex),
94 .exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex),
95 .ofl_lock = __ARCH_SPIN_LOCK_UNLOCKED,
96};
97
98/* Dump rcu_node combining tree at boot to verify correct setup. */
99static bool dump_tree;
100module_param(dump_tree, bool, 0444);
101/* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */
102static bool use_softirq = !IS_ENABLED(CONFIG_PREEMPT_RT);
103#ifndef CONFIG_PREEMPT_RT
104module_param(use_softirq, bool, 0444);
105#endif
106/* Control rcu_node-tree auto-balancing at boot time. */
107static bool rcu_fanout_exact;
108module_param(rcu_fanout_exact, bool, 0444);
109/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
110static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
111module_param(rcu_fanout_leaf, int, 0444);
112int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
113/* Number of rcu_nodes at specified level. */
114int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
115int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
116
117/*
118 * The rcu_scheduler_active variable is initialized to the value
119 * RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the
120 * first task is spawned. So when this variable is RCU_SCHEDULER_INACTIVE,
121 * RCU can assume that there is but one task, allowing RCU to (for example)
122 * optimize synchronize_rcu() to a simple barrier(). When this variable
123 * is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required
124 * to detect real grace periods. This variable is also used to suppress
125 * boot-time false positives from lockdep-RCU error checking. Finally, it
126 * transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU
127 * is fully initialized, including all of its kthreads having been spawned.
128 */
129int rcu_scheduler_active __read_mostly;
130EXPORT_SYMBOL_GPL(rcu_scheduler_active);
131
132/*
133 * The rcu_scheduler_fully_active variable transitions from zero to one
134 * during the early_initcall() processing, which is after the scheduler
135 * is capable of creating new tasks. So RCU processing (for example,
136 * creating tasks for RCU priority boosting) must be delayed until after
137 * rcu_scheduler_fully_active transitions from zero to one. We also
138 * currently delay invocation of any RCU callbacks until after this point.
139 *
140 * It might later prove better for people registering RCU callbacks during
141 * early boot to take responsibility for these callbacks, but one step at
142 * a time.
143 */
144static int rcu_scheduler_fully_active __read_mostly;
145
146static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
147 unsigned long gps, unsigned long flags);
148static struct task_struct *rcu_boost_task(struct rcu_node *rnp);
149static void invoke_rcu_core(void);
150static void rcu_report_exp_rdp(struct rcu_data *rdp);
151static void sync_sched_exp_online_cleanup(int cpu);
152static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp);
153static bool rcu_rdp_is_offloaded(struct rcu_data *rdp);
154static bool rcu_rdp_cpu_online(struct rcu_data *rdp);
155static bool rcu_init_invoked(void);
156static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
157static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
158
159/*
160 * rcuc/rcub/rcuop kthread realtime priority. The "rcuop"
161 * real-time priority(enabling/disabling) is controlled by
162 * the extra CONFIG_RCU_NOCB_CPU_CB_BOOST configuration.
163 */
164static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
165module_param(kthread_prio, int, 0444);
166
167/* Delay in jiffies for grace-period initialization delays, debug only. */
168
169static int gp_preinit_delay;
170module_param(gp_preinit_delay, int, 0444);
171static int gp_init_delay;
172module_param(gp_init_delay, int, 0444);
173static int gp_cleanup_delay;
174module_param(gp_cleanup_delay, int, 0444);
175
176// Add delay to rcu_read_unlock() for strict grace periods.
177static int rcu_unlock_delay;
178#ifdef CONFIG_RCU_STRICT_GRACE_PERIOD
179module_param(rcu_unlock_delay, int, 0444);
180#endif
181
182/*
183 * This rcu parameter is runtime-read-only. It reflects
184 * a minimum allowed number of objects which can be cached
185 * per-CPU. Object size is equal to one page. This value
186 * can be changed at boot time.
187 */
188static int rcu_min_cached_objs = 5;
189module_param(rcu_min_cached_objs, int, 0444);
190
191// A page shrinker can ask for pages to be freed to make them
192// available for other parts of the system. This usually happens
193// under low memory conditions, and in that case we should also
194// defer page-cache filling for a short time period.
195//
196// The default value is 5 seconds, which is long enough to reduce
197// interference with the shrinker while it asks other systems to
198// drain their caches.
199static int rcu_delay_page_cache_fill_msec = 5000;
200module_param(rcu_delay_page_cache_fill_msec, int, 0444);
201
202/* Retrieve RCU kthreads priority for rcutorture */
203int rcu_get_gp_kthreads_prio(void)
204{
205 return kthread_prio;
206}
207EXPORT_SYMBOL_GPL(rcu_get_gp_kthreads_prio);
208
209/*
210 * Number of grace periods between delays, normalized by the duration of
211 * the delay. The longer the delay, the more the grace periods between
212 * each delay. The reason for this normalization is that it means that,
213 * for non-zero delays, the overall slowdown of grace periods is constant
214 * regardless of the duration of the delay. This arrangement balances
215 * the need for long delays to increase some race probabilities with the
216 * need for fast grace periods to increase other race probabilities.
217 */
218#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays for debugging. */
219
220/*
221 * Return true if an RCU grace period is in progress. The READ_ONCE()s
222 * permit this function to be invoked without holding the root rcu_node
223 * structure's ->lock, but of course results can be subject to change.
224 */
225static int rcu_gp_in_progress(void)
226{
227 return rcu_seq_state(rcu_seq_current(&rcu_state.gp_seq));
228}
229
230/*
231 * Return the number of callbacks queued on the specified CPU.
232 * Handles both the nocbs and normal cases.
233 */
234static long rcu_get_n_cbs_cpu(int cpu)
235{
236 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
237
238 if (rcu_segcblist_is_enabled(&rdp->cblist))
239 return rcu_segcblist_n_cbs(&rdp->cblist);
240 return 0;
241}
242
243void rcu_softirq_qs(void)
244{
245 rcu_qs();
246 rcu_preempt_deferred_qs(current);
247 rcu_tasks_qs(current, false);
248}
249
250/*
251 * Reset the current CPU's ->dynticks counter to indicate that the
252 * newly onlined CPU is no longer in an extended quiescent state.
253 * This will either leave the counter unchanged, or increment it
254 * to the next non-quiescent value.
255 *
256 * The non-atomic test/increment sequence works because the upper bits
257 * of the ->dynticks counter are manipulated only by the corresponding CPU,
258 * or when the corresponding CPU is offline.
259 */
260static void rcu_dynticks_eqs_online(void)
261{
262 if (ct_dynticks() & RCU_DYNTICKS_IDX)
263 return;
264 ct_state_inc(RCU_DYNTICKS_IDX);
265}
266
267/*
268 * Snapshot the ->dynticks counter with full ordering so as to allow
269 * stable comparison of this counter with past and future snapshots.
270 */
271static int rcu_dynticks_snap(int cpu)
272{
273 smp_mb(); // Fundamental RCU ordering guarantee.
274 return ct_dynticks_cpu_acquire(cpu);
275}
276
277/*
278 * Return true if the snapshot returned from rcu_dynticks_snap()
279 * indicates that RCU is in an extended quiescent state.
280 */
281static bool rcu_dynticks_in_eqs(int snap)
282{
283 return !(snap & RCU_DYNTICKS_IDX);
284}
285
286/*
287 * Return true if the CPU corresponding to the specified rcu_data
288 * structure has spent some time in an extended quiescent state since
289 * rcu_dynticks_snap() returned the specified snapshot.
290 */
291static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap)
292{
293 return snap != rcu_dynticks_snap(rdp->cpu);
294}
295
296/*
297 * Return true if the referenced integer is zero while the specified
298 * CPU remains within a single extended quiescent state.
299 */
300bool rcu_dynticks_zero_in_eqs(int cpu, int *vp)
301{
302 int snap;
303
304 // If not quiescent, force back to earlier extended quiescent state.
305 snap = ct_dynticks_cpu(cpu) & ~RCU_DYNTICKS_IDX;
306 smp_rmb(); // Order ->dynticks and *vp reads.
307 if (READ_ONCE(*vp))
308 return false; // Non-zero, so report failure;
309 smp_rmb(); // Order *vp read and ->dynticks re-read.
310
311 // If still in the same extended quiescent state, we are good!
312 return snap == ct_dynticks_cpu(cpu);
313}
314
315/*
316 * Let the RCU core know that this CPU has gone through the scheduler,
317 * which is a quiescent state. This is called when the need for a
318 * quiescent state is urgent, so we burn an atomic operation and full
319 * memory barriers to let the RCU core know about it, regardless of what
320 * this CPU might (or might not) do in the near future.
321 *
322 * We inform the RCU core by emulating a zero-duration dyntick-idle period.
323 *
324 * The caller must have disabled interrupts and must not be idle.
325 */
326notrace void rcu_momentary_dyntick_idle(void)
327{
328 int seq;
329
330 raw_cpu_write(rcu_data.rcu_need_heavy_qs, false);
331 seq = ct_state_inc(2 * RCU_DYNTICKS_IDX);
332 /* It is illegal to call this from idle state. */
333 WARN_ON_ONCE(!(seq & RCU_DYNTICKS_IDX));
334 rcu_preempt_deferred_qs(current);
335}
336EXPORT_SYMBOL_GPL(rcu_momentary_dyntick_idle);
337
338/**
339 * rcu_is_cpu_rrupt_from_idle - see if 'interrupted' from idle
340 *
341 * If the current CPU is idle and running at a first-level (not nested)
342 * interrupt, or directly, from idle, return true.
343 *
344 * The caller must have at least disabled IRQs.
345 */
346static int rcu_is_cpu_rrupt_from_idle(void)
347{
348 long nesting;
349
350 /*
351 * Usually called from the tick; but also used from smp_function_call()
352 * for expedited grace periods. This latter can result in running from
353 * the idle task, instead of an actual IPI.
354 */
355 lockdep_assert_irqs_disabled();
356
357 /* Check for counter underflows */
358 RCU_LOCKDEP_WARN(ct_dynticks_nesting() < 0,
359 "RCU dynticks_nesting counter underflow!");
360 RCU_LOCKDEP_WARN(ct_dynticks_nmi_nesting() <= 0,
361 "RCU dynticks_nmi_nesting counter underflow/zero!");
362
363 /* Are we at first interrupt nesting level? */
364 nesting = ct_dynticks_nmi_nesting();
365 if (nesting > 1)
366 return false;
367
368 /*
369 * If we're not in an interrupt, we must be in the idle task!
370 */
371 WARN_ON_ONCE(!nesting && !is_idle_task(current));
372
373 /* Does CPU appear to be idle from an RCU standpoint? */
374 return ct_dynticks_nesting() == 0;
375}
376
377#define DEFAULT_RCU_BLIMIT (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 1000 : 10)
378 // Maximum callbacks per rcu_do_batch ...
379#define DEFAULT_MAX_RCU_BLIMIT 10000 // ... even during callback flood.
380static long blimit = DEFAULT_RCU_BLIMIT;
381#define DEFAULT_RCU_QHIMARK 10000 // If this many pending, ignore blimit.
382static long qhimark = DEFAULT_RCU_QHIMARK;
383#define DEFAULT_RCU_QLOMARK 100 // Once only this many pending, use blimit.
384static long qlowmark = DEFAULT_RCU_QLOMARK;
385#define DEFAULT_RCU_QOVLD_MULT 2
386#define DEFAULT_RCU_QOVLD (DEFAULT_RCU_QOVLD_MULT * DEFAULT_RCU_QHIMARK)
387static long qovld = DEFAULT_RCU_QOVLD; // If this many pending, hammer QS.
388static long qovld_calc = -1; // No pre-initialization lock acquisitions!
389
390module_param(blimit, long, 0444);
391module_param(qhimark, long, 0444);
392module_param(qlowmark, long, 0444);
393module_param(qovld, long, 0444);
394
395static ulong jiffies_till_first_fqs = IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 0 : ULONG_MAX;
396static ulong jiffies_till_next_fqs = ULONG_MAX;
397static bool rcu_kick_kthreads;
398static int rcu_divisor = 7;
399module_param(rcu_divisor, int, 0644);
400
401/* Force an exit from rcu_do_batch() after 3 milliseconds. */
402static long rcu_resched_ns = 3 * NSEC_PER_MSEC;
403module_param(rcu_resched_ns, long, 0644);
404
405/*
406 * How long the grace period must be before we start recruiting
407 * quiescent-state help from rcu_note_context_switch().
408 */
409static ulong jiffies_till_sched_qs = ULONG_MAX;
410module_param(jiffies_till_sched_qs, ulong, 0444);
411static ulong jiffies_to_sched_qs; /* See adjust_jiffies_till_sched_qs(). */
412module_param(jiffies_to_sched_qs, ulong, 0444); /* Display only! */
413
414/*
415 * Make sure that we give the grace-period kthread time to detect any
416 * idle CPUs before taking active measures to force quiescent states.
417 * However, don't go below 100 milliseconds, adjusted upwards for really
418 * large systems.
419 */
420static void adjust_jiffies_till_sched_qs(void)
421{
422 unsigned long j;
423
424 /* If jiffies_till_sched_qs was specified, respect the request. */
425 if (jiffies_till_sched_qs != ULONG_MAX) {
426 WRITE_ONCE(jiffies_to_sched_qs, jiffies_till_sched_qs);
427 return;
428 }
429 /* Otherwise, set to third fqs scan, but bound below on large system. */
430 j = READ_ONCE(jiffies_till_first_fqs) +
431 2 * READ_ONCE(jiffies_till_next_fqs);
432 if (j < HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV)
433 j = HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
434 pr_info("RCU calculated value of scheduler-enlistment delay is %ld jiffies.\n", j);
435 WRITE_ONCE(jiffies_to_sched_qs, j);
436}
437
438static int param_set_first_fqs_jiffies(const char *val, const struct kernel_param *kp)
439{
440 ulong j;
441 int ret = kstrtoul(val, 0, &j);
442
443 if (!ret) {
444 WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : j);
445 adjust_jiffies_till_sched_qs();
446 }
447 return ret;
448}
449
450static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param *kp)
451{
452 ulong j;
453 int ret = kstrtoul(val, 0, &j);
454
455 if (!ret) {
456 WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : (j ?: 1));
457 adjust_jiffies_till_sched_qs();
458 }
459 return ret;
460}
461
462static const struct kernel_param_ops first_fqs_jiffies_ops = {
463 .set = param_set_first_fqs_jiffies,
464 .get = param_get_ulong,
465};
466
467static const struct kernel_param_ops next_fqs_jiffies_ops = {
468 .set = param_set_next_fqs_jiffies,
469 .get = param_get_ulong,
470};
471
472module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, &jiffies_till_first_fqs, 0644);
473module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next_fqs, 0644);
474module_param(rcu_kick_kthreads, bool, 0644);
475
476static void force_qs_rnp(int (*f)(struct rcu_data *rdp));
477static int rcu_pending(int user);
478
479/*
480 * Return the number of RCU GPs completed thus far for debug & stats.
481 */
482unsigned long rcu_get_gp_seq(void)
483{
484 return READ_ONCE(rcu_state.gp_seq);
485}
486EXPORT_SYMBOL_GPL(rcu_get_gp_seq);
487
488/*
489 * Return the number of RCU expedited batches completed thus far for
490 * debug & stats. Odd numbers mean that a batch is in progress, even
491 * numbers mean idle. The value returned will thus be roughly double
492 * the cumulative batches since boot.
493 */
494unsigned long rcu_exp_batches_completed(void)
495{
496 return rcu_state.expedited_sequence;
497}
498EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
499
500/*
501 * Return the root node of the rcu_state structure.
502 */
503static struct rcu_node *rcu_get_root(void)
504{
505 return &rcu_state.node[0];
506}
507
508/*
509 * Send along grace-period-related data for rcutorture diagnostics.
510 */
511void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
512 unsigned long *gp_seq)
513{
514 switch (test_type) {
515 case RCU_FLAVOR:
516 *flags = READ_ONCE(rcu_state.gp_flags);
517 *gp_seq = rcu_seq_current(&rcu_state.gp_seq);
518 break;
519 default:
520 break;
521 }
522}
523EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
524
525#if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK))
526/*
527 * An empty function that will trigger a reschedule on
528 * IRQ tail once IRQs get re-enabled on userspace/guest resume.
529 */
530static void late_wakeup_func(struct irq_work *work)
531{
532}
533
534static DEFINE_PER_CPU(struct irq_work, late_wakeup_work) =
535 IRQ_WORK_INIT(late_wakeup_func);
536
537/*
538 * If either:
539 *
540 * 1) the task is about to enter in guest mode and $ARCH doesn't support KVM generic work
541 * 2) the task is about to enter in user mode and $ARCH doesn't support generic entry.
542 *
543 * In these cases the late RCU wake ups aren't supported in the resched loops and our
544 * last resort is to fire a local irq_work that will trigger a reschedule once IRQs
545 * get re-enabled again.
546 */
547noinstr void rcu_irq_work_resched(void)
548{
549 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
550
551 if (IS_ENABLED(CONFIG_GENERIC_ENTRY) && !(current->flags & PF_VCPU))
552 return;
553
554 if (IS_ENABLED(CONFIG_KVM_XFER_TO_GUEST_WORK) && (current->flags & PF_VCPU))
555 return;
556
557 instrumentation_begin();
558 if (do_nocb_deferred_wakeup(rdp) && need_resched()) {
559 irq_work_queue(this_cpu_ptr(&late_wakeup_work));
560 }
561 instrumentation_end();
562}
563#endif /* #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK)) */
564
565#ifdef CONFIG_PROVE_RCU
566/**
567 * rcu_irq_exit_check_preempt - Validate that scheduling is possible
568 */
569void rcu_irq_exit_check_preempt(void)
570{
571 lockdep_assert_irqs_disabled();
572
573 RCU_LOCKDEP_WARN(ct_dynticks_nesting() <= 0,
574 "RCU dynticks_nesting counter underflow/zero!");
575 RCU_LOCKDEP_WARN(ct_dynticks_nmi_nesting() !=
576 DYNTICK_IRQ_NONIDLE,
577 "Bad RCU dynticks_nmi_nesting counter\n");
578 RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),
579 "RCU in extended quiescent state!");
580}
581#endif /* #ifdef CONFIG_PROVE_RCU */
582
583#ifdef CONFIG_NO_HZ_FULL
584/**
585 * __rcu_irq_enter_check_tick - Enable scheduler tick on CPU if RCU needs it.
586 *
587 * The scheduler tick is not normally enabled when CPUs enter the kernel
588 * from nohz_full userspace execution. After all, nohz_full userspace
589 * execution is an RCU quiescent state and the time executing in the kernel
590 * is quite short. Except of course when it isn't. And it is not hard to
591 * cause a large system to spend tens of seconds or even minutes looping
592 * in the kernel, which can cause a number of problems, include RCU CPU
593 * stall warnings.
594 *
595 * Therefore, if a nohz_full CPU fails to report a quiescent state
596 * in a timely manner, the RCU grace-period kthread sets that CPU's
597 * ->rcu_urgent_qs flag with the expectation that the next interrupt or
598 * exception will invoke this function, which will turn on the scheduler
599 * tick, which will enable RCU to detect that CPU's quiescent states,
600 * for example, due to cond_resched() calls in CONFIG_PREEMPT=n kernels.
601 * The tick will be disabled once a quiescent state is reported for
602 * this CPU.
603 *
604 * Of course, in carefully tuned systems, there might never be an
605 * interrupt or exception. In that case, the RCU grace-period kthread
606 * will eventually cause one to happen. However, in less carefully
607 * controlled environments, this function allows RCU to get what it
608 * needs without creating otherwise useless interruptions.
609 */
610void __rcu_irq_enter_check_tick(void)
611{
612 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
613
614 // If we're here from NMI there's nothing to do.
615 if (in_nmi())
616 return;
617
618 RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),
619 "Illegal rcu_irq_enter_check_tick() from extended quiescent state");
620
621 if (!tick_nohz_full_cpu(rdp->cpu) ||
622 !READ_ONCE(rdp->rcu_urgent_qs) ||
623 READ_ONCE(rdp->rcu_forced_tick)) {
624 // RCU doesn't need nohz_full help from this CPU, or it is
625 // already getting that help.
626 return;
627 }
628
629 // We get here only when not in an extended quiescent state and
630 // from interrupts (as opposed to NMIs). Therefore, (1) RCU is
631 // already watching and (2) The fact that we are in an interrupt
632 // handler and that the rcu_node lock is an irq-disabled lock
633 // prevents self-deadlock. So we can safely recheck under the lock.
634 // Note that the nohz_full state currently cannot change.
635 raw_spin_lock_rcu_node(rdp->mynode);
636 if (READ_ONCE(rdp->rcu_urgent_qs) && !rdp->rcu_forced_tick) {
637 // A nohz_full CPU is in the kernel and RCU needs a
638 // quiescent state. Turn on the tick!
639 WRITE_ONCE(rdp->rcu_forced_tick, true);
640 tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
641 }
642 raw_spin_unlock_rcu_node(rdp->mynode);
643}
644NOKPROBE_SYMBOL(__rcu_irq_enter_check_tick);
645#endif /* CONFIG_NO_HZ_FULL */
646
647/*
648 * Check to see if any future non-offloaded RCU-related work will need
649 * to be done by the current CPU, even if none need be done immediately,
650 * returning 1 if so. This function is part of the RCU implementation;
651 * it is -not- an exported member of the RCU API. This is used by
652 * the idle-entry code to figure out whether it is safe to disable the
653 * scheduler-clock interrupt.
654 *
655 * Just check whether or not this CPU has non-offloaded RCU callbacks
656 * queued.
657 */
658int rcu_needs_cpu(void)
659{
660 return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) &&
661 !rcu_rdp_is_offloaded(this_cpu_ptr(&rcu_data));
662}
663
664/*
665 * If any sort of urgency was applied to the current CPU (for example,
666 * the scheduler-clock interrupt was enabled on a nohz_full CPU) in order
667 * to get to a quiescent state, disable it.
668 */
669static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp)
670{
671 raw_lockdep_assert_held_rcu_node(rdp->mynode);
672 WRITE_ONCE(rdp->rcu_urgent_qs, false);
673 WRITE_ONCE(rdp->rcu_need_heavy_qs, false);
674 if (tick_nohz_full_cpu(rdp->cpu) && rdp->rcu_forced_tick) {
675 tick_dep_clear_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
676 WRITE_ONCE(rdp->rcu_forced_tick, false);
677 }
678}
679
680/**
681 * rcu_is_watching - RCU read-side critical sections permitted on current CPU?
682 *
683 * Return @true if RCU is watching the running CPU and @false otherwise.
684 * An @true return means that this CPU can safely enter RCU read-side
685 * critical sections.
686 *
687 * Although calls to rcu_is_watching() from most parts of the kernel
688 * will return @true, there are important exceptions. For example, if the
689 * current CPU is deep within its idle loop, in kernel entry/exit code,
690 * or offline, rcu_is_watching() will return @false.
691 *
692 * Make notrace because it can be called by the internal functions of
693 * ftrace, and making this notrace removes unnecessary recursion calls.
694 */
695notrace bool rcu_is_watching(void)
696{
697 bool ret;
698
699 preempt_disable_notrace();
700 ret = !rcu_dynticks_curr_cpu_in_eqs();
701 preempt_enable_notrace();
702 return ret;
703}
704EXPORT_SYMBOL_GPL(rcu_is_watching);
705
706/*
707 * If a holdout task is actually running, request an urgent quiescent
708 * state from its CPU. This is unsynchronized, so migrations can cause
709 * the request to go to the wrong CPU. Which is OK, all that will happen
710 * is that the CPU's next context switch will be a bit slower and next
711 * time around this task will generate another request.
712 */
713void rcu_request_urgent_qs_task(struct task_struct *t)
714{
715 int cpu;
716
717 barrier();
718 cpu = task_cpu(t);
719 if (!task_curr(t))
720 return; /* This task is not running on that CPU. */
721 smp_store_release(per_cpu_ptr(&rcu_data.rcu_urgent_qs, cpu), true);
722}
723
724/*
725 * When trying to report a quiescent state on behalf of some other CPU,
726 * it is our responsibility to check for and handle potential overflow
727 * of the rcu_node ->gp_seq counter with respect to the rcu_data counters.
728 * After all, the CPU might be in deep idle state, and thus executing no
729 * code whatsoever.
730 */
731static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
732{
733 raw_lockdep_assert_held_rcu_node(rnp);
734 if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + ULONG_MAX / 4,
735 rnp->gp_seq))
736 WRITE_ONCE(rdp->gpwrap, true);
737 if (ULONG_CMP_LT(rdp->rcu_iw_gp_seq + ULONG_MAX / 4, rnp->gp_seq))
738 rdp->rcu_iw_gp_seq = rnp->gp_seq + ULONG_MAX / 4;
739}
740
741/*
742 * Snapshot the specified CPU's dynticks counter so that we can later
743 * credit them with an implicit quiescent state. Return 1 if this CPU
744 * is in dynticks idle mode, which is an extended quiescent state.
745 */
746static int dyntick_save_progress_counter(struct rcu_data *rdp)
747{
748 rdp->dynticks_snap = rcu_dynticks_snap(rdp->cpu);
749 if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
750 trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
751 rcu_gpnum_ovf(rdp->mynode, rdp);
752 return 1;
753 }
754 return 0;
755}
756
757/*
758 * Returns positive if the specified CPU has passed through a quiescent state
759 * by virtue of being in or having passed through an dynticks idle state since
760 * the last call to dyntick_save_progress_counter() for this same CPU, or by
761 * virtue of having been offline.
762 *
763 * Returns negative if the specified CPU needs a force resched.
764 *
765 * Returns zero otherwise.
766 */
767static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
768{
769 unsigned long jtsq;
770 int ret = 0;
771 struct rcu_node *rnp = rdp->mynode;
772
773 /*
774 * If the CPU passed through or entered a dynticks idle phase with
775 * no active irq/NMI handlers, then we can safely pretend that the CPU
776 * already acknowledged the request to pass through a quiescent
777 * state. Either way, that CPU cannot possibly be in an RCU
778 * read-side critical section that started before the beginning
779 * of the current RCU grace period.
780 */
781 if (rcu_dynticks_in_eqs_since(rdp, rdp->dynticks_snap)) {
782 trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
783 rcu_gpnum_ovf(rnp, rdp);
784 return 1;
785 }
786
787 /*
788 * Complain if a CPU that is considered to be offline from RCU's
789 * perspective has not yet reported a quiescent state. After all,
790 * the offline CPU should have reported a quiescent state during
791 * the CPU-offline process, or, failing that, by rcu_gp_init()
792 * if it ran concurrently with either the CPU going offline or the
793 * last task on a leaf rcu_node structure exiting its RCU read-side
794 * critical section while all CPUs corresponding to that structure
795 * are offline. This added warning detects bugs in any of these
796 * code paths.
797 *
798 * The rcu_node structure's ->lock is held here, which excludes
799 * the relevant portions the CPU-hotplug code, the grace-period
800 * initialization code, and the rcu_read_unlock() code paths.
801 *
802 * For more detail, please refer to the "Hotplug CPU" section
803 * of RCU's Requirements documentation.
804 */
805 if (WARN_ON_ONCE(!rcu_rdp_cpu_online(rdp))) {
806 struct rcu_node *rnp1;
807
808 pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
809 __func__, rnp->grplo, rnp->grphi, rnp->level,
810 (long)rnp->gp_seq, (long)rnp->completedqs);
811 for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
812 pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx ->rcu_gp_init_mask %#lx\n",
813 __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext, rnp1->rcu_gp_init_mask);
814 pr_info("%s %d: %c online: %ld(%d) offline: %ld(%d)\n",
815 __func__, rdp->cpu, ".o"[rcu_rdp_cpu_online(rdp)],
816 (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
817 (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
818 return 1; /* Break things loose after complaining. */
819 }
820
821 /*
822 * A CPU running for an extended time within the kernel can
823 * delay RCU grace periods: (1) At age jiffies_to_sched_qs,
824 * set .rcu_urgent_qs, (2) At age 2*jiffies_to_sched_qs, set
825 * both .rcu_need_heavy_qs and .rcu_urgent_qs. Note that the
826 * unsynchronized assignments to the per-CPU rcu_need_heavy_qs
827 * variable are safe because the assignments are repeated if this
828 * CPU failed to pass through a quiescent state. This code
829 * also checks .jiffies_resched in case jiffies_to_sched_qs
830 * is set way high.
831 */
832 jtsq = READ_ONCE(jiffies_to_sched_qs);
833 if (!READ_ONCE(rdp->rcu_need_heavy_qs) &&
834 (time_after(jiffies, rcu_state.gp_start + jtsq * 2) ||
835 time_after(jiffies, rcu_state.jiffies_resched) ||
836 rcu_state.cbovld)) {
837 WRITE_ONCE(rdp->rcu_need_heavy_qs, true);
838 /* Store rcu_need_heavy_qs before rcu_urgent_qs. */
839 smp_store_release(&rdp->rcu_urgent_qs, true);
840 } else if (time_after(jiffies, rcu_state.gp_start + jtsq)) {
841 WRITE_ONCE(rdp->rcu_urgent_qs, true);
842 }
843
844 /*
845 * NO_HZ_FULL CPUs can run in-kernel without rcu_sched_clock_irq!
846 * The above code handles this, but only for straight cond_resched().
847 * And some in-kernel loops check need_resched() before calling
848 * cond_resched(), which defeats the above code for CPUs that are
849 * running in-kernel with scheduling-clock interrupts disabled.
850 * So hit them over the head with the resched_cpu() hammer!
851 */
852 if (tick_nohz_full_cpu(rdp->cpu) &&
853 (time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq * 3) ||
854 rcu_state.cbovld)) {
855 WRITE_ONCE(rdp->rcu_urgent_qs, true);
856 WRITE_ONCE(rdp->last_fqs_resched, jiffies);
857 ret = -1;
858 }
859
860 /*
861 * If more than halfway to RCU CPU stall-warning time, invoke
862 * resched_cpu() more frequently to try to loosen things up a bit.
863 * Also check to see if the CPU is getting hammered with interrupts,
864 * but only once per grace period, just to keep the IPIs down to
865 * a dull roar.
866 */
867 if (time_after(jiffies, rcu_state.jiffies_resched)) {
868 if (time_after(jiffies,
869 READ_ONCE(rdp->last_fqs_resched) + jtsq)) {
870 WRITE_ONCE(rdp->last_fqs_resched, jiffies);
871 ret = -1;
872 }
873 if (IS_ENABLED(CONFIG_IRQ_WORK) &&
874 !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
875 (rnp->ffmask & rdp->grpmask)) {
876 rdp->rcu_iw_pending = true;
877 rdp->rcu_iw_gp_seq = rnp->gp_seq;
878 irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
879 }
880
881 if (rcu_cpu_stall_cputime && rdp->snap_record.gp_seq != rdp->gp_seq) {
882 int cpu = rdp->cpu;
883 struct rcu_snap_record *rsrp;
884 struct kernel_cpustat *kcsp;
885
886 kcsp = &kcpustat_cpu(cpu);
887
888 rsrp = &rdp->snap_record;
889 rsrp->cputime_irq = kcpustat_field(kcsp, CPUTIME_IRQ, cpu);
890 rsrp->cputime_softirq = kcpustat_field(kcsp, CPUTIME_SOFTIRQ, cpu);
891 rsrp->cputime_system = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu);
892 rsrp->nr_hardirqs = kstat_cpu_irqs_sum(rdp->cpu);
893 rsrp->nr_softirqs = kstat_cpu_softirqs_sum(rdp->cpu);
894 rsrp->nr_csw = nr_context_switches_cpu(rdp->cpu);
895 rsrp->jiffies = jiffies;
896 rsrp->gp_seq = rdp->gp_seq;
897 }
898 }
899
900 return ret;
901}
902
903/* Trace-event wrapper function for trace_rcu_future_grace_period. */
904static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
905 unsigned long gp_seq_req, const char *s)
906{
907 trace_rcu_future_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
908 gp_seq_req, rnp->level,
909 rnp->grplo, rnp->grphi, s);
910}
911
912/*
913 * rcu_start_this_gp - Request the start of a particular grace period
914 * @rnp_start: The leaf node of the CPU from which to start.
915 * @rdp: The rcu_data corresponding to the CPU from which to start.
916 * @gp_seq_req: The gp_seq of the grace period to start.
917 *
918 * Start the specified grace period, as needed to handle newly arrived
919 * callbacks. The required future grace periods are recorded in each
920 * rcu_node structure's ->gp_seq_needed field. Returns true if there
921 * is reason to awaken the grace-period kthread.
922 *
923 * The caller must hold the specified rcu_node structure's ->lock, which
924 * is why the caller is responsible for waking the grace-period kthread.
925 *
926 * Returns true if the GP thread needs to be awakened else false.
927 */
928static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
929 unsigned long gp_seq_req)
930{
931 bool ret = false;
932 struct rcu_node *rnp;
933
934 /*
935 * Use funnel locking to either acquire the root rcu_node
936 * structure's lock or bail out if the need for this grace period
937 * has already been recorded -- or if that grace period has in
938 * fact already started. If there is already a grace period in
939 * progress in a non-leaf node, no recording is needed because the
940 * end of the grace period will scan the leaf rcu_node structures.
941 * Note that rnp_start->lock must not be released.
942 */
943 raw_lockdep_assert_held_rcu_node(rnp_start);
944 trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startleaf"));
945 for (rnp = rnp_start; 1; rnp = rnp->parent) {
946 if (rnp != rnp_start)
947 raw_spin_lock_rcu_node(rnp);
948 if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req) ||
949 rcu_seq_started(&rnp->gp_seq, gp_seq_req) ||
950 (rnp != rnp_start &&
951 rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))) {
952 trace_rcu_this_gp(rnp, rdp, gp_seq_req,
953 TPS("Prestarted"));
954 goto unlock_out;
955 }
956 WRITE_ONCE(rnp->gp_seq_needed, gp_seq_req);
957 if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) {
958 /*
959 * We just marked the leaf or internal node, and a
960 * grace period is in progress, which means that
961 * rcu_gp_cleanup() will see the marking. Bail to
962 * reduce contention.
963 */
964 trace_rcu_this_gp(rnp_start, rdp, gp_seq_req,
965 TPS("Startedleaf"));
966 goto unlock_out;
967 }
968 if (rnp != rnp_start && rnp->parent != NULL)
969 raw_spin_unlock_rcu_node(rnp);
970 if (!rnp->parent)
971 break; /* At root, and perhaps also leaf. */
972 }
973
974 /* If GP already in progress, just leave, otherwise start one. */
975 if (rcu_gp_in_progress()) {
976 trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedleafroot"));
977 goto unlock_out;
978 }
979 trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
980 WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
981 WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
982 if (!READ_ONCE(rcu_state.gp_kthread)) {
983 trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
984 goto unlock_out;
985 }
986 trace_rcu_grace_period(rcu_state.name, data_race(rcu_state.gp_seq), TPS("newreq"));
987 ret = true; /* Caller must wake GP kthread. */
988unlock_out:
989 /* Push furthest requested GP to leaf node and rcu_data structure. */
990 if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) {
991 WRITE_ONCE(rnp_start->gp_seq_needed, rnp->gp_seq_needed);
992 WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
993 }
994 if (rnp != rnp_start)
995 raw_spin_unlock_rcu_node(rnp);
996 return ret;
997}
998
999/*
1000 * Clean up any old requests for the just-ended grace period. Also return
1001 * whether any additional grace periods have been requested.
1002 */
1003static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
1004{
1005 bool needmore;
1006 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1007
1008 needmore = ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed);
1009 if (!needmore)
1010 rnp->gp_seq_needed = rnp->gp_seq; /* Avoid counter wrap. */
1011 trace_rcu_this_gp(rnp, rdp, rnp->gp_seq,
1012 needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1013 return needmore;
1014}
1015
1016static void swake_up_one_online_ipi(void *arg)
1017{
1018 struct swait_queue_head *wqh = arg;
1019
1020 swake_up_one(wqh);
1021}
1022
1023static void swake_up_one_online(struct swait_queue_head *wqh)
1024{
1025 int cpu = get_cpu();
1026
1027 /*
1028 * If called from rcutree_report_cpu_starting(), wake up
1029 * is dangerous that late in the CPU-down hotplug process. The
1030 * scheduler might queue an ignored hrtimer. Defer the wake up
1031 * to an online CPU instead.
1032 */
1033 if (unlikely(cpu_is_offline(cpu))) {
1034 int target;
1035
1036 target = cpumask_any_and(housekeeping_cpumask(HK_TYPE_RCU),
1037 cpu_online_mask);
1038
1039 smp_call_function_single(target, swake_up_one_online_ipi,
1040 wqh, 0);
1041 put_cpu();
1042 } else {
1043 put_cpu();
1044 swake_up_one(wqh);
1045 }
1046}
1047
1048/*
1049 * Awaken the grace-period kthread. Don't do a self-awaken (unless in an
1050 * interrupt or softirq handler, in which case we just might immediately
1051 * sleep upon return, resulting in a grace-period hang), and don't bother
1052 * awakening when there is nothing for the grace-period kthread to do
1053 * (as in several CPUs raced to awaken, we lost), and finally don't try
1054 * to awaken a kthread that has not yet been created. If all those checks
1055 * are passed, track some debug information and awaken.
1056 *
1057 * So why do the self-wakeup when in an interrupt or softirq handler
1058 * in the grace-period kthread's context? Because the kthread might have
1059 * been interrupted just as it was going to sleep, and just after the final
1060 * pre-sleep check of the awaken condition. In this case, a wakeup really
1061 * is required, and is therefore supplied.
1062 */
1063static void rcu_gp_kthread_wake(void)
1064{
1065 struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
1066
1067 if ((current == t && !in_hardirq() && !in_serving_softirq()) ||
1068 !READ_ONCE(rcu_state.gp_flags) || !t)
1069 return;
1070 WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
1071 WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
1072 swake_up_one_online(&rcu_state.gp_wq);
1073}
1074
1075/*
1076 * If there is room, assign a ->gp_seq number to any callbacks on this
1077 * CPU that have not already been assigned. Also accelerate any callbacks
1078 * that were previously assigned a ->gp_seq number that has since proven
1079 * to be too conservative, which can happen if callbacks get assigned a
1080 * ->gp_seq number while RCU is idle, but with reference to a non-root
1081 * rcu_node structure. This function is idempotent, so it does not hurt
1082 * to call it repeatedly. Returns an flag saying that we should awaken
1083 * the RCU grace-period kthread.
1084 *
1085 * The caller must hold rnp->lock with interrupts disabled.
1086 */
1087static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
1088{
1089 unsigned long gp_seq_req;
1090 bool ret = false;
1091
1092 rcu_lockdep_assert_cblist_protected(rdp);
1093 raw_lockdep_assert_held_rcu_node(rnp);
1094
1095 /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
1096 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1097 return false;
1098
1099 trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPreAcc"));
1100
1101 /*
1102 * Callbacks are often registered with incomplete grace-period
1103 * information. Something about the fact that getting exact
1104 * information requires acquiring a global lock... RCU therefore
1105 * makes a conservative estimate of the grace period number at which
1106 * a given callback will become ready to invoke. The following
1107 * code checks this estimate and improves it when possible, thus
1108 * accelerating callback invocation to an earlier grace-period
1109 * number.
1110 */
1111 gp_seq_req = rcu_seq_snap(&rcu_state.gp_seq);
1112 if (rcu_segcblist_accelerate(&rdp->cblist, gp_seq_req))
1113 ret = rcu_start_this_gp(rnp, rdp, gp_seq_req);
1114
1115 /* Trace depending on how much we were able to accelerate. */
1116 if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
1117 trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccWaitCB"));
1118 else
1119 trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccReadyCB"));
1120
1121 trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPostAcc"));
1122
1123 return ret;
1124}
1125
1126/*
1127 * Similar to rcu_accelerate_cbs(), but does not require that the leaf
1128 * rcu_node structure's ->lock be held. It consults the cached value
1129 * of ->gp_seq_needed in the rcu_data structure, and if that indicates
1130 * that a new grace-period request be made, invokes rcu_accelerate_cbs()
1131 * while holding the leaf rcu_node structure's ->lock.
1132 */
1133static void rcu_accelerate_cbs_unlocked(struct rcu_node *rnp,
1134 struct rcu_data *rdp)
1135{
1136 unsigned long c;
1137 bool needwake;
1138
1139 rcu_lockdep_assert_cblist_protected(rdp);
1140 c = rcu_seq_snap(&rcu_state.gp_seq);
1141 if (!READ_ONCE(rdp->gpwrap) && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {
1142 /* Old request still live, so mark recent callbacks. */
1143 (void)rcu_segcblist_accelerate(&rdp->cblist, c);
1144 return;
1145 }
1146 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
1147 needwake = rcu_accelerate_cbs(rnp, rdp);
1148 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
1149 if (needwake)
1150 rcu_gp_kthread_wake();
1151}
1152
1153/*
1154 * Move any callbacks whose grace period has completed to the
1155 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1156 * assign ->gp_seq numbers to any callbacks in the RCU_NEXT_TAIL
1157 * sublist. This function is idempotent, so it does not hurt to
1158 * invoke it repeatedly. As long as it is not invoked -too- often...
1159 * Returns true if the RCU grace-period kthread needs to be awakened.
1160 *
1161 * The caller must hold rnp->lock with interrupts disabled.
1162 */
1163static bool rcu_advance_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
1164{
1165 rcu_lockdep_assert_cblist_protected(rdp);
1166 raw_lockdep_assert_held_rcu_node(rnp);
1167
1168 /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
1169 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1170 return false;
1171
1172 /*
1173 * Find all callbacks whose ->gp_seq numbers indicate that they
1174 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1175 */
1176 rcu_segcblist_advance(&rdp->cblist, rnp->gp_seq);
1177
1178 /* Classify any remaining callbacks. */
1179 return rcu_accelerate_cbs(rnp, rdp);
1180}
1181
1182/*
1183 * Move and classify callbacks, but only if doing so won't require
1184 * that the RCU grace-period kthread be awakened.
1185 */
1186static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp,
1187 struct rcu_data *rdp)
1188{
1189 rcu_lockdep_assert_cblist_protected(rdp);
1190 if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) || !raw_spin_trylock_rcu_node(rnp))
1191 return;
1192 // The grace period cannot end while we hold the rcu_node lock.
1193 if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))
1194 WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp));
1195 raw_spin_unlock_rcu_node(rnp);
1196}
1197
1198/*
1199 * In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, attempt to generate a
1200 * quiescent state. This is intended to be invoked when the CPU notices
1201 * a new grace period.
1202 */
1203static void rcu_strict_gp_check_qs(void)
1204{
1205 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
1206 rcu_read_lock();
1207 rcu_read_unlock();
1208 }
1209}
1210
1211/*
1212 * Update CPU-local rcu_data state to record the beginnings and ends of
1213 * grace periods. The caller must hold the ->lock of the leaf rcu_node
1214 * structure corresponding to the current CPU, and must have irqs disabled.
1215 * Returns true if the grace-period kthread needs to be awakened.
1216 */
1217static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
1218{
1219 bool ret = false;
1220 bool need_qs;
1221 const bool offloaded = rcu_rdp_is_offloaded(rdp);
1222
1223 raw_lockdep_assert_held_rcu_node(rnp);
1224
1225 if (rdp->gp_seq == rnp->gp_seq)
1226 return false; /* Nothing to do. */
1227
1228 /* Handle the ends of any preceding grace periods first. */
1229 if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) ||
1230 unlikely(READ_ONCE(rdp->gpwrap))) {
1231 if (!offloaded)
1232 ret = rcu_advance_cbs(rnp, rdp); /* Advance CBs. */
1233 rdp->core_needs_qs = false;
1234 trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuend"));
1235 } else {
1236 if (!offloaded)
1237 ret = rcu_accelerate_cbs(rnp, rdp); /* Recent CBs. */
1238 if (rdp->core_needs_qs)
1239 rdp->core_needs_qs = !!(rnp->qsmask & rdp->grpmask);
1240 }
1241
1242 /* Now handle the beginnings of any new-to-this-CPU grace periods. */
1243 if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) ||
1244 unlikely(READ_ONCE(rdp->gpwrap))) {
1245 /*
1246 * If the current grace period is waiting for this CPU,
1247 * set up to detect a quiescent state, otherwise don't
1248 * go looking for one.
1249 */
1250 trace_rcu_grace_period(rcu_state.name, rnp->gp_seq, TPS("cpustart"));
1251 need_qs = !!(rnp->qsmask & rdp->grpmask);
1252 rdp->cpu_no_qs.b.norm = need_qs;
1253 rdp->core_needs_qs = need_qs;
1254 zero_cpu_stall_ticks(rdp);
1255 }
1256 rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */
1257 if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap)
1258 WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
1259 if (IS_ENABLED(CONFIG_PROVE_RCU) && READ_ONCE(rdp->gpwrap))
1260 WRITE_ONCE(rdp->last_sched_clock, jiffies);
1261 WRITE_ONCE(rdp->gpwrap, false);
1262 rcu_gpnum_ovf(rnp, rdp);
1263 return ret;
1264}
1265
1266static void note_gp_changes(struct rcu_data *rdp)
1267{
1268 unsigned long flags;
1269 bool needwake;
1270 struct rcu_node *rnp;
1271
1272 local_irq_save(flags);
1273 rnp = rdp->mynode;
1274 if ((rdp->gp_seq == rcu_seq_current(&rnp->gp_seq) &&
1275 !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
1276 !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
1277 local_irq_restore(flags);
1278 return;
1279 }
1280 needwake = __note_gp_changes(rnp, rdp);
1281 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1282 rcu_strict_gp_check_qs();
1283 if (needwake)
1284 rcu_gp_kthread_wake();
1285}
1286
1287static atomic_t *rcu_gp_slow_suppress;
1288
1289/* Register a counter to suppress debugging grace-period delays. */
1290void rcu_gp_slow_register(atomic_t *rgssp)
1291{
1292 WARN_ON_ONCE(rcu_gp_slow_suppress);
1293
1294 WRITE_ONCE(rcu_gp_slow_suppress, rgssp);
1295}
1296EXPORT_SYMBOL_GPL(rcu_gp_slow_register);
1297
1298/* Unregister a counter, with NULL for not caring which. */
1299void rcu_gp_slow_unregister(atomic_t *rgssp)
1300{
1301 WARN_ON_ONCE(rgssp && rgssp != rcu_gp_slow_suppress && rcu_gp_slow_suppress != NULL);
1302
1303 WRITE_ONCE(rcu_gp_slow_suppress, NULL);
1304}
1305EXPORT_SYMBOL_GPL(rcu_gp_slow_unregister);
1306
1307static bool rcu_gp_slow_is_suppressed(void)
1308{
1309 atomic_t *rgssp = READ_ONCE(rcu_gp_slow_suppress);
1310
1311 return rgssp && atomic_read(rgssp);
1312}
1313
1314static void rcu_gp_slow(int delay)
1315{
1316 if (!rcu_gp_slow_is_suppressed() && delay > 0 &&
1317 !(rcu_seq_ctr(rcu_state.gp_seq) % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
1318 schedule_timeout_idle(delay);
1319}
1320
1321static unsigned long sleep_duration;
1322
1323/* Allow rcutorture to stall the grace-period kthread. */
1324void rcu_gp_set_torture_wait(int duration)
1325{
1326 if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST) && duration > 0)
1327 WRITE_ONCE(sleep_duration, duration);
1328}
1329EXPORT_SYMBOL_GPL(rcu_gp_set_torture_wait);
1330
1331/* Actually implement the aforementioned wait. */
1332static void rcu_gp_torture_wait(void)
1333{
1334 unsigned long duration;
1335
1336 if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST))
1337 return;
1338 duration = xchg(&sleep_duration, 0UL);
1339 if (duration > 0) {
1340 pr_alert("%s: Waiting %lu jiffies\n", __func__, duration);
1341 schedule_timeout_idle(duration);
1342 pr_alert("%s: Wait complete\n", __func__);
1343 }
1344}
1345
1346/*
1347 * Handler for on_each_cpu() to invoke the target CPU's RCU core
1348 * processing.
1349 */
1350static void rcu_strict_gp_boundary(void *unused)
1351{
1352 invoke_rcu_core();
1353}
1354
1355// Make the polled API aware of the beginning of a grace period.
1356static void rcu_poll_gp_seq_start(unsigned long *snap)
1357{
1358 struct rcu_node *rnp = rcu_get_root();
1359
1360 if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
1361 raw_lockdep_assert_held_rcu_node(rnp);
1362
1363 // If RCU was idle, note beginning of GP.
1364 if (!rcu_seq_state(rcu_state.gp_seq_polled))
1365 rcu_seq_start(&rcu_state.gp_seq_polled);
1366
1367 // Either way, record current state.
1368 *snap = rcu_state.gp_seq_polled;
1369}
1370
1371// Make the polled API aware of the end of a grace period.
1372static void rcu_poll_gp_seq_end(unsigned long *snap)
1373{
1374 struct rcu_node *rnp = rcu_get_root();
1375
1376 if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
1377 raw_lockdep_assert_held_rcu_node(rnp);
1378
1379 // If the previously noted GP is still in effect, record the
1380 // end of that GP. Either way, zero counter to avoid counter-wrap
1381 // problems.
1382 if (*snap && *snap == rcu_state.gp_seq_polled) {
1383 rcu_seq_end(&rcu_state.gp_seq_polled);
1384 rcu_state.gp_seq_polled_snap = 0;
1385 rcu_state.gp_seq_polled_exp_snap = 0;
1386 } else {
1387 *snap = 0;
1388 }
1389}
1390
1391// Make the polled API aware of the beginning of a grace period, but
1392// where caller does not hold the root rcu_node structure's lock.
1393static void rcu_poll_gp_seq_start_unlocked(unsigned long *snap)
1394{
1395 unsigned long flags;
1396 struct rcu_node *rnp = rcu_get_root();
1397
1398 if (rcu_init_invoked()) {
1399 if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
1400 lockdep_assert_irqs_enabled();
1401 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1402 }
1403 rcu_poll_gp_seq_start(snap);
1404 if (rcu_init_invoked())
1405 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1406}
1407
1408// Make the polled API aware of the end of a grace period, but where
1409// caller does not hold the root rcu_node structure's lock.
1410static void rcu_poll_gp_seq_end_unlocked(unsigned long *snap)
1411{
1412 unsigned long flags;
1413 struct rcu_node *rnp = rcu_get_root();
1414
1415 if (rcu_init_invoked()) {
1416 if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
1417 lockdep_assert_irqs_enabled();
1418 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1419 }
1420 rcu_poll_gp_seq_end(snap);
1421 if (rcu_init_invoked())
1422 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1423}
1424
1425/*
1426 * Initialize a new grace period. Return false if no grace period required.
1427 */
1428static noinline_for_stack bool rcu_gp_init(void)
1429{
1430 unsigned long flags;
1431 unsigned long oldmask;
1432 unsigned long mask;
1433 struct rcu_data *rdp;
1434 struct rcu_node *rnp = rcu_get_root();
1435
1436 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1437 raw_spin_lock_irq_rcu_node(rnp);
1438 if (!READ_ONCE(rcu_state.gp_flags)) {
1439 /* Spurious wakeup, tell caller to go back to sleep. */
1440 raw_spin_unlock_irq_rcu_node(rnp);
1441 return false;
1442 }
1443 WRITE_ONCE(rcu_state.gp_flags, 0); /* Clear all flags: New GP. */
1444
1445 if (WARN_ON_ONCE(rcu_gp_in_progress())) {
1446 /*
1447 * Grace period already in progress, don't start another.
1448 * Not supposed to be able to happen.
1449 */
1450 raw_spin_unlock_irq_rcu_node(rnp);
1451 return false;
1452 }
1453
1454 /* Advance to a new grace period and initialize state. */
1455 record_gp_stall_check_time();
1456 /* Record GP times before starting GP, hence rcu_seq_start(). */
1457 rcu_seq_start(&rcu_state.gp_seq);
1458 ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
1459 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start"));
1460 rcu_poll_gp_seq_start(&rcu_state.gp_seq_polled_snap);
1461 raw_spin_unlock_irq_rcu_node(rnp);
1462
1463 /*
1464 * Apply per-leaf buffered online and offline operations to
1465 * the rcu_node tree. Note that this new grace period need not
1466 * wait for subsequent online CPUs, and that RCU hooks in the CPU
1467 * offlining path, when combined with checks in this function,
1468 * will handle CPUs that are currently going offline or that will
1469 * go offline later. Please also refer to "Hotplug CPU" section
1470 * of RCU's Requirements documentation.
1471 */
1472 WRITE_ONCE(rcu_state.gp_state, RCU_GP_ONOFF);
1473 /* Exclude CPU hotplug operations. */
1474 rcu_for_each_leaf_node(rnp) {
1475 local_irq_save(flags);
1476 arch_spin_lock(&rcu_state.ofl_lock);
1477 raw_spin_lock_rcu_node(rnp);
1478 if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
1479 !rnp->wait_blkd_tasks) {
1480 /* Nothing to do on this leaf rcu_node structure. */
1481 raw_spin_unlock_rcu_node(rnp);
1482 arch_spin_unlock(&rcu_state.ofl_lock);
1483 local_irq_restore(flags);
1484 continue;
1485 }
1486
1487 /* Record old state, apply changes to ->qsmaskinit field. */
1488 oldmask = rnp->qsmaskinit;
1489 rnp->qsmaskinit = rnp->qsmaskinitnext;
1490
1491 /* If zero-ness of ->qsmaskinit changed, propagate up tree. */
1492 if (!oldmask != !rnp->qsmaskinit) {
1493 if (!oldmask) { /* First online CPU for rcu_node. */
1494 if (!rnp->wait_blkd_tasks) /* Ever offline? */
1495 rcu_init_new_rnp(rnp);
1496 } else if (rcu_preempt_has_tasks(rnp)) {
1497 rnp->wait_blkd_tasks = true; /* blocked tasks */
1498 } else { /* Last offline CPU and can propagate. */
1499 rcu_cleanup_dead_rnp(rnp);
1500 }
1501 }
1502
1503 /*
1504 * If all waited-on tasks from prior grace period are
1505 * done, and if all this rcu_node structure's CPUs are
1506 * still offline, propagate up the rcu_node tree and
1507 * clear ->wait_blkd_tasks. Otherwise, if one of this
1508 * rcu_node structure's CPUs has since come back online,
1509 * simply clear ->wait_blkd_tasks.
1510 */
1511 if (rnp->wait_blkd_tasks &&
1512 (!rcu_preempt_has_tasks(rnp) || rnp->qsmaskinit)) {
1513 rnp->wait_blkd_tasks = false;
1514 if (!rnp->qsmaskinit)
1515 rcu_cleanup_dead_rnp(rnp);
1516 }
1517
1518 raw_spin_unlock_rcu_node(rnp);
1519 arch_spin_unlock(&rcu_state.ofl_lock);
1520 local_irq_restore(flags);
1521 }
1522 rcu_gp_slow(gp_preinit_delay); /* Races with CPU hotplug. */
1523
1524 /*
1525 * Set the quiescent-state-needed bits in all the rcu_node
1526 * structures for all currently online CPUs in breadth-first
1527 * order, starting from the root rcu_node structure, relying on the
1528 * layout of the tree within the rcu_state.node[] array. Note that
1529 * other CPUs will access only the leaves of the hierarchy, thus
1530 * seeing that no grace period is in progress, at least until the
1531 * corresponding leaf node has been initialized.
1532 *
1533 * The grace period cannot complete until the initialization
1534 * process finishes, because this kthread handles both.
1535 */
1536 WRITE_ONCE(rcu_state.gp_state, RCU_GP_INIT);
1537 rcu_for_each_node_breadth_first(rnp) {
1538 rcu_gp_slow(gp_init_delay);
1539 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1540 rdp = this_cpu_ptr(&rcu_data);
1541 rcu_preempt_check_blocked_tasks(rnp);
1542 rnp->qsmask = rnp->qsmaskinit;
1543 WRITE_ONCE(rnp->gp_seq, rcu_state.gp_seq);
1544 if (rnp == rdp->mynode)
1545 (void)__note_gp_changes(rnp, rdp);
1546 rcu_preempt_boost_start_gp(rnp);
1547 trace_rcu_grace_period_init(rcu_state.name, rnp->gp_seq,
1548 rnp->level, rnp->grplo,
1549 rnp->grphi, rnp->qsmask);
1550 /* Quiescent states for tasks on any now-offline CPUs. */
1551 mask = rnp->qsmask & ~rnp->qsmaskinitnext;
1552 rnp->rcu_gp_init_mask = mask;
1553 if ((mask || rnp->wait_blkd_tasks) && rcu_is_leaf_node(rnp))
1554 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
1555 else
1556 raw_spin_unlock_irq_rcu_node(rnp);
1557 cond_resched_tasks_rcu_qs();
1558 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1559 }
1560
1561 // If strict, make all CPUs aware of new grace period.
1562 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
1563 on_each_cpu(rcu_strict_gp_boundary, NULL, 0);
1564
1565 return true;
1566}
1567
1568/*
1569 * Helper function for swait_event_idle_exclusive() wakeup at force-quiescent-state
1570 * time.
1571 */
1572static bool rcu_gp_fqs_check_wake(int *gfp)
1573{
1574 struct rcu_node *rnp = rcu_get_root();
1575
1576 // If under overload conditions, force an immediate FQS scan.
1577 if (*gfp & RCU_GP_FLAG_OVLD)
1578 return true;
1579
1580 // Someone like call_rcu() requested a force-quiescent-state scan.
1581 *gfp = READ_ONCE(rcu_state.gp_flags);
1582 if (*gfp & RCU_GP_FLAG_FQS)
1583 return true;
1584
1585 // The current grace period has completed.
1586 if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
1587 return true;
1588
1589 return false;
1590}
1591
1592/*
1593 * Do one round of quiescent-state forcing.
1594 */
1595static void rcu_gp_fqs(bool first_time)
1596{
1597 int nr_fqs = READ_ONCE(rcu_state.nr_fqs_jiffies_stall);
1598 struct rcu_node *rnp = rcu_get_root();
1599
1600 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1601 WRITE_ONCE(rcu_state.n_force_qs, rcu_state.n_force_qs + 1);
1602
1603 WARN_ON_ONCE(nr_fqs > 3);
1604 /* Only countdown nr_fqs for stall purposes if jiffies moves. */
1605 if (nr_fqs) {
1606 if (nr_fqs == 1) {
1607 WRITE_ONCE(rcu_state.jiffies_stall,
1608 jiffies + rcu_jiffies_till_stall_check());
1609 }
1610 WRITE_ONCE(rcu_state.nr_fqs_jiffies_stall, --nr_fqs);
1611 }
1612
1613 if (first_time) {
1614 /* Collect dyntick-idle snapshots. */
1615 force_qs_rnp(dyntick_save_progress_counter);
1616 } else {
1617 /* Handle dyntick-idle and offline CPUs. */
1618 force_qs_rnp(rcu_implicit_dynticks_qs);
1619 }
1620 /* Clear flag to prevent immediate re-entry. */
1621 if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
1622 raw_spin_lock_irq_rcu_node(rnp);
1623 WRITE_ONCE(rcu_state.gp_flags,
1624 READ_ONCE(rcu_state.gp_flags) & ~RCU_GP_FLAG_FQS);
1625 raw_spin_unlock_irq_rcu_node(rnp);
1626 }
1627}
1628
1629/*
1630 * Loop doing repeated quiescent-state forcing until the grace period ends.
1631 */
1632static noinline_for_stack void rcu_gp_fqs_loop(void)
1633{
1634 bool first_gp_fqs = true;
1635 int gf = 0;
1636 unsigned long j;
1637 int ret;
1638 struct rcu_node *rnp = rcu_get_root();
1639
1640 j = READ_ONCE(jiffies_till_first_fqs);
1641 if (rcu_state.cbovld)
1642 gf = RCU_GP_FLAG_OVLD;
1643 ret = 0;
1644 for (;;) {
1645 if (rcu_state.cbovld) {
1646 j = (j + 2) / 3;
1647 if (j <= 0)
1648 j = 1;
1649 }
1650 if (!ret || time_before(jiffies + j, rcu_state.jiffies_force_qs)) {
1651 WRITE_ONCE(rcu_state.jiffies_force_qs, jiffies + j);
1652 /*
1653 * jiffies_force_qs before RCU_GP_WAIT_FQS state
1654 * update; required for stall checks.
1655 */
1656 smp_wmb();
1657 WRITE_ONCE(rcu_state.jiffies_kick_kthreads,
1658 jiffies + (j ? 3 * j : 2));
1659 }
1660 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
1661 TPS("fqswait"));
1662 WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_FQS);
1663 (void)swait_event_idle_timeout_exclusive(rcu_state.gp_wq,
1664 rcu_gp_fqs_check_wake(&gf), j);
1665 rcu_gp_torture_wait();
1666 WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS);
1667 /* Locking provides needed memory barriers. */
1668 /*
1669 * Exit the loop if the root rcu_node structure indicates that the grace period
1670 * has ended, leave the loop. The rcu_preempt_blocked_readers_cgp(rnp) check
1671 * is required only for single-node rcu_node trees because readers blocking
1672 * the current grace period are queued only on leaf rcu_node structures.
1673 * For multi-node trees, checking the root node's ->qsmask suffices, because a
1674 * given root node's ->qsmask bit is cleared only when all CPUs and tasks from
1675 * the corresponding leaf nodes have passed through their quiescent state.
1676 */
1677 if (!READ_ONCE(rnp->qsmask) &&
1678 !rcu_preempt_blocked_readers_cgp(rnp))
1679 break;
1680 /* If time for quiescent-state forcing, do it. */
1681 if (!time_after(rcu_state.jiffies_force_qs, jiffies) ||
1682 (gf & (RCU_GP_FLAG_FQS | RCU_GP_FLAG_OVLD))) {
1683 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
1684 TPS("fqsstart"));
1685 rcu_gp_fqs(first_gp_fqs);
1686 gf = 0;
1687 if (first_gp_fqs) {
1688 first_gp_fqs = false;
1689 gf = rcu_state.cbovld ? RCU_GP_FLAG_OVLD : 0;
1690 }
1691 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
1692 TPS("fqsend"));
1693 cond_resched_tasks_rcu_qs();
1694 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1695 ret = 0; /* Force full wait till next FQS. */
1696 j = READ_ONCE(jiffies_till_next_fqs);
1697 } else {
1698 /* Deal with stray signal. */
1699 cond_resched_tasks_rcu_qs();
1700 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1701 WARN_ON(signal_pending(current));
1702 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
1703 TPS("fqswaitsig"));
1704 ret = 1; /* Keep old FQS timing. */
1705 j = jiffies;
1706 if (time_after(jiffies, rcu_state.jiffies_force_qs))
1707 j = 1;
1708 else
1709 j = rcu_state.jiffies_force_qs - j;
1710 gf = 0;
1711 }
1712 }
1713}
1714
1715/*
1716 * Clean up after the old grace period.
1717 */
1718static noinline void rcu_gp_cleanup(void)
1719{
1720 int cpu;
1721 bool needgp = false;
1722 unsigned long gp_duration;
1723 unsigned long new_gp_seq;
1724 bool offloaded;
1725 struct rcu_data *rdp;
1726 struct rcu_node *rnp = rcu_get_root();
1727 struct swait_queue_head *sq;
1728
1729 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1730 raw_spin_lock_irq_rcu_node(rnp);
1731 rcu_state.gp_end = jiffies;
1732 gp_duration = rcu_state.gp_end - rcu_state.gp_start;
1733 if (gp_duration > rcu_state.gp_max)
1734 rcu_state.gp_max = gp_duration;
1735
1736 /*
1737 * We know the grace period is complete, but to everyone else
1738 * it appears to still be ongoing. But it is also the case
1739 * that to everyone else it looks like there is nothing that
1740 * they can do to advance the grace period. It is therefore
1741 * safe for us to drop the lock in order to mark the grace
1742 * period as completed in all of the rcu_node structures.
1743 */
1744 rcu_poll_gp_seq_end(&rcu_state.gp_seq_polled_snap);
1745 raw_spin_unlock_irq_rcu_node(rnp);
1746
1747 /*
1748 * Propagate new ->gp_seq value to rcu_node structures so that
1749 * other CPUs don't have to wait until the start of the next grace
1750 * period to process their callbacks. This also avoids some nasty
1751 * RCU grace-period initialization races by forcing the end of
1752 * the current grace period to be completely recorded in all of
1753 * the rcu_node structures before the beginning of the next grace
1754 * period is recorded in any of the rcu_node structures.
1755 */
1756 new_gp_seq = rcu_state.gp_seq;
1757 rcu_seq_end(&new_gp_seq);
1758 rcu_for_each_node_breadth_first(rnp) {
1759 raw_spin_lock_irq_rcu_node(rnp);
1760 if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
1761 dump_blkd_tasks(rnp, 10);
1762 WARN_ON_ONCE(rnp->qsmask);
1763 WRITE_ONCE(rnp->gp_seq, new_gp_seq);
1764 if (!rnp->parent)
1765 smp_mb(); // Order against failing poll_state_synchronize_rcu_full().
1766 rdp = this_cpu_ptr(&rcu_data);
1767 if (rnp == rdp->mynode)
1768 needgp = __note_gp_changes(rnp, rdp) || needgp;
1769 /* smp_mb() provided by prior unlock-lock pair. */
1770 needgp = rcu_future_gp_cleanup(rnp) || needgp;
1771 // Reset overload indication for CPUs no longer overloaded
1772 if (rcu_is_leaf_node(rnp))
1773 for_each_leaf_node_cpu_mask(rnp, cpu, rnp->cbovldmask) {
1774 rdp = per_cpu_ptr(&rcu_data, cpu);
1775 check_cb_ovld_locked(rdp, rnp);
1776 }
1777 sq = rcu_nocb_gp_get(rnp);
1778 raw_spin_unlock_irq_rcu_node(rnp);
1779 rcu_nocb_gp_cleanup(sq);
1780 cond_resched_tasks_rcu_qs();
1781 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1782 rcu_gp_slow(gp_cleanup_delay);
1783 }
1784 rnp = rcu_get_root();
1785 raw_spin_lock_irq_rcu_node(rnp); /* GP before ->gp_seq update. */
1786
1787 /* Declare grace period done, trace first to use old GP number. */
1788 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end"));
1789 rcu_seq_end(&rcu_state.gp_seq);
1790 ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
1791 WRITE_ONCE(rcu_state.gp_state, RCU_GP_IDLE);
1792 /* Check for GP requests since above loop. */
1793 rdp = this_cpu_ptr(&rcu_data);
1794 if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) {
1795 trace_rcu_this_gp(rnp, rdp, rnp->gp_seq_needed,
1796 TPS("CleanupMore"));
1797 needgp = true;
1798 }
1799 /* Advance CBs to reduce false positives below. */
1800 offloaded = rcu_rdp_is_offloaded(rdp);
1801 if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {
1802
1803 // We get here if a grace period was needed (“needgp”)
1804 // and the above call to rcu_accelerate_cbs() did not set
1805 // the RCU_GP_FLAG_INIT bit in ->gp_state (which records
1806 // the need for another grace period). The purpose
1807 // of the “offloaded” check is to avoid invoking
1808 // rcu_accelerate_cbs() on an offloaded CPU because we do not
1809 // hold the ->nocb_lock needed to safely access an offloaded
1810 // ->cblist. We do not want to acquire that lock because
1811 // it can be heavily contended during callback floods.
1812
1813 WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);
1814 WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
1815 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("newreq"));
1816 } else {
1817
1818 // We get here either if there is no need for an
1819 // additional grace period or if rcu_accelerate_cbs() has
1820 // already set the RCU_GP_FLAG_INIT bit in ->gp_flags.
1821 // So all we need to do is to clear all of the other
1822 // ->gp_flags bits.
1823
1824 WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags & RCU_GP_FLAG_INIT);
1825 }
1826 raw_spin_unlock_irq_rcu_node(rnp);
1827
1828 // If strict, make all CPUs aware of the end of the old grace period.
1829 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
1830 on_each_cpu(rcu_strict_gp_boundary, NULL, 0);
1831}
1832
1833/*
1834 * Body of kthread that handles grace periods.
1835 */
1836static int __noreturn rcu_gp_kthread(void *unused)
1837{
1838 rcu_bind_gp_kthread();
1839 for (;;) {
1840
1841 /* Handle grace-period start. */
1842 for (;;) {
1843 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
1844 TPS("reqwait"));
1845 WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_GPS);
1846 swait_event_idle_exclusive(rcu_state.gp_wq,
1847 READ_ONCE(rcu_state.gp_flags) &
1848 RCU_GP_FLAG_INIT);
1849 rcu_gp_torture_wait();
1850 WRITE_ONCE(rcu_state.gp_state, RCU_GP_DONE_GPS);
1851 /* Locking provides needed memory barrier. */
1852 if (rcu_gp_init())
1853 break;
1854 cond_resched_tasks_rcu_qs();
1855 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1856 WARN_ON(signal_pending(current));
1857 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
1858 TPS("reqwaitsig"));
1859 }
1860
1861 /* Handle quiescent-state forcing. */
1862 rcu_gp_fqs_loop();
1863
1864 /* Handle grace-period end. */
1865 WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANUP);
1866 rcu_gp_cleanup();
1867 WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANED);
1868 }
1869}
1870
1871/*
1872 * Report a full set of quiescent states to the rcu_state data structure.
1873 * Invoke rcu_gp_kthread_wake() to awaken the grace-period kthread if
1874 * another grace period is required. Whether we wake the grace-period
1875 * kthread or it awakens itself for the next round of quiescent-state
1876 * forcing, that kthread will clean up after the just-completed grace
1877 * period. Note that the caller must hold rnp->lock, which is released
1878 * before return.
1879 */
1880static void rcu_report_qs_rsp(unsigned long flags)
1881 __releases(rcu_get_root()->lock)
1882{
1883 raw_lockdep_assert_held_rcu_node(rcu_get_root());
1884 WARN_ON_ONCE(!rcu_gp_in_progress());
1885 WRITE_ONCE(rcu_state.gp_flags,
1886 READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
1887 raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(), flags);
1888 rcu_gp_kthread_wake();
1889}
1890
1891/*
1892 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
1893 * Allows quiescent states for a group of CPUs to be reported at one go
1894 * to the specified rcu_node structure, though all the CPUs in the group
1895 * must be represented by the same rcu_node structure (which need not be a
1896 * leaf rcu_node structure, though it often will be). The gps parameter
1897 * is the grace-period snapshot, which means that the quiescent states
1898 * are valid only if rnp->gp_seq is equal to gps. That structure's lock
1899 * must be held upon entry, and it is released before return.
1900 *
1901 * As a special case, if mask is zero, the bit-already-cleared check is
1902 * disabled. This allows propagating quiescent state due to resumed tasks
1903 * during grace-period initialization.
1904 */
1905static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
1906 unsigned long gps, unsigned long flags)
1907 __releases(rnp->lock)
1908{
1909 unsigned long oldmask = 0;
1910 struct rcu_node *rnp_c;
1911
1912 raw_lockdep_assert_held_rcu_node(rnp);
1913
1914 /* Walk up the rcu_node hierarchy. */
1915 for (;;) {
1916 if ((!(rnp->qsmask & mask) && mask) || rnp->gp_seq != gps) {
1917
1918 /*
1919 * Our bit has already been cleared, or the
1920 * relevant grace period is already over, so done.
1921 */
1922 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1923 return;
1924 }
1925 WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
1926 WARN_ON_ONCE(!rcu_is_leaf_node(rnp) &&
1927 rcu_preempt_blocked_readers_cgp(rnp));
1928 WRITE_ONCE(rnp->qsmask, rnp->qsmask & ~mask);
1929 trace_rcu_quiescent_state_report(rcu_state.name, rnp->gp_seq,
1930 mask, rnp->qsmask, rnp->level,
1931 rnp->grplo, rnp->grphi,
1932 !!rnp->gp_tasks);
1933 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
1934
1935 /* Other bits still set at this level, so done. */
1936 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1937 return;
1938 }
1939 rnp->completedqs = rnp->gp_seq;
1940 mask = rnp->grpmask;
1941 if (rnp->parent == NULL) {
1942
1943 /* No more levels. Exit loop holding root lock. */
1944
1945 break;
1946 }
1947 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1948 rnp_c = rnp;
1949 rnp = rnp->parent;
1950 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1951 oldmask = READ_ONCE(rnp_c->qsmask);
1952 }
1953
1954 /*
1955 * Get here if we are the last CPU to pass through a quiescent
1956 * state for this grace period. Invoke rcu_report_qs_rsp()
1957 * to clean up and start the next grace period if one is needed.
1958 */
1959 rcu_report_qs_rsp(flags); /* releases rnp->lock. */
1960}
1961
1962/*
1963 * Record a quiescent state for all tasks that were previously queued
1964 * on the specified rcu_node structure and that were blocking the current
1965 * RCU grace period. The caller must hold the corresponding rnp->lock with
1966 * irqs disabled, and this lock is released upon return, but irqs remain
1967 * disabled.
1968 */
1969static void __maybe_unused
1970rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
1971 __releases(rnp->lock)
1972{
1973 unsigned long gps;
1974 unsigned long mask;
1975 struct rcu_node *rnp_p;
1976
1977 raw_lockdep_assert_held_rcu_node(rnp);
1978 if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT_RCU)) ||
1979 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)) ||
1980 rnp->qsmask != 0) {
1981 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1982 return; /* Still need more quiescent states! */
1983 }
1984
1985 rnp->completedqs = rnp->gp_seq;
1986 rnp_p = rnp->parent;
1987 if (rnp_p == NULL) {
1988 /*
1989 * Only one rcu_node structure in the tree, so don't
1990 * try to report up to its nonexistent parent!
1991 */
1992 rcu_report_qs_rsp(flags);
1993 return;
1994 }
1995
1996 /* Report up the rest of the hierarchy, tracking current ->gp_seq. */
1997 gps = rnp->gp_seq;
1998 mask = rnp->grpmask;
1999 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2000 raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */
2001 rcu_report_qs_rnp(mask, rnp_p, gps, flags);
2002}
2003
2004/*
2005 * Record a quiescent state for the specified CPU to that CPU's rcu_data
2006 * structure. This must be called from the specified CPU.
2007 */
2008static void
2009rcu_report_qs_rdp(struct rcu_data *rdp)
2010{
2011 unsigned long flags;
2012 unsigned long mask;
2013 bool needacc = false;
2014 struct rcu_node *rnp;
2015
2016 WARN_ON_ONCE(rdp->cpu != smp_processor_id());
2017 rnp = rdp->mynode;
2018 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2019 if (rdp->cpu_no_qs.b.norm || rdp->gp_seq != rnp->gp_seq ||
2020 rdp->gpwrap) {
2021
2022 /*
2023 * The grace period in which this quiescent state was
2024 * recorded has ended, so don't report it upwards.
2025 * We will instead need a new quiescent state that lies
2026 * within the current grace period.
2027 */
2028 rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */
2029 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2030 return;
2031 }
2032 mask = rdp->grpmask;
2033 rdp->core_needs_qs = false;
2034 if ((rnp->qsmask & mask) == 0) {
2035 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2036 } else {
2037 /*
2038 * This GP can't end until cpu checks in, so all of our
2039 * callbacks can be processed during the next GP.
2040 *
2041 * NOCB kthreads have their own way to deal with that...
2042 */
2043 if (!rcu_rdp_is_offloaded(rdp)) {
2044 /*
2045 * The current GP has not yet ended, so it
2046 * should not be possible for rcu_accelerate_cbs()
2047 * to return true. So complain, but don't awaken.
2048 */
2049 WARN_ON_ONCE(rcu_accelerate_cbs(rnp, rdp));
2050 } else if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) {
2051 /*
2052 * ...but NOCB kthreads may miss or delay callbacks acceleration
2053 * if in the middle of a (de-)offloading process.
2054 */
2055 needacc = true;
2056 }
2057
2058 rcu_disable_urgency_upon_qs(rdp);
2059 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
2060 /* ^^^ Released rnp->lock */
2061
2062 if (needacc) {
2063 rcu_nocb_lock_irqsave(rdp, flags);
2064 rcu_accelerate_cbs_unlocked(rnp, rdp);
2065 rcu_nocb_unlock_irqrestore(rdp, flags);
2066 }
2067 }
2068}
2069
2070/*
2071 * Check to see if there is a new grace period of which this CPU
2072 * is not yet aware, and if so, set up local rcu_data state for it.
2073 * Otherwise, see if this CPU has just passed through its first
2074 * quiescent state for this grace period, and record that fact if so.
2075 */
2076static void
2077rcu_check_quiescent_state(struct rcu_data *rdp)
2078{
2079 /* Check for grace-period ends and beginnings. */
2080 note_gp_changes(rdp);
2081
2082 /*
2083 * Does this CPU still need to do its part for current grace period?
2084 * If no, return and let the other CPUs do their part as well.
2085 */
2086 if (!rdp->core_needs_qs)
2087 return;
2088
2089 /*
2090 * Was there a quiescent state since the beginning of the grace
2091 * period? If no, then exit and wait for the next call.
2092 */
2093 if (rdp->cpu_no_qs.b.norm)
2094 return;
2095
2096 /*
2097 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
2098 * judge of that).
2099 */
2100 rcu_report_qs_rdp(rdp);
2101}
2102
2103/* Return true if callback-invocation time limit exceeded. */
2104static bool rcu_do_batch_check_time(long count, long tlimit,
2105 bool jlimit_check, unsigned long jlimit)
2106{
2107 // Invoke local_clock() only once per 32 consecutive callbacks.
2108 return unlikely(tlimit) &&
2109 (!likely(count & 31) ||
2110 (IS_ENABLED(CONFIG_RCU_DOUBLE_CHECK_CB_TIME) &&
2111 jlimit_check && time_after(jiffies, jlimit))) &&
2112 local_clock() >= tlimit;
2113}
2114
2115/*
2116 * Invoke any RCU callbacks that have made it to the end of their grace
2117 * period. Throttle as specified by rdp->blimit.
2118 */
2119static void rcu_do_batch(struct rcu_data *rdp)
2120{
2121 long bl;
2122 long count = 0;
2123 int div;
2124 bool __maybe_unused empty;
2125 unsigned long flags;
2126 unsigned long jlimit;
2127 bool jlimit_check = false;
2128 long pending;
2129 struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
2130 struct rcu_head *rhp;
2131 long tlimit = 0;
2132
2133 /* If no callbacks are ready, just return. */
2134 if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
2135 trace_rcu_batch_start(rcu_state.name,
2136 rcu_segcblist_n_cbs(&rdp->cblist), 0);
2137 trace_rcu_batch_end(rcu_state.name, 0,
2138 !rcu_segcblist_empty(&rdp->cblist),
2139 need_resched(), is_idle_task(current),
2140 rcu_is_callbacks_kthread(rdp));
2141 return;
2142 }
2143
2144 /*
2145 * Extract the list of ready callbacks, disabling IRQs to prevent
2146 * races with call_rcu() from interrupt handlers. Leave the
2147 * callback counts, as rcu_barrier() needs to be conservative.
2148 *
2149 * Callbacks execution is fully ordered against preceding grace period
2150 * completion (materialized by rnp->gp_seq update) thanks to the
2151 * smp_mb__after_unlock_lock() upon node locking required for callbacks
2152 * advancing. In NOCB mode this ordering is then further relayed through
2153 * the nocb locking that protects both callbacks advancing and extraction.
2154 */
2155 rcu_nocb_lock_irqsave(rdp, flags);
2156 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2157 pending = rcu_segcblist_get_seglen(&rdp->cblist, RCU_DONE_TAIL);
2158 div = READ_ONCE(rcu_divisor);
2159 div = div < 0 ? 7 : div > sizeof(long) * 8 - 2 ? sizeof(long) * 8 - 2 : div;
2160 bl = max(rdp->blimit, pending >> div);
2161 if ((in_serving_softirq() || rdp->rcu_cpu_kthread_status == RCU_KTHREAD_RUNNING) &&
2162 (IS_ENABLED(CONFIG_RCU_DOUBLE_CHECK_CB_TIME) || unlikely(bl > 100))) {
2163 const long npj = NSEC_PER_SEC / HZ;
2164 long rrn = READ_ONCE(rcu_resched_ns);
2165
2166 rrn = rrn < NSEC_PER_MSEC ? NSEC_PER_MSEC : rrn > NSEC_PER_SEC ? NSEC_PER_SEC : rrn;
2167 tlimit = local_clock() + rrn;
2168 jlimit = jiffies + (rrn + npj + 1) / npj;
2169 jlimit_check = true;
2170 }
2171 trace_rcu_batch_start(rcu_state.name,
2172 rcu_segcblist_n_cbs(&rdp->cblist), bl);
2173 rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
2174 if (rcu_rdp_is_offloaded(rdp))
2175 rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
2176
2177 trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbDequeued"));
2178 rcu_nocb_unlock_irqrestore(rdp, flags);
2179
2180 /* Invoke callbacks. */
2181 tick_dep_set_task(current, TICK_DEP_BIT_RCU);
2182 rhp = rcu_cblist_dequeue(&rcl);
2183
2184 for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
2185 rcu_callback_t f;
2186
2187 count++;
2188 debug_rcu_head_unqueue(rhp);
2189
2190 rcu_lock_acquire(&rcu_callback_map);
2191 trace_rcu_invoke_callback(rcu_state.name, rhp);
2192
2193 f = rhp->func;
2194 debug_rcu_head_callback(rhp);
2195 WRITE_ONCE(rhp->func, (rcu_callback_t)0L);
2196 f(rhp);
2197
2198 rcu_lock_release(&rcu_callback_map);
2199
2200 /*
2201 * Stop only if limit reached and CPU has something to do.
2202 */
2203 if (in_serving_softirq()) {
2204 if (count >= bl && (need_resched() || !is_idle_task(current)))
2205 break;
2206 /*
2207 * Make sure we don't spend too much time here and deprive other
2208 * softirq vectors of CPU cycles.
2209 */
2210 if (rcu_do_batch_check_time(count, tlimit, jlimit_check, jlimit))
2211 break;
2212 } else {
2213 // In rcuc/rcuoc context, so no worries about
2214 // depriving other softirq vectors of CPU cycles.
2215 local_bh_enable();
2216 lockdep_assert_irqs_enabled();
2217 cond_resched_tasks_rcu_qs();
2218 lockdep_assert_irqs_enabled();
2219 local_bh_disable();
2220 // But rcuc kthreads can delay quiescent-state
2221 // reporting, so check time limits for them.
2222 if (rdp->rcu_cpu_kthread_status == RCU_KTHREAD_RUNNING &&
2223 rcu_do_batch_check_time(count, tlimit, jlimit_check, jlimit)) {
2224 rdp->rcu_cpu_has_work = 1;
2225 break;
2226 }
2227 }
2228 }
2229
2230 rcu_nocb_lock_irqsave(rdp, flags);
2231 rdp->n_cbs_invoked += count;
2232 trace_rcu_batch_end(rcu_state.name, count, !!rcl.head, need_resched(),
2233 is_idle_task(current), rcu_is_callbacks_kthread(rdp));
2234
2235 /* Update counts and requeue any remaining callbacks. */
2236 rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
2237 rcu_segcblist_add_len(&rdp->cblist, -count);
2238
2239 /* Reinstate batch limit if we have worked down the excess. */
2240 count = rcu_segcblist_n_cbs(&rdp->cblist);
2241 if (rdp->blimit >= DEFAULT_MAX_RCU_BLIMIT && count <= qlowmark)
2242 rdp->blimit = blimit;
2243
2244 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2245 if (count == 0 && rdp->qlen_last_fqs_check != 0) {
2246 rdp->qlen_last_fqs_check = 0;
2247 rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
2248 } else if (count < rdp->qlen_last_fqs_check - qhimark)
2249 rdp->qlen_last_fqs_check = count;
2250
2251 /*
2252 * The following usually indicates a double call_rcu(). To track
2253 * this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.
2254 */
2255 empty = rcu_segcblist_empty(&rdp->cblist);
2256 WARN_ON_ONCE(count == 0 && !empty);
2257 WARN_ON_ONCE(!IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
2258 count != 0 && empty);
2259 WARN_ON_ONCE(count == 0 && rcu_segcblist_n_segment_cbs(&rdp->cblist) != 0);
2260 WARN_ON_ONCE(!empty && rcu_segcblist_n_segment_cbs(&rdp->cblist) == 0);
2261
2262 rcu_nocb_unlock_irqrestore(rdp, flags);
2263
2264 tick_dep_clear_task(current, TICK_DEP_BIT_RCU);
2265}
2266
2267/*
2268 * This function is invoked from each scheduling-clock interrupt,
2269 * and checks to see if this CPU is in a non-context-switch quiescent
2270 * state, for example, user mode or idle loop. It also schedules RCU
2271 * core processing. If the current grace period has gone on too long,
2272 * it will ask the scheduler to manufacture a context switch for the sole
2273 * purpose of providing the needed quiescent state.
2274 */
2275void rcu_sched_clock_irq(int user)
2276{
2277 unsigned long j;
2278
2279 if (IS_ENABLED(CONFIG_PROVE_RCU)) {
2280 j = jiffies;
2281 WARN_ON_ONCE(time_before(j, __this_cpu_read(rcu_data.last_sched_clock)));
2282 __this_cpu_write(rcu_data.last_sched_clock, j);
2283 }
2284 trace_rcu_utilization(TPS("Start scheduler-tick"));
2285 lockdep_assert_irqs_disabled();
2286 raw_cpu_inc(rcu_data.ticks_this_gp);
2287 /* The load-acquire pairs with the store-release setting to true. */
2288 if (smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
2289 /* Idle and userspace execution already are quiescent states. */
2290 if (!rcu_is_cpu_rrupt_from_idle() && !user) {
2291 set_tsk_need_resched(current);
2292 set_preempt_need_resched();
2293 }
2294 __this_cpu_write(rcu_data.rcu_urgent_qs, false);
2295 }
2296 rcu_flavor_sched_clock_irq(user);
2297 if (rcu_pending(user))
2298 invoke_rcu_core();
2299 if (user || rcu_is_cpu_rrupt_from_idle())
2300 rcu_note_voluntary_context_switch(current);
2301 lockdep_assert_irqs_disabled();
2302
2303 trace_rcu_utilization(TPS("End scheduler-tick"));
2304}
2305
2306/*
2307 * Scan the leaf rcu_node structures. For each structure on which all
2308 * CPUs have reported a quiescent state and on which there are tasks
2309 * blocking the current grace period, initiate RCU priority boosting.
2310 * Otherwise, invoke the specified function to check dyntick state for
2311 * each CPU that has not yet reported a quiescent state.
2312 */
2313static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
2314{
2315 int cpu;
2316 unsigned long flags;
2317 struct rcu_node *rnp;
2318
2319 rcu_state.cbovld = rcu_state.cbovldnext;
2320 rcu_state.cbovldnext = false;
2321 rcu_for_each_leaf_node(rnp) {
2322 unsigned long mask = 0;
2323 unsigned long rsmask = 0;
2324
2325 cond_resched_tasks_rcu_qs();
2326 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2327 rcu_state.cbovldnext |= !!rnp->cbovldmask;
2328 if (rnp->qsmask == 0) {
2329 if (rcu_preempt_blocked_readers_cgp(rnp)) {
2330 /*
2331 * No point in scanning bits because they
2332 * are all zero. But we might need to
2333 * priority-boost blocked readers.
2334 */
2335 rcu_initiate_boost(rnp, flags);
2336 /* rcu_initiate_boost() releases rnp->lock */
2337 continue;
2338 }
2339 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2340 continue;
2341 }
2342 for_each_leaf_node_cpu_mask(rnp, cpu, rnp->qsmask) {
2343 struct rcu_data *rdp;
2344 int ret;
2345
2346 rdp = per_cpu_ptr(&rcu_data, cpu);
2347 ret = f(rdp);
2348 if (ret > 0) {
2349 mask |= rdp->grpmask;
2350 rcu_disable_urgency_upon_qs(rdp);
2351 }
2352 if (ret < 0)
2353 rsmask |= rdp->grpmask;
2354 }
2355 if (mask != 0) {
2356 /* Idle/offline CPUs, report (releases rnp->lock). */
2357 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
2358 } else {
2359 /* Nothing to do here, so just drop the lock. */
2360 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2361 }
2362
2363 for_each_leaf_node_cpu_mask(rnp, cpu, rsmask)
2364 resched_cpu(cpu);
2365 }
2366}
2367
2368/*
2369 * Force quiescent states on reluctant CPUs, and also detect which
2370 * CPUs are in dyntick-idle mode.
2371 */
2372void rcu_force_quiescent_state(void)
2373{
2374 unsigned long flags;
2375 bool ret;
2376 struct rcu_node *rnp;
2377 struct rcu_node *rnp_old = NULL;
2378
2379 if (!rcu_gp_in_progress())
2380 return;
2381 /* Funnel through hierarchy to reduce memory contention. */
2382 rnp = raw_cpu_read(rcu_data.mynode);
2383 for (; rnp != NULL; rnp = rnp->parent) {
2384 ret = (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) ||
2385 !raw_spin_trylock(&rnp->fqslock);
2386 if (rnp_old != NULL)
2387 raw_spin_unlock(&rnp_old->fqslock);
2388 if (ret)
2389 return;
2390 rnp_old = rnp;
2391 }
2392 /* rnp_old == rcu_get_root(), rnp == NULL. */
2393
2394 /* Reached the root of the rcu_node tree, acquire lock. */
2395 raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
2396 raw_spin_unlock(&rnp_old->fqslock);
2397 if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
2398 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2399 return; /* Someone beat us to it. */
2400 }
2401 WRITE_ONCE(rcu_state.gp_flags,
2402 READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
2403 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2404 rcu_gp_kthread_wake();
2405}
2406EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
2407
2408// Workqueue handler for an RCU reader for kernels enforcing struct RCU
2409// grace periods.
2410static void strict_work_handler(struct work_struct *work)
2411{
2412 rcu_read_lock();
2413 rcu_read_unlock();
2414}
2415
2416/* Perform RCU core processing work for the current CPU. */
2417static __latent_entropy void rcu_core(void)
2418{
2419 unsigned long flags;
2420 struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
2421 struct rcu_node *rnp = rdp->mynode;
2422 /*
2423 * On RT rcu_core() can be preempted when IRQs aren't disabled.
2424 * Therefore this function can race with concurrent NOCB (de-)offloading
2425 * on this CPU and the below condition must be considered volatile.
2426 * However if we race with:
2427 *
2428 * _ Offloading: In the worst case we accelerate or process callbacks
2429 * concurrently with NOCB kthreads. We are guaranteed to
2430 * call rcu_nocb_lock() if that happens.
2431 *
2432 * _ Deoffloading: In the worst case we miss callbacks acceleration or
2433 * processing. This is fine because the early stage
2434 * of deoffloading invokes rcu_core() after setting
2435 * SEGCBLIST_RCU_CORE. So we guarantee that we'll process
2436 * what could have been dismissed without the need to wait
2437 * for the next rcu_pending() check in the next jiffy.
2438 */
2439 const bool do_batch = !rcu_segcblist_completely_offloaded(&rdp->cblist);
2440
2441 if (cpu_is_offline(smp_processor_id()))
2442 return;
2443 trace_rcu_utilization(TPS("Start RCU core"));
2444 WARN_ON_ONCE(!rdp->beenonline);
2445
2446 /* Report any deferred quiescent states if preemption enabled. */
2447 if (IS_ENABLED(CONFIG_PREEMPT_COUNT) && (!(preempt_count() & PREEMPT_MASK))) {
2448 rcu_preempt_deferred_qs(current);
2449 } else if (rcu_preempt_need_deferred_qs(current)) {
2450 set_tsk_need_resched(current);
2451 set_preempt_need_resched();
2452 }
2453
2454 /* Update RCU state based on any recent quiescent states. */
2455 rcu_check_quiescent_state(rdp);
2456
2457 /* No grace period and unregistered callbacks? */
2458 if (!rcu_gp_in_progress() &&
2459 rcu_segcblist_is_enabled(&rdp->cblist) && do_batch) {
2460 rcu_nocb_lock_irqsave(rdp, flags);
2461 if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
2462 rcu_accelerate_cbs_unlocked(rnp, rdp);
2463 rcu_nocb_unlock_irqrestore(rdp, flags);
2464 }
2465
2466 rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check());
2467
2468 /* If there are callbacks ready, invoke them. */
2469 if (do_batch && rcu_segcblist_ready_cbs(&rdp->cblist) &&
2470 likely(READ_ONCE(rcu_scheduler_fully_active))) {
2471 rcu_do_batch(rdp);
2472 /* Re-invoke RCU core processing if there are callbacks remaining. */
2473 if (rcu_segcblist_ready_cbs(&rdp->cblist))
2474 invoke_rcu_core();
2475 }
2476
2477 /* Do any needed deferred wakeups of rcuo kthreads. */
2478 do_nocb_deferred_wakeup(rdp);
2479 trace_rcu_utilization(TPS("End RCU core"));
2480
2481 // If strict GPs, schedule an RCU reader in a clean environment.
2482 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
2483 queue_work_on(rdp->cpu, rcu_gp_wq, &rdp->strict_work);
2484}
2485
2486static void rcu_core_si(struct softirq_action *h)
2487{
2488 rcu_core();
2489}
2490
2491static void rcu_wake_cond(struct task_struct *t, int status)
2492{
2493 /*
2494 * If the thread is yielding, only wake it when this
2495 * is invoked from idle
2496 */
2497 if (t && (status != RCU_KTHREAD_YIELDING || is_idle_task(current)))
2498 wake_up_process(t);
2499}
2500
2501static void invoke_rcu_core_kthread(void)
2502{
2503 struct task_struct *t;
2504 unsigned long flags;
2505
2506 local_irq_save(flags);
2507 __this_cpu_write(rcu_data.rcu_cpu_has_work, 1);
2508 t = __this_cpu_read(rcu_data.rcu_cpu_kthread_task);
2509 if (t != NULL && t != current)
2510 rcu_wake_cond(t, __this_cpu_read(rcu_data.rcu_cpu_kthread_status));
2511 local_irq_restore(flags);
2512}
2513
2514/*
2515 * Wake up this CPU's rcuc kthread to do RCU core processing.
2516 */
2517static void invoke_rcu_core(void)
2518{
2519 if (!cpu_online(smp_processor_id()))
2520 return;
2521 if (use_softirq)
2522 raise_softirq(RCU_SOFTIRQ);
2523 else
2524 invoke_rcu_core_kthread();
2525}
2526
2527static void rcu_cpu_kthread_park(unsigned int cpu)
2528{
2529 per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
2530}
2531
2532static int rcu_cpu_kthread_should_run(unsigned int cpu)
2533{
2534 return __this_cpu_read(rcu_data.rcu_cpu_has_work);
2535}
2536
2537/*
2538 * Per-CPU kernel thread that invokes RCU callbacks. This replaces
2539 * the RCU softirq used in configurations of RCU that do not support RCU
2540 * priority boosting.
2541 */
2542static void rcu_cpu_kthread(unsigned int cpu)
2543{
2544 unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status);
2545 char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work);
2546 unsigned long *j = this_cpu_ptr(&rcu_data.rcuc_activity);
2547 int spincnt;
2548
2549 trace_rcu_utilization(TPS("Start CPU kthread@rcu_run"));
2550 for (spincnt = 0; spincnt < 10; spincnt++) {
2551 WRITE_ONCE(*j, jiffies);
2552 local_bh_disable();
2553 *statusp = RCU_KTHREAD_RUNNING;
2554 local_irq_disable();
2555 work = *workp;
2556 WRITE_ONCE(*workp, 0);
2557 local_irq_enable();
2558 if (work)
2559 rcu_core();
2560 local_bh_enable();
2561 if (!READ_ONCE(*workp)) {
2562 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
2563 *statusp = RCU_KTHREAD_WAITING;
2564 return;
2565 }
2566 }
2567 *statusp = RCU_KTHREAD_YIELDING;
2568 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
2569 schedule_timeout_idle(2);
2570 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
2571 *statusp = RCU_KTHREAD_WAITING;
2572 WRITE_ONCE(*j, jiffies);
2573}
2574
2575static struct smp_hotplug_thread rcu_cpu_thread_spec = {
2576 .store = &rcu_data.rcu_cpu_kthread_task,
2577 .thread_should_run = rcu_cpu_kthread_should_run,
2578 .thread_fn = rcu_cpu_kthread,
2579 .thread_comm = "rcuc/%u",
2580 .setup = rcu_cpu_kthread_setup,
2581 .park = rcu_cpu_kthread_park,
2582};
2583
2584/*
2585 * Spawn per-CPU RCU core processing kthreads.
2586 */
2587static int __init rcu_spawn_core_kthreads(void)
2588{
2589 int cpu;
2590
2591 for_each_possible_cpu(cpu)
2592 per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0;
2593 if (use_softirq)
2594 return 0;
2595 WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec),
2596 "%s: Could not start rcuc kthread, OOM is now expected behavior\n", __func__);
2597 return 0;
2598}
2599
2600static void rcutree_enqueue(struct rcu_data *rdp, struct rcu_head *head, rcu_callback_t func)
2601{
2602 rcu_segcblist_enqueue(&rdp->cblist, head);
2603 if (__is_kvfree_rcu_offset((unsigned long)func))
2604 trace_rcu_kvfree_callback(rcu_state.name, head,
2605 (unsigned long)func,
2606 rcu_segcblist_n_cbs(&rdp->cblist));
2607 else
2608 trace_rcu_callback(rcu_state.name, head,
2609 rcu_segcblist_n_cbs(&rdp->cblist));
2610 trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCBQueued"));
2611}
2612
2613/*
2614 * Handle any core-RCU processing required by a call_rcu() invocation.
2615 */
2616static void call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
2617 rcu_callback_t func, unsigned long flags)
2618{
2619 rcutree_enqueue(rdp, head, func);
2620 /*
2621 * If called from an extended quiescent state, invoke the RCU
2622 * core in order to force a re-evaluation of RCU's idleness.
2623 */
2624 if (!rcu_is_watching())
2625 invoke_rcu_core();
2626
2627 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2628 if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2629 return;
2630
2631 /*
2632 * Force the grace period if too many callbacks or too long waiting.
2633 * Enforce hysteresis, and don't invoke rcu_force_quiescent_state()
2634 * if some other CPU has recently done so. Also, don't bother
2635 * invoking rcu_force_quiescent_state() if the newly enqueued callback
2636 * is the only one waiting for a grace period to complete.
2637 */
2638 if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
2639 rdp->qlen_last_fqs_check + qhimark)) {
2640
2641 /* Are we ignoring a completed grace period? */
2642 note_gp_changes(rdp);
2643
2644 /* Start a new grace period if one not already started. */
2645 if (!rcu_gp_in_progress()) {
2646 rcu_accelerate_cbs_unlocked(rdp->mynode, rdp);
2647 } else {
2648 /* Give the grace period a kick. */
2649 rdp->blimit = DEFAULT_MAX_RCU_BLIMIT;
2650 if (READ_ONCE(rcu_state.n_force_qs) == rdp->n_force_qs_snap &&
2651 rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
2652 rcu_force_quiescent_state();
2653 rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
2654 rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
2655 }
2656 }
2657}
2658
2659/*
2660 * RCU callback function to leak a callback.
2661 */
2662static void rcu_leak_callback(struct rcu_head *rhp)
2663{
2664}
2665
2666/*
2667 * Check and if necessary update the leaf rcu_node structure's
2668 * ->cbovldmask bit corresponding to the current CPU based on that CPU's
2669 * number of queued RCU callbacks. The caller must hold the leaf rcu_node
2670 * structure's ->lock.
2671 */
2672static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp)
2673{
2674 raw_lockdep_assert_held_rcu_node(rnp);
2675 if (qovld_calc <= 0)
2676 return; // Early boot and wildcard value set.
2677 if (rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc)
2678 WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask | rdp->grpmask);
2679 else
2680 WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask & ~rdp->grpmask);
2681}
2682
2683/*
2684 * Check and if necessary update the leaf rcu_node structure's
2685 * ->cbovldmask bit corresponding to the current CPU based on that CPU's
2686 * number of queued RCU callbacks. No locks need be held, but the
2687 * caller must have disabled interrupts.
2688 *
2689 * Note that this function ignores the possibility that there are a lot
2690 * of callbacks all of which have already seen the end of their respective
2691 * grace periods. This omission is due to the need for no-CBs CPUs to
2692 * be holding ->nocb_lock to do this check, which is too heavy for a
2693 * common-case operation.
2694 */
2695static void check_cb_ovld(struct rcu_data *rdp)
2696{
2697 struct rcu_node *const rnp = rdp->mynode;
2698
2699 if (qovld_calc <= 0 ||
2700 ((rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc) ==
2701 !!(READ_ONCE(rnp->cbovldmask) & rdp->grpmask)))
2702 return; // Early boot wildcard value or already set correctly.
2703 raw_spin_lock_rcu_node(rnp);
2704 check_cb_ovld_locked(rdp, rnp);
2705 raw_spin_unlock_rcu_node(rnp);
2706}
2707
2708static void
2709__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
2710{
2711 static atomic_t doublefrees;
2712 unsigned long flags;
2713 bool lazy;
2714 struct rcu_data *rdp;
2715
2716 /* Misaligned rcu_head! */
2717 WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
2718
2719 if (debug_rcu_head_queue(head)) {
2720 /*
2721 * Probable double call_rcu(), so leak the callback.
2722 * Use rcu:rcu_callback trace event to find the previous
2723 * time callback was passed to call_rcu().
2724 */
2725 if (atomic_inc_return(&doublefrees) < 4) {
2726 pr_err("%s(): Double-freed CB %p->%pS()!!! ", __func__, head, head->func);
2727 mem_dump_obj(head);
2728 }
2729 WRITE_ONCE(head->func, rcu_leak_callback);
2730 return;
2731 }
2732 head->func = func;
2733 head->next = NULL;
2734 kasan_record_aux_stack_noalloc(head);
2735 local_irq_save(flags);
2736 rdp = this_cpu_ptr(&rcu_data);
2737 lazy = lazy_in && !rcu_async_should_hurry();
2738
2739 /* Add the callback to our list. */
2740 if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) {
2741 // This can trigger due to call_rcu() from offline CPU:
2742 WARN_ON_ONCE(rcu_scheduler_active != RCU_SCHEDULER_INACTIVE);
2743 WARN_ON_ONCE(!rcu_is_watching());
2744 // Very early boot, before rcu_init(). Initialize if needed
2745 // and then drop through to queue the callback.
2746 if (rcu_segcblist_empty(&rdp->cblist))
2747 rcu_segcblist_init(&rdp->cblist);
2748 }
2749
2750 check_cb_ovld(rdp);
2751
2752 if (unlikely(rcu_rdp_is_offloaded(rdp)))
2753 call_rcu_nocb(rdp, head, func, flags, lazy);
2754 else
2755 call_rcu_core(rdp, head, func, flags);
2756 local_irq_restore(flags);
2757}
2758
2759#ifdef CONFIG_RCU_LAZY
2760static bool enable_rcu_lazy __read_mostly = !IS_ENABLED(CONFIG_RCU_LAZY_DEFAULT_OFF);
2761module_param(enable_rcu_lazy, bool, 0444);
2762
2763/**
2764 * call_rcu_hurry() - Queue RCU callback for invocation after grace period, and
2765 * flush all lazy callbacks (including the new one) to the main ->cblist while
2766 * doing so.
2767 *
2768 * @head: structure to be used for queueing the RCU updates.
2769 * @func: actual callback function to be invoked after the grace period
2770 *
2771 * The callback function will be invoked some time after a full grace
2772 * period elapses, in other words after all pre-existing RCU read-side
2773 * critical sections have completed.
2774 *
2775 * Use this API instead of call_rcu() if you don't want the callback to be
2776 * invoked after very long periods of time, which can happen on systems without
2777 * memory pressure and on systems which are lightly loaded or mostly idle.
2778 * This function will cause callbacks to be invoked sooner than later at the
2779 * expense of extra power. Other than that, this function is identical to, and
2780 * reuses call_rcu()'s logic. Refer to call_rcu() for more details about memory
2781 * ordering and other functionality.
2782 */
2783void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func)
2784{
2785 __call_rcu_common(head, func, false);
2786}
2787EXPORT_SYMBOL_GPL(call_rcu_hurry);
2788#else
2789#define enable_rcu_lazy false
2790#endif
2791
2792/**
2793 * call_rcu() - Queue an RCU callback for invocation after a grace period.
2794 * By default the callbacks are 'lazy' and are kept hidden from the main
2795 * ->cblist to prevent starting of grace periods too soon.
2796 * If you desire grace periods to start very soon, use call_rcu_hurry().
2797 *
2798 * @head: structure to be used for queueing the RCU updates.
2799 * @func: actual callback function to be invoked after the grace period
2800 *
2801 * The callback function will be invoked some time after a full grace
2802 * period elapses, in other words after all pre-existing RCU read-side
2803 * critical sections have completed. However, the callback function
2804 * might well execute concurrently with RCU read-side critical sections
2805 * that started after call_rcu() was invoked.
2806 *
2807 * RCU read-side critical sections are delimited by rcu_read_lock()
2808 * and rcu_read_unlock(), and may be nested. In addition, but only in
2809 * v5.0 and later, regions of code across which interrupts, preemption,
2810 * or softirqs have been disabled also serve as RCU read-side critical
2811 * sections. This includes hardware interrupt handlers, softirq handlers,
2812 * and NMI handlers.
2813 *
2814 * Note that all CPUs must agree that the grace period extended beyond
2815 * all pre-existing RCU read-side critical section. On systems with more
2816 * than one CPU, this means that when "func()" is invoked, each CPU is
2817 * guaranteed to have executed a full memory barrier since the end of its
2818 * last RCU read-side critical section whose beginning preceded the call
2819 * to call_rcu(). It also means that each CPU executing an RCU read-side
2820 * critical section that continues beyond the start of "func()" must have
2821 * executed a memory barrier after the call_rcu() but before the beginning
2822 * of that RCU read-side critical section. Note that these guarantees
2823 * include CPUs that are offline, idle, or executing in user mode, as
2824 * well as CPUs that are executing in the kernel.
2825 *
2826 * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
2827 * resulting RCU callback function "func()", then both CPU A and CPU B are
2828 * guaranteed to execute a full memory barrier during the time interval
2829 * between the call to call_rcu() and the invocation of "func()" -- even
2830 * if CPU A and CPU B are the same CPU (but again only if the system has
2831 * more than one CPU).
2832 *
2833 * Implementation of these memory-ordering guarantees is described here:
2834 * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
2835 */
2836void call_rcu(struct rcu_head *head, rcu_callback_t func)
2837{
2838 __call_rcu_common(head, func, enable_rcu_lazy);
2839}
2840EXPORT_SYMBOL_GPL(call_rcu);
2841
2842/* Maximum number of jiffies to wait before draining a batch. */
2843#define KFREE_DRAIN_JIFFIES (5 * HZ)
2844#define KFREE_N_BATCHES 2
2845#define FREE_N_CHANNELS 2
2846
2847/**
2848 * struct kvfree_rcu_bulk_data - single block to store kvfree_rcu() pointers
2849 * @list: List node. All blocks are linked between each other
2850 * @gp_snap: Snapshot of RCU state for objects placed to this bulk
2851 * @nr_records: Number of active pointers in the array
2852 * @records: Array of the kvfree_rcu() pointers
2853 */
2854struct kvfree_rcu_bulk_data {
2855 struct list_head list;
2856 struct rcu_gp_oldstate gp_snap;
2857 unsigned long nr_records;
2858 void *records[];
2859};
2860
2861/*
2862 * This macro defines how many entries the "records" array
2863 * will contain. It is based on the fact that the size of
2864 * kvfree_rcu_bulk_data structure becomes exactly one page.
2865 */
2866#define KVFREE_BULK_MAX_ENTR \
2867 ((PAGE_SIZE - sizeof(struct kvfree_rcu_bulk_data)) / sizeof(void *))
2868
2869/**
2870 * struct kfree_rcu_cpu_work - single batch of kfree_rcu() requests
2871 * @rcu_work: Let queue_rcu_work() invoke workqueue handler after grace period
2872 * @head_free: List of kfree_rcu() objects waiting for a grace period
2873 * @head_free_gp_snap: Grace-period snapshot to check for attempted premature frees.
2874 * @bulk_head_free: Bulk-List of kvfree_rcu() objects waiting for a grace period
2875 * @krcp: Pointer to @kfree_rcu_cpu structure
2876 */
2877
2878struct kfree_rcu_cpu_work {
2879 struct rcu_work rcu_work;
2880 struct rcu_head *head_free;
2881 struct rcu_gp_oldstate head_free_gp_snap;
2882 struct list_head bulk_head_free[FREE_N_CHANNELS];
2883 struct kfree_rcu_cpu *krcp;
2884};
2885
2886/**
2887 * struct kfree_rcu_cpu - batch up kfree_rcu() requests for RCU grace period
2888 * @head: List of kfree_rcu() objects not yet waiting for a grace period
2889 * @head_gp_snap: Snapshot of RCU state for objects placed to "@head"
2890 * @bulk_head: Bulk-List of kvfree_rcu() objects not yet waiting for a grace period
2891 * @krw_arr: Array of batches of kfree_rcu() objects waiting for a grace period
2892 * @lock: Synchronize access to this structure
2893 * @monitor_work: Promote @head to @head_free after KFREE_DRAIN_JIFFIES
2894 * @initialized: The @rcu_work fields have been initialized
2895 * @head_count: Number of objects in rcu_head singular list
2896 * @bulk_count: Number of objects in bulk-list
2897 * @bkvcache:
2898 * A simple cache list that contains objects for reuse purpose.
2899 * In order to save some per-cpu space the list is singular.
2900 * Even though it is lockless an access has to be protected by the
2901 * per-cpu lock.
2902 * @page_cache_work: A work to refill the cache when it is empty
2903 * @backoff_page_cache_fill: Delay cache refills
2904 * @work_in_progress: Indicates that page_cache_work is running
2905 * @hrtimer: A hrtimer for scheduling a page_cache_work
2906 * @nr_bkv_objs: number of allocated objects at @bkvcache.
2907 *
2908 * This is a per-CPU structure. The reason that it is not included in
2909 * the rcu_data structure is to permit this code to be extracted from
2910 * the RCU files. Such extraction could allow further optimization of
2911 * the interactions with the slab allocators.
2912 */
2913struct kfree_rcu_cpu {
2914 // Objects queued on a linked list
2915 // through their rcu_head structures.
2916 struct rcu_head *head;
2917 unsigned long head_gp_snap;
2918 atomic_t head_count;
2919
2920 // Objects queued on a bulk-list.
2921 struct list_head bulk_head[FREE_N_CHANNELS];
2922 atomic_t bulk_count[FREE_N_CHANNELS];
2923
2924 struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES];
2925 raw_spinlock_t lock;
2926 struct delayed_work monitor_work;
2927 bool initialized;
2928
2929 struct delayed_work page_cache_work;
2930 atomic_t backoff_page_cache_fill;
2931 atomic_t work_in_progress;
2932 struct hrtimer hrtimer;
2933
2934 struct llist_head bkvcache;
2935 int nr_bkv_objs;
2936};
2937
2938static DEFINE_PER_CPU(struct kfree_rcu_cpu, krc) = {
2939 .lock = __RAW_SPIN_LOCK_UNLOCKED(krc.lock),
2940};
2941
2942static __always_inline void
2943debug_rcu_bhead_unqueue(struct kvfree_rcu_bulk_data *bhead)
2944{
2945#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
2946 int i;
2947
2948 for (i = 0; i < bhead->nr_records; i++)
2949 debug_rcu_head_unqueue((struct rcu_head *)(bhead->records[i]));
2950#endif
2951}
2952
2953static inline struct kfree_rcu_cpu *
2954krc_this_cpu_lock(unsigned long *flags)
2955{
2956 struct kfree_rcu_cpu *krcp;
2957
2958 local_irq_save(*flags); // For safely calling this_cpu_ptr().
2959 krcp = this_cpu_ptr(&krc);
2960 raw_spin_lock(&krcp->lock);
2961
2962 return krcp;
2963}
2964
2965static inline void
2966krc_this_cpu_unlock(struct kfree_rcu_cpu *krcp, unsigned long flags)
2967{
2968 raw_spin_unlock_irqrestore(&krcp->lock, flags);
2969}
2970
2971static inline struct kvfree_rcu_bulk_data *
2972get_cached_bnode(struct kfree_rcu_cpu *krcp)
2973{
2974 if (!krcp->nr_bkv_objs)
2975 return NULL;
2976
2977 WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs - 1);
2978 return (struct kvfree_rcu_bulk_data *)
2979 llist_del_first(&krcp->bkvcache);
2980}
2981
2982static inline bool
2983put_cached_bnode(struct kfree_rcu_cpu *krcp,
2984 struct kvfree_rcu_bulk_data *bnode)
2985{
2986 // Check the limit.
2987 if (krcp->nr_bkv_objs >= rcu_min_cached_objs)
2988 return false;
2989
2990 llist_add((struct llist_node *) bnode, &krcp->bkvcache);
2991 WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs + 1);
2992 return true;
2993}
2994
2995static int
2996drain_page_cache(struct kfree_rcu_cpu *krcp)
2997{
2998 unsigned long flags;
2999 struct llist_node *page_list, *pos, *n;
3000 int freed = 0;
3001
3002 if (!rcu_min_cached_objs)
3003 return 0;
3004
3005 raw_spin_lock_irqsave(&krcp->lock, flags);
3006 page_list = llist_del_all(&krcp->bkvcache);
3007 WRITE_ONCE(krcp->nr_bkv_objs, 0);
3008 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3009
3010 llist_for_each_safe(pos, n, page_list) {
3011 free_page((unsigned long)pos);
3012 freed++;
3013 }
3014
3015 return freed;
3016}
3017
3018static void
3019kvfree_rcu_bulk(struct kfree_rcu_cpu *krcp,
3020 struct kvfree_rcu_bulk_data *bnode, int idx)
3021{
3022 unsigned long flags;
3023 int i;
3024
3025 if (!WARN_ON_ONCE(!poll_state_synchronize_rcu_full(&bnode->gp_snap))) {
3026 debug_rcu_bhead_unqueue(bnode);
3027 rcu_lock_acquire(&rcu_callback_map);
3028 if (idx == 0) { // kmalloc() / kfree().
3029 trace_rcu_invoke_kfree_bulk_callback(
3030 rcu_state.name, bnode->nr_records,
3031 bnode->records);
3032
3033 kfree_bulk(bnode->nr_records, bnode->records);
3034 } else { // vmalloc() / vfree().
3035 for (i = 0; i < bnode->nr_records; i++) {
3036 trace_rcu_invoke_kvfree_callback(
3037 rcu_state.name, bnode->records[i], 0);
3038
3039 vfree(bnode->records[i]);
3040 }
3041 }
3042 rcu_lock_release(&rcu_callback_map);
3043 }
3044
3045 raw_spin_lock_irqsave(&krcp->lock, flags);
3046 if (put_cached_bnode(krcp, bnode))
3047 bnode = NULL;
3048 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3049
3050 if (bnode)
3051 free_page((unsigned long) bnode);
3052
3053 cond_resched_tasks_rcu_qs();
3054}
3055
3056static void
3057kvfree_rcu_list(struct rcu_head *head)
3058{
3059 struct rcu_head *next;
3060
3061 for (; head; head = next) {
3062 void *ptr = (void *) head->func;
3063 unsigned long offset = (void *) head - ptr;
3064
3065 next = head->next;
3066 debug_rcu_head_unqueue((struct rcu_head *)ptr);
3067 rcu_lock_acquire(&rcu_callback_map);
3068 trace_rcu_invoke_kvfree_callback(rcu_state.name, head, offset);
3069
3070 if (!WARN_ON_ONCE(!__is_kvfree_rcu_offset(offset)))
3071 kvfree(ptr);
3072
3073 rcu_lock_release(&rcu_callback_map);
3074 cond_resched_tasks_rcu_qs();
3075 }
3076}
3077
3078/*
3079 * This function is invoked in workqueue context after a grace period.
3080 * It frees all the objects queued on ->bulk_head_free or ->head_free.
3081 */
3082static void kfree_rcu_work(struct work_struct *work)
3083{
3084 unsigned long flags;
3085 struct kvfree_rcu_bulk_data *bnode, *n;
3086 struct list_head bulk_head[FREE_N_CHANNELS];
3087 struct rcu_head *head;
3088 struct kfree_rcu_cpu *krcp;
3089 struct kfree_rcu_cpu_work *krwp;
3090 struct rcu_gp_oldstate head_gp_snap;
3091 int i;
3092
3093 krwp = container_of(to_rcu_work(work),
3094 struct kfree_rcu_cpu_work, rcu_work);
3095 krcp = krwp->krcp;
3096
3097 raw_spin_lock_irqsave(&krcp->lock, flags);
3098 // Channels 1 and 2.
3099 for (i = 0; i < FREE_N_CHANNELS; i++)
3100 list_replace_init(&krwp->bulk_head_free[i], &bulk_head[i]);
3101
3102 // Channel 3.
3103 head = krwp->head_free;
3104 krwp->head_free = NULL;
3105 head_gp_snap = krwp->head_free_gp_snap;
3106 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3107
3108 // Handle the first two channels.
3109 for (i = 0; i < FREE_N_CHANNELS; i++) {
3110 // Start from the tail page, so a GP is likely passed for it.
3111 list_for_each_entry_safe(bnode, n, &bulk_head[i], list)
3112 kvfree_rcu_bulk(krcp, bnode, i);
3113 }
3114
3115 /*
3116 * This is used when the "bulk" path can not be used for the
3117 * double-argument of kvfree_rcu(). This happens when the
3118 * page-cache is empty, which means that objects are instead
3119 * queued on a linked list through their rcu_head structures.
3120 * This list is named "Channel 3".
3121 */
3122 if (head && !WARN_ON_ONCE(!poll_state_synchronize_rcu_full(&head_gp_snap)))
3123 kvfree_rcu_list(head);
3124}
3125
3126static bool
3127need_offload_krc(struct kfree_rcu_cpu *krcp)
3128{
3129 int i;
3130
3131 for (i = 0; i < FREE_N_CHANNELS; i++)
3132 if (!list_empty(&krcp->bulk_head[i]))
3133 return true;
3134
3135 return !!READ_ONCE(krcp->head);
3136}
3137
3138static bool
3139need_wait_for_krwp_work(struct kfree_rcu_cpu_work *krwp)
3140{
3141 int i;
3142
3143 for (i = 0; i < FREE_N_CHANNELS; i++)
3144 if (!list_empty(&krwp->bulk_head_free[i]))
3145 return true;
3146
3147 return !!krwp->head_free;
3148}
3149
3150static int krc_count(struct kfree_rcu_cpu *krcp)
3151{
3152 int sum = atomic_read(&krcp->head_count);
3153 int i;
3154
3155 for (i = 0; i < FREE_N_CHANNELS; i++)
3156 sum += atomic_read(&krcp->bulk_count[i]);
3157
3158 return sum;
3159}
3160
3161static void
3162schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp)
3163{
3164 long delay, delay_left;
3165
3166 delay = krc_count(krcp) >= KVFREE_BULK_MAX_ENTR ? 1:KFREE_DRAIN_JIFFIES;
3167 if (delayed_work_pending(&krcp->monitor_work)) {
3168 delay_left = krcp->monitor_work.timer.expires - jiffies;
3169 if (delay < delay_left)
3170 mod_delayed_work(system_wq, &krcp->monitor_work, delay);
3171 return;
3172 }
3173 queue_delayed_work(system_wq, &krcp->monitor_work, delay);
3174}
3175
3176static void
3177kvfree_rcu_drain_ready(struct kfree_rcu_cpu *krcp)
3178{
3179 struct list_head bulk_ready[FREE_N_CHANNELS];
3180 struct kvfree_rcu_bulk_data *bnode, *n;
3181 struct rcu_head *head_ready = NULL;
3182 unsigned long flags;
3183 int i;
3184
3185 raw_spin_lock_irqsave(&krcp->lock, flags);
3186 for (i = 0; i < FREE_N_CHANNELS; i++) {
3187 INIT_LIST_HEAD(&bulk_ready[i]);
3188
3189 list_for_each_entry_safe_reverse(bnode, n, &krcp->bulk_head[i], list) {
3190 if (!poll_state_synchronize_rcu_full(&bnode->gp_snap))
3191 break;
3192
3193 atomic_sub(bnode->nr_records, &krcp->bulk_count[i]);
3194 list_move(&bnode->list, &bulk_ready[i]);
3195 }
3196 }
3197
3198 if (krcp->head && poll_state_synchronize_rcu(krcp->head_gp_snap)) {
3199 head_ready = krcp->head;
3200 atomic_set(&krcp->head_count, 0);
3201 WRITE_ONCE(krcp->head, NULL);
3202 }
3203 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3204
3205 for (i = 0; i < FREE_N_CHANNELS; i++) {
3206 list_for_each_entry_safe(bnode, n, &bulk_ready[i], list)
3207 kvfree_rcu_bulk(krcp, bnode, i);
3208 }
3209
3210 if (head_ready)
3211 kvfree_rcu_list(head_ready);
3212}
3213
3214/*
3215 * This function is invoked after the KFREE_DRAIN_JIFFIES timeout.
3216 */
3217static void kfree_rcu_monitor(struct work_struct *work)
3218{
3219 struct kfree_rcu_cpu *krcp = container_of(work,
3220 struct kfree_rcu_cpu, monitor_work.work);
3221 unsigned long flags;
3222 int i, j;
3223
3224 // Drain ready for reclaim.
3225 kvfree_rcu_drain_ready(krcp);
3226
3227 raw_spin_lock_irqsave(&krcp->lock, flags);
3228
3229 // Attempt to start a new batch.
3230 for (i = 0; i < KFREE_N_BATCHES; i++) {
3231 struct kfree_rcu_cpu_work *krwp = &(krcp->krw_arr[i]);
3232
3233 // Try to detach bulk_head or head and attach it, only when
3234 // all channels are free. Any channel is not free means at krwp
3235 // there is on-going rcu work to handle krwp's free business.
3236 if (need_wait_for_krwp_work(krwp))
3237 continue;
3238
3239 // kvfree_rcu_drain_ready() might handle this krcp, if so give up.
3240 if (need_offload_krc(krcp)) {
3241 // Channel 1 corresponds to the SLAB-pointer bulk path.
3242 // Channel 2 corresponds to vmalloc-pointer bulk path.
3243 for (j = 0; j < FREE_N_CHANNELS; j++) {
3244 if (list_empty(&krwp->bulk_head_free[j])) {
3245 atomic_set(&krcp->bulk_count[j], 0);
3246 list_replace_init(&krcp->bulk_head[j],
3247 &krwp->bulk_head_free[j]);
3248 }
3249 }
3250
3251 // Channel 3 corresponds to both SLAB and vmalloc
3252 // objects queued on the linked list.
3253 if (!krwp->head_free) {
3254 krwp->head_free = krcp->head;
3255 get_state_synchronize_rcu_full(&krwp->head_free_gp_snap);
3256 atomic_set(&krcp->head_count, 0);
3257 WRITE_ONCE(krcp->head, NULL);
3258 }
3259
3260 // One work is per one batch, so there are three
3261 // "free channels", the batch can handle. It can
3262 // be that the work is in the pending state when
3263 // channels have been detached following by each
3264 // other.
3265 queue_rcu_work(system_wq, &krwp->rcu_work);
3266 }
3267 }
3268
3269 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3270
3271 // If there is nothing to detach, it means that our job is
3272 // successfully done here. In case of having at least one
3273 // of the channels that is still busy we should rearm the
3274 // work to repeat an attempt. Because previous batches are
3275 // still in progress.
3276 if (need_offload_krc(krcp))
3277 schedule_delayed_monitor_work(krcp);
3278}
3279
3280static enum hrtimer_restart
3281schedule_page_work_fn(struct hrtimer *t)
3282{
3283 struct kfree_rcu_cpu *krcp =
3284 container_of(t, struct kfree_rcu_cpu, hrtimer);
3285
3286 queue_delayed_work(system_highpri_wq, &krcp->page_cache_work, 0);
3287 return HRTIMER_NORESTART;
3288}
3289
3290static void fill_page_cache_func(struct work_struct *work)
3291{
3292 struct kvfree_rcu_bulk_data *bnode;
3293 struct kfree_rcu_cpu *krcp =
3294 container_of(work, struct kfree_rcu_cpu,
3295 page_cache_work.work);
3296 unsigned long flags;
3297 int nr_pages;
3298 bool pushed;
3299 int i;
3300
3301 nr_pages = atomic_read(&krcp->backoff_page_cache_fill) ?
3302 1 : rcu_min_cached_objs;
3303
3304 for (i = READ_ONCE(krcp->nr_bkv_objs); i < nr_pages; i++) {
3305 bnode = (struct kvfree_rcu_bulk_data *)
3306 __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
3307
3308 if (!bnode)
3309 break;
3310
3311 raw_spin_lock_irqsave(&krcp->lock, flags);
3312 pushed = put_cached_bnode(krcp, bnode);
3313 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3314
3315 if (!pushed) {
3316 free_page((unsigned long) bnode);
3317 break;
3318 }
3319 }
3320
3321 atomic_set(&krcp->work_in_progress, 0);
3322 atomic_set(&krcp->backoff_page_cache_fill, 0);
3323}
3324
3325static void
3326run_page_cache_worker(struct kfree_rcu_cpu *krcp)
3327{
3328 // If cache disabled, bail out.
3329 if (!rcu_min_cached_objs)
3330 return;
3331
3332 if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
3333 !atomic_xchg(&krcp->work_in_progress, 1)) {
3334 if (atomic_read(&krcp->backoff_page_cache_fill)) {
3335 queue_delayed_work(system_wq,
3336 &krcp->page_cache_work,
3337 msecs_to_jiffies(rcu_delay_page_cache_fill_msec));
3338 } else {
3339 hrtimer_init(&krcp->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
3340 krcp->hrtimer.function = schedule_page_work_fn;
3341 hrtimer_start(&krcp->hrtimer, 0, HRTIMER_MODE_REL);
3342 }
3343 }
3344}
3345
3346// Record ptr in a page managed by krcp, with the pre-krc_this_cpu_lock()
3347// state specified by flags. If can_alloc is true, the caller must
3348// be schedulable and not be holding any locks or mutexes that might be
3349// acquired by the memory allocator or anything that it might invoke.
3350// Returns true if ptr was successfully recorded, else the caller must
3351// use a fallback.
3352static inline bool
3353add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
3354 unsigned long *flags, void *ptr, bool can_alloc)
3355{
3356 struct kvfree_rcu_bulk_data *bnode;
3357 int idx;
3358
3359 *krcp = krc_this_cpu_lock(flags);
3360 if (unlikely(!(*krcp)->initialized))
3361 return false;
3362
3363 idx = !!is_vmalloc_addr(ptr);
3364 bnode = list_first_entry_or_null(&(*krcp)->bulk_head[idx],
3365 struct kvfree_rcu_bulk_data, list);
3366
3367 /* Check if a new block is required. */
3368 if (!bnode || bnode->nr_records == KVFREE_BULK_MAX_ENTR) {
3369 bnode = get_cached_bnode(*krcp);
3370 if (!bnode && can_alloc) {
3371 krc_this_cpu_unlock(*krcp, *flags);
3372
3373 // __GFP_NORETRY - allows a light-weight direct reclaim
3374 // what is OK from minimizing of fallback hitting point of
3375 // view. Apart of that it forbids any OOM invoking what is
3376 // also beneficial since we are about to release memory soon.
3377 //
3378 // __GFP_NOMEMALLOC - prevents from consuming of all the
3379 // memory reserves. Please note we have a fallback path.
3380 //
3381 // __GFP_NOWARN - it is supposed that an allocation can
3382 // be failed under low memory or high memory pressure
3383 // scenarios.
3384 bnode = (struct kvfree_rcu_bulk_data *)
3385 __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
3386 raw_spin_lock_irqsave(&(*krcp)->lock, *flags);
3387 }
3388
3389 if (!bnode)
3390 return false;
3391
3392 // Initialize the new block and attach it.
3393 bnode->nr_records = 0;
3394 list_add(&bnode->list, &(*krcp)->bulk_head[idx]);
3395 }
3396
3397 // Finally insert and update the GP for this page.
3398 bnode->records[bnode->nr_records++] = ptr;
3399 get_state_synchronize_rcu_full(&bnode->gp_snap);
3400 atomic_inc(&(*krcp)->bulk_count[idx]);
3401
3402 return true;
3403}
3404
3405/*
3406 * Queue a request for lazy invocation of the appropriate free routine
3407 * after a grace period. Please note that three paths are maintained,
3408 * two for the common case using arrays of pointers and a third one that
3409 * is used only when the main paths cannot be used, for example, due to
3410 * memory pressure.
3411 *
3412 * Each kvfree_call_rcu() request is added to a batch. The batch will be drained
3413 * every KFREE_DRAIN_JIFFIES number of jiffies. All the objects in the batch will
3414 * be free'd in workqueue context. This allows us to: batch requests together to
3415 * reduce the number of grace periods during heavy kfree_rcu()/kvfree_rcu() load.
3416 */
3417void kvfree_call_rcu(struct rcu_head *head, void *ptr)
3418{
3419 unsigned long flags;
3420 struct kfree_rcu_cpu *krcp;
3421 bool success;
3422
3423 /*
3424 * Please note there is a limitation for the head-less
3425 * variant, that is why there is a clear rule for such
3426 * objects: it can be used from might_sleep() context
3427 * only. For other places please embed an rcu_head to
3428 * your data.
3429 */
3430 if (!head)
3431 might_sleep();
3432
3433 // Queue the object but don't yet schedule the batch.
3434 if (debug_rcu_head_queue(ptr)) {
3435 // Probable double kfree_rcu(), just leak.
3436 WARN_ONCE(1, "%s(): Double-freed call. rcu_head %p\n",
3437 __func__, head);
3438
3439 // Mark as success and leave.
3440 return;
3441 }
3442
3443 kasan_record_aux_stack_noalloc(ptr);
3444 success = add_ptr_to_bulk_krc_lock(&krcp, &flags, ptr, !head);
3445 if (!success) {
3446 run_page_cache_worker(krcp);
3447
3448 if (head == NULL)
3449 // Inline if kvfree_rcu(one_arg) call.
3450 goto unlock_return;
3451
3452 head->func = ptr;
3453 head->next = krcp->head;
3454 WRITE_ONCE(krcp->head, head);
3455 atomic_inc(&krcp->head_count);
3456
3457 // Take a snapshot for this krcp.
3458 krcp->head_gp_snap = get_state_synchronize_rcu();
3459 success = true;
3460 }
3461
3462 /*
3463 * The kvfree_rcu() caller considers the pointer freed at this point
3464 * and likely removes any references to it. Since the actual slab
3465 * freeing (and kmemleak_free()) is deferred, tell kmemleak to ignore
3466 * this object (no scanning or false positives reporting).
3467 */
3468 kmemleak_ignore(ptr);
3469
3470 // Set timer to drain after KFREE_DRAIN_JIFFIES.
3471 if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING)
3472 schedule_delayed_monitor_work(krcp);
3473
3474unlock_return:
3475 krc_this_cpu_unlock(krcp, flags);
3476
3477 /*
3478 * Inline kvfree() after synchronize_rcu(). We can do
3479 * it from might_sleep() context only, so the current
3480 * CPU can pass the QS state.
3481 */
3482 if (!success) {
3483 debug_rcu_head_unqueue((struct rcu_head *) ptr);
3484 synchronize_rcu();
3485 kvfree(ptr);
3486 }
3487}
3488EXPORT_SYMBOL_GPL(kvfree_call_rcu);
3489
3490static unsigned long
3491kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
3492{
3493 int cpu;
3494 unsigned long count = 0;
3495
3496 /* Snapshot count of all CPUs */
3497 for_each_possible_cpu(cpu) {
3498 struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
3499
3500 count += krc_count(krcp);
3501 count += READ_ONCE(krcp->nr_bkv_objs);
3502 atomic_set(&krcp->backoff_page_cache_fill, 1);
3503 }
3504
3505 return count == 0 ? SHRINK_EMPTY : count;
3506}
3507
3508static unsigned long
3509kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
3510{
3511 int cpu, freed = 0;
3512
3513 for_each_possible_cpu(cpu) {
3514 int count;
3515 struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
3516
3517 count = krc_count(krcp);
3518 count += drain_page_cache(krcp);
3519 kfree_rcu_monitor(&krcp->monitor_work.work);
3520
3521 sc->nr_to_scan -= count;
3522 freed += count;
3523
3524 if (sc->nr_to_scan <= 0)
3525 break;
3526 }
3527
3528 return freed == 0 ? SHRINK_STOP : freed;
3529}
3530
3531void __init kfree_rcu_scheduler_running(void)
3532{
3533 int cpu;
3534
3535 for_each_possible_cpu(cpu) {
3536 struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
3537
3538 if (need_offload_krc(krcp))
3539 schedule_delayed_monitor_work(krcp);
3540 }
3541}
3542
3543/*
3544 * During early boot, any blocking grace-period wait automatically
3545 * implies a grace period.
3546 *
3547 * Later on, this could in theory be the case for kernels built with
3548 * CONFIG_SMP=y && CONFIG_PREEMPTION=y running on a single CPU, but this
3549 * is not a common case. Furthermore, this optimization would cause
3550 * the rcu_gp_oldstate structure to expand by 50%, so this potential
3551 * grace-period optimization is ignored once the scheduler is running.
3552 */
3553static int rcu_blocking_is_gp(void)
3554{
3555 if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE) {
3556 might_sleep();
3557 return false;
3558 }
3559 return true;
3560}
3561
3562/**
3563 * synchronize_rcu - wait until a grace period has elapsed.
3564 *
3565 * Control will return to the caller some time after a full grace
3566 * period has elapsed, in other words after all currently executing RCU
3567 * read-side critical sections have completed. Note, however, that
3568 * upon return from synchronize_rcu(), the caller might well be executing
3569 * concurrently with new RCU read-side critical sections that began while
3570 * synchronize_rcu() was waiting.
3571 *
3572 * RCU read-side critical sections are delimited by rcu_read_lock()
3573 * and rcu_read_unlock(), and may be nested. In addition, but only in
3574 * v5.0 and later, regions of code across which interrupts, preemption,
3575 * or softirqs have been disabled also serve as RCU read-side critical
3576 * sections. This includes hardware interrupt handlers, softirq handlers,
3577 * and NMI handlers.
3578 *
3579 * Note that this guarantee implies further memory-ordering guarantees.
3580 * On systems with more than one CPU, when synchronize_rcu() returns,
3581 * each CPU is guaranteed to have executed a full memory barrier since
3582 * the end of its last RCU read-side critical section whose beginning
3583 * preceded the call to synchronize_rcu(). In addition, each CPU having
3584 * an RCU read-side critical section that extends beyond the return from
3585 * synchronize_rcu() is guaranteed to have executed a full memory barrier
3586 * after the beginning of synchronize_rcu() and before the beginning of
3587 * that RCU read-side critical section. Note that these guarantees include
3588 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
3589 * that are executing in the kernel.
3590 *
3591 * Furthermore, if CPU A invoked synchronize_rcu(), which returned
3592 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
3593 * to have executed a full memory barrier during the execution of
3594 * synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but
3595 * again only if the system has more than one CPU).
3596 *
3597 * Implementation of these memory-ordering guarantees is described here:
3598 * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
3599 */
3600void synchronize_rcu(void)
3601{
3602 unsigned long flags;
3603 struct rcu_node *rnp;
3604
3605 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
3606 lock_is_held(&rcu_lock_map) ||
3607 lock_is_held(&rcu_sched_lock_map),
3608 "Illegal synchronize_rcu() in RCU read-side critical section");
3609 if (!rcu_blocking_is_gp()) {
3610 if (rcu_gp_is_expedited())
3611 synchronize_rcu_expedited();
3612 else
3613 wait_rcu_gp(call_rcu_hurry);
3614 return;
3615 }
3616
3617 // Context allows vacuous grace periods.
3618 // Note well that this code runs with !PREEMPT && !SMP.
3619 // In addition, all code that advances grace periods runs at
3620 // process level. Therefore, this normal GP overlaps with other
3621 // normal GPs only by being fully nested within them, which allows
3622 // reuse of ->gp_seq_polled_snap.
3623 rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_snap);
3624 rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_snap);
3625
3626 // Update the normal grace-period counters to record
3627 // this grace period, but only those used by the boot CPU.
3628 // The rcu_scheduler_starting() will take care of the rest of
3629 // these counters.
3630 local_irq_save(flags);
3631 WARN_ON_ONCE(num_online_cpus() > 1);
3632 rcu_state.gp_seq += (1 << RCU_SEQ_CTR_SHIFT);
3633 for (rnp = this_cpu_ptr(&rcu_data)->mynode; rnp; rnp = rnp->parent)
3634 rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq;
3635 local_irq_restore(flags);
3636}
3637EXPORT_SYMBOL_GPL(synchronize_rcu);
3638
3639/**
3640 * get_completed_synchronize_rcu_full - Return a full pre-completed polled state cookie
3641 * @rgosp: Place to put state cookie
3642 *
3643 * Stores into @rgosp a value that will always be treated by functions
3644 * like poll_state_synchronize_rcu_full() as a cookie whose grace period
3645 * has already completed.
3646 */
3647void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
3648{
3649 rgosp->rgos_norm = RCU_GET_STATE_COMPLETED;
3650 rgosp->rgos_exp = RCU_GET_STATE_COMPLETED;
3651}
3652EXPORT_SYMBOL_GPL(get_completed_synchronize_rcu_full);
3653
3654/**
3655 * get_state_synchronize_rcu - Snapshot current RCU state
3656 *
3657 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
3658 * or poll_state_synchronize_rcu() to determine whether or not a full
3659 * grace period has elapsed in the meantime.
3660 */
3661unsigned long get_state_synchronize_rcu(void)
3662{
3663 /*
3664 * Any prior manipulation of RCU-protected data must happen
3665 * before the load from ->gp_seq.
3666 */
3667 smp_mb(); /* ^^^ */
3668 return rcu_seq_snap(&rcu_state.gp_seq_polled);
3669}
3670EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
3671
3672/**
3673 * get_state_synchronize_rcu_full - Snapshot RCU state, both normal and expedited
3674 * @rgosp: location to place combined normal/expedited grace-period state
3675 *
3676 * Places the normal and expedited grace-period states in @rgosp. This
3677 * state value can be passed to a later call to cond_synchronize_rcu_full()
3678 * or poll_state_synchronize_rcu_full() to determine whether or not a
3679 * grace period (whether normal or expedited) has elapsed in the meantime.
3680 * The rcu_gp_oldstate structure takes up twice the memory of an unsigned
3681 * long, but is guaranteed to see all grace periods. In contrast, the
3682 * combined state occupies less memory, but can sometimes fail to take
3683 * grace periods into account.
3684 *
3685 * This does not guarantee that the needed grace period will actually
3686 * start.
3687 */
3688void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
3689{
3690 struct rcu_node *rnp = rcu_get_root();
3691
3692 /*
3693 * Any prior manipulation of RCU-protected data must happen
3694 * before the loads from ->gp_seq and ->expedited_sequence.
3695 */
3696 smp_mb(); /* ^^^ */
3697 rgosp->rgos_norm = rcu_seq_snap(&rnp->gp_seq);
3698 rgosp->rgos_exp = rcu_seq_snap(&rcu_state.expedited_sequence);
3699}
3700EXPORT_SYMBOL_GPL(get_state_synchronize_rcu_full);
3701
3702/*
3703 * Helper function for start_poll_synchronize_rcu() and
3704 * start_poll_synchronize_rcu_full().
3705 */
3706static void start_poll_synchronize_rcu_common(void)
3707{
3708 unsigned long flags;
3709 bool needwake;
3710 struct rcu_data *rdp;
3711 struct rcu_node *rnp;
3712
3713 lockdep_assert_irqs_enabled();
3714 local_irq_save(flags);
3715 rdp = this_cpu_ptr(&rcu_data);
3716 rnp = rdp->mynode;
3717 raw_spin_lock_rcu_node(rnp); // irqs already disabled.
3718 // Note it is possible for a grace period to have elapsed between
3719 // the above call to get_state_synchronize_rcu() and the below call
3720 // to rcu_seq_snap. This is OK, the worst that happens is that we
3721 // get a grace period that no one needed. These accesses are ordered
3722 // by smp_mb(), and we are accessing them in the opposite order
3723 // from which they are updated at grace-period start, as required.
3724 needwake = rcu_start_this_gp(rnp, rdp, rcu_seq_snap(&rcu_state.gp_seq));
3725 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3726 if (needwake)
3727 rcu_gp_kthread_wake();
3728}
3729
3730/**
3731 * start_poll_synchronize_rcu - Snapshot and start RCU grace period
3732 *
3733 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
3734 * or poll_state_synchronize_rcu() to determine whether or not a full
3735 * grace period has elapsed in the meantime. If the needed grace period
3736 * is not already slated to start, notifies RCU core of the need for that
3737 * grace period.
3738 *
3739 * Interrupts must be enabled for the case where it is necessary to awaken
3740 * the grace-period kthread.
3741 */
3742unsigned long start_poll_synchronize_rcu(void)
3743{
3744 unsigned long gp_seq = get_state_synchronize_rcu();
3745
3746 start_poll_synchronize_rcu_common();
3747 return gp_seq;
3748}
3749EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu);
3750
3751/**
3752 * start_poll_synchronize_rcu_full - Take a full snapshot and start RCU grace period
3753 * @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full()
3754 *
3755 * Places the normal and expedited grace-period states in *@rgos. This
3756 * state value can be passed to a later call to cond_synchronize_rcu_full()
3757 * or poll_state_synchronize_rcu_full() to determine whether or not a
3758 * grace period (whether normal or expedited) has elapsed in the meantime.
3759 * If the needed grace period is not already slated to start, notifies
3760 * RCU core of the need for that grace period.
3761 *
3762 * Interrupts must be enabled for the case where it is necessary to awaken
3763 * the grace-period kthread.
3764 */
3765void start_poll_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
3766{
3767 get_state_synchronize_rcu_full(rgosp);
3768
3769 start_poll_synchronize_rcu_common();
3770}
3771EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_full);
3772
3773/**
3774 * poll_state_synchronize_rcu - Has the specified RCU grace period completed?
3775 * @oldstate: value from get_state_synchronize_rcu() or start_poll_synchronize_rcu()
3776 *
3777 * If a full RCU grace period has elapsed since the earlier call from
3778 * which @oldstate was obtained, return @true, otherwise return @false.
3779 * If @false is returned, it is the caller's responsibility to invoke this
3780 * function later on until it does return @true. Alternatively, the caller
3781 * can explicitly wait for a grace period, for example, by passing @oldstate
3782 * to either cond_synchronize_rcu() or cond_synchronize_rcu_expedited()
3783 * on the one hand or by directly invoking either synchronize_rcu() or
3784 * synchronize_rcu_expedited() on the other.
3785 *
3786 * Yes, this function does not take counter wrap into account.
3787 * But counter wrap is harmless. If the counter wraps, we have waited for
3788 * more than a billion grace periods (and way more on a 64-bit system!).
3789 * Those needing to keep old state values for very long time periods
3790 * (many hours even on 32-bit systems) should check them occasionally and
3791 * either refresh them or set a flag indicating that the grace period has
3792 * completed. Alternatively, they can use get_completed_synchronize_rcu()
3793 * to get a guaranteed-completed grace-period state.
3794 *
3795 * In addition, because oldstate compresses the grace-period state for
3796 * both normal and expedited grace periods into a single unsigned long,
3797 * it can miss a grace period when synchronize_rcu() runs concurrently
3798 * with synchronize_rcu_expedited(). If this is unacceptable, please
3799 * instead use the _full() variant of these polling APIs.
3800 *
3801 * This function provides the same memory-ordering guarantees that
3802 * would be provided by a synchronize_rcu() that was invoked at the call
3803 * to the function that provided @oldstate, and that returned at the end
3804 * of this function.
3805 */
3806bool poll_state_synchronize_rcu(unsigned long oldstate)
3807{
3808 if (oldstate == RCU_GET_STATE_COMPLETED ||
3809 rcu_seq_done_exact(&rcu_state.gp_seq_polled, oldstate)) {
3810 smp_mb(); /* Ensure GP ends before subsequent accesses. */
3811 return true;
3812 }
3813 return false;
3814}
3815EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
3816
3817/**
3818 * poll_state_synchronize_rcu_full - Has the specified RCU grace period completed?
3819 * @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full()
3820 *
3821 * If a full RCU grace period has elapsed since the earlier call from
3822 * which *rgosp was obtained, return @true, otherwise return @false.
3823 * If @false is returned, it is the caller's responsibility to invoke this
3824 * function later on until it does return @true. Alternatively, the caller
3825 * can explicitly wait for a grace period, for example, by passing @rgosp
3826 * to cond_synchronize_rcu() or by directly invoking synchronize_rcu().
3827 *
3828 * Yes, this function does not take counter wrap into account.
3829 * But counter wrap is harmless. If the counter wraps, we have waited
3830 * for more than a billion grace periods (and way more on a 64-bit
3831 * system!). Those needing to keep rcu_gp_oldstate values for very
3832 * long time periods (many hours even on 32-bit systems) should check
3833 * them occasionally and either refresh them or set a flag indicating
3834 * that the grace period has completed. Alternatively, they can use
3835 * get_completed_synchronize_rcu_full() to get a guaranteed-completed
3836 * grace-period state.
3837 *
3838 * This function provides the same memory-ordering guarantees that would
3839 * be provided by a synchronize_rcu() that was invoked at the call to
3840 * the function that provided @rgosp, and that returned at the end of this
3841 * function. And this guarantee requires that the root rcu_node structure's
3842 * ->gp_seq field be checked instead of that of the rcu_state structure.
3843 * The problem is that the just-ending grace-period's callbacks can be
3844 * invoked between the time that the root rcu_node structure's ->gp_seq
3845 * field is updated and the time that the rcu_state structure's ->gp_seq
3846 * field is updated. Therefore, if a single synchronize_rcu() is to
3847 * cause a subsequent poll_state_synchronize_rcu_full() to return @true,
3848 * then the root rcu_node structure is the one that needs to be polled.
3849 */
3850bool poll_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
3851{
3852 struct rcu_node *rnp = rcu_get_root();
3853
3854 smp_mb(); // Order against root rcu_node structure grace-period cleanup.
3855 if (rgosp->rgos_norm == RCU_GET_STATE_COMPLETED ||
3856 rcu_seq_done_exact(&rnp->gp_seq, rgosp->rgos_norm) ||
3857 rgosp->rgos_exp == RCU_GET_STATE_COMPLETED ||
3858 rcu_seq_done_exact(&rcu_state.expedited_sequence, rgosp->rgos_exp)) {
3859 smp_mb(); /* Ensure GP ends before subsequent accesses. */
3860 return true;
3861 }
3862 return false;
3863}
3864EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu_full);
3865
3866/**
3867 * cond_synchronize_rcu - Conditionally wait for an RCU grace period
3868 * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
3869 *
3870 * If a full RCU grace period has elapsed since the earlier call to
3871 * get_state_synchronize_rcu() or start_poll_synchronize_rcu(), just return.
3872 * Otherwise, invoke synchronize_rcu() to wait for a full grace period.
3873 *
3874 * Yes, this function does not take counter wrap into account.
3875 * But counter wrap is harmless. If the counter wraps, we have waited for
3876 * more than 2 billion grace periods (and way more on a 64-bit system!),
3877 * so waiting for a couple of additional grace periods should be just fine.
3878 *
3879 * This function provides the same memory-ordering guarantees that
3880 * would be provided by a synchronize_rcu() that was invoked at the call
3881 * to the function that provided @oldstate and that returned at the end
3882 * of this function.
3883 */
3884void cond_synchronize_rcu(unsigned long oldstate)
3885{
3886 if (!poll_state_synchronize_rcu(oldstate))
3887 synchronize_rcu();
3888}
3889EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
3890
3891/**
3892 * cond_synchronize_rcu_full - Conditionally wait for an RCU grace period
3893 * @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full()
3894 *
3895 * If a full RCU grace period has elapsed since the call to
3896 * get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(),
3897 * or start_poll_synchronize_rcu_expedited_full() from which @rgosp was
3898 * obtained, just return. Otherwise, invoke synchronize_rcu() to wait
3899 * for a full grace period.
3900 *
3901 * Yes, this function does not take counter wrap into account.
3902 * But counter wrap is harmless. If the counter wraps, we have waited for
3903 * more than 2 billion grace periods (and way more on a 64-bit system!),
3904 * so waiting for a couple of additional grace periods should be just fine.
3905 *
3906 * This function provides the same memory-ordering guarantees that
3907 * would be provided by a synchronize_rcu() that was invoked at the call
3908 * to the function that provided @rgosp and that returned at the end of
3909 * this function.
3910 */
3911void cond_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
3912{
3913 if (!poll_state_synchronize_rcu_full(rgosp))
3914 synchronize_rcu();
3915}
3916EXPORT_SYMBOL_GPL(cond_synchronize_rcu_full);
3917
3918/*
3919 * Check to see if there is any immediate RCU-related work to be done by
3920 * the current CPU, returning 1 if so and zero otherwise. The checks are
3921 * in order of increasing expense: checks that can be carried out against
3922 * CPU-local state are performed first. However, we must check for CPU
3923 * stalls first, else we might not get a chance.
3924 */
3925static int rcu_pending(int user)
3926{
3927 bool gp_in_progress;
3928 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
3929 struct rcu_node *rnp = rdp->mynode;
3930
3931 lockdep_assert_irqs_disabled();
3932
3933 /* Check for CPU stalls, if enabled. */
3934 check_cpu_stall(rdp);
3935
3936 /* Does this CPU need a deferred NOCB wakeup? */
3937 if (rcu_nocb_need_deferred_wakeup(rdp, RCU_NOCB_WAKE))
3938 return 1;
3939
3940 /* Is this a nohz_full CPU in userspace or idle? (Ignore RCU if so.) */
3941 if ((user || rcu_is_cpu_rrupt_from_idle()) && rcu_nohz_full_cpu())
3942 return 0;
3943
3944 /* Is the RCU core waiting for a quiescent state from this CPU? */
3945 gp_in_progress = rcu_gp_in_progress();
3946 if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm && gp_in_progress)
3947 return 1;
3948
3949 /* Does this CPU have callbacks ready to invoke? */
3950 if (!rcu_rdp_is_offloaded(rdp) &&
3951 rcu_segcblist_ready_cbs(&rdp->cblist))
3952 return 1;
3953
3954 /* Has RCU gone idle with this CPU needing another grace period? */
3955 if (!gp_in_progress && rcu_segcblist_is_enabled(&rdp->cblist) &&
3956 !rcu_rdp_is_offloaded(rdp) &&
3957 !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
3958 return 1;
3959
3960 /* Have RCU grace period completed or started? */
3961 if (rcu_seq_current(&rnp->gp_seq) != rdp->gp_seq ||
3962 unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */
3963 return 1;
3964
3965 /* nothing to do */
3966 return 0;
3967}
3968
3969/*
3970 * Helper function for rcu_barrier() tracing. If tracing is disabled,
3971 * the compiler is expected to optimize this away.
3972 */
3973static void rcu_barrier_trace(const char *s, int cpu, unsigned long done)
3974{
3975 trace_rcu_barrier(rcu_state.name, s, cpu,
3976 atomic_read(&rcu_state.barrier_cpu_count), done);
3977}
3978
3979/*
3980 * RCU callback function for rcu_barrier(). If we are last, wake
3981 * up the task executing rcu_barrier().
3982 *
3983 * Note that the value of rcu_state.barrier_sequence must be captured
3984 * before the atomic_dec_and_test(). Otherwise, if this CPU is not last,
3985 * other CPUs might count the value down to zero before this CPU gets
3986 * around to invoking rcu_barrier_trace(), which might result in bogus
3987 * data from the next instance of rcu_barrier().
3988 */
3989static void rcu_barrier_callback(struct rcu_head *rhp)
3990{
3991 unsigned long __maybe_unused s = rcu_state.barrier_sequence;
3992
3993 if (atomic_dec_and_test(&rcu_state.barrier_cpu_count)) {
3994 rcu_barrier_trace(TPS("LastCB"), -1, s);
3995 complete(&rcu_state.barrier_completion);
3996 } else {
3997 rcu_barrier_trace(TPS("CB"), -1, s);
3998 }
3999}
4000
4001/*
4002 * If needed, entrain an rcu_barrier() callback on rdp->cblist.
4003 */
4004static void rcu_barrier_entrain(struct rcu_data *rdp)
4005{
4006 unsigned long gseq = READ_ONCE(rcu_state.barrier_sequence);
4007 unsigned long lseq = READ_ONCE(rdp->barrier_seq_snap);
4008 bool wake_nocb = false;
4009 bool was_alldone = false;
4010
4011 lockdep_assert_held(&rcu_state.barrier_lock);
4012 if (rcu_seq_state(lseq) || !rcu_seq_state(gseq) || rcu_seq_ctr(lseq) != rcu_seq_ctr(gseq))
4013 return;
4014 rcu_barrier_trace(TPS("IRQ"), -1, rcu_state.barrier_sequence);
4015 rdp->barrier_head.func = rcu_barrier_callback;
4016 debug_rcu_head_queue(&rdp->barrier_head);
4017 rcu_nocb_lock(rdp);
4018 /*
4019 * Flush bypass and wakeup rcuog if we add callbacks to an empty regular
4020 * queue. This way we don't wait for bypass timer that can reach seconds
4021 * if it's fully lazy.
4022 */
4023 was_alldone = rcu_rdp_is_offloaded(rdp) && !rcu_segcblist_pend_cbs(&rdp->cblist);
4024 WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false));
4025 wake_nocb = was_alldone && rcu_segcblist_pend_cbs(&rdp->cblist);
4026 if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head)) {
4027 atomic_inc(&rcu_state.barrier_cpu_count);
4028 } else {
4029 debug_rcu_head_unqueue(&rdp->barrier_head);
4030 rcu_barrier_trace(TPS("IRQNQ"), -1, rcu_state.barrier_sequence);
4031 }
4032 rcu_nocb_unlock(rdp);
4033 if (wake_nocb)
4034 wake_nocb_gp(rdp, false);
4035 smp_store_release(&rdp->barrier_seq_snap, gseq);
4036}
4037
4038/*
4039 * Called with preemption disabled, and from cross-cpu IRQ context.
4040 */
4041static void rcu_barrier_handler(void *cpu_in)
4042{
4043 uintptr_t cpu = (uintptr_t)cpu_in;
4044 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4045
4046 lockdep_assert_irqs_disabled();
4047 WARN_ON_ONCE(cpu != rdp->cpu);
4048 WARN_ON_ONCE(cpu != smp_processor_id());
4049 raw_spin_lock(&rcu_state.barrier_lock);
4050 rcu_barrier_entrain(rdp);
4051 raw_spin_unlock(&rcu_state.barrier_lock);
4052}
4053
4054/**
4055 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
4056 *
4057 * Note that this primitive does not necessarily wait for an RCU grace period
4058 * to complete. For example, if there are no RCU callbacks queued anywhere
4059 * in the system, then rcu_barrier() is within its rights to return
4060 * immediately, without waiting for anything, much less an RCU grace period.
4061 */
4062void rcu_barrier(void)
4063{
4064 uintptr_t cpu;
4065 unsigned long flags;
4066 unsigned long gseq;
4067 struct rcu_data *rdp;
4068 unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
4069
4070 rcu_barrier_trace(TPS("Begin"), -1, s);
4071
4072 /* Take mutex to serialize concurrent rcu_barrier() requests. */
4073 mutex_lock(&rcu_state.barrier_mutex);
4074
4075 /* Did someone else do our work for us? */
4076 if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
4077 rcu_barrier_trace(TPS("EarlyExit"), -1, rcu_state.barrier_sequence);
4078 smp_mb(); /* caller's subsequent code after above check. */
4079 mutex_unlock(&rcu_state.barrier_mutex);
4080 return;
4081 }
4082
4083 /* Mark the start of the barrier operation. */
4084 raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
4085 rcu_seq_start(&rcu_state.barrier_sequence);
4086 gseq = rcu_state.barrier_sequence;
4087 rcu_barrier_trace(TPS("Inc1"), -1, rcu_state.barrier_sequence);
4088
4089 /*
4090 * Initialize the count to two rather than to zero in order
4091 * to avoid a too-soon return to zero in case of an immediate
4092 * invocation of the just-enqueued callback (or preemption of
4093 * this task). Exclude CPU-hotplug operations to ensure that no
4094 * offline non-offloaded CPU has callbacks queued.
4095 */
4096 init_completion(&rcu_state.barrier_completion);
4097 atomic_set(&rcu_state.barrier_cpu_count, 2);
4098 raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
4099
4100 /*
4101 * Force each CPU with callbacks to register a new callback.
4102 * When that callback is invoked, we will know that all of the
4103 * corresponding CPU's preceding callbacks have been invoked.
4104 */
4105 for_each_possible_cpu(cpu) {
4106 rdp = per_cpu_ptr(&rcu_data, cpu);
4107retry:
4108 if (smp_load_acquire(&rdp->barrier_seq_snap) == gseq)
4109 continue;
4110 raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
4111 if (!rcu_segcblist_n_cbs(&rdp->cblist)) {
4112 WRITE_ONCE(rdp->barrier_seq_snap, gseq);
4113 raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
4114 rcu_barrier_trace(TPS("NQ"), cpu, rcu_state.barrier_sequence);
4115 continue;
4116 }
4117 if (!rcu_rdp_cpu_online(rdp)) {
4118 rcu_barrier_entrain(rdp);
4119 WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq);
4120 raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
4121 rcu_barrier_trace(TPS("OfflineNoCBQ"), cpu, rcu_state.barrier_sequence);
4122 continue;
4123 }
4124 raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
4125 if (smp_call_function_single(cpu, rcu_barrier_handler, (void *)cpu, 1)) {
4126 schedule_timeout_uninterruptible(1);
4127 goto retry;
4128 }
4129 WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq);
4130 rcu_barrier_trace(TPS("OnlineQ"), cpu, rcu_state.barrier_sequence);
4131 }
4132
4133 /*
4134 * Now that we have an rcu_barrier_callback() callback on each
4135 * CPU, and thus each counted, remove the initial count.
4136 */
4137 if (atomic_sub_and_test(2, &rcu_state.barrier_cpu_count))
4138 complete(&rcu_state.barrier_completion);
4139
4140 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
4141 wait_for_completion(&rcu_state.barrier_completion);
4142
4143 /* Mark the end of the barrier operation. */
4144 rcu_barrier_trace(TPS("Inc2"), -1, rcu_state.barrier_sequence);
4145 rcu_seq_end(&rcu_state.barrier_sequence);
4146 gseq = rcu_state.barrier_sequence;
4147 for_each_possible_cpu(cpu) {
4148 rdp = per_cpu_ptr(&rcu_data, cpu);
4149
4150 WRITE_ONCE(rdp->barrier_seq_snap, gseq);
4151 }
4152
4153 /* Other rcu_barrier() invocations can now safely proceed. */
4154 mutex_unlock(&rcu_state.barrier_mutex);
4155}
4156EXPORT_SYMBOL_GPL(rcu_barrier);
4157
4158static unsigned long rcu_barrier_last_throttle;
4159
4160/**
4161 * rcu_barrier_throttled - Do rcu_barrier(), but limit to one per second
4162 *
4163 * This can be thought of as guard rails around rcu_barrier() that
4164 * permits unrestricted userspace use, at least assuming the hardware's
4165 * try_cmpxchg() is robust. There will be at most one call per second to
4166 * rcu_barrier() system-wide from use of this function, which means that
4167 * callers might needlessly wait a second or three.
4168 *
4169 * This is intended for use by test suites to avoid OOM by flushing RCU
4170 * callbacks from the previous test before starting the next. See the
4171 * rcutree.do_rcu_barrier module parameter for more information.
4172 *
4173 * Why not simply make rcu_barrier() more scalable? That might be
4174 * the eventual endpoint, but let's keep it simple for the time being.
4175 * Note that the module parameter infrastructure serializes calls to a
4176 * given .set() function, but should concurrent .set() invocation ever be
4177 * possible, we are ready!
4178 */
4179static void rcu_barrier_throttled(void)
4180{
4181 unsigned long j = jiffies;
4182 unsigned long old = READ_ONCE(rcu_barrier_last_throttle);
4183 unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
4184
4185 while (time_in_range(j, old, old + HZ / 16) ||
4186 !try_cmpxchg(&rcu_barrier_last_throttle, &old, j)) {
4187 schedule_timeout_idle(HZ / 16);
4188 if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
4189 smp_mb(); /* caller's subsequent code after above check. */
4190 return;
4191 }
4192 j = jiffies;
4193 old = READ_ONCE(rcu_barrier_last_throttle);
4194 }
4195 rcu_barrier();
4196}
4197
4198/*
4199 * Invoke rcu_barrier_throttled() when a rcutree.do_rcu_barrier
4200 * request arrives. We insist on a true value to allow for possible
4201 * future expansion.
4202 */
4203static int param_set_do_rcu_barrier(const char *val, const struct kernel_param *kp)
4204{
4205 bool b;
4206 int ret;
4207
4208 if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING)
4209 return -EAGAIN;
4210 ret = kstrtobool(val, &b);
4211 if (!ret && b) {
4212 atomic_inc((atomic_t *)kp->arg);
4213 rcu_barrier_throttled();
4214 atomic_dec((atomic_t *)kp->arg);
4215 }
4216 return ret;
4217}
4218
4219/*
4220 * Output the number of outstanding rcutree.do_rcu_barrier requests.
4221 */
4222static int param_get_do_rcu_barrier(char *buffer, const struct kernel_param *kp)
4223{
4224 return sprintf(buffer, "%d\n", atomic_read((atomic_t *)kp->arg));
4225}
4226
4227static const struct kernel_param_ops do_rcu_barrier_ops = {
4228 .set = param_set_do_rcu_barrier,
4229 .get = param_get_do_rcu_barrier,
4230};
4231static atomic_t do_rcu_barrier;
4232module_param_cb(do_rcu_barrier, &do_rcu_barrier_ops, &do_rcu_barrier, 0644);
4233
4234/*
4235 * Compute the mask of online CPUs for the specified rcu_node structure.
4236 * This will not be stable unless the rcu_node structure's ->lock is
4237 * held, but the bit corresponding to the current CPU will be stable
4238 * in most contexts.
4239 */
4240static unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
4241{
4242 return READ_ONCE(rnp->qsmaskinitnext);
4243}
4244
4245/*
4246 * Is the CPU corresponding to the specified rcu_data structure online
4247 * from RCU's perspective? This perspective is given by that structure's
4248 * ->qsmaskinitnext field rather than by the global cpu_online_mask.
4249 */
4250static bool rcu_rdp_cpu_online(struct rcu_data *rdp)
4251{
4252 return !!(rdp->grpmask & rcu_rnp_online_cpus(rdp->mynode));
4253}
4254
4255bool rcu_cpu_online(int cpu)
4256{
4257 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4258
4259 return rcu_rdp_cpu_online(rdp);
4260}
4261
4262#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
4263
4264/*
4265 * Is the current CPU online as far as RCU is concerned?
4266 *
4267 * Disable preemption to avoid false positives that could otherwise
4268 * happen due to the current CPU number being sampled, this task being
4269 * preempted, its old CPU being taken offline, resuming on some other CPU,
4270 * then determining that its old CPU is now offline.
4271 *
4272 * Disable checking if in an NMI handler because we cannot safely
4273 * report errors from NMI handlers anyway. In addition, it is OK to use
4274 * RCU on an offline processor during initial boot, hence the check for
4275 * rcu_scheduler_fully_active.
4276 */
4277bool rcu_lockdep_current_cpu_online(void)
4278{
4279 struct rcu_data *rdp;
4280 bool ret = false;
4281
4282 if (in_nmi() || !rcu_scheduler_fully_active)
4283 return true;
4284 preempt_disable_notrace();
4285 rdp = this_cpu_ptr(&rcu_data);
4286 /*
4287 * Strictly, we care here about the case where the current CPU is
4288 * in rcutree_report_cpu_starting() and thus has an excuse for rdp->grpmask
4289 * not being up to date. So arch_spin_is_locked() might have a
4290 * false positive if it's held by some *other* CPU, but that's
4291 * OK because that just means a false *negative* on the warning.
4292 */
4293 if (rcu_rdp_cpu_online(rdp) || arch_spin_is_locked(&rcu_state.ofl_lock))
4294 ret = true;
4295 preempt_enable_notrace();
4296 return ret;
4297}
4298EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
4299
4300#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
4301
4302// Has rcu_init() been invoked? This is used (for example) to determine
4303// whether spinlocks may be acquired safely.
4304static bool rcu_init_invoked(void)
4305{
4306 return !!rcu_state.n_online_cpus;
4307}
4308
4309/*
4310 * All CPUs for the specified rcu_node structure have gone offline,
4311 * and all tasks that were preempted within an RCU read-side critical
4312 * section while running on one of those CPUs have since exited their RCU
4313 * read-side critical section. Some other CPU is reporting this fact with
4314 * the specified rcu_node structure's ->lock held and interrupts disabled.
4315 * This function therefore goes up the tree of rcu_node structures,
4316 * clearing the corresponding bits in the ->qsmaskinit fields. Note that
4317 * the leaf rcu_node structure's ->qsmaskinit field has already been
4318 * updated.
4319 *
4320 * This function does check that the specified rcu_node structure has
4321 * all CPUs offline and no blocked tasks, so it is OK to invoke it
4322 * prematurely. That said, invoking it after the fact will cost you
4323 * a needless lock acquisition. So once it has done its work, don't
4324 * invoke it again.
4325 */
4326static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
4327{
4328 long mask;
4329 struct rcu_node *rnp = rnp_leaf;
4330
4331 raw_lockdep_assert_held_rcu_node(rnp_leaf);
4332 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
4333 WARN_ON_ONCE(rnp_leaf->qsmaskinit) ||
4334 WARN_ON_ONCE(rcu_preempt_has_tasks(rnp_leaf)))
4335 return;
4336 for (;;) {
4337 mask = rnp->grpmask;
4338 rnp = rnp->parent;
4339 if (!rnp)
4340 break;
4341 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
4342 rnp->qsmaskinit &= ~mask;
4343 /* Between grace periods, so better already be zero! */
4344 WARN_ON_ONCE(rnp->qsmask);
4345 if (rnp->qsmaskinit) {
4346 raw_spin_unlock_rcu_node(rnp);
4347 /* irqs remain disabled. */
4348 return;
4349 }
4350 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
4351 }
4352}
4353
4354/*
4355 * Propagate ->qsinitmask bits up the rcu_node tree to account for the
4356 * first CPU in a given leaf rcu_node structure coming online. The caller
4357 * must hold the corresponding leaf rcu_node ->lock with interrupts
4358 * disabled.
4359 */
4360static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
4361{
4362 long mask;
4363 long oldmask;
4364 struct rcu_node *rnp = rnp_leaf;
4365
4366 raw_lockdep_assert_held_rcu_node(rnp_leaf);
4367 WARN_ON_ONCE(rnp->wait_blkd_tasks);
4368 for (;;) {
4369 mask = rnp->grpmask;
4370 rnp = rnp->parent;
4371 if (rnp == NULL)
4372 return;
4373 raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
4374 oldmask = rnp->qsmaskinit;
4375 rnp->qsmaskinit |= mask;
4376 raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
4377 if (oldmask)
4378 return;
4379 }
4380}
4381
4382/*
4383 * Do boot-time initialization of a CPU's per-CPU RCU data.
4384 */
4385static void __init
4386rcu_boot_init_percpu_data(int cpu)
4387{
4388 struct context_tracking *ct = this_cpu_ptr(&context_tracking);
4389 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4390
4391 /* Set up local state, ensuring consistent view of global state. */
4392 rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
4393 INIT_WORK(&rdp->strict_work, strict_work_handler);
4394 WARN_ON_ONCE(ct->dynticks_nesting != 1);
4395 WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu)));
4396 rdp->barrier_seq_snap = rcu_state.barrier_sequence;
4397 rdp->rcu_ofl_gp_seq = rcu_state.gp_seq;
4398 rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED;
4399 rdp->rcu_onl_gp_seq = rcu_state.gp_seq;
4400 rdp->rcu_onl_gp_flags = RCU_GP_CLEANED;
4401 rdp->last_sched_clock = jiffies;
4402 rdp->cpu = cpu;
4403 rcu_boot_init_nocb_percpu_data(rdp);
4404}
4405
4406struct kthread_worker *rcu_exp_gp_kworker;
4407
4408static void rcu_spawn_exp_par_gp_kworker(struct rcu_node *rnp)
4409{
4410 struct kthread_worker *kworker;
4411 const char *name = "rcu_exp_par_gp_kthread_worker/%d";
4412 struct sched_param param = { .sched_priority = kthread_prio };
4413 int rnp_index = rnp - rcu_get_root();
4414
4415 if (rnp->exp_kworker)
4416 return;
4417
4418 kworker = kthread_create_worker(0, name, rnp_index);
4419 if (IS_ERR_OR_NULL(kworker)) {
4420 pr_err("Failed to create par gp kworker on %d/%d\n",
4421 rnp->grplo, rnp->grphi);
4422 return;
4423 }
4424 WRITE_ONCE(rnp->exp_kworker, kworker);
4425
4426 if (IS_ENABLED(CONFIG_RCU_EXP_KTHREAD))
4427 sched_setscheduler_nocheck(kworker->task, SCHED_FIFO, ¶m);
4428}
4429
4430static struct task_struct *rcu_exp_par_gp_task(struct rcu_node *rnp)
4431{
4432 struct kthread_worker *kworker = READ_ONCE(rnp->exp_kworker);
4433
4434 if (!kworker)
4435 return NULL;
4436
4437 return kworker->task;
4438}
4439
4440static void __init rcu_start_exp_gp_kworker(void)
4441{
4442 const char *name = "rcu_exp_gp_kthread_worker";
4443 struct sched_param param = { .sched_priority = kthread_prio };
4444
4445 rcu_exp_gp_kworker = kthread_create_worker(0, name);
4446 if (IS_ERR_OR_NULL(rcu_exp_gp_kworker)) {
4447 pr_err("Failed to create %s!\n", name);
4448 rcu_exp_gp_kworker = NULL;
4449 return;
4450 }
4451
4452 if (IS_ENABLED(CONFIG_RCU_EXP_KTHREAD))
4453 sched_setscheduler_nocheck(rcu_exp_gp_kworker->task, SCHED_FIFO, ¶m);
4454}
4455
4456static void rcu_spawn_rnp_kthreads(struct rcu_node *rnp)
4457{
4458 if (rcu_scheduler_fully_active) {
4459 mutex_lock(&rnp->kthread_mutex);
4460 rcu_spawn_one_boost_kthread(rnp);
4461 rcu_spawn_exp_par_gp_kworker(rnp);
4462 mutex_unlock(&rnp->kthread_mutex);
4463 }
4464}
4465
4466/*
4467 * Invoked early in the CPU-online process, when pretty much all services
4468 * are available. The incoming CPU is not present.
4469 *
4470 * Initializes a CPU's per-CPU RCU data. Note that only one online or
4471 * offline event can be happening at a given time. Note also that we can
4472 * accept some slop in the rsp->gp_seq access due to the fact that this
4473 * CPU cannot possibly have any non-offloaded RCU callbacks in flight yet.
4474 * And any offloaded callbacks are being numbered elsewhere.
4475 */
4476int rcutree_prepare_cpu(unsigned int cpu)
4477{
4478 unsigned long flags;
4479 struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
4480 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4481 struct rcu_node *rnp = rcu_get_root();
4482
4483 /* Set up local state, ensuring consistent view of global state. */
4484 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4485 rdp->qlen_last_fqs_check = 0;
4486 rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
4487 rdp->blimit = blimit;
4488 ct->dynticks_nesting = 1; /* CPU not up, no tearing. */
4489 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
4490
4491 /*
4492 * Only non-NOCB CPUs that didn't have early-boot callbacks need to be
4493 * (re-)initialized.
4494 */
4495 if (!rcu_segcblist_is_enabled(&rdp->cblist))
4496 rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
4497
4498 /*
4499 * Add CPU to leaf rcu_node pending-online bitmask. Any needed
4500 * propagation up the rcu_node tree will happen at the beginning
4501 * of the next grace period.
4502 */
4503 rnp = rdp->mynode;
4504 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
4505 rdp->gp_seq = READ_ONCE(rnp->gp_seq);
4506 rdp->gp_seq_needed = rdp->gp_seq;
4507 rdp->cpu_no_qs.b.norm = true;
4508 rdp->core_needs_qs = false;
4509 rdp->rcu_iw_pending = false;
4510 rdp->rcu_iw = IRQ_WORK_INIT_HARD(rcu_iw_handler);
4511 rdp->rcu_iw_gp_seq = rdp->gp_seq - 1;
4512 trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl"));
4513 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4514 rcu_spawn_rnp_kthreads(rnp);
4515 rcu_spawn_cpu_nocb_kthread(cpu);
4516 WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus + 1);
4517
4518 return 0;
4519}
4520
4521/*
4522 * Update kthreads affinity during CPU-hotplug changes.
4523 *
4524 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
4525 * served by the rcu_node in question. The CPU hotplug lock is still
4526 * held, so the value of rnp->qsmaskinit will be stable.
4527 *
4528 * We don't include outgoingcpu in the affinity set, use -1 if there is
4529 * no outgoing CPU. If there are no CPUs left in the affinity set,
4530 * this function allows the kthread to execute on any CPU.
4531 *
4532 * Any future concurrent calls are serialized via ->kthread_mutex.
4533 */
4534static void rcutree_affinity_setting(unsigned int cpu, int outgoingcpu)
4535{
4536 cpumask_var_t cm;
4537 unsigned long mask;
4538 struct rcu_data *rdp;
4539 struct rcu_node *rnp;
4540 struct task_struct *task_boost, *task_exp;
4541
4542 rdp = per_cpu_ptr(&rcu_data, cpu);
4543 rnp = rdp->mynode;
4544
4545 task_boost = rcu_boost_task(rnp);
4546 task_exp = rcu_exp_par_gp_task(rnp);
4547
4548 /*
4549 * If CPU is the boot one, those tasks are created later from early
4550 * initcall since kthreadd must be created first.
4551 */
4552 if (!task_boost && !task_exp)
4553 return;
4554
4555 if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
4556 return;
4557
4558 mutex_lock(&rnp->kthread_mutex);
4559 mask = rcu_rnp_online_cpus(rnp);
4560 for_each_leaf_node_possible_cpu(rnp, cpu)
4561 if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
4562 cpu != outgoingcpu)
4563 cpumask_set_cpu(cpu, cm);
4564 cpumask_and(cm, cm, housekeeping_cpumask(HK_TYPE_RCU));
4565 if (cpumask_empty(cm)) {
4566 cpumask_copy(cm, housekeeping_cpumask(HK_TYPE_RCU));
4567 if (outgoingcpu >= 0)
4568 cpumask_clear_cpu(outgoingcpu, cm);
4569 }
4570
4571 if (task_exp)
4572 set_cpus_allowed_ptr(task_exp, cm);
4573
4574 if (task_boost)
4575 set_cpus_allowed_ptr(task_boost, cm);
4576
4577 mutex_unlock(&rnp->kthread_mutex);
4578
4579 free_cpumask_var(cm);
4580}
4581
4582/*
4583 * Has the specified (known valid) CPU ever been fully online?
4584 */
4585bool rcu_cpu_beenfullyonline(int cpu)
4586{
4587 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4588
4589 return smp_load_acquire(&rdp->beenonline);
4590}
4591
4592/*
4593 * Near the end of the CPU-online process. Pretty much all services
4594 * enabled, and the CPU is now very much alive.
4595 */
4596int rcutree_online_cpu(unsigned int cpu)
4597{
4598 unsigned long flags;
4599 struct rcu_data *rdp;
4600 struct rcu_node *rnp;
4601
4602 rdp = per_cpu_ptr(&rcu_data, cpu);
4603 rnp = rdp->mynode;
4604 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4605 rnp->ffmask |= rdp->grpmask;
4606 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4607 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
4608 return 0; /* Too early in boot for scheduler work. */
4609 sync_sched_exp_online_cleanup(cpu);
4610 rcutree_affinity_setting(cpu, -1);
4611
4612 // Stop-machine done, so allow nohz_full to disable tick.
4613 tick_dep_clear(TICK_DEP_BIT_RCU);
4614 return 0;
4615}
4616
4617/*
4618 * Mark the specified CPU as being online so that subsequent grace periods
4619 * (both expedited and normal) will wait on it. Note that this means that
4620 * incoming CPUs are not allowed to use RCU read-side critical sections
4621 * until this function is called. Failing to observe this restriction
4622 * will result in lockdep splats.
4623 *
4624 * Note that this function is special in that it is invoked directly
4625 * from the incoming CPU rather than from the cpuhp_step mechanism.
4626 * This is because this function must be invoked at a precise location.
4627 * This incoming CPU must not have enabled interrupts yet.
4628 *
4629 * This mirrors the effects of rcutree_report_cpu_dead().
4630 */
4631void rcutree_report_cpu_starting(unsigned int cpu)
4632{
4633 unsigned long mask;
4634 struct rcu_data *rdp;
4635 struct rcu_node *rnp;
4636 bool newcpu;
4637
4638 lockdep_assert_irqs_disabled();
4639 rdp = per_cpu_ptr(&rcu_data, cpu);
4640 if (rdp->cpu_started)
4641 return;
4642 rdp->cpu_started = true;
4643
4644 rnp = rdp->mynode;
4645 mask = rdp->grpmask;
4646 arch_spin_lock(&rcu_state.ofl_lock);
4647 rcu_dynticks_eqs_online();
4648 raw_spin_lock(&rcu_state.barrier_lock);
4649 raw_spin_lock_rcu_node(rnp);
4650 WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask);
4651 raw_spin_unlock(&rcu_state.barrier_lock);
4652 newcpu = !(rnp->expmaskinitnext & mask);
4653 rnp->expmaskinitnext |= mask;
4654 /* Allow lockless access for expedited grace periods. */
4655 smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + newcpu); /* ^^^ */
4656 ASSERT_EXCLUSIVE_WRITER(rcu_state.ncpus);
4657 rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */
4658 rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
4659 rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags);
4660
4661 /* An incoming CPU should never be blocking a grace period. */
4662 if (WARN_ON_ONCE(rnp->qsmask & mask)) { /* RCU waiting on incoming CPU? */
4663 /* rcu_report_qs_rnp() *really* wants some flags to restore */
4664 unsigned long flags;
4665
4666 local_irq_save(flags);
4667 rcu_disable_urgency_upon_qs(rdp);
4668 /* Report QS -after- changing ->qsmaskinitnext! */
4669 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
4670 } else {
4671 raw_spin_unlock_rcu_node(rnp);
4672 }
4673 arch_spin_unlock(&rcu_state.ofl_lock);
4674 smp_store_release(&rdp->beenonline, true);
4675 smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
4676}
4677
4678/*
4679 * The outgoing function has no further need of RCU, so remove it from
4680 * the rcu_node tree's ->qsmaskinitnext bit masks.
4681 *
4682 * Note that this function is special in that it is invoked directly
4683 * from the outgoing CPU rather than from the cpuhp_step mechanism.
4684 * This is because this function must be invoked at a precise location.
4685 *
4686 * This mirrors the effect of rcutree_report_cpu_starting().
4687 */
4688void rcutree_report_cpu_dead(void)
4689{
4690 unsigned long flags;
4691 unsigned long mask;
4692 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
4693 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
4694
4695 /*
4696 * IRQS must be disabled from now on and until the CPU dies, or an interrupt
4697 * may introduce a new READ-side while it is actually off the QS masks.
4698 */
4699 lockdep_assert_irqs_disabled();
4700 // Do any dangling deferred wakeups.
4701 do_nocb_deferred_wakeup(rdp);
4702
4703 rcu_preempt_deferred_qs(current);
4704
4705 /* Remove outgoing CPU from mask in the leaf rcu_node structure. */
4706 mask = rdp->grpmask;
4707 arch_spin_lock(&rcu_state.ofl_lock);
4708 raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
4709 rdp->rcu_ofl_gp_seq = READ_ONCE(rcu_state.gp_seq);
4710 rdp->rcu_ofl_gp_flags = READ_ONCE(rcu_state.gp_flags);
4711 if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */
4712 /* Report quiescent state -before- changing ->qsmaskinitnext! */
4713 rcu_disable_urgency_upon_qs(rdp);
4714 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
4715 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4716 }
4717 WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext & ~mask);
4718 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4719 arch_spin_unlock(&rcu_state.ofl_lock);
4720 rdp->cpu_started = false;
4721}
4722
4723#ifdef CONFIG_HOTPLUG_CPU
4724/*
4725 * The outgoing CPU has just passed through the dying-idle state, and we
4726 * are being invoked from the CPU that was IPIed to continue the offline
4727 * operation. Migrate the outgoing CPU's callbacks to the current CPU.
4728 */
4729void rcutree_migrate_callbacks(int cpu)
4730{
4731 unsigned long flags;
4732 struct rcu_data *my_rdp;
4733 struct rcu_node *my_rnp;
4734 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4735 bool needwake;
4736
4737 if (rcu_rdp_is_offloaded(rdp) ||
4738 rcu_segcblist_empty(&rdp->cblist))
4739 return; /* No callbacks to migrate. */
4740
4741 raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
4742 WARN_ON_ONCE(rcu_rdp_cpu_online(rdp));
4743 rcu_barrier_entrain(rdp);
4744 my_rdp = this_cpu_ptr(&rcu_data);
4745 my_rnp = my_rdp->mynode;
4746 rcu_nocb_lock(my_rdp); /* irqs already disabled. */
4747 WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies, false));
4748 raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */
4749 /* Leverage recent GPs and set GP for new callbacks. */
4750 needwake = rcu_advance_cbs(my_rnp, rdp) ||
4751 rcu_advance_cbs(my_rnp, my_rdp);
4752 rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
4753 raw_spin_unlock(&rcu_state.barrier_lock); /* irqs remain disabled. */
4754 needwake = needwake || rcu_advance_cbs(my_rnp, my_rdp);
4755 rcu_segcblist_disable(&rdp->cblist);
4756 WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != !rcu_segcblist_n_cbs(&my_rdp->cblist));
4757 check_cb_ovld_locked(my_rdp, my_rnp);
4758 if (rcu_rdp_is_offloaded(my_rdp)) {
4759 raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */
4760 __call_rcu_nocb_wake(my_rdp, true, flags);
4761 } else {
4762 rcu_nocb_unlock(my_rdp); /* irqs remain disabled. */
4763 raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */
4764 }
4765 local_irq_restore(flags);
4766 if (needwake)
4767 rcu_gp_kthread_wake();
4768 lockdep_assert_irqs_enabled();
4769 WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
4770 !rcu_segcblist_empty(&rdp->cblist),
4771 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
4772 cpu, rcu_segcblist_n_cbs(&rdp->cblist),
4773 rcu_segcblist_first_cb(&rdp->cblist));
4774}
4775
4776/*
4777 * The CPU has been completely removed, and some other CPU is reporting
4778 * this fact from process context. Do the remainder of the cleanup.
4779 * There can only be one CPU hotplug operation at a time, so no need for
4780 * explicit locking.
4781 */
4782int rcutree_dead_cpu(unsigned int cpu)
4783{
4784 WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1);
4785 // Stop-machine done, so allow nohz_full to disable tick.
4786 tick_dep_clear(TICK_DEP_BIT_RCU);
4787 return 0;
4788}
4789
4790/*
4791 * Near the end of the offline process. Trace the fact that this CPU
4792 * is going offline.
4793 */
4794int rcutree_dying_cpu(unsigned int cpu)
4795{
4796 bool blkd;
4797 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4798 struct rcu_node *rnp = rdp->mynode;
4799
4800 blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask);
4801 trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
4802 blkd ? TPS("cpuofl-bgp") : TPS("cpuofl"));
4803 return 0;
4804}
4805
4806/*
4807 * Near the beginning of the process. The CPU is still very much alive
4808 * with pretty much all services enabled.
4809 */
4810int rcutree_offline_cpu(unsigned int cpu)
4811{
4812 unsigned long flags;
4813 struct rcu_data *rdp;
4814 struct rcu_node *rnp;
4815
4816 rdp = per_cpu_ptr(&rcu_data, cpu);
4817 rnp = rdp->mynode;
4818 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4819 rnp->ffmask &= ~rdp->grpmask;
4820 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4821
4822 rcutree_affinity_setting(cpu, cpu);
4823
4824 // nohz_full CPUs need the tick for stop-machine to work quickly
4825 tick_dep_set(TICK_DEP_BIT_RCU);
4826 return 0;
4827}
4828#endif /* #ifdef CONFIG_HOTPLUG_CPU */
4829
4830/*
4831 * On non-huge systems, use expedited RCU grace periods to make suspend
4832 * and hibernation run faster.
4833 */
4834static int rcu_pm_notify(struct notifier_block *self,
4835 unsigned long action, void *hcpu)
4836{
4837 switch (action) {
4838 case PM_HIBERNATION_PREPARE:
4839 case PM_SUSPEND_PREPARE:
4840 rcu_async_hurry();
4841 rcu_expedite_gp();
4842 break;
4843 case PM_POST_HIBERNATION:
4844 case PM_POST_SUSPEND:
4845 rcu_unexpedite_gp();
4846 rcu_async_relax();
4847 break;
4848 default:
4849 break;
4850 }
4851 return NOTIFY_OK;
4852}
4853
4854/*
4855 * Spawn the kthreads that handle RCU's grace periods.
4856 */
4857static int __init rcu_spawn_gp_kthread(void)
4858{
4859 unsigned long flags;
4860 struct rcu_node *rnp;
4861 struct sched_param sp;
4862 struct task_struct *t;
4863 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
4864
4865 rcu_scheduler_fully_active = 1;
4866 t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name);
4867 if (WARN_ONCE(IS_ERR(t), "%s: Could not start grace-period kthread, OOM is now expected behavior\n", __func__))
4868 return 0;
4869 if (kthread_prio) {
4870 sp.sched_priority = kthread_prio;
4871 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
4872 }
4873 rnp = rcu_get_root();
4874 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4875 WRITE_ONCE(rcu_state.gp_activity, jiffies);
4876 WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
4877 // Reset .gp_activity and .gp_req_activity before setting .gp_kthread.
4878 smp_store_release(&rcu_state.gp_kthread, t); /* ^^^ */
4879 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4880 wake_up_process(t);
4881 /* This is a pre-SMP initcall, we expect a single CPU */
4882 WARN_ON(num_online_cpus() > 1);
4883 /*
4884 * Those kthreads couldn't be created on rcu_init() -> rcutree_prepare_cpu()
4885 * due to rcu_scheduler_fully_active.
4886 */
4887 rcu_spawn_cpu_nocb_kthread(smp_processor_id());
4888 rcu_spawn_rnp_kthreads(rdp->mynode);
4889 rcu_spawn_core_kthreads();
4890 /* Create kthread worker for expedited GPs */
4891 rcu_start_exp_gp_kworker();
4892 return 0;
4893}
4894early_initcall(rcu_spawn_gp_kthread);
4895
4896/*
4897 * This function is invoked towards the end of the scheduler's
4898 * initialization process. Before this is called, the idle task might
4899 * contain synchronous grace-period primitives (during which time, this idle
4900 * task is booting the system, and such primitives are no-ops). After this
4901 * function is called, any synchronous grace-period primitives are run as
4902 * expedited, with the requesting task driving the grace period forward.
4903 * A later core_initcall() rcu_set_runtime_mode() will switch to full
4904 * runtime RCU functionality.
4905 */
4906void rcu_scheduler_starting(void)
4907{
4908 unsigned long flags;
4909 struct rcu_node *rnp;
4910
4911 WARN_ON(num_online_cpus() != 1);
4912 WARN_ON(nr_context_switches() > 0);
4913 rcu_test_sync_prims();
4914
4915 // Fix up the ->gp_seq counters.
4916 local_irq_save(flags);
4917 rcu_for_each_node_breadth_first(rnp)
4918 rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq;
4919 local_irq_restore(flags);
4920
4921 // Switch out of early boot mode.
4922 rcu_scheduler_active = RCU_SCHEDULER_INIT;
4923 rcu_test_sync_prims();
4924}
4925
4926/*
4927 * Helper function for rcu_init() that initializes the rcu_state structure.
4928 */
4929static void __init rcu_init_one(void)
4930{
4931 static const char * const buf[] = RCU_NODE_NAME_INIT;
4932 static const char * const fqs[] = RCU_FQS_NAME_INIT;
4933 static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
4934 static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
4935
4936 int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */
4937 int cpustride = 1;
4938 int i;
4939 int j;
4940 struct rcu_node *rnp;
4941
4942 BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
4943
4944 /* Silence gcc 4.8 false positive about array index out of range. */
4945 if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
4946 panic("rcu_init_one: rcu_num_lvls out of range");
4947
4948 /* Initialize the level-tracking arrays. */
4949
4950 for (i = 1; i < rcu_num_lvls; i++)
4951 rcu_state.level[i] =
4952 rcu_state.level[i - 1] + num_rcu_lvl[i - 1];
4953 rcu_init_levelspread(levelspread, num_rcu_lvl);
4954
4955 /* Initialize the elements themselves, starting from the leaves. */
4956
4957 for (i = rcu_num_lvls - 1; i >= 0; i--) {
4958 cpustride *= levelspread[i];
4959 rnp = rcu_state.level[i];
4960 for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
4961 raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
4962 lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
4963 &rcu_node_class[i], buf[i]);
4964 raw_spin_lock_init(&rnp->fqslock);
4965 lockdep_set_class_and_name(&rnp->fqslock,
4966 &rcu_fqs_class[i], fqs[i]);
4967 rnp->gp_seq = rcu_state.gp_seq;
4968 rnp->gp_seq_needed = rcu_state.gp_seq;
4969 rnp->completedqs = rcu_state.gp_seq;
4970 rnp->qsmask = 0;
4971 rnp->qsmaskinit = 0;
4972 rnp->grplo = j * cpustride;
4973 rnp->grphi = (j + 1) * cpustride - 1;
4974 if (rnp->grphi >= nr_cpu_ids)
4975 rnp->grphi = nr_cpu_ids - 1;
4976 if (i == 0) {
4977 rnp->grpnum = 0;
4978 rnp->grpmask = 0;
4979 rnp->parent = NULL;
4980 } else {
4981 rnp->grpnum = j % levelspread[i - 1];
4982 rnp->grpmask = BIT(rnp->grpnum);
4983 rnp->parent = rcu_state.level[i - 1] +
4984 j / levelspread[i - 1];
4985 }
4986 rnp->level = i;
4987 INIT_LIST_HEAD(&rnp->blkd_tasks);
4988 rcu_init_one_nocb(rnp);
4989 init_waitqueue_head(&rnp->exp_wq[0]);
4990 init_waitqueue_head(&rnp->exp_wq[1]);
4991 init_waitqueue_head(&rnp->exp_wq[2]);
4992 init_waitqueue_head(&rnp->exp_wq[3]);
4993 spin_lock_init(&rnp->exp_lock);
4994 mutex_init(&rnp->kthread_mutex);
4995 raw_spin_lock_init(&rnp->exp_poll_lock);
4996 rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
4997 INIT_WORK(&rnp->exp_poll_wq, sync_rcu_do_polled_gp);
4998 }
4999 }
5000
5001 init_swait_queue_head(&rcu_state.gp_wq);
5002 init_swait_queue_head(&rcu_state.expedited_wq);
5003 rnp = rcu_first_leaf_node();
5004 for_each_possible_cpu(i) {
5005 while (i > rnp->grphi)
5006 rnp++;
5007 per_cpu_ptr(&rcu_data, i)->mynode = rnp;
5008 rcu_boot_init_percpu_data(i);
5009 }
5010}
5011
5012/*
5013 * Force priority from the kernel command-line into range.
5014 */
5015static void __init sanitize_kthread_prio(void)
5016{
5017 int kthread_prio_in = kthread_prio;
5018
5019 if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 2
5020 && IS_BUILTIN(CONFIG_RCU_TORTURE_TEST))
5021 kthread_prio = 2;
5022 else if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
5023 kthread_prio = 1;
5024 else if (kthread_prio < 0)
5025 kthread_prio = 0;
5026 else if (kthread_prio > 99)
5027 kthread_prio = 99;
5028
5029 if (kthread_prio != kthread_prio_in)
5030 pr_alert("%s: Limited prio to %d from %d\n",
5031 __func__, kthread_prio, kthread_prio_in);
5032}
5033
5034/*
5035 * Compute the rcu_node tree geometry from kernel parameters. This cannot
5036 * replace the definitions in tree.h because those are needed to size
5037 * the ->node array in the rcu_state structure.
5038 */
5039void rcu_init_geometry(void)
5040{
5041 ulong d;
5042 int i;
5043 static unsigned long old_nr_cpu_ids;
5044 int rcu_capacity[RCU_NUM_LVLS];
5045 static bool initialized;
5046
5047 if (initialized) {
5048 /*
5049 * Warn if setup_nr_cpu_ids() had not yet been invoked,
5050 * unless nr_cpus_ids == NR_CPUS, in which case who cares?
5051 */
5052 WARN_ON_ONCE(old_nr_cpu_ids != nr_cpu_ids);
5053 return;
5054 }
5055
5056 old_nr_cpu_ids = nr_cpu_ids;
5057 initialized = true;
5058
5059 /*
5060 * Initialize any unspecified boot parameters.
5061 * The default values of jiffies_till_first_fqs and
5062 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
5063 * value, which is a function of HZ, then adding one for each
5064 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
5065 */
5066 d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
5067 if (jiffies_till_first_fqs == ULONG_MAX)
5068 jiffies_till_first_fqs = d;
5069 if (jiffies_till_next_fqs == ULONG_MAX)
5070 jiffies_till_next_fqs = d;
5071 adjust_jiffies_till_sched_qs();
5072
5073 /* If the compile-time values are accurate, just leave. */
5074 if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
5075 nr_cpu_ids == NR_CPUS)
5076 return;
5077 pr_info("Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%u\n",
5078 rcu_fanout_leaf, nr_cpu_ids);
5079
5080 /*
5081 * The boot-time rcu_fanout_leaf parameter must be at least two
5082 * and cannot exceed the number of bits in the rcu_node masks.
5083 * Complain and fall back to the compile-time values if this
5084 * limit is exceeded.
5085 */
5086 if (rcu_fanout_leaf < 2 ||
5087 rcu_fanout_leaf > sizeof(unsigned long) * 8) {
5088 rcu_fanout_leaf = RCU_FANOUT_LEAF;
5089 WARN_ON(1);
5090 return;
5091 }
5092
5093 /*
5094 * Compute number of nodes that can be handled an rcu_node tree
5095 * with the given number of levels.
5096 */
5097 rcu_capacity[0] = rcu_fanout_leaf;
5098 for (i = 1; i < RCU_NUM_LVLS; i++)
5099 rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
5100
5101 /*
5102 * The tree must be able to accommodate the configured number of CPUs.
5103 * If this limit is exceeded, fall back to the compile-time values.
5104 */
5105 if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
5106 rcu_fanout_leaf = RCU_FANOUT_LEAF;
5107 WARN_ON(1);
5108 return;
5109 }
5110
5111 /* Calculate the number of levels in the tree. */
5112 for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
5113 }
5114 rcu_num_lvls = i + 1;
5115
5116 /* Calculate the number of rcu_nodes at each level of the tree. */
5117 for (i = 0; i < rcu_num_lvls; i++) {
5118 int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
5119 num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
5120 }
5121
5122 /* Calculate the total number of rcu_node structures. */
5123 rcu_num_nodes = 0;
5124 for (i = 0; i < rcu_num_lvls; i++)
5125 rcu_num_nodes += num_rcu_lvl[i];
5126}
5127
5128/*
5129 * Dump out the structure of the rcu_node combining tree associated
5130 * with the rcu_state structure.
5131 */
5132static void __init rcu_dump_rcu_node_tree(void)
5133{
5134 int level = 0;
5135 struct rcu_node *rnp;
5136
5137 pr_info("rcu_node tree layout dump\n");
5138 pr_info(" ");
5139 rcu_for_each_node_breadth_first(rnp) {
5140 if (rnp->level != level) {
5141 pr_cont("\n");
5142 pr_info(" ");
5143 level = rnp->level;
5144 }
5145 pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum);
5146 }
5147 pr_cont("\n");
5148}
5149
5150struct workqueue_struct *rcu_gp_wq;
5151
5152static void __init kfree_rcu_batch_init(void)
5153{
5154 int cpu;
5155 int i, j;
5156 struct shrinker *kfree_rcu_shrinker;
5157
5158 /* Clamp it to [0:100] seconds interval. */
5159 if (rcu_delay_page_cache_fill_msec < 0 ||
5160 rcu_delay_page_cache_fill_msec > 100 * MSEC_PER_SEC) {
5161
5162 rcu_delay_page_cache_fill_msec =
5163 clamp(rcu_delay_page_cache_fill_msec, 0,
5164 (int) (100 * MSEC_PER_SEC));
5165
5166 pr_info("Adjusting rcutree.rcu_delay_page_cache_fill_msec to %d ms.\n",
5167 rcu_delay_page_cache_fill_msec);
5168 }
5169
5170 for_each_possible_cpu(cpu) {
5171 struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
5172
5173 for (i = 0; i < KFREE_N_BATCHES; i++) {
5174 INIT_RCU_WORK(&krcp->krw_arr[i].rcu_work, kfree_rcu_work);
5175 krcp->krw_arr[i].krcp = krcp;
5176
5177 for (j = 0; j < FREE_N_CHANNELS; j++)
5178 INIT_LIST_HEAD(&krcp->krw_arr[i].bulk_head_free[j]);
5179 }
5180
5181 for (i = 0; i < FREE_N_CHANNELS; i++)
5182 INIT_LIST_HEAD(&krcp->bulk_head[i]);
5183
5184 INIT_DELAYED_WORK(&krcp->monitor_work, kfree_rcu_monitor);
5185 INIT_DELAYED_WORK(&krcp->page_cache_work, fill_page_cache_func);
5186 krcp->initialized = true;
5187 }
5188
5189 kfree_rcu_shrinker = shrinker_alloc(0, "rcu-kfree");
5190 if (!kfree_rcu_shrinker) {
5191 pr_err("Failed to allocate kfree_rcu() shrinker!\n");
5192 return;
5193 }
5194
5195 kfree_rcu_shrinker->count_objects = kfree_rcu_shrink_count;
5196 kfree_rcu_shrinker->scan_objects = kfree_rcu_shrink_scan;
5197
5198 shrinker_register(kfree_rcu_shrinker);
5199}
5200
5201void __init rcu_init(void)
5202{
5203 int cpu = smp_processor_id();
5204
5205 rcu_early_boot_tests();
5206
5207 kfree_rcu_batch_init();
5208 rcu_bootup_announce();
5209 sanitize_kthread_prio();
5210 rcu_init_geometry();
5211 rcu_init_one();
5212 if (dump_tree)
5213 rcu_dump_rcu_node_tree();
5214 if (use_softirq)
5215 open_softirq(RCU_SOFTIRQ, rcu_core_si);
5216
5217 /*
5218 * We don't need protection against CPU-hotplug here because
5219 * this is called early in boot, before either interrupts
5220 * or the scheduler are operational.
5221 */
5222 pm_notifier(rcu_pm_notify, 0);
5223 WARN_ON(num_online_cpus() > 1); // Only one CPU this early in boot.
5224 rcutree_prepare_cpu(cpu);
5225 rcutree_report_cpu_starting(cpu);
5226 rcutree_online_cpu(cpu);
5227
5228 /* Create workqueue for Tree SRCU and for expedited GPs. */
5229 rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
5230 WARN_ON(!rcu_gp_wq);
5231
5232 /* Fill in default value for rcutree.qovld boot parameter. */
5233 /* -After- the rcu_node ->lock fields are initialized! */
5234 if (qovld < 0)
5235 qovld_calc = DEFAULT_RCU_QOVLD_MULT * qhimark;
5236 else
5237 qovld_calc = qovld;
5238
5239 // Kick-start in case any polled grace periods started early.
5240 (void)start_poll_synchronize_rcu_expedited();
5241
5242 rcu_test_sync_prims();
5243
5244 tasks_cblist_init_generic();
5245}
5246
5247#include "tree_stall.h"
5248#include "tree_exp.h"
5249#include "tree_nocb.h"
5250#include "tree_plugin.h"
1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
4 *
5 * Copyright IBM Corporation, 2008
6 *
7 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
8 * Manfred Spraul <manfred@colorfullife.com>
9 * Paul E. McKenney <paulmck@linux.ibm.com>
10 *
11 * Based on the original work by Paul McKenney <paulmck@linux.ibm.com>
12 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
13 *
14 * For detailed explanation of Read-Copy Update mechanism see -
15 * Documentation/RCU
16 */
17
18#define pr_fmt(fmt) "rcu: " fmt
19
20#include <linux/types.h>
21#include <linux/kernel.h>
22#include <linux/init.h>
23#include <linux/spinlock.h>
24#include <linux/smp.h>
25#include <linux/rcupdate_wait.h>
26#include <linux/interrupt.h>
27#include <linux/sched.h>
28#include <linux/sched/debug.h>
29#include <linux/nmi.h>
30#include <linux/atomic.h>
31#include <linux/bitops.h>
32#include <linux/export.h>
33#include <linux/completion.h>
34#include <linux/moduleparam.h>
35#include <linux/panic.h>
36#include <linux/panic_notifier.h>
37#include <linux/percpu.h>
38#include <linux/notifier.h>
39#include <linux/cpu.h>
40#include <linux/mutex.h>
41#include <linux/time.h>
42#include <linux/kernel_stat.h>
43#include <linux/wait.h>
44#include <linux/kthread.h>
45#include <uapi/linux/sched/types.h>
46#include <linux/prefetch.h>
47#include <linux/delay.h>
48#include <linux/random.h>
49#include <linux/trace_events.h>
50#include <linux/suspend.h>
51#include <linux/ftrace.h>
52#include <linux/tick.h>
53#include <linux/sysrq.h>
54#include <linux/kprobes.h>
55#include <linux/gfp.h>
56#include <linux/oom.h>
57#include <linux/smpboot.h>
58#include <linux/jiffies.h>
59#include <linux/slab.h>
60#include <linux/sched/isolation.h>
61#include <linux/sched/clock.h>
62#include <linux/vmalloc.h>
63#include <linux/mm.h>
64#include <linux/kasan.h>
65#include "../time/tick-internal.h"
66
67#include "tree.h"
68#include "rcu.h"
69
70#ifdef MODULE_PARAM_PREFIX
71#undef MODULE_PARAM_PREFIX
72#endif
73#define MODULE_PARAM_PREFIX "rcutree."
74
75/* Data structures. */
76
77/*
78 * Steal a bit from the bottom of ->dynticks for idle entry/exit
79 * control. Initially this is for TLB flushing.
80 */
81#define RCU_DYNTICK_CTRL_MASK 0x1
82#define RCU_DYNTICK_CTRL_CTR (RCU_DYNTICK_CTRL_MASK + 1)
83
84static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
85 .dynticks_nesting = 1,
86 .dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
87 .dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR),
88#ifdef CONFIG_RCU_NOCB_CPU
89 .cblist.flags = SEGCBLIST_SOFTIRQ_ONLY,
90#endif
91};
92static struct rcu_state rcu_state = {
93 .level = { &rcu_state.node[0] },
94 .gp_state = RCU_GP_IDLE,
95 .gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT,
96 .barrier_mutex = __MUTEX_INITIALIZER(rcu_state.barrier_mutex),
97 .name = RCU_NAME,
98 .abbr = RCU_ABBR,
99 .exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex),
100 .exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex),
101 .ofl_lock = __RAW_SPIN_LOCK_UNLOCKED(rcu_state.ofl_lock),
102};
103
104/* Dump rcu_node combining tree at boot to verify correct setup. */
105static bool dump_tree;
106module_param(dump_tree, bool, 0444);
107/* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */
108static bool use_softirq = !IS_ENABLED(CONFIG_PREEMPT_RT);
109#ifndef CONFIG_PREEMPT_RT
110module_param(use_softirq, bool, 0444);
111#endif
112/* Control rcu_node-tree auto-balancing at boot time. */
113static bool rcu_fanout_exact;
114module_param(rcu_fanout_exact, bool, 0444);
115/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
116static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
117module_param(rcu_fanout_leaf, int, 0444);
118int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
119/* Number of rcu_nodes at specified level. */
120int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
121int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
122
123/*
124 * The rcu_scheduler_active variable is initialized to the value
125 * RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the
126 * first task is spawned. So when this variable is RCU_SCHEDULER_INACTIVE,
127 * RCU can assume that there is but one task, allowing RCU to (for example)
128 * optimize synchronize_rcu() to a simple barrier(). When this variable
129 * is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required
130 * to detect real grace periods. This variable is also used to suppress
131 * boot-time false positives from lockdep-RCU error checking. Finally, it
132 * transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU
133 * is fully initialized, including all of its kthreads having been spawned.
134 */
135int rcu_scheduler_active __read_mostly;
136EXPORT_SYMBOL_GPL(rcu_scheduler_active);
137
138/*
139 * The rcu_scheduler_fully_active variable transitions from zero to one
140 * during the early_initcall() processing, which is after the scheduler
141 * is capable of creating new tasks. So RCU processing (for example,
142 * creating tasks for RCU priority boosting) must be delayed until after
143 * rcu_scheduler_fully_active transitions from zero to one. We also
144 * currently delay invocation of any RCU callbacks until after this point.
145 *
146 * It might later prove better for people registering RCU callbacks during
147 * early boot to take responsibility for these callbacks, but one step at
148 * a time.
149 */
150static int rcu_scheduler_fully_active __read_mostly;
151
152static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
153 unsigned long gps, unsigned long flags);
154static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
155static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
156static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
157static void invoke_rcu_core(void);
158static void rcu_report_exp_rdp(struct rcu_data *rdp);
159static void sync_sched_exp_online_cleanup(int cpu);
160static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp);
161static bool rcu_rdp_is_offloaded(struct rcu_data *rdp);
162
163/* rcuc/rcub kthread realtime priority */
164static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
165module_param(kthread_prio, int, 0444);
166
167/* Delay in jiffies for grace-period initialization delays, debug only. */
168
169static int gp_preinit_delay;
170module_param(gp_preinit_delay, int, 0444);
171static int gp_init_delay;
172module_param(gp_init_delay, int, 0444);
173static int gp_cleanup_delay;
174module_param(gp_cleanup_delay, int, 0444);
175
176// Add delay to rcu_read_unlock() for strict grace periods.
177static int rcu_unlock_delay;
178#ifdef CONFIG_RCU_STRICT_GRACE_PERIOD
179module_param(rcu_unlock_delay, int, 0444);
180#endif
181
182/*
183 * This rcu parameter is runtime-read-only. It reflects
184 * a minimum allowed number of objects which can be cached
185 * per-CPU. Object size is equal to one page. This value
186 * can be changed at boot time.
187 */
188static int rcu_min_cached_objs = 5;
189module_param(rcu_min_cached_objs, int, 0444);
190
191// A page shrinker can ask for pages to be freed to make them
192// available for other parts of the system. This usually happens
193// under low memory conditions, and in that case we should also
194// defer page-cache filling for a short time period.
195//
196// The default value is 5 seconds, which is long enough to reduce
197// interference with the shrinker while it asks other systems to
198// drain their caches.
199static int rcu_delay_page_cache_fill_msec = 5000;
200module_param(rcu_delay_page_cache_fill_msec, int, 0444);
201
202/* Retrieve RCU kthreads priority for rcutorture */
203int rcu_get_gp_kthreads_prio(void)
204{
205 return kthread_prio;
206}
207EXPORT_SYMBOL_GPL(rcu_get_gp_kthreads_prio);
208
209/*
210 * Number of grace periods between delays, normalized by the duration of
211 * the delay. The longer the delay, the more the grace periods between
212 * each delay. The reason for this normalization is that it means that,
213 * for non-zero delays, the overall slowdown of grace periods is constant
214 * regardless of the duration of the delay. This arrangement balances
215 * the need for long delays to increase some race probabilities with the
216 * need for fast grace periods to increase other race probabilities.
217 */
218#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays for debugging. */
219
220/*
221 * Compute the mask of online CPUs for the specified rcu_node structure.
222 * This will not be stable unless the rcu_node structure's ->lock is
223 * held, but the bit corresponding to the current CPU will be stable
224 * in most contexts.
225 */
226static unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
227{
228 return READ_ONCE(rnp->qsmaskinitnext);
229}
230
231/*
232 * Return true if an RCU grace period is in progress. The READ_ONCE()s
233 * permit this function to be invoked without holding the root rcu_node
234 * structure's ->lock, but of course results can be subject to change.
235 */
236static int rcu_gp_in_progress(void)
237{
238 return rcu_seq_state(rcu_seq_current(&rcu_state.gp_seq));
239}
240
241/*
242 * Return the number of callbacks queued on the specified CPU.
243 * Handles both the nocbs and normal cases.
244 */
245static long rcu_get_n_cbs_cpu(int cpu)
246{
247 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
248
249 if (rcu_segcblist_is_enabled(&rdp->cblist))
250 return rcu_segcblist_n_cbs(&rdp->cblist);
251 return 0;
252}
253
254void rcu_softirq_qs(void)
255{
256 rcu_qs();
257 rcu_preempt_deferred_qs(current);
258 rcu_tasks_qs(current, false);
259}
260
261/*
262 * Record entry into an extended quiescent state. This is only to be
263 * called when not already in an extended quiescent state, that is,
264 * RCU is watching prior to the call to this function and is no longer
265 * watching upon return.
266 */
267static noinstr void rcu_dynticks_eqs_enter(void)
268{
269 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
270 int seq;
271
272 /*
273 * CPUs seeing atomic_add_return() must see prior RCU read-side
274 * critical sections, and we also must force ordering with the
275 * next idle sojourn.
276 */
277 rcu_dynticks_task_trace_enter(); // Before ->dynticks update!
278 seq = arch_atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
279 // RCU is no longer watching. Better be in extended quiescent state!
280 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
281 (seq & RCU_DYNTICK_CTRL_CTR));
282 /* Better not have special action (TLB flush) pending! */
283 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
284 (seq & RCU_DYNTICK_CTRL_MASK));
285}
286
287/*
288 * Record exit from an extended quiescent state. This is only to be
289 * called from an extended quiescent state, that is, RCU is not watching
290 * prior to the call to this function and is watching upon return.
291 */
292static noinstr void rcu_dynticks_eqs_exit(void)
293{
294 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
295 int seq;
296
297 /*
298 * CPUs seeing atomic_add_return() must see prior idle sojourns,
299 * and we also must force ordering with the next RCU read-side
300 * critical section.
301 */
302 seq = arch_atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
303 // RCU is now watching. Better not be in an extended quiescent state!
304 rcu_dynticks_task_trace_exit(); // After ->dynticks update!
305 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
306 !(seq & RCU_DYNTICK_CTRL_CTR));
307 if (seq & RCU_DYNTICK_CTRL_MASK) {
308 arch_atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks);
309 smp_mb__after_atomic(); /* _exit after clearing mask. */
310 }
311}
312
313/*
314 * Reset the current CPU's ->dynticks counter to indicate that the
315 * newly onlined CPU is no longer in an extended quiescent state.
316 * This will either leave the counter unchanged, or increment it
317 * to the next non-quiescent value.
318 *
319 * The non-atomic test/increment sequence works because the upper bits
320 * of the ->dynticks counter are manipulated only by the corresponding CPU,
321 * or when the corresponding CPU is offline.
322 */
323static void rcu_dynticks_eqs_online(void)
324{
325 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
326
327 if (atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR)
328 return;
329 atomic_add(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
330}
331
332/*
333 * Is the current CPU in an extended quiescent state?
334 *
335 * No ordering, as we are sampling CPU-local information.
336 */
337static __always_inline bool rcu_dynticks_curr_cpu_in_eqs(void)
338{
339 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
340
341 return !(arch_atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR);
342}
343
344/*
345 * Snapshot the ->dynticks counter with full ordering so as to allow
346 * stable comparison of this counter with past and future snapshots.
347 */
348static int rcu_dynticks_snap(struct rcu_data *rdp)
349{
350 int snap = atomic_add_return(0, &rdp->dynticks);
351
352 return snap & ~RCU_DYNTICK_CTRL_MASK;
353}
354
355/*
356 * Return true if the snapshot returned from rcu_dynticks_snap()
357 * indicates that RCU is in an extended quiescent state.
358 */
359static bool rcu_dynticks_in_eqs(int snap)
360{
361 return !(snap & RCU_DYNTICK_CTRL_CTR);
362}
363
364/* Return true if the specified CPU is currently idle from an RCU viewpoint. */
365bool rcu_is_idle_cpu(int cpu)
366{
367 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
368
369 return rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp));
370}
371
372/*
373 * Return true if the CPU corresponding to the specified rcu_data
374 * structure has spent some time in an extended quiescent state since
375 * rcu_dynticks_snap() returned the specified snapshot.
376 */
377static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap)
378{
379 return snap != rcu_dynticks_snap(rdp);
380}
381
382/*
383 * Return true if the referenced integer is zero while the specified
384 * CPU remains within a single extended quiescent state.
385 */
386bool rcu_dynticks_zero_in_eqs(int cpu, int *vp)
387{
388 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
389 int snap;
390
391 // If not quiescent, force back to earlier extended quiescent state.
392 snap = atomic_read(&rdp->dynticks) & ~(RCU_DYNTICK_CTRL_MASK |
393 RCU_DYNTICK_CTRL_CTR);
394
395 smp_rmb(); // Order ->dynticks and *vp reads.
396 if (READ_ONCE(*vp))
397 return false; // Non-zero, so report failure;
398 smp_rmb(); // Order *vp read and ->dynticks re-read.
399
400 // If still in the same extended quiescent state, we are good!
401 return snap == (atomic_read(&rdp->dynticks) & ~RCU_DYNTICK_CTRL_MASK);
402}
403
404/*
405 * Set the special (bottom) bit of the specified CPU so that it
406 * will take special action (such as flushing its TLB) on the
407 * next exit from an extended quiescent state. Returns true if
408 * the bit was successfully set, or false if the CPU was not in
409 * an extended quiescent state.
410 */
411bool rcu_eqs_special_set(int cpu)
412{
413 int old;
414 int new;
415 int new_old;
416 struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
417
418 new_old = atomic_read(&rdp->dynticks);
419 do {
420 old = new_old;
421 if (old & RCU_DYNTICK_CTRL_CTR)
422 return false;
423 new = old | RCU_DYNTICK_CTRL_MASK;
424 new_old = atomic_cmpxchg(&rdp->dynticks, old, new);
425 } while (new_old != old);
426 return true;
427}
428
429/*
430 * Let the RCU core know that this CPU has gone through the scheduler,
431 * which is a quiescent state. This is called when the need for a
432 * quiescent state is urgent, so we burn an atomic operation and full
433 * memory barriers to let the RCU core know about it, regardless of what
434 * this CPU might (or might not) do in the near future.
435 *
436 * We inform the RCU core by emulating a zero-duration dyntick-idle period.
437 *
438 * The caller must have disabled interrupts and must not be idle.
439 */
440notrace void rcu_momentary_dyntick_idle(void)
441{
442 int special;
443
444 raw_cpu_write(rcu_data.rcu_need_heavy_qs, false);
445 special = atomic_add_return(2 * RCU_DYNTICK_CTRL_CTR,
446 &this_cpu_ptr(&rcu_data)->dynticks);
447 /* It is illegal to call this from idle state. */
448 WARN_ON_ONCE(!(special & RCU_DYNTICK_CTRL_CTR));
449 rcu_preempt_deferred_qs(current);
450}
451EXPORT_SYMBOL_GPL(rcu_momentary_dyntick_idle);
452
453/**
454 * rcu_is_cpu_rrupt_from_idle - see if 'interrupted' from idle
455 *
456 * If the current CPU is idle and running at a first-level (not nested)
457 * interrupt, or directly, from idle, return true.
458 *
459 * The caller must have at least disabled IRQs.
460 */
461static int rcu_is_cpu_rrupt_from_idle(void)
462{
463 long nesting;
464
465 /*
466 * Usually called from the tick; but also used from smp_function_call()
467 * for expedited grace periods. This latter can result in running from
468 * the idle task, instead of an actual IPI.
469 */
470 lockdep_assert_irqs_disabled();
471
472 /* Check for counter underflows */
473 RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) < 0,
474 "RCU dynticks_nesting counter underflow!");
475 RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) <= 0,
476 "RCU dynticks_nmi_nesting counter underflow/zero!");
477
478 /* Are we at first interrupt nesting level? */
479 nesting = __this_cpu_read(rcu_data.dynticks_nmi_nesting);
480 if (nesting > 1)
481 return false;
482
483 /*
484 * If we're not in an interrupt, we must be in the idle task!
485 */
486 WARN_ON_ONCE(!nesting && !is_idle_task(current));
487
488 /* Does CPU appear to be idle from an RCU standpoint? */
489 return __this_cpu_read(rcu_data.dynticks_nesting) == 0;
490}
491
492#define DEFAULT_RCU_BLIMIT (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 1000 : 10)
493 // Maximum callbacks per rcu_do_batch ...
494#define DEFAULT_MAX_RCU_BLIMIT 10000 // ... even during callback flood.
495static long blimit = DEFAULT_RCU_BLIMIT;
496#define DEFAULT_RCU_QHIMARK 10000 // If this many pending, ignore blimit.
497static long qhimark = DEFAULT_RCU_QHIMARK;
498#define DEFAULT_RCU_QLOMARK 100 // Once only this many pending, use blimit.
499static long qlowmark = DEFAULT_RCU_QLOMARK;
500#define DEFAULT_RCU_QOVLD_MULT 2
501#define DEFAULT_RCU_QOVLD (DEFAULT_RCU_QOVLD_MULT * DEFAULT_RCU_QHIMARK)
502static long qovld = DEFAULT_RCU_QOVLD; // If this many pending, hammer QS.
503static long qovld_calc = -1; // No pre-initialization lock acquisitions!
504
505module_param(blimit, long, 0444);
506module_param(qhimark, long, 0444);
507module_param(qlowmark, long, 0444);
508module_param(qovld, long, 0444);
509
510static ulong jiffies_till_first_fqs = IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 0 : ULONG_MAX;
511static ulong jiffies_till_next_fqs = ULONG_MAX;
512static bool rcu_kick_kthreads;
513static int rcu_divisor = 7;
514module_param(rcu_divisor, int, 0644);
515
516/* Force an exit from rcu_do_batch() after 3 milliseconds. */
517static long rcu_resched_ns = 3 * NSEC_PER_MSEC;
518module_param(rcu_resched_ns, long, 0644);
519
520/*
521 * How long the grace period must be before we start recruiting
522 * quiescent-state help from rcu_note_context_switch().
523 */
524static ulong jiffies_till_sched_qs = ULONG_MAX;
525module_param(jiffies_till_sched_qs, ulong, 0444);
526static ulong jiffies_to_sched_qs; /* See adjust_jiffies_till_sched_qs(). */
527module_param(jiffies_to_sched_qs, ulong, 0444); /* Display only! */
528
529/*
530 * Make sure that we give the grace-period kthread time to detect any
531 * idle CPUs before taking active measures to force quiescent states.
532 * However, don't go below 100 milliseconds, adjusted upwards for really
533 * large systems.
534 */
535static void adjust_jiffies_till_sched_qs(void)
536{
537 unsigned long j;
538
539 /* If jiffies_till_sched_qs was specified, respect the request. */
540 if (jiffies_till_sched_qs != ULONG_MAX) {
541 WRITE_ONCE(jiffies_to_sched_qs, jiffies_till_sched_qs);
542 return;
543 }
544 /* Otherwise, set to third fqs scan, but bound below on large system. */
545 j = READ_ONCE(jiffies_till_first_fqs) +
546 2 * READ_ONCE(jiffies_till_next_fqs);
547 if (j < HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV)
548 j = HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
549 pr_info("RCU calculated value of scheduler-enlistment delay is %ld jiffies.\n", j);
550 WRITE_ONCE(jiffies_to_sched_qs, j);
551}
552
553static int param_set_first_fqs_jiffies(const char *val, const struct kernel_param *kp)
554{
555 ulong j;
556 int ret = kstrtoul(val, 0, &j);
557
558 if (!ret) {
559 WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : j);
560 adjust_jiffies_till_sched_qs();
561 }
562 return ret;
563}
564
565static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param *kp)
566{
567 ulong j;
568 int ret = kstrtoul(val, 0, &j);
569
570 if (!ret) {
571 WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : (j ?: 1));
572 adjust_jiffies_till_sched_qs();
573 }
574 return ret;
575}
576
577static const struct kernel_param_ops first_fqs_jiffies_ops = {
578 .set = param_set_first_fqs_jiffies,
579 .get = param_get_ulong,
580};
581
582static const struct kernel_param_ops next_fqs_jiffies_ops = {
583 .set = param_set_next_fqs_jiffies,
584 .get = param_get_ulong,
585};
586
587module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, &jiffies_till_first_fqs, 0644);
588module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next_fqs, 0644);
589module_param(rcu_kick_kthreads, bool, 0644);
590
591static void force_qs_rnp(int (*f)(struct rcu_data *rdp));
592static int rcu_pending(int user);
593
594/*
595 * Return the number of RCU GPs completed thus far for debug & stats.
596 */
597unsigned long rcu_get_gp_seq(void)
598{
599 return READ_ONCE(rcu_state.gp_seq);
600}
601EXPORT_SYMBOL_GPL(rcu_get_gp_seq);
602
603/*
604 * Return the number of RCU expedited batches completed thus far for
605 * debug & stats. Odd numbers mean that a batch is in progress, even
606 * numbers mean idle. The value returned will thus be roughly double
607 * the cumulative batches since boot.
608 */
609unsigned long rcu_exp_batches_completed(void)
610{
611 return rcu_state.expedited_sequence;
612}
613EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
614
615/*
616 * Return the root node of the rcu_state structure.
617 */
618static struct rcu_node *rcu_get_root(void)
619{
620 return &rcu_state.node[0];
621}
622
623/*
624 * Send along grace-period-related data for rcutorture diagnostics.
625 */
626void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
627 unsigned long *gp_seq)
628{
629 switch (test_type) {
630 case RCU_FLAVOR:
631 *flags = READ_ONCE(rcu_state.gp_flags);
632 *gp_seq = rcu_seq_current(&rcu_state.gp_seq);
633 break;
634 default:
635 break;
636 }
637}
638EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
639
640/*
641 * Enter an RCU extended quiescent state, which can be either the
642 * idle loop or adaptive-tickless usermode execution.
643 *
644 * We crowbar the ->dynticks_nmi_nesting field to zero to allow for
645 * the possibility of usermode upcalls having messed up our count
646 * of interrupt nesting level during the prior busy period.
647 */
648static noinstr void rcu_eqs_enter(bool user)
649{
650 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
651
652 WARN_ON_ONCE(rdp->dynticks_nmi_nesting != DYNTICK_IRQ_NONIDLE);
653 WRITE_ONCE(rdp->dynticks_nmi_nesting, 0);
654 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
655 rdp->dynticks_nesting == 0);
656 if (rdp->dynticks_nesting != 1) {
657 // RCU will still be watching, so just do accounting and leave.
658 rdp->dynticks_nesting--;
659 return;
660 }
661
662 lockdep_assert_irqs_disabled();
663 instrumentation_begin();
664 trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, atomic_read(&rdp->dynticks));
665 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
666 rcu_prepare_for_idle();
667 rcu_preempt_deferred_qs(current);
668
669 // instrumentation for the noinstr rcu_dynticks_eqs_enter()
670 instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
671
672 instrumentation_end();
673 WRITE_ONCE(rdp->dynticks_nesting, 0); /* Avoid irq-access tearing. */
674 // RCU is watching here ...
675 rcu_dynticks_eqs_enter();
676 // ... but is no longer watching here.
677 rcu_dynticks_task_enter();
678}
679
680/**
681 * rcu_idle_enter - inform RCU that current CPU is entering idle
682 *
683 * Enter idle mode, in other words, -leave- the mode in which RCU
684 * read-side critical sections can occur. (Though RCU read-side
685 * critical sections can occur in irq handlers in idle, a possibility
686 * handled by irq_enter() and irq_exit().)
687 *
688 * If you add or remove a call to rcu_idle_enter(), be sure to test with
689 * CONFIG_RCU_EQS_DEBUG=y.
690 */
691void rcu_idle_enter(void)
692{
693 lockdep_assert_irqs_disabled();
694 rcu_eqs_enter(false);
695}
696EXPORT_SYMBOL_GPL(rcu_idle_enter);
697
698#ifdef CONFIG_NO_HZ_FULL
699
700#if !defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK)
701/*
702 * An empty function that will trigger a reschedule on
703 * IRQ tail once IRQs get re-enabled on userspace/guest resume.
704 */
705static void late_wakeup_func(struct irq_work *work)
706{
707}
708
709static DEFINE_PER_CPU(struct irq_work, late_wakeup_work) =
710 IRQ_WORK_INIT(late_wakeup_func);
711
712/*
713 * If either:
714 *
715 * 1) the task is about to enter in guest mode and $ARCH doesn't support KVM generic work
716 * 2) the task is about to enter in user mode and $ARCH doesn't support generic entry.
717 *
718 * In these cases the late RCU wake ups aren't supported in the resched loops and our
719 * last resort is to fire a local irq_work that will trigger a reschedule once IRQs
720 * get re-enabled again.
721 */
722noinstr static void rcu_irq_work_resched(void)
723{
724 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
725
726 if (IS_ENABLED(CONFIG_GENERIC_ENTRY) && !(current->flags & PF_VCPU))
727 return;
728
729 if (IS_ENABLED(CONFIG_KVM_XFER_TO_GUEST_WORK) && (current->flags & PF_VCPU))
730 return;
731
732 instrumentation_begin();
733 if (do_nocb_deferred_wakeup(rdp) && need_resched()) {
734 irq_work_queue(this_cpu_ptr(&late_wakeup_work));
735 }
736 instrumentation_end();
737}
738
739#else
740static inline void rcu_irq_work_resched(void) { }
741#endif
742
743/**
744 * rcu_user_enter - inform RCU that we are resuming userspace.
745 *
746 * Enter RCU idle mode right before resuming userspace. No use of RCU
747 * is permitted between this call and rcu_user_exit(). This way the
748 * CPU doesn't need to maintain the tick for RCU maintenance purposes
749 * when the CPU runs in userspace.
750 *
751 * If you add or remove a call to rcu_user_enter(), be sure to test with
752 * CONFIG_RCU_EQS_DEBUG=y.
753 */
754noinstr void rcu_user_enter(void)
755{
756 lockdep_assert_irqs_disabled();
757
758 /*
759 * Other than generic entry implementation, we may be past the last
760 * rescheduling opportunity in the entry code. Trigger a self IPI
761 * that will fire and reschedule once we resume in user/guest mode.
762 */
763 rcu_irq_work_resched();
764 rcu_eqs_enter(true);
765}
766
767#endif /* CONFIG_NO_HZ_FULL */
768
769/**
770 * rcu_nmi_exit - inform RCU of exit from NMI context
771 *
772 * If we are returning from the outermost NMI handler that interrupted an
773 * RCU-idle period, update rdp->dynticks and rdp->dynticks_nmi_nesting
774 * to let the RCU grace-period handling know that the CPU is back to
775 * being RCU-idle.
776 *
777 * If you add or remove a call to rcu_nmi_exit(), be sure to test
778 * with CONFIG_RCU_EQS_DEBUG=y.
779 */
780noinstr void rcu_nmi_exit(void)
781{
782 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
783
784 instrumentation_begin();
785 /*
786 * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
787 * (We are exiting an NMI handler, so RCU better be paying attention
788 * to us!)
789 */
790 WARN_ON_ONCE(rdp->dynticks_nmi_nesting <= 0);
791 WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs());
792
793 /*
794 * If the nesting level is not 1, the CPU wasn't RCU-idle, so
795 * leave it in non-RCU-idle state.
796 */
797 if (rdp->dynticks_nmi_nesting != 1) {
798 trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2,
799 atomic_read(&rdp->dynticks));
800 WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */
801 rdp->dynticks_nmi_nesting - 2);
802 instrumentation_end();
803 return;
804 }
805
806 /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
807 trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks));
808 WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
809
810 if (!in_nmi())
811 rcu_prepare_for_idle();
812
813 // instrumentation for the noinstr rcu_dynticks_eqs_enter()
814 instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
815 instrumentation_end();
816
817 // RCU is watching here ...
818 rcu_dynticks_eqs_enter();
819 // ... but is no longer watching here.
820
821 if (!in_nmi())
822 rcu_dynticks_task_enter();
823}
824
825/**
826 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
827 *
828 * Exit from an interrupt handler, which might possibly result in entering
829 * idle mode, in other words, leaving the mode in which read-side critical
830 * sections can occur. The caller must have disabled interrupts.
831 *
832 * This code assumes that the idle loop never does anything that might
833 * result in unbalanced calls to irq_enter() and irq_exit(). If your
834 * architecture's idle loop violates this assumption, RCU will give you what
835 * you deserve, good and hard. But very infrequently and irreproducibly.
836 *
837 * Use things like work queues to work around this limitation.
838 *
839 * You have been warned.
840 *
841 * If you add or remove a call to rcu_irq_exit(), be sure to test with
842 * CONFIG_RCU_EQS_DEBUG=y.
843 */
844void noinstr rcu_irq_exit(void)
845{
846 lockdep_assert_irqs_disabled();
847 rcu_nmi_exit();
848}
849
850#ifdef CONFIG_PROVE_RCU
851/**
852 * rcu_irq_exit_check_preempt - Validate that scheduling is possible
853 */
854void rcu_irq_exit_check_preempt(void)
855{
856 lockdep_assert_irqs_disabled();
857
858 RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) <= 0,
859 "RCU dynticks_nesting counter underflow/zero!");
860 RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) !=
861 DYNTICK_IRQ_NONIDLE,
862 "Bad RCU dynticks_nmi_nesting counter\n");
863 RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),
864 "RCU in extended quiescent state!");
865}
866#endif /* #ifdef CONFIG_PROVE_RCU */
867
868/*
869 * Wrapper for rcu_irq_exit() where interrupts are enabled.
870 *
871 * If you add or remove a call to rcu_irq_exit_irqson(), be sure to test
872 * with CONFIG_RCU_EQS_DEBUG=y.
873 */
874void rcu_irq_exit_irqson(void)
875{
876 unsigned long flags;
877
878 local_irq_save(flags);
879 rcu_irq_exit();
880 local_irq_restore(flags);
881}
882
883/*
884 * Exit an RCU extended quiescent state, which can be either the
885 * idle loop or adaptive-tickless usermode execution.
886 *
887 * We crowbar the ->dynticks_nmi_nesting field to DYNTICK_IRQ_NONIDLE to
888 * allow for the possibility of usermode upcalls messing up our count of
889 * interrupt nesting level during the busy period that is just now starting.
890 */
891static void noinstr rcu_eqs_exit(bool user)
892{
893 struct rcu_data *rdp;
894 long oldval;
895
896 lockdep_assert_irqs_disabled();
897 rdp = this_cpu_ptr(&rcu_data);
898 oldval = rdp->dynticks_nesting;
899 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
900 if (oldval) {
901 // RCU was already watching, so just do accounting and leave.
902 rdp->dynticks_nesting++;
903 return;
904 }
905 rcu_dynticks_task_exit();
906 // RCU is not watching here ...
907 rcu_dynticks_eqs_exit();
908 // ... but is watching here.
909 instrumentation_begin();
910
911 // instrumentation for the noinstr rcu_dynticks_eqs_exit()
912 instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
913
914 rcu_cleanup_after_idle();
915 trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, atomic_read(&rdp->dynticks));
916 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
917 WRITE_ONCE(rdp->dynticks_nesting, 1);
918 WARN_ON_ONCE(rdp->dynticks_nmi_nesting);
919 WRITE_ONCE(rdp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE);
920 instrumentation_end();
921}
922
923/**
924 * rcu_idle_exit - inform RCU that current CPU is leaving idle
925 *
926 * Exit idle mode, in other words, -enter- the mode in which RCU
927 * read-side critical sections can occur.
928 *
929 * If you add or remove a call to rcu_idle_exit(), be sure to test with
930 * CONFIG_RCU_EQS_DEBUG=y.
931 */
932void rcu_idle_exit(void)
933{
934 unsigned long flags;
935
936 local_irq_save(flags);
937 rcu_eqs_exit(false);
938 local_irq_restore(flags);
939}
940EXPORT_SYMBOL_GPL(rcu_idle_exit);
941
942#ifdef CONFIG_NO_HZ_FULL
943/**
944 * rcu_user_exit - inform RCU that we are exiting userspace.
945 *
946 * Exit RCU idle mode while entering the kernel because it can
947 * run a RCU read side critical section anytime.
948 *
949 * If you add or remove a call to rcu_user_exit(), be sure to test with
950 * CONFIG_RCU_EQS_DEBUG=y.
951 */
952void noinstr rcu_user_exit(void)
953{
954 rcu_eqs_exit(true);
955}
956
957/**
958 * __rcu_irq_enter_check_tick - Enable scheduler tick on CPU if RCU needs it.
959 *
960 * The scheduler tick is not normally enabled when CPUs enter the kernel
961 * from nohz_full userspace execution. After all, nohz_full userspace
962 * execution is an RCU quiescent state and the time executing in the kernel
963 * is quite short. Except of course when it isn't. And it is not hard to
964 * cause a large system to spend tens of seconds or even minutes looping
965 * in the kernel, which can cause a number of problems, include RCU CPU
966 * stall warnings.
967 *
968 * Therefore, if a nohz_full CPU fails to report a quiescent state
969 * in a timely manner, the RCU grace-period kthread sets that CPU's
970 * ->rcu_urgent_qs flag with the expectation that the next interrupt or
971 * exception will invoke this function, which will turn on the scheduler
972 * tick, which will enable RCU to detect that CPU's quiescent states,
973 * for example, due to cond_resched() calls in CONFIG_PREEMPT=n kernels.
974 * The tick will be disabled once a quiescent state is reported for
975 * this CPU.
976 *
977 * Of course, in carefully tuned systems, there might never be an
978 * interrupt or exception. In that case, the RCU grace-period kthread
979 * will eventually cause one to happen. However, in less carefully
980 * controlled environments, this function allows RCU to get what it
981 * needs without creating otherwise useless interruptions.
982 */
983void __rcu_irq_enter_check_tick(void)
984{
985 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
986
987 // If we're here from NMI there's nothing to do.
988 if (in_nmi())
989 return;
990
991 RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),
992 "Illegal rcu_irq_enter_check_tick() from extended quiescent state");
993
994 if (!tick_nohz_full_cpu(rdp->cpu) ||
995 !READ_ONCE(rdp->rcu_urgent_qs) ||
996 READ_ONCE(rdp->rcu_forced_tick)) {
997 // RCU doesn't need nohz_full help from this CPU, or it is
998 // already getting that help.
999 return;
1000 }
1001
1002 // We get here only when not in an extended quiescent state and
1003 // from interrupts (as opposed to NMIs). Therefore, (1) RCU is
1004 // already watching and (2) The fact that we are in an interrupt
1005 // handler and that the rcu_node lock is an irq-disabled lock
1006 // prevents self-deadlock. So we can safely recheck under the lock.
1007 // Note that the nohz_full state currently cannot change.
1008 raw_spin_lock_rcu_node(rdp->mynode);
1009 if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
1010 // A nohz_full CPU is in the kernel and RCU needs a
1011 // quiescent state. Turn on the tick!
1012 WRITE_ONCE(rdp->rcu_forced_tick, true);
1013 tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
1014 }
1015 raw_spin_unlock_rcu_node(rdp->mynode);
1016}
1017#endif /* CONFIG_NO_HZ_FULL */
1018
1019/**
1020 * rcu_nmi_enter - inform RCU of entry to NMI context
1021 *
1022 * If the CPU was idle from RCU's viewpoint, update rdp->dynticks and
1023 * rdp->dynticks_nmi_nesting to let the RCU grace-period handling know
1024 * that the CPU is active. This implementation permits nested NMIs, as
1025 * long as the nesting level does not overflow an int. (You will probably
1026 * run out of stack space first.)
1027 *
1028 * If you add or remove a call to rcu_nmi_enter(), be sure to test
1029 * with CONFIG_RCU_EQS_DEBUG=y.
1030 */
1031noinstr void rcu_nmi_enter(void)
1032{
1033 long incby = 2;
1034 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1035
1036 /* Complain about underflow. */
1037 WARN_ON_ONCE(rdp->dynticks_nmi_nesting < 0);
1038
1039 /*
1040 * If idle from RCU viewpoint, atomically increment ->dynticks
1041 * to mark non-idle and increment ->dynticks_nmi_nesting by one.
1042 * Otherwise, increment ->dynticks_nmi_nesting by two. This means
1043 * if ->dynticks_nmi_nesting is equal to one, we are guaranteed
1044 * to be in the outermost NMI handler that interrupted an RCU-idle
1045 * period (observation due to Andy Lutomirski).
1046 */
1047 if (rcu_dynticks_curr_cpu_in_eqs()) {
1048
1049 if (!in_nmi())
1050 rcu_dynticks_task_exit();
1051
1052 // RCU is not watching here ...
1053 rcu_dynticks_eqs_exit();
1054 // ... but is watching here.
1055
1056 if (!in_nmi()) {
1057 instrumentation_begin();
1058 rcu_cleanup_after_idle();
1059 instrumentation_end();
1060 }
1061
1062 instrumentation_begin();
1063 // instrumentation for the noinstr rcu_dynticks_curr_cpu_in_eqs()
1064 instrument_atomic_read(&rdp->dynticks, sizeof(rdp->dynticks));
1065 // instrumentation for the noinstr rcu_dynticks_eqs_exit()
1066 instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
1067
1068 incby = 1;
1069 } else if (!in_nmi()) {
1070 instrumentation_begin();
1071 rcu_irq_enter_check_tick();
1072 } else {
1073 instrumentation_begin();
1074 }
1075
1076 trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
1077 rdp->dynticks_nmi_nesting,
1078 rdp->dynticks_nmi_nesting + incby, atomic_read(&rdp->dynticks));
1079 instrumentation_end();
1080 WRITE_ONCE(rdp->dynticks_nmi_nesting, /* Prevent store tearing. */
1081 rdp->dynticks_nmi_nesting + incby);
1082 barrier();
1083}
1084
1085/**
1086 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
1087 *
1088 * Enter an interrupt handler, which might possibly result in exiting
1089 * idle mode, in other words, entering the mode in which read-side critical
1090 * sections can occur. The caller must have disabled interrupts.
1091 *
1092 * Note that the Linux kernel is fully capable of entering an interrupt
1093 * handler that it never exits, for example when doing upcalls to user mode!
1094 * This code assumes that the idle loop never does upcalls to user mode.
1095 * If your architecture's idle loop does do upcalls to user mode (or does
1096 * anything else that results in unbalanced calls to the irq_enter() and
1097 * irq_exit() functions), RCU will give you what you deserve, good and hard.
1098 * But very infrequently and irreproducibly.
1099 *
1100 * Use things like work queues to work around this limitation.
1101 *
1102 * You have been warned.
1103 *
1104 * If you add or remove a call to rcu_irq_enter(), be sure to test with
1105 * CONFIG_RCU_EQS_DEBUG=y.
1106 */
1107noinstr void rcu_irq_enter(void)
1108{
1109 lockdep_assert_irqs_disabled();
1110 rcu_nmi_enter();
1111}
1112
1113/*
1114 * Wrapper for rcu_irq_enter() where interrupts are enabled.
1115 *
1116 * If you add or remove a call to rcu_irq_enter_irqson(), be sure to test
1117 * with CONFIG_RCU_EQS_DEBUG=y.
1118 */
1119void rcu_irq_enter_irqson(void)
1120{
1121 unsigned long flags;
1122
1123 local_irq_save(flags);
1124 rcu_irq_enter();
1125 local_irq_restore(flags);
1126}
1127
1128/*
1129 * If any sort of urgency was applied to the current CPU (for example,
1130 * the scheduler-clock interrupt was enabled on a nohz_full CPU) in order
1131 * to get to a quiescent state, disable it.
1132 */
1133static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp)
1134{
1135 raw_lockdep_assert_held_rcu_node(rdp->mynode);
1136 WRITE_ONCE(rdp->rcu_urgent_qs, false);
1137 WRITE_ONCE(rdp->rcu_need_heavy_qs, false);
1138 if (tick_nohz_full_cpu(rdp->cpu) && rdp->rcu_forced_tick) {
1139 tick_dep_clear_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
1140 WRITE_ONCE(rdp->rcu_forced_tick, false);
1141 }
1142}
1143
1144/**
1145 * rcu_is_watching - see if RCU thinks that the current CPU is not idle
1146 *
1147 * Return true if RCU is watching the running CPU, which means that this
1148 * CPU can safely enter RCU read-side critical sections. In other words,
1149 * if the current CPU is not in its idle loop or is in an interrupt or
1150 * NMI handler, return true.
1151 *
1152 * Make notrace because it can be called by the internal functions of
1153 * ftrace, and making this notrace removes unnecessary recursion calls.
1154 */
1155notrace bool rcu_is_watching(void)
1156{
1157 bool ret;
1158
1159 preempt_disable_notrace();
1160 ret = !rcu_dynticks_curr_cpu_in_eqs();
1161 preempt_enable_notrace();
1162 return ret;
1163}
1164EXPORT_SYMBOL_GPL(rcu_is_watching);
1165
1166/*
1167 * If a holdout task is actually running, request an urgent quiescent
1168 * state from its CPU. This is unsynchronized, so migrations can cause
1169 * the request to go to the wrong CPU. Which is OK, all that will happen
1170 * is that the CPU's next context switch will be a bit slower and next
1171 * time around this task will generate another request.
1172 */
1173void rcu_request_urgent_qs_task(struct task_struct *t)
1174{
1175 int cpu;
1176
1177 barrier();
1178 cpu = task_cpu(t);
1179 if (!task_curr(t))
1180 return; /* This task is not running on that CPU. */
1181 smp_store_release(per_cpu_ptr(&rcu_data.rcu_urgent_qs, cpu), true);
1182}
1183
1184#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
1185
1186/*
1187 * Is the current CPU online as far as RCU is concerned?
1188 *
1189 * Disable preemption to avoid false positives that could otherwise
1190 * happen due to the current CPU number being sampled, this task being
1191 * preempted, its old CPU being taken offline, resuming on some other CPU,
1192 * then determining that its old CPU is now offline.
1193 *
1194 * Disable checking if in an NMI handler because we cannot safely
1195 * report errors from NMI handlers anyway. In addition, it is OK to use
1196 * RCU on an offline processor during initial boot, hence the check for
1197 * rcu_scheduler_fully_active.
1198 */
1199bool rcu_lockdep_current_cpu_online(void)
1200{
1201 struct rcu_data *rdp;
1202 struct rcu_node *rnp;
1203 bool ret = false;
1204
1205 if (in_nmi() || !rcu_scheduler_fully_active)
1206 return true;
1207 preempt_disable_notrace();
1208 rdp = this_cpu_ptr(&rcu_data);
1209 rnp = rdp->mynode;
1210 if (rdp->grpmask & rcu_rnp_online_cpus(rnp) || READ_ONCE(rnp->ofl_seq) & 0x1)
1211 ret = true;
1212 preempt_enable_notrace();
1213 return ret;
1214}
1215EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
1216
1217#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
1218
1219/*
1220 * When trying to report a quiescent state on behalf of some other CPU,
1221 * it is our responsibility to check for and handle potential overflow
1222 * of the rcu_node ->gp_seq counter with respect to the rcu_data counters.
1223 * After all, the CPU might be in deep idle state, and thus executing no
1224 * code whatsoever.
1225 */
1226static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
1227{
1228 raw_lockdep_assert_held_rcu_node(rnp);
1229 if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + ULONG_MAX / 4,
1230 rnp->gp_seq))
1231 WRITE_ONCE(rdp->gpwrap, true);
1232 if (ULONG_CMP_LT(rdp->rcu_iw_gp_seq + ULONG_MAX / 4, rnp->gp_seq))
1233 rdp->rcu_iw_gp_seq = rnp->gp_seq + ULONG_MAX / 4;
1234}
1235
1236/*
1237 * Snapshot the specified CPU's dynticks counter so that we can later
1238 * credit them with an implicit quiescent state. Return 1 if this CPU
1239 * is in dynticks idle mode, which is an extended quiescent state.
1240 */
1241static int dyntick_save_progress_counter(struct rcu_data *rdp)
1242{
1243 rdp->dynticks_snap = rcu_dynticks_snap(rdp);
1244 if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
1245 trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
1246 rcu_gpnum_ovf(rdp->mynode, rdp);
1247 return 1;
1248 }
1249 return 0;
1250}
1251
1252/*
1253 * Return true if the specified CPU has passed through a quiescent
1254 * state by virtue of being in or having passed through an dynticks
1255 * idle state since the last call to dyntick_save_progress_counter()
1256 * for this same CPU, or by virtue of having been offline.
1257 */
1258static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
1259{
1260 unsigned long jtsq;
1261 bool *rnhqp;
1262 bool *ruqp;
1263 struct rcu_node *rnp = rdp->mynode;
1264
1265 /*
1266 * If the CPU passed through or entered a dynticks idle phase with
1267 * no active irq/NMI handlers, then we can safely pretend that the CPU
1268 * already acknowledged the request to pass through a quiescent
1269 * state. Either way, that CPU cannot possibly be in an RCU
1270 * read-side critical section that started before the beginning
1271 * of the current RCU grace period.
1272 */
1273 if (rcu_dynticks_in_eqs_since(rdp, rdp->dynticks_snap)) {
1274 trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
1275 rcu_gpnum_ovf(rnp, rdp);
1276 return 1;
1277 }
1278
1279 /*
1280 * Complain if a CPU that is considered to be offline from RCU's
1281 * perspective has not yet reported a quiescent state. After all,
1282 * the offline CPU should have reported a quiescent state during
1283 * the CPU-offline process, or, failing that, by rcu_gp_init()
1284 * if it ran concurrently with either the CPU going offline or the
1285 * last task on a leaf rcu_node structure exiting its RCU read-side
1286 * critical section while all CPUs corresponding to that structure
1287 * are offline. This added warning detects bugs in any of these
1288 * code paths.
1289 *
1290 * The rcu_node structure's ->lock is held here, which excludes
1291 * the relevant portions the CPU-hotplug code, the grace-period
1292 * initialization code, and the rcu_read_unlock() code paths.
1293 *
1294 * For more detail, please refer to the "Hotplug CPU" section
1295 * of RCU's Requirements documentation.
1296 */
1297 if (WARN_ON_ONCE(!(rdp->grpmask & rcu_rnp_online_cpus(rnp)))) {
1298 bool onl;
1299 struct rcu_node *rnp1;
1300
1301 pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
1302 __func__, rnp->grplo, rnp->grphi, rnp->level,
1303 (long)rnp->gp_seq, (long)rnp->completedqs);
1304 for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
1305 pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx ->rcu_gp_init_mask %#lx\n",
1306 __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext, rnp1->rcu_gp_init_mask);
1307 onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
1308 pr_info("%s %d: %c online: %ld(%d) offline: %ld(%d)\n",
1309 __func__, rdp->cpu, ".o"[onl],
1310 (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
1311 (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
1312 return 1; /* Break things loose after complaining. */
1313 }
1314
1315 /*
1316 * A CPU running for an extended time within the kernel can
1317 * delay RCU grace periods: (1) At age jiffies_to_sched_qs,
1318 * set .rcu_urgent_qs, (2) At age 2*jiffies_to_sched_qs, set
1319 * both .rcu_need_heavy_qs and .rcu_urgent_qs. Note that the
1320 * unsynchronized assignments to the per-CPU rcu_need_heavy_qs
1321 * variable are safe because the assignments are repeated if this
1322 * CPU failed to pass through a quiescent state. This code
1323 * also checks .jiffies_resched in case jiffies_to_sched_qs
1324 * is set way high.
1325 */
1326 jtsq = READ_ONCE(jiffies_to_sched_qs);
1327 ruqp = per_cpu_ptr(&rcu_data.rcu_urgent_qs, rdp->cpu);
1328 rnhqp = &per_cpu(rcu_data.rcu_need_heavy_qs, rdp->cpu);
1329 if (!READ_ONCE(*rnhqp) &&
1330 (time_after(jiffies, rcu_state.gp_start + jtsq * 2) ||
1331 time_after(jiffies, rcu_state.jiffies_resched) ||
1332 rcu_state.cbovld)) {
1333 WRITE_ONCE(*rnhqp, true);
1334 /* Store rcu_need_heavy_qs before rcu_urgent_qs. */
1335 smp_store_release(ruqp, true);
1336 } else if (time_after(jiffies, rcu_state.gp_start + jtsq)) {
1337 WRITE_ONCE(*ruqp, true);
1338 }
1339
1340 /*
1341 * NO_HZ_FULL CPUs can run in-kernel without rcu_sched_clock_irq!
1342 * The above code handles this, but only for straight cond_resched().
1343 * And some in-kernel loops check need_resched() before calling
1344 * cond_resched(), which defeats the above code for CPUs that are
1345 * running in-kernel with scheduling-clock interrupts disabled.
1346 * So hit them over the head with the resched_cpu() hammer!
1347 */
1348 if (tick_nohz_full_cpu(rdp->cpu) &&
1349 (time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq * 3) ||
1350 rcu_state.cbovld)) {
1351 WRITE_ONCE(*ruqp, true);
1352 resched_cpu(rdp->cpu);
1353 WRITE_ONCE(rdp->last_fqs_resched, jiffies);
1354 }
1355
1356 /*
1357 * If more than halfway to RCU CPU stall-warning time, invoke
1358 * resched_cpu() more frequently to try to loosen things up a bit.
1359 * Also check to see if the CPU is getting hammered with interrupts,
1360 * but only once per grace period, just to keep the IPIs down to
1361 * a dull roar.
1362 */
1363 if (time_after(jiffies, rcu_state.jiffies_resched)) {
1364 if (time_after(jiffies,
1365 READ_ONCE(rdp->last_fqs_resched) + jtsq)) {
1366 resched_cpu(rdp->cpu);
1367 WRITE_ONCE(rdp->last_fqs_resched, jiffies);
1368 }
1369 if (IS_ENABLED(CONFIG_IRQ_WORK) &&
1370 !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
1371 (rnp->ffmask & rdp->grpmask)) {
1372 rdp->rcu_iw_pending = true;
1373 rdp->rcu_iw_gp_seq = rnp->gp_seq;
1374 irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
1375 }
1376 }
1377
1378 return 0;
1379}
1380
1381/* Trace-event wrapper function for trace_rcu_future_grace_period. */
1382static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1383 unsigned long gp_seq_req, const char *s)
1384{
1385 trace_rcu_future_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
1386 gp_seq_req, rnp->level,
1387 rnp->grplo, rnp->grphi, s);
1388}
1389
1390/*
1391 * rcu_start_this_gp - Request the start of a particular grace period
1392 * @rnp_start: The leaf node of the CPU from which to start.
1393 * @rdp: The rcu_data corresponding to the CPU from which to start.
1394 * @gp_seq_req: The gp_seq of the grace period to start.
1395 *
1396 * Start the specified grace period, as needed to handle newly arrived
1397 * callbacks. The required future grace periods are recorded in each
1398 * rcu_node structure's ->gp_seq_needed field. Returns true if there
1399 * is reason to awaken the grace-period kthread.
1400 *
1401 * The caller must hold the specified rcu_node structure's ->lock, which
1402 * is why the caller is responsible for waking the grace-period kthread.
1403 *
1404 * Returns true if the GP thread needs to be awakened else false.
1405 */
1406static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
1407 unsigned long gp_seq_req)
1408{
1409 bool ret = false;
1410 struct rcu_node *rnp;
1411
1412 /*
1413 * Use funnel locking to either acquire the root rcu_node
1414 * structure's lock or bail out if the need for this grace period
1415 * has already been recorded -- or if that grace period has in
1416 * fact already started. If there is already a grace period in
1417 * progress in a non-leaf node, no recording is needed because the
1418 * end of the grace period will scan the leaf rcu_node structures.
1419 * Note that rnp_start->lock must not be released.
1420 */
1421 raw_lockdep_assert_held_rcu_node(rnp_start);
1422 trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startleaf"));
1423 for (rnp = rnp_start; 1; rnp = rnp->parent) {
1424 if (rnp != rnp_start)
1425 raw_spin_lock_rcu_node(rnp);
1426 if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req) ||
1427 rcu_seq_started(&rnp->gp_seq, gp_seq_req) ||
1428 (rnp != rnp_start &&
1429 rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))) {
1430 trace_rcu_this_gp(rnp, rdp, gp_seq_req,
1431 TPS("Prestarted"));
1432 goto unlock_out;
1433 }
1434 WRITE_ONCE(rnp->gp_seq_needed, gp_seq_req);
1435 if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) {
1436 /*
1437 * We just marked the leaf or internal node, and a
1438 * grace period is in progress, which means that
1439 * rcu_gp_cleanup() will see the marking. Bail to
1440 * reduce contention.
1441 */
1442 trace_rcu_this_gp(rnp_start, rdp, gp_seq_req,
1443 TPS("Startedleaf"));
1444 goto unlock_out;
1445 }
1446 if (rnp != rnp_start && rnp->parent != NULL)
1447 raw_spin_unlock_rcu_node(rnp);
1448 if (!rnp->parent)
1449 break; /* At root, and perhaps also leaf. */
1450 }
1451
1452 /* If GP already in progress, just leave, otherwise start one. */
1453 if (rcu_gp_in_progress()) {
1454 trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedleafroot"));
1455 goto unlock_out;
1456 }
1457 trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
1458 WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
1459 WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
1460 if (!READ_ONCE(rcu_state.gp_kthread)) {
1461 trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
1462 goto unlock_out;
1463 }
1464 trace_rcu_grace_period(rcu_state.name, data_race(rcu_state.gp_seq), TPS("newreq"));
1465 ret = true; /* Caller must wake GP kthread. */
1466unlock_out:
1467 /* Push furthest requested GP to leaf node and rcu_data structure. */
1468 if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) {
1469 WRITE_ONCE(rnp_start->gp_seq_needed, rnp->gp_seq_needed);
1470 WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
1471 }
1472 if (rnp != rnp_start)
1473 raw_spin_unlock_rcu_node(rnp);
1474 return ret;
1475}
1476
1477/*
1478 * Clean up any old requests for the just-ended grace period. Also return
1479 * whether any additional grace periods have been requested.
1480 */
1481static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
1482{
1483 bool needmore;
1484 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1485
1486 needmore = ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed);
1487 if (!needmore)
1488 rnp->gp_seq_needed = rnp->gp_seq; /* Avoid counter wrap. */
1489 trace_rcu_this_gp(rnp, rdp, rnp->gp_seq,
1490 needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1491 return needmore;
1492}
1493
1494/*
1495 * Awaken the grace-period kthread. Don't do a self-awaken (unless in an
1496 * interrupt or softirq handler, in which case we just might immediately
1497 * sleep upon return, resulting in a grace-period hang), and don't bother
1498 * awakening when there is nothing for the grace-period kthread to do
1499 * (as in several CPUs raced to awaken, we lost), and finally don't try
1500 * to awaken a kthread that has not yet been created. If all those checks
1501 * are passed, track some debug information and awaken.
1502 *
1503 * So why do the self-wakeup when in an interrupt or softirq handler
1504 * in the grace-period kthread's context? Because the kthread might have
1505 * been interrupted just as it was going to sleep, and just after the final
1506 * pre-sleep check of the awaken condition. In this case, a wakeup really
1507 * is required, and is therefore supplied.
1508 */
1509static void rcu_gp_kthread_wake(void)
1510{
1511 struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
1512
1513 if ((current == t && !in_irq() && !in_serving_softirq()) ||
1514 !READ_ONCE(rcu_state.gp_flags) || !t)
1515 return;
1516 WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
1517 WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
1518 swake_up_one(&rcu_state.gp_wq);
1519}
1520
1521/*
1522 * If there is room, assign a ->gp_seq number to any callbacks on this
1523 * CPU that have not already been assigned. Also accelerate any callbacks
1524 * that were previously assigned a ->gp_seq number that has since proven
1525 * to be too conservative, which can happen if callbacks get assigned a
1526 * ->gp_seq number while RCU is idle, but with reference to a non-root
1527 * rcu_node structure. This function is idempotent, so it does not hurt
1528 * to call it repeatedly. Returns an flag saying that we should awaken
1529 * the RCU grace-period kthread.
1530 *
1531 * The caller must hold rnp->lock with interrupts disabled.
1532 */
1533static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
1534{
1535 unsigned long gp_seq_req;
1536 bool ret = false;
1537
1538 rcu_lockdep_assert_cblist_protected(rdp);
1539 raw_lockdep_assert_held_rcu_node(rnp);
1540
1541 /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
1542 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1543 return false;
1544
1545 trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPreAcc"));
1546
1547 /*
1548 * Callbacks are often registered with incomplete grace-period
1549 * information. Something about the fact that getting exact
1550 * information requires acquiring a global lock... RCU therefore
1551 * makes a conservative estimate of the grace period number at which
1552 * a given callback will become ready to invoke. The following
1553 * code checks this estimate and improves it when possible, thus
1554 * accelerating callback invocation to an earlier grace-period
1555 * number.
1556 */
1557 gp_seq_req = rcu_seq_snap(&rcu_state.gp_seq);
1558 if (rcu_segcblist_accelerate(&rdp->cblist, gp_seq_req))
1559 ret = rcu_start_this_gp(rnp, rdp, gp_seq_req);
1560
1561 /* Trace depending on how much we were able to accelerate. */
1562 if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
1563 trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccWaitCB"));
1564 else
1565 trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccReadyCB"));
1566
1567 trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPostAcc"));
1568
1569 return ret;
1570}
1571
1572/*
1573 * Similar to rcu_accelerate_cbs(), but does not require that the leaf
1574 * rcu_node structure's ->lock be held. It consults the cached value
1575 * of ->gp_seq_needed in the rcu_data structure, and if that indicates
1576 * that a new grace-period request be made, invokes rcu_accelerate_cbs()
1577 * while holding the leaf rcu_node structure's ->lock.
1578 */
1579static void rcu_accelerate_cbs_unlocked(struct rcu_node *rnp,
1580 struct rcu_data *rdp)
1581{
1582 unsigned long c;
1583 bool needwake;
1584
1585 rcu_lockdep_assert_cblist_protected(rdp);
1586 c = rcu_seq_snap(&rcu_state.gp_seq);
1587 if (!READ_ONCE(rdp->gpwrap) && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {
1588 /* Old request still live, so mark recent callbacks. */
1589 (void)rcu_segcblist_accelerate(&rdp->cblist, c);
1590 return;
1591 }
1592 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
1593 needwake = rcu_accelerate_cbs(rnp, rdp);
1594 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
1595 if (needwake)
1596 rcu_gp_kthread_wake();
1597}
1598
1599/*
1600 * Move any callbacks whose grace period has completed to the
1601 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1602 * assign ->gp_seq numbers to any callbacks in the RCU_NEXT_TAIL
1603 * sublist. This function is idempotent, so it does not hurt to
1604 * invoke it repeatedly. As long as it is not invoked -too- often...
1605 * Returns true if the RCU grace-period kthread needs to be awakened.
1606 *
1607 * The caller must hold rnp->lock with interrupts disabled.
1608 */
1609static bool rcu_advance_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
1610{
1611 rcu_lockdep_assert_cblist_protected(rdp);
1612 raw_lockdep_assert_held_rcu_node(rnp);
1613
1614 /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
1615 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1616 return false;
1617
1618 /*
1619 * Find all callbacks whose ->gp_seq numbers indicate that they
1620 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1621 */
1622 rcu_segcblist_advance(&rdp->cblist, rnp->gp_seq);
1623
1624 /* Classify any remaining callbacks. */
1625 return rcu_accelerate_cbs(rnp, rdp);
1626}
1627
1628/*
1629 * Move and classify callbacks, but only if doing so won't require
1630 * that the RCU grace-period kthread be awakened.
1631 */
1632static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp,
1633 struct rcu_data *rdp)
1634{
1635 rcu_lockdep_assert_cblist_protected(rdp);
1636 if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) ||
1637 !raw_spin_trylock_rcu_node(rnp))
1638 return;
1639 WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp));
1640 raw_spin_unlock_rcu_node(rnp);
1641}
1642
1643/*
1644 * In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, attempt to generate a
1645 * quiescent state. This is intended to be invoked when the CPU notices
1646 * a new grace period.
1647 */
1648static void rcu_strict_gp_check_qs(void)
1649{
1650 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
1651 rcu_read_lock();
1652 rcu_read_unlock();
1653 }
1654}
1655
1656/*
1657 * Update CPU-local rcu_data state to record the beginnings and ends of
1658 * grace periods. The caller must hold the ->lock of the leaf rcu_node
1659 * structure corresponding to the current CPU, and must have irqs disabled.
1660 * Returns true if the grace-period kthread needs to be awakened.
1661 */
1662static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
1663{
1664 bool ret = false;
1665 bool need_qs;
1666 const bool offloaded = rcu_rdp_is_offloaded(rdp);
1667
1668 raw_lockdep_assert_held_rcu_node(rnp);
1669
1670 if (rdp->gp_seq == rnp->gp_seq)
1671 return false; /* Nothing to do. */
1672
1673 /* Handle the ends of any preceding grace periods first. */
1674 if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) ||
1675 unlikely(READ_ONCE(rdp->gpwrap))) {
1676 if (!offloaded)
1677 ret = rcu_advance_cbs(rnp, rdp); /* Advance CBs. */
1678 rdp->core_needs_qs = false;
1679 trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuend"));
1680 } else {
1681 if (!offloaded)
1682 ret = rcu_accelerate_cbs(rnp, rdp); /* Recent CBs. */
1683 if (rdp->core_needs_qs)
1684 rdp->core_needs_qs = !!(rnp->qsmask & rdp->grpmask);
1685 }
1686
1687 /* Now handle the beginnings of any new-to-this-CPU grace periods. */
1688 if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) ||
1689 unlikely(READ_ONCE(rdp->gpwrap))) {
1690 /*
1691 * If the current grace period is waiting for this CPU,
1692 * set up to detect a quiescent state, otherwise don't
1693 * go looking for one.
1694 */
1695 trace_rcu_grace_period(rcu_state.name, rnp->gp_seq, TPS("cpustart"));
1696 need_qs = !!(rnp->qsmask & rdp->grpmask);
1697 rdp->cpu_no_qs.b.norm = need_qs;
1698 rdp->core_needs_qs = need_qs;
1699 zero_cpu_stall_ticks(rdp);
1700 }
1701 rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */
1702 if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap)
1703 WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
1704 WRITE_ONCE(rdp->gpwrap, false);
1705 rcu_gpnum_ovf(rnp, rdp);
1706 return ret;
1707}
1708
1709static void note_gp_changes(struct rcu_data *rdp)
1710{
1711 unsigned long flags;
1712 bool needwake;
1713 struct rcu_node *rnp;
1714
1715 local_irq_save(flags);
1716 rnp = rdp->mynode;
1717 if ((rdp->gp_seq == rcu_seq_current(&rnp->gp_seq) &&
1718 !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
1719 !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
1720 local_irq_restore(flags);
1721 return;
1722 }
1723 needwake = __note_gp_changes(rnp, rdp);
1724 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1725 rcu_strict_gp_check_qs();
1726 if (needwake)
1727 rcu_gp_kthread_wake();
1728}
1729
1730static void rcu_gp_slow(int delay)
1731{
1732 if (delay > 0 &&
1733 !(rcu_seq_ctr(rcu_state.gp_seq) %
1734 (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
1735 schedule_timeout_idle(delay);
1736}
1737
1738static unsigned long sleep_duration;
1739
1740/* Allow rcutorture to stall the grace-period kthread. */
1741void rcu_gp_set_torture_wait(int duration)
1742{
1743 if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST) && duration > 0)
1744 WRITE_ONCE(sleep_duration, duration);
1745}
1746EXPORT_SYMBOL_GPL(rcu_gp_set_torture_wait);
1747
1748/* Actually implement the aforementioned wait. */
1749static void rcu_gp_torture_wait(void)
1750{
1751 unsigned long duration;
1752
1753 if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST))
1754 return;
1755 duration = xchg(&sleep_duration, 0UL);
1756 if (duration > 0) {
1757 pr_alert("%s: Waiting %lu jiffies\n", __func__, duration);
1758 schedule_timeout_idle(duration);
1759 pr_alert("%s: Wait complete\n", __func__);
1760 }
1761}
1762
1763/*
1764 * Handler for on_each_cpu() to invoke the target CPU's RCU core
1765 * processing.
1766 */
1767static void rcu_strict_gp_boundary(void *unused)
1768{
1769 invoke_rcu_core();
1770}
1771
1772/*
1773 * Initialize a new grace period. Return false if no grace period required.
1774 */
1775static bool rcu_gp_init(void)
1776{
1777 unsigned long firstseq;
1778 unsigned long flags;
1779 unsigned long oldmask;
1780 unsigned long mask;
1781 struct rcu_data *rdp;
1782 struct rcu_node *rnp = rcu_get_root();
1783
1784 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1785 raw_spin_lock_irq_rcu_node(rnp);
1786 if (!READ_ONCE(rcu_state.gp_flags)) {
1787 /* Spurious wakeup, tell caller to go back to sleep. */
1788 raw_spin_unlock_irq_rcu_node(rnp);
1789 return false;
1790 }
1791 WRITE_ONCE(rcu_state.gp_flags, 0); /* Clear all flags: New GP. */
1792
1793 if (WARN_ON_ONCE(rcu_gp_in_progress())) {
1794 /*
1795 * Grace period already in progress, don't start another.
1796 * Not supposed to be able to happen.
1797 */
1798 raw_spin_unlock_irq_rcu_node(rnp);
1799 return false;
1800 }
1801
1802 /* Advance to a new grace period and initialize state. */
1803 record_gp_stall_check_time();
1804 /* Record GP times before starting GP, hence rcu_seq_start(). */
1805 rcu_seq_start(&rcu_state.gp_seq);
1806 ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
1807 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start"));
1808 raw_spin_unlock_irq_rcu_node(rnp);
1809
1810 /*
1811 * Apply per-leaf buffered online and offline operations to
1812 * the rcu_node tree. Note that this new grace period need not
1813 * wait for subsequent online CPUs, and that RCU hooks in the CPU
1814 * offlining path, when combined with checks in this function,
1815 * will handle CPUs that are currently going offline or that will
1816 * go offline later. Please also refer to "Hotplug CPU" section
1817 * of RCU's Requirements documentation.
1818 */
1819 WRITE_ONCE(rcu_state.gp_state, RCU_GP_ONOFF);
1820 rcu_for_each_leaf_node(rnp) {
1821 smp_mb(); // Pair with barriers used when updating ->ofl_seq to odd values.
1822 firstseq = READ_ONCE(rnp->ofl_seq);
1823 if (firstseq & 0x1)
1824 while (firstseq == READ_ONCE(rnp->ofl_seq))
1825 schedule_timeout_idle(1); // Can't wake unless RCU is watching.
1826 smp_mb(); // Pair with barriers used when updating ->ofl_seq to even values.
1827 raw_spin_lock(&rcu_state.ofl_lock);
1828 raw_spin_lock_irq_rcu_node(rnp);
1829 if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
1830 !rnp->wait_blkd_tasks) {
1831 /* Nothing to do on this leaf rcu_node structure. */
1832 raw_spin_unlock_irq_rcu_node(rnp);
1833 raw_spin_unlock(&rcu_state.ofl_lock);
1834 continue;
1835 }
1836
1837 /* Record old state, apply changes to ->qsmaskinit field. */
1838 oldmask = rnp->qsmaskinit;
1839 rnp->qsmaskinit = rnp->qsmaskinitnext;
1840
1841 /* If zero-ness of ->qsmaskinit changed, propagate up tree. */
1842 if (!oldmask != !rnp->qsmaskinit) {
1843 if (!oldmask) { /* First online CPU for rcu_node. */
1844 if (!rnp->wait_blkd_tasks) /* Ever offline? */
1845 rcu_init_new_rnp(rnp);
1846 } else if (rcu_preempt_has_tasks(rnp)) {
1847 rnp->wait_blkd_tasks = true; /* blocked tasks */
1848 } else { /* Last offline CPU and can propagate. */
1849 rcu_cleanup_dead_rnp(rnp);
1850 }
1851 }
1852
1853 /*
1854 * If all waited-on tasks from prior grace period are
1855 * done, and if all this rcu_node structure's CPUs are
1856 * still offline, propagate up the rcu_node tree and
1857 * clear ->wait_blkd_tasks. Otherwise, if one of this
1858 * rcu_node structure's CPUs has since come back online,
1859 * simply clear ->wait_blkd_tasks.
1860 */
1861 if (rnp->wait_blkd_tasks &&
1862 (!rcu_preempt_has_tasks(rnp) || rnp->qsmaskinit)) {
1863 rnp->wait_blkd_tasks = false;
1864 if (!rnp->qsmaskinit)
1865 rcu_cleanup_dead_rnp(rnp);
1866 }
1867
1868 raw_spin_unlock_irq_rcu_node(rnp);
1869 raw_spin_unlock(&rcu_state.ofl_lock);
1870 }
1871 rcu_gp_slow(gp_preinit_delay); /* Races with CPU hotplug. */
1872
1873 /*
1874 * Set the quiescent-state-needed bits in all the rcu_node
1875 * structures for all currently online CPUs in breadth-first
1876 * order, starting from the root rcu_node structure, relying on the
1877 * layout of the tree within the rcu_state.node[] array. Note that
1878 * other CPUs will access only the leaves of the hierarchy, thus
1879 * seeing that no grace period is in progress, at least until the
1880 * corresponding leaf node has been initialized.
1881 *
1882 * The grace period cannot complete until the initialization
1883 * process finishes, because this kthread handles both.
1884 */
1885 WRITE_ONCE(rcu_state.gp_state, RCU_GP_INIT);
1886 rcu_for_each_node_breadth_first(rnp) {
1887 rcu_gp_slow(gp_init_delay);
1888 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1889 rdp = this_cpu_ptr(&rcu_data);
1890 rcu_preempt_check_blocked_tasks(rnp);
1891 rnp->qsmask = rnp->qsmaskinit;
1892 WRITE_ONCE(rnp->gp_seq, rcu_state.gp_seq);
1893 if (rnp == rdp->mynode)
1894 (void)__note_gp_changes(rnp, rdp);
1895 rcu_preempt_boost_start_gp(rnp);
1896 trace_rcu_grace_period_init(rcu_state.name, rnp->gp_seq,
1897 rnp->level, rnp->grplo,
1898 rnp->grphi, rnp->qsmask);
1899 /* Quiescent states for tasks on any now-offline CPUs. */
1900 mask = rnp->qsmask & ~rnp->qsmaskinitnext;
1901 rnp->rcu_gp_init_mask = mask;
1902 if ((mask || rnp->wait_blkd_tasks) && rcu_is_leaf_node(rnp))
1903 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
1904 else
1905 raw_spin_unlock_irq_rcu_node(rnp);
1906 cond_resched_tasks_rcu_qs();
1907 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1908 }
1909
1910 // If strict, make all CPUs aware of new grace period.
1911 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
1912 on_each_cpu(rcu_strict_gp_boundary, NULL, 0);
1913
1914 return true;
1915}
1916
1917/*
1918 * Helper function for swait_event_idle_exclusive() wakeup at force-quiescent-state
1919 * time.
1920 */
1921static bool rcu_gp_fqs_check_wake(int *gfp)
1922{
1923 struct rcu_node *rnp = rcu_get_root();
1924
1925 // If under overload conditions, force an immediate FQS scan.
1926 if (*gfp & RCU_GP_FLAG_OVLD)
1927 return true;
1928
1929 // Someone like call_rcu() requested a force-quiescent-state scan.
1930 *gfp = READ_ONCE(rcu_state.gp_flags);
1931 if (*gfp & RCU_GP_FLAG_FQS)
1932 return true;
1933
1934 // The current grace period has completed.
1935 if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
1936 return true;
1937
1938 return false;
1939}
1940
1941/*
1942 * Do one round of quiescent-state forcing.
1943 */
1944static void rcu_gp_fqs(bool first_time)
1945{
1946 struct rcu_node *rnp = rcu_get_root();
1947
1948 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1949 rcu_state.n_force_qs++;
1950 if (first_time) {
1951 /* Collect dyntick-idle snapshots. */
1952 force_qs_rnp(dyntick_save_progress_counter);
1953 } else {
1954 /* Handle dyntick-idle and offline CPUs. */
1955 force_qs_rnp(rcu_implicit_dynticks_qs);
1956 }
1957 /* Clear flag to prevent immediate re-entry. */
1958 if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
1959 raw_spin_lock_irq_rcu_node(rnp);
1960 WRITE_ONCE(rcu_state.gp_flags,
1961 READ_ONCE(rcu_state.gp_flags) & ~RCU_GP_FLAG_FQS);
1962 raw_spin_unlock_irq_rcu_node(rnp);
1963 }
1964}
1965
1966/*
1967 * Loop doing repeated quiescent-state forcing until the grace period ends.
1968 */
1969static void rcu_gp_fqs_loop(void)
1970{
1971 bool first_gp_fqs;
1972 int gf = 0;
1973 unsigned long j;
1974 int ret;
1975 struct rcu_node *rnp = rcu_get_root();
1976
1977 first_gp_fqs = true;
1978 j = READ_ONCE(jiffies_till_first_fqs);
1979 if (rcu_state.cbovld)
1980 gf = RCU_GP_FLAG_OVLD;
1981 ret = 0;
1982 for (;;) {
1983 if (!ret) {
1984 WRITE_ONCE(rcu_state.jiffies_force_qs, jiffies + j);
1985 /*
1986 * jiffies_force_qs before RCU_GP_WAIT_FQS state
1987 * update; required for stall checks.
1988 */
1989 smp_wmb();
1990 WRITE_ONCE(rcu_state.jiffies_kick_kthreads,
1991 jiffies + (j ? 3 * j : 2));
1992 }
1993 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
1994 TPS("fqswait"));
1995 WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_FQS);
1996 ret = swait_event_idle_timeout_exclusive(
1997 rcu_state.gp_wq, rcu_gp_fqs_check_wake(&gf), j);
1998 rcu_gp_torture_wait();
1999 WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS);
2000 /* Locking provides needed memory barriers. */
2001 /* If grace period done, leave loop. */
2002 if (!READ_ONCE(rnp->qsmask) &&
2003 !rcu_preempt_blocked_readers_cgp(rnp))
2004 break;
2005 /* If time for quiescent-state forcing, do it. */
2006 if (!time_after(rcu_state.jiffies_force_qs, jiffies) ||
2007 (gf & (RCU_GP_FLAG_FQS | RCU_GP_FLAG_OVLD))) {
2008 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
2009 TPS("fqsstart"));
2010 rcu_gp_fqs(first_gp_fqs);
2011 gf = 0;
2012 if (first_gp_fqs) {
2013 first_gp_fqs = false;
2014 gf = rcu_state.cbovld ? RCU_GP_FLAG_OVLD : 0;
2015 }
2016 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
2017 TPS("fqsend"));
2018 cond_resched_tasks_rcu_qs();
2019 WRITE_ONCE(rcu_state.gp_activity, jiffies);
2020 ret = 0; /* Force full wait till next FQS. */
2021 j = READ_ONCE(jiffies_till_next_fqs);
2022 } else {
2023 /* Deal with stray signal. */
2024 cond_resched_tasks_rcu_qs();
2025 WRITE_ONCE(rcu_state.gp_activity, jiffies);
2026 WARN_ON(signal_pending(current));
2027 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
2028 TPS("fqswaitsig"));
2029 ret = 1; /* Keep old FQS timing. */
2030 j = jiffies;
2031 if (time_after(jiffies, rcu_state.jiffies_force_qs))
2032 j = 1;
2033 else
2034 j = rcu_state.jiffies_force_qs - j;
2035 gf = 0;
2036 }
2037 }
2038}
2039
2040/*
2041 * Clean up after the old grace period.
2042 */
2043static noinline void rcu_gp_cleanup(void)
2044{
2045 int cpu;
2046 bool needgp = false;
2047 unsigned long gp_duration;
2048 unsigned long new_gp_seq;
2049 bool offloaded;
2050 struct rcu_data *rdp;
2051 struct rcu_node *rnp = rcu_get_root();
2052 struct swait_queue_head *sq;
2053
2054 WRITE_ONCE(rcu_state.gp_activity, jiffies);
2055 raw_spin_lock_irq_rcu_node(rnp);
2056 rcu_state.gp_end = jiffies;
2057 gp_duration = rcu_state.gp_end - rcu_state.gp_start;
2058 if (gp_duration > rcu_state.gp_max)
2059 rcu_state.gp_max = gp_duration;
2060
2061 /*
2062 * We know the grace period is complete, but to everyone else
2063 * it appears to still be ongoing. But it is also the case
2064 * that to everyone else it looks like there is nothing that
2065 * they can do to advance the grace period. It is therefore
2066 * safe for us to drop the lock in order to mark the grace
2067 * period as completed in all of the rcu_node structures.
2068 */
2069 raw_spin_unlock_irq_rcu_node(rnp);
2070
2071 /*
2072 * Propagate new ->gp_seq value to rcu_node structures so that
2073 * other CPUs don't have to wait until the start of the next grace
2074 * period to process their callbacks. This also avoids some nasty
2075 * RCU grace-period initialization races by forcing the end of
2076 * the current grace period to be completely recorded in all of
2077 * the rcu_node structures before the beginning of the next grace
2078 * period is recorded in any of the rcu_node structures.
2079 */
2080 new_gp_seq = rcu_state.gp_seq;
2081 rcu_seq_end(&new_gp_seq);
2082 rcu_for_each_node_breadth_first(rnp) {
2083 raw_spin_lock_irq_rcu_node(rnp);
2084 if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
2085 dump_blkd_tasks(rnp, 10);
2086 WARN_ON_ONCE(rnp->qsmask);
2087 WRITE_ONCE(rnp->gp_seq, new_gp_seq);
2088 rdp = this_cpu_ptr(&rcu_data);
2089 if (rnp == rdp->mynode)
2090 needgp = __note_gp_changes(rnp, rdp) || needgp;
2091 /* smp_mb() provided by prior unlock-lock pair. */
2092 needgp = rcu_future_gp_cleanup(rnp) || needgp;
2093 // Reset overload indication for CPUs no longer overloaded
2094 if (rcu_is_leaf_node(rnp))
2095 for_each_leaf_node_cpu_mask(rnp, cpu, rnp->cbovldmask) {
2096 rdp = per_cpu_ptr(&rcu_data, cpu);
2097 check_cb_ovld_locked(rdp, rnp);
2098 }
2099 sq = rcu_nocb_gp_get(rnp);
2100 raw_spin_unlock_irq_rcu_node(rnp);
2101 rcu_nocb_gp_cleanup(sq);
2102 cond_resched_tasks_rcu_qs();
2103 WRITE_ONCE(rcu_state.gp_activity, jiffies);
2104 rcu_gp_slow(gp_cleanup_delay);
2105 }
2106 rnp = rcu_get_root();
2107 raw_spin_lock_irq_rcu_node(rnp); /* GP before ->gp_seq update. */
2108
2109 /* Declare grace period done, trace first to use old GP number. */
2110 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end"));
2111 rcu_seq_end(&rcu_state.gp_seq);
2112 ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
2113 WRITE_ONCE(rcu_state.gp_state, RCU_GP_IDLE);
2114 /* Check for GP requests since above loop. */
2115 rdp = this_cpu_ptr(&rcu_data);
2116 if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) {
2117 trace_rcu_this_gp(rnp, rdp, rnp->gp_seq_needed,
2118 TPS("CleanupMore"));
2119 needgp = true;
2120 }
2121 /* Advance CBs to reduce false positives below. */
2122 offloaded = rcu_rdp_is_offloaded(rdp);
2123 if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {
2124 WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);
2125 WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
2126 trace_rcu_grace_period(rcu_state.name,
2127 rcu_state.gp_seq,
2128 TPS("newreq"));
2129 } else {
2130 WRITE_ONCE(rcu_state.gp_flags,
2131 rcu_state.gp_flags & RCU_GP_FLAG_INIT);
2132 }
2133 raw_spin_unlock_irq_rcu_node(rnp);
2134
2135 // If strict, make all CPUs aware of the end of the old grace period.
2136 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
2137 on_each_cpu(rcu_strict_gp_boundary, NULL, 0);
2138}
2139
2140/*
2141 * Body of kthread that handles grace periods.
2142 */
2143static int __noreturn rcu_gp_kthread(void *unused)
2144{
2145 rcu_bind_gp_kthread();
2146 for (;;) {
2147
2148 /* Handle grace-period start. */
2149 for (;;) {
2150 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
2151 TPS("reqwait"));
2152 WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_GPS);
2153 swait_event_idle_exclusive(rcu_state.gp_wq,
2154 READ_ONCE(rcu_state.gp_flags) &
2155 RCU_GP_FLAG_INIT);
2156 rcu_gp_torture_wait();
2157 WRITE_ONCE(rcu_state.gp_state, RCU_GP_DONE_GPS);
2158 /* Locking provides needed memory barrier. */
2159 if (rcu_gp_init())
2160 break;
2161 cond_resched_tasks_rcu_qs();
2162 WRITE_ONCE(rcu_state.gp_activity, jiffies);
2163 WARN_ON(signal_pending(current));
2164 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
2165 TPS("reqwaitsig"));
2166 }
2167
2168 /* Handle quiescent-state forcing. */
2169 rcu_gp_fqs_loop();
2170
2171 /* Handle grace-period end. */
2172 WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANUP);
2173 rcu_gp_cleanup();
2174 WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANED);
2175 }
2176}
2177
2178/*
2179 * Report a full set of quiescent states to the rcu_state data structure.
2180 * Invoke rcu_gp_kthread_wake() to awaken the grace-period kthread if
2181 * another grace period is required. Whether we wake the grace-period
2182 * kthread or it awakens itself for the next round of quiescent-state
2183 * forcing, that kthread will clean up after the just-completed grace
2184 * period. Note that the caller must hold rnp->lock, which is released
2185 * before return.
2186 */
2187static void rcu_report_qs_rsp(unsigned long flags)
2188 __releases(rcu_get_root()->lock)
2189{
2190 raw_lockdep_assert_held_rcu_node(rcu_get_root());
2191 WARN_ON_ONCE(!rcu_gp_in_progress());
2192 WRITE_ONCE(rcu_state.gp_flags,
2193 READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
2194 raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(), flags);
2195 rcu_gp_kthread_wake();
2196}
2197
2198/*
2199 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
2200 * Allows quiescent states for a group of CPUs to be reported at one go
2201 * to the specified rcu_node structure, though all the CPUs in the group
2202 * must be represented by the same rcu_node structure (which need not be a
2203 * leaf rcu_node structure, though it often will be). The gps parameter
2204 * is the grace-period snapshot, which means that the quiescent states
2205 * are valid only if rnp->gp_seq is equal to gps. That structure's lock
2206 * must be held upon entry, and it is released before return.
2207 *
2208 * As a special case, if mask is zero, the bit-already-cleared check is
2209 * disabled. This allows propagating quiescent state due to resumed tasks
2210 * during grace-period initialization.
2211 */
2212static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
2213 unsigned long gps, unsigned long flags)
2214 __releases(rnp->lock)
2215{
2216 unsigned long oldmask = 0;
2217 struct rcu_node *rnp_c;
2218
2219 raw_lockdep_assert_held_rcu_node(rnp);
2220
2221 /* Walk up the rcu_node hierarchy. */
2222 for (;;) {
2223 if ((!(rnp->qsmask & mask) && mask) || rnp->gp_seq != gps) {
2224
2225 /*
2226 * Our bit has already been cleared, or the
2227 * relevant grace period is already over, so done.
2228 */
2229 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2230 return;
2231 }
2232 WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
2233 WARN_ON_ONCE(!rcu_is_leaf_node(rnp) &&
2234 rcu_preempt_blocked_readers_cgp(rnp));
2235 WRITE_ONCE(rnp->qsmask, rnp->qsmask & ~mask);
2236 trace_rcu_quiescent_state_report(rcu_state.name, rnp->gp_seq,
2237 mask, rnp->qsmask, rnp->level,
2238 rnp->grplo, rnp->grphi,
2239 !!rnp->gp_tasks);
2240 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2241
2242 /* Other bits still set at this level, so done. */
2243 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2244 return;
2245 }
2246 rnp->completedqs = rnp->gp_seq;
2247 mask = rnp->grpmask;
2248 if (rnp->parent == NULL) {
2249
2250 /* No more levels. Exit loop holding root lock. */
2251
2252 break;
2253 }
2254 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2255 rnp_c = rnp;
2256 rnp = rnp->parent;
2257 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2258 oldmask = READ_ONCE(rnp_c->qsmask);
2259 }
2260
2261 /*
2262 * Get here if we are the last CPU to pass through a quiescent
2263 * state for this grace period. Invoke rcu_report_qs_rsp()
2264 * to clean up and start the next grace period if one is needed.
2265 */
2266 rcu_report_qs_rsp(flags); /* releases rnp->lock. */
2267}
2268
2269/*
2270 * Record a quiescent state for all tasks that were previously queued
2271 * on the specified rcu_node structure and that were blocking the current
2272 * RCU grace period. The caller must hold the corresponding rnp->lock with
2273 * irqs disabled, and this lock is released upon return, but irqs remain
2274 * disabled.
2275 */
2276static void __maybe_unused
2277rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
2278 __releases(rnp->lock)
2279{
2280 unsigned long gps;
2281 unsigned long mask;
2282 struct rcu_node *rnp_p;
2283
2284 raw_lockdep_assert_held_rcu_node(rnp);
2285 if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT_RCU)) ||
2286 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)) ||
2287 rnp->qsmask != 0) {
2288 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2289 return; /* Still need more quiescent states! */
2290 }
2291
2292 rnp->completedqs = rnp->gp_seq;
2293 rnp_p = rnp->parent;
2294 if (rnp_p == NULL) {
2295 /*
2296 * Only one rcu_node structure in the tree, so don't
2297 * try to report up to its nonexistent parent!
2298 */
2299 rcu_report_qs_rsp(flags);
2300 return;
2301 }
2302
2303 /* Report up the rest of the hierarchy, tracking current ->gp_seq. */
2304 gps = rnp->gp_seq;
2305 mask = rnp->grpmask;
2306 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2307 raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */
2308 rcu_report_qs_rnp(mask, rnp_p, gps, flags);
2309}
2310
2311/*
2312 * Record a quiescent state for the specified CPU to that CPU's rcu_data
2313 * structure. This must be called from the specified CPU.
2314 */
2315static void
2316rcu_report_qs_rdp(struct rcu_data *rdp)
2317{
2318 unsigned long flags;
2319 unsigned long mask;
2320 bool needwake = false;
2321 const bool offloaded = rcu_rdp_is_offloaded(rdp);
2322 struct rcu_node *rnp;
2323
2324 WARN_ON_ONCE(rdp->cpu != smp_processor_id());
2325 rnp = rdp->mynode;
2326 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2327 if (rdp->cpu_no_qs.b.norm || rdp->gp_seq != rnp->gp_seq ||
2328 rdp->gpwrap) {
2329
2330 /*
2331 * The grace period in which this quiescent state was
2332 * recorded has ended, so don't report it upwards.
2333 * We will instead need a new quiescent state that lies
2334 * within the current grace period.
2335 */
2336 rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */
2337 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2338 return;
2339 }
2340 mask = rdp->grpmask;
2341 rdp->core_needs_qs = false;
2342 if ((rnp->qsmask & mask) == 0) {
2343 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2344 } else {
2345 /*
2346 * This GP can't end until cpu checks in, so all of our
2347 * callbacks can be processed during the next GP.
2348 */
2349 if (!offloaded)
2350 needwake = rcu_accelerate_cbs(rnp, rdp);
2351
2352 rcu_disable_urgency_upon_qs(rdp);
2353 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
2354 /* ^^^ Released rnp->lock */
2355 if (needwake)
2356 rcu_gp_kthread_wake();
2357 }
2358}
2359
2360/*
2361 * Check to see if there is a new grace period of which this CPU
2362 * is not yet aware, and if so, set up local rcu_data state for it.
2363 * Otherwise, see if this CPU has just passed through its first
2364 * quiescent state for this grace period, and record that fact if so.
2365 */
2366static void
2367rcu_check_quiescent_state(struct rcu_data *rdp)
2368{
2369 /* Check for grace-period ends and beginnings. */
2370 note_gp_changes(rdp);
2371
2372 /*
2373 * Does this CPU still need to do its part for current grace period?
2374 * If no, return and let the other CPUs do their part as well.
2375 */
2376 if (!rdp->core_needs_qs)
2377 return;
2378
2379 /*
2380 * Was there a quiescent state since the beginning of the grace
2381 * period? If no, then exit and wait for the next call.
2382 */
2383 if (rdp->cpu_no_qs.b.norm)
2384 return;
2385
2386 /*
2387 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
2388 * judge of that).
2389 */
2390 rcu_report_qs_rdp(rdp);
2391}
2392
2393/*
2394 * Near the end of the offline process. Trace the fact that this CPU
2395 * is going offline.
2396 */
2397int rcutree_dying_cpu(unsigned int cpu)
2398{
2399 bool blkd;
2400 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
2401 struct rcu_node *rnp = rdp->mynode;
2402
2403 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2404 return 0;
2405
2406 blkd = !!(rnp->qsmask & rdp->grpmask);
2407 trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
2408 blkd ? TPS("cpuofl-bgp") : TPS("cpuofl"));
2409 return 0;
2410}
2411
2412/*
2413 * All CPUs for the specified rcu_node structure have gone offline,
2414 * and all tasks that were preempted within an RCU read-side critical
2415 * section while running on one of those CPUs have since exited their RCU
2416 * read-side critical section. Some other CPU is reporting this fact with
2417 * the specified rcu_node structure's ->lock held and interrupts disabled.
2418 * This function therefore goes up the tree of rcu_node structures,
2419 * clearing the corresponding bits in the ->qsmaskinit fields. Note that
2420 * the leaf rcu_node structure's ->qsmaskinit field has already been
2421 * updated.
2422 *
2423 * This function does check that the specified rcu_node structure has
2424 * all CPUs offline and no blocked tasks, so it is OK to invoke it
2425 * prematurely. That said, invoking it after the fact will cost you
2426 * a needless lock acquisition. So once it has done its work, don't
2427 * invoke it again.
2428 */
2429static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
2430{
2431 long mask;
2432 struct rcu_node *rnp = rnp_leaf;
2433
2434 raw_lockdep_assert_held_rcu_node(rnp_leaf);
2435 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
2436 WARN_ON_ONCE(rnp_leaf->qsmaskinit) ||
2437 WARN_ON_ONCE(rcu_preempt_has_tasks(rnp_leaf)))
2438 return;
2439 for (;;) {
2440 mask = rnp->grpmask;
2441 rnp = rnp->parent;
2442 if (!rnp)
2443 break;
2444 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
2445 rnp->qsmaskinit &= ~mask;
2446 /* Between grace periods, so better already be zero! */
2447 WARN_ON_ONCE(rnp->qsmask);
2448 if (rnp->qsmaskinit) {
2449 raw_spin_unlock_rcu_node(rnp);
2450 /* irqs remain disabled. */
2451 return;
2452 }
2453 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2454 }
2455}
2456
2457/*
2458 * The CPU has been completely removed, and some other CPU is reporting
2459 * this fact from process context. Do the remainder of the cleanup.
2460 * There can only be one CPU hotplug operation at a time, so no need for
2461 * explicit locking.
2462 */
2463int rcutree_dead_cpu(unsigned int cpu)
2464{
2465 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
2466 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
2467
2468 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2469 return 0;
2470
2471 WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1);
2472 /* Adjust any no-longer-needed kthreads. */
2473 rcu_boost_kthread_setaffinity(rnp, -1);
2474 /* Do any needed no-CB deferred wakeups from this CPU. */
2475 do_nocb_deferred_wakeup(per_cpu_ptr(&rcu_data, cpu));
2476
2477 // Stop-machine done, so allow nohz_full to disable tick.
2478 tick_dep_clear(TICK_DEP_BIT_RCU);
2479 return 0;
2480}
2481
2482/*
2483 * Invoke any RCU callbacks that have made it to the end of their grace
2484 * period. Throttle as specified by rdp->blimit.
2485 */
2486static void rcu_do_batch(struct rcu_data *rdp)
2487{
2488 int div;
2489 bool __maybe_unused empty;
2490 unsigned long flags;
2491 const bool offloaded = rcu_rdp_is_offloaded(rdp);
2492 struct rcu_head *rhp;
2493 struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
2494 long bl, count = 0;
2495 long pending, tlimit = 0;
2496
2497 /* If no callbacks are ready, just return. */
2498 if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
2499 trace_rcu_batch_start(rcu_state.name,
2500 rcu_segcblist_n_cbs(&rdp->cblist), 0);
2501 trace_rcu_batch_end(rcu_state.name, 0,
2502 !rcu_segcblist_empty(&rdp->cblist),
2503 need_resched(), is_idle_task(current),
2504 rcu_is_callbacks_kthread());
2505 return;
2506 }
2507
2508 /*
2509 * Extract the list of ready callbacks, disabling to prevent
2510 * races with call_rcu() from interrupt handlers. Leave the
2511 * callback counts, as rcu_barrier() needs to be conservative.
2512 */
2513 local_irq_save(flags);
2514 rcu_nocb_lock(rdp);
2515 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2516 pending = rcu_segcblist_n_cbs(&rdp->cblist);
2517 div = READ_ONCE(rcu_divisor);
2518 div = div < 0 ? 7 : div > sizeof(long) * 8 - 2 ? sizeof(long) * 8 - 2 : div;
2519 bl = max(rdp->blimit, pending >> div);
2520 if (unlikely(bl > 100)) {
2521 long rrn = READ_ONCE(rcu_resched_ns);
2522
2523 rrn = rrn < NSEC_PER_MSEC ? NSEC_PER_MSEC : rrn > NSEC_PER_SEC ? NSEC_PER_SEC : rrn;
2524 tlimit = local_clock() + rrn;
2525 }
2526 trace_rcu_batch_start(rcu_state.name,
2527 rcu_segcblist_n_cbs(&rdp->cblist), bl);
2528 rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
2529 if (offloaded)
2530 rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
2531
2532 trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbDequeued"));
2533 rcu_nocb_unlock_irqrestore(rdp, flags);
2534
2535 /* Invoke callbacks. */
2536 tick_dep_set_task(current, TICK_DEP_BIT_RCU);
2537 rhp = rcu_cblist_dequeue(&rcl);
2538
2539 for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
2540 rcu_callback_t f;
2541
2542 count++;
2543 debug_rcu_head_unqueue(rhp);
2544
2545 rcu_lock_acquire(&rcu_callback_map);
2546 trace_rcu_invoke_callback(rcu_state.name, rhp);
2547
2548 f = rhp->func;
2549 WRITE_ONCE(rhp->func, (rcu_callback_t)0L);
2550 f(rhp);
2551
2552 rcu_lock_release(&rcu_callback_map);
2553
2554 /*
2555 * Stop only if limit reached and CPU has something to do.
2556 */
2557 if (count >= bl && !offloaded &&
2558 (need_resched() ||
2559 (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
2560 break;
2561 if (unlikely(tlimit)) {
2562 /* only call local_clock() every 32 callbacks */
2563 if (likely((count & 31) || local_clock() < tlimit))
2564 continue;
2565 /* Exceeded the time limit, so leave. */
2566 break;
2567 }
2568 if (!in_serving_softirq()) {
2569 local_bh_enable();
2570 lockdep_assert_irqs_enabled();
2571 cond_resched_tasks_rcu_qs();
2572 lockdep_assert_irqs_enabled();
2573 local_bh_disable();
2574 }
2575 }
2576
2577 local_irq_save(flags);
2578 rcu_nocb_lock(rdp);
2579 rdp->n_cbs_invoked += count;
2580 trace_rcu_batch_end(rcu_state.name, count, !!rcl.head, need_resched(),
2581 is_idle_task(current), rcu_is_callbacks_kthread());
2582
2583 /* Update counts and requeue any remaining callbacks. */
2584 rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
2585 rcu_segcblist_add_len(&rdp->cblist, -count);
2586
2587 /* Reinstate batch limit if we have worked down the excess. */
2588 count = rcu_segcblist_n_cbs(&rdp->cblist);
2589 if (rdp->blimit >= DEFAULT_MAX_RCU_BLIMIT && count <= qlowmark)
2590 rdp->blimit = blimit;
2591
2592 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2593 if (count == 0 && rdp->qlen_last_fqs_check != 0) {
2594 rdp->qlen_last_fqs_check = 0;
2595 rdp->n_force_qs_snap = rcu_state.n_force_qs;
2596 } else if (count < rdp->qlen_last_fqs_check - qhimark)
2597 rdp->qlen_last_fqs_check = count;
2598
2599 /*
2600 * The following usually indicates a double call_rcu(). To track
2601 * this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.
2602 */
2603 empty = rcu_segcblist_empty(&rdp->cblist);
2604 WARN_ON_ONCE(count == 0 && !empty);
2605 WARN_ON_ONCE(!IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
2606 count != 0 && empty);
2607 WARN_ON_ONCE(count == 0 && rcu_segcblist_n_segment_cbs(&rdp->cblist) != 0);
2608 WARN_ON_ONCE(!empty && rcu_segcblist_n_segment_cbs(&rdp->cblist) == 0);
2609
2610 rcu_nocb_unlock_irqrestore(rdp, flags);
2611
2612 /* Re-invoke RCU core processing if there are callbacks remaining. */
2613 if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist))
2614 invoke_rcu_core();
2615 tick_dep_clear_task(current, TICK_DEP_BIT_RCU);
2616}
2617
2618/*
2619 * This function is invoked from each scheduling-clock interrupt,
2620 * and checks to see if this CPU is in a non-context-switch quiescent
2621 * state, for example, user mode or idle loop. It also schedules RCU
2622 * core processing. If the current grace period has gone on too long,
2623 * it will ask the scheduler to manufacture a context switch for the sole
2624 * purpose of providing the needed quiescent state.
2625 */
2626void rcu_sched_clock_irq(int user)
2627{
2628 trace_rcu_utilization(TPS("Start scheduler-tick"));
2629 lockdep_assert_irqs_disabled();
2630 raw_cpu_inc(rcu_data.ticks_this_gp);
2631 /* The load-acquire pairs with the store-release setting to true. */
2632 if (smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
2633 /* Idle and userspace execution already are quiescent states. */
2634 if (!rcu_is_cpu_rrupt_from_idle() && !user) {
2635 set_tsk_need_resched(current);
2636 set_preempt_need_resched();
2637 }
2638 __this_cpu_write(rcu_data.rcu_urgent_qs, false);
2639 }
2640 rcu_flavor_sched_clock_irq(user);
2641 if (rcu_pending(user))
2642 invoke_rcu_core();
2643 lockdep_assert_irqs_disabled();
2644
2645 trace_rcu_utilization(TPS("End scheduler-tick"));
2646}
2647
2648/*
2649 * Scan the leaf rcu_node structures. For each structure on which all
2650 * CPUs have reported a quiescent state and on which there are tasks
2651 * blocking the current grace period, initiate RCU priority boosting.
2652 * Otherwise, invoke the specified function to check dyntick state for
2653 * each CPU that has not yet reported a quiescent state.
2654 */
2655static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
2656{
2657 int cpu;
2658 unsigned long flags;
2659 unsigned long mask;
2660 struct rcu_data *rdp;
2661 struct rcu_node *rnp;
2662
2663 rcu_state.cbovld = rcu_state.cbovldnext;
2664 rcu_state.cbovldnext = false;
2665 rcu_for_each_leaf_node(rnp) {
2666 cond_resched_tasks_rcu_qs();
2667 mask = 0;
2668 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2669 rcu_state.cbovldnext |= !!rnp->cbovldmask;
2670 if (rnp->qsmask == 0) {
2671 if (rcu_preempt_blocked_readers_cgp(rnp)) {
2672 /*
2673 * No point in scanning bits because they
2674 * are all zero. But we might need to
2675 * priority-boost blocked readers.
2676 */
2677 rcu_initiate_boost(rnp, flags);
2678 /* rcu_initiate_boost() releases rnp->lock */
2679 continue;
2680 }
2681 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2682 continue;
2683 }
2684 for_each_leaf_node_cpu_mask(rnp, cpu, rnp->qsmask) {
2685 rdp = per_cpu_ptr(&rcu_data, cpu);
2686 if (f(rdp)) {
2687 mask |= rdp->grpmask;
2688 rcu_disable_urgency_upon_qs(rdp);
2689 }
2690 }
2691 if (mask != 0) {
2692 /* Idle/offline CPUs, report (releases rnp->lock). */
2693 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
2694 } else {
2695 /* Nothing to do here, so just drop the lock. */
2696 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2697 }
2698 }
2699}
2700
2701/*
2702 * Force quiescent states on reluctant CPUs, and also detect which
2703 * CPUs are in dyntick-idle mode.
2704 */
2705void rcu_force_quiescent_state(void)
2706{
2707 unsigned long flags;
2708 bool ret;
2709 struct rcu_node *rnp;
2710 struct rcu_node *rnp_old = NULL;
2711
2712 /* Funnel through hierarchy to reduce memory contention. */
2713 rnp = __this_cpu_read(rcu_data.mynode);
2714 for (; rnp != NULL; rnp = rnp->parent) {
2715 ret = (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) ||
2716 !raw_spin_trylock(&rnp->fqslock);
2717 if (rnp_old != NULL)
2718 raw_spin_unlock(&rnp_old->fqslock);
2719 if (ret)
2720 return;
2721 rnp_old = rnp;
2722 }
2723 /* rnp_old == rcu_get_root(), rnp == NULL. */
2724
2725 /* Reached the root of the rcu_node tree, acquire lock. */
2726 raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
2727 raw_spin_unlock(&rnp_old->fqslock);
2728 if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
2729 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2730 return; /* Someone beat us to it. */
2731 }
2732 WRITE_ONCE(rcu_state.gp_flags,
2733 READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
2734 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2735 rcu_gp_kthread_wake();
2736}
2737EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
2738
2739// Workqueue handler for an RCU reader for kernels enforcing struct RCU
2740// grace periods.
2741static void strict_work_handler(struct work_struct *work)
2742{
2743 rcu_read_lock();
2744 rcu_read_unlock();
2745}
2746
2747/* Perform RCU core processing work for the current CPU. */
2748static __latent_entropy void rcu_core(void)
2749{
2750 unsigned long flags;
2751 struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
2752 struct rcu_node *rnp = rdp->mynode;
2753 const bool do_batch = !rcu_segcblist_completely_offloaded(&rdp->cblist);
2754
2755 if (cpu_is_offline(smp_processor_id()))
2756 return;
2757 trace_rcu_utilization(TPS("Start RCU core"));
2758 WARN_ON_ONCE(!rdp->beenonline);
2759
2760 /* Report any deferred quiescent states if preemption enabled. */
2761 if (!(preempt_count() & PREEMPT_MASK)) {
2762 rcu_preempt_deferred_qs(current);
2763 } else if (rcu_preempt_need_deferred_qs(current)) {
2764 set_tsk_need_resched(current);
2765 set_preempt_need_resched();
2766 }
2767
2768 /* Update RCU state based on any recent quiescent states. */
2769 rcu_check_quiescent_state(rdp);
2770
2771 /* No grace period and unregistered callbacks? */
2772 if (!rcu_gp_in_progress() &&
2773 rcu_segcblist_is_enabled(&rdp->cblist) && do_batch) {
2774 rcu_nocb_lock_irqsave(rdp, flags);
2775 if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
2776 rcu_accelerate_cbs_unlocked(rnp, rdp);
2777 rcu_nocb_unlock_irqrestore(rdp, flags);
2778 }
2779
2780 rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check());
2781
2782 /* If there are callbacks ready, invoke them. */
2783 if (do_batch && rcu_segcblist_ready_cbs(&rdp->cblist) &&
2784 likely(READ_ONCE(rcu_scheduler_fully_active)))
2785 rcu_do_batch(rdp);
2786
2787 /* Do any needed deferred wakeups of rcuo kthreads. */
2788 do_nocb_deferred_wakeup(rdp);
2789 trace_rcu_utilization(TPS("End RCU core"));
2790
2791 // If strict GPs, schedule an RCU reader in a clean environment.
2792 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
2793 queue_work_on(rdp->cpu, rcu_gp_wq, &rdp->strict_work);
2794}
2795
2796static void rcu_core_si(struct softirq_action *h)
2797{
2798 rcu_core();
2799}
2800
2801static void rcu_wake_cond(struct task_struct *t, int status)
2802{
2803 /*
2804 * If the thread is yielding, only wake it when this
2805 * is invoked from idle
2806 */
2807 if (t && (status != RCU_KTHREAD_YIELDING || is_idle_task(current)))
2808 wake_up_process(t);
2809}
2810
2811static void invoke_rcu_core_kthread(void)
2812{
2813 struct task_struct *t;
2814 unsigned long flags;
2815
2816 local_irq_save(flags);
2817 __this_cpu_write(rcu_data.rcu_cpu_has_work, 1);
2818 t = __this_cpu_read(rcu_data.rcu_cpu_kthread_task);
2819 if (t != NULL && t != current)
2820 rcu_wake_cond(t, __this_cpu_read(rcu_data.rcu_cpu_kthread_status));
2821 local_irq_restore(flags);
2822}
2823
2824/*
2825 * Wake up this CPU's rcuc kthread to do RCU core processing.
2826 */
2827static void invoke_rcu_core(void)
2828{
2829 if (!cpu_online(smp_processor_id()))
2830 return;
2831 if (use_softirq)
2832 raise_softirq(RCU_SOFTIRQ);
2833 else
2834 invoke_rcu_core_kthread();
2835}
2836
2837static void rcu_cpu_kthread_park(unsigned int cpu)
2838{
2839 per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
2840}
2841
2842static int rcu_cpu_kthread_should_run(unsigned int cpu)
2843{
2844 return __this_cpu_read(rcu_data.rcu_cpu_has_work);
2845}
2846
2847/*
2848 * Per-CPU kernel thread that invokes RCU callbacks. This replaces
2849 * the RCU softirq used in configurations of RCU that do not support RCU
2850 * priority boosting.
2851 */
2852static void rcu_cpu_kthread(unsigned int cpu)
2853{
2854 unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status);
2855 char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work);
2856 int spincnt;
2857
2858 trace_rcu_utilization(TPS("Start CPU kthread@rcu_run"));
2859 for (spincnt = 0; spincnt < 10; spincnt++) {
2860 local_bh_disable();
2861 *statusp = RCU_KTHREAD_RUNNING;
2862 local_irq_disable();
2863 work = *workp;
2864 *workp = 0;
2865 local_irq_enable();
2866 if (work)
2867 rcu_core();
2868 local_bh_enable();
2869 if (*workp == 0) {
2870 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
2871 *statusp = RCU_KTHREAD_WAITING;
2872 return;
2873 }
2874 }
2875 *statusp = RCU_KTHREAD_YIELDING;
2876 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
2877 schedule_timeout_idle(2);
2878 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
2879 *statusp = RCU_KTHREAD_WAITING;
2880}
2881
2882static struct smp_hotplug_thread rcu_cpu_thread_spec = {
2883 .store = &rcu_data.rcu_cpu_kthread_task,
2884 .thread_should_run = rcu_cpu_kthread_should_run,
2885 .thread_fn = rcu_cpu_kthread,
2886 .thread_comm = "rcuc/%u",
2887 .setup = rcu_cpu_kthread_setup,
2888 .park = rcu_cpu_kthread_park,
2889};
2890
2891/*
2892 * Spawn per-CPU RCU core processing kthreads.
2893 */
2894static int __init rcu_spawn_core_kthreads(void)
2895{
2896 int cpu;
2897
2898 for_each_possible_cpu(cpu)
2899 per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0;
2900 if (!IS_ENABLED(CONFIG_RCU_BOOST) && use_softirq)
2901 return 0;
2902 WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec),
2903 "%s: Could not start rcuc kthread, OOM is now expected behavior\n", __func__);
2904 return 0;
2905}
2906
2907/*
2908 * Handle any core-RCU processing required by a call_rcu() invocation.
2909 */
2910static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
2911 unsigned long flags)
2912{
2913 /*
2914 * If called from an extended quiescent state, invoke the RCU
2915 * core in order to force a re-evaluation of RCU's idleness.
2916 */
2917 if (!rcu_is_watching())
2918 invoke_rcu_core();
2919
2920 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2921 if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2922 return;
2923
2924 /*
2925 * Force the grace period if too many callbacks or too long waiting.
2926 * Enforce hysteresis, and don't invoke rcu_force_quiescent_state()
2927 * if some other CPU has recently done so. Also, don't bother
2928 * invoking rcu_force_quiescent_state() if the newly enqueued callback
2929 * is the only one waiting for a grace period to complete.
2930 */
2931 if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
2932 rdp->qlen_last_fqs_check + qhimark)) {
2933
2934 /* Are we ignoring a completed grace period? */
2935 note_gp_changes(rdp);
2936
2937 /* Start a new grace period if one not already started. */
2938 if (!rcu_gp_in_progress()) {
2939 rcu_accelerate_cbs_unlocked(rdp->mynode, rdp);
2940 } else {
2941 /* Give the grace period a kick. */
2942 rdp->blimit = DEFAULT_MAX_RCU_BLIMIT;
2943 if (rcu_state.n_force_qs == rdp->n_force_qs_snap &&
2944 rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
2945 rcu_force_quiescent_state();
2946 rdp->n_force_qs_snap = rcu_state.n_force_qs;
2947 rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
2948 }
2949 }
2950}
2951
2952/*
2953 * RCU callback function to leak a callback.
2954 */
2955static void rcu_leak_callback(struct rcu_head *rhp)
2956{
2957}
2958
2959/*
2960 * Check and if necessary update the leaf rcu_node structure's
2961 * ->cbovldmask bit corresponding to the current CPU based on that CPU's
2962 * number of queued RCU callbacks. The caller must hold the leaf rcu_node
2963 * structure's ->lock.
2964 */
2965static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp)
2966{
2967 raw_lockdep_assert_held_rcu_node(rnp);
2968 if (qovld_calc <= 0)
2969 return; // Early boot and wildcard value set.
2970 if (rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc)
2971 WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask | rdp->grpmask);
2972 else
2973 WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask & ~rdp->grpmask);
2974}
2975
2976/*
2977 * Check and if necessary update the leaf rcu_node structure's
2978 * ->cbovldmask bit corresponding to the current CPU based on that CPU's
2979 * number of queued RCU callbacks. No locks need be held, but the
2980 * caller must have disabled interrupts.
2981 *
2982 * Note that this function ignores the possibility that there are a lot
2983 * of callbacks all of which have already seen the end of their respective
2984 * grace periods. This omission is due to the need for no-CBs CPUs to
2985 * be holding ->nocb_lock to do this check, which is too heavy for a
2986 * common-case operation.
2987 */
2988static void check_cb_ovld(struct rcu_data *rdp)
2989{
2990 struct rcu_node *const rnp = rdp->mynode;
2991
2992 if (qovld_calc <= 0 ||
2993 ((rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc) ==
2994 !!(READ_ONCE(rnp->cbovldmask) & rdp->grpmask)))
2995 return; // Early boot wildcard value or already set correctly.
2996 raw_spin_lock_rcu_node(rnp);
2997 check_cb_ovld_locked(rdp, rnp);
2998 raw_spin_unlock_rcu_node(rnp);
2999}
3000
3001/* Helper function for call_rcu() and friends. */
3002static void
3003__call_rcu(struct rcu_head *head, rcu_callback_t func)
3004{
3005 static atomic_t doublefrees;
3006 unsigned long flags;
3007 struct rcu_data *rdp;
3008 bool was_alldone;
3009
3010 /* Misaligned rcu_head! */
3011 WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
3012
3013 if (debug_rcu_head_queue(head)) {
3014 /*
3015 * Probable double call_rcu(), so leak the callback.
3016 * Use rcu:rcu_callback trace event to find the previous
3017 * time callback was passed to __call_rcu().
3018 */
3019 if (atomic_inc_return(&doublefrees) < 4) {
3020 pr_err("%s(): Double-freed CB %p->%pS()!!! ", __func__, head, head->func);
3021 mem_dump_obj(head);
3022 }
3023 WRITE_ONCE(head->func, rcu_leak_callback);
3024 return;
3025 }
3026 head->func = func;
3027 head->next = NULL;
3028 local_irq_save(flags);
3029 kasan_record_aux_stack(head);
3030 rdp = this_cpu_ptr(&rcu_data);
3031
3032 /* Add the callback to our list. */
3033 if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) {
3034 // This can trigger due to call_rcu() from offline CPU:
3035 WARN_ON_ONCE(rcu_scheduler_active != RCU_SCHEDULER_INACTIVE);
3036 WARN_ON_ONCE(!rcu_is_watching());
3037 // Very early boot, before rcu_init(). Initialize if needed
3038 // and then drop through to queue the callback.
3039 if (rcu_segcblist_empty(&rdp->cblist))
3040 rcu_segcblist_init(&rdp->cblist);
3041 }
3042
3043 check_cb_ovld(rdp);
3044 if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags))
3045 return; // Enqueued onto ->nocb_bypass, so just leave.
3046 // If no-CBs CPU gets here, rcu_nocb_try_bypass() acquired ->nocb_lock.
3047 rcu_segcblist_enqueue(&rdp->cblist, head);
3048 if (__is_kvfree_rcu_offset((unsigned long)func))
3049 trace_rcu_kvfree_callback(rcu_state.name, head,
3050 (unsigned long)func,
3051 rcu_segcblist_n_cbs(&rdp->cblist));
3052 else
3053 trace_rcu_callback(rcu_state.name, head,
3054 rcu_segcblist_n_cbs(&rdp->cblist));
3055
3056 trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCBQueued"));
3057
3058 /* Go handle any RCU core processing required. */
3059 if (unlikely(rcu_rdp_is_offloaded(rdp))) {
3060 __call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
3061 } else {
3062 __call_rcu_core(rdp, head, flags);
3063 local_irq_restore(flags);
3064 }
3065}
3066
3067/**
3068 * call_rcu() - Queue an RCU callback for invocation after a grace period.
3069 * @head: structure to be used for queueing the RCU updates.
3070 * @func: actual callback function to be invoked after the grace period
3071 *
3072 * The callback function will be invoked some time after a full grace
3073 * period elapses, in other words after all pre-existing RCU read-side
3074 * critical sections have completed. However, the callback function
3075 * might well execute concurrently with RCU read-side critical sections
3076 * that started after call_rcu() was invoked.
3077 *
3078 * RCU read-side critical sections are delimited by rcu_read_lock()
3079 * and rcu_read_unlock(), and may be nested. In addition, but only in
3080 * v5.0 and later, regions of code across which interrupts, preemption,
3081 * or softirqs have been disabled also serve as RCU read-side critical
3082 * sections. This includes hardware interrupt handlers, softirq handlers,
3083 * and NMI handlers.
3084 *
3085 * Note that all CPUs must agree that the grace period extended beyond
3086 * all pre-existing RCU read-side critical section. On systems with more
3087 * than one CPU, this means that when "func()" is invoked, each CPU is
3088 * guaranteed to have executed a full memory barrier since the end of its
3089 * last RCU read-side critical section whose beginning preceded the call
3090 * to call_rcu(). It also means that each CPU executing an RCU read-side
3091 * critical section that continues beyond the start of "func()" must have
3092 * executed a memory barrier after the call_rcu() but before the beginning
3093 * of that RCU read-side critical section. Note that these guarantees
3094 * include CPUs that are offline, idle, or executing in user mode, as
3095 * well as CPUs that are executing in the kernel.
3096 *
3097 * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
3098 * resulting RCU callback function "func()", then both CPU A and CPU B are
3099 * guaranteed to execute a full memory barrier during the time interval
3100 * between the call to call_rcu() and the invocation of "func()" -- even
3101 * if CPU A and CPU B are the same CPU (but again only if the system has
3102 * more than one CPU).
3103 *
3104 * Implementation of these memory-ordering guarantees is described here:
3105 * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
3106 */
3107void call_rcu(struct rcu_head *head, rcu_callback_t func)
3108{
3109 __call_rcu(head, func);
3110}
3111EXPORT_SYMBOL_GPL(call_rcu);
3112
3113
3114/* Maximum number of jiffies to wait before draining a batch. */
3115#define KFREE_DRAIN_JIFFIES (HZ / 50)
3116#define KFREE_N_BATCHES 2
3117#define FREE_N_CHANNELS 2
3118
3119/**
3120 * struct kvfree_rcu_bulk_data - single block to store kvfree_rcu() pointers
3121 * @nr_records: Number of active pointers in the array
3122 * @next: Next bulk object in the block chain
3123 * @records: Array of the kvfree_rcu() pointers
3124 */
3125struct kvfree_rcu_bulk_data {
3126 unsigned long nr_records;
3127 struct kvfree_rcu_bulk_data *next;
3128 void *records[];
3129};
3130
3131/*
3132 * This macro defines how many entries the "records" array
3133 * will contain. It is based on the fact that the size of
3134 * kvfree_rcu_bulk_data structure becomes exactly one page.
3135 */
3136#define KVFREE_BULK_MAX_ENTR \
3137 ((PAGE_SIZE - sizeof(struct kvfree_rcu_bulk_data)) / sizeof(void *))
3138
3139/**
3140 * struct kfree_rcu_cpu_work - single batch of kfree_rcu() requests
3141 * @rcu_work: Let queue_rcu_work() invoke workqueue handler after grace period
3142 * @head_free: List of kfree_rcu() objects waiting for a grace period
3143 * @bkvhead_free: Bulk-List of kvfree_rcu() objects waiting for a grace period
3144 * @krcp: Pointer to @kfree_rcu_cpu structure
3145 */
3146
3147struct kfree_rcu_cpu_work {
3148 struct rcu_work rcu_work;
3149 struct rcu_head *head_free;
3150 struct kvfree_rcu_bulk_data *bkvhead_free[FREE_N_CHANNELS];
3151 struct kfree_rcu_cpu *krcp;
3152};
3153
3154/**
3155 * struct kfree_rcu_cpu - batch up kfree_rcu() requests for RCU grace period
3156 * @head: List of kfree_rcu() objects not yet waiting for a grace period
3157 * @bkvhead: Bulk-List of kvfree_rcu() objects not yet waiting for a grace period
3158 * @krw_arr: Array of batches of kfree_rcu() objects waiting for a grace period
3159 * @lock: Synchronize access to this structure
3160 * @monitor_work: Promote @head to @head_free after KFREE_DRAIN_JIFFIES
3161 * @monitor_todo: Tracks whether a @monitor_work delayed work is pending
3162 * @initialized: The @rcu_work fields have been initialized
3163 * @count: Number of objects for which GP not started
3164 * @bkvcache:
3165 * A simple cache list that contains objects for reuse purpose.
3166 * In order to save some per-cpu space the list is singular.
3167 * Even though it is lockless an access has to be protected by the
3168 * per-cpu lock.
3169 * @page_cache_work: A work to refill the cache when it is empty
3170 * @backoff_page_cache_fill: Delay cache refills
3171 * @work_in_progress: Indicates that page_cache_work is running
3172 * @hrtimer: A hrtimer for scheduling a page_cache_work
3173 * @nr_bkv_objs: number of allocated objects at @bkvcache.
3174 *
3175 * This is a per-CPU structure. The reason that it is not included in
3176 * the rcu_data structure is to permit this code to be extracted from
3177 * the RCU files. Such extraction could allow further optimization of
3178 * the interactions with the slab allocators.
3179 */
3180struct kfree_rcu_cpu {
3181 struct rcu_head *head;
3182 struct kvfree_rcu_bulk_data *bkvhead[FREE_N_CHANNELS];
3183 struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES];
3184 raw_spinlock_t lock;
3185 struct delayed_work monitor_work;
3186 bool monitor_todo;
3187 bool initialized;
3188 int count;
3189
3190 struct delayed_work page_cache_work;
3191 atomic_t backoff_page_cache_fill;
3192 atomic_t work_in_progress;
3193 struct hrtimer hrtimer;
3194
3195 struct llist_head bkvcache;
3196 int nr_bkv_objs;
3197};
3198
3199static DEFINE_PER_CPU(struct kfree_rcu_cpu, krc) = {
3200 .lock = __RAW_SPIN_LOCK_UNLOCKED(krc.lock),
3201};
3202
3203static __always_inline void
3204debug_rcu_bhead_unqueue(struct kvfree_rcu_bulk_data *bhead)
3205{
3206#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
3207 int i;
3208
3209 for (i = 0; i < bhead->nr_records; i++)
3210 debug_rcu_head_unqueue((struct rcu_head *)(bhead->records[i]));
3211#endif
3212}
3213
3214static inline struct kfree_rcu_cpu *
3215krc_this_cpu_lock(unsigned long *flags)
3216{
3217 struct kfree_rcu_cpu *krcp;
3218
3219 local_irq_save(*flags); // For safely calling this_cpu_ptr().
3220 krcp = this_cpu_ptr(&krc);
3221 raw_spin_lock(&krcp->lock);
3222
3223 return krcp;
3224}
3225
3226static inline void
3227krc_this_cpu_unlock(struct kfree_rcu_cpu *krcp, unsigned long flags)
3228{
3229 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3230}
3231
3232static inline struct kvfree_rcu_bulk_data *
3233get_cached_bnode(struct kfree_rcu_cpu *krcp)
3234{
3235 if (!krcp->nr_bkv_objs)
3236 return NULL;
3237
3238 WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs - 1);
3239 return (struct kvfree_rcu_bulk_data *)
3240 llist_del_first(&krcp->bkvcache);
3241}
3242
3243static inline bool
3244put_cached_bnode(struct kfree_rcu_cpu *krcp,
3245 struct kvfree_rcu_bulk_data *bnode)
3246{
3247 // Check the limit.
3248 if (krcp->nr_bkv_objs >= rcu_min_cached_objs)
3249 return false;
3250
3251 llist_add((struct llist_node *) bnode, &krcp->bkvcache);
3252 WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs + 1);
3253 return true;
3254}
3255
3256static int
3257drain_page_cache(struct kfree_rcu_cpu *krcp)
3258{
3259 unsigned long flags;
3260 struct llist_node *page_list, *pos, *n;
3261 int freed = 0;
3262
3263 raw_spin_lock_irqsave(&krcp->lock, flags);
3264 page_list = llist_del_all(&krcp->bkvcache);
3265 WRITE_ONCE(krcp->nr_bkv_objs, 0);
3266 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3267
3268 llist_for_each_safe(pos, n, page_list) {
3269 free_page((unsigned long)pos);
3270 freed++;
3271 }
3272
3273 return freed;
3274}
3275
3276/*
3277 * This function is invoked in workqueue context after a grace period.
3278 * It frees all the objects queued on ->bkvhead_free or ->head_free.
3279 */
3280static void kfree_rcu_work(struct work_struct *work)
3281{
3282 unsigned long flags;
3283 struct kvfree_rcu_bulk_data *bkvhead[FREE_N_CHANNELS], *bnext;
3284 struct rcu_head *head, *next;
3285 struct kfree_rcu_cpu *krcp;
3286 struct kfree_rcu_cpu_work *krwp;
3287 int i, j;
3288
3289 krwp = container_of(to_rcu_work(work),
3290 struct kfree_rcu_cpu_work, rcu_work);
3291 krcp = krwp->krcp;
3292
3293 raw_spin_lock_irqsave(&krcp->lock, flags);
3294 // Channels 1 and 2.
3295 for (i = 0; i < FREE_N_CHANNELS; i++) {
3296 bkvhead[i] = krwp->bkvhead_free[i];
3297 krwp->bkvhead_free[i] = NULL;
3298 }
3299
3300 // Channel 3.
3301 head = krwp->head_free;
3302 krwp->head_free = NULL;
3303 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3304
3305 // Handle the first two channels.
3306 for (i = 0; i < FREE_N_CHANNELS; i++) {
3307 for (; bkvhead[i]; bkvhead[i] = bnext) {
3308 bnext = bkvhead[i]->next;
3309 debug_rcu_bhead_unqueue(bkvhead[i]);
3310
3311 rcu_lock_acquire(&rcu_callback_map);
3312 if (i == 0) { // kmalloc() / kfree().
3313 trace_rcu_invoke_kfree_bulk_callback(
3314 rcu_state.name, bkvhead[i]->nr_records,
3315 bkvhead[i]->records);
3316
3317 kfree_bulk(bkvhead[i]->nr_records,
3318 bkvhead[i]->records);
3319 } else { // vmalloc() / vfree().
3320 for (j = 0; j < bkvhead[i]->nr_records; j++) {
3321 trace_rcu_invoke_kvfree_callback(
3322 rcu_state.name,
3323 bkvhead[i]->records[j], 0);
3324
3325 vfree(bkvhead[i]->records[j]);
3326 }
3327 }
3328 rcu_lock_release(&rcu_callback_map);
3329
3330 raw_spin_lock_irqsave(&krcp->lock, flags);
3331 if (put_cached_bnode(krcp, bkvhead[i]))
3332 bkvhead[i] = NULL;
3333 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3334
3335 if (bkvhead[i])
3336 free_page((unsigned long) bkvhead[i]);
3337
3338 cond_resched_tasks_rcu_qs();
3339 }
3340 }
3341
3342 /*
3343 * This is used when the "bulk" path can not be used for the
3344 * double-argument of kvfree_rcu(). This happens when the
3345 * page-cache is empty, which means that objects are instead
3346 * queued on a linked list through their rcu_head structures.
3347 * This list is named "Channel 3".
3348 */
3349 for (; head; head = next) {
3350 unsigned long offset = (unsigned long)head->func;
3351 void *ptr = (void *)head - offset;
3352
3353 next = head->next;
3354 debug_rcu_head_unqueue((struct rcu_head *)ptr);
3355 rcu_lock_acquire(&rcu_callback_map);
3356 trace_rcu_invoke_kvfree_callback(rcu_state.name, head, offset);
3357
3358 if (!WARN_ON_ONCE(!__is_kvfree_rcu_offset(offset)))
3359 kvfree(ptr);
3360
3361 rcu_lock_release(&rcu_callback_map);
3362 cond_resched_tasks_rcu_qs();
3363 }
3364}
3365
3366/*
3367 * This function is invoked after the KFREE_DRAIN_JIFFIES timeout.
3368 */
3369static void kfree_rcu_monitor(struct work_struct *work)
3370{
3371 struct kfree_rcu_cpu *krcp = container_of(work,
3372 struct kfree_rcu_cpu, monitor_work.work);
3373 unsigned long flags;
3374 int i, j;
3375
3376 raw_spin_lock_irqsave(&krcp->lock, flags);
3377
3378 // Attempt to start a new batch.
3379 for (i = 0; i < KFREE_N_BATCHES; i++) {
3380 struct kfree_rcu_cpu_work *krwp = &(krcp->krw_arr[i]);
3381
3382 // Try to detach bkvhead or head and attach it over any
3383 // available corresponding free channel. It can be that
3384 // a previous RCU batch is in progress, it means that
3385 // immediately to queue another one is not possible so
3386 // in that case the monitor work is rearmed.
3387 if ((krcp->bkvhead[0] && !krwp->bkvhead_free[0]) ||
3388 (krcp->bkvhead[1] && !krwp->bkvhead_free[1]) ||
3389 (krcp->head && !krwp->head_free)) {
3390 // Channel 1 corresponds to the SLAB-pointer bulk path.
3391 // Channel 2 corresponds to vmalloc-pointer bulk path.
3392 for (j = 0; j < FREE_N_CHANNELS; j++) {
3393 if (!krwp->bkvhead_free[j]) {
3394 krwp->bkvhead_free[j] = krcp->bkvhead[j];
3395 krcp->bkvhead[j] = NULL;
3396 }
3397 }
3398
3399 // Channel 3 corresponds to both SLAB and vmalloc
3400 // objects queued on the linked list.
3401 if (!krwp->head_free) {
3402 krwp->head_free = krcp->head;
3403 krcp->head = NULL;
3404 }
3405
3406 WRITE_ONCE(krcp->count, 0);
3407
3408 // One work is per one batch, so there are three
3409 // "free channels", the batch can handle. It can
3410 // be that the work is in the pending state when
3411 // channels have been detached following by each
3412 // other.
3413 queue_rcu_work(system_wq, &krwp->rcu_work);
3414 }
3415 }
3416
3417 // If there is nothing to detach, it means that our job is
3418 // successfully done here. In case of having at least one
3419 // of the channels that is still busy we should rearm the
3420 // work to repeat an attempt. Because previous batches are
3421 // still in progress.
3422 if (!krcp->bkvhead[0] && !krcp->bkvhead[1] && !krcp->head)
3423 krcp->monitor_todo = false;
3424 else
3425 schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
3426
3427 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3428}
3429
3430static enum hrtimer_restart
3431schedule_page_work_fn(struct hrtimer *t)
3432{
3433 struct kfree_rcu_cpu *krcp =
3434 container_of(t, struct kfree_rcu_cpu, hrtimer);
3435
3436 queue_delayed_work(system_highpri_wq, &krcp->page_cache_work, 0);
3437 return HRTIMER_NORESTART;
3438}
3439
3440static void fill_page_cache_func(struct work_struct *work)
3441{
3442 struct kvfree_rcu_bulk_data *bnode;
3443 struct kfree_rcu_cpu *krcp =
3444 container_of(work, struct kfree_rcu_cpu,
3445 page_cache_work.work);
3446 unsigned long flags;
3447 int nr_pages;
3448 bool pushed;
3449 int i;
3450
3451 nr_pages = atomic_read(&krcp->backoff_page_cache_fill) ?
3452 1 : rcu_min_cached_objs;
3453
3454 for (i = 0; i < nr_pages; i++) {
3455 bnode = (struct kvfree_rcu_bulk_data *)
3456 __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
3457
3458 if (bnode) {
3459 raw_spin_lock_irqsave(&krcp->lock, flags);
3460 pushed = put_cached_bnode(krcp, bnode);
3461 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3462
3463 if (!pushed) {
3464 free_page((unsigned long) bnode);
3465 break;
3466 }
3467 }
3468 }
3469
3470 atomic_set(&krcp->work_in_progress, 0);
3471 atomic_set(&krcp->backoff_page_cache_fill, 0);
3472}
3473
3474static void
3475run_page_cache_worker(struct kfree_rcu_cpu *krcp)
3476{
3477 if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
3478 !atomic_xchg(&krcp->work_in_progress, 1)) {
3479 if (atomic_read(&krcp->backoff_page_cache_fill)) {
3480 queue_delayed_work(system_wq,
3481 &krcp->page_cache_work,
3482 msecs_to_jiffies(rcu_delay_page_cache_fill_msec));
3483 } else {
3484 hrtimer_init(&krcp->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
3485 krcp->hrtimer.function = schedule_page_work_fn;
3486 hrtimer_start(&krcp->hrtimer, 0, HRTIMER_MODE_REL);
3487 }
3488 }
3489}
3490
3491// Record ptr in a page managed by krcp, with the pre-krc_this_cpu_lock()
3492// state specified by flags. If can_alloc is true, the caller must
3493// be schedulable and not be holding any locks or mutexes that might be
3494// acquired by the memory allocator or anything that it might invoke.
3495// Returns true if ptr was successfully recorded, else the caller must
3496// use a fallback.
3497static inline bool
3498add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
3499 unsigned long *flags, void *ptr, bool can_alloc)
3500{
3501 struct kvfree_rcu_bulk_data *bnode;
3502 int idx;
3503
3504 *krcp = krc_this_cpu_lock(flags);
3505 if (unlikely(!(*krcp)->initialized))
3506 return false;
3507
3508 idx = !!is_vmalloc_addr(ptr);
3509
3510 /* Check if a new block is required. */
3511 if (!(*krcp)->bkvhead[idx] ||
3512 (*krcp)->bkvhead[idx]->nr_records == KVFREE_BULK_MAX_ENTR) {
3513 bnode = get_cached_bnode(*krcp);
3514 if (!bnode && can_alloc) {
3515 krc_this_cpu_unlock(*krcp, *flags);
3516
3517 // __GFP_NORETRY - allows a light-weight direct reclaim
3518 // what is OK from minimizing of fallback hitting point of
3519 // view. Apart of that it forbids any OOM invoking what is
3520 // also beneficial since we are about to release memory soon.
3521 //
3522 // __GFP_NOMEMALLOC - prevents from consuming of all the
3523 // memory reserves. Please note we have a fallback path.
3524 //
3525 // __GFP_NOWARN - it is supposed that an allocation can
3526 // be failed under low memory or high memory pressure
3527 // scenarios.
3528 bnode = (struct kvfree_rcu_bulk_data *)
3529 __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
3530 *krcp = krc_this_cpu_lock(flags);
3531 }
3532
3533 if (!bnode)
3534 return false;
3535
3536 /* Initialize the new block. */
3537 bnode->nr_records = 0;
3538 bnode->next = (*krcp)->bkvhead[idx];
3539
3540 /* Attach it to the head. */
3541 (*krcp)->bkvhead[idx] = bnode;
3542 }
3543
3544 /* Finally insert. */
3545 (*krcp)->bkvhead[idx]->records
3546 [(*krcp)->bkvhead[idx]->nr_records++] = ptr;
3547
3548 return true;
3549}
3550
3551/*
3552 * Queue a request for lazy invocation of the appropriate free routine
3553 * after a grace period. Please note that three paths are maintained,
3554 * two for the common case using arrays of pointers and a third one that
3555 * is used only when the main paths cannot be used, for example, due to
3556 * memory pressure.
3557 *
3558 * Each kvfree_call_rcu() request is added to a batch. The batch will be drained
3559 * every KFREE_DRAIN_JIFFIES number of jiffies. All the objects in the batch will
3560 * be free'd in workqueue context. This allows us to: batch requests together to
3561 * reduce the number of grace periods during heavy kfree_rcu()/kvfree_rcu() load.
3562 */
3563void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
3564{
3565 unsigned long flags;
3566 struct kfree_rcu_cpu *krcp;
3567 bool success;
3568 void *ptr;
3569
3570 if (head) {
3571 ptr = (void *) head - (unsigned long) func;
3572 } else {
3573 /*
3574 * Please note there is a limitation for the head-less
3575 * variant, that is why there is a clear rule for such
3576 * objects: it can be used from might_sleep() context
3577 * only. For other places please embed an rcu_head to
3578 * your data.
3579 */
3580 might_sleep();
3581 ptr = (unsigned long *) func;
3582 }
3583
3584 // Queue the object but don't yet schedule the batch.
3585 if (debug_rcu_head_queue(ptr)) {
3586 // Probable double kfree_rcu(), just leak.
3587 WARN_ONCE(1, "%s(): Double-freed call. rcu_head %p\n",
3588 __func__, head);
3589
3590 // Mark as success and leave.
3591 return;
3592 }
3593
3594 kasan_record_aux_stack(ptr);
3595 success = add_ptr_to_bulk_krc_lock(&krcp, &flags, ptr, !head);
3596 if (!success) {
3597 run_page_cache_worker(krcp);
3598
3599 if (head == NULL)
3600 // Inline if kvfree_rcu(one_arg) call.
3601 goto unlock_return;
3602
3603 head->func = func;
3604 head->next = krcp->head;
3605 krcp->head = head;
3606 success = true;
3607 }
3608
3609 WRITE_ONCE(krcp->count, krcp->count + 1);
3610
3611 // Set timer to drain after KFREE_DRAIN_JIFFIES.
3612 if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
3613 !krcp->monitor_todo) {
3614 krcp->monitor_todo = true;
3615 schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES);
3616 }
3617
3618unlock_return:
3619 krc_this_cpu_unlock(krcp, flags);
3620
3621 /*
3622 * Inline kvfree() after synchronize_rcu(). We can do
3623 * it from might_sleep() context only, so the current
3624 * CPU can pass the QS state.
3625 */
3626 if (!success) {
3627 debug_rcu_head_unqueue((struct rcu_head *) ptr);
3628 synchronize_rcu();
3629 kvfree(ptr);
3630 }
3631}
3632EXPORT_SYMBOL_GPL(kvfree_call_rcu);
3633
3634static unsigned long
3635kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
3636{
3637 int cpu;
3638 unsigned long count = 0;
3639
3640 /* Snapshot count of all CPUs */
3641 for_each_possible_cpu(cpu) {
3642 struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
3643
3644 count += READ_ONCE(krcp->count);
3645 count += READ_ONCE(krcp->nr_bkv_objs);
3646 atomic_set(&krcp->backoff_page_cache_fill, 1);
3647 }
3648
3649 return count;
3650}
3651
3652static unsigned long
3653kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
3654{
3655 int cpu, freed = 0;
3656
3657 for_each_possible_cpu(cpu) {
3658 int count;
3659 struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
3660
3661 count = krcp->count;
3662 count += drain_page_cache(krcp);
3663 kfree_rcu_monitor(&krcp->monitor_work.work);
3664
3665 sc->nr_to_scan -= count;
3666 freed += count;
3667
3668 if (sc->nr_to_scan <= 0)
3669 break;
3670 }
3671
3672 return freed == 0 ? SHRINK_STOP : freed;
3673}
3674
3675static struct shrinker kfree_rcu_shrinker = {
3676 .count_objects = kfree_rcu_shrink_count,
3677 .scan_objects = kfree_rcu_shrink_scan,
3678 .batch = 0,
3679 .seeks = DEFAULT_SEEKS,
3680};
3681
3682void __init kfree_rcu_scheduler_running(void)
3683{
3684 int cpu;
3685 unsigned long flags;
3686
3687 for_each_possible_cpu(cpu) {
3688 struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
3689
3690 raw_spin_lock_irqsave(&krcp->lock, flags);
3691 if ((!krcp->bkvhead[0] && !krcp->bkvhead[1] && !krcp->head) ||
3692 krcp->monitor_todo) {
3693 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3694 continue;
3695 }
3696 krcp->monitor_todo = true;
3697 schedule_delayed_work_on(cpu, &krcp->monitor_work,
3698 KFREE_DRAIN_JIFFIES);
3699 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3700 }
3701}
3702
3703/*
3704 * During early boot, any blocking grace-period wait automatically
3705 * implies a grace period. Later on, this is never the case for PREEMPTION.
3706 *
3707 * However, because a context switch is a grace period for !PREEMPTION, any
3708 * blocking grace-period wait automatically implies a grace period if
3709 * there is only one CPU online at any point time during execution of
3710 * either synchronize_rcu() or synchronize_rcu_expedited(). It is OK to
3711 * occasionally incorrectly indicate that there are multiple CPUs online
3712 * when there was in fact only one the whole time, as this just adds some
3713 * overhead: RCU still operates correctly.
3714 */
3715static int rcu_blocking_is_gp(void)
3716{
3717 int ret;
3718
3719 if (IS_ENABLED(CONFIG_PREEMPTION))
3720 return rcu_scheduler_active == RCU_SCHEDULER_INACTIVE;
3721 might_sleep(); /* Check for RCU read-side critical section. */
3722 preempt_disable();
3723 /*
3724 * If the rcu_state.n_online_cpus counter is equal to one,
3725 * there is only one CPU, and that CPU sees all prior accesses
3726 * made by any CPU that was online at the time of its access.
3727 * Furthermore, if this counter is equal to one, its value cannot
3728 * change until after the preempt_enable() below.
3729 *
3730 * Furthermore, if rcu_state.n_online_cpus is equal to one here,
3731 * all later CPUs (both this one and any that come online later
3732 * on) are guaranteed to see all accesses prior to this point
3733 * in the code, without the need for additional memory barriers.
3734 * Those memory barriers are provided by CPU-hotplug code.
3735 */
3736 ret = READ_ONCE(rcu_state.n_online_cpus) <= 1;
3737 preempt_enable();
3738 return ret;
3739}
3740
3741/**
3742 * synchronize_rcu - wait until a grace period has elapsed.
3743 *
3744 * Control will return to the caller some time after a full grace
3745 * period has elapsed, in other words after all currently executing RCU
3746 * read-side critical sections have completed. Note, however, that
3747 * upon return from synchronize_rcu(), the caller might well be executing
3748 * concurrently with new RCU read-side critical sections that began while
3749 * synchronize_rcu() was waiting.
3750 *
3751 * RCU read-side critical sections are delimited by rcu_read_lock()
3752 * and rcu_read_unlock(), and may be nested. In addition, but only in
3753 * v5.0 and later, regions of code across which interrupts, preemption,
3754 * or softirqs have been disabled also serve as RCU read-side critical
3755 * sections. This includes hardware interrupt handlers, softirq handlers,
3756 * and NMI handlers.
3757 *
3758 * Note that this guarantee implies further memory-ordering guarantees.
3759 * On systems with more than one CPU, when synchronize_rcu() returns,
3760 * each CPU is guaranteed to have executed a full memory barrier since
3761 * the end of its last RCU read-side critical section whose beginning
3762 * preceded the call to synchronize_rcu(). In addition, each CPU having
3763 * an RCU read-side critical section that extends beyond the return from
3764 * synchronize_rcu() is guaranteed to have executed a full memory barrier
3765 * after the beginning of synchronize_rcu() and before the beginning of
3766 * that RCU read-side critical section. Note that these guarantees include
3767 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
3768 * that are executing in the kernel.
3769 *
3770 * Furthermore, if CPU A invoked synchronize_rcu(), which returned
3771 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
3772 * to have executed a full memory barrier during the execution of
3773 * synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but
3774 * again only if the system has more than one CPU).
3775 *
3776 * Implementation of these memory-ordering guarantees is described here:
3777 * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
3778 */
3779void synchronize_rcu(void)
3780{
3781 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
3782 lock_is_held(&rcu_lock_map) ||
3783 lock_is_held(&rcu_sched_lock_map),
3784 "Illegal synchronize_rcu() in RCU read-side critical section");
3785 if (rcu_blocking_is_gp())
3786 return; // Context allows vacuous grace periods.
3787 if (rcu_gp_is_expedited())
3788 synchronize_rcu_expedited();
3789 else
3790 wait_rcu_gp(call_rcu);
3791}
3792EXPORT_SYMBOL_GPL(synchronize_rcu);
3793
3794/**
3795 * get_state_synchronize_rcu - Snapshot current RCU state
3796 *
3797 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
3798 * or poll_state_synchronize_rcu() to determine whether or not a full
3799 * grace period has elapsed in the meantime.
3800 */
3801unsigned long get_state_synchronize_rcu(void)
3802{
3803 /*
3804 * Any prior manipulation of RCU-protected data must happen
3805 * before the load from ->gp_seq.
3806 */
3807 smp_mb(); /* ^^^ */
3808 return rcu_seq_snap(&rcu_state.gp_seq);
3809}
3810EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
3811
3812/**
3813 * start_poll_synchronize_rcu - Snapshot and start RCU grace period
3814 *
3815 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
3816 * or poll_state_synchronize_rcu() to determine whether or not a full
3817 * grace period has elapsed in the meantime. If the needed grace period
3818 * is not already slated to start, notifies RCU core of the need for that
3819 * grace period.
3820 *
3821 * Interrupts must be enabled for the case where it is necessary to awaken
3822 * the grace-period kthread.
3823 */
3824unsigned long start_poll_synchronize_rcu(void)
3825{
3826 unsigned long flags;
3827 unsigned long gp_seq = get_state_synchronize_rcu();
3828 bool needwake;
3829 struct rcu_data *rdp;
3830 struct rcu_node *rnp;
3831
3832 lockdep_assert_irqs_enabled();
3833 local_irq_save(flags);
3834 rdp = this_cpu_ptr(&rcu_data);
3835 rnp = rdp->mynode;
3836 raw_spin_lock_rcu_node(rnp); // irqs already disabled.
3837 needwake = rcu_start_this_gp(rnp, rdp, gp_seq);
3838 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3839 if (needwake)
3840 rcu_gp_kthread_wake();
3841 return gp_seq;
3842}
3843EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu);
3844
3845/**
3846 * poll_state_synchronize_rcu - Conditionally wait for an RCU grace period
3847 *
3848 * @oldstate: value from get_state_synchronize_rcu() or start_poll_synchronize_rcu()
3849 *
3850 * If a full RCU grace period has elapsed since the earlier call from
3851 * which oldstate was obtained, return @true, otherwise return @false.
3852 * If @false is returned, it is the caller's responsibility to invoke this
3853 * function later on until it does return @true. Alternatively, the caller
3854 * can explicitly wait for a grace period, for example, by passing @oldstate
3855 * to cond_synchronize_rcu() or by directly invoking synchronize_rcu().
3856 *
3857 * Yes, this function does not take counter wrap into account.
3858 * But counter wrap is harmless. If the counter wraps, we have waited for
3859 * more than 2 billion grace periods (and way more on a 64-bit system!).
3860 * Those needing to keep oldstate values for very long time periods
3861 * (many hours even on 32-bit systems) should check them occasionally
3862 * and either refresh them or set a flag indicating that the grace period
3863 * has completed.
3864 *
3865 * This function provides the same memory-ordering guarantees that
3866 * would be provided by a synchronize_rcu() that was invoked at the call
3867 * to the function that provided @oldstate, and that returned at the end
3868 * of this function.
3869 */
3870bool poll_state_synchronize_rcu(unsigned long oldstate)
3871{
3872 if (rcu_seq_done(&rcu_state.gp_seq, oldstate)) {
3873 smp_mb(); /* Ensure GP ends before subsequent accesses. */
3874 return true;
3875 }
3876 return false;
3877}
3878EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
3879
3880/**
3881 * cond_synchronize_rcu - Conditionally wait for an RCU grace period
3882 *
3883 * @oldstate: value from get_state_synchronize_rcu() or start_poll_synchronize_rcu()
3884 *
3885 * If a full RCU grace period has elapsed since the earlier call to
3886 * get_state_synchronize_rcu() or start_poll_synchronize_rcu(), just return.
3887 * Otherwise, invoke synchronize_rcu() to wait for a full grace period.
3888 *
3889 * Yes, this function does not take counter wrap into account. But
3890 * counter wrap is harmless. If the counter wraps, we have waited for
3891 * more than 2 billion grace periods (and way more on a 64-bit system!),
3892 * so waiting for one additional grace period should be just fine.
3893 *
3894 * This function provides the same memory-ordering guarantees that
3895 * would be provided by a synchronize_rcu() that was invoked at the call
3896 * to the function that provided @oldstate, and that returned at the end
3897 * of this function.
3898 */
3899void cond_synchronize_rcu(unsigned long oldstate)
3900{
3901 if (!poll_state_synchronize_rcu(oldstate))
3902 synchronize_rcu();
3903}
3904EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
3905
3906/*
3907 * Check to see if there is any immediate RCU-related work to be done by
3908 * the current CPU, returning 1 if so and zero otherwise. The checks are
3909 * in order of increasing expense: checks that can be carried out against
3910 * CPU-local state are performed first. However, we must check for CPU
3911 * stalls first, else we might not get a chance.
3912 */
3913static int rcu_pending(int user)
3914{
3915 bool gp_in_progress;
3916 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
3917 struct rcu_node *rnp = rdp->mynode;
3918
3919 lockdep_assert_irqs_disabled();
3920
3921 /* Check for CPU stalls, if enabled. */
3922 check_cpu_stall(rdp);
3923
3924 /* Does this CPU need a deferred NOCB wakeup? */
3925 if (rcu_nocb_need_deferred_wakeup(rdp, RCU_NOCB_WAKE))
3926 return 1;
3927
3928 /* Is this a nohz_full CPU in userspace or idle? (Ignore RCU if so.) */
3929 if ((user || rcu_is_cpu_rrupt_from_idle()) && rcu_nohz_full_cpu())
3930 return 0;
3931
3932 /* Is the RCU core waiting for a quiescent state from this CPU? */
3933 gp_in_progress = rcu_gp_in_progress();
3934 if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm && gp_in_progress)
3935 return 1;
3936
3937 /* Does this CPU have callbacks ready to invoke? */
3938 if (!rcu_rdp_is_offloaded(rdp) &&
3939 rcu_segcblist_ready_cbs(&rdp->cblist))
3940 return 1;
3941
3942 /* Has RCU gone idle with this CPU needing another grace period? */
3943 if (!gp_in_progress && rcu_segcblist_is_enabled(&rdp->cblist) &&
3944 !rcu_rdp_is_offloaded(rdp) &&
3945 !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
3946 return 1;
3947
3948 /* Have RCU grace period completed or started? */
3949 if (rcu_seq_current(&rnp->gp_seq) != rdp->gp_seq ||
3950 unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */
3951 return 1;
3952
3953 /* nothing to do */
3954 return 0;
3955}
3956
3957/*
3958 * Helper function for rcu_barrier() tracing. If tracing is disabled,
3959 * the compiler is expected to optimize this away.
3960 */
3961static void rcu_barrier_trace(const char *s, int cpu, unsigned long done)
3962{
3963 trace_rcu_barrier(rcu_state.name, s, cpu,
3964 atomic_read(&rcu_state.barrier_cpu_count), done);
3965}
3966
3967/*
3968 * RCU callback function for rcu_barrier(). If we are last, wake
3969 * up the task executing rcu_barrier().
3970 *
3971 * Note that the value of rcu_state.barrier_sequence must be captured
3972 * before the atomic_dec_and_test(). Otherwise, if this CPU is not last,
3973 * other CPUs might count the value down to zero before this CPU gets
3974 * around to invoking rcu_barrier_trace(), which might result in bogus
3975 * data from the next instance of rcu_barrier().
3976 */
3977static void rcu_barrier_callback(struct rcu_head *rhp)
3978{
3979 unsigned long __maybe_unused s = rcu_state.barrier_sequence;
3980
3981 if (atomic_dec_and_test(&rcu_state.barrier_cpu_count)) {
3982 rcu_barrier_trace(TPS("LastCB"), -1, s);
3983 complete(&rcu_state.barrier_completion);
3984 } else {
3985 rcu_barrier_trace(TPS("CB"), -1, s);
3986 }
3987}
3988
3989/*
3990 * Called with preemption disabled, and from cross-cpu IRQ context.
3991 */
3992static void rcu_barrier_func(void *cpu_in)
3993{
3994 uintptr_t cpu = (uintptr_t)cpu_in;
3995 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
3996
3997 rcu_barrier_trace(TPS("IRQ"), -1, rcu_state.barrier_sequence);
3998 rdp->barrier_head.func = rcu_barrier_callback;
3999 debug_rcu_head_queue(&rdp->barrier_head);
4000 rcu_nocb_lock(rdp);
4001 WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies));
4002 if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head)) {
4003 atomic_inc(&rcu_state.barrier_cpu_count);
4004 } else {
4005 debug_rcu_head_unqueue(&rdp->barrier_head);
4006 rcu_barrier_trace(TPS("IRQNQ"), -1,
4007 rcu_state.barrier_sequence);
4008 }
4009 rcu_nocb_unlock(rdp);
4010}
4011
4012/**
4013 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
4014 *
4015 * Note that this primitive does not necessarily wait for an RCU grace period
4016 * to complete. For example, if there are no RCU callbacks queued anywhere
4017 * in the system, then rcu_barrier() is within its rights to return
4018 * immediately, without waiting for anything, much less an RCU grace period.
4019 */
4020void rcu_barrier(void)
4021{
4022 uintptr_t cpu;
4023 struct rcu_data *rdp;
4024 unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
4025
4026 rcu_barrier_trace(TPS("Begin"), -1, s);
4027
4028 /* Take mutex to serialize concurrent rcu_barrier() requests. */
4029 mutex_lock(&rcu_state.barrier_mutex);
4030
4031 /* Did someone else do our work for us? */
4032 if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
4033 rcu_barrier_trace(TPS("EarlyExit"), -1,
4034 rcu_state.barrier_sequence);
4035 smp_mb(); /* caller's subsequent code after above check. */
4036 mutex_unlock(&rcu_state.barrier_mutex);
4037 return;
4038 }
4039
4040 /* Mark the start of the barrier operation. */
4041 rcu_seq_start(&rcu_state.barrier_sequence);
4042 rcu_barrier_trace(TPS("Inc1"), -1, rcu_state.barrier_sequence);
4043
4044 /*
4045 * Initialize the count to two rather than to zero in order
4046 * to avoid a too-soon return to zero in case of an immediate
4047 * invocation of the just-enqueued callback (or preemption of
4048 * this task). Exclude CPU-hotplug operations to ensure that no
4049 * offline non-offloaded CPU has callbacks queued.
4050 */
4051 init_completion(&rcu_state.barrier_completion);
4052 atomic_set(&rcu_state.barrier_cpu_count, 2);
4053 get_online_cpus();
4054
4055 /*
4056 * Force each CPU with callbacks to register a new callback.
4057 * When that callback is invoked, we will know that all of the
4058 * corresponding CPU's preceding callbacks have been invoked.
4059 */
4060 for_each_possible_cpu(cpu) {
4061 rdp = per_cpu_ptr(&rcu_data, cpu);
4062 if (cpu_is_offline(cpu) &&
4063 !rcu_rdp_is_offloaded(rdp))
4064 continue;
4065 if (rcu_segcblist_n_cbs(&rdp->cblist) && cpu_online(cpu)) {
4066 rcu_barrier_trace(TPS("OnlineQ"), cpu,
4067 rcu_state.barrier_sequence);
4068 smp_call_function_single(cpu, rcu_barrier_func, (void *)cpu, 1);
4069 } else if (rcu_segcblist_n_cbs(&rdp->cblist) &&
4070 cpu_is_offline(cpu)) {
4071 rcu_barrier_trace(TPS("OfflineNoCBQ"), cpu,
4072 rcu_state.barrier_sequence);
4073 local_irq_disable();
4074 rcu_barrier_func((void *)cpu);
4075 local_irq_enable();
4076 } else if (cpu_is_offline(cpu)) {
4077 rcu_barrier_trace(TPS("OfflineNoCBNoQ"), cpu,
4078 rcu_state.barrier_sequence);
4079 } else {
4080 rcu_barrier_trace(TPS("OnlineNQ"), cpu,
4081 rcu_state.barrier_sequence);
4082 }
4083 }
4084 put_online_cpus();
4085
4086 /*
4087 * Now that we have an rcu_barrier_callback() callback on each
4088 * CPU, and thus each counted, remove the initial count.
4089 */
4090 if (atomic_sub_and_test(2, &rcu_state.barrier_cpu_count))
4091 complete(&rcu_state.barrier_completion);
4092
4093 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
4094 wait_for_completion(&rcu_state.barrier_completion);
4095
4096 /* Mark the end of the barrier operation. */
4097 rcu_barrier_trace(TPS("Inc2"), -1, rcu_state.barrier_sequence);
4098 rcu_seq_end(&rcu_state.barrier_sequence);
4099
4100 /* Other rcu_barrier() invocations can now safely proceed. */
4101 mutex_unlock(&rcu_state.barrier_mutex);
4102}
4103EXPORT_SYMBOL_GPL(rcu_barrier);
4104
4105/*
4106 * Propagate ->qsinitmask bits up the rcu_node tree to account for the
4107 * first CPU in a given leaf rcu_node structure coming online. The caller
4108 * must hold the corresponding leaf rcu_node ->lock with interrupts
4109 * disabled.
4110 */
4111static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
4112{
4113 long mask;
4114 long oldmask;
4115 struct rcu_node *rnp = rnp_leaf;
4116
4117 raw_lockdep_assert_held_rcu_node(rnp_leaf);
4118 WARN_ON_ONCE(rnp->wait_blkd_tasks);
4119 for (;;) {
4120 mask = rnp->grpmask;
4121 rnp = rnp->parent;
4122 if (rnp == NULL)
4123 return;
4124 raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
4125 oldmask = rnp->qsmaskinit;
4126 rnp->qsmaskinit |= mask;
4127 raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
4128 if (oldmask)
4129 return;
4130 }
4131}
4132
4133/*
4134 * Do boot-time initialization of a CPU's per-CPU RCU data.
4135 */
4136static void __init
4137rcu_boot_init_percpu_data(int cpu)
4138{
4139 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4140
4141 /* Set up local state, ensuring consistent view of global state. */
4142 rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
4143 INIT_WORK(&rdp->strict_work, strict_work_handler);
4144 WARN_ON_ONCE(rdp->dynticks_nesting != 1);
4145 WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp)));
4146 rdp->rcu_ofl_gp_seq = rcu_state.gp_seq;
4147 rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED;
4148 rdp->rcu_onl_gp_seq = rcu_state.gp_seq;
4149 rdp->rcu_onl_gp_flags = RCU_GP_CLEANED;
4150 rdp->cpu = cpu;
4151 rcu_boot_init_nocb_percpu_data(rdp);
4152}
4153
4154/*
4155 * Invoked early in the CPU-online process, when pretty much all services
4156 * are available. The incoming CPU is not present.
4157 *
4158 * Initializes a CPU's per-CPU RCU data. Note that only one online or
4159 * offline event can be happening at a given time. Note also that we can
4160 * accept some slop in the rsp->gp_seq access due to the fact that this
4161 * CPU cannot possibly have any non-offloaded RCU callbacks in flight yet.
4162 * And any offloaded callbacks are being numbered elsewhere.
4163 */
4164int rcutree_prepare_cpu(unsigned int cpu)
4165{
4166 unsigned long flags;
4167 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4168 struct rcu_node *rnp = rcu_get_root();
4169
4170 /* Set up local state, ensuring consistent view of global state. */
4171 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4172 rdp->qlen_last_fqs_check = 0;
4173 rdp->n_force_qs_snap = rcu_state.n_force_qs;
4174 rdp->blimit = blimit;
4175 rdp->dynticks_nesting = 1; /* CPU not up, no tearing. */
4176 rcu_dynticks_eqs_online();
4177 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
4178
4179 /*
4180 * Only non-NOCB CPUs that didn't have early-boot callbacks need to be
4181 * (re-)initialized.
4182 */
4183 if (!rcu_segcblist_is_enabled(&rdp->cblist))
4184 rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
4185
4186 /*
4187 * Add CPU to leaf rcu_node pending-online bitmask. Any needed
4188 * propagation up the rcu_node tree will happen at the beginning
4189 * of the next grace period.
4190 */
4191 rnp = rdp->mynode;
4192 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
4193 rdp->beenonline = true; /* We have now been online. */
4194 rdp->gp_seq = READ_ONCE(rnp->gp_seq);
4195 rdp->gp_seq_needed = rdp->gp_seq;
4196 rdp->cpu_no_qs.b.norm = true;
4197 rdp->core_needs_qs = false;
4198 rdp->rcu_iw_pending = false;
4199 rdp->rcu_iw = IRQ_WORK_INIT_HARD(rcu_iw_handler);
4200 rdp->rcu_iw_gp_seq = rdp->gp_seq - 1;
4201 trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl"));
4202 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4203 rcu_spawn_one_boost_kthread(rnp);
4204 rcu_spawn_cpu_nocb_kthread(cpu);
4205 WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus + 1);
4206
4207 return 0;
4208}
4209
4210/*
4211 * Update RCU priority boot kthread affinity for CPU-hotplug changes.
4212 */
4213static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
4214{
4215 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4216
4217 rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
4218}
4219
4220/*
4221 * Near the end of the CPU-online process. Pretty much all services
4222 * enabled, and the CPU is now very much alive.
4223 */
4224int rcutree_online_cpu(unsigned int cpu)
4225{
4226 unsigned long flags;
4227 struct rcu_data *rdp;
4228 struct rcu_node *rnp;
4229
4230 rdp = per_cpu_ptr(&rcu_data, cpu);
4231 rnp = rdp->mynode;
4232 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4233 rnp->ffmask |= rdp->grpmask;
4234 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4235 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
4236 return 0; /* Too early in boot for scheduler work. */
4237 sync_sched_exp_online_cleanup(cpu);
4238 rcutree_affinity_setting(cpu, -1);
4239
4240 // Stop-machine done, so allow nohz_full to disable tick.
4241 tick_dep_clear(TICK_DEP_BIT_RCU);
4242 return 0;
4243}
4244
4245/*
4246 * Near the beginning of the process. The CPU is still very much alive
4247 * with pretty much all services enabled.
4248 */
4249int rcutree_offline_cpu(unsigned int cpu)
4250{
4251 unsigned long flags;
4252 struct rcu_data *rdp;
4253 struct rcu_node *rnp;
4254
4255 rdp = per_cpu_ptr(&rcu_data, cpu);
4256 rnp = rdp->mynode;
4257 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4258 rnp->ffmask &= ~rdp->grpmask;
4259 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4260
4261 rcutree_affinity_setting(cpu, cpu);
4262
4263 // nohz_full CPUs need the tick for stop-machine to work quickly
4264 tick_dep_set(TICK_DEP_BIT_RCU);
4265 return 0;
4266}
4267
4268/*
4269 * Mark the specified CPU as being online so that subsequent grace periods
4270 * (both expedited and normal) will wait on it. Note that this means that
4271 * incoming CPUs are not allowed to use RCU read-side critical sections
4272 * until this function is called. Failing to observe this restriction
4273 * will result in lockdep splats.
4274 *
4275 * Note that this function is special in that it is invoked directly
4276 * from the incoming CPU rather than from the cpuhp_step mechanism.
4277 * This is because this function must be invoked at a precise location.
4278 */
4279void rcu_cpu_starting(unsigned int cpu)
4280{
4281 unsigned long flags;
4282 unsigned long mask;
4283 struct rcu_data *rdp;
4284 struct rcu_node *rnp;
4285 bool newcpu;
4286
4287 rdp = per_cpu_ptr(&rcu_data, cpu);
4288 if (rdp->cpu_started)
4289 return;
4290 rdp->cpu_started = true;
4291
4292 rnp = rdp->mynode;
4293 mask = rdp->grpmask;
4294 WRITE_ONCE(rnp->ofl_seq, rnp->ofl_seq + 1);
4295 WARN_ON_ONCE(!(rnp->ofl_seq & 0x1));
4296 smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier().
4297 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4298 WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask);
4299 newcpu = !(rnp->expmaskinitnext & mask);
4300 rnp->expmaskinitnext |= mask;
4301 /* Allow lockless access for expedited grace periods. */
4302 smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + newcpu); /* ^^^ */
4303 ASSERT_EXCLUSIVE_WRITER(rcu_state.ncpus);
4304 rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */
4305 rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
4306 rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags);
4307
4308 /* An incoming CPU should never be blocking a grace period. */
4309 if (WARN_ON_ONCE(rnp->qsmask & mask)) { /* RCU waiting on incoming CPU? */
4310 rcu_disable_urgency_upon_qs(rdp);
4311 /* Report QS -after- changing ->qsmaskinitnext! */
4312 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
4313 } else {
4314 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4315 }
4316 smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier().
4317 WRITE_ONCE(rnp->ofl_seq, rnp->ofl_seq + 1);
4318 WARN_ON_ONCE(rnp->ofl_seq & 0x1);
4319 smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
4320}
4321
4322/*
4323 * The outgoing function has no further need of RCU, so remove it from
4324 * the rcu_node tree's ->qsmaskinitnext bit masks.
4325 *
4326 * Note that this function is special in that it is invoked directly
4327 * from the outgoing CPU rather than from the cpuhp_step mechanism.
4328 * This is because this function must be invoked at a precise location.
4329 */
4330void rcu_report_dead(unsigned int cpu)
4331{
4332 unsigned long flags;
4333 unsigned long mask;
4334 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4335 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
4336
4337 // Do any dangling deferred wakeups.
4338 do_nocb_deferred_wakeup(rdp);
4339
4340 /* QS for any half-done expedited grace period. */
4341 preempt_disable();
4342 rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
4343 preempt_enable();
4344 rcu_preempt_deferred_qs(current);
4345
4346 /* Remove outgoing CPU from mask in the leaf rcu_node structure. */
4347 mask = rdp->grpmask;
4348 WRITE_ONCE(rnp->ofl_seq, rnp->ofl_seq + 1);
4349 WARN_ON_ONCE(!(rnp->ofl_seq & 0x1));
4350 smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier().
4351 raw_spin_lock(&rcu_state.ofl_lock);
4352 raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
4353 rdp->rcu_ofl_gp_seq = READ_ONCE(rcu_state.gp_seq);
4354 rdp->rcu_ofl_gp_flags = READ_ONCE(rcu_state.gp_flags);
4355 if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */
4356 /* Report quiescent state -before- changing ->qsmaskinitnext! */
4357 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
4358 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4359 }
4360 WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext & ~mask);
4361 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4362 raw_spin_unlock(&rcu_state.ofl_lock);
4363 smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier().
4364 WRITE_ONCE(rnp->ofl_seq, rnp->ofl_seq + 1);
4365 WARN_ON_ONCE(rnp->ofl_seq & 0x1);
4366
4367 rdp->cpu_started = false;
4368}
4369
4370#ifdef CONFIG_HOTPLUG_CPU
4371/*
4372 * The outgoing CPU has just passed through the dying-idle state, and we
4373 * are being invoked from the CPU that was IPIed to continue the offline
4374 * operation. Migrate the outgoing CPU's callbacks to the current CPU.
4375 */
4376void rcutree_migrate_callbacks(int cpu)
4377{
4378 unsigned long flags;
4379 struct rcu_data *my_rdp;
4380 struct rcu_node *my_rnp;
4381 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4382 bool needwake;
4383
4384 if (rcu_rdp_is_offloaded(rdp) ||
4385 rcu_segcblist_empty(&rdp->cblist))
4386 return; /* No callbacks to migrate. */
4387
4388 local_irq_save(flags);
4389 my_rdp = this_cpu_ptr(&rcu_data);
4390 my_rnp = my_rdp->mynode;
4391 rcu_nocb_lock(my_rdp); /* irqs already disabled. */
4392 WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies));
4393 raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */
4394 /* Leverage recent GPs and set GP for new callbacks. */
4395 needwake = rcu_advance_cbs(my_rnp, rdp) ||
4396 rcu_advance_cbs(my_rnp, my_rdp);
4397 rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
4398 needwake = needwake || rcu_advance_cbs(my_rnp, my_rdp);
4399 rcu_segcblist_disable(&rdp->cblist);
4400 WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) !=
4401 !rcu_segcblist_n_cbs(&my_rdp->cblist));
4402 if (rcu_rdp_is_offloaded(my_rdp)) {
4403 raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */
4404 __call_rcu_nocb_wake(my_rdp, true, flags);
4405 } else {
4406 rcu_nocb_unlock(my_rdp); /* irqs remain disabled. */
4407 raw_spin_unlock_irqrestore_rcu_node(my_rnp, flags);
4408 }
4409 if (needwake)
4410 rcu_gp_kthread_wake();
4411 lockdep_assert_irqs_enabled();
4412 WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
4413 !rcu_segcblist_empty(&rdp->cblist),
4414 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
4415 cpu, rcu_segcblist_n_cbs(&rdp->cblist),
4416 rcu_segcblist_first_cb(&rdp->cblist));
4417}
4418#endif
4419
4420/*
4421 * On non-huge systems, use expedited RCU grace periods to make suspend
4422 * and hibernation run faster.
4423 */
4424static int rcu_pm_notify(struct notifier_block *self,
4425 unsigned long action, void *hcpu)
4426{
4427 switch (action) {
4428 case PM_HIBERNATION_PREPARE:
4429 case PM_SUSPEND_PREPARE:
4430 rcu_expedite_gp();
4431 break;
4432 case PM_POST_HIBERNATION:
4433 case PM_POST_SUSPEND:
4434 rcu_unexpedite_gp();
4435 break;
4436 default:
4437 break;
4438 }
4439 return NOTIFY_OK;
4440}
4441
4442/*
4443 * Spawn the kthreads that handle RCU's grace periods.
4444 */
4445static int __init rcu_spawn_gp_kthread(void)
4446{
4447 unsigned long flags;
4448 int kthread_prio_in = kthread_prio;
4449 struct rcu_node *rnp;
4450 struct sched_param sp;
4451 struct task_struct *t;
4452
4453 /* Force priority into range. */
4454 if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 2
4455 && IS_BUILTIN(CONFIG_RCU_TORTURE_TEST))
4456 kthread_prio = 2;
4457 else if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
4458 kthread_prio = 1;
4459 else if (kthread_prio < 0)
4460 kthread_prio = 0;
4461 else if (kthread_prio > 99)
4462 kthread_prio = 99;
4463
4464 if (kthread_prio != kthread_prio_in)
4465 pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
4466 kthread_prio, kthread_prio_in);
4467
4468 rcu_scheduler_fully_active = 1;
4469 t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name);
4470 if (WARN_ONCE(IS_ERR(t), "%s: Could not start grace-period kthread, OOM is now expected behavior\n", __func__))
4471 return 0;
4472 if (kthread_prio) {
4473 sp.sched_priority = kthread_prio;
4474 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
4475 }
4476 rnp = rcu_get_root();
4477 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4478 WRITE_ONCE(rcu_state.gp_activity, jiffies);
4479 WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
4480 // Reset .gp_activity and .gp_req_activity before setting .gp_kthread.
4481 smp_store_release(&rcu_state.gp_kthread, t); /* ^^^ */
4482 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4483 wake_up_process(t);
4484 rcu_spawn_nocb_kthreads();
4485 rcu_spawn_boost_kthreads();
4486 rcu_spawn_core_kthreads();
4487 return 0;
4488}
4489early_initcall(rcu_spawn_gp_kthread);
4490
4491/*
4492 * This function is invoked towards the end of the scheduler's
4493 * initialization process. Before this is called, the idle task might
4494 * contain synchronous grace-period primitives (during which time, this idle
4495 * task is booting the system, and such primitives are no-ops). After this
4496 * function is called, any synchronous grace-period primitives are run as
4497 * expedited, with the requesting task driving the grace period forward.
4498 * A later core_initcall() rcu_set_runtime_mode() will switch to full
4499 * runtime RCU functionality.
4500 */
4501void rcu_scheduler_starting(void)
4502{
4503 WARN_ON(num_online_cpus() != 1);
4504 WARN_ON(nr_context_switches() > 0);
4505 rcu_test_sync_prims();
4506 rcu_scheduler_active = RCU_SCHEDULER_INIT;
4507 rcu_test_sync_prims();
4508}
4509
4510/*
4511 * Helper function for rcu_init() that initializes the rcu_state structure.
4512 */
4513static void __init rcu_init_one(void)
4514{
4515 static const char * const buf[] = RCU_NODE_NAME_INIT;
4516 static const char * const fqs[] = RCU_FQS_NAME_INIT;
4517 static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
4518 static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
4519
4520 int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */
4521 int cpustride = 1;
4522 int i;
4523 int j;
4524 struct rcu_node *rnp;
4525
4526 BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
4527
4528 /* Silence gcc 4.8 false positive about array index out of range. */
4529 if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
4530 panic("rcu_init_one: rcu_num_lvls out of range");
4531
4532 /* Initialize the level-tracking arrays. */
4533
4534 for (i = 1; i < rcu_num_lvls; i++)
4535 rcu_state.level[i] =
4536 rcu_state.level[i - 1] + num_rcu_lvl[i - 1];
4537 rcu_init_levelspread(levelspread, num_rcu_lvl);
4538
4539 /* Initialize the elements themselves, starting from the leaves. */
4540
4541 for (i = rcu_num_lvls - 1; i >= 0; i--) {
4542 cpustride *= levelspread[i];
4543 rnp = rcu_state.level[i];
4544 for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
4545 raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
4546 lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
4547 &rcu_node_class[i], buf[i]);
4548 raw_spin_lock_init(&rnp->fqslock);
4549 lockdep_set_class_and_name(&rnp->fqslock,
4550 &rcu_fqs_class[i], fqs[i]);
4551 rnp->gp_seq = rcu_state.gp_seq;
4552 rnp->gp_seq_needed = rcu_state.gp_seq;
4553 rnp->completedqs = rcu_state.gp_seq;
4554 rnp->qsmask = 0;
4555 rnp->qsmaskinit = 0;
4556 rnp->grplo = j * cpustride;
4557 rnp->grphi = (j + 1) * cpustride - 1;
4558 if (rnp->grphi >= nr_cpu_ids)
4559 rnp->grphi = nr_cpu_ids - 1;
4560 if (i == 0) {
4561 rnp->grpnum = 0;
4562 rnp->grpmask = 0;
4563 rnp->parent = NULL;
4564 } else {
4565 rnp->grpnum = j % levelspread[i - 1];
4566 rnp->grpmask = BIT(rnp->grpnum);
4567 rnp->parent = rcu_state.level[i - 1] +
4568 j / levelspread[i - 1];
4569 }
4570 rnp->level = i;
4571 INIT_LIST_HEAD(&rnp->blkd_tasks);
4572 rcu_init_one_nocb(rnp);
4573 init_waitqueue_head(&rnp->exp_wq[0]);
4574 init_waitqueue_head(&rnp->exp_wq[1]);
4575 init_waitqueue_head(&rnp->exp_wq[2]);
4576 init_waitqueue_head(&rnp->exp_wq[3]);
4577 spin_lock_init(&rnp->exp_lock);
4578 }
4579 }
4580
4581 init_swait_queue_head(&rcu_state.gp_wq);
4582 init_swait_queue_head(&rcu_state.expedited_wq);
4583 rnp = rcu_first_leaf_node();
4584 for_each_possible_cpu(i) {
4585 while (i > rnp->grphi)
4586 rnp++;
4587 per_cpu_ptr(&rcu_data, i)->mynode = rnp;
4588 rcu_boot_init_percpu_data(i);
4589 }
4590}
4591
4592/*
4593 * Compute the rcu_node tree geometry from kernel parameters. This cannot
4594 * replace the definitions in tree.h because those are needed to size
4595 * the ->node array in the rcu_state structure.
4596 */
4597void rcu_init_geometry(void)
4598{
4599 ulong d;
4600 int i;
4601 static unsigned long old_nr_cpu_ids;
4602 int rcu_capacity[RCU_NUM_LVLS];
4603 static bool initialized;
4604
4605 if (initialized) {
4606 /*
4607 * Warn if setup_nr_cpu_ids() had not yet been invoked,
4608 * unless nr_cpus_ids == NR_CPUS, in which case who cares?
4609 */
4610 WARN_ON_ONCE(old_nr_cpu_ids != nr_cpu_ids);
4611 return;
4612 }
4613
4614 old_nr_cpu_ids = nr_cpu_ids;
4615 initialized = true;
4616
4617 /*
4618 * Initialize any unspecified boot parameters.
4619 * The default values of jiffies_till_first_fqs and
4620 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
4621 * value, which is a function of HZ, then adding one for each
4622 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
4623 */
4624 d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
4625 if (jiffies_till_first_fqs == ULONG_MAX)
4626 jiffies_till_first_fqs = d;
4627 if (jiffies_till_next_fqs == ULONG_MAX)
4628 jiffies_till_next_fqs = d;
4629 adjust_jiffies_till_sched_qs();
4630
4631 /* If the compile-time values are accurate, just leave. */
4632 if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
4633 nr_cpu_ids == NR_CPUS)
4634 return;
4635 pr_info("Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%u\n",
4636 rcu_fanout_leaf, nr_cpu_ids);
4637
4638 /*
4639 * The boot-time rcu_fanout_leaf parameter must be at least two
4640 * and cannot exceed the number of bits in the rcu_node masks.
4641 * Complain and fall back to the compile-time values if this
4642 * limit is exceeded.
4643 */
4644 if (rcu_fanout_leaf < 2 ||
4645 rcu_fanout_leaf > sizeof(unsigned long) * 8) {
4646 rcu_fanout_leaf = RCU_FANOUT_LEAF;
4647 WARN_ON(1);
4648 return;
4649 }
4650
4651 /*
4652 * Compute number of nodes that can be handled an rcu_node tree
4653 * with the given number of levels.
4654 */
4655 rcu_capacity[0] = rcu_fanout_leaf;
4656 for (i = 1; i < RCU_NUM_LVLS; i++)
4657 rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
4658
4659 /*
4660 * The tree must be able to accommodate the configured number of CPUs.
4661 * If this limit is exceeded, fall back to the compile-time values.
4662 */
4663 if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
4664 rcu_fanout_leaf = RCU_FANOUT_LEAF;
4665 WARN_ON(1);
4666 return;
4667 }
4668
4669 /* Calculate the number of levels in the tree. */
4670 for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
4671 }
4672 rcu_num_lvls = i + 1;
4673
4674 /* Calculate the number of rcu_nodes at each level of the tree. */
4675 for (i = 0; i < rcu_num_lvls; i++) {
4676 int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
4677 num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
4678 }
4679
4680 /* Calculate the total number of rcu_node structures. */
4681 rcu_num_nodes = 0;
4682 for (i = 0; i < rcu_num_lvls; i++)
4683 rcu_num_nodes += num_rcu_lvl[i];
4684}
4685
4686/*
4687 * Dump out the structure of the rcu_node combining tree associated
4688 * with the rcu_state structure.
4689 */
4690static void __init rcu_dump_rcu_node_tree(void)
4691{
4692 int level = 0;
4693 struct rcu_node *rnp;
4694
4695 pr_info("rcu_node tree layout dump\n");
4696 pr_info(" ");
4697 rcu_for_each_node_breadth_first(rnp) {
4698 if (rnp->level != level) {
4699 pr_cont("\n");
4700 pr_info(" ");
4701 level = rnp->level;
4702 }
4703 pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum);
4704 }
4705 pr_cont("\n");
4706}
4707
4708struct workqueue_struct *rcu_gp_wq;
4709struct workqueue_struct *rcu_par_gp_wq;
4710
4711static void __init kfree_rcu_batch_init(void)
4712{
4713 int cpu;
4714 int i;
4715
4716 /* Clamp it to [0:100] seconds interval. */
4717 if (rcu_delay_page_cache_fill_msec < 0 ||
4718 rcu_delay_page_cache_fill_msec > 100 * MSEC_PER_SEC) {
4719
4720 rcu_delay_page_cache_fill_msec =
4721 clamp(rcu_delay_page_cache_fill_msec, 0,
4722 (int) (100 * MSEC_PER_SEC));
4723
4724 pr_info("Adjusting rcutree.rcu_delay_page_cache_fill_msec to %d ms.\n",
4725 rcu_delay_page_cache_fill_msec);
4726 }
4727
4728 for_each_possible_cpu(cpu) {
4729 struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
4730
4731 for (i = 0; i < KFREE_N_BATCHES; i++) {
4732 INIT_RCU_WORK(&krcp->krw_arr[i].rcu_work, kfree_rcu_work);
4733 krcp->krw_arr[i].krcp = krcp;
4734 }
4735
4736 INIT_DELAYED_WORK(&krcp->monitor_work, kfree_rcu_monitor);
4737 INIT_DELAYED_WORK(&krcp->page_cache_work, fill_page_cache_func);
4738 krcp->initialized = true;
4739 }
4740 if (register_shrinker(&kfree_rcu_shrinker))
4741 pr_err("Failed to register kfree_rcu() shrinker!\n");
4742}
4743
4744void __init rcu_init(void)
4745{
4746 int cpu;
4747
4748 rcu_early_boot_tests();
4749
4750 kfree_rcu_batch_init();
4751 rcu_bootup_announce();
4752 rcu_init_geometry();
4753 rcu_init_one();
4754 if (dump_tree)
4755 rcu_dump_rcu_node_tree();
4756 if (use_softirq)
4757 open_softirq(RCU_SOFTIRQ, rcu_core_si);
4758
4759 /*
4760 * We don't need protection against CPU-hotplug here because
4761 * this is called early in boot, before either interrupts
4762 * or the scheduler are operational.
4763 */
4764 pm_notifier(rcu_pm_notify, 0);
4765 for_each_online_cpu(cpu) {
4766 rcutree_prepare_cpu(cpu);
4767 rcu_cpu_starting(cpu);
4768 rcutree_online_cpu(cpu);
4769 }
4770
4771 /* Create workqueue for Tree SRCU and for expedited GPs. */
4772 rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
4773 WARN_ON(!rcu_gp_wq);
4774 rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0);
4775 WARN_ON(!rcu_par_gp_wq);
4776
4777 /* Fill in default value for rcutree.qovld boot parameter. */
4778 /* -After- the rcu_node ->lock fields are initialized! */
4779 if (qovld < 0)
4780 qovld_calc = DEFAULT_RCU_QOVLD_MULT * qhimark;
4781 else
4782 qovld_calc = qovld;
4783}
4784
4785#include "tree_stall.h"
4786#include "tree_exp.h"
4787#include "tree_plugin.h"