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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/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 <linux/context_tracking.h>
66#include "../time/tick-internal.h"
67
68#include "tree.h"
69#include "rcu.h"
70
71#ifdef MODULE_PARAM_PREFIX
72#undef MODULE_PARAM_PREFIX
73#endif
74#define MODULE_PARAM_PREFIX "rcutree."
75
76/* Data structures. */
77
78static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
79 .gpwrap = true,
80#ifdef CONFIG_RCU_NOCB_CPU
81 .cblist.flags = SEGCBLIST_RCU_CORE,
82#endif
83};
84static struct rcu_state rcu_state = {
85 .level = { &rcu_state.node[0] },
86 .gp_state = RCU_GP_IDLE,
87 .gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT,
88 .barrier_mutex = __MUTEX_INITIALIZER(rcu_state.barrier_mutex),
89 .barrier_lock = __RAW_SPIN_LOCK_UNLOCKED(rcu_state.barrier_lock),
90 .name = RCU_NAME,
91 .abbr = RCU_ABBR,
92 .exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex),
93 .exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex),
94 .ofl_lock = __ARCH_SPIN_LOCK_UNLOCKED,
95};
96
97/* Dump rcu_node combining tree at boot to verify correct setup. */
98static bool dump_tree;
99module_param(dump_tree, bool, 0444);
100/* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */
101static bool use_softirq = !IS_ENABLED(CONFIG_PREEMPT_RT);
102#ifndef CONFIG_PREEMPT_RT
103module_param(use_softirq, bool, 0444);
104#endif
105/* Control rcu_node-tree auto-balancing at boot time. */
106static bool rcu_fanout_exact;
107module_param(rcu_fanout_exact, bool, 0444);
108/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
109static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
110module_param(rcu_fanout_leaf, int, 0444);
111int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
112/* Number of rcu_nodes at specified level. */
113int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
114int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
115
116/*
117 * The rcu_scheduler_active variable is initialized to the value
118 * RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the
119 * first task is spawned. So when this variable is RCU_SCHEDULER_INACTIVE,
120 * RCU can assume that there is but one task, allowing RCU to (for example)
121 * optimize synchronize_rcu() to a simple barrier(). When this variable
122 * is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required
123 * to detect real grace periods. This variable is also used to suppress
124 * boot-time false positives from lockdep-RCU error checking. Finally, it
125 * transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU
126 * is fully initialized, including all of its kthreads having been spawned.
127 */
128int rcu_scheduler_active __read_mostly;
129EXPORT_SYMBOL_GPL(rcu_scheduler_active);
130
131/*
132 * The rcu_scheduler_fully_active variable transitions from zero to one
133 * during the early_initcall() processing, which is after the scheduler
134 * is capable of creating new tasks. So RCU processing (for example,
135 * creating tasks for RCU priority boosting) must be delayed until after
136 * rcu_scheduler_fully_active transitions from zero to one. We also
137 * currently delay invocation of any RCU callbacks until after this point.
138 *
139 * It might later prove better for people registering RCU callbacks during
140 * early boot to take responsibility for these callbacks, but one step at
141 * a time.
142 */
143static int rcu_scheduler_fully_active __read_mostly;
144
145static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
146 unsigned long gps, unsigned long flags);
147static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
148static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
149static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
150static void invoke_rcu_core(void);
151static void rcu_report_exp_rdp(struct rcu_data *rdp);
152static void sync_sched_exp_online_cleanup(int cpu);
153static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp);
154static bool rcu_rdp_is_offloaded(struct rcu_data *rdp);
155
156/*
157 * rcuc/rcub/rcuop kthread realtime priority. The "rcuop"
158 * real-time priority(enabling/disabling) is controlled by
159 * the extra CONFIG_RCU_NOCB_CPU_CB_BOOST configuration.
160 */
161static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
162module_param(kthread_prio, int, 0444);
163
164/* Delay in jiffies for grace-period initialization delays, debug only. */
165
166static int gp_preinit_delay;
167module_param(gp_preinit_delay, int, 0444);
168static int gp_init_delay;
169module_param(gp_init_delay, int, 0444);
170static int gp_cleanup_delay;
171module_param(gp_cleanup_delay, int, 0444);
172
173// Add delay to rcu_read_unlock() for strict grace periods.
174static int rcu_unlock_delay;
175#ifdef CONFIG_RCU_STRICT_GRACE_PERIOD
176module_param(rcu_unlock_delay, int, 0444);
177#endif
178
179/*
180 * This rcu parameter is runtime-read-only. It reflects
181 * a minimum allowed number of objects which can be cached
182 * per-CPU. Object size is equal to one page. This value
183 * can be changed at boot time.
184 */
185static int rcu_min_cached_objs = 5;
186module_param(rcu_min_cached_objs, int, 0444);
187
188// A page shrinker can ask for pages to be freed to make them
189// available for other parts of the system. This usually happens
190// under low memory conditions, and in that case we should also
191// defer page-cache filling for a short time period.
192//
193// The default value is 5 seconds, which is long enough to reduce
194// interference with the shrinker while it asks other systems to
195// drain their caches.
196static int rcu_delay_page_cache_fill_msec = 5000;
197module_param(rcu_delay_page_cache_fill_msec, int, 0444);
198
199/* Retrieve RCU kthreads priority for rcutorture */
200int rcu_get_gp_kthreads_prio(void)
201{
202 return kthread_prio;
203}
204EXPORT_SYMBOL_GPL(rcu_get_gp_kthreads_prio);
205
206/*
207 * Number of grace periods between delays, normalized by the duration of
208 * the delay. The longer the delay, the more the grace periods between
209 * each delay. The reason for this normalization is that it means that,
210 * for non-zero delays, the overall slowdown of grace periods is constant
211 * regardless of the duration of the delay. This arrangement balances
212 * the need for long delays to increase some race probabilities with the
213 * need for fast grace periods to increase other race probabilities.
214 */
215#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays for debugging. */
216
217/*
218 * Compute the mask of online CPUs for the specified rcu_node structure.
219 * This will not be stable unless the rcu_node structure's ->lock is
220 * held, but the bit corresponding to the current CPU will be stable
221 * in most contexts.
222 */
223static unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
224{
225 return READ_ONCE(rnp->qsmaskinitnext);
226}
227
228/*
229 * Is the CPU corresponding to the specified rcu_data structure online
230 * from RCU's perspective? This perspective is given by that structure's
231 * ->qsmaskinitnext field rather than by the global cpu_online_mask.
232 */
233static bool rcu_rdp_cpu_online(struct rcu_data *rdp)
234{
235 return !!(rdp->grpmask & rcu_rnp_online_cpus(rdp->mynode));
236}
237
238/*
239 * Return true if an RCU grace period is in progress. The READ_ONCE()s
240 * permit this function to be invoked without holding the root rcu_node
241 * structure's ->lock, but of course results can be subject to change.
242 */
243static int rcu_gp_in_progress(void)
244{
245 return rcu_seq_state(rcu_seq_current(&rcu_state.gp_seq));
246}
247
248/*
249 * Return the number of callbacks queued on the specified CPU.
250 * Handles both the nocbs and normal cases.
251 */
252static long rcu_get_n_cbs_cpu(int cpu)
253{
254 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
255
256 if (rcu_segcblist_is_enabled(&rdp->cblist))
257 return rcu_segcblist_n_cbs(&rdp->cblist);
258 return 0;
259}
260
261void rcu_softirq_qs(void)
262{
263 rcu_qs();
264 rcu_preempt_deferred_qs(current);
265 rcu_tasks_qs(current, false);
266}
267
268/*
269 * Reset the current CPU's ->dynticks counter to indicate that the
270 * newly onlined CPU is no longer in an extended quiescent state.
271 * This will either leave the counter unchanged, or increment it
272 * to the next non-quiescent value.
273 *
274 * The non-atomic test/increment sequence works because the upper bits
275 * of the ->dynticks counter are manipulated only by the corresponding CPU,
276 * or when the corresponding CPU is offline.
277 */
278static void rcu_dynticks_eqs_online(void)
279{
280 if (ct_dynticks() & RCU_DYNTICKS_IDX)
281 return;
282 ct_state_inc(RCU_DYNTICKS_IDX);
283}
284
285/*
286 * Snapshot the ->dynticks counter with full ordering so as to allow
287 * stable comparison of this counter with past and future snapshots.
288 */
289static int rcu_dynticks_snap(int cpu)
290{
291 smp_mb(); // Fundamental RCU ordering guarantee.
292 return ct_dynticks_cpu_acquire(cpu);
293}
294
295/*
296 * Return true if the snapshot returned from rcu_dynticks_snap()
297 * indicates that RCU is in an extended quiescent state.
298 */
299static bool rcu_dynticks_in_eqs(int snap)
300{
301 return !(snap & RCU_DYNTICKS_IDX);
302}
303
304/*
305 * Return true if the CPU corresponding to the specified rcu_data
306 * structure has spent some time in an extended quiescent state since
307 * rcu_dynticks_snap() returned the specified snapshot.
308 */
309static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap)
310{
311 return snap != rcu_dynticks_snap(rdp->cpu);
312}
313
314/*
315 * Return true if the referenced integer is zero while the specified
316 * CPU remains within a single extended quiescent state.
317 */
318bool rcu_dynticks_zero_in_eqs(int cpu, int *vp)
319{
320 int snap;
321
322 // If not quiescent, force back to earlier extended quiescent state.
323 snap = ct_dynticks_cpu(cpu) & ~RCU_DYNTICKS_IDX;
324 smp_rmb(); // Order ->dynticks and *vp reads.
325 if (READ_ONCE(*vp))
326 return false; // Non-zero, so report failure;
327 smp_rmb(); // Order *vp read and ->dynticks re-read.
328
329 // If still in the same extended quiescent state, we are good!
330 return snap == ct_dynticks_cpu(cpu);
331}
332
333/*
334 * Let the RCU core know that this CPU has gone through the scheduler,
335 * which is a quiescent state. This is called when the need for a
336 * quiescent state is urgent, so we burn an atomic operation and full
337 * memory barriers to let the RCU core know about it, regardless of what
338 * this CPU might (or might not) do in the near future.
339 *
340 * We inform the RCU core by emulating a zero-duration dyntick-idle period.
341 *
342 * The caller must have disabled interrupts and must not be idle.
343 */
344notrace void rcu_momentary_dyntick_idle(void)
345{
346 int seq;
347
348 raw_cpu_write(rcu_data.rcu_need_heavy_qs, false);
349 seq = ct_state_inc(2 * RCU_DYNTICKS_IDX);
350 /* It is illegal to call this from idle state. */
351 WARN_ON_ONCE(!(seq & RCU_DYNTICKS_IDX));
352 rcu_preempt_deferred_qs(current);
353}
354EXPORT_SYMBOL_GPL(rcu_momentary_dyntick_idle);
355
356/**
357 * rcu_is_cpu_rrupt_from_idle - see if 'interrupted' from idle
358 *
359 * If the current CPU is idle and running at a first-level (not nested)
360 * interrupt, or directly, from idle, return true.
361 *
362 * The caller must have at least disabled IRQs.
363 */
364static int rcu_is_cpu_rrupt_from_idle(void)
365{
366 long nesting;
367
368 /*
369 * Usually called from the tick; but also used from smp_function_call()
370 * for expedited grace periods. This latter can result in running from
371 * the idle task, instead of an actual IPI.
372 */
373 lockdep_assert_irqs_disabled();
374
375 /* Check for counter underflows */
376 RCU_LOCKDEP_WARN(ct_dynticks_nesting() < 0,
377 "RCU dynticks_nesting counter underflow!");
378 RCU_LOCKDEP_WARN(ct_dynticks_nmi_nesting() <= 0,
379 "RCU dynticks_nmi_nesting counter underflow/zero!");
380
381 /* Are we at first interrupt nesting level? */
382 nesting = ct_dynticks_nmi_nesting();
383 if (nesting > 1)
384 return false;
385
386 /*
387 * If we're not in an interrupt, we must be in the idle task!
388 */
389 WARN_ON_ONCE(!nesting && !is_idle_task(current));
390
391 /* Does CPU appear to be idle from an RCU standpoint? */
392 return ct_dynticks_nesting() == 0;
393}
394
395#define DEFAULT_RCU_BLIMIT (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 1000 : 10)
396 // Maximum callbacks per rcu_do_batch ...
397#define DEFAULT_MAX_RCU_BLIMIT 10000 // ... even during callback flood.
398static long blimit = DEFAULT_RCU_BLIMIT;
399#define DEFAULT_RCU_QHIMARK 10000 // If this many pending, ignore blimit.
400static long qhimark = DEFAULT_RCU_QHIMARK;
401#define DEFAULT_RCU_QLOMARK 100 // Once only this many pending, use blimit.
402static long qlowmark = DEFAULT_RCU_QLOMARK;
403#define DEFAULT_RCU_QOVLD_MULT 2
404#define DEFAULT_RCU_QOVLD (DEFAULT_RCU_QOVLD_MULT * DEFAULT_RCU_QHIMARK)
405static long qovld = DEFAULT_RCU_QOVLD; // If this many pending, hammer QS.
406static long qovld_calc = -1; // No pre-initialization lock acquisitions!
407
408module_param(blimit, long, 0444);
409module_param(qhimark, long, 0444);
410module_param(qlowmark, long, 0444);
411module_param(qovld, long, 0444);
412
413static ulong jiffies_till_first_fqs = IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 0 : ULONG_MAX;
414static ulong jiffies_till_next_fqs = ULONG_MAX;
415static bool rcu_kick_kthreads;
416static int rcu_divisor = 7;
417module_param(rcu_divisor, int, 0644);
418
419/* Force an exit from rcu_do_batch() after 3 milliseconds. */
420static long rcu_resched_ns = 3 * NSEC_PER_MSEC;
421module_param(rcu_resched_ns, long, 0644);
422
423/*
424 * How long the grace period must be before we start recruiting
425 * quiescent-state help from rcu_note_context_switch().
426 */
427static ulong jiffies_till_sched_qs = ULONG_MAX;
428module_param(jiffies_till_sched_qs, ulong, 0444);
429static ulong jiffies_to_sched_qs; /* See adjust_jiffies_till_sched_qs(). */
430module_param(jiffies_to_sched_qs, ulong, 0444); /* Display only! */
431
432/*
433 * Make sure that we give the grace-period kthread time to detect any
434 * idle CPUs before taking active measures to force quiescent states.
435 * However, don't go below 100 milliseconds, adjusted upwards for really
436 * large systems.
437 */
438static void adjust_jiffies_till_sched_qs(void)
439{
440 unsigned long j;
441
442 /* If jiffies_till_sched_qs was specified, respect the request. */
443 if (jiffies_till_sched_qs != ULONG_MAX) {
444 WRITE_ONCE(jiffies_to_sched_qs, jiffies_till_sched_qs);
445 return;
446 }
447 /* Otherwise, set to third fqs scan, but bound below on large system. */
448 j = READ_ONCE(jiffies_till_first_fqs) +
449 2 * READ_ONCE(jiffies_till_next_fqs);
450 if (j < HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV)
451 j = HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
452 pr_info("RCU calculated value of scheduler-enlistment delay is %ld jiffies.\n", j);
453 WRITE_ONCE(jiffies_to_sched_qs, j);
454}
455
456static int param_set_first_fqs_jiffies(const char *val, const struct kernel_param *kp)
457{
458 ulong j;
459 int ret = kstrtoul(val, 0, &j);
460
461 if (!ret) {
462 WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : j);
463 adjust_jiffies_till_sched_qs();
464 }
465 return ret;
466}
467
468static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param *kp)
469{
470 ulong j;
471 int ret = kstrtoul(val, 0, &j);
472
473 if (!ret) {
474 WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : (j ?: 1));
475 adjust_jiffies_till_sched_qs();
476 }
477 return ret;
478}
479
480static const struct kernel_param_ops first_fqs_jiffies_ops = {
481 .set = param_set_first_fqs_jiffies,
482 .get = param_get_ulong,
483};
484
485static const struct kernel_param_ops next_fqs_jiffies_ops = {
486 .set = param_set_next_fqs_jiffies,
487 .get = param_get_ulong,
488};
489
490module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, &jiffies_till_first_fqs, 0644);
491module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next_fqs, 0644);
492module_param(rcu_kick_kthreads, bool, 0644);
493
494static void force_qs_rnp(int (*f)(struct rcu_data *rdp));
495static int rcu_pending(int user);
496
497/*
498 * Return the number of RCU GPs completed thus far for debug & stats.
499 */
500unsigned long rcu_get_gp_seq(void)
501{
502 return READ_ONCE(rcu_state.gp_seq);
503}
504EXPORT_SYMBOL_GPL(rcu_get_gp_seq);
505
506/*
507 * Return the number of RCU expedited batches completed thus far for
508 * debug & stats. Odd numbers mean that a batch is in progress, even
509 * numbers mean idle. The value returned will thus be roughly double
510 * the cumulative batches since boot.
511 */
512unsigned long rcu_exp_batches_completed(void)
513{
514 return rcu_state.expedited_sequence;
515}
516EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
517
518/*
519 * Return the root node of the rcu_state structure.
520 */
521static struct rcu_node *rcu_get_root(void)
522{
523 return &rcu_state.node[0];
524}
525
526/*
527 * Send along grace-period-related data for rcutorture diagnostics.
528 */
529void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
530 unsigned long *gp_seq)
531{
532 switch (test_type) {
533 case RCU_FLAVOR:
534 *flags = READ_ONCE(rcu_state.gp_flags);
535 *gp_seq = rcu_seq_current(&rcu_state.gp_seq);
536 break;
537 default:
538 break;
539 }
540}
541EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
542
543#if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK))
544/*
545 * An empty function that will trigger a reschedule on
546 * IRQ tail once IRQs get re-enabled on userspace/guest resume.
547 */
548static void late_wakeup_func(struct irq_work *work)
549{
550}
551
552static DEFINE_PER_CPU(struct irq_work, late_wakeup_work) =
553 IRQ_WORK_INIT(late_wakeup_func);
554
555/*
556 * If either:
557 *
558 * 1) the task is about to enter in guest mode and $ARCH doesn't support KVM generic work
559 * 2) the task is about to enter in user mode and $ARCH doesn't support generic entry.
560 *
561 * In these cases the late RCU wake ups aren't supported in the resched loops and our
562 * last resort is to fire a local irq_work that will trigger a reschedule once IRQs
563 * get re-enabled again.
564 */
565noinstr void rcu_irq_work_resched(void)
566{
567 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
568
569 if (IS_ENABLED(CONFIG_GENERIC_ENTRY) && !(current->flags & PF_VCPU))
570 return;
571
572 if (IS_ENABLED(CONFIG_KVM_XFER_TO_GUEST_WORK) && (current->flags & PF_VCPU))
573 return;
574
575 instrumentation_begin();
576 if (do_nocb_deferred_wakeup(rdp) && need_resched()) {
577 irq_work_queue(this_cpu_ptr(&late_wakeup_work));
578 }
579 instrumentation_end();
580}
581#endif /* #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK)) */
582
583#ifdef CONFIG_PROVE_RCU
584/**
585 * rcu_irq_exit_check_preempt - Validate that scheduling is possible
586 */
587void rcu_irq_exit_check_preempt(void)
588{
589 lockdep_assert_irqs_disabled();
590
591 RCU_LOCKDEP_WARN(ct_dynticks_nesting() <= 0,
592 "RCU dynticks_nesting counter underflow/zero!");
593 RCU_LOCKDEP_WARN(ct_dynticks_nmi_nesting() !=
594 DYNTICK_IRQ_NONIDLE,
595 "Bad RCU dynticks_nmi_nesting counter\n");
596 RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),
597 "RCU in extended quiescent state!");
598}
599#endif /* #ifdef CONFIG_PROVE_RCU */
600
601#ifdef CONFIG_NO_HZ_FULL
602/**
603 * __rcu_irq_enter_check_tick - Enable scheduler tick on CPU if RCU needs it.
604 *
605 * The scheduler tick is not normally enabled when CPUs enter the kernel
606 * from nohz_full userspace execution. After all, nohz_full userspace
607 * execution is an RCU quiescent state and the time executing in the kernel
608 * is quite short. Except of course when it isn't. And it is not hard to
609 * cause a large system to spend tens of seconds or even minutes looping
610 * in the kernel, which can cause a number of problems, include RCU CPU
611 * stall warnings.
612 *
613 * Therefore, if a nohz_full CPU fails to report a quiescent state
614 * in a timely manner, the RCU grace-period kthread sets that CPU's
615 * ->rcu_urgent_qs flag with the expectation that the next interrupt or
616 * exception will invoke this function, which will turn on the scheduler
617 * tick, which will enable RCU to detect that CPU's quiescent states,
618 * for example, due to cond_resched() calls in CONFIG_PREEMPT=n kernels.
619 * The tick will be disabled once a quiescent state is reported for
620 * this CPU.
621 *
622 * Of course, in carefully tuned systems, there might never be an
623 * interrupt or exception. In that case, the RCU grace-period kthread
624 * will eventually cause one to happen. However, in less carefully
625 * controlled environments, this function allows RCU to get what it
626 * needs without creating otherwise useless interruptions.
627 */
628void __rcu_irq_enter_check_tick(void)
629{
630 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
631
632 // If we're here from NMI there's nothing to do.
633 if (in_nmi())
634 return;
635
636 RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),
637 "Illegal rcu_irq_enter_check_tick() from extended quiescent state");
638
639 if (!tick_nohz_full_cpu(rdp->cpu) ||
640 !READ_ONCE(rdp->rcu_urgent_qs) ||
641 READ_ONCE(rdp->rcu_forced_tick)) {
642 // RCU doesn't need nohz_full help from this CPU, or it is
643 // already getting that help.
644 return;
645 }
646
647 // We get here only when not in an extended quiescent state and
648 // from interrupts (as opposed to NMIs). Therefore, (1) RCU is
649 // already watching and (2) The fact that we are in an interrupt
650 // handler and that the rcu_node lock is an irq-disabled lock
651 // prevents self-deadlock. So we can safely recheck under the lock.
652 // Note that the nohz_full state currently cannot change.
653 raw_spin_lock_rcu_node(rdp->mynode);
654 if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
655 // A nohz_full CPU is in the kernel and RCU needs a
656 // quiescent state. Turn on the tick!
657 WRITE_ONCE(rdp->rcu_forced_tick, true);
658 tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
659 }
660 raw_spin_unlock_rcu_node(rdp->mynode);
661}
662#endif /* CONFIG_NO_HZ_FULL */
663
664/*
665 * Check to see if any future non-offloaded RCU-related work will need
666 * to be done by the current CPU, even if none need be done immediately,
667 * returning 1 if so. This function is part of the RCU implementation;
668 * it is -not- an exported member of the RCU API. This is used by
669 * the idle-entry code to figure out whether it is safe to disable the
670 * scheduler-clock interrupt.
671 *
672 * Just check whether or not this CPU has non-offloaded RCU callbacks
673 * queued.
674 */
675int rcu_needs_cpu(void)
676{
677 return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) &&
678 !rcu_rdp_is_offloaded(this_cpu_ptr(&rcu_data));
679}
680
681/*
682 * If any sort of urgency was applied to the current CPU (for example,
683 * the scheduler-clock interrupt was enabled on a nohz_full CPU) in order
684 * to get to a quiescent state, disable it.
685 */
686static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp)
687{
688 raw_lockdep_assert_held_rcu_node(rdp->mynode);
689 WRITE_ONCE(rdp->rcu_urgent_qs, false);
690 WRITE_ONCE(rdp->rcu_need_heavy_qs, false);
691 if (tick_nohz_full_cpu(rdp->cpu) && rdp->rcu_forced_tick) {
692 tick_dep_clear_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
693 WRITE_ONCE(rdp->rcu_forced_tick, false);
694 }
695}
696
697/**
698 * rcu_is_watching - see if RCU thinks that the current CPU is not idle
699 *
700 * Return true if RCU is watching the running CPU, which means that this
701 * CPU can safely enter RCU read-side critical sections. In other words,
702 * if the current CPU is not in its idle loop or is in an interrupt or
703 * NMI handler, return true.
704 *
705 * Make notrace because it can be called by the internal functions of
706 * ftrace, and making this notrace removes unnecessary recursion calls.
707 */
708notrace bool rcu_is_watching(void)
709{
710 bool ret;
711
712 preempt_disable_notrace();
713 ret = !rcu_dynticks_curr_cpu_in_eqs();
714 preempt_enable_notrace();
715 return ret;
716}
717EXPORT_SYMBOL_GPL(rcu_is_watching);
718
719/*
720 * If a holdout task is actually running, request an urgent quiescent
721 * state from its CPU. This is unsynchronized, so migrations can cause
722 * the request to go to the wrong CPU. Which is OK, all that will happen
723 * is that the CPU's next context switch will be a bit slower and next
724 * time around this task will generate another request.
725 */
726void rcu_request_urgent_qs_task(struct task_struct *t)
727{
728 int cpu;
729
730 barrier();
731 cpu = task_cpu(t);
732 if (!task_curr(t))
733 return; /* This task is not running on that CPU. */
734 smp_store_release(per_cpu_ptr(&rcu_data.rcu_urgent_qs, cpu), true);
735}
736
737#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
738
739/*
740 * Is the current CPU online as far as RCU is concerned?
741 *
742 * Disable preemption to avoid false positives that could otherwise
743 * happen due to the current CPU number being sampled, this task being
744 * preempted, its old CPU being taken offline, resuming on some other CPU,
745 * then determining that its old CPU is now offline.
746 *
747 * Disable checking if in an NMI handler because we cannot safely
748 * report errors from NMI handlers anyway. In addition, it is OK to use
749 * RCU on an offline processor during initial boot, hence the check for
750 * rcu_scheduler_fully_active.
751 */
752bool rcu_lockdep_current_cpu_online(void)
753{
754 struct rcu_data *rdp;
755 bool ret = false;
756
757 if (in_nmi() || !rcu_scheduler_fully_active)
758 return true;
759 preempt_disable_notrace();
760 rdp = this_cpu_ptr(&rcu_data);
761 /*
762 * Strictly, we care here about the case where the current CPU is
763 * in rcu_cpu_starting() and thus has an excuse for rdp->grpmask
764 * not being up to date. So arch_spin_is_locked() might have a
765 * false positive if it's held by some *other* CPU, but that's
766 * OK because that just means a false *negative* on the warning.
767 */
768 if (rcu_rdp_cpu_online(rdp) || arch_spin_is_locked(&rcu_state.ofl_lock))
769 ret = true;
770 preempt_enable_notrace();
771 return ret;
772}
773EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
774
775#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
776
777/*
778 * When trying to report a quiescent state on behalf of some other CPU,
779 * it is our responsibility to check for and handle potential overflow
780 * of the rcu_node ->gp_seq counter with respect to the rcu_data counters.
781 * After all, the CPU might be in deep idle state, and thus executing no
782 * code whatsoever.
783 */
784static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
785{
786 raw_lockdep_assert_held_rcu_node(rnp);
787 if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + ULONG_MAX / 4,
788 rnp->gp_seq))
789 WRITE_ONCE(rdp->gpwrap, true);
790 if (ULONG_CMP_LT(rdp->rcu_iw_gp_seq + ULONG_MAX / 4, rnp->gp_seq))
791 rdp->rcu_iw_gp_seq = rnp->gp_seq + ULONG_MAX / 4;
792}
793
794/*
795 * Snapshot the specified CPU's dynticks counter so that we can later
796 * credit them with an implicit quiescent state. Return 1 if this CPU
797 * is in dynticks idle mode, which is an extended quiescent state.
798 */
799static int dyntick_save_progress_counter(struct rcu_data *rdp)
800{
801 rdp->dynticks_snap = rcu_dynticks_snap(rdp->cpu);
802 if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
803 trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
804 rcu_gpnum_ovf(rdp->mynode, rdp);
805 return 1;
806 }
807 return 0;
808}
809
810/*
811 * Return true if the specified CPU has passed through a quiescent
812 * state by virtue of being in or having passed through an dynticks
813 * idle state since the last call to dyntick_save_progress_counter()
814 * for this same CPU, or by virtue of having been offline.
815 */
816static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
817{
818 unsigned long jtsq;
819 struct rcu_node *rnp = rdp->mynode;
820
821 /*
822 * If the CPU passed through or entered a dynticks idle phase with
823 * no active irq/NMI handlers, then we can safely pretend that the CPU
824 * already acknowledged the request to pass through a quiescent
825 * state. Either way, that CPU cannot possibly be in an RCU
826 * read-side critical section that started before the beginning
827 * of the current RCU grace period.
828 */
829 if (rcu_dynticks_in_eqs_since(rdp, rdp->dynticks_snap)) {
830 trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
831 rcu_gpnum_ovf(rnp, rdp);
832 return 1;
833 }
834
835 /*
836 * Complain if a CPU that is considered to be offline from RCU's
837 * perspective has not yet reported a quiescent state. After all,
838 * the offline CPU should have reported a quiescent state during
839 * the CPU-offline process, or, failing that, by rcu_gp_init()
840 * if it ran concurrently with either the CPU going offline or the
841 * last task on a leaf rcu_node structure exiting its RCU read-side
842 * critical section while all CPUs corresponding to that structure
843 * are offline. This added warning detects bugs in any of these
844 * code paths.
845 *
846 * The rcu_node structure's ->lock is held here, which excludes
847 * the relevant portions the CPU-hotplug code, the grace-period
848 * initialization code, and the rcu_read_unlock() code paths.
849 *
850 * For more detail, please refer to the "Hotplug CPU" section
851 * of RCU's Requirements documentation.
852 */
853 if (WARN_ON_ONCE(!rcu_rdp_cpu_online(rdp))) {
854 struct rcu_node *rnp1;
855
856 pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
857 __func__, rnp->grplo, rnp->grphi, rnp->level,
858 (long)rnp->gp_seq, (long)rnp->completedqs);
859 for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
860 pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx ->rcu_gp_init_mask %#lx\n",
861 __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext, rnp1->rcu_gp_init_mask);
862 pr_info("%s %d: %c online: %ld(%d) offline: %ld(%d)\n",
863 __func__, rdp->cpu, ".o"[rcu_rdp_cpu_online(rdp)],
864 (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
865 (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
866 return 1; /* Break things loose after complaining. */
867 }
868
869 /*
870 * A CPU running for an extended time within the kernel can
871 * delay RCU grace periods: (1) At age jiffies_to_sched_qs,
872 * set .rcu_urgent_qs, (2) At age 2*jiffies_to_sched_qs, set
873 * both .rcu_need_heavy_qs and .rcu_urgent_qs. Note that the
874 * unsynchronized assignments to the per-CPU rcu_need_heavy_qs
875 * variable are safe because the assignments are repeated if this
876 * CPU failed to pass through a quiescent state. This code
877 * also checks .jiffies_resched in case jiffies_to_sched_qs
878 * is set way high.
879 */
880 jtsq = READ_ONCE(jiffies_to_sched_qs);
881 if (!READ_ONCE(rdp->rcu_need_heavy_qs) &&
882 (time_after(jiffies, rcu_state.gp_start + jtsq * 2) ||
883 time_after(jiffies, rcu_state.jiffies_resched) ||
884 rcu_state.cbovld)) {
885 WRITE_ONCE(rdp->rcu_need_heavy_qs, true);
886 /* Store rcu_need_heavy_qs before rcu_urgent_qs. */
887 smp_store_release(&rdp->rcu_urgent_qs, true);
888 } else if (time_after(jiffies, rcu_state.gp_start + jtsq)) {
889 WRITE_ONCE(rdp->rcu_urgent_qs, true);
890 }
891
892 /*
893 * NO_HZ_FULL CPUs can run in-kernel without rcu_sched_clock_irq!
894 * The above code handles this, but only for straight cond_resched().
895 * And some in-kernel loops check need_resched() before calling
896 * cond_resched(), which defeats the above code for CPUs that are
897 * running in-kernel with scheduling-clock interrupts disabled.
898 * So hit them over the head with the resched_cpu() hammer!
899 */
900 if (tick_nohz_full_cpu(rdp->cpu) &&
901 (time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq * 3) ||
902 rcu_state.cbovld)) {
903 WRITE_ONCE(rdp->rcu_urgent_qs, true);
904 resched_cpu(rdp->cpu);
905 WRITE_ONCE(rdp->last_fqs_resched, jiffies);
906 }
907
908 /*
909 * If more than halfway to RCU CPU stall-warning time, invoke
910 * resched_cpu() more frequently to try to loosen things up a bit.
911 * Also check to see if the CPU is getting hammered with interrupts,
912 * but only once per grace period, just to keep the IPIs down to
913 * a dull roar.
914 */
915 if (time_after(jiffies, rcu_state.jiffies_resched)) {
916 if (time_after(jiffies,
917 READ_ONCE(rdp->last_fqs_resched) + jtsq)) {
918 resched_cpu(rdp->cpu);
919 WRITE_ONCE(rdp->last_fqs_resched, jiffies);
920 }
921 if (IS_ENABLED(CONFIG_IRQ_WORK) &&
922 !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
923 (rnp->ffmask & rdp->grpmask)) {
924 rdp->rcu_iw_pending = true;
925 rdp->rcu_iw_gp_seq = rnp->gp_seq;
926 irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
927 }
928 }
929
930 return 0;
931}
932
933/* Trace-event wrapper function for trace_rcu_future_grace_period. */
934static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
935 unsigned long gp_seq_req, const char *s)
936{
937 trace_rcu_future_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
938 gp_seq_req, rnp->level,
939 rnp->grplo, rnp->grphi, s);
940}
941
942/*
943 * rcu_start_this_gp - Request the start of a particular grace period
944 * @rnp_start: The leaf node of the CPU from which to start.
945 * @rdp: The rcu_data corresponding to the CPU from which to start.
946 * @gp_seq_req: The gp_seq of the grace period to start.
947 *
948 * Start the specified grace period, as needed to handle newly arrived
949 * callbacks. The required future grace periods are recorded in each
950 * rcu_node structure's ->gp_seq_needed field. Returns true if there
951 * is reason to awaken the grace-period kthread.
952 *
953 * The caller must hold the specified rcu_node structure's ->lock, which
954 * is why the caller is responsible for waking the grace-period kthread.
955 *
956 * Returns true if the GP thread needs to be awakened else false.
957 */
958static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
959 unsigned long gp_seq_req)
960{
961 bool ret = false;
962 struct rcu_node *rnp;
963
964 /*
965 * Use funnel locking to either acquire the root rcu_node
966 * structure's lock or bail out if the need for this grace period
967 * has already been recorded -- or if that grace period has in
968 * fact already started. If there is already a grace period in
969 * progress in a non-leaf node, no recording is needed because the
970 * end of the grace period will scan the leaf rcu_node structures.
971 * Note that rnp_start->lock must not be released.
972 */
973 raw_lockdep_assert_held_rcu_node(rnp_start);
974 trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startleaf"));
975 for (rnp = rnp_start; 1; rnp = rnp->parent) {
976 if (rnp != rnp_start)
977 raw_spin_lock_rcu_node(rnp);
978 if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req) ||
979 rcu_seq_started(&rnp->gp_seq, gp_seq_req) ||
980 (rnp != rnp_start &&
981 rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))) {
982 trace_rcu_this_gp(rnp, rdp, gp_seq_req,
983 TPS("Prestarted"));
984 goto unlock_out;
985 }
986 WRITE_ONCE(rnp->gp_seq_needed, gp_seq_req);
987 if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) {
988 /*
989 * We just marked the leaf or internal node, and a
990 * grace period is in progress, which means that
991 * rcu_gp_cleanup() will see the marking. Bail to
992 * reduce contention.
993 */
994 trace_rcu_this_gp(rnp_start, rdp, gp_seq_req,
995 TPS("Startedleaf"));
996 goto unlock_out;
997 }
998 if (rnp != rnp_start && rnp->parent != NULL)
999 raw_spin_unlock_rcu_node(rnp);
1000 if (!rnp->parent)
1001 break; /* At root, and perhaps also leaf. */
1002 }
1003
1004 /* If GP already in progress, just leave, otherwise start one. */
1005 if (rcu_gp_in_progress()) {
1006 trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedleafroot"));
1007 goto unlock_out;
1008 }
1009 trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
1010 WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
1011 WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
1012 if (!READ_ONCE(rcu_state.gp_kthread)) {
1013 trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
1014 goto unlock_out;
1015 }
1016 trace_rcu_grace_period(rcu_state.name, data_race(rcu_state.gp_seq), TPS("newreq"));
1017 ret = true; /* Caller must wake GP kthread. */
1018unlock_out:
1019 /* Push furthest requested GP to leaf node and rcu_data structure. */
1020 if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) {
1021 WRITE_ONCE(rnp_start->gp_seq_needed, rnp->gp_seq_needed);
1022 WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
1023 }
1024 if (rnp != rnp_start)
1025 raw_spin_unlock_rcu_node(rnp);
1026 return ret;
1027}
1028
1029/*
1030 * Clean up any old requests for the just-ended grace period. Also return
1031 * whether any additional grace periods have been requested.
1032 */
1033static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
1034{
1035 bool needmore;
1036 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1037
1038 needmore = ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed);
1039 if (!needmore)
1040 rnp->gp_seq_needed = rnp->gp_seq; /* Avoid counter wrap. */
1041 trace_rcu_this_gp(rnp, rdp, rnp->gp_seq,
1042 needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1043 return needmore;
1044}
1045
1046/*
1047 * Awaken the grace-period kthread. Don't do a self-awaken (unless in an
1048 * interrupt or softirq handler, in which case we just might immediately
1049 * sleep upon return, resulting in a grace-period hang), and don't bother
1050 * awakening when there is nothing for the grace-period kthread to do
1051 * (as in several CPUs raced to awaken, we lost), and finally don't try
1052 * to awaken a kthread that has not yet been created. If all those checks
1053 * are passed, track some debug information and awaken.
1054 *
1055 * So why do the self-wakeup when in an interrupt or softirq handler
1056 * in the grace-period kthread's context? Because the kthread might have
1057 * been interrupted just as it was going to sleep, and just after the final
1058 * pre-sleep check of the awaken condition. In this case, a wakeup really
1059 * is required, and is therefore supplied.
1060 */
1061static void rcu_gp_kthread_wake(void)
1062{
1063 struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
1064
1065 if ((current == t && !in_hardirq() && !in_serving_softirq()) ||
1066 !READ_ONCE(rcu_state.gp_flags) || !t)
1067 return;
1068 WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
1069 WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
1070 swake_up_one(&rcu_state.gp_wq);
1071}
1072
1073/*
1074 * If there is room, assign a ->gp_seq number to any callbacks on this
1075 * CPU that have not already been assigned. Also accelerate any callbacks
1076 * that were previously assigned a ->gp_seq number that has since proven
1077 * to be too conservative, which can happen if callbacks get assigned a
1078 * ->gp_seq number while RCU is idle, but with reference to a non-root
1079 * rcu_node structure. This function is idempotent, so it does not hurt
1080 * to call it repeatedly. Returns an flag saying that we should awaken
1081 * the RCU grace-period kthread.
1082 *
1083 * The caller must hold rnp->lock with interrupts disabled.
1084 */
1085static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
1086{
1087 unsigned long gp_seq_req;
1088 bool ret = false;
1089
1090 rcu_lockdep_assert_cblist_protected(rdp);
1091 raw_lockdep_assert_held_rcu_node(rnp);
1092
1093 /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
1094 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1095 return false;
1096
1097 trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPreAcc"));
1098
1099 /*
1100 * Callbacks are often registered with incomplete grace-period
1101 * information. Something about the fact that getting exact
1102 * information requires acquiring a global lock... RCU therefore
1103 * makes a conservative estimate of the grace period number at which
1104 * a given callback will become ready to invoke. The following
1105 * code checks this estimate and improves it when possible, thus
1106 * accelerating callback invocation to an earlier grace-period
1107 * number.
1108 */
1109 gp_seq_req = rcu_seq_snap(&rcu_state.gp_seq);
1110 if (rcu_segcblist_accelerate(&rdp->cblist, gp_seq_req))
1111 ret = rcu_start_this_gp(rnp, rdp, gp_seq_req);
1112
1113 /* Trace depending on how much we were able to accelerate. */
1114 if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
1115 trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccWaitCB"));
1116 else
1117 trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccReadyCB"));
1118
1119 trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPostAcc"));
1120
1121 return ret;
1122}
1123
1124/*
1125 * Similar to rcu_accelerate_cbs(), but does not require that the leaf
1126 * rcu_node structure's ->lock be held. It consults the cached value
1127 * of ->gp_seq_needed in the rcu_data structure, and if that indicates
1128 * that a new grace-period request be made, invokes rcu_accelerate_cbs()
1129 * while holding the leaf rcu_node structure's ->lock.
1130 */
1131static void rcu_accelerate_cbs_unlocked(struct rcu_node *rnp,
1132 struct rcu_data *rdp)
1133{
1134 unsigned long c;
1135 bool needwake;
1136
1137 rcu_lockdep_assert_cblist_protected(rdp);
1138 c = rcu_seq_snap(&rcu_state.gp_seq);
1139 if (!READ_ONCE(rdp->gpwrap) && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {
1140 /* Old request still live, so mark recent callbacks. */
1141 (void)rcu_segcblist_accelerate(&rdp->cblist, c);
1142 return;
1143 }
1144 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
1145 needwake = rcu_accelerate_cbs(rnp, rdp);
1146 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
1147 if (needwake)
1148 rcu_gp_kthread_wake();
1149}
1150
1151/*
1152 * Move any callbacks whose grace period has completed to the
1153 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1154 * assign ->gp_seq numbers to any callbacks in the RCU_NEXT_TAIL
1155 * sublist. This function is idempotent, so it does not hurt to
1156 * invoke it repeatedly. As long as it is not invoked -too- often...
1157 * Returns true if the RCU grace-period kthread needs to be awakened.
1158 *
1159 * The caller must hold rnp->lock with interrupts disabled.
1160 */
1161static bool rcu_advance_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
1162{
1163 rcu_lockdep_assert_cblist_protected(rdp);
1164 raw_lockdep_assert_held_rcu_node(rnp);
1165
1166 /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
1167 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1168 return false;
1169
1170 /*
1171 * Find all callbacks whose ->gp_seq numbers indicate that they
1172 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1173 */
1174 rcu_segcblist_advance(&rdp->cblist, rnp->gp_seq);
1175
1176 /* Classify any remaining callbacks. */
1177 return rcu_accelerate_cbs(rnp, rdp);
1178}
1179
1180/*
1181 * Move and classify callbacks, but only if doing so won't require
1182 * that the RCU grace-period kthread be awakened.
1183 */
1184static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp,
1185 struct rcu_data *rdp)
1186{
1187 rcu_lockdep_assert_cblist_protected(rdp);
1188 if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) || !raw_spin_trylock_rcu_node(rnp))
1189 return;
1190 // The grace period cannot end while we hold the rcu_node lock.
1191 if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))
1192 WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp));
1193 raw_spin_unlock_rcu_node(rnp);
1194}
1195
1196/*
1197 * In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, attempt to generate a
1198 * quiescent state. This is intended to be invoked when the CPU notices
1199 * a new grace period.
1200 */
1201static void rcu_strict_gp_check_qs(void)
1202{
1203 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) {
1204 rcu_read_lock();
1205 rcu_read_unlock();
1206 }
1207}
1208
1209/*
1210 * Update CPU-local rcu_data state to record the beginnings and ends of
1211 * grace periods. The caller must hold the ->lock of the leaf rcu_node
1212 * structure corresponding to the current CPU, and must have irqs disabled.
1213 * Returns true if the grace-period kthread needs to be awakened.
1214 */
1215static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
1216{
1217 bool ret = false;
1218 bool need_qs;
1219 const bool offloaded = rcu_rdp_is_offloaded(rdp);
1220
1221 raw_lockdep_assert_held_rcu_node(rnp);
1222
1223 if (rdp->gp_seq == rnp->gp_seq)
1224 return false; /* Nothing to do. */
1225
1226 /* Handle the ends of any preceding grace periods first. */
1227 if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) ||
1228 unlikely(READ_ONCE(rdp->gpwrap))) {
1229 if (!offloaded)
1230 ret = rcu_advance_cbs(rnp, rdp); /* Advance CBs. */
1231 rdp->core_needs_qs = false;
1232 trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuend"));
1233 } else {
1234 if (!offloaded)
1235 ret = rcu_accelerate_cbs(rnp, rdp); /* Recent CBs. */
1236 if (rdp->core_needs_qs)
1237 rdp->core_needs_qs = !!(rnp->qsmask & rdp->grpmask);
1238 }
1239
1240 /* Now handle the beginnings of any new-to-this-CPU grace periods. */
1241 if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) ||
1242 unlikely(READ_ONCE(rdp->gpwrap))) {
1243 /*
1244 * If the current grace period is waiting for this CPU,
1245 * set up to detect a quiescent state, otherwise don't
1246 * go looking for one.
1247 */
1248 trace_rcu_grace_period(rcu_state.name, rnp->gp_seq, TPS("cpustart"));
1249 need_qs = !!(rnp->qsmask & rdp->grpmask);
1250 rdp->cpu_no_qs.b.norm = need_qs;
1251 rdp->core_needs_qs = need_qs;
1252 zero_cpu_stall_ticks(rdp);
1253 }
1254 rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */
1255 if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap)
1256 WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed);
1257 if (IS_ENABLED(CONFIG_PROVE_RCU) && READ_ONCE(rdp->gpwrap))
1258 WRITE_ONCE(rdp->last_sched_clock, jiffies);
1259 WRITE_ONCE(rdp->gpwrap, false);
1260 rcu_gpnum_ovf(rnp, rdp);
1261 return ret;
1262}
1263
1264static void note_gp_changes(struct rcu_data *rdp)
1265{
1266 unsigned long flags;
1267 bool needwake;
1268 struct rcu_node *rnp;
1269
1270 local_irq_save(flags);
1271 rnp = rdp->mynode;
1272 if ((rdp->gp_seq == rcu_seq_current(&rnp->gp_seq) &&
1273 !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
1274 !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
1275 local_irq_restore(flags);
1276 return;
1277 }
1278 needwake = __note_gp_changes(rnp, rdp);
1279 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1280 rcu_strict_gp_check_qs();
1281 if (needwake)
1282 rcu_gp_kthread_wake();
1283}
1284
1285static atomic_t *rcu_gp_slow_suppress;
1286
1287/* Register a counter to suppress debugging grace-period delays. */
1288void rcu_gp_slow_register(atomic_t *rgssp)
1289{
1290 WARN_ON_ONCE(rcu_gp_slow_suppress);
1291
1292 WRITE_ONCE(rcu_gp_slow_suppress, rgssp);
1293}
1294EXPORT_SYMBOL_GPL(rcu_gp_slow_register);
1295
1296/* Unregister a counter, with NULL for not caring which. */
1297void rcu_gp_slow_unregister(atomic_t *rgssp)
1298{
1299 WARN_ON_ONCE(rgssp && rgssp != rcu_gp_slow_suppress);
1300
1301 WRITE_ONCE(rcu_gp_slow_suppress, NULL);
1302}
1303EXPORT_SYMBOL_GPL(rcu_gp_slow_unregister);
1304
1305static bool rcu_gp_slow_is_suppressed(void)
1306{
1307 atomic_t *rgssp = READ_ONCE(rcu_gp_slow_suppress);
1308
1309 return rgssp && atomic_read(rgssp);
1310}
1311
1312static void rcu_gp_slow(int delay)
1313{
1314 if (!rcu_gp_slow_is_suppressed() && delay > 0 &&
1315 !(rcu_seq_ctr(rcu_state.gp_seq) % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
1316 schedule_timeout_idle(delay);
1317}
1318
1319static unsigned long sleep_duration;
1320
1321/* Allow rcutorture to stall the grace-period kthread. */
1322void rcu_gp_set_torture_wait(int duration)
1323{
1324 if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST) && duration > 0)
1325 WRITE_ONCE(sleep_duration, duration);
1326}
1327EXPORT_SYMBOL_GPL(rcu_gp_set_torture_wait);
1328
1329/* Actually implement the aforementioned wait. */
1330static void rcu_gp_torture_wait(void)
1331{
1332 unsigned long duration;
1333
1334 if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST))
1335 return;
1336 duration = xchg(&sleep_duration, 0UL);
1337 if (duration > 0) {
1338 pr_alert("%s: Waiting %lu jiffies\n", __func__, duration);
1339 schedule_timeout_idle(duration);
1340 pr_alert("%s: Wait complete\n", __func__);
1341 }
1342}
1343
1344/*
1345 * Handler for on_each_cpu() to invoke the target CPU's RCU core
1346 * processing.
1347 */
1348static void rcu_strict_gp_boundary(void *unused)
1349{
1350 invoke_rcu_core();
1351}
1352
1353// Has rcu_init() been invoked? This is used (for example) to determine
1354// whether spinlocks may be acquired safely.
1355static bool rcu_init_invoked(void)
1356{
1357 return !!rcu_state.n_online_cpus;
1358}
1359
1360// Make the polled API aware of the beginning of a grace period.
1361static void rcu_poll_gp_seq_start(unsigned long *snap)
1362{
1363 struct rcu_node *rnp = rcu_get_root();
1364
1365 if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
1366 raw_lockdep_assert_held_rcu_node(rnp);
1367
1368 // If RCU was idle, note beginning of GP.
1369 if (!rcu_seq_state(rcu_state.gp_seq_polled))
1370 rcu_seq_start(&rcu_state.gp_seq_polled);
1371
1372 // Either way, record current state.
1373 *snap = rcu_state.gp_seq_polled;
1374}
1375
1376// Make the polled API aware of the end of a grace period.
1377static void rcu_poll_gp_seq_end(unsigned long *snap)
1378{
1379 struct rcu_node *rnp = rcu_get_root();
1380
1381 if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
1382 raw_lockdep_assert_held_rcu_node(rnp);
1383
1384 // If the previously noted GP is still in effect, record the
1385 // end of that GP. Either way, zero counter to avoid counter-wrap
1386 // problems.
1387 if (*snap && *snap == rcu_state.gp_seq_polled) {
1388 rcu_seq_end(&rcu_state.gp_seq_polled);
1389 rcu_state.gp_seq_polled_snap = 0;
1390 rcu_state.gp_seq_polled_exp_snap = 0;
1391 } else {
1392 *snap = 0;
1393 }
1394}
1395
1396// Make the polled API aware of the beginning of a grace period, but
1397// where caller does not hold the root rcu_node structure's lock.
1398static void rcu_poll_gp_seq_start_unlocked(unsigned long *snap)
1399{
1400 unsigned long flags;
1401 struct rcu_node *rnp = rcu_get_root();
1402
1403 if (rcu_init_invoked()) {
1404 if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
1405 lockdep_assert_irqs_enabled();
1406 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1407 }
1408 rcu_poll_gp_seq_start(snap);
1409 if (rcu_init_invoked())
1410 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1411}
1412
1413// Make the polled API aware of the end of a grace period, but where
1414// caller does not hold the root rcu_node structure's lock.
1415static void rcu_poll_gp_seq_end_unlocked(unsigned long *snap)
1416{
1417 unsigned long flags;
1418 struct rcu_node *rnp = rcu_get_root();
1419
1420 if (rcu_init_invoked()) {
1421 if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
1422 lockdep_assert_irqs_enabled();
1423 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1424 }
1425 rcu_poll_gp_seq_end(snap);
1426 if (rcu_init_invoked())
1427 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1428}
1429
1430/*
1431 * Initialize a new grace period. Return false if no grace period required.
1432 */
1433static noinline_for_stack bool rcu_gp_init(void)
1434{
1435 unsigned long flags;
1436 unsigned long oldmask;
1437 unsigned long mask;
1438 struct rcu_data *rdp;
1439 struct rcu_node *rnp = rcu_get_root();
1440
1441 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1442 raw_spin_lock_irq_rcu_node(rnp);
1443 if (!READ_ONCE(rcu_state.gp_flags)) {
1444 /* Spurious wakeup, tell caller to go back to sleep. */
1445 raw_spin_unlock_irq_rcu_node(rnp);
1446 return false;
1447 }
1448 WRITE_ONCE(rcu_state.gp_flags, 0); /* Clear all flags: New GP. */
1449
1450 if (WARN_ON_ONCE(rcu_gp_in_progress())) {
1451 /*
1452 * Grace period already in progress, don't start another.
1453 * Not supposed to be able to happen.
1454 */
1455 raw_spin_unlock_irq_rcu_node(rnp);
1456 return false;
1457 }
1458
1459 /* Advance to a new grace period and initialize state. */
1460 record_gp_stall_check_time();
1461 /* Record GP times before starting GP, hence rcu_seq_start(). */
1462 rcu_seq_start(&rcu_state.gp_seq);
1463 ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
1464 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start"));
1465 rcu_poll_gp_seq_start(&rcu_state.gp_seq_polled_snap);
1466 raw_spin_unlock_irq_rcu_node(rnp);
1467
1468 /*
1469 * Apply per-leaf buffered online and offline operations to
1470 * the rcu_node tree. Note that this new grace period need not
1471 * wait for subsequent online CPUs, and that RCU hooks in the CPU
1472 * offlining path, when combined with checks in this function,
1473 * will handle CPUs that are currently going offline or that will
1474 * go offline later. Please also refer to "Hotplug CPU" section
1475 * of RCU's Requirements documentation.
1476 */
1477 WRITE_ONCE(rcu_state.gp_state, RCU_GP_ONOFF);
1478 /* Exclude CPU hotplug operations. */
1479 rcu_for_each_leaf_node(rnp) {
1480 local_irq_save(flags);
1481 arch_spin_lock(&rcu_state.ofl_lock);
1482 raw_spin_lock_rcu_node(rnp);
1483 if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
1484 !rnp->wait_blkd_tasks) {
1485 /* Nothing to do on this leaf rcu_node structure. */
1486 raw_spin_unlock_rcu_node(rnp);
1487 arch_spin_unlock(&rcu_state.ofl_lock);
1488 local_irq_restore(flags);
1489 continue;
1490 }
1491
1492 /* Record old state, apply changes to ->qsmaskinit field. */
1493 oldmask = rnp->qsmaskinit;
1494 rnp->qsmaskinit = rnp->qsmaskinitnext;
1495
1496 /* If zero-ness of ->qsmaskinit changed, propagate up tree. */
1497 if (!oldmask != !rnp->qsmaskinit) {
1498 if (!oldmask) { /* First online CPU for rcu_node. */
1499 if (!rnp->wait_blkd_tasks) /* Ever offline? */
1500 rcu_init_new_rnp(rnp);
1501 } else if (rcu_preempt_has_tasks(rnp)) {
1502 rnp->wait_blkd_tasks = true; /* blocked tasks */
1503 } else { /* Last offline CPU and can propagate. */
1504 rcu_cleanup_dead_rnp(rnp);
1505 }
1506 }
1507
1508 /*
1509 * If all waited-on tasks from prior grace period are
1510 * done, and if all this rcu_node structure's CPUs are
1511 * still offline, propagate up the rcu_node tree and
1512 * clear ->wait_blkd_tasks. Otherwise, if one of this
1513 * rcu_node structure's CPUs has since come back online,
1514 * simply clear ->wait_blkd_tasks.
1515 */
1516 if (rnp->wait_blkd_tasks &&
1517 (!rcu_preempt_has_tasks(rnp) || rnp->qsmaskinit)) {
1518 rnp->wait_blkd_tasks = false;
1519 if (!rnp->qsmaskinit)
1520 rcu_cleanup_dead_rnp(rnp);
1521 }
1522
1523 raw_spin_unlock_rcu_node(rnp);
1524 arch_spin_unlock(&rcu_state.ofl_lock);
1525 local_irq_restore(flags);
1526 }
1527 rcu_gp_slow(gp_preinit_delay); /* Races with CPU hotplug. */
1528
1529 /*
1530 * Set the quiescent-state-needed bits in all the rcu_node
1531 * structures for all currently online CPUs in breadth-first
1532 * order, starting from the root rcu_node structure, relying on the
1533 * layout of the tree within the rcu_state.node[] array. Note that
1534 * other CPUs will access only the leaves of the hierarchy, thus
1535 * seeing that no grace period is in progress, at least until the
1536 * corresponding leaf node has been initialized.
1537 *
1538 * The grace period cannot complete until the initialization
1539 * process finishes, because this kthread handles both.
1540 */
1541 WRITE_ONCE(rcu_state.gp_state, RCU_GP_INIT);
1542 rcu_for_each_node_breadth_first(rnp) {
1543 rcu_gp_slow(gp_init_delay);
1544 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1545 rdp = this_cpu_ptr(&rcu_data);
1546 rcu_preempt_check_blocked_tasks(rnp);
1547 rnp->qsmask = rnp->qsmaskinit;
1548 WRITE_ONCE(rnp->gp_seq, rcu_state.gp_seq);
1549 if (rnp == rdp->mynode)
1550 (void)__note_gp_changes(rnp, rdp);
1551 rcu_preempt_boost_start_gp(rnp);
1552 trace_rcu_grace_period_init(rcu_state.name, rnp->gp_seq,
1553 rnp->level, rnp->grplo,
1554 rnp->grphi, rnp->qsmask);
1555 /* Quiescent states for tasks on any now-offline CPUs. */
1556 mask = rnp->qsmask & ~rnp->qsmaskinitnext;
1557 rnp->rcu_gp_init_mask = mask;
1558 if ((mask || rnp->wait_blkd_tasks) && rcu_is_leaf_node(rnp))
1559 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
1560 else
1561 raw_spin_unlock_irq_rcu_node(rnp);
1562 cond_resched_tasks_rcu_qs();
1563 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1564 }
1565
1566 // If strict, make all CPUs aware of new grace period.
1567 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
1568 on_each_cpu(rcu_strict_gp_boundary, NULL, 0);
1569
1570 return true;
1571}
1572
1573/*
1574 * Helper function for swait_event_idle_exclusive() wakeup at force-quiescent-state
1575 * time.
1576 */
1577static bool rcu_gp_fqs_check_wake(int *gfp)
1578{
1579 struct rcu_node *rnp = rcu_get_root();
1580
1581 // If under overload conditions, force an immediate FQS scan.
1582 if (*gfp & RCU_GP_FLAG_OVLD)
1583 return true;
1584
1585 // Someone like call_rcu() requested a force-quiescent-state scan.
1586 *gfp = READ_ONCE(rcu_state.gp_flags);
1587 if (*gfp & RCU_GP_FLAG_FQS)
1588 return true;
1589
1590 // The current grace period has completed.
1591 if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
1592 return true;
1593
1594 return false;
1595}
1596
1597/*
1598 * Do one round of quiescent-state forcing.
1599 */
1600static void rcu_gp_fqs(bool first_time)
1601{
1602 struct rcu_node *rnp = rcu_get_root();
1603
1604 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1605 WRITE_ONCE(rcu_state.n_force_qs, rcu_state.n_force_qs + 1);
1606 if (first_time) {
1607 /* Collect dyntick-idle snapshots. */
1608 force_qs_rnp(dyntick_save_progress_counter);
1609 } else {
1610 /* Handle dyntick-idle and offline CPUs. */
1611 force_qs_rnp(rcu_implicit_dynticks_qs);
1612 }
1613 /* Clear flag to prevent immediate re-entry. */
1614 if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
1615 raw_spin_lock_irq_rcu_node(rnp);
1616 WRITE_ONCE(rcu_state.gp_flags,
1617 READ_ONCE(rcu_state.gp_flags) & ~RCU_GP_FLAG_FQS);
1618 raw_spin_unlock_irq_rcu_node(rnp);
1619 }
1620}
1621
1622/*
1623 * Loop doing repeated quiescent-state forcing until the grace period ends.
1624 */
1625static noinline_for_stack void rcu_gp_fqs_loop(void)
1626{
1627 bool first_gp_fqs = true;
1628 int gf = 0;
1629 unsigned long j;
1630 int ret;
1631 struct rcu_node *rnp = rcu_get_root();
1632
1633 j = READ_ONCE(jiffies_till_first_fqs);
1634 if (rcu_state.cbovld)
1635 gf = RCU_GP_FLAG_OVLD;
1636 ret = 0;
1637 for (;;) {
1638 if (rcu_state.cbovld) {
1639 j = (j + 2) / 3;
1640 if (j <= 0)
1641 j = 1;
1642 }
1643 if (!ret || time_before(jiffies + j, rcu_state.jiffies_force_qs)) {
1644 WRITE_ONCE(rcu_state.jiffies_force_qs, jiffies + j);
1645 /*
1646 * jiffies_force_qs before RCU_GP_WAIT_FQS state
1647 * update; required for stall checks.
1648 */
1649 smp_wmb();
1650 WRITE_ONCE(rcu_state.jiffies_kick_kthreads,
1651 jiffies + (j ? 3 * j : 2));
1652 }
1653 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
1654 TPS("fqswait"));
1655 WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_FQS);
1656 (void)swait_event_idle_timeout_exclusive(rcu_state.gp_wq,
1657 rcu_gp_fqs_check_wake(&gf), j);
1658 rcu_gp_torture_wait();
1659 WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS);
1660 /* Locking provides needed memory barriers. */
1661 /*
1662 * Exit the loop if the root rcu_node structure indicates that the grace period
1663 * has ended, leave the loop. The rcu_preempt_blocked_readers_cgp(rnp) check
1664 * is required only for single-node rcu_node trees because readers blocking
1665 * the current grace period are queued only on leaf rcu_node structures.
1666 * For multi-node trees, checking the root node's ->qsmask suffices, because a
1667 * given root node's ->qsmask bit is cleared only when all CPUs and tasks from
1668 * the corresponding leaf nodes have passed through their quiescent state.
1669 */
1670 if (!READ_ONCE(rnp->qsmask) &&
1671 !rcu_preempt_blocked_readers_cgp(rnp))
1672 break;
1673 /* If time for quiescent-state forcing, do it. */
1674 if (!time_after(rcu_state.jiffies_force_qs, jiffies) ||
1675 (gf & (RCU_GP_FLAG_FQS | RCU_GP_FLAG_OVLD))) {
1676 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
1677 TPS("fqsstart"));
1678 rcu_gp_fqs(first_gp_fqs);
1679 gf = 0;
1680 if (first_gp_fqs) {
1681 first_gp_fqs = false;
1682 gf = rcu_state.cbovld ? RCU_GP_FLAG_OVLD : 0;
1683 }
1684 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
1685 TPS("fqsend"));
1686 cond_resched_tasks_rcu_qs();
1687 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1688 ret = 0; /* Force full wait till next FQS. */
1689 j = READ_ONCE(jiffies_till_next_fqs);
1690 } else {
1691 /* Deal with stray signal. */
1692 cond_resched_tasks_rcu_qs();
1693 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1694 WARN_ON(signal_pending(current));
1695 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
1696 TPS("fqswaitsig"));
1697 ret = 1; /* Keep old FQS timing. */
1698 j = jiffies;
1699 if (time_after(jiffies, rcu_state.jiffies_force_qs))
1700 j = 1;
1701 else
1702 j = rcu_state.jiffies_force_qs - j;
1703 gf = 0;
1704 }
1705 }
1706}
1707
1708/*
1709 * Clean up after the old grace period.
1710 */
1711static noinline void rcu_gp_cleanup(void)
1712{
1713 int cpu;
1714 bool needgp = false;
1715 unsigned long gp_duration;
1716 unsigned long new_gp_seq;
1717 bool offloaded;
1718 struct rcu_data *rdp;
1719 struct rcu_node *rnp = rcu_get_root();
1720 struct swait_queue_head *sq;
1721
1722 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1723 raw_spin_lock_irq_rcu_node(rnp);
1724 rcu_state.gp_end = jiffies;
1725 gp_duration = rcu_state.gp_end - rcu_state.gp_start;
1726 if (gp_duration > rcu_state.gp_max)
1727 rcu_state.gp_max = gp_duration;
1728
1729 /*
1730 * We know the grace period is complete, but to everyone else
1731 * it appears to still be ongoing. But it is also the case
1732 * that to everyone else it looks like there is nothing that
1733 * they can do to advance the grace period. It is therefore
1734 * safe for us to drop the lock in order to mark the grace
1735 * period as completed in all of the rcu_node structures.
1736 */
1737 rcu_poll_gp_seq_end(&rcu_state.gp_seq_polled_snap);
1738 raw_spin_unlock_irq_rcu_node(rnp);
1739
1740 /*
1741 * Propagate new ->gp_seq value to rcu_node structures so that
1742 * other CPUs don't have to wait until the start of the next grace
1743 * period to process their callbacks. This also avoids some nasty
1744 * RCU grace-period initialization races by forcing the end of
1745 * the current grace period to be completely recorded in all of
1746 * the rcu_node structures before the beginning of the next grace
1747 * period is recorded in any of the rcu_node structures.
1748 */
1749 new_gp_seq = rcu_state.gp_seq;
1750 rcu_seq_end(&new_gp_seq);
1751 rcu_for_each_node_breadth_first(rnp) {
1752 raw_spin_lock_irq_rcu_node(rnp);
1753 if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
1754 dump_blkd_tasks(rnp, 10);
1755 WARN_ON_ONCE(rnp->qsmask);
1756 WRITE_ONCE(rnp->gp_seq, new_gp_seq);
1757 if (!rnp->parent)
1758 smp_mb(); // Order against failing poll_state_synchronize_rcu_full().
1759 rdp = this_cpu_ptr(&rcu_data);
1760 if (rnp == rdp->mynode)
1761 needgp = __note_gp_changes(rnp, rdp) || needgp;
1762 /* smp_mb() provided by prior unlock-lock pair. */
1763 needgp = rcu_future_gp_cleanup(rnp) || needgp;
1764 // Reset overload indication for CPUs no longer overloaded
1765 if (rcu_is_leaf_node(rnp))
1766 for_each_leaf_node_cpu_mask(rnp, cpu, rnp->cbovldmask) {
1767 rdp = per_cpu_ptr(&rcu_data, cpu);
1768 check_cb_ovld_locked(rdp, rnp);
1769 }
1770 sq = rcu_nocb_gp_get(rnp);
1771 raw_spin_unlock_irq_rcu_node(rnp);
1772 rcu_nocb_gp_cleanup(sq);
1773 cond_resched_tasks_rcu_qs();
1774 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1775 rcu_gp_slow(gp_cleanup_delay);
1776 }
1777 rnp = rcu_get_root();
1778 raw_spin_lock_irq_rcu_node(rnp); /* GP before ->gp_seq update. */
1779
1780 /* Declare grace period done, trace first to use old GP number. */
1781 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end"));
1782 rcu_seq_end(&rcu_state.gp_seq);
1783 ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq);
1784 WRITE_ONCE(rcu_state.gp_state, RCU_GP_IDLE);
1785 /* Check for GP requests since above loop. */
1786 rdp = this_cpu_ptr(&rcu_data);
1787 if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) {
1788 trace_rcu_this_gp(rnp, rdp, rnp->gp_seq_needed,
1789 TPS("CleanupMore"));
1790 needgp = true;
1791 }
1792 /* Advance CBs to reduce false positives below. */
1793 offloaded = rcu_rdp_is_offloaded(rdp);
1794 if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {
1795
1796 // We get here if a grace period was needed (“needgp”)
1797 // and the above call to rcu_accelerate_cbs() did not set
1798 // the RCU_GP_FLAG_INIT bit in ->gp_state (which records
1799 // the need for another grace period). The purpose
1800 // of the “offloaded” check is to avoid invoking
1801 // rcu_accelerate_cbs() on an offloaded CPU because we do not
1802 // hold the ->nocb_lock needed to safely access an offloaded
1803 // ->cblist. We do not want to acquire that lock because
1804 // it can be heavily contended during callback floods.
1805
1806 WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);
1807 WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
1808 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("newreq"));
1809 } else {
1810
1811 // We get here either if there is no need for an
1812 // additional grace period or if rcu_accelerate_cbs() has
1813 // already set the RCU_GP_FLAG_INIT bit in ->gp_flags.
1814 // So all we need to do is to clear all of the other
1815 // ->gp_flags bits.
1816
1817 WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags & RCU_GP_FLAG_INIT);
1818 }
1819 raw_spin_unlock_irq_rcu_node(rnp);
1820
1821 // If strict, make all CPUs aware of the end of the old grace period.
1822 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
1823 on_each_cpu(rcu_strict_gp_boundary, NULL, 0);
1824}
1825
1826/*
1827 * Body of kthread that handles grace periods.
1828 */
1829static int __noreturn rcu_gp_kthread(void *unused)
1830{
1831 rcu_bind_gp_kthread();
1832 for (;;) {
1833
1834 /* Handle grace-period start. */
1835 for (;;) {
1836 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
1837 TPS("reqwait"));
1838 WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_GPS);
1839 swait_event_idle_exclusive(rcu_state.gp_wq,
1840 READ_ONCE(rcu_state.gp_flags) &
1841 RCU_GP_FLAG_INIT);
1842 rcu_gp_torture_wait();
1843 WRITE_ONCE(rcu_state.gp_state, RCU_GP_DONE_GPS);
1844 /* Locking provides needed memory barrier. */
1845 if (rcu_gp_init())
1846 break;
1847 cond_resched_tasks_rcu_qs();
1848 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1849 WARN_ON(signal_pending(current));
1850 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
1851 TPS("reqwaitsig"));
1852 }
1853
1854 /* Handle quiescent-state forcing. */
1855 rcu_gp_fqs_loop();
1856
1857 /* Handle grace-period end. */
1858 WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANUP);
1859 rcu_gp_cleanup();
1860 WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANED);
1861 }
1862}
1863
1864/*
1865 * Report a full set of quiescent states to the rcu_state data structure.
1866 * Invoke rcu_gp_kthread_wake() to awaken the grace-period kthread if
1867 * another grace period is required. Whether we wake the grace-period
1868 * kthread or it awakens itself for the next round of quiescent-state
1869 * forcing, that kthread will clean up after the just-completed grace
1870 * period. Note that the caller must hold rnp->lock, which is released
1871 * before return.
1872 */
1873static void rcu_report_qs_rsp(unsigned long flags)
1874 __releases(rcu_get_root()->lock)
1875{
1876 raw_lockdep_assert_held_rcu_node(rcu_get_root());
1877 WARN_ON_ONCE(!rcu_gp_in_progress());
1878 WRITE_ONCE(rcu_state.gp_flags,
1879 READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
1880 raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(), flags);
1881 rcu_gp_kthread_wake();
1882}
1883
1884/*
1885 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
1886 * Allows quiescent states for a group of CPUs to be reported at one go
1887 * to the specified rcu_node structure, though all the CPUs in the group
1888 * must be represented by the same rcu_node structure (which need not be a
1889 * leaf rcu_node structure, though it often will be). The gps parameter
1890 * is the grace-period snapshot, which means that the quiescent states
1891 * are valid only if rnp->gp_seq is equal to gps. That structure's lock
1892 * must be held upon entry, and it is released before return.
1893 *
1894 * As a special case, if mask is zero, the bit-already-cleared check is
1895 * disabled. This allows propagating quiescent state due to resumed tasks
1896 * during grace-period initialization.
1897 */
1898static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
1899 unsigned long gps, unsigned long flags)
1900 __releases(rnp->lock)
1901{
1902 unsigned long oldmask = 0;
1903 struct rcu_node *rnp_c;
1904
1905 raw_lockdep_assert_held_rcu_node(rnp);
1906
1907 /* Walk up the rcu_node hierarchy. */
1908 for (;;) {
1909 if ((!(rnp->qsmask & mask) && mask) || rnp->gp_seq != gps) {
1910
1911 /*
1912 * Our bit has already been cleared, or the
1913 * relevant grace period is already over, so done.
1914 */
1915 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1916 return;
1917 }
1918 WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
1919 WARN_ON_ONCE(!rcu_is_leaf_node(rnp) &&
1920 rcu_preempt_blocked_readers_cgp(rnp));
1921 WRITE_ONCE(rnp->qsmask, rnp->qsmask & ~mask);
1922 trace_rcu_quiescent_state_report(rcu_state.name, rnp->gp_seq,
1923 mask, rnp->qsmask, rnp->level,
1924 rnp->grplo, rnp->grphi,
1925 !!rnp->gp_tasks);
1926 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
1927
1928 /* Other bits still set at this level, so done. */
1929 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1930 return;
1931 }
1932 rnp->completedqs = rnp->gp_seq;
1933 mask = rnp->grpmask;
1934 if (rnp->parent == NULL) {
1935
1936 /* No more levels. Exit loop holding root lock. */
1937
1938 break;
1939 }
1940 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1941 rnp_c = rnp;
1942 rnp = rnp->parent;
1943 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1944 oldmask = READ_ONCE(rnp_c->qsmask);
1945 }
1946
1947 /*
1948 * Get here if we are the last CPU to pass through a quiescent
1949 * state for this grace period. Invoke rcu_report_qs_rsp()
1950 * to clean up and start the next grace period if one is needed.
1951 */
1952 rcu_report_qs_rsp(flags); /* releases rnp->lock. */
1953}
1954
1955/*
1956 * Record a quiescent state for all tasks that were previously queued
1957 * on the specified rcu_node structure and that were blocking the current
1958 * RCU grace period. The caller must hold the corresponding rnp->lock with
1959 * irqs disabled, and this lock is released upon return, but irqs remain
1960 * disabled.
1961 */
1962static void __maybe_unused
1963rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
1964 __releases(rnp->lock)
1965{
1966 unsigned long gps;
1967 unsigned long mask;
1968 struct rcu_node *rnp_p;
1969
1970 raw_lockdep_assert_held_rcu_node(rnp);
1971 if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT_RCU)) ||
1972 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)) ||
1973 rnp->qsmask != 0) {
1974 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1975 return; /* Still need more quiescent states! */
1976 }
1977
1978 rnp->completedqs = rnp->gp_seq;
1979 rnp_p = rnp->parent;
1980 if (rnp_p == NULL) {
1981 /*
1982 * Only one rcu_node structure in the tree, so don't
1983 * try to report up to its nonexistent parent!
1984 */
1985 rcu_report_qs_rsp(flags);
1986 return;
1987 }
1988
1989 /* Report up the rest of the hierarchy, tracking current ->gp_seq. */
1990 gps = rnp->gp_seq;
1991 mask = rnp->grpmask;
1992 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
1993 raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */
1994 rcu_report_qs_rnp(mask, rnp_p, gps, flags);
1995}
1996
1997/*
1998 * Record a quiescent state for the specified CPU to that CPU's rcu_data
1999 * structure. This must be called from the specified CPU.
2000 */
2001static void
2002rcu_report_qs_rdp(struct rcu_data *rdp)
2003{
2004 unsigned long flags;
2005 unsigned long mask;
2006 bool needwake = false;
2007 bool needacc = false;
2008 struct rcu_node *rnp;
2009
2010 WARN_ON_ONCE(rdp->cpu != smp_processor_id());
2011 rnp = rdp->mynode;
2012 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2013 if (rdp->cpu_no_qs.b.norm || rdp->gp_seq != rnp->gp_seq ||
2014 rdp->gpwrap) {
2015
2016 /*
2017 * The grace period in which this quiescent state was
2018 * recorded has ended, so don't report it upwards.
2019 * We will instead need a new quiescent state that lies
2020 * within the current grace period.
2021 */
2022 rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */
2023 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2024 return;
2025 }
2026 mask = rdp->grpmask;
2027 rdp->core_needs_qs = false;
2028 if ((rnp->qsmask & mask) == 0) {
2029 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2030 } else {
2031 /*
2032 * This GP can't end until cpu checks in, so all of our
2033 * callbacks can be processed during the next GP.
2034 *
2035 * NOCB kthreads have their own way to deal with that...
2036 */
2037 if (!rcu_rdp_is_offloaded(rdp)) {
2038 needwake = rcu_accelerate_cbs(rnp, rdp);
2039 } else if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) {
2040 /*
2041 * ...but NOCB kthreads may miss or delay callbacks acceleration
2042 * if in the middle of a (de-)offloading process.
2043 */
2044 needacc = true;
2045 }
2046
2047 rcu_disable_urgency_upon_qs(rdp);
2048 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
2049 /* ^^^ Released rnp->lock */
2050 if (needwake)
2051 rcu_gp_kthread_wake();
2052
2053 if (needacc) {
2054 rcu_nocb_lock_irqsave(rdp, flags);
2055 rcu_accelerate_cbs_unlocked(rnp, rdp);
2056 rcu_nocb_unlock_irqrestore(rdp, flags);
2057 }
2058 }
2059}
2060
2061/*
2062 * Check to see if there is a new grace period of which this CPU
2063 * is not yet aware, and if so, set up local rcu_data state for it.
2064 * Otherwise, see if this CPU has just passed through its first
2065 * quiescent state for this grace period, and record that fact if so.
2066 */
2067static void
2068rcu_check_quiescent_state(struct rcu_data *rdp)
2069{
2070 /* Check for grace-period ends and beginnings. */
2071 note_gp_changes(rdp);
2072
2073 /*
2074 * Does this CPU still need to do its part for current grace period?
2075 * If no, return and let the other CPUs do their part as well.
2076 */
2077 if (!rdp->core_needs_qs)
2078 return;
2079
2080 /*
2081 * Was there a quiescent state since the beginning of the grace
2082 * period? If no, then exit and wait for the next call.
2083 */
2084 if (rdp->cpu_no_qs.b.norm)
2085 return;
2086
2087 /*
2088 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
2089 * judge of that).
2090 */
2091 rcu_report_qs_rdp(rdp);
2092}
2093
2094/*
2095 * Near the end of the offline process. Trace the fact that this CPU
2096 * is going offline.
2097 */
2098int rcutree_dying_cpu(unsigned int cpu)
2099{
2100 bool blkd;
2101 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
2102 struct rcu_node *rnp = rdp->mynode;
2103
2104 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2105 return 0;
2106
2107 blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask);
2108 trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
2109 blkd ? TPS("cpuofl-bgp") : TPS("cpuofl"));
2110 return 0;
2111}
2112
2113/*
2114 * All CPUs for the specified rcu_node structure have gone offline,
2115 * and all tasks that were preempted within an RCU read-side critical
2116 * section while running on one of those CPUs have since exited their RCU
2117 * read-side critical section. Some other CPU is reporting this fact with
2118 * the specified rcu_node structure's ->lock held and interrupts disabled.
2119 * This function therefore goes up the tree of rcu_node structures,
2120 * clearing the corresponding bits in the ->qsmaskinit fields. Note that
2121 * the leaf rcu_node structure's ->qsmaskinit field has already been
2122 * updated.
2123 *
2124 * This function does check that the specified rcu_node structure has
2125 * all CPUs offline and no blocked tasks, so it is OK to invoke it
2126 * prematurely. That said, invoking it after the fact will cost you
2127 * a needless lock acquisition. So once it has done its work, don't
2128 * invoke it again.
2129 */
2130static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
2131{
2132 long mask;
2133 struct rcu_node *rnp = rnp_leaf;
2134
2135 raw_lockdep_assert_held_rcu_node(rnp_leaf);
2136 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
2137 WARN_ON_ONCE(rnp_leaf->qsmaskinit) ||
2138 WARN_ON_ONCE(rcu_preempt_has_tasks(rnp_leaf)))
2139 return;
2140 for (;;) {
2141 mask = rnp->grpmask;
2142 rnp = rnp->parent;
2143 if (!rnp)
2144 break;
2145 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
2146 rnp->qsmaskinit &= ~mask;
2147 /* Between grace periods, so better already be zero! */
2148 WARN_ON_ONCE(rnp->qsmask);
2149 if (rnp->qsmaskinit) {
2150 raw_spin_unlock_rcu_node(rnp);
2151 /* irqs remain disabled. */
2152 return;
2153 }
2154 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2155 }
2156}
2157
2158/*
2159 * The CPU has been completely removed, and some other CPU is reporting
2160 * this fact from process context. Do the remainder of the cleanup.
2161 * There can only be one CPU hotplug operation at a time, so no need for
2162 * explicit locking.
2163 */
2164int rcutree_dead_cpu(unsigned int cpu)
2165{
2166 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
2167 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
2168
2169 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2170 return 0;
2171
2172 WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1);
2173 /* Adjust any no-longer-needed kthreads. */
2174 rcu_boost_kthread_setaffinity(rnp, -1);
2175 // Stop-machine done, so allow nohz_full to disable tick.
2176 tick_dep_clear(TICK_DEP_BIT_RCU);
2177 return 0;
2178}
2179
2180/*
2181 * Invoke any RCU callbacks that have made it to the end of their grace
2182 * period. Throttle as specified by rdp->blimit.
2183 */
2184static void rcu_do_batch(struct rcu_data *rdp)
2185{
2186 int div;
2187 bool __maybe_unused empty;
2188 unsigned long flags;
2189 struct rcu_head *rhp;
2190 struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
2191 long bl, count = 0;
2192 long pending, tlimit = 0;
2193
2194 /* If no callbacks are ready, just return. */
2195 if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
2196 trace_rcu_batch_start(rcu_state.name,
2197 rcu_segcblist_n_cbs(&rdp->cblist), 0);
2198 trace_rcu_batch_end(rcu_state.name, 0,
2199 !rcu_segcblist_empty(&rdp->cblist),
2200 need_resched(), is_idle_task(current),
2201 rcu_is_callbacks_kthread(rdp));
2202 return;
2203 }
2204
2205 /*
2206 * Extract the list of ready callbacks, disabling IRQs to prevent
2207 * races with call_rcu() from interrupt handlers. Leave the
2208 * callback counts, as rcu_barrier() needs to be conservative.
2209 */
2210 rcu_nocb_lock_irqsave(rdp, flags);
2211 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2212 pending = rcu_segcblist_n_cbs(&rdp->cblist);
2213 div = READ_ONCE(rcu_divisor);
2214 div = div < 0 ? 7 : div > sizeof(long) * 8 - 2 ? sizeof(long) * 8 - 2 : div;
2215 bl = max(rdp->blimit, pending >> div);
2216 if (in_serving_softirq() && unlikely(bl > 100)) {
2217 long rrn = READ_ONCE(rcu_resched_ns);
2218
2219 rrn = rrn < NSEC_PER_MSEC ? NSEC_PER_MSEC : rrn > NSEC_PER_SEC ? NSEC_PER_SEC : rrn;
2220 tlimit = local_clock() + rrn;
2221 }
2222 trace_rcu_batch_start(rcu_state.name,
2223 rcu_segcblist_n_cbs(&rdp->cblist), bl);
2224 rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
2225 if (rcu_rdp_is_offloaded(rdp))
2226 rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
2227
2228 trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbDequeued"));
2229 rcu_nocb_unlock_irqrestore(rdp, flags);
2230
2231 /* Invoke callbacks. */
2232 tick_dep_set_task(current, TICK_DEP_BIT_RCU);
2233 rhp = rcu_cblist_dequeue(&rcl);
2234
2235 for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
2236 rcu_callback_t f;
2237
2238 count++;
2239 debug_rcu_head_unqueue(rhp);
2240
2241 rcu_lock_acquire(&rcu_callback_map);
2242 trace_rcu_invoke_callback(rcu_state.name, rhp);
2243
2244 f = rhp->func;
2245 WRITE_ONCE(rhp->func, (rcu_callback_t)0L);
2246 f(rhp);
2247
2248 rcu_lock_release(&rcu_callback_map);
2249
2250 /*
2251 * Stop only if limit reached and CPU has something to do.
2252 */
2253 if (in_serving_softirq()) {
2254 if (count >= bl && (need_resched() || !is_idle_task(current)))
2255 break;
2256 /*
2257 * Make sure we don't spend too much time here and deprive other
2258 * softirq vectors of CPU cycles.
2259 */
2260 if (unlikely(tlimit)) {
2261 /* only call local_clock() every 32 callbacks */
2262 if (likely((count & 31) || local_clock() < tlimit))
2263 continue;
2264 /* Exceeded the time limit, so leave. */
2265 break;
2266 }
2267 } else {
2268 local_bh_enable();
2269 lockdep_assert_irqs_enabled();
2270 cond_resched_tasks_rcu_qs();
2271 lockdep_assert_irqs_enabled();
2272 local_bh_disable();
2273 }
2274 }
2275
2276 rcu_nocb_lock_irqsave(rdp, flags);
2277 rdp->n_cbs_invoked += count;
2278 trace_rcu_batch_end(rcu_state.name, count, !!rcl.head, need_resched(),
2279 is_idle_task(current), rcu_is_callbacks_kthread(rdp));
2280
2281 /* Update counts and requeue any remaining callbacks. */
2282 rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
2283 rcu_segcblist_add_len(&rdp->cblist, -count);
2284
2285 /* Reinstate batch limit if we have worked down the excess. */
2286 count = rcu_segcblist_n_cbs(&rdp->cblist);
2287 if (rdp->blimit >= DEFAULT_MAX_RCU_BLIMIT && count <= qlowmark)
2288 rdp->blimit = blimit;
2289
2290 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2291 if (count == 0 && rdp->qlen_last_fqs_check != 0) {
2292 rdp->qlen_last_fqs_check = 0;
2293 rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
2294 } else if (count < rdp->qlen_last_fqs_check - qhimark)
2295 rdp->qlen_last_fqs_check = count;
2296
2297 /*
2298 * The following usually indicates a double call_rcu(). To track
2299 * this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.
2300 */
2301 empty = rcu_segcblist_empty(&rdp->cblist);
2302 WARN_ON_ONCE(count == 0 && !empty);
2303 WARN_ON_ONCE(!IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
2304 count != 0 && empty);
2305 WARN_ON_ONCE(count == 0 && rcu_segcblist_n_segment_cbs(&rdp->cblist) != 0);
2306 WARN_ON_ONCE(!empty && rcu_segcblist_n_segment_cbs(&rdp->cblist) == 0);
2307
2308 rcu_nocb_unlock_irqrestore(rdp, flags);
2309
2310 tick_dep_clear_task(current, TICK_DEP_BIT_RCU);
2311}
2312
2313/*
2314 * This function is invoked from each scheduling-clock interrupt,
2315 * and checks to see if this CPU is in a non-context-switch quiescent
2316 * state, for example, user mode or idle loop. It also schedules RCU
2317 * core processing. If the current grace period has gone on too long,
2318 * it will ask the scheduler to manufacture a context switch for the sole
2319 * purpose of providing the needed quiescent state.
2320 */
2321void rcu_sched_clock_irq(int user)
2322{
2323 unsigned long j;
2324
2325 if (IS_ENABLED(CONFIG_PROVE_RCU)) {
2326 j = jiffies;
2327 WARN_ON_ONCE(time_before(j, __this_cpu_read(rcu_data.last_sched_clock)));
2328 __this_cpu_write(rcu_data.last_sched_clock, j);
2329 }
2330 trace_rcu_utilization(TPS("Start scheduler-tick"));
2331 lockdep_assert_irqs_disabled();
2332 raw_cpu_inc(rcu_data.ticks_this_gp);
2333 /* The load-acquire pairs with the store-release setting to true. */
2334 if (smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
2335 /* Idle and userspace execution already are quiescent states. */
2336 if (!rcu_is_cpu_rrupt_from_idle() && !user) {
2337 set_tsk_need_resched(current);
2338 set_preempt_need_resched();
2339 }
2340 __this_cpu_write(rcu_data.rcu_urgent_qs, false);
2341 }
2342 rcu_flavor_sched_clock_irq(user);
2343 if (rcu_pending(user))
2344 invoke_rcu_core();
2345 if (user || rcu_is_cpu_rrupt_from_idle())
2346 rcu_note_voluntary_context_switch(current);
2347 lockdep_assert_irqs_disabled();
2348
2349 trace_rcu_utilization(TPS("End scheduler-tick"));
2350}
2351
2352/*
2353 * Scan the leaf rcu_node structures. For each structure on which all
2354 * CPUs have reported a quiescent state and on which there are tasks
2355 * blocking the current grace period, initiate RCU priority boosting.
2356 * Otherwise, invoke the specified function to check dyntick state for
2357 * each CPU that has not yet reported a quiescent state.
2358 */
2359static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
2360{
2361 int cpu;
2362 unsigned long flags;
2363 unsigned long mask;
2364 struct rcu_data *rdp;
2365 struct rcu_node *rnp;
2366
2367 rcu_state.cbovld = rcu_state.cbovldnext;
2368 rcu_state.cbovldnext = false;
2369 rcu_for_each_leaf_node(rnp) {
2370 cond_resched_tasks_rcu_qs();
2371 mask = 0;
2372 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2373 rcu_state.cbovldnext |= !!rnp->cbovldmask;
2374 if (rnp->qsmask == 0) {
2375 if (rcu_preempt_blocked_readers_cgp(rnp)) {
2376 /*
2377 * No point in scanning bits because they
2378 * are all zero. But we might need to
2379 * priority-boost blocked readers.
2380 */
2381 rcu_initiate_boost(rnp, flags);
2382 /* rcu_initiate_boost() releases rnp->lock */
2383 continue;
2384 }
2385 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2386 continue;
2387 }
2388 for_each_leaf_node_cpu_mask(rnp, cpu, rnp->qsmask) {
2389 rdp = per_cpu_ptr(&rcu_data, cpu);
2390 if (f(rdp)) {
2391 mask |= rdp->grpmask;
2392 rcu_disable_urgency_upon_qs(rdp);
2393 }
2394 }
2395 if (mask != 0) {
2396 /* Idle/offline CPUs, report (releases rnp->lock). */
2397 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
2398 } else {
2399 /* Nothing to do here, so just drop the lock. */
2400 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2401 }
2402 }
2403}
2404
2405/*
2406 * Force quiescent states on reluctant CPUs, and also detect which
2407 * CPUs are in dyntick-idle mode.
2408 */
2409void rcu_force_quiescent_state(void)
2410{
2411 unsigned long flags;
2412 bool ret;
2413 struct rcu_node *rnp;
2414 struct rcu_node *rnp_old = NULL;
2415
2416 /* Funnel through hierarchy to reduce memory contention. */
2417 rnp = raw_cpu_read(rcu_data.mynode);
2418 for (; rnp != NULL; rnp = rnp->parent) {
2419 ret = (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) ||
2420 !raw_spin_trylock(&rnp->fqslock);
2421 if (rnp_old != NULL)
2422 raw_spin_unlock(&rnp_old->fqslock);
2423 if (ret)
2424 return;
2425 rnp_old = rnp;
2426 }
2427 /* rnp_old == rcu_get_root(), rnp == NULL. */
2428
2429 /* Reached the root of the rcu_node tree, acquire lock. */
2430 raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
2431 raw_spin_unlock(&rnp_old->fqslock);
2432 if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
2433 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2434 return; /* Someone beat us to it. */
2435 }
2436 WRITE_ONCE(rcu_state.gp_flags,
2437 READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
2438 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2439 rcu_gp_kthread_wake();
2440}
2441EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
2442
2443// Workqueue handler for an RCU reader for kernels enforcing struct RCU
2444// grace periods.
2445static void strict_work_handler(struct work_struct *work)
2446{
2447 rcu_read_lock();
2448 rcu_read_unlock();
2449}
2450
2451/* Perform RCU core processing work for the current CPU. */
2452static __latent_entropy void rcu_core(void)
2453{
2454 unsigned long flags;
2455 struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
2456 struct rcu_node *rnp = rdp->mynode;
2457 /*
2458 * On RT rcu_core() can be preempted when IRQs aren't disabled.
2459 * Therefore this function can race with concurrent NOCB (de-)offloading
2460 * on this CPU and the below condition must be considered volatile.
2461 * However if we race with:
2462 *
2463 * _ Offloading: In the worst case we accelerate or process callbacks
2464 * concurrently with NOCB kthreads. We are guaranteed to
2465 * call rcu_nocb_lock() if that happens.
2466 *
2467 * _ Deoffloading: In the worst case we miss callbacks acceleration or
2468 * processing. This is fine because the early stage
2469 * of deoffloading invokes rcu_core() after setting
2470 * SEGCBLIST_RCU_CORE. So we guarantee that we'll process
2471 * what could have been dismissed without the need to wait
2472 * for the next rcu_pending() check in the next jiffy.
2473 */
2474 const bool do_batch = !rcu_segcblist_completely_offloaded(&rdp->cblist);
2475
2476 if (cpu_is_offline(smp_processor_id()))
2477 return;
2478 trace_rcu_utilization(TPS("Start RCU core"));
2479 WARN_ON_ONCE(!rdp->beenonline);
2480
2481 /* Report any deferred quiescent states if preemption enabled. */
2482 if (IS_ENABLED(CONFIG_PREEMPT_COUNT) && (!(preempt_count() & PREEMPT_MASK))) {
2483 rcu_preempt_deferred_qs(current);
2484 } else if (rcu_preempt_need_deferred_qs(current)) {
2485 set_tsk_need_resched(current);
2486 set_preempt_need_resched();
2487 }
2488
2489 /* Update RCU state based on any recent quiescent states. */
2490 rcu_check_quiescent_state(rdp);
2491
2492 /* No grace period and unregistered callbacks? */
2493 if (!rcu_gp_in_progress() &&
2494 rcu_segcblist_is_enabled(&rdp->cblist) && do_batch) {
2495 rcu_nocb_lock_irqsave(rdp, flags);
2496 if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
2497 rcu_accelerate_cbs_unlocked(rnp, rdp);
2498 rcu_nocb_unlock_irqrestore(rdp, flags);
2499 }
2500
2501 rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check());
2502
2503 /* If there are callbacks ready, invoke them. */
2504 if (do_batch && rcu_segcblist_ready_cbs(&rdp->cblist) &&
2505 likely(READ_ONCE(rcu_scheduler_fully_active))) {
2506 rcu_do_batch(rdp);
2507 /* Re-invoke RCU core processing if there are callbacks remaining. */
2508 if (rcu_segcblist_ready_cbs(&rdp->cblist))
2509 invoke_rcu_core();
2510 }
2511
2512 /* Do any needed deferred wakeups of rcuo kthreads. */
2513 do_nocb_deferred_wakeup(rdp);
2514 trace_rcu_utilization(TPS("End RCU core"));
2515
2516 // If strict GPs, schedule an RCU reader in a clean environment.
2517 if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
2518 queue_work_on(rdp->cpu, rcu_gp_wq, &rdp->strict_work);
2519}
2520
2521static void rcu_core_si(struct softirq_action *h)
2522{
2523 rcu_core();
2524}
2525
2526static void rcu_wake_cond(struct task_struct *t, int status)
2527{
2528 /*
2529 * If the thread is yielding, only wake it when this
2530 * is invoked from idle
2531 */
2532 if (t && (status != RCU_KTHREAD_YIELDING || is_idle_task(current)))
2533 wake_up_process(t);
2534}
2535
2536static void invoke_rcu_core_kthread(void)
2537{
2538 struct task_struct *t;
2539 unsigned long flags;
2540
2541 local_irq_save(flags);
2542 __this_cpu_write(rcu_data.rcu_cpu_has_work, 1);
2543 t = __this_cpu_read(rcu_data.rcu_cpu_kthread_task);
2544 if (t != NULL && t != current)
2545 rcu_wake_cond(t, __this_cpu_read(rcu_data.rcu_cpu_kthread_status));
2546 local_irq_restore(flags);
2547}
2548
2549/*
2550 * Wake up this CPU's rcuc kthread to do RCU core processing.
2551 */
2552static void invoke_rcu_core(void)
2553{
2554 if (!cpu_online(smp_processor_id()))
2555 return;
2556 if (use_softirq)
2557 raise_softirq(RCU_SOFTIRQ);
2558 else
2559 invoke_rcu_core_kthread();
2560}
2561
2562static void rcu_cpu_kthread_park(unsigned int cpu)
2563{
2564 per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
2565}
2566
2567static int rcu_cpu_kthread_should_run(unsigned int cpu)
2568{
2569 return __this_cpu_read(rcu_data.rcu_cpu_has_work);
2570}
2571
2572/*
2573 * Per-CPU kernel thread that invokes RCU callbacks. This replaces
2574 * the RCU softirq used in configurations of RCU that do not support RCU
2575 * priority boosting.
2576 */
2577static void rcu_cpu_kthread(unsigned int cpu)
2578{
2579 unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status);
2580 char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work);
2581 unsigned long *j = this_cpu_ptr(&rcu_data.rcuc_activity);
2582 int spincnt;
2583
2584 trace_rcu_utilization(TPS("Start CPU kthread@rcu_run"));
2585 for (spincnt = 0; spincnt < 10; spincnt++) {
2586 WRITE_ONCE(*j, jiffies);
2587 local_bh_disable();
2588 *statusp = RCU_KTHREAD_RUNNING;
2589 local_irq_disable();
2590 work = *workp;
2591 *workp = 0;
2592 local_irq_enable();
2593 if (work)
2594 rcu_core();
2595 local_bh_enable();
2596 if (*workp == 0) {
2597 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
2598 *statusp = RCU_KTHREAD_WAITING;
2599 return;
2600 }
2601 }
2602 *statusp = RCU_KTHREAD_YIELDING;
2603 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
2604 schedule_timeout_idle(2);
2605 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
2606 *statusp = RCU_KTHREAD_WAITING;
2607 WRITE_ONCE(*j, jiffies);
2608}
2609
2610static struct smp_hotplug_thread rcu_cpu_thread_spec = {
2611 .store = &rcu_data.rcu_cpu_kthread_task,
2612 .thread_should_run = rcu_cpu_kthread_should_run,
2613 .thread_fn = rcu_cpu_kthread,
2614 .thread_comm = "rcuc/%u",
2615 .setup = rcu_cpu_kthread_setup,
2616 .park = rcu_cpu_kthread_park,
2617};
2618
2619/*
2620 * Spawn per-CPU RCU core processing kthreads.
2621 */
2622static int __init rcu_spawn_core_kthreads(void)
2623{
2624 int cpu;
2625
2626 for_each_possible_cpu(cpu)
2627 per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0;
2628 if (use_softirq)
2629 return 0;
2630 WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec),
2631 "%s: Could not start rcuc kthread, OOM is now expected behavior\n", __func__);
2632 return 0;
2633}
2634
2635/*
2636 * Handle any core-RCU processing required by a call_rcu() invocation.
2637 */
2638static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
2639 unsigned long flags)
2640{
2641 /*
2642 * If called from an extended quiescent state, invoke the RCU
2643 * core in order to force a re-evaluation of RCU's idleness.
2644 */
2645 if (!rcu_is_watching())
2646 invoke_rcu_core();
2647
2648 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2649 if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2650 return;
2651
2652 /*
2653 * Force the grace period if too many callbacks or too long waiting.
2654 * Enforce hysteresis, and don't invoke rcu_force_quiescent_state()
2655 * if some other CPU has recently done so. Also, don't bother
2656 * invoking rcu_force_quiescent_state() if the newly enqueued callback
2657 * is the only one waiting for a grace period to complete.
2658 */
2659 if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
2660 rdp->qlen_last_fqs_check + qhimark)) {
2661
2662 /* Are we ignoring a completed grace period? */
2663 note_gp_changes(rdp);
2664
2665 /* Start a new grace period if one not already started. */
2666 if (!rcu_gp_in_progress()) {
2667 rcu_accelerate_cbs_unlocked(rdp->mynode, rdp);
2668 } else {
2669 /* Give the grace period a kick. */
2670 rdp->blimit = DEFAULT_MAX_RCU_BLIMIT;
2671 if (READ_ONCE(rcu_state.n_force_qs) == rdp->n_force_qs_snap &&
2672 rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
2673 rcu_force_quiescent_state();
2674 rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
2675 rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
2676 }
2677 }
2678}
2679
2680/*
2681 * RCU callback function to leak a callback.
2682 */
2683static void rcu_leak_callback(struct rcu_head *rhp)
2684{
2685}
2686
2687/*
2688 * Check and if necessary update the leaf rcu_node structure's
2689 * ->cbovldmask bit corresponding to the current CPU based on that CPU's
2690 * number of queued RCU callbacks. The caller must hold the leaf rcu_node
2691 * structure's ->lock.
2692 */
2693static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp)
2694{
2695 raw_lockdep_assert_held_rcu_node(rnp);
2696 if (qovld_calc <= 0)
2697 return; // Early boot and wildcard value set.
2698 if (rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc)
2699 WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask | rdp->grpmask);
2700 else
2701 WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask & ~rdp->grpmask);
2702}
2703
2704/*
2705 * Check and if necessary update the leaf rcu_node structure's
2706 * ->cbovldmask bit corresponding to the current CPU based on that CPU's
2707 * number of queued RCU callbacks. No locks need be held, but the
2708 * caller must have disabled interrupts.
2709 *
2710 * Note that this function ignores the possibility that there are a lot
2711 * of callbacks all of which have already seen the end of their respective
2712 * grace periods. This omission is due to the need for no-CBs CPUs to
2713 * be holding ->nocb_lock to do this check, which is too heavy for a
2714 * common-case operation.
2715 */
2716static void check_cb_ovld(struct rcu_data *rdp)
2717{
2718 struct rcu_node *const rnp = rdp->mynode;
2719
2720 if (qovld_calc <= 0 ||
2721 ((rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc) ==
2722 !!(READ_ONCE(rnp->cbovldmask) & rdp->grpmask)))
2723 return; // Early boot wildcard value or already set correctly.
2724 raw_spin_lock_rcu_node(rnp);
2725 check_cb_ovld_locked(rdp, rnp);
2726 raw_spin_unlock_rcu_node(rnp);
2727}
2728
2729static void
2730__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy)
2731{
2732 static atomic_t doublefrees;
2733 unsigned long flags;
2734 struct rcu_data *rdp;
2735 bool was_alldone;
2736
2737 /* Misaligned rcu_head! */
2738 WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
2739
2740 if (debug_rcu_head_queue(head)) {
2741 /*
2742 * Probable double call_rcu(), so leak the callback.
2743 * Use rcu:rcu_callback trace event to find the previous
2744 * time callback was passed to call_rcu().
2745 */
2746 if (atomic_inc_return(&doublefrees) < 4) {
2747 pr_err("%s(): Double-freed CB %p->%pS()!!! ", __func__, head, head->func);
2748 mem_dump_obj(head);
2749 }
2750 WRITE_ONCE(head->func, rcu_leak_callback);
2751 return;
2752 }
2753 head->func = func;
2754 head->next = NULL;
2755 kasan_record_aux_stack_noalloc(head);
2756 local_irq_save(flags);
2757 rdp = this_cpu_ptr(&rcu_data);
2758
2759 /* Add the callback to our list. */
2760 if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) {
2761 // This can trigger due to call_rcu() from offline CPU:
2762 WARN_ON_ONCE(rcu_scheduler_active != RCU_SCHEDULER_INACTIVE);
2763 WARN_ON_ONCE(!rcu_is_watching());
2764 // Very early boot, before rcu_init(). Initialize if needed
2765 // and then drop through to queue the callback.
2766 if (rcu_segcblist_empty(&rdp->cblist))
2767 rcu_segcblist_init(&rdp->cblist);
2768 }
2769
2770 check_cb_ovld(rdp);
2771 if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags, lazy))
2772 return; // Enqueued onto ->nocb_bypass, so just leave.
2773 // If no-CBs CPU gets here, rcu_nocb_try_bypass() acquired ->nocb_lock.
2774 rcu_segcblist_enqueue(&rdp->cblist, head);
2775 if (__is_kvfree_rcu_offset((unsigned long)func))
2776 trace_rcu_kvfree_callback(rcu_state.name, head,
2777 (unsigned long)func,
2778 rcu_segcblist_n_cbs(&rdp->cblist));
2779 else
2780 trace_rcu_callback(rcu_state.name, head,
2781 rcu_segcblist_n_cbs(&rdp->cblist));
2782
2783 trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCBQueued"));
2784
2785 /* Go handle any RCU core processing required. */
2786 if (unlikely(rcu_rdp_is_offloaded(rdp))) {
2787 __call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
2788 } else {
2789 __call_rcu_core(rdp, head, flags);
2790 local_irq_restore(flags);
2791 }
2792}
2793
2794#ifdef CONFIG_RCU_LAZY
2795/**
2796 * call_rcu_hurry() - Queue RCU callback for invocation after grace period, and
2797 * flush all lazy callbacks (including the new one) to the main ->cblist while
2798 * doing so.
2799 *
2800 * @head: structure to be used for queueing the RCU updates.
2801 * @func: actual callback function to be invoked after the grace period
2802 *
2803 * The callback function will be invoked some time after a full grace
2804 * period elapses, in other words after all pre-existing RCU read-side
2805 * critical sections have completed.
2806 *
2807 * Use this API instead of call_rcu() if you don't want the callback to be
2808 * invoked after very long periods of time, which can happen on systems without
2809 * memory pressure and on systems which are lightly loaded or mostly idle.
2810 * This function will cause callbacks to be invoked sooner than later at the
2811 * expense of extra power. Other than that, this function is identical to, and
2812 * reuses call_rcu()'s logic. Refer to call_rcu() for more details about memory
2813 * ordering and other functionality.
2814 */
2815void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func)
2816{
2817 return __call_rcu_common(head, func, false);
2818}
2819EXPORT_SYMBOL_GPL(call_rcu_hurry);
2820#endif
2821
2822/**
2823 * call_rcu() - Queue an RCU callback for invocation after a grace period.
2824 * By default the callbacks are 'lazy' and are kept hidden from the main
2825 * ->cblist to prevent starting of grace periods too soon.
2826 * If you desire grace periods to start very soon, use call_rcu_hurry().
2827 *
2828 * @head: structure to be used for queueing the RCU updates.
2829 * @func: actual callback function to be invoked after the grace period
2830 *
2831 * The callback function will be invoked some time after a full grace
2832 * period elapses, in other words after all pre-existing RCU read-side
2833 * critical sections have completed. However, the callback function
2834 * might well execute concurrently with RCU read-side critical sections
2835 * that started after call_rcu() was invoked.
2836 *
2837 * RCU read-side critical sections are delimited by rcu_read_lock()
2838 * and rcu_read_unlock(), and may be nested. In addition, but only in
2839 * v5.0 and later, regions of code across which interrupts, preemption,
2840 * or softirqs have been disabled also serve as RCU read-side critical
2841 * sections. This includes hardware interrupt handlers, softirq handlers,
2842 * and NMI handlers.
2843 *
2844 * Note that all CPUs must agree that the grace period extended beyond
2845 * all pre-existing RCU read-side critical section. On systems with more
2846 * than one CPU, this means that when "func()" is invoked, each CPU is
2847 * guaranteed to have executed a full memory barrier since the end of its
2848 * last RCU read-side critical section whose beginning preceded the call
2849 * to call_rcu(). It also means that each CPU executing an RCU read-side
2850 * critical section that continues beyond the start of "func()" must have
2851 * executed a memory barrier after the call_rcu() but before the beginning
2852 * of that RCU read-side critical section. Note that these guarantees
2853 * include CPUs that are offline, idle, or executing in user mode, as
2854 * well as CPUs that are executing in the kernel.
2855 *
2856 * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
2857 * resulting RCU callback function "func()", then both CPU A and CPU B are
2858 * guaranteed to execute a full memory barrier during the time interval
2859 * between the call to call_rcu() and the invocation of "func()" -- even
2860 * if CPU A and CPU B are the same CPU (but again only if the system has
2861 * more than one CPU).
2862 *
2863 * Implementation of these memory-ordering guarantees is described here:
2864 * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
2865 */
2866void call_rcu(struct rcu_head *head, rcu_callback_t func)
2867{
2868 return __call_rcu_common(head, func, IS_ENABLED(CONFIG_RCU_LAZY));
2869}
2870EXPORT_SYMBOL_GPL(call_rcu);
2871
2872/* Maximum number of jiffies to wait before draining a batch. */
2873#define KFREE_DRAIN_JIFFIES (5 * HZ)
2874#define KFREE_N_BATCHES 2
2875#define FREE_N_CHANNELS 2
2876
2877/**
2878 * struct kvfree_rcu_bulk_data - single block to store kvfree_rcu() pointers
2879 * @nr_records: Number of active pointers in the array
2880 * @next: Next bulk object in the block chain
2881 * @records: Array of the kvfree_rcu() pointers
2882 */
2883struct kvfree_rcu_bulk_data {
2884 unsigned long nr_records;
2885 struct kvfree_rcu_bulk_data *next;
2886 void *records[];
2887};
2888
2889/*
2890 * This macro defines how many entries the "records" array
2891 * will contain. It is based on the fact that the size of
2892 * kvfree_rcu_bulk_data structure becomes exactly one page.
2893 */
2894#define KVFREE_BULK_MAX_ENTR \
2895 ((PAGE_SIZE - sizeof(struct kvfree_rcu_bulk_data)) / sizeof(void *))
2896
2897/**
2898 * struct kfree_rcu_cpu_work - single batch of kfree_rcu() requests
2899 * @rcu_work: Let queue_rcu_work() invoke workqueue handler after grace period
2900 * @head_free: List of kfree_rcu() objects waiting for a grace period
2901 * @bkvhead_free: Bulk-List of kvfree_rcu() objects waiting for a grace period
2902 * @krcp: Pointer to @kfree_rcu_cpu structure
2903 */
2904
2905struct kfree_rcu_cpu_work {
2906 struct rcu_work rcu_work;
2907 struct rcu_head *head_free;
2908 struct kvfree_rcu_bulk_data *bkvhead_free[FREE_N_CHANNELS];
2909 struct kfree_rcu_cpu *krcp;
2910};
2911
2912/**
2913 * struct kfree_rcu_cpu - batch up kfree_rcu() requests for RCU grace period
2914 * @head: List of kfree_rcu() objects not yet waiting for a grace period
2915 * @bkvhead: Bulk-List of kvfree_rcu() objects not yet waiting for a grace period
2916 * @krw_arr: Array of batches of kfree_rcu() objects waiting for a grace period
2917 * @lock: Synchronize access to this structure
2918 * @monitor_work: Promote @head to @head_free after KFREE_DRAIN_JIFFIES
2919 * @initialized: The @rcu_work fields have been initialized
2920 * @count: Number of objects for which GP not started
2921 * @bkvcache:
2922 * A simple cache list that contains objects for reuse purpose.
2923 * In order to save some per-cpu space the list is singular.
2924 * Even though it is lockless an access has to be protected by the
2925 * per-cpu lock.
2926 * @page_cache_work: A work to refill the cache when it is empty
2927 * @backoff_page_cache_fill: Delay cache refills
2928 * @work_in_progress: Indicates that page_cache_work is running
2929 * @hrtimer: A hrtimer for scheduling a page_cache_work
2930 * @nr_bkv_objs: number of allocated objects at @bkvcache.
2931 *
2932 * This is a per-CPU structure. The reason that it is not included in
2933 * the rcu_data structure is to permit this code to be extracted from
2934 * the RCU files. Such extraction could allow further optimization of
2935 * the interactions with the slab allocators.
2936 */
2937struct kfree_rcu_cpu {
2938 struct rcu_head *head;
2939 struct kvfree_rcu_bulk_data *bkvhead[FREE_N_CHANNELS];
2940 struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES];
2941 raw_spinlock_t lock;
2942 struct delayed_work monitor_work;
2943 bool initialized;
2944 int count;
2945
2946 struct delayed_work page_cache_work;
2947 atomic_t backoff_page_cache_fill;
2948 atomic_t work_in_progress;
2949 struct hrtimer hrtimer;
2950
2951 struct llist_head bkvcache;
2952 int nr_bkv_objs;
2953};
2954
2955static DEFINE_PER_CPU(struct kfree_rcu_cpu, krc) = {
2956 .lock = __RAW_SPIN_LOCK_UNLOCKED(krc.lock),
2957};
2958
2959static __always_inline void
2960debug_rcu_bhead_unqueue(struct kvfree_rcu_bulk_data *bhead)
2961{
2962#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
2963 int i;
2964
2965 for (i = 0; i < bhead->nr_records; i++)
2966 debug_rcu_head_unqueue((struct rcu_head *)(bhead->records[i]));
2967#endif
2968}
2969
2970static inline struct kfree_rcu_cpu *
2971krc_this_cpu_lock(unsigned long *flags)
2972{
2973 struct kfree_rcu_cpu *krcp;
2974
2975 local_irq_save(*flags); // For safely calling this_cpu_ptr().
2976 krcp = this_cpu_ptr(&krc);
2977 raw_spin_lock(&krcp->lock);
2978
2979 return krcp;
2980}
2981
2982static inline void
2983krc_this_cpu_unlock(struct kfree_rcu_cpu *krcp, unsigned long flags)
2984{
2985 raw_spin_unlock_irqrestore(&krcp->lock, flags);
2986}
2987
2988static inline struct kvfree_rcu_bulk_data *
2989get_cached_bnode(struct kfree_rcu_cpu *krcp)
2990{
2991 if (!krcp->nr_bkv_objs)
2992 return NULL;
2993
2994 WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs - 1);
2995 return (struct kvfree_rcu_bulk_data *)
2996 llist_del_first(&krcp->bkvcache);
2997}
2998
2999static inline bool
3000put_cached_bnode(struct kfree_rcu_cpu *krcp,
3001 struct kvfree_rcu_bulk_data *bnode)
3002{
3003 // Check the limit.
3004 if (krcp->nr_bkv_objs >= rcu_min_cached_objs)
3005 return false;
3006
3007 llist_add((struct llist_node *) bnode, &krcp->bkvcache);
3008 WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs + 1);
3009 return true;
3010}
3011
3012static int
3013drain_page_cache(struct kfree_rcu_cpu *krcp)
3014{
3015 unsigned long flags;
3016 struct llist_node *page_list, *pos, *n;
3017 int freed = 0;
3018
3019 raw_spin_lock_irqsave(&krcp->lock, flags);
3020 page_list = llist_del_all(&krcp->bkvcache);
3021 WRITE_ONCE(krcp->nr_bkv_objs, 0);
3022 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3023
3024 llist_for_each_safe(pos, n, page_list) {
3025 free_page((unsigned long)pos);
3026 freed++;
3027 }
3028
3029 return freed;
3030}
3031
3032/*
3033 * This function is invoked in workqueue context after a grace period.
3034 * It frees all the objects queued on ->bkvhead_free or ->head_free.
3035 */
3036static void kfree_rcu_work(struct work_struct *work)
3037{
3038 unsigned long flags;
3039 struct kvfree_rcu_bulk_data *bkvhead[FREE_N_CHANNELS], *bnext;
3040 struct rcu_head *head, *next;
3041 struct kfree_rcu_cpu *krcp;
3042 struct kfree_rcu_cpu_work *krwp;
3043 int i, j;
3044
3045 krwp = container_of(to_rcu_work(work),
3046 struct kfree_rcu_cpu_work, rcu_work);
3047 krcp = krwp->krcp;
3048
3049 raw_spin_lock_irqsave(&krcp->lock, flags);
3050 // Channels 1 and 2.
3051 for (i = 0; i < FREE_N_CHANNELS; i++) {
3052 bkvhead[i] = krwp->bkvhead_free[i];
3053 krwp->bkvhead_free[i] = NULL;
3054 }
3055
3056 // Channel 3.
3057 head = krwp->head_free;
3058 krwp->head_free = NULL;
3059 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3060
3061 // Handle the first two channels.
3062 for (i = 0; i < FREE_N_CHANNELS; i++) {
3063 for (; bkvhead[i]; bkvhead[i] = bnext) {
3064 bnext = bkvhead[i]->next;
3065 debug_rcu_bhead_unqueue(bkvhead[i]);
3066
3067 rcu_lock_acquire(&rcu_callback_map);
3068 if (i == 0) { // kmalloc() / kfree().
3069 trace_rcu_invoke_kfree_bulk_callback(
3070 rcu_state.name, bkvhead[i]->nr_records,
3071 bkvhead[i]->records);
3072
3073 kfree_bulk(bkvhead[i]->nr_records,
3074 bkvhead[i]->records);
3075 } else { // vmalloc() / vfree().
3076 for (j = 0; j < bkvhead[i]->nr_records; j++) {
3077 trace_rcu_invoke_kvfree_callback(
3078 rcu_state.name,
3079 bkvhead[i]->records[j], 0);
3080
3081 vfree(bkvhead[i]->records[j]);
3082 }
3083 }
3084 rcu_lock_release(&rcu_callback_map);
3085
3086 raw_spin_lock_irqsave(&krcp->lock, flags);
3087 if (put_cached_bnode(krcp, bkvhead[i]))
3088 bkvhead[i] = NULL;
3089 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3090
3091 if (bkvhead[i])
3092 free_page((unsigned long) bkvhead[i]);
3093
3094 cond_resched_tasks_rcu_qs();
3095 }
3096 }
3097
3098 /*
3099 * This is used when the "bulk" path can not be used for the
3100 * double-argument of kvfree_rcu(). This happens when the
3101 * page-cache is empty, which means that objects are instead
3102 * queued on a linked list through their rcu_head structures.
3103 * This list is named "Channel 3".
3104 */
3105 for (; head; head = next) {
3106 unsigned long offset = (unsigned long)head->func;
3107 void *ptr = (void *)head - offset;
3108
3109 next = head->next;
3110 debug_rcu_head_unqueue((struct rcu_head *)ptr);
3111 rcu_lock_acquire(&rcu_callback_map);
3112 trace_rcu_invoke_kvfree_callback(rcu_state.name, head, offset);
3113
3114 if (!WARN_ON_ONCE(!__is_kvfree_rcu_offset(offset)))
3115 kvfree(ptr);
3116
3117 rcu_lock_release(&rcu_callback_map);
3118 cond_resched_tasks_rcu_qs();
3119 }
3120}
3121
3122static bool
3123need_offload_krc(struct kfree_rcu_cpu *krcp)
3124{
3125 int i;
3126
3127 for (i = 0; i < FREE_N_CHANNELS; i++)
3128 if (krcp->bkvhead[i])
3129 return true;
3130
3131 return !!krcp->head;
3132}
3133
3134static void
3135schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp)
3136{
3137 long delay, delay_left;
3138
3139 delay = READ_ONCE(krcp->count) >= KVFREE_BULK_MAX_ENTR ? 1:KFREE_DRAIN_JIFFIES;
3140 if (delayed_work_pending(&krcp->monitor_work)) {
3141 delay_left = krcp->monitor_work.timer.expires - jiffies;
3142 if (delay < delay_left)
3143 mod_delayed_work(system_wq, &krcp->monitor_work, delay);
3144 return;
3145 }
3146 queue_delayed_work(system_wq, &krcp->monitor_work, delay);
3147}
3148
3149/*
3150 * This function is invoked after the KFREE_DRAIN_JIFFIES timeout.
3151 */
3152static void kfree_rcu_monitor(struct work_struct *work)
3153{
3154 struct kfree_rcu_cpu *krcp = container_of(work,
3155 struct kfree_rcu_cpu, monitor_work.work);
3156 unsigned long flags;
3157 int i, j;
3158
3159 raw_spin_lock_irqsave(&krcp->lock, flags);
3160
3161 // Attempt to start a new batch.
3162 for (i = 0; i < KFREE_N_BATCHES; i++) {
3163 struct kfree_rcu_cpu_work *krwp = &(krcp->krw_arr[i]);
3164
3165 // Try to detach bkvhead or head and attach it over any
3166 // available corresponding free channel. It can be that
3167 // a previous RCU batch is in progress, it means that
3168 // immediately to queue another one is not possible so
3169 // in that case the monitor work is rearmed.
3170 if ((krcp->bkvhead[0] && !krwp->bkvhead_free[0]) ||
3171 (krcp->bkvhead[1] && !krwp->bkvhead_free[1]) ||
3172 (krcp->head && !krwp->head_free)) {
3173 // Channel 1 corresponds to the SLAB-pointer bulk path.
3174 // Channel 2 corresponds to vmalloc-pointer bulk path.
3175 for (j = 0; j < FREE_N_CHANNELS; j++) {
3176 if (!krwp->bkvhead_free[j]) {
3177 krwp->bkvhead_free[j] = krcp->bkvhead[j];
3178 krcp->bkvhead[j] = NULL;
3179 }
3180 }
3181
3182 // Channel 3 corresponds to both SLAB and vmalloc
3183 // objects queued on the linked list.
3184 if (!krwp->head_free) {
3185 krwp->head_free = krcp->head;
3186 krcp->head = NULL;
3187 }
3188
3189 WRITE_ONCE(krcp->count, 0);
3190
3191 // One work is per one batch, so there are three
3192 // "free channels", the batch can handle. It can
3193 // be that the work is in the pending state when
3194 // channels have been detached following by each
3195 // other.
3196 queue_rcu_work(system_wq, &krwp->rcu_work);
3197 }
3198 }
3199
3200 // If there is nothing to detach, it means that our job is
3201 // successfully done here. In case of having at least one
3202 // of the channels that is still busy we should rearm the
3203 // work to repeat an attempt. Because previous batches are
3204 // still in progress.
3205 if (need_offload_krc(krcp))
3206 schedule_delayed_monitor_work(krcp);
3207
3208 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3209}
3210
3211static enum hrtimer_restart
3212schedule_page_work_fn(struct hrtimer *t)
3213{
3214 struct kfree_rcu_cpu *krcp =
3215 container_of(t, struct kfree_rcu_cpu, hrtimer);
3216
3217 queue_delayed_work(system_highpri_wq, &krcp->page_cache_work, 0);
3218 return HRTIMER_NORESTART;
3219}
3220
3221static void fill_page_cache_func(struct work_struct *work)
3222{
3223 struct kvfree_rcu_bulk_data *bnode;
3224 struct kfree_rcu_cpu *krcp =
3225 container_of(work, struct kfree_rcu_cpu,
3226 page_cache_work.work);
3227 unsigned long flags;
3228 int nr_pages;
3229 bool pushed;
3230 int i;
3231
3232 nr_pages = atomic_read(&krcp->backoff_page_cache_fill) ?
3233 1 : rcu_min_cached_objs;
3234
3235 for (i = 0; i < nr_pages; i++) {
3236 bnode = (struct kvfree_rcu_bulk_data *)
3237 __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
3238
3239 if (!bnode)
3240 break;
3241
3242 raw_spin_lock_irqsave(&krcp->lock, flags);
3243 pushed = put_cached_bnode(krcp, bnode);
3244 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3245
3246 if (!pushed) {
3247 free_page((unsigned long) bnode);
3248 break;
3249 }
3250 }
3251
3252 atomic_set(&krcp->work_in_progress, 0);
3253 atomic_set(&krcp->backoff_page_cache_fill, 0);
3254}
3255
3256static void
3257run_page_cache_worker(struct kfree_rcu_cpu *krcp)
3258{
3259 if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING &&
3260 !atomic_xchg(&krcp->work_in_progress, 1)) {
3261 if (atomic_read(&krcp->backoff_page_cache_fill)) {
3262 queue_delayed_work(system_wq,
3263 &krcp->page_cache_work,
3264 msecs_to_jiffies(rcu_delay_page_cache_fill_msec));
3265 } else {
3266 hrtimer_init(&krcp->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
3267 krcp->hrtimer.function = schedule_page_work_fn;
3268 hrtimer_start(&krcp->hrtimer, 0, HRTIMER_MODE_REL);
3269 }
3270 }
3271}
3272
3273// Record ptr in a page managed by krcp, with the pre-krc_this_cpu_lock()
3274// state specified by flags. If can_alloc is true, the caller must
3275// be schedulable and not be holding any locks or mutexes that might be
3276// acquired by the memory allocator or anything that it might invoke.
3277// Returns true if ptr was successfully recorded, else the caller must
3278// use a fallback.
3279static inline bool
3280add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
3281 unsigned long *flags, void *ptr, bool can_alloc)
3282{
3283 struct kvfree_rcu_bulk_data *bnode;
3284 int idx;
3285
3286 *krcp = krc_this_cpu_lock(flags);
3287 if (unlikely(!(*krcp)->initialized))
3288 return false;
3289
3290 idx = !!is_vmalloc_addr(ptr);
3291
3292 /* Check if a new block is required. */
3293 if (!(*krcp)->bkvhead[idx] ||
3294 (*krcp)->bkvhead[idx]->nr_records == KVFREE_BULK_MAX_ENTR) {
3295 bnode = get_cached_bnode(*krcp);
3296 if (!bnode && can_alloc) {
3297 krc_this_cpu_unlock(*krcp, *flags);
3298
3299 // __GFP_NORETRY - allows a light-weight direct reclaim
3300 // what is OK from minimizing of fallback hitting point of
3301 // view. Apart of that it forbids any OOM invoking what is
3302 // also beneficial since we are about to release memory soon.
3303 //
3304 // __GFP_NOMEMALLOC - prevents from consuming of all the
3305 // memory reserves. Please note we have a fallback path.
3306 //
3307 // __GFP_NOWARN - it is supposed that an allocation can
3308 // be failed under low memory or high memory pressure
3309 // scenarios.
3310 bnode = (struct kvfree_rcu_bulk_data *)
3311 __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
3312 *krcp = krc_this_cpu_lock(flags);
3313 }
3314
3315 if (!bnode)
3316 return false;
3317
3318 /* Initialize the new block. */
3319 bnode->nr_records = 0;
3320 bnode->next = (*krcp)->bkvhead[idx];
3321
3322 /* Attach it to the head. */
3323 (*krcp)->bkvhead[idx] = bnode;
3324 }
3325
3326 /* Finally insert. */
3327 (*krcp)->bkvhead[idx]->records
3328 [(*krcp)->bkvhead[idx]->nr_records++] = ptr;
3329
3330 return true;
3331}
3332
3333/*
3334 * Queue a request for lazy invocation of the appropriate free routine
3335 * after a grace period. Please note that three paths are maintained,
3336 * two for the common case using arrays of pointers and a third one that
3337 * is used only when the main paths cannot be used, for example, due to
3338 * memory pressure.
3339 *
3340 * Each kvfree_call_rcu() request is added to a batch. The batch will be drained
3341 * every KFREE_DRAIN_JIFFIES number of jiffies. All the objects in the batch will
3342 * be free'd in workqueue context. This allows us to: batch requests together to
3343 * reduce the number of grace periods during heavy kfree_rcu()/kvfree_rcu() load.
3344 */
3345void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
3346{
3347 unsigned long flags;
3348 struct kfree_rcu_cpu *krcp;
3349 bool success;
3350 void *ptr;
3351
3352 if (head) {
3353 ptr = (void *) head - (unsigned long) func;
3354 } else {
3355 /*
3356 * Please note there is a limitation for the head-less
3357 * variant, that is why there is a clear rule for such
3358 * objects: it can be used from might_sleep() context
3359 * only. For other places please embed an rcu_head to
3360 * your data.
3361 */
3362 might_sleep();
3363 ptr = (unsigned long *) func;
3364 }
3365
3366 // Queue the object but don't yet schedule the batch.
3367 if (debug_rcu_head_queue(ptr)) {
3368 // Probable double kfree_rcu(), just leak.
3369 WARN_ONCE(1, "%s(): Double-freed call. rcu_head %p\n",
3370 __func__, head);
3371
3372 // Mark as success and leave.
3373 return;
3374 }
3375
3376 kasan_record_aux_stack_noalloc(ptr);
3377 success = add_ptr_to_bulk_krc_lock(&krcp, &flags, ptr, !head);
3378 if (!success) {
3379 run_page_cache_worker(krcp);
3380
3381 if (head == NULL)
3382 // Inline if kvfree_rcu(one_arg) call.
3383 goto unlock_return;
3384
3385 head->func = func;
3386 head->next = krcp->head;
3387 krcp->head = head;
3388 success = true;
3389 }
3390
3391 WRITE_ONCE(krcp->count, krcp->count + 1);
3392
3393 // Set timer to drain after KFREE_DRAIN_JIFFIES.
3394 if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING)
3395 schedule_delayed_monitor_work(krcp);
3396
3397unlock_return:
3398 krc_this_cpu_unlock(krcp, flags);
3399
3400 /*
3401 * Inline kvfree() after synchronize_rcu(). We can do
3402 * it from might_sleep() context only, so the current
3403 * CPU can pass the QS state.
3404 */
3405 if (!success) {
3406 debug_rcu_head_unqueue((struct rcu_head *) ptr);
3407 synchronize_rcu();
3408 kvfree(ptr);
3409 }
3410}
3411EXPORT_SYMBOL_GPL(kvfree_call_rcu);
3412
3413static unsigned long
3414kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
3415{
3416 int cpu;
3417 unsigned long count = 0;
3418
3419 /* Snapshot count of all CPUs */
3420 for_each_possible_cpu(cpu) {
3421 struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
3422
3423 count += READ_ONCE(krcp->count);
3424 count += READ_ONCE(krcp->nr_bkv_objs);
3425 atomic_set(&krcp->backoff_page_cache_fill, 1);
3426 }
3427
3428 return count == 0 ? SHRINK_EMPTY : count;
3429}
3430
3431static unsigned long
3432kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
3433{
3434 int cpu, freed = 0;
3435
3436 for_each_possible_cpu(cpu) {
3437 int count;
3438 struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
3439
3440 count = krcp->count;
3441 count += drain_page_cache(krcp);
3442 kfree_rcu_monitor(&krcp->monitor_work.work);
3443
3444 sc->nr_to_scan -= count;
3445 freed += count;
3446
3447 if (sc->nr_to_scan <= 0)
3448 break;
3449 }
3450
3451 return freed == 0 ? SHRINK_STOP : freed;
3452}
3453
3454static struct shrinker kfree_rcu_shrinker = {
3455 .count_objects = kfree_rcu_shrink_count,
3456 .scan_objects = kfree_rcu_shrink_scan,
3457 .batch = 0,
3458 .seeks = DEFAULT_SEEKS,
3459};
3460
3461void __init kfree_rcu_scheduler_running(void)
3462{
3463 int cpu;
3464 unsigned long flags;
3465
3466 for_each_possible_cpu(cpu) {
3467 struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
3468
3469 raw_spin_lock_irqsave(&krcp->lock, flags);
3470 if (need_offload_krc(krcp))
3471 schedule_delayed_monitor_work(krcp);
3472 raw_spin_unlock_irqrestore(&krcp->lock, flags);
3473 }
3474}
3475
3476/*
3477 * During early boot, any blocking grace-period wait automatically
3478 * implies a grace period.
3479 *
3480 * Later on, this could in theory be the case for kernels built with
3481 * CONFIG_SMP=y && CONFIG_PREEMPTION=y running on a single CPU, but this
3482 * is not a common case. Furthermore, this optimization would cause
3483 * the rcu_gp_oldstate structure to expand by 50%, so this potential
3484 * grace-period optimization is ignored once the scheduler is running.
3485 */
3486static int rcu_blocking_is_gp(void)
3487{
3488 if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE)
3489 return false;
3490 might_sleep(); /* Check for RCU read-side critical section. */
3491 return true;
3492}
3493
3494/**
3495 * synchronize_rcu - wait until a grace period has elapsed.
3496 *
3497 * Control will return to the caller some time after a full grace
3498 * period has elapsed, in other words after all currently executing RCU
3499 * read-side critical sections have completed. Note, however, that
3500 * upon return from synchronize_rcu(), the caller might well be executing
3501 * concurrently with new RCU read-side critical sections that began while
3502 * synchronize_rcu() was waiting.
3503 *
3504 * RCU read-side critical sections are delimited by rcu_read_lock()
3505 * and rcu_read_unlock(), and may be nested. In addition, but only in
3506 * v5.0 and later, regions of code across which interrupts, preemption,
3507 * or softirqs have been disabled also serve as RCU read-side critical
3508 * sections. This includes hardware interrupt handlers, softirq handlers,
3509 * and NMI handlers.
3510 *
3511 * Note that this guarantee implies further memory-ordering guarantees.
3512 * On systems with more than one CPU, when synchronize_rcu() returns,
3513 * each CPU is guaranteed to have executed a full memory barrier since
3514 * the end of its last RCU read-side critical section whose beginning
3515 * preceded the call to synchronize_rcu(). In addition, each CPU having
3516 * an RCU read-side critical section that extends beyond the return from
3517 * synchronize_rcu() is guaranteed to have executed a full memory barrier
3518 * after the beginning of synchronize_rcu() and before the beginning of
3519 * that RCU read-side critical section. Note that these guarantees include
3520 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
3521 * that are executing in the kernel.
3522 *
3523 * Furthermore, if CPU A invoked synchronize_rcu(), which returned
3524 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
3525 * to have executed a full memory barrier during the execution of
3526 * synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but
3527 * again only if the system has more than one CPU).
3528 *
3529 * Implementation of these memory-ordering guarantees is described here:
3530 * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst.
3531 */
3532void synchronize_rcu(void)
3533{
3534 unsigned long flags;
3535 struct rcu_node *rnp;
3536
3537 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
3538 lock_is_held(&rcu_lock_map) ||
3539 lock_is_held(&rcu_sched_lock_map),
3540 "Illegal synchronize_rcu() in RCU read-side critical section");
3541 if (!rcu_blocking_is_gp()) {
3542 if (rcu_gp_is_expedited())
3543 synchronize_rcu_expedited();
3544 else
3545 wait_rcu_gp(call_rcu_hurry);
3546 return;
3547 }
3548
3549 // Context allows vacuous grace periods.
3550 // Note well that this code runs with !PREEMPT && !SMP.
3551 // In addition, all code that advances grace periods runs at
3552 // process level. Therefore, this normal GP overlaps with other
3553 // normal GPs only by being fully nested within them, which allows
3554 // reuse of ->gp_seq_polled_snap.
3555 rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_snap);
3556 rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_snap);
3557
3558 // Update the normal grace-period counters to record
3559 // this grace period, but only those used by the boot CPU.
3560 // The rcu_scheduler_starting() will take care of the rest of
3561 // these counters.
3562 local_irq_save(flags);
3563 WARN_ON_ONCE(num_online_cpus() > 1);
3564 rcu_state.gp_seq += (1 << RCU_SEQ_CTR_SHIFT);
3565 for (rnp = this_cpu_ptr(&rcu_data)->mynode; rnp; rnp = rnp->parent)
3566 rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq;
3567 local_irq_restore(flags);
3568}
3569EXPORT_SYMBOL_GPL(synchronize_rcu);
3570
3571/**
3572 * get_completed_synchronize_rcu_full - Return a full pre-completed polled state cookie
3573 * @rgosp: Place to put state cookie
3574 *
3575 * Stores into @rgosp a value that will always be treated by functions
3576 * like poll_state_synchronize_rcu_full() as a cookie whose grace period
3577 * has already completed.
3578 */
3579void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
3580{
3581 rgosp->rgos_norm = RCU_GET_STATE_COMPLETED;
3582 rgosp->rgos_exp = RCU_GET_STATE_COMPLETED;
3583}
3584EXPORT_SYMBOL_GPL(get_completed_synchronize_rcu_full);
3585
3586/**
3587 * get_state_synchronize_rcu - Snapshot current RCU state
3588 *
3589 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
3590 * or poll_state_synchronize_rcu() to determine whether or not a full
3591 * grace period has elapsed in the meantime.
3592 */
3593unsigned long get_state_synchronize_rcu(void)
3594{
3595 /*
3596 * Any prior manipulation of RCU-protected data must happen
3597 * before the load from ->gp_seq.
3598 */
3599 smp_mb(); /* ^^^ */
3600 return rcu_seq_snap(&rcu_state.gp_seq_polled);
3601}
3602EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
3603
3604/**
3605 * get_state_synchronize_rcu_full - Snapshot RCU state, both normal and expedited
3606 * @rgosp: location to place combined normal/expedited grace-period state
3607 *
3608 * Places the normal and expedited grace-period states in @rgosp. This
3609 * state value can be passed to a later call to cond_synchronize_rcu_full()
3610 * or poll_state_synchronize_rcu_full() to determine whether or not a
3611 * grace period (whether normal or expedited) has elapsed in the meantime.
3612 * The rcu_gp_oldstate structure takes up twice the memory of an unsigned
3613 * long, but is guaranteed to see all grace periods. In contrast, the
3614 * combined state occupies less memory, but can sometimes fail to take
3615 * grace periods into account.
3616 *
3617 * This does not guarantee that the needed grace period will actually
3618 * start.
3619 */
3620void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
3621{
3622 struct rcu_node *rnp = rcu_get_root();
3623
3624 /*
3625 * Any prior manipulation of RCU-protected data must happen
3626 * before the loads from ->gp_seq and ->expedited_sequence.
3627 */
3628 smp_mb(); /* ^^^ */
3629 rgosp->rgos_norm = rcu_seq_snap(&rnp->gp_seq);
3630 rgosp->rgos_exp = rcu_seq_snap(&rcu_state.expedited_sequence);
3631}
3632EXPORT_SYMBOL_GPL(get_state_synchronize_rcu_full);
3633
3634/*
3635 * Helper function for start_poll_synchronize_rcu() and
3636 * start_poll_synchronize_rcu_full().
3637 */
3638static void start_poll_synchronize_rcu_common(void)
3639{
3640 unsigned long flags;
3641 bool needwake;
3642 struct rcu_data *rdp;
3643 struct rcu_node *rnp;
3644
3645 lockdep_assert_irqs_enabled();
3646 local_irq_save(flags);
3647 rdp = this_cpu_ptr(&rcu_data);
3648 rnp = rdp->mynode;
3649 raw_spin_lock_rcu_node(rnp); // irqs already disabled.
3650 // Note it is possible for a grace period to have elapsed between
3651 // the above call to get_state_synchronize_rcu() and the below call
3652 // to rcu_seq_snap. This is OK, the worst that happens is that we
3653 // get a grace period that no one needed. These accesses are ordered
3654 // by smp_mb(), and we are accessing them in the opposite order
3655 // from which they are updated at grace-period start, as required.
3656 needwake = rcu_start_this_gp(rnp, rdp, rcu_seq_snap(&rcu_state.gp_seq));
3657 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3658 if (needwake)
3659 rcu_gp_kthread_wake();
3660}
3661
3662/**
3663 * start_poll_synchronize_rcu - Snapshot and start RCU grace period
3664 *
3665 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
3666 * or poll_state_synchronize_rcu() to determine whether or not a full
3667 * grace period has elapsed in the meantime. If the needed grace period
3668 * is not already slated to start, notifies RCU core of the need for that
3669 * grace period.
3670 *
3671 * Interrupts must be enabled for the case where it is necessary to awaken
3672 * the grace-period kthread.
3673 */
3674unsigned long start_poll_synchronize_rcu(void)
3675{
3676 unsigned long gp_seq = get_state_synchronize_rcu();
3677
3678 start_poll_synchronize_rcu_common();
3679 return gp_seq;
3680}
3681EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu);
3682
3683/**
3684 * start_poll_synchronize_rcu_full - Take a full snapshot and start RCU grace period
3685 * @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full()
3686 *
3687 * Places the normal and expedited grace-period states in *@rgos. This
3688 * state value can be passed to a later call to cond_synchronize_rcu_full()
3689 * or poll_state_synchronize_rcu_full() to determine whether or not a
3690 * grace period (whether normal or expedited) has elapsed in the meantime.
3691 * If the needed grace period is not already slated to start, notifies
3692 * RCU core of the need for that grace period.
3693 *
3694 * Interrupts must be enabled for the case where it is necessary to awaken
3695 * the grace-period kthread.
3696 */
3697void start_poll_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
3698{
3699 get_state_synchronize_rcu_full(rgosp);
3700
3701 start_poll_synchronize_rcu_common();
3702}
3703EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_full);
3704
3705/**
3706 * poll_state_synchronize_rcu - Has the specified RCU grace period completed?
3707 * @oldstate: value from get_state_synchronize_rcu() or start_poll_synchronize_rcu()
3708 *
3709 * If a full RCU grace period has elapsed since the earlier call from
3710 * which @oldstate was obtained, return @true, otherwise return @false.
3711 * If @false is returned, it is the caller's responsibility to invoke this
3712 * function later on until it does return @true. Alternatively, the caller
3713 * can explicitly wait for a grace period, for example, by passing @oldstate
3714 * to cond_synchronize_rcu() or by directly invoking synchronize_rcu().
3715 *
3716 * Yes, this function does not take counter wrap into account.
3717 * But counter wrap is harmless. If the counter wraps, we have waited for
3718 * more than a billion grace periods (and way more on a 64-bit system!).
3719 * Those needing to keep old state values for very long time periods
3720 * (many hours even on 32-bit systems) should check them occasionally and
3721 * either refresh them or set a flag indicating that the grace period has
3722 * completed. Alternatively, they can use get_completed_synchronize_rcu()
3723 * to get a guaranteed-completed grace-period state.
3724 *
3725 * This function provides the same memory-ordering guarantees that
3726 * would be provided by a synchronize_rcu() that was invoked at the call
3727 * to the function that provided @oldstate, and that returned at the end
3728 * of this function.
3729 */
3730bool poll_state_synchronize_rcu(unsigned long oldstate)
3731{
3732 if (oldstate == RCU_GET_STATE_COMPLETED ||
3733 rcu_seq_done_exact(&rcu_state.gp_seq_polled, oldstate)) {
3734 smp_mb(); /* Ensure GP ends before subsequent accesses. */
3735 return true;
3736 }
3737 return false;
3738}
3739EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
3740
3741/**
3742 * poll_state_synchronize_rcu_full - Has the specified RCU grace period completed?
3743 * @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full()
3744 *
3745 * If a full RCU grace period has elapsed since the earlier call from
3746 * which *rgosp was obtained, return @true, otherwise return @false.
3747 * If @false is returned, it is the caller's responsibility to invoke this
3748 * function later on until it does return @true. Alternatively, the caller
3749 * can explicitly wait for a grace period, for example, by passing @rgosp
3750 * to cond_synchronize_rcu() or by directly invoking synchronize_rcu().
3751 *
3752 * Yes, this function does not take counter wrap into account.
3753 * But counter wrap is harmless. If the counter wraps, we have waited
3754 * for more than a billion grace periods (and way more on a 64-bit
3755 * system!). Those needing to keep rcu_gp_oldstate values for very
3756 * long time periods (many hours even on 32-bit systems) should check
3757 * them occasionally and either refresh them or set a flag indicating
3758 * that the grace period has completed. Alternatively, they can use
3759 * get_completed_synchronize_rcu_full() to get a guaranteed-completed
3760 * grace-period state.
3761 *
3762 * This function provides the same memory-ordering guarantees that would
3763 * be provided by a synchronize_rcu() that was invoked at the call to
3764 * the function that provided @rgosp, and that returned at the end of this
3765 * function. And this guarantee requires that the root rcu_node structure's
3766 * ->gp_seq field be checked instead of that of the rcu_state structure.
3767 * The problem is that the just-ending grace-period's callbacks can be
3768 * invoked between the time that the root rcu_node structure's ->gp_seq
3769 * field is updated and the time that the rcu_state structure's ->gp_seq
3770 * field is updated. Therefore, if a single synchronize_rcu() is to
3771 * cause a subsequent poll_state_synchronize_rcu_full() to return @true,
3772 * then the root rcu_node structure is the one that needs to be polled.
3773 */
3774bool poll_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
3775{
3776 struct rcu_node *rnp = rcu_get_root();
3777
3778 smp_mb(); // Order against root rcu_node structure grace-period cleanup.
3779 if (rgosp->rgos_norm == RCU_GET_STATE_COMPLETED ||
3780 rcu_seq_done_exact(&rnp->gp_seq, rgosp->rgos_norm) ||
3781 rgosp->rgos_exp == RCU_GET_STATE_COMPLETED ||
3782 rcu_seq_done_exact(&rcu_state.expedited_sequence, rgosp->rgos_exp)) {
3783 smp_mb(); /* Ensure GP ends before subsequent accesses. */
3784 return true;
3785 }
3786 return false;
3787}
3788EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu_full);
3789
3790/**
3791 * cond_synchronize_rcu - Conditionally wait for an RCU grace period
3792 * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
3793 *
3794 * If a full RCU grace period has elapsed since the earlier call to
3795 * get_state_synchronize_rcu() or start_poll_synchronize_rcu(), just return.
3796 * Otherwise, invoke synchronize_rcu() to wait for a full grace period.
3797 *
3798 * Yes, this function does not take counter wrap into account.
3799 * But counter wrap is harmless. If the counter wraps, we have waited for
3800 * more than 2 billion grace periods (and way more on a 64-bit system!),
3801 * so waiting for a couple of additional grace periods should be just fine.
3802 *
3803 * This function provides the same memory-ordering guarantees that
3804 * would be provided by a synchronize_rcu() that was invoked at the call
3805 * to the function that provided @oldstate and that returned at the end
3806 * of this function.
3807 */
3808void cond_synchronize_rcu(unsigned long oldstate)
3809{
3810 if (!poll_state_synchronize_rcu(oldstate))
3811 synchronize_rcu();
3812}
3813EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
3814
3815/**
3816 * cond_synchronize_rcu_full - Conditionally wait for an RCU grace period
3817 * @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full()
3818 *
3819 * If a full RCU grace period has elapsed since the call to
3820 * get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(),
3821 * or start_poll_synchronize_rcu_expedited_full() from which @rgosp was
3822 * obtained, just return. Otherwise, invoke synchronize_rcu() to wait
3823 * for a full grace period.
3824 *
3825 * Yes, this function does not take counter wrap into account.
3826 * But counter wrap is harmless. If the counter wraps, we have waited for
3827 * more than 2 billion grace periods (and way more on a 64-bit system!),
3828 * so waiting for a couple of additional grace periods should be just fine.
3829 *
3830 * This function provides the same memory-ordering guarantees that
3831 * would be provided by a synchronize_rcu() that was invoked at the call
3832 * to the function that provided @rgosp and that returned at the end of
3833 * this function.
3834 */
3835void cond_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
3836{
3837 if (!poll_state_synchronize_rcu_full(rgosp))
3838 synchronize_rcu();
3839}
3840EXPORT_SYMBOL_GPL(cond_synchronize_rcu_full);
3841
3842/*
3843 * Check to see if there is any immediate RCU-related work to be done by
3844 * the current CPU, returning 1 if so and zero otherwise. The checks are
3845 * in order of increasing expense: checks that can be carried out against
3846 * CPU-local state are performed first. However, we must check for CPU
3847 * stalls first, else we might not get a chance.
3848 */
3849static int rcu_pending(int user)
3850{
3851 bool gp_in_progress;
3852 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
3853 struct rcu_node *rnp = rdp->mynode;
3854
3855 lockdep_assert_irqs_disabled();
3856
3857 /* Check for CPU stalls, if enabled. */
3858 check_cpu_stall(rdp);
3859
3860 /* Does this CPU need a deferred NOCB wakeup? */
3861 if (rcu_nocb_need_deferred_wakeup(rdp, RCU_NOCB_WAKE))
3862 return 1;
3863
3864 /* Is this a nohz_full CPU in userspace or idle? (Ignore RCU if so.) */
3865 if ((user || rcu_is_cpu_rrupt_from_idle()) && rcu_nohz_full_cpu())
3866 return 0;
3867
3868 /* Is the RCU core waiting for a quiescent state from this CPU? */
3869 gp_in_progress = rcu_gp_in_progress();
3870 if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm && gp_in_progress)
3871 return 1;
3872
3873 /* Does this CPU have callbacks ready to invoke? */
3874 if (!rcu_rdp_is_offloaded(rdp) &&
3875 rcu_segcblist_ready_cbs(&rdp->cblist))
3876 return 1;
3877
3878 /* Has RCU gone idle with this CPU needing another grace period? */
3879 if (!gp_in_progress && rcu_segcblist_is_enabled(&rdp->cblist) &&
3880 !rcu_rdp_is_offloaded(rdp) &&
3881 !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
3882 return 1;
3883
3884 /* Have RCU grace period completed or started? */
3885 if (rcu_seq_current(&rnp->gp_seq) != rdp->gp_seq ||
3886 unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */
3887 return 1;
3888
3889 /* nothing to do */
3890 return 0;
3891}
3892
3893/*
3894 * Helper function for rcu_barrier() tracing. If tracing is disabled,
3895 * the compiler is expected to optimize this away.
3896 */
3897static void rcu_barrier_trace(const char *s, int cpu, unsigned long done)
3898{
3899 trace_rcu_barrier(rcu_state.name, s, cpu,
3900 atomic_read(&rcu_state.barrier_cpu_count), done);
3901}
3902
3903/*
3904 * RCU callback function for rcu_barrier(). If we are last, wake
3905 * up the task executing rcu_barrier().
3906 *
3907 * Note that the value of rcu_state.barrier_sequence must be captured
3908 * before the atomic_dec_and_test(). Otherwise, if this CPU is not last,
3909 * other CPUs might count the value down to zero before this CPU gets
3910 * around to invoking rcu_barrier_trace(), which might result in bogus
3911 * data from the next instance of rcu_barrier().
3912 */
3913static void rcu_barrier_callback(struct rcu_head *rhp)
3914{
3915 unsigned long __maybe_unused s = rcu_state.barrier_sequence;
3916
3917 if (atomic_dec_and_test(&rcu_state.barrier_cpu_count)) {
3918 rcu_barrier_trace(TPS("LastCB"), -1, s);
3919 complete(&rcu_state.barrier_completion);
3920 } else {
3921 rcu_barrier_trace(TPS("CB"), -1, s);
3922 }
3923}
3924
3925/*
3926 * If needed, entrain an rcu_barrier() callback on rdp->cblist.
3927 */
3928static void rcu_barrier_entrain(struct rcu_data *rdp)
3929{
3930 unsigned long gseq = READ_ONCE(rcu_state.barrier_sequence);
3931 unsigned long lseq = READ_ONCE(rdp->barrier_seq_snap);
3932 bool wake_nocb = false;
3933 bool was_alldone = false;
3934
3935 lockdep_assert_held(&rcu_state.barrier_lock);
3936 if (rcu_seq_state(lseq) || !rcu_seq_state(gseq) || rcu_seq_ctr(lseq) != rcu_seq_ctr(gseq))
3937 return;
3938 rcu_barrier_trace(TPS("IRQ"), -1, rcu_state.barrier_sequence);
3939 rdp->barrier_head.func = rcu_barrier_callback;
3940 debug_rcu_head_queue(&rdp->barrier_head);
3941 rcu_nocb_lock(rdp);
3942 /*
3943 * Flush bypass and wakeup rcuog if we add callbacks to an empty regular
3944 * queue. This way we don't wait for bypass timer that can reach seconds
3945 * if it's fully lazy.
3946 */
3947 was_alldone = rcu_rdp_is_offloaded(rdp) && !rcu_segcblist_pend_cbs(&rdp->cblist);
3948 WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false));
3949 wake_nocb = was_alldone && rcu_segcblist_pend_cbs(&rdp->cblist);
3950 if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head)) {
3951 atomic_inc(&rcu_state.barrier_cpu_count);
3952 } else {
3953 debug_rcu_head_unqueue(&rdp->barrier_head);
3954 rcu_barrier_trace(TPS("IRQNQ"), -1, rcu_state.barrier_sequence);
3955 }
3956 rcu_nocb_unlock(rdp);
3957 if (wake_nocb)
3958 wake_nocb_gp(rdp, false);
3959 smp_store_release(&rdp->barrier_seq_snap, gseq);
3960}
3961
3962/*
3963 * Called with preemption disabled, and from cross-cpu IRQ context.
3964 */
3965static void rcu_barrier_handler(void *cpu_in)
3966{
3967 uintptr_t cpu = (uintptr_t)cpu_in;
3968 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
3969
3970 lockdep_assert_irqs_disabled();
3971 WARN_ON_ONCE(cpu != rdp->cpu);
3972 WARN_ON_ONCE(cpu != smp_processor_id());
3973 raw_spin_lock(&rcu_state.barrier_lock);
3974 rcu_barrier_entrain(rdp);
3975 raw_spin_unlock(&rcu_state.barrier_lock);
3976}
3977
3978/**
3979 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
3980 *
3981 * Note that this primitive does not necessarily wait for an RCU grace period
3982 * to complete. For example, if there are no RCU callbacks queued anywhere
3983 * in the system, then rcu_barrier() is within its rights to return
3984 * immediately, without waiting for anything, much less an RCU grace period.
3985 */
3986void rcu_barrier(void)
3987{
3988 uintptr_t cpu;
3989 unsigned long flags;
3990 unsigned long gseq;
3991 struct rcu_data *rdp;
3992 unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
3993
3994 rcu_barrier_trace(TPS("Begin"), -1, s);
3995
3996 /* Take mutex to serialize concurrent rcu_barrier() requests. */
3997 mutex_lock(&rcu_state.barrier_mutex);
3998
3999 /* Did someone else do our work for us? */
4000 if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
4001 rcu_barrier_trace(TPS("EarlyExit"), -1, rcu_state.barrier_sequence);
4002 smp_mb(); /* caller's subsequent code after above check. */
4003 mutex_unlock(&rcu_state.barrier_mutex);
4004 return;
4005 }
4006
4007 /* Mark the start of the barrier operation. */
4008 raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
4009 rcu_seq_start(&rcu_state.barrier_sequence);
4010 gseq = rcu_state.barrier_sequence;
4011 rcu_barrier_trace(TPS("Inc1"), -1, rcu_state.barrier_sequence);
4012
4013 /*
4014 * Initialize the count to two rather than to zero in order
4015 * to avoid a too-soon return to zero in case of an immediate
4016 * invocation of the just-enqueued callback (or preemption of
4017 * this task). Exclude CPU-hotplug operations to ensure that no
4018 * offline non-offloaded CPU has callbacks queued.
4019 */
4020 init_completion(&rcu_state.barrier_completion);
4021 atomic_set(&rcu_state.barrier_cpu_count, 2);
4022 raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
4023
4024 /*
4025 * Force each CPU with callbacks to register a new callback.
4026 * When that callback is invoked, we will know that all of the
4027 * corresponding CPU's preceding callbacks have been invoked.
4028 */
4029 for_each_possible_cpu(cpu) {
4030 rdp = per_cpu_ptr(&rcu_data, cpu);
4031retry:
4032 if (smp_load_acquire(&rdp->barrier_seq_snap) == gseq)
4033 continue;
4034 raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
4035 if (!rcu_segcblist_n_cbs(&rdp->cblist)) {
4036 WRITE_ONCE(rdp->barrier_seq_snap, gseq);
4037 raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
4038 rcu_barrier_trace(TPS("NQ"), cpu, rcu_state.barrier_sequence);
4039 continue;
4040 }
4041 if (!rcu_rdp_cpu_online(rdp)) {
4042 rcu_barrier_entrain(rdp);
4043 WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq);
4044 raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
4045 rcu_barrier_trace(TPS("OfflineNoCBQ"), cpu, rcu_state.barrier_sequence);
4046 continue;
4047 }
4048 raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
4049 if (smp_call_function_single(cpu, rcu_barrier_handler, (void *)cpu, 1)) {
4050 schedule_timeout_uninterruptible(1);
4051 goto retry;
4052 }
4053 WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq);
4054 rcu_barrier_trace(TPS("OnlineQ"), cpu, rcu_state.barrier_sequence);
4055 }
4056
4057 /*
4058 * Now that we have an rcu_barrier_callback() callback on each
4059 * CPU, and thus each counted, remove the initial count.
4060 */
4061 if (atomic_sub_and_test(2, &rcu_state.barrier_cpu_count))
4062 complete(&rcu_state.barrier_completion);
4063
4064 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
4065 wait_for_completion(&rcu_state.barrier_completion);
4066
4067 /* Mark the end of the barrier operation. */
4068 rcu_barrier_trace(TPS("Inc2"), -1, rcu_state.barrier_sequence);
4069 rcu_seq_end(&rcu_state.barrier_sequence);
4070 gseq = rcu_state.barrier_sequence;
4071 for_each_possible_cpu(cpu) {
4072 rdp = per_cpu_ptr(&rcu_data, cpu);
4073
4074 WRITE_ONCE(rdp->barrier_seq_snap, gseq);
4075 }
4076
4077 /* Other rcu_barrier() invocations can now safely proceed. */
4078 mutex_unlock(&rcu_state.barrier_mutex);
4079}
4080EXPORT_SYMBOL_GPL(rcu_barrier);
4081
4082/*
4083 * Propagate ->qsinitmask bits up the rcu_node tree to account for the
4084 * first CPU in a given leaf rcu_node structure coming online. The caller
4085 * must hold the corresponding leaf rcu_node ->lock with interrupts
4086 * disabled.
4087 */
4088static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
4089{
4090 long mask;
4091 long oldmask;
4092 struct rcu_node *rnp = rnp_leaf;
4093
4094 raw_lockdep_assert_held_rcu_node(rnp_leaf);
4095 WARN_ON_ONCE(rnp->wait_blkd_tasks);
4096 for (;;) {
4097 mask = rnp->grpmask;
4098 rnp = rnp->parent;
4099 if (rnp == NULL)
4100 return;
4101 raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
4102 oldmask = rnp->qsmaskinit;
4103 rnp->qsmaskinit |= mask;
4104 raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
4105 if (oldmask)
4106 return;
4107 }
4108}
4109
4110/*
4111 * Do boot-time initialization of a CPU's per-CPU RCU data.
4112 */
4113static void __init
4114rcu_boot_init_percpu_data(int cpu)
4115{
4116 struct context_tracking *ct = this_cpu_ptr(&context_tracking);
4117 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4118
4119 /* Set up local state, ensuring consistent view of global state. */
4120 rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
4121 INIT_WORK(&rdp->strict_work, strict_work_handler);
4122 WARN_ON_ONCE(ct->dynticks_nesting != 1);
4123 WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu)));
4124 rdp->barrier_seq_snap = rcu_state.barrier_sequence;
4125 rdp->rcu_ofl_gp_seq = rcu_state.gp_seq;
4126 rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED;
4127 rdp->rcu_onl_gp_seq = rcu_state.gp_seq;
4128 rdp->rcu_onl_gp_flags = RCU_GP_CLEANED;
4129 rdp->last_sched_clock = jiffies;
4130 rdp->cpu = cpu;
4131 rcu_boot_init_nocb_percpu_data(rdp);
4132}
4133
4134/*
4135 * Invoked early in the CPU-online process, when pretty much all services
4136 * are available. The incoming CPU is not present.
4137 *
4138 * Initializes a CPU's per-CPU RCU data. Note that only one online or
4139 * offline event can be happening at a given time. Note also that we can
4140 * accept some slop in the rsp->gp_seq access due to the fact that this
4141 * CPU cannot possibly have any non-offloaded RCU callbacks in flight yet.
4142 * And any offloaded callbacks are being numbered elsewhere.
4143 */
4144int rcutree_prepare_cpu(unsigned int cpu)
4145{
4146 unsigned long flags;
4147 struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
4148 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4149 struct rcu_node *rnp = rcu_get_root();
4150
4151 /* Set up local state, ensuring consistent view of global state. */
4152 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4153 rdp->qlen_last_fqs_check = 0;
4154 rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
4155 rdp->blimit = blimit;
4156 ct->dynticks_nesting = 1; /* CPU not up, no tearing. */
4157 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
4158
4159 /*
4160 * Only non-NOCB CPUs that didn't have early-boot callbacks need to be
4161 * (re-)initialized.
4162 */
4163 if (!rcu_segcblist_is_enabled(&rdp->cblist))
4164 rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
4165
4166 /*
4167 * Add CPU to leaf rcu_node pending-online bitmask. Any needed
4168 * propagation up the rcu_node tree will happen at the beginning
4169 * of the next grace period.
4170 */
4171 rnp = rdp->mynode;
4172 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
4173 rdp->beenonline = true; /* We have now been online. */
4174 rdp->gp_seq = READ_ONCE(rnp->gp_seq);
4175 rdp->gp_seq_needed = rdp->gp_seq;
4176 rdp->cpu_no_qs.b.norm = true;
4177 rdp->core_needs_qs = false;
4178 rdp->rcu_iw_pending = false;
4179 rdp->rcu_iw = IRQ_WORK_INIT_HARD(rcu_iw_handler);
4180 rdp->rcu_iw_gp_seq = rdp->gp_seq - 1;
4181 trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl"));
4182 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4183 rcu_spawn_one_boost_kthread(rnp);
4184 rcu_spawn_cpu_nocb_kthread(cpu);
4185 WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus + 1);
4186
4187 return 0;
4188}
4189
4190/*
4191 * Update RCU priority boot kthread affinity for CPU-hotplug changes.
4192 */
4193static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
4194{
4195 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4196
4197 rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
4198}
4199
4200/*
4201 * Near the end of the CPU-online process. Pretty much all services
4202 * enabled, and the CPU is now very much alive.
4203 */
4204int rcutree_online_cpu(unsigned int cpu)
4205{
4206 unsigned long flags;
4207 struct rcu_data *rdp;
4208 struct rcu_node *rnp;
4209
4210 rdp = per_cpu_ptr(&rcu_data, cpu);
4211 rnp = rdp->mynode;
4212 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4213 rnp->ffmask |= rdp->grpmask;
4214 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4215 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
4216 return 0; /* Too early in boot for scheduler work. */
4217 sync_sched_exp_online_cleanup(cpu);
4218 rcutree_affinity_setting(cpu, -1);
4219
4220 // Stop-machine done, so allow nohz_full to disable tick.
4221 tick_dep_clear(TICK_DEP_BIT_RCU);
4222 return 0;
4223}
4224
4225/*
4226 * Near the beginning of the process. The CPU is still very much alive
4227 * with pretty much all services enabled.
4228 */
4229int rcutree_offline_cpu(unsigned int cpu)
4230{
4231 unsigned long flags;
4232 struct rcu_data *rdp;
4233 struct rcu_node *rnp;
4234
4235 rdp = per_cpu_ptr(&rcu_data, cpu);
4236 rnp = rdp->mynode;
4237 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4238 rnp->ffmask &= ~rdp->grpmask;
4239 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4240
4241 rcutree_affinity_setting(cpu, cpu);
4242
4243 // nohz_full CPUs need the tick for stop-machine to work quickly
4244 tick_dep_set(TICK_DEP_BIT_RCU);
4245 return 0;
4246}
4247
4248/*
4249 * Mark the specified CPU as being online so that subsequent grace periods
4250 * (both expedited and normal) will wait on it. Note that this means that
4251 * incoming CPUs are not allowed to use RCU read-side critical sections
4252 * until this function is called. Failing to observe this restriction
4253 * will result in lockdep splats.
4254 *
4255 * Note that this function is special in that it is invoked directly
4256 * from the incoming CPU rather than from the cpuhp_step mechanism.
4257 * This is because this function must be invoked at a precise location.
4258 */
4259void rcu_cpu_starting(unsigned int cpu)
4260{
4261 unsigned long flags;
4262 unsigned long mask;
4263 struct rcu_data *rdp;
4264 struct rcu_node *rnp;
4265 bool newcpu;
4266
4267 rdp = per_cpu_ptr(&rcu_data, cpu);
4268 if (rdp->cpu_started)
4269 return;
4270 rdp->cpu_started = true;
4271
4272 rnp = rdp->mynode;
4273 mask = rdp->grpmask;
4274 local_irq_save(flags);
4275 arch_spin_lock(&rcu_state.ofl_lock);
4276 rcu_dynticks_eqs_online();
4277 raw_spin_lock(&rcu_state.barrier_lock);
4278 raw_spin_lock_rcu_node(rnp);
4279 WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask);
4280 raw_spin_unlock(&rcu_state.barrier_lock);
4281 newcpu = !(rnp->expmaskinitnext & mask);
4282 rnp->expmaskinitnext |= mask;
4283 /* Allow lockless access for expedited grace periods. */
4284 smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + newcpu); /* ^^^ */
4285 ASSERT_EXCLUSIVE_WRITER(rcu_state.ncpus);
4286 rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */
4287 rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
4288 rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags);
4289
4290 /* An incoming CPU should never be blocking a grace period. */
4291 if (WARN_ON_ONCE(rnp->qsmask & mask)) { /* RCU waiting on incoming CPU? */
4292 /* rcu_report_qs_rnp() *really* wants some flags to restore */
4293 unsigned long flags2;
4294
4295 local_irq_save(flags2);
4296 rcu_disable_urgency_upon_qs(rdp);
4297 /* Report QS -after- changing ->qsmaskinitnext! */
4298 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags2);
4299 } else {
4300 raw_spin_unlock_rcu_node(rnp);
4301 }
4302 arch_spin_unlock(&rcu_state.ofl_lock);
4303 local_irq_restore(flags);
4304 smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
4305}
4306
4307/*
4308 * The outgoing function has no further need of RCU, so remove it from
4309 * the rcu_node tree's ->qsmaskinitnext bit masks.
4310 *
4311 * Note that this function is special in that it is invoked directly
4312 * from the outgoing CPU rather than from the cpuhp_step mechanism.
4313 * This is because this function must be invoked at a precise location.
4314 */
4315void rcu_report_dead(unsigned int cpu)
4316{
4317 unsigned long flags, seq_flags;
4318 unsigned long mask;
4319 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4320 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
4321
4322 // Do any dangling deferred wakeups.
4323 do_nocb_deferred_wakeup(rdp);
4324
4325 rcu_preempt_deferred_qs(current);
4326
4327 /* Remove outgoing CPU from mask in the leaf rcu_node structure. */
4328 mask = rdp->grpmask;
4329 local_irq_save(seq_flags);
4330 arch_spin_lock(&rcu_state.ofl_lock);
4331 raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
4332 rdp->rcu_ofl_gp_seq = READ_ONCE(rcu_state.gp_seq);
4333 rdp->rcu_ofl_gp_flags = READ_ONCE(rcu_state.gp_flags);
4334 if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */
4335 /* Report quiescent state -before- changing ->qsmaskinitnext! */
4336 rcu_disable_urgency_upon_qs(rdp);
4337 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
4338 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4339 }
4340 WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext & ~mask);
4341 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4342 arch_spin_unlock(&rcu_state.ofl_lock);
4343 local_irq_restore(seq_flags);
4344
4345 rdp->cpu_started = false;
4346}
4347
4348#ifdef CONFIG_HOTPLUG_CPU
4349/*
4350 * The outgoing CPU has just passed through the dying-idle state, and we
4351 * are being invoked from the CPU that was IPIed to continue the offline
4352 * operation. Migrate the outgoing CPU's callbacks to the current CPU.
4353 */
4354void rcutree_migrate_callbacks(int cpu)
4355{
4356 unsigned long flags;
4357 struct rcu_data *my_rdp;
4358 struct rcu_node *my_rnp;
4359 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
4360 bool needwake;
4361
4362 if (rcu_rdp_is_offloaded(rdp) ||
4363 rcu_segcblist_empty(&rdp->cblist))
4364 return; /* No callbacks to migrate. */
4365
4366 raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags);
4367 WARN_ON_ONCE(rcu_rdp_cpu_online(rdp));
4368 rcu_barrier_entrain(rdp);
4369 my_rdp = this_cpu_ptr(&rcu_data);
4370 my_rnp = my_rdp->mynode;
4371 rcu_nocb_lock(my_rdp); /* irqs already disabled. */
4372 WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies, false));
4373 raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */
4374 /* Leverage recent GPs and set GP for new callbacks. */
4375 needwake = rcu_advance_cbs(my_rnp, rdp) ||
4376 rcu_advance_cbs(my_rnp, my_rdp);
4377 rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
4378 raw_spin_unlock(&rcu_state.barrier_lock); /* irqs remain disabled. */
4379 needwake = needwake || rcu_advance_cbs(my_rnp, my_rdp);
4380 rcu_segcblist_disable(&rdp->cblist);
4381 WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != !rcu_segcblist_n_cbs(&my_rdp->cblist));
4382 check_cb_ovld_locked(my_rdp, my_rnp);
4383 if (rcu_rdp_is_offloaded(my_rdp)) {
4384 raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */
4385 __call_rcu_nocb_wake(my_rdp, true, flags);
4386 } else {
4387 rcu_nocb_unlock(my_rdp); /* irqs remain disabled. */
4388 raw_spin_unlock_irqrestore_rcu_node(my_rnp, flags);
4389 }
4390 if (needwake)
4391 rcu_gp_kthread_wake();
4392 lockdep_assert_irqs_enabled();
4393 WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
4394 !rcu_segcblist_empty(&rdp->cblist),
4395 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
4396 cpu, rcu_segcblist_n_cbs(&rdp->cblist),
4397 rcu_segcblist_first_cb(&rdp->cblist));
4398}
4399#endif
4400
4401/*
4402 * On non-huge systems, use expedited RCU grace periods to make suspend
4403 * and hibernation run faster.
4404 */
4405static int rcu_pm_notify(struct notifier_block *self,
4406 unsigned long action, void *hcpu)
4407{
4408 switch (action) {
4409 case PM_HIBERNATION_PREPARE:
4410 case PM_SUSPEND_PREPARE:
4411 rcu_expedite_gp();
4412 break;
4413 case PM_POST_HIBERNATION:
4414 case PM_POST_SUSPEND:
4415 rcu_unexpedite_gp();
4416 break;
4417 default:
4418 break;
4419 }
4420 return NOTIFY_OK;
4421}
4422
4423#ifdef CONFIG_RCU_EXP_KTHREAD
4424struct kthread_worker *rcu_exp_gp_kworker;
4425struct kthread_worker *rcu_exp_par_gp_kworker;
4426
4427static void __init rcu_start_exp_gp_kworkers(void)
4428{
4429 const char *par_gp_kworker_name = "rcu_exp_par_gp_kthread_worker";
4430 const char *gp_kworker_name = "rcu_exp_gp_kthread_worker";
4431 struct sched_param param = { .sched_priority = kthread_prio };
4432
4433 rcu_exp_gp_kworker = kthread_create_worker(0, gp_kworker_name);
4434 if (IS_ERR_OR_NULL(rcu_exp_gp_kworker)) {
4435 pr_err("Failed to create %s!\n", gp_kworker_name);
4436 return;
4437 }
4438
4439 rcu_exp_par_gp_kworker = kthread_create_worker(0, par_gp_kworker_name);
4440 if (IS_ERR_OR_NULL(rcu_exp_par_gp_kworker)) {
4441 pr_err("Failed to create %s!\n", par_gp_kworker_name);
4442 kthread_destroy_worker(rcu_exp_gp_kworker);
4443 return;
4444 }
4445
4446 sched_setscheduler_nocheck(rcu_exp_gp_kworker->task, SCHED_FIFO, ¶m);
4447 sched_setscheduler_nocheck(rcu_exp_par_gp_kworker->task, SCHED_FIFO,
4448 ¶m);
4449}
4450
4451static inline void rcu_alloc_par_gp_wq(void)
4452{
4453}
4454#else /* !CONFIG_RCU_EXP_KTHREAD */
4455struct workqueue_struct *rcu_par_gp_wq;
4456
4457static void __init rcu_start_exp_gp_kworkers(void)
4458{
4459}
4460
4461static inline void rcu_alloc_par_gp_wq(void)
4462{
4463 rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0);
4464 WARN_ON(!rcu_par_gp_wq);
4465}
4466#endif /* CONFIG_RCU_EXP_KTHREAD */
4467
4468/*
4469 * Spawn the kthreads that handle RCU's grace periods.
4470 */
4471static int __init rcu_spawn_gp_kthread(void)
4472{
4473 unsigned long flags;
4474 struct rcu_node *rnp;
4475 struct sched_param sp;
4476 struct task_struct *t;
4477 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
4478
4479 rcu_scheduler_fully_active = 1;
4480 t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name);
4481 if (WARN_ONCE(IS_ERR(t), "%s: Could not start grace-period kthread, OOM is now expected behavior\n", __func__))
4482 return 0;
4483 if (kthread_prio) {
4484 sp.sched_priority = kthread_prio;
4485 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
4486 }
4487 rnp = rcu_get_root();
4488 raw_spin_lock_irqsave_rcu_node(rnp, flags);
4489 WRITE_ONCE(rcu_state.gp_activity, jiffies);
4490 WRITE_ONCE(rcu_state.gp_req_activity, jiffies);
4491 // Reset .gp_activity and .gp_req_activity before setting .gp_kthread.
4492 smp_store_release(&rcu_state.gp_kthread, t); /* ^^^ */
4493 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
4494 wake_up_process(t);
4495 /* This is a pre-SMP initcall, we expect a single CPU */
4496 WARN_ON(num_online_cpus() > 1);
4497 /*
4498 * Those kthreads couldn't be created on rcu_init() -> rcutree_prepare_cpu()
4499 * due to rcu_scheduler_fully_active.
4500 */
4501 rcu_spawn_cpu_nocb_kthread(smp_processor_id());
4502 rcu_spawn_one_boost_kthread(rdp->mynode);
4503 rcu_spawn_core_kthreads();
4504 /* Create kthread worker for expedited GPs */
4505 rcu_start_exp_gp_kworkers();
4506 return 0;
4507}
4508early_initcall(rcu_spawn_gp_kthread);
4509
4510/*
4511 * This function is invoked towards the end of the scheduler's
4512 * initialization process. Before this is called, the idle task might
4513 * contain synchronous grace-period primitives (during which time, this idle
4514 * task is booting the system, and such primitives are no-ops). After this
4515 * function is called, any synchronous grace-period primitives are run as
4516 * expedited, with the requesting task driving the grace period forward.
4517 * A later core_initcall() rcu_set_runtime_mode() will switch to full
4518 * runtime RCU functionality.
4519 */
4520void rcu_scheduler_starting(void)
4521{
4522 unsigned long flags;
4523 struct rcu_node *rnp;
4524
4525 WARN_ON(num_online_cpus() != 1);
4526 WARN_ON(nr_context_switches() > 0);
4527 rcu_test_sync_prims();
4528
4529 // Fix up the ->gp_seq counters.
4530 local_irq_save(flags);
4531 rcu_for_each_node_breadth_first(rnp)
4532 rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq;
4533 local_irq_restore(flags);
4534
4535 // Switch out of early boot mode.
4536 rcu_scheduler_active = RCU_SCHEDULER_INIT;
4537 rcu_test_sync_prims();
4538}
4539
4540/*
4541 * Helper function for rcu_init() that initializes the rcu_state structure.
4542 */
4543static void __init rcu_init_one(void)
4544{
4545 static const char * const buf[] = RCU_NODE_NAME_INIT;
4546 static const char * const fqs[] = RCU_FQS_NAME_INIT;
4547 static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
4548 static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
4549
4550 int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */
4551 int cpustride = 1;
4552 int i;
4553 int j;
4554 struct rcu_node *rnp;
4555
4556 BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
4557
4558 /* Silence gcc 4.8 false positive about array index out of range. */
4559 if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
4560 panic("rcu_init_one: rcu_num_lvls out of range");
4561
4562 /* Initialize the level-tracking arrays. */
4563
4564 for (i = 1; i < rcu_num_lvls; i++)
4565 rcu_state.level[i] =
4566 rcu_state.level[i - 1] + num_rcu_lvl[i - 1];
4567 rcu_init_levelspread(levelspread, num_rcu_lvl);
4568
4569 /* Initialize the elements themselves, starting from the leaves. */
4570
4571 for (i = rcu_num_lvls - 1; i >= 0; i--) {
4572 cpustride *= levelspread[i];
4573 rnp = rcu_state.level[i];
4574 for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
4575 raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
4576 lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
4577 &rcu_node_class[i], buf[i]);
4578 raw_spin_lock_init(&rnp->fqslock);
4579 lockdep_set_class_and_name(&rnp->fqslock,
4580 &rcu_fqs_class[i], fqs[i]);
4581 rnp->gp_seq = rcu_state.gp_seq;
4582 rnp->gp_seq_needed = rcu_state.gp_seq;
4583 rnp->completedqs = rcu_state.gp_seq;
4584 rnp->qsmask = 0;
4585 rnp->qsmaskinit = 0;
4586 rnp->grplo = j * cpustride;
4587 rnp->grphi = (j + 1) * cpustride - 1;
4588 if (rnp->grphi >= nr_cpu_ids)
4589 rnp->grphi = nr_cpu_ids - 1;
4590 if (i == 0) {
4591 rnp->grpnum = 0;
4592 rnp->grpmask = 0;
4593 rnp->parent = NULL;
4594 } else {
4595 rnp->grpnum = j % levelspread[i - 1];
4596 rnp->grpmask = BIT(rnp->grpnum);
4597 rnp->parent = rcu_state.level[i - 1] +
4598 j / levelspread[i - 1];
4599 }
4600 rnp->level = i;
4601 INIT_LIST_HEAD(&rnp->blkd_tasks);
4602 rcu_init_one_nocb(rnp);
4603 init_waitqueue_head(&rnp->exp_wq[0]);
4604 init_waitqueue_head(&rnp->exp_wq[1]);
4605 init_waitqueue_head(&rnp->exp_wq[2]);
4606 init_waitqueue_head(&rnp->exp_wq[3]);
4607 spin_lock_init(&rnp->exp_lock);
4608 mutex_init(&rnp->boost_kthread_mutex);
4609 raw_spin_lock_init(&rnp->exp_poll_lock);
4610 rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
4611 INIT_WORK(&rnp->exp_poll_wq, sync_rcu_do_polled_gp);
4612 }
4613 }
4614
4615 init_swait_queue_head(&rcu_state.gp_wq);
4616 init_swait_queue_head(&rcu_state.expedited_wq);
4617 rnp = rcu_first_leaf_node();
4618 for_each_possible_cpu(i) {
4619 while (i > rnp->grphi)
4620 rnp++;
4621 per_cpu_ptr(&rcu_data, i)->mynode = rnp;
4622 rcu_boot_init_percpu_data(i);
4623 }
4624}
4625
4626/*
4627 * Force priority from the kernel command-line into range.
4628 */
4629static void __init sanitize_kthread_prio(void)
4630{
4631 int kthread_prio_in = kthread_prio;
4632
4633 if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 2
4634 && IS_BUILTIN(CONFIG_RCU_TORTURE_TEST))
4635 kthread_prio = 2;
4636 else if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
4637 kthread_prio = 1;
4638 else if (kthread_prio < 0)
4639 kthread_prio = 0;
4640 else if (kthread_prio > 99)
4641 kthread_prio = 99;
4642
4643 if (kthread_prio != kthread_prio_in)
4644 pr_alert("%s: Limited prio to %d from %d\n",
4645 __func__, kthread_prio, kthread_prio_in);
4646}
4647
4648/*
4649 * Compute the rcu_node tree geometry from kernel parameters. This cannot
4650 * replace the definitions in tree.h because those are needed to size
4651 * the ->node array in the rcu_state structure.
4652 */
4653void rcu_init_geometry(void)
4654{
4655 ulong d;
4656 int i;
4657 static unsigned long old_nr_cpu_ids;
4658 int rcu_capacity[RCU_NUM_LVLS];
4659 static bool initialized;
4660
4661 if (initialized) {
4662 /*
4663 * Warn if setup_nr_cpu_ids() had not yet been invoked,
4664 * unless nr_cpus_ids == NR_CPUS, in which case who cares?
4665 */
4666 WARN_ON_ONCE(old_nr_cpu_ids != nr_cpu_ids);
4667 return;
4668 }
4669
4670 old_nr_cpu_ids = nr_cpu_ids;
4671 initialized = true;
4672
4673 /*
4674 * Initialize any unspecified boot parameters.
4675 * The default values of jiffies_till_first_fqs and
4676 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
4677 * value, which is a function of HZ, then adding one for each
4678 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
4679 */
4680 d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
4681 if (jiffies_till_first_fqs == ULONG_MAX)
4682 jiffies_till_first_fqs = d;
4683 if (jiffies_till_next_fqs == ULONG_MAX)
4684 jiffies_till_next_fqs = d;
4685 adjust_jiffies_till_sched_qs();
4686
4687 /* If the compile-time values are accurate, just leave. */
4688 if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
4689 nr_cpu_ids == NR_CPUS)
4690 return;
4691 pr_info("Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%u\n",
4692 rcu_fanout_leaf, nr_cpu_ids);
4693
4694 /*
4695 * The boot-time rcu_fanout_leaf parameter must be at least two
4696 * and cannot exceed the number of bits in the rcu_node masks.
4697 * Complain and fall back to the compile-time values if this
4698 * limit is exceeded.
4699 */
4700 if (rcu_fanout_leaf < 2 ||
4701 rcu_fanout_leaf > sizeof(unsigned long) * 8) {
4702 rcu_fanout_leaf = RCU_FANOUT_LEAF;
4703 WARN_ON(1);
4704 return;
4705 }
4706
4707 /*
4708 * Compute number of nodes that can be handled an rcu_node tree
4709 * with the given number of levels.
4710 */
4711 rcu_capacity[0] = rcu_fanout_leaf;
4712 for (i = 1; i < RCU_NUM_LVLS; i++)
4713 rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
4714
4715 /*
4716 * The tree must be able to accommodate the configured number of CPUs.
4717 * If this limit is exceeded, fall back to the compile-time values.
4718 */
4719 if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
4720 rcu_fanout_leaf = RCU_FANOUT_LEAF;
4721 WARN_ON(1);
4722 return;
4723 }
4724
4725 /* Calculate the number of levels in the tree. */
4726 for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
4727 }
4728 rcu_num_lvls = i + 1;
4729
4730 /* Calculate the number of rcu_nodes at each level of the tree. */
4731 for (i = 0; i < rcu_num_lvls; i++) {
4732 int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
4733 num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
4734 }
4735
4736 /* Calculate the total number of rcu_node structures. */
4737 rcu_num_nodes = 0;
4738 for (i = 0; i < rcu_num_lvls; i++)
4739 rcu_num_nodes += num_rcu_lvl[i];
4740}
4741
4742/*
4743 * Dump out the structure of the rcu_node combining tree associated
4744 * with the rcu_state structure.
4745 */
4746static void __init rcu_dump_rcu_node_tree(void)
4747{
4748 int level = 0;
4749 struct rcu_node *rnp;
4750
4751 pr_info("rcu_node tree layout dump\n");
4752 pr_info(" ");
4753 rcu_for_each_node_breadth_first(rnp) {
4754 if (rnp->level != level) {
4755 pr_cont("\n");
4756 pr_info(" ");
4757 level = rnp->level;
4758 }
4759 pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum);
4760 }
4761 pr_cont("\n");
4762}
4763
4764struct workqueue_struct *rcu_gp_wq;
4765
4766static void __init kfree_rcu_batch_init(void)
4767{
4768 int cpu;
4769 int i;
4770
4771 /* Clamp it to [0:100] seconds interval. */
4772 if (rcu_delay_page_cache_fill_msec < 0 ||
4773 rcu_delay_page_cache_fill_msec > 100 * MSEC_PER_SEC) {
4774
4775 rcu_delay_page_cache_fill_msec =
4776 clamp(rcu_delay_page_cache_fill_msec, 0,
4777 (int) (100 * MSEC_PER_SEC));
4778
4779 pr_info("Adjusting rcutree.rcu_delay_page_cache_fill_msec to %d ms.\n",
4780 rcu_delay_page_cache_fill_msec);
4781 }
4782
4783 for_each_possible_cpu(cpu) {
4784 struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu);
4785
4786 for (i = 0; i < KFREE_N_BATCHES; i++) {
4787 INIT_RCU_WORK(&krcp->krw_arr[i].rcu_work, kfree_rcu_work);
4788 krcp->krw_arr[i].krcp = krcp;
4789 }
4790
4791 INIT_DELAYED_WORK(&krcp->monitor_work, kfree_rcu_monitor);
4792 INIT_DELAYED_WORK(&krcp->page_cache_work, fill_page_cache_func);
4793 krcp->initialized = true;
4794 }
4795 if (register_shrinker(&kfree_rcu_shrinker, "rcu-kfree"))
4796 pr_err("Failed to register kfree_rcu() shrinker!\n");
4797}
4798
4799void __init rcu_init(void)
4800{
4801 int cpu = smp_processor_id();
4802
4803 rcu_early_boot_tests();
4804
4805 kfree_rcu_batch_init();
4806 rcu_bootup_announce();
4807 sanitize_kthread_prio();
4808 rcu_init_geometry();
4809 rcu_init_one();
4810 if (dump_tree)
4811 rcu_dump_rcu_node_tree();
4812 if (use_softirq)
4813 open_softirq(RCU_SOFTIRQ, rcu_core_si);
4814
4815 /*
4816 * We don't need protection against CPU-hotplug here because
4817 * this is called early in boot, before either interrupts
4818 * or the scheduler are operational.
4819 */
4820 pm_notifier(rcu_pm_notify, 0);
4821 WARN_ON(num_online_cpus() > 1); // Only one CPU this early in boot.
4822 rcutree_prepare_cpu(cpu);
4823 rcu_cpu_starting(cpu);
4824 rcutree_online_cpu(cpu);
4825
4826 /* Create workqueue for Tree SRCU and for expedited GPs. */
4827 rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
4828 WARN_ON(!rcu_gp_wq);
4829 rcu_alloc_par_gp_wq();
4830
4831 /* Fill in default value for rcutree.qovld boot parameter. */
4832 /* -After- the rcu_node ->lock fields are initialized! */
4833 if (qovld < 0)
4834 qovld_calc = DEFAULT_RCU_QOVLD_MULT * qhimark;
4835 else
4836 qovld_calc = qovld;
4837
4838 // Kick-start any polled grace periods that started early.
4839 if (!(per_cpu_ptr(&rcu_data, cpu)->mynode->exp_seq_poll_rq & 0x1))
4840 (void)start_poll_synchronize_rcu_expedited();
4841}
4842
4843#include "tree_stall.h"
4844#include "tree_exp.h"
4845#include "tree_nocb.h"
4846#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"