Loading...
1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * Read-Copy Update mechanism for mutual exclusion
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> Hierarchical version
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/percpu.h>
36#include <linux/notifier.h>
37#include <linux/cpu.h>
38#include <linux/mutex.h>
39#include <linux/time.h>
40#include <linux/kernel_stat.h>
41#include <linux/wait.h>
42#include <linux/kthread.h>
43#include <uapi/linux/sched/types.h>
44#include <linux/prefetch.h>
45#include <linux/delay.h>
46#include <linux/stop_machine.h>
47#include <linux/random.h>
48#include <linux/trace_events.h>
49#include <linux/suspend.h>
50#include <linux/ftrace.h>
51#include <linux/tick.h>
52#include <linux/sysrq.h>
53#include <linux/kprobes.h>
54#include <linux/gfp.h>
55#include <linux/oom.h>
56#include <linux/smpboot.h>
57#include <linux/jiffies.h>
58#include <linux/sched/isolation.h>
59#include <linux/sched/clock.h>
60#include "../time/tick-internal.h"
61
62#include "tree.h"
63#include "rcu.h"
64
65#ifdef MODULE_PARAM_PREFIX
66#undef MODULE_PARAM_PREFIX
67#endif
68#define MODULE_PARAM_PREFIX "rcutree."
69
70/* Data structures. */
71
72/*
73 * Steal a bit from the bottom of ->dynticks for idle entry/exit
74 * control. Initially this is for TLB flushing.
75 */
76#define RCU_DYNTICK_CTRL_MASK 0x1
77#define RCU_DYNTICK_CTRL_CTR (RCU_DYNTICK_CTRL_MASK + 1)
78#ifndef rcu_eqs_special_exit
79#define rcu_eqs_special_exit() do { } while (0)
80#endif
81
82static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
83 .dynticks_nesting = 1,
84 .dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
85 .dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR),
86};
87struct rcu_state rcu_state = {
88 .level = { &rcu_state.node[0] },
89 .gp_state = RCU_GP_IDLE,
90 .gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT,
91 .barrier_mutex = __MUTEX_INITIALIZER(rcu_state.barrier_mutex),
92 .name = RCU_NAME,
93 .abbr = RCU_ABBR,
94 .exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex),
95 .exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex),
96 .ofl_lock = __RAW_SPIN_LOCK_UNLOCKED(rcu_state.ofl_lock),
97};
98
99/* Dump rcu_node combining tree at boot to verify correct setup. */
100static bool dump_tree;
101module_param(dump_tree, bool, 0444);
102/* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */
103static bool use_softirq = 1;
104module_param(use_softirq, bool, 0444);
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);
153
154/* rcuc/rcub kthread realtime priority */
155static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
156module_param(kthread_prio, int, 0444);
157
158/* Delay in jiffies for grace-period initialization delays, debug only. */
159
160static int gp_preinit_delay;
161module_param(gp_preinit_delay, int, 0444);
162static int gp_init_delay;
163module_param(gp_init_delay, int, 0444);
164static int gp_cleanup_delay;
165module_param(gp_cleanup_delay, int, 0444);
166
167/* Retrieve RCU kthreads priority for rcutorture */
168int rcu_get_gp_kthreads_prio(void)
169{
170 return kthread_prio;
171}
172EXPORT_SYMBOL_GPL(rcu_get_gp_kthreads_prio);
173
174/*
175 * Number of grace periods between delays, normalized by the duration of
176 * the delay. The longer the delay, the more the grace periods between
177 * each delay. The reason for this normalization is that it means that,
178 * for non-zero delays, the overall slowdown of grace periods is constant
179 * regardless of the duration of the delay. This arrangement balances
180 * the need for long delays to increase some race probabilities with the
181 * need for fast grace periods to increase other race probabilities.
182 */
183#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays. */
184
185/*
186 * Compute the mask of online CPUs for the specified rcu_node structure.
187 * This will not be stable unless the rcu_node structure's ->lock is
188 * held, but the bit corresponding to the current CPU will be stable
189 * in most contexts.
190 */
191unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
192{
193 return READ_ONCE(rnp->qsmaskinitnext);
194}
195
196/*
197 * Return true if an RCU grace period is in progress. The READ_ONCE()s
198 * permit this function to be invoked without holding the root rcu_node
199 * structure's ->lock, but of course results can be subject to change.
200 */
201static int rcu_gp_in_progress(void)
202{
203 return rcu_seq_state(rcu_seq_current(&rcu_state.gp_seq));
204}
205
206/*
207 * Return the number of callbacks queued on the specified CPU.
208 * Handles both the nocbs and normal cases.
209 */
210static long rcu_get_n_cbs_cpu(int cpu)
211{
212 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
213
214 if (rcu_segcblist_is_enabled(&rdp->cblist))
215 return rcu_segcblist_n_cbs(&rdp->cblist);
216 return 0;
217}
218
219void rcu_softirq_qs(void)
220{
221 rcu_qs();
222 rcu_preempt_deferred_qs(current);
223}
224
225/*
226 * Record entry into an extended quiescent state. This is only to be
227 * called when not already in an extended quiescent state.
228 */
229static void rcu_dynticks_eqs_enter(void)
230{
231 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
232 int seq;
233
234 /*
235 * CPUs seeing atomic_add_return() must see prior RCU read-side
236 * critical sections, and we also must force ordering with the
237 * next idle sojourn.
238 */
239 seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
240 /* Better be in an extended quiescent state! */
241 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
242 (seq & RCU_DYNTICK_CTRL_CTR));
243 /* Better not have special action (TLB flush) pending! */
244 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
245 (seq & RCU_DYNTICK_CTRL_MASK));
246}
247
248/*
249 * Record exit from an extended quiescent state. This is only to be
250 * called from an extended quiescent state.
251 */
252static void rcu_dynticks_eqs_exit(void)
253{
254 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
255 int seq;
256
257 /*
258 * CPUs seeing atomic_add_return() must see prior idle sojourns,
259 * and we also must force ordering with the next RCU read-side
260 * critical section.
261 */
262 seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
263 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
264 !(seq & RCU_DYNTICK_CTRL_CTR));
265 if (seq & RCU_DYNTICK_CTRL_MASK) {
266 atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks);
267 smp_mb__after_atomic(); /* _exit after clearing mask. */
268 /* Prefer duplicate flushes to losing a flush. */
269 rcu_eqs_special_exit();
270 }
271}
272
273/*
274 * Reset the current CPU's ->dynticks counter to indicate that the
275 * newly onlined CPU is no longer in an extended quiescent state.
276 * This will either leave the counter unchanged, or increment it
277 * to the next non-quiescent value.
278 *
279 * The non-atomic test/increment sequence works because the upper bits
280 * of the ->dynticks counter are manipulated only by the corresponding CPU,
281 * or when the corresponding CPU is offline.
282 */
283static void rcu_dynticks_eqs_online(void)
284{
285 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
286
287 if (atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR)
288 return;
289 atomic_add(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks);
290}
291
292/*
293 * Is the current CPU in an extended quiescent state?
294 *
295 * No ordering, as we are sampling CPU-local information.
296 */
297bool rcu_dynticks_curr_cpu_in_eqs(void)
298{
299 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
300
301 return !(atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR);
302}
303
304/*
305 * Snapshot the ->dynticks counter with full ordering so as to allow
306 * stable comparison of this counter with past and future snapshots.
307 */
308int rcu_dynticks_snap(struct rcu_data *rdp)
309{
310 int snap = atomic_add_return(0, &rdp->dynticks);
311
312 return snap & ~RCU_DYNTICK_CTRL_MASK;
313}
314
315/*
316 * Return true if the snapshot returned from rcu_dynticks_snap()
317 * indicates that RCU is in an extended quiescent state.
318 */
319static bool rcu_dynticks_in_eqs(int snap)
320{
321 return !(snap & RCU_DYNTICK_CTRL_CTR);
322}
323
324/*
325 * Return true if the CPU corresponding to the specified rcu_data
326 * structure has spent some time in an extended quiescent state since
327 * rcu_dynticks_snap() returned the specified snapshot.
328 */
329static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap)
330{
331 return snap != rcu_dynticks_snap(rdp);
332}
333
334/*
335 * Set the special (bottom) bit of the specified CPU so that it
336 * will take special action (such as flushing its TLB) on the
337 * next exit from an extended quiescent state. Returns true if
338 * the bit was successfully set, or false if the CPU was not in
339 * an extended quiescent state.
340 */
341bool rcu_eqs_special_set(int cpu)
342{
343 int old;
344 int new;
345 struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
346
347 do {
348 old = atomic_read(&rdp->dynticks);
349 if (old & RCU_DYNTICK_CTRL_CTR)
350 return false;
351 new = old | RCU_DYNTICK_CTRL_MASK;
352 } while (atomic_cmpxchg(&rdp->dynticks, old, new) != old);
353 return true;
354}
355
356/*
357 * Let the RCU core know that this CPU has gone through the scheduler,
358 * which is a quiescent state. This is called when the need for a
359 * quiescent state is urgent, so we burn an atomic operation and full
360 * memory barriers to let the RCU core know about it, regardless of what
361 * this CPU might (or might not) do in the near future.
362 *
363 * We inform the RCU core by emulating a zero-duration dyntick-idle period.
364 *
365 * The caller must have disabled interrupts and must not be idle.
366 */
367static void __maybe_unused rcu_momentary_dyntick_idle(void)
368{
369 int special;
370
371 raw_cpu_write(rcu_data.rcu_need_heavy_qs, false);
372 special = atomic_add_return(2 * RCU_DYNTICK_CTRL_CTR,
373 &this_cpu_ptr(&rcu_data)->dynticks);
374 /* It is illegal to call this from idle state. */
375 WARN_ON_ONCE(!(special & RCU_DYNTICK_CTRL_CTR));
376 rcu_preempt_deferred_qs(current);
377}
378
379/**
380 * rcu_is_cpu_rrupt_from_idle - see if interrupted from idle
381 *
382 * If the current CPU is idle and running at a first-level (not nested)
383 * interrupt from idle, return true. The caller must have at least
384 * disabled preemption.
385 */
386static int rcu_is_cpu_rrupt_from_idle(void)
387{
388 /* Called only from within the scheduling-clock interrupt */
389 lockdep_assert_in_irq();
390
391 /* Check for counter underflows */
392 RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) < 0,
393 "RCU dynticks_nesting counter underflow!");
394 RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) <= 0,
395 "RCU dynticks_nmi_nesting counter underflow/zero!");
396
397 /* Are we at first interrupt nesting level? */
398 if (__this_cpu_read(rcu_data.dynticks_nmi_nesting) != 1)
399 return false;
400
401 /* Does CPU appear to be idle from an RCU standpoint? */
402 return __this_cpu_read(rcu_data.dynticks_nesting) == 0;
403}
404
405#define DEFAULT_RCU_BLIMIT 10 /* Maximum callbacks per rcu_do_batch ... */
406#define DEFAULT_MAX_RCU_BLIMIT 10000 /* ... even during callback flood. */
407static long blimit = DEFAULT_RCU_BLIMIT;
408#define DEFAULT_RCU_QHIMARK 10000 /* If this many pending, ignore blimit. */
409static long qhimark = DEFAULT_RCU_QHIMARK;
410#define DEFAULT_RCU_QLOMARK 100 /* Once only this many pending, use blimit. */
411static long qlowmark = DEFAULT_RCU_QLOMARK;
412
413module_param(blimit, long, 0444);
414module_param(qhimark, long, 0444);
415module_param(qlowmark, long, 0444);
416
417static ulong jiffies_till_first_fqs = ULONG_MAX;
418static ulong jiffies_till_next_fqs = ULONG_MAX;
419static bool rcu_kick_kthreads;
420static int rcu_divisor = 7;
421module_param(rcu_divisor, int, 0644);
422
423/* Force an exit from rcu_do_batch() after 3 milliseconds. */
424static long rcu_resched_ns = 3 * NSEC_PER_MSEC;
425module_param(rcu_resched_ns, long, 0644);
426
427/*
428 * How long the grace period must be before we start recruiting
429 * quiescent-state help from rcu_note_context_switch().
430 */
431static ulong jiffies_till_sched_qs = ULONG_MAX;
432module_param(jiffies_till_sched_qs, ulong, 0444);
433static ulong jiffies_to_sched_qs; /* See adjust_jiffies_till_sched_qs(). */
434module_param(jiffies_to_sched_qs, ulong, 0444); /* Display only! */
435
436/*
437 * Make sure that we give the grace-period kthread time to detect any
438 * idle CPUs before taking active measures to force quiescent states.
439 * However, don't go below 100 milliseconds, adjusted upwards for really
440 * large systems.
441 */
442static void adjust_jiffies_till_sched_qs(void)
443{
444 unsigned long j;
445
446 /* If jiffies_till_sched_qs was specified, respect the request. */
447 if (jiffies_till_sched_qs != ULONG_MAX) {
448 WRITE_ONCE(jiffies_to_sched_qs, jiffies_till_sched_qs);
449 return;
450 }
451 /* Otherwise, set to third fqs scan, but bound below on large system. */
452 j = READ_ONCE(jiffies_till_first_fqs) +
453 2 * READ_ONCE(jiffies_till_next_fqs);
454 if (j < HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV)
455 j = HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
456 pr_info("RCU calculated value of scheduler-enlistment delay is %ld jiffies.\n", j);
457 WRITE_ONCE(jiffies_to_sched_qs, j);
458}
459
460static int param_set_first_fqs_jiffies(const char *val, const struct kernel_param *kp)
461{
462 ulong j;
463 int ret = kstrtoul(val, 0, &j);
464
465 if (!ret) {
466 WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : j);
467 adjust_jiffies_till_sched_qs();
468 }
469 return ret;
470}
471
472static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param *kp)
473{
474 ulong j;
475 int ret = kstrtoul(val, 0, &j);
476
477 if (!ret) {
478 WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : (j ?: 1));
479 adjust_jiffies_till_sched_qs();
480 }
481 return ret;
482}
483
484static struct kernel_param_ops first_fqs_jiffies_ops = {
485 .set = param_set_first_fqs_jiffies,
486 .get = param_get_ulong,
487};
488
489static struct kernel_param_ops next_fqs_jiffies_ops = {
490 .set = param_set_next_fqs_jiffies,
491 .get = param_get_ulong,
492};
493
494module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, &jiffies_till_first_fqs, 0644);
495module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next_fqs, 0644);
496module_param(rcu_kick_kthreads, bool, 0644);
497
498static void force_qs_rnp(int (*f)(struct rcu_data *rdp));
499static int rcu_pending(void);
500
501/*
502 * Return the number of RCU GPs completed thus far for debug & stats.
503 */
504unsigned long rcu_get_gp_seq(void)
505{
506 return READ_ONCE(rcu_state.gp_seq);
507}
508EXPORT_SYMBOL_GPL(rcu_get_gp_seq);
509
510/*
511 * Return the number of RCU expedited batches completed thus far for
512 * debug & stats. Odd numbers mean that a batch is in progress, even
513 * numbers mean idle. The value returned will thus be roughly double
514 * the cumulative batches since boot.
515 */
516unsigned long rcu_exp_batches_completed(void)
517{
518 return rcu_state.expedited_sequence;
519}
520EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
521
522/*
523 * Return the root node of the rcu_state structure.
524 */
525static struct rcu_node *rcu_get_root(void)
526{
527 return &rcu_state.node[0];
528}
529
530/*
531 * Convert a ->gp_state value to a character string.
532 */
533static const char *gp_state_getname(short gs)
534{
535 if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
536 return "???";
537 return gp_state_names[gs];
538}
539
540/*
541 * Send along grace-period-related data for rcutorture diagnostics.
542 */
543void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
544 unsigned long *gp_seq)
545{
546 switch (test_type) {
547 case RCU_FLAVOR:
548 *flags = READ_ONCE(rcu_state.gp_flags);
549 *gp_seq = rcu_seq_current(&rcu_state.gp_seq);
550 break;
551 default:
552 break;
553 }
554}
555EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
556
557/*
558 * Enter an RCU extended quiescent state, which can be either the
559 * idle loop or adaptive-tickless usermode execution.
560 *
561 * We crowbar the ->dynticks_nmi_nesting field to zero to allow for
562 * the possibility of usermode upcalls having messed up our count
563 * of interrupt nesting level during the prior busy period.
564 */
565static void rcu_eqs_enter(bool user)
566{
567 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
568
569 WARN_ON_ONCE(rdp->dynticks_nmi_nesting != DYNTICK_IRQ_NONIDLE);
570 WRITE_ONCE(rdp->dynticks_nmi_nesting, 0);
571 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
572 rdp->dynticks_nesting == 0);
573 if (rdp->dynticks_nesting != 1) {
574 rdp->dynticks_nesting--;
575 return;
576 }
577
578 lockdep_assert_irqs_disabled();
579 trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, rdp->dynticks);
580 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
581 rdp = this_cpu_ptr(&rcu_data);
582 do_nocb_deferred_wakeup(rdp);
583 rcu_prepare_for_idle();
584 rcu_preempt_deferred_qs(current);
585 WRITE_ONCE(rdp->dynticks_nesting, 0); /* Avoid irq-access tearing. */
586 rcu_dynticks_eqs_enter();
587 rcu_dynticks_task_enter();
588}
589
590/**
591 * rcu_idle_enter - inform RCU that current CPU is entering idle
592 *
593 * Enter idle mode, in other words, -leave- the mode in which RCU
594 * read-side critical sections can occur. (Though RCU read-side
595 * critical sections can occur in irq handlers in idle, a possibility
596 * handled by irq_enter() and irq_exit().)
597 *
598 * If you add or remove a call to rcu_idle_enter(), be sure to test with
599 * CONFIG_RCU_EQS_DEBUG=y.
600 */
601void rcu_idle_enter(void)
602{
603 lockdep_assert_irqs_disabled();
604 rcu_eqs_enter(false);
605}
606
607#ifdef CONFIG_NO_HZ_FULL
608/**
609 * rcu_user_enter - inform RCU that we are resuming userspace.
610 *
611 * Enter RCU idle mode right before resuming userspace. No use of RCU
612 * is permitted between this call and rcu_user_exit(). This way the
613 * CPU doesn't need to maintain the tick for RCU maintenance purposes
614 * when the CPU runs in userspace.
615 *
616 * If you add or remove a call to rcu_user_enter(), be sure to test with
617 * CONFIG_RCU_EQS_DEBUG=y.
618 */
619void rcu_user_enter(void)
620{
621 lockdep_assert_irqs_disabled();
622 rcu_eqs_enter(true);
623}
624#endif /* CONFIG_NO_HZ_FULL */
625
626/*
627 * If we are returning from the outermost NMI handler that interrupted an
628 * RCU-idle period, update rdp->dynticks and rdp->dynticks_nmi_nesting
629 * to let the RCU grace-period handling know that the CPU is back to
630 * being RCU-idle.
631 *
632 * If you add or remove a call to rcu_nmi_exit_common(), be sure to test
633 * with CONFIG_RCU_EQS_DEBUG=y.
634 */
635static __always_inline void rcu_nmi_exit_common(bool irq)
636{
637 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
638
639 /*
640 * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
641 * (We are exiting an NMI handler, so RCU better be paying attention
642 * to us!)
643 */
644 WARN_ON_ONCE(rdp->dynticks_nmi_nesting <= 0);
645 WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs());
646
647 /*
648 * If the nesting level is not 1, the CPU wasn't RCU-idle, so
649 * leave it in non-RCU-idle state.
650 */
651 if (rdp->dynticks_nmi_nesting != 1) {
652 trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2, rdp->dynticks);
653 WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */
654 rdp->dynticks_nmi_nesting - 2);
655 return;
656 }
657
658 /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
659 trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, rdp->dynticks);
660 WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
661
662 if (irq)
663 rcu_prepare_for_idle();
664
665 rcu_dynticks_eqs_enter();
666
667 if (irq)
668 rcu_dynticks_task_enter();
669}
670
671/**
672 * rcu_nmi_exit - inform RCU of exit from NMI context
673 *
674 * If you add or remove a call to rcu_nmi_exit(), be sure to test
675 * with CONFIG_RCU_EQS_DEBUG=y.
676 */
677void rcu_nmi_exit(void)
678{
679 rcu_nmi_exit_common(false);
680}
681
682/**
683 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
684 *
685 * Exit from an interrupt handler, which might possibly result in entering
686 * idle mode, in other words, leaving the mode in which read-side critical
687 * sections can occur. The caller must have disabled interrupts.
688 *
689 * This code assumes that the idle loop never does anything that might
690 * result in unbalanced calls to irq_enter() and irq_exit(). If your
691 * architecture's idle loop violates this assumption, RCU will give you what
692 * you deserve, good and hard. But very infrequently and irreproducibly.
693 *
694 * Use things like work queues to work around this limitation.
695 *
696 * You have been warned.
697 *
698 * If you add or remove a call to rcu_irq_exit(), be sure to test with
699 * CONFIG_RCU_EQS_DEBUG=y.
700 */
701void rcu_irq_exit(void)
702{
703 lockdep_assert_irqs_disabled();
704 rcu_nmi_exit_common(true);
705}
706
707/*
708 * Wrapper for rcu_irq_exit() where interrupts are enabled.
709 *
710 * If you add or remove a call to rcu_irq_exit_irqson(), be sure to test
711 * with CONFIG_RCU_EQS_DEBUG=y.
712 */
713void rcu_irq_exit_irqson(void)
714{
715 unsigned long flags;
716
717 local_irq_save(flags);
718 rcu_irq_exit();
719 local_irq_restore(flags);
720}
721
722/*
723 * Exit an RCU extended quiescent state, which can be either the
724 * idle loop or adaptive-tickless usermode execution.
725 *
726 * We crowbar the ->dynticks_nmi_nesting field to DYNTICK_IRQ_NONIDLE to
727 * allow for the possibility of usermode upcalls messing up our count of
728 * interrupt nesting level during the busy period that is just now starting.
729 */
730static void rcu_eqs_exit(bool user)
731{
732 struct rcu_data *rdp;
733 long oldval;
734
735 lockdep_assert_irqs_disabled();
736 rdp = this_cpu_ptr(&rcu_data);
737 oldval = rdp->dynticks_nesting;
738 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
739 if (oldval) {
740 rdp->dynticks_nesting++;
741 return;
742 }
743 rcu_dynticks_task_exit();
744 rcu_dynticks_eqs_exit();
745 rcu_cleanup_after_idle();
746 trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, rdp->dynticks);
747 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
748 WRITE_ONCE(rdp->dynticks_nesting, 1);
749 WARN_ON_ONCE(rdp->dynticks_nmi_nesting);
750 WRITE_ONCE(rdp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE);
751}
752
753/**
754 * rcu_idle_exit - inform RCU that current CPU is leaving idle
755 *
756 * Exit idle mode, in other words, -enter- the mode in which RCU
757 * read-side critical sections can occur.
758 *
759 * If you add or remove a call to rcu_idle_exit(), be sure to test with
760 * CONFIG_RCU_EQS_DEBUG=y.
761 */
762void rcu_idle_exit(void)
763{
764 unsigned long flags;
765
766 local_irq_save(flags);
767 rcu_eqs_exit(false);
768 local_irq_restore(flags);
769}
770
771#ifdef CONFIG_NO_HZ_FULL
772/**
773 * rcu_user_exit - inform RCU that we are exiting userspace.
774 *
775 * Exit RCU idle mode while entering the kernel because it can
776 * run a RCU read side critical section anytime.
777 *
778 * If you add or remove a call to rcu_user_exit(), be sure to test with
779 * CONFIG_RCU_EQS_DEBUG=y.
780 */
781void rcu_user_exit(void)
782{
783 rcu_eqs_exit(1);
784}
785#endif /* CONFIG_NO_HZ_FULL */
786
787/**
788 * rcu_nmi_enter_common - inform RCU of entry to NMI context
789 * @irq: Is this call from rcu_irq_enter?
790 *
791 * If the CPU was idle from RCU's viewpoint, update rdp->dynticks and
792 * rdp->dynticks_nmi_nesting to let the RCU grace-period handling know
793 * that the CPU is active. This implementation permits nested NMIs, as
794 * long as the nesting level does not overflow an int. (You will probably
795 * run out of stack space first.)
796 *
797 * If you add or remove a call to rcu_nmi_enter_common(), be sure to test
798 * with CONFIG_RCU_EQS_DEBUG=y.
799 */
800static __always_inline void rcu_nmi_enter_common(bool irq)
801{
802 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
803 long incby = 2;
804
805 /* Complain about underflow. */
806 WARN_ON_ONCE(rdp->dynticks_nmi_nesting < 0);
807
808 /*
809 * If idle from RCU viewpoint, atomically increment ->dynticks
810 * to mark non-idle and increment ->dynticks_nmi_nesting by one.
811 * Otherwise, increment ->dynticks_nmi_nesting by two. This means
812 * if ->dynticks_nmi_nesting is equal to one, we are guaranteed
813 * to be in the outermost NMI handler that interrupted an RCU-idle
814 * period (observation due to Andy Lutomirski).
815 */
816 if (rcu_dynticks_curr_cpu_in_eqs()) {
817
818 if (irq)
819 rcu_dynticks_task_exit();
820
821 rcu_dynticks_eqs_exit();
822
823 if (irq)
824 rcu_cleanup_after_idle();
825
826 incby = 1;
827 }
828 trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
829 rdp->dynticks_nmi_nesting,
830 rdp->dynticks_nmi_nesting + incby, rdp->dynticks);
831 WRITE_ONCE(rdp->dynticks_nmi_nesting, /* Prevent store tearing. */
832 rdp->dynticks_nmi_nesting + incby);
833 barrier();
834}
835
836/**
837 * rcu_nmi_enter - inform RCU of entry to NMI context
838 */
839void rcu_nmi_enter(void)
840{
841 rcu_nmi_enter_common(false);
842}
843NOKPROBE_SYMBOL(rcu_nmi_enter);
844
845/**
846 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
847 *
848 * Enter an interrupt handler, which might possibly result in exiting
849 * idle mode, in other words, entering the mode in which read-side critical
850 * sections can occur. The caller must have disabled interrupts.
851 *
852 * Note that the Linux kernel is fully capable of entering an interrupt
853 * handler that it never exits, for example when doing upcalls to user mode!
854 * This code assumes that the idle loop never does upcalls to user mode.
855 * If your architecture's idle loop does do upcalls to user mode (or does
856 * anything else that results in unbalanced calls to the irq_enter() and
857 * irq_exit() functions), RCU will give you what you deserve, good and hard.
858 * But very infrequently and irreproducibly.
859 *
860 * Use things like work queues to work around this limitation.
861 *
862 * You have been warned.
863 *
864 * If you add or remove a call to rcu_irq_enter(), be sure to test with
865 * CONFIG_RCU_EQS_DEBUG=y.
866 */
867void rcu_irq_enter(void)
868{
869 lockdep_assert_irqs_disabled();
870 rcu_nmi_enter_common(true);
871}
872
873/*
874 * Wrapper for rcu_irq_enter() where interrupts are enabled.
875 *
876 * If you add or remove a call to rcu_irq_enter_irqson(), be sure to test
877 * with CONFIG_RCU_EQS_DEBUG=y.
878 */
879void rcu_irq_enter_irqson(void)
880{
881 unsigned long flags;
882
883 local_irq_save(flags);
884 rcu_irq_enter();
885 local_irq_restore(flags);
886}
887
888/**
889 * rcu_is_watching - see if RCU thinks that the current CPU is not idle
890 *
891 * Return true if RCU is watching the running CPU, which means that this
892 * CPU can safely enter RCU read-side critical sections. In other words,
893 * if the current CPU is not in its idle loop or is in an interrupt or
894 * NMI handler, return true.
895 */
896bool notrace rcu_is_watching(void)
897{
898 bool ret;
899
900 preempt_disable_notrace();
901 ret = !rcu_dynticks_curr_cpu_in_eqs();
902 preempt_enable_notrace();
903 return ret;
904}
905EXPORT_SYMBOL_GPL(rcu_is_watching);
906
907/*
908 * If a holdout task is actually running, request an urgent quiescent
909 * state from its CPU. This is unsynchronized, so migrations can cause
910 * the request to go to the wrong CPU. Which is OK, all that will happen
911 * is that the CPU's next context switch will be a bit slower and next
912 * time around this task will generate another request.
913 */
914void rcu_request_urgent_qs_task(struct task_struct *t)
915{
916 int cpu;
917
918 barrier();
919 cpu = task_cpu(t);
920 if (!task_curr(t))
921 return; /* This task is not running on that CPU. */
922 smp_store_release(per_cpu_ptr(&rcu_data.rcu_urgent_qs, cpu), true);
923}
924
925#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
926
927/*
928 * Is the current CPU online as far as RCU is concerned?
929 *
930 * Disable preemption to avoid false positives that could otherwise
931 * happen due to the current CPU number being sampled, this task being
932 * preempted, its old CPU being taken offline, resuming on some other CPU,
933 * then determining that its old CPU is now offline.
934 *
935 * Disable checking if in an NMI handler because we cannot safely
936 * report errors from NMI handlers anyway. In addition, it is OK to use
937 * RCU on an offline processor during initial boot, hence the check for
938 * rcu_scheduler_fully_active.
939 */
940bool rcu_lockdep_current_cpu_online(void)
941{
942 struct rcu_data *rdp;
943 struct rcu_node *rnp;
944 bool ret = false;
945
946 if (in_nmi() || !rcu_scheduler_fully_active)
947 return true;
948 preempt_disable();
949 rdp = this_cpu_ptr(&rcu_data);
950 rnp = rdp->mynode;
951 if (rdp->grpmask & rcu_rnp_online_cpus(rnp))
952 ret = true;
953 preempt_enable();
954 return ret;
955}
956EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
957
958#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
959
960/*
961 * We are reporting a quiescent state on behalf of some other CPU, so
962 * it is our responsibility to check for and handle potential overflow
963 * of the rcu_node ->gp_seq counter with respect to the rcu_data counters.
964 * After all, the CPU might be in deep idle state, and thus executing no
965 * code whatsoever.
966 */
967static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
968{
969 raw_lockdep_assert_held_rcu_node(rnp);
970 if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + ULONG_MAX / 4,
971 rnp->gp_seq))
972 WRITE_ONCE(rdp->gpwrap, true);
973 if (ULONG_CMP_LT(rdp->rcu_iw_gp_seq + ULONG_MAX / 4, rnp->gp_seq))
974 rdp->rcu_iw_gp_seq = rnp->gp_seq + ULONG_MAX / 4;
975}
976
977/*
978 * Snapshot the specified CPU's dynticks counter so that we can later
979 * credit them with an implicit quiescent state. Return 1 if this CPU
980 * is in dynticks idle mode, which is an extended quiescent state.
981 */
982static int dyntick_save_progress_counter(struct rcu_data *rdp)
983{
984 rdp->dynticks_snap = rcu_dynticks_snap(rdp);
985 if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
986 trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
987 rcu_gpnum_ovf(rdp->mynode, rdp);
988 return 1;
989 }
990 return 0;
991}
992
993/*
994 * Return true if the specified CPU has passed through a quiescent
995 * state by virtue of being in or having passed through an dynticks
996 * idle state since the last call to dyntick_save_progress_counter()
997 * for this same CPU, or by virtue of having been offline.
998 */
999static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
1000{
1001 unsigned long jtsq;
1002 bool *rnhqp;
1003 bool *ruqp;
1004 struct rcu_node *rnp = rdp->mynode;
1005
1006 /*
1007 * If the CPU passed through or entered a dynticks idle phase with
1008 * no active irq/NMI handlers, then we can safely pretend that the CPU
1009 * already acknowledged the request to pass through a quiescent
1010 * state. Either way, that CPU cannot possibly be in an RCU
1011 * read-side critical section that started before the beginning
1012 * of the current RCU grace period.
1013 */
1014 if (rcu_dynticks_in_eqs_since(rdp, rdp->dynticks_snap)) {
1015 trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
1016 rcu_gpnum_ovf(rnp, rdp);
1017 return 1;
1018 }
1019
1020 /* If waiting too long on an offline CPU, complain. */
1021 if (!(rdp->grpmask & rcu_rnp_online_cpus(rnp)) &&
1022 time_after(jiffies, rcu_state.gp_start + HZ)) {
1023 bool onl;
1024 struct rcu_node *rnp1;
1025
1026 WARN_ON(1); /* Offline CPUs are supposed to report QS! */
1027 pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
1028 __func__, rnp->grplo, rnp->grphi, rnp->level,
1029 (long)rnp->gp_seq, (long)rnp->completedqs);
1030 for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
1031 pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx ->rcu_gp_init_mask %#lx\n",
1032 __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext, rnp1->rcu_gp_init_mask);
1033 onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
1034 pr_info("%s %d: %c online: %ld(%d) offline: %ld(%d)\n",
1035 __func__, rdp->cpu, ".o"[onl],
1036 (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
1037 (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
1038 return 1; /* Break things loose after complaining. */
1039 }
1040
1041 /*
1042 * A CPU running for an extended time within the kernel can
1043 * delay RCU grace periods: (1) At age jiffies_to_sched_qs,
1044 * set .rcu_urgent_qs, (2) At age 2*jiffies_to_sched_qs, set
1045 * both .rcu_need_heavy_qs and .rcu_urgent_qs. Note that the
1046 * unsynchronized assignments to the per-CPU rcu_need_heavy_qs
1047 * variable are safe because the assignments are repeated if this
1048 * CPU failed to pass through a quiescent state. This code
1049 * also checks .jiffies_resched in case jiffies_to_sched_qs
1050 * is set way high.
1051 */
1052 jtsq = READ_ONCE(jiffies_to_sched_qs);
1053 ruqp = per_cpu_ptr(&rcu_data.rcu_urgent_qs, rdp->cpu);
1054 rnhqp = &per_cpu(rcu_data.rcu_need_heavy_qs, rdp->cpu);
1055 if (!READ_ONCE(*rnhqp) &&
1056 (time_after(jiffies, rcu_state.gp_start + jtsq * 2) ||
1057 time_after(jiffies, rcu_state.jiffies_resched))) {
1058 WRITE_ONCE(*rnhqp, true);
1059 /* Store rcu_need_heavy_qs before rcu_urgent_qs. */
1060 smp_store_release(ruqp, true);
1061 } else if (time_after(jiffies, rcu_state.gp_start + jtsq)) {
1062 WRITE_ONCE(*ruqp, true);
1063 }
1064
1065 /*
1066 * NO_HZ_FULL CPUs can run in-kernel without rcu_sched_clock_irq!
1067 * The above code handles this, but only for straight cond_resched().
1068 * And some in-kernel loops check need_resched() before calling
1069 * cond_resched(), which defeats the above code for CPUs that are
1070 * running in-kernel with scheduling-clock interrupts disabled.
1071 * So hit them over the head with the resched_cpu() hammer!
1072 */
1073 if (tick_nohz_full_cpu(rdp->cpu) &&
1074 time_after(jiffies,
1075 READ_ONCE(rdp->last_fqs_resched) + jtsq * 3)) {
1076 resched_cpu(rdp->cpu);
1077 WRITE_ONCE(rdp->last_fqs_resched, jiffies);
1078 }
1079
1080 /*
1081 * If more than halfway to RCU CPU stall-warning time, invoke
1082 * resched_cpu() more frequently to try to loosen things up a bit.
1083 * Also check to see if the CPU is getting hammered with interrupts,
1084 * but only once per grace period, just to keep the IPIs down to
1085 * a dull roar.
1086 */
1087 if (time_after(jiffies, rcu_state.jiffies_resched)) {
1088 if (time_after(jiffies,
1089 READ_ONCE(rdp->last_fqs_resched) + jtsq)) {
1090 resched_cpu(rdp->cpu);
1091 WRITE_ONCE(rdp->last_fqs_resched, jiffies);
1092 }
1093 if (IS_ENABLED(CONFIG_IRQ_WORK) &&
1094 !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
1095 (rnp->ffmask & rdp->grpmask)) {
1096 init_irq_work(&rdp->rcu_iw, rcu_iw_handler);
1097 rdp->rcu_iw_pending = true;
1098 rdp->rcu_iw_gp_seq = rnp->gp_seq;
1099 irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
1100 }
1101 }
1102
1103 return 0;
1104}
1105
1106/* Trace-event wrapper function for trace_rcu_future_grace_period. */
1107static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1108 unsigned long gp_seq_req, const char *s)
1109{
1110 trace_rcu_future_grace_period(rcu_state.name, rnp->gp_seq, gp_seq_req,
1111 rnp->level, rnp->grplo, rnp->grphi, s);
1112}
1113
1114/*
1115 * rcu_start_this_gp - Request the start of a particular grace period
1116 * @rnp_start: The leaf node of the CPU from which to start.
1117 * @rdp: The rcu_data corresponding to the CPU from which to start.
1118 * @gp_seq_req: The gp_seq of the grace period to start.
1119 *
1120 * Start the specified grace period, as needed to handle newly arrived
1121 * callbacks. The required future grace periods are recorded in each
1122 * rcu_node structure's ->gp_seq_needed field. Returns true if there
1123 * is reason to awaken the grace-period kthread.
1124 *
1125 * The caller must hold the specified rcu_node structure's ->lock, which
1126 * is why the caller is responsible for waking the grace-period kthread.
1127 *
1128 * Returns true if the GP thread needs to be awakened else false.
1129 */
1130static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp,
1131 unsigned long gp_seq_req)
1132{
1133 bool ret = false;
1134 struct rcu_node *rnp;
1135
1136 /*
1137 * Use funnel locking to either acquire the root rcu_node
1138 * structure's lock or bail out if the need for this grace period
1139 * has already been recorded -- or if that grace period has in
1140 * fact already started. If there is already a grace period in
1141 * progress in a non-leaf node, no recording is needed because the
1142 * end of the grace period will scan the leaf rcu_node structures.
1143 * Note that rnp_start->lock must not be released.
1144 */
1145 raw_lockdep_assert_held_rcu_node(rnp_start);
1146 trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startleaf"));
1147 for (rnp = rnp_start; 1; rnp = rnp->parent) {
1148 if (rnp != rnp_start)
1149 raw_spin_lock_rcu_node(rnp);
1150 if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req) ||
1151 rcu_seq_started(&rnp->gp_seq, gp_seq_req) ||
1152 (rnp != rnp_start &&
1153 rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))) {
1154 trace_rcu_this_gp(rnp, rdp, gp_seq_req,
1155 TPS("Prestarted"));
1156 goto unlock_out;
1157 }
1158 rnp->gp_seq_needed = gp_seq_req;
1159 if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) {
1160 /*
1161 * We just marked the leaf or internal node, and a
1162 * grace period is in progress, which means that
1163 * rcu_gp_cleanup() will see the marking. Bail to
1164 * reduce contention.
1165 */
1166 trace_rcu_this_gp(rnp_start, rdp, gp_seq_req,
1167 TPS("Startedleaf"));
1168 goto unlock_out;
1169 }
1170 if (rnp != rnp_start && rnp->parent != NULL)
1171 raw_spin_unlock_rcu_node(rnp);
1172 if (!rnp->parent)
1173 break; /* At root, and perhaps also leaf. */
1174 }
1175
1176 /* If GP already in progress, just leave, otherwise start one. */
1177 if (rcu_gp_in_progress()) {
1178 trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedleafroot"));
1179 goto unlock_out;
1180 }
1181 trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot"));
1182 WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT);
1183 rcu_state.gp_req_activity = jiffies;
1184 if (!rcu_state.gp_kthread) {
1185 trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread"));
1186 goto unlock_out;
1187 }
1188 trace_rcu_grace_period(rcu_state.name, READ_ONCE(rcu_state.gp_seq), TPS("newreq"));
1189 ret = true; /* Caller must wake GP kthread. */
1190unlock_out:
1191 /* Push furthest requested GP to leaf node and rcu_data structure. */
1192 if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) {
1193 rnp_start->gp_seq_needed = rnp->gp_seq_needed;
1194 rdp->gp_seq_needed = rnp->gp_seq_needed;
1195 }
1196 if (rnp != rnp_start)
1197 raw_spin_unlock_rcu_node(rnp);
1198 return ret;
1199}
1200
1201/*
1202 * Clean up any old requests for the just-ended grace period. Also return
1203 * whether any additional grace periods have been requested.
1204 */
1205static bool rcu_future_gp_cleanup(struct rcu_node *rnp)
1206{
1207 bool needmore;
1208 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1209
1210 needmore = ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed);
1211 if (!needmore)
1212 rnp->gp_seq_needed = rnp->gp_seq; /* Avoid counter wrap. */
1213 trace_rcu_this_gp(rnp, rdp, rnp->gp_seq,
1214 needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1215 return needmore;
1216}
1217
1218/*
1219 * Awaken the grace-period kthread. Don't do a self-awaken (unless in
1220 * an interrupt or softirq handler), and don't bother awakening when there
1221 * is nothing for the grace-period kthread to do (as in several CPUs raced
1222 * to awaken, and we lost), and finally don't try to awaken a kthread that
1223 * has not yet been created. If all those checks are passed, track some
1224 * debug information and awaken.
1225 *
1226 * So why do the self-wakeup when in an interrupt or softirq handler
1227 * in the grace-period kthread's context? Because the kthread might have
1228 * been interrupted just as it was going to sleep, and just after the final
1229 * pre-sleep check of the awaken condition. In this case, a wakeup really
1230 * is required, and is therefore supplied.
1231 */
1232static void rcu_gp_kthread_wake(void)
1233{
1234 if ((current == rcu_state.gp_kthread &&
1235 !in_irq() && !in_serving_softirq()) ||
1236 !READ_ONCE(rcu_state.gp_flags) ||
1237 !rcu_state.gp_kthread)
1238 return;
1239 WRITE_ONCE(rcu_state.gp_wake_time, jiffies);
1240 WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq));
1241 swake_up_one(&rcu_state.gp_wq);
1242}
1243
1244/*
1245 * If there is room, assign a ->gp_seq number to any callbacks on this
1246 * CPU that have not already been assigned. Also accelerate any callbacks
1247 * that were previously assigned a ->gp_seq number that has since proven
1248 * to be too conservative, which can happen if callbacks get assigned a
1249 * ->gp_seq number while RCU is idle, but with reference to a non-root
1250 * rcu_node structure. This function is idempotent, so it does not hurt
1251 * to call it repeatedly. Returns an flag saying that we should awaken
1252 * the RCU grace-period kthread.
1253 *
1254 * The caller must hold rnp->lock with interrupts disabled.
1255 */
1256static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
1257{
1258 unsigned long gp_seq_req;
1259 bool ret = false;
1260
1261 rcu_lockdep_assert_cblist_protected(rdp);
1262 raw_lockdep_assert_held_rcu_node(rnp);
1263
1264 /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
1265 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1266 return false;
1267
1268 /*
1269 * Callbacks are often registered with incomplete grace-period
1270 * information. Something about the fact that getting exact
1271 * information requires acquiring a global lock... RCU therefore
1272 * makes a conservative estimate of the grace period number at which
1273 * a given callback will become ready to invoke. The following
1274 * code checks this estimate and improves it when possible, thus
1275 * accelerating callback invocation to an earlier grace-period
1276 * number.
1277 */
1278 gp_seq_req = rcu_seq_snap(&rcu_state.gp_seq);
1279 if (rcu_segcblist_accelerate(&rdp->cblist, gp_seq_req))
1280 ret = rcu_start_this_gp(rnp, rdp, gp_seq_req);
1281
1282 /* Trace depending on how much we were able to accelerate. */
1283 if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
1284 trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("AccWaitCB"));
1285 else
1286 trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("AccReadyCB"));
1287 return ret;
1288}
1289
1290/*
1291 * Similar to rcu_accelerate_cbs(), but does not require that the leaf
1292 * rcu_node structure's ->lock be held. It consults the cached value
1293 * of ->gp_seq_needed in the rcu_data structure, and if that indicates
1294 * that a new grace-period request be made, invokes rcu_accelerate_cbs()
1295 * while holding the leaf rcu_node structure's ->lock.
1296 */
1297static void rcu_accelerate_cbs_unlocked(struct rcu_node *rnp,
1298 struct rcu_data *rdp)
1299{
1300 unsigned long c;
1301 bool needwake;
1302
1303 rcu_lockdep_assert_cblist_protected(rdp);
1304 c = rcu_seq_snap(&rcu_state.gp_seq);
1305 if (!rdp->gpwrap && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {
1306 /* Old request still live, so mark recent callbacks. */
1307 (void)rcu_segcblist_accelerate(&rdp->cblist, c);
1308 return;
1309 }
1310 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
1311 needwake = rcu_accelerate_cbs(rnp, rdp);
1312 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
1313 if (needwake)
1314 rcu_gp_kthread_wake();
1315}
1316
1317/*
1318 * Move any callbacks whose grace period has completed to the
1319 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1320 * assign ->gp_seq numbers to any callbacks in the RCU_NEXT_TAIL
1321 * sublist. This function is idempotent, so it does not hurt to
1322 * invoke it repeatedly. As long as it is not invoked -too- often...
1323 * Returns true if the RCU grace-period kthread needs to be awakened.
1324 *
1325 * The caller must hold rnp->lock with interrupts disabled.
1326 */
1327static bool rcu_advance_cbs(struct rcu_node *rnp, struct rcu_data *rdp)
1328{
1329 rcu_lockdep_assert_cblist_protected(rdp);
1330 raw_lockdep_assert_held_rcu_node(rnp);
1331
1332 /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
1333 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1334 return false;
1335
1336 /*
1337 * Find all callbacks whose ->gp_seq numbers indicate that they
1338 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1339 */
1340 rcu_segcblist_advance(&rdp->cblist, rnp->gp_seq);
1341
1342 /* Classify any remaining callbacks. */
1343 return rcu_accelerate_cbs(rnp, rdp);
1344}
1345
1346/*
1347 * Move and classify callbacks, but only if doing so won't require
1348 * that the RCU grace-period kthread be awakened.
1349 */
1350static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp,
1351 struct rcu_data *rdp)
1352{
1353 rcu_lockdep_assert_cblist_protected(rdp);
1354 if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) ||
1355 !raw_spin_trylock_rcu_node(rnp))
1356 return;
1357 WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp));
1358 raw_spin_unlock_rcu_node(rnp);
1359}
1360
1361/*
1362 * Update CPU-local rcu_data state to record the beginnings and ends of
1363 * grace periods. The caller must hold the ->lock of the leaf rcu_node
1364 * structure corresponding to the current CPU, and must have irqs disabled.
1365 * Returns true if the grace-period kthread needs to be awakened.
1366 */
1367static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp)
1368{
1369 bool ret = false;
1370 bool need_gp;
1371 const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
1372 rcu_segcblist_is_offloaded(&rdp->cblist);
1373
1374 raw_lockdep_assert_held_rcu_node(rnp);
1375
1376 if (rdp->gp_seq == rnp->gp_seq)
1377 return false; /* Nothing to do. */
1378
1379 /* Handle the ends of any preceding grace periods first. */
1380 if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) ||
1381 unlikely(READ_ONCE(rdp->gpwrap))) {
1382 if (!offloaded)
1383 ret = rcu_advance_cbs(rnp, rdp); /* Advance CBs. */
1384 trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuend"));
1385 } else {
1386 if (!offloaded)
1387 ret = rcu_accelerate_cbs(rnp, rdp); /* Recent CBs. */
1388 }
1389
1390 /* Now handle the beginnings of any new-to-this-CPU grace periods. */
1391 if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) ||
1392 unlikely(READ_ONCE(rdp->gpwrap))) {
1393 /*
1394 * If the current grace period is waiting for this CPU,
1395 * set up to detect a quiescent state, otherwise don't
1396 * go looking for one.
1397 */
1398 trace_rcu_grace_period(rcu_state.name, rnp->gp_seq, TPS("cpustart"));
1399 need_gp = !!(rnp->qsmask & rdp->grpmask);
1400 rdp->cpu_no_qs.b.norm = need_gp;
1401 rdp->core_needs_qs = need_gp;
1402 zero_cpu_stall_ticks(rdp);
1403 }
1404 rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */
1405 if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap)
1406 rdp->gp_seq_needed = rnp->gp_seq_needed;
1407 WRITE_ONCE(rdp->gpwrap, false);
1408 rcu_gpnum_ovf(rnp, rdp);
1409 return ret;
1410}
1411
1412static void note_gp_changes(struct rcu_data *rdp)
1413{
1414 unsigned long flags;
1415 bool needwake;
1416 struct rcu_node *rnp;
1417
1418 local_irq_save(flags);
1419 rnp = rdp->mynode;
1420 if ((rdp->gp_seq == rcu_seq_current(&rnp->gp_seq) &&
1421 !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
1422 !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
1423 local_irq_restore(flags);
1424 return;
1425 }
1426 needwake = __note_gp_changes(rnp, rdp);
1427 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1428 if (needwake)
1429 rcu_gp_kthread_wake();
1430}
1431
1432static void rcu_gp_slow(int delay)
1433{
1434 if (delay > 0 &&
1435 !(rcu_seq_ctr(rcu_state.gp_seq) %
1436 (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
1437 schedule_timeout_uninterruptible(delay);
1438}
1439
1440/*
1441 * Initialize a new grace period. Return false if no grace period required.
1442 */
1443static bool rcu_gp_init(void)
1444{
1445 unsigned long flags;
1446 unsigned long oldmask;
1447 unsigned long mask;
1448 struct rcu_data *rdp;
1449 struct rcu_node *rnp = rcu_get_root();
1450
1451 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1452 raw_spin_lock_irq_rcu_node(rnp);
1453 if (!READ_ONCE(rcu_state.gp_flags)) {
1454 /* Spurious wakeup, tell caller to go back to sleep. */
1455 raw_spin_unlock_irq_rcu_node(rnp);
1456 return false;
1457 }
1458 WRITE_ONCE(rcu_state.gp_flags, 0); /* Clear all flags: New GP. */
1459
1460 if (WARN_ON_ONCE(rcu_gp_in_progress())) {
1461 /*
1462 * Grace period already in progress, don't start another.
1463 * Not supposed to be able to happen.
1464 */
1465 raw_spin_unlock_irq_rcu_node(rnp);
1466 return false;
1467 }
1468
1469 /* Advance to a new grace period and initialize state. */
1470 record_gp_stall_check_time();
1471 /* Record GP times before starting GP, hence rcu_seq_start(). */
1472 rcu_seq_start(&rcu_state.gp_seq);
1473 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start"));
1474 raw_spin_unlock_irq_rcu_node(rnp);
1475
1476 /*
1477 * Apply per-leaf buffered online and offline operations to the
1478 * rcu_node tree. Note that this new grace period need not wait
1479 * for subsequent online CPUs, and that quiescent-state forcing
1480 * will handle subsequent offline CPUs.
1481 */
1482 rcu_state.gp_state = RCU_GP_ONOFF;
1483 rcu_for_each_leaf_node(rnp) {
1484 raw_spin_lock(&rcu_state.ofl_lock);
1485 raw_spin_lock_irq_rcu_node(rnp);
1486 if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
1487 !rnp->wait_blkd_tasks) {
1488 /* Nothing to do on this leaf rcu_node structure. */
1489 raw_spin_unlock_irq_rcu_node(rnp);
1490 raw_spin_unlock(&rcu_state.ofl_lock);
1491 continue;
1492 }
1493
1494 /* Record old state, apply changes to ->qsmaskinit field. */
1495 oldmask = rnp->qsmaskinit;
1496 rnp->qsmaskinit = rnp->qsmaskinitnext;
1497
1498 /* If zero-ness of ->qsmaskinit changed, propagate up tree. */
1499 if (!oldmask != !rnp->qsmaskinit) {
1500 if (!oldmask) { /* First online CPU for rcu_node. */
1501 if (!rnp->wait_blkd_tasks) /* Ever offline? */
1502 rcu_init_new_rnp(rnp);
1503 } else if (rcu_preempt_has_tasks(rnp)) {
1504 rnp->wait_blkd_tasks = true; /* blocked tasks */
1505 } else { /* Last offline CPU and can propagate. */
1506 rcu_cleanup_dead_rnp(rnp);
1507 }
1508 }
1509
1510 /*
1511 * If all waited-on tasks from prior grace period are
1512 * done, and if all this rcu_node structure's CPUs are
1513 * still offline, propagate up the rcu_node tree and
1514 * clear ->wait_blkd_tasks. Otherwise, if one of this
1515 * rcu_node structure's CPUs has since come back online,
1516 * simply clear ->wait_blkd_tasks.
1517 */
1518 if (rnp->wait_blkd_tasks &&
1519 (!rcu_preempt_has_tasks(rnp) || rnp->qsmaskinit)) {
1520 rnp->wait_blkd_tasks = false;
1521 if (!rnp->qsmaskinit)
1522 rcu_cleanup_dead_rnp(rnp);
1523 }
1524
1525 raw_spin_unlock_irq_rcu_node(rnp);
1526 raw_spin_unlock(&rcu_state.ofl_lock);
1527 }
1528 rcu_gp_slow(gp_preinit_delay); /* Races with CPU hotplug. */
1529
1530 /*
1531 * Set the quiescent-state-needed bits in all the rcu_node
1532 * structures for all currently online CPUs in breadth-first
1533 * order, starting from the root rcu_node structure, relying on the
1534 * layout of the tree within the rcu_state.node[] array. Note that
1535 * other CPUs will access only the leaves of the hierarchy, thus
1536 * seeing that no grace period is in progress, at least until the
1537 * corresponding leaf node has been initialized.
1538 *
1539 * The grace period cannot complete until the initialization
1540 * process finishes, because this kthread handles both.
1541 */
1542 rcu_state.gp_state = RCU_GP_INIT;
1543 rcu_for_each_node_breadth_first(rnp) {
1544 rcu_gp_slow(gp_init_delay);
1545 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1546 rdp = this_cpu_ptr(&rcu_data);
1547 rcu_preempt_check_blocked_tasks(rnp);
1548 rnp->qsmask = rnp->qsmaskinit;
1549 WRITE_ONCE(rnp->gp_seq, rcu_state.gp_seq);
1550 if (rnp == rdp->mynode)
1551 (void)__note_gp_changes(rnp, rdp);
1552 rcu_preempt_boost_start_gp(rnp);
1553 trace_rcu_grace_period_init(rcu_state.name, rnp->gp_seq,
1554 rnp->level, rnp->grplo,
1555 rnp->grphi, rnp->qsmask);
1556 /* Quiescent states for tasks on any now-offline CPUs. */
1557 mask = rnp->qsmask & ~rnp->qsmaskinitnext;
1558 rnp->rcu_gp_init_mask = mask;
1559 if ((mask || rnp->wait_blkd_tasks) && rcu_is_leaf_node(rnp))
1560 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
1561 else
1562 raw_spin_unlock_irq_rcu_node(rnp);
1563 cond_resched_tasks_rcu_qs();
1564 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1565 }
1566
1567 return true;
1568}
1569
1570/*
1571 * Helper function for swait_event_idle_exclusive() wakeup at force-quiescent-state
1572 * time.
1573 */
1574static bool rcu_gp_fqs_check_wake(int *gfp)
1575{
1576 struct rcu_node *rnp = rcu_get_root();
1577
1578 /* Someone like call_rcu() requested a force-quiescent-state scan. */
1579 *gfp = READ_ONCE(rcu_state.gp_flags);
1580 if (*gfp & RCU_GP_FLAG_FQS)
1581 return true;
1582
1583 /* The current grace period has completed. */
1584 if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
1585 return true;
1586
1587 return false;
1588}
1589
1590/*
1591 * Do one round of quiescent-state forcing.
1592 */
1593static void rcu_gp_fqs(bool first_time)
1594{
1595 struct rcu_node *rnp = rcu_get_root();
1596
1597 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1598 rcu_state.n_force_qs++;
1599 if (first_time) {
1600 /* Collect dyntick-idle snapshots. */
1601 force_qs_rnp(dyntick_save_progress_counter);
1602 } else {
1603 /* Handle dyntick-idle and offline CPUs. */
1604 force_qs_rnp(rcu_implicit_dynticks_qs);
1605 }
1606 /* Clear flag to prevent immediate re-entry. */
1607 if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
1608 raw_spin_lock_irq_rcu_node(rnp);
1609 WRITE_ONCE(rcu_state.gp_flags,
1610 READ_ONCE(rcu_state.gp_flags) & ~RCU_GP_FLAG_FQS);
1611 raw_spin_unlock_irq_rcu_node(rnp);
1612 }
1613}
1614
1615/*
1616 * Loop doing repeated quiescent-state forcing until the grace period ends.
1617 */
1618static void rcu_gp_fqs_loop(void)
1619{
1620 bool first_gp_fqs;
1621 int gf;
1622 unsigned long j;
1623 int ret;
1624 struct rcu_node *rnp = rcu_get_root();
1625
1626 first_gp_fqs = true;
1627 j = READ_ONCE(jiffies_till_first_fqs);
1628 ret = 0;
1629 for (;;) {
1630 if (!ret) {
1631 rcu_state.jiffies_force_qs = jiffies + j;
1632 WRITE_ONCE(rcu_state.jiffies_kick_kthreads,
1633 jiffies + (j ? 3 * j : 2));
1634 }
1635 trace_rcu_grace_period(rcu_state.name,
1636 READ_ONCE(rcu_state.gp_seq),
1637 TPS("fqswait"));
1638 rcu_state.gp_state = RCU_GP_WAIT_FQS;
1639 ret = swait_event_idle_timeout_exclusive(
1640 rcu_state.gp_wq, rcu_gp_fqs_check_wake(&gf), j);
1641 rcu_state.gp_state = RCU_GP_DOING_FQS;
1642 /* Locking provides needed memory barriers. */
1643 /* If grace period done, leave loop. */
1644 if (!READ_ONCE(rnp->qsmask) &&
1645 !rcu_preempt_blocked_readers_cgp(rnp))
1646 break;
1647 /* If time for quiescent-state forcing, do it. */
1648 if (ULONG_CMP_GE(jiffies, rcu_state.jiffies_force_qs) ||
1649 (gf & RCU_GP_FLAG_FQS)) {
1650 trace_rcu_grace_period(rcu_state.name,
1651 READ_ONCE(rcu_state.gp_seq),
1652 TPS("fqsstart"));
1653 rcu_gp_fqs(first_gp_fqs);
1654 first_gp_fqs = false;
1655 trace_rcu_grace_period(rcu_state.name,
1656 READ_ONCE(rcu_state.gp_seq),
1657 TPS("fqsend"));
1658 cond_resched_tasks_rcu_qs();
1659 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1660 ret = 0; /* Force full wait till next FQS. */
1661 j = READ_ONCE(jiffies_till_next_fqs);
1662 } else {
1663 /* Deal with stray signal. */
1664 cond_resched_tasks_rcu_qs();
1665 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1666 WARN_ON(signal_pending(current));
1667 trace_rcu_grace_period(rcu_state.name,
1668 READ_ONCE(rcu_state.gp_seq),
1669 TPS("fqswaitsig"));
1670 ret = 1; /* Keep old FQS timing. */
1671 j = jiffies;
1672 if (time_after(jiffies, rcu_state.jiffies_force_qs))
1673 j = 1;
1674 else
1675 j = rcu_state.jiffies_force_qs - j;
1676 }
1677 }
1678}
1679
1680/*
1681 * Clean up after the old grace period.
1682 */
1683static void rcu_gp_cleanup(void)
1684{
1685 unsigned long gp_duration;
1686 bool needgp = false;
1687 unsigned long new_gp_seq;
1688 bool offloaded;
1689 struct rcu_data *rdp;
1690 struct rcu_node *rnp = rcu_get_root();
1691 struct swait_queue_head *sq;
1692
1693 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1694 raw_spin_lock_irq_rcu_node(rnp);
1695 rcu_state.gp_end = jiffies;
1696 gp_duration = rcu_state.gp_end - rcu_state.gp_start;
1697 if (gp_duration > rcu_state.gp_max)
1698 rcu_state.gp_max = gp_duration;
1699
1700 /*
1701 * We know the grace period is complete, but to everyone else
1702 * it appears to still be ongoing. But it is also the case
1703 * that to everyone else it looks like there is nothing that
1704 * they can do to advance the grace period. It is therefore
1705 * safe for us to drop the lock in order to mark the grace
1706 * period as completed in all of the rcu_node structures.
1707 */
1708 raw_spin_unlock_irq_rcu_node(rnp);
1709
1710 /*
1711 * Propagate new ->gp_seq value to rcu_node structures so that
1712 * other CPUs don't have to wait until the start of the next grace
1713 * period to process their callbacks. This also avoids some nasty
1714 * RCU grace-period initialization races by forcing the end of
1715 * the current grace period to be completely recorded in all of
1716 * the rcu_node structures before the beginning of the next grace
1717 * period is recorded in any of the rcu_node structures.
1718 */
1719 new_gp_seq = rcu_state.gp_seq;
1720 rcu_seq_end(&new_gp_seq);
1721 rcu_for_each_node_breadth_first(rnp) {
1722 raw_spin_lock_irq_rcu_node(rnp);
1723 if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
1724 dump_blkd_tasks(rnp, 10);
1725 WARN_ON_ONCE(rnp->qsmask);
1726 WRITE_ONCE(rnp->gp_seq, new_gp_seq);
1727 rdp = this_cpu_ptr(&rcu_data);
1728 if (rnp == rdp->mynode)
1729 needgp = __note_gp_changes(rnp, rdp) || needgp;
1730 /* smp_mb() provided by prior unlock-lock pair. */
1731 needgp = rcu_future_gp_cleanup(rnp) || needgp;
1732 sq = rcu_nocb_gp_get(rnp);
1733 raw_spin_unlock_irq_rcu_node(rnp);
1734 rcu_nocb_gp_cleanup(sq);
1735 cond_resched_tasks_rcu_qs();
1736 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1737 rcu_gp_slow(gp_cleanup_delay);
1738 }
1739 rnp = rcu_get_root();
1740 raw_spin_lock_irq_rcu_node(rnp); /* GP before ->gp_seq update. */
1741
1742 /* Declare grace period done, trace first to use old GP number. */
1743 trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end"));
1744 rcu_seq_end(&rcu_state.gp_seq);
1745 rcu_state.gp_state = RCU_GP_IDLE;
1746 /* Check for GP requests since above loop. */
1747 rdp = this_cpu_ptr(&rcu_data);
1748 if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) {
1749 trace_rcu_this_gp(rnp, rdp, rnp->gp_seq_needed,
1750 TPS("CleanupMore"));
1751 needgp = true;
1752 }
1753 /* Advance CBs to reduce false positives below. */
1754 offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
1755 rcu_segcblist_is_offloaded(&rdp->cblist);
1756 if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {
1757 WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT);
1758 rcu_state.gp_req_activity = jiffies;
1759 trace_rcu_grace_period(rcu_state.name,
1760 READ_ONCE(rcu_state.gp_seq),
1761 TPS("newreq"));
1762 } else {
1763 WRITE_ONCE(rcu_state.gp_flags,
1764 rcu_state.gp_flags & RCU_GP_FLAG_INIT);
1765 }
1766 raw_spin_unlock_irq_rcu_node(rnp);
1767}
1768
1769/*
1770 * Body of kthread that handles grace periods.
1771 */
1772static int __noreturn rcu_gp_kthread(void *unused)
1773{
1774 rcu_bind_gp_kthread();
1775 for (;;) {
1776
1777 /* Handle grace-period start. */
1778 for (;;) {
1779 trace_rcu_grace_period(rcu_state.name,
1780 READ_ONCE(rcu_state.gp_seq),
1781 TPS("reqwait"));
1782 rcu_state.gp_state = RCU_GP_WAIT_GPS;
1783 swait_event_idle_exclusive(rcu_state.gp_wq,
1784 READ_ONCE(rcu_state.gp_flags) &
1785 RCU_GP_FLAG_INIT);
1786 rcu_state.gp_state = RCU_GP_DONE_GPS;
1787 /* Locking provides needed memory barrier. */
1788 if (rcu_gp_init())
1789 break;
1790 cond_resched_tasks_rcu_qs();
1791 WRITE_ONCE(rcu_state.gp_activity, jiffies);
1792 WARN_ON(signal_pending(current));
1793 trace_rcu_grace_period(rcu_state.name,
1794 READ_ONCE(rcu_state.gp_seq),
1795 TPS("reqwaitsig"));
1796 }
1797
1798 /* Handle quiescent-state forcing. */
1799 rcu_gp_fqs_loop();
1800
1801 /* Handle grace-period end. */
1802 rcu_state.gp_state = RCU_GP_CLEANUP;
1803 rcu_gp_cleanup();
1804 rcu_state.gp_state = RCU_GP_CLEANED;
1805 }
1806}
1807
1808/*
1809 * Report a full set of quiescent states to the rcu_state data structure.
1810 * Invoke rcu_gp_kthread_wake() to awaken the grace-period kthread if
1811 * another grace period is required. Whether we wake the grace-period
1812 * kthread or it awakens itself for the next round of quiescent-state
1813 * forcing, that kthread will clean up after the just-completed grace
1814 * period. Note that the caller must hold rnp->lock, which is released
1815 * before return.
1816 */
1817static void rcu_report_qs_rsp(unsigned long flags)
1818 __releases(rcu_get_root()->lock)
1819{
1820 raw_lockdep_assert_held_rcu_node(rcu_get_root());
1821 WARN_ON_ONCE(!rcu_gp_in_progress());
1822 WRITE_ONCE(rcu_state.gp_flags,
1823 READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
1824 raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(), flags);
1825 rcu_gp_kthread_wake();
1826}
1827
1828/*
1829 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
1830 * Allows quiescent states for a group of CPUs to be reported at one go
1831 * to the specified rcu_node structure, though all the CPUs in the group
1832 * must be represented by the same rcu_node structure (which need not be a
1833 * leaf rcu_node structure, though it often will be). The gps parameter
1834 * is the grace-period snapshot, which means that the quiescent states
1835 * are valid only if rnp->gp_seq is equal to gps. That structure's lock
1836 * must be held upon entry, and it is released before return.
1837 *
1838 * As a special case, if mask is zero, the bit-already-cleared check is
1839 * disabled. This allows propagating quiescent state due to resumed tasks
1840 * during grace-period initialization.
1841 */
1842static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp,
1843 unsigned long gps, unsigned long flags)
1844 __releases(rnp->lock)
1845{
1846 unsigned long oldmask = 0;
1847 struct rcu_node *rnp_c;
1848
1849 raw_lockdep_assert_held_rcu_node(rnp);
1850
1851 /* Walk up the rcu_node hierarchy. */
1852 for (;;) {
1853 if ((!(rnp->qsmask & mask) && mask) || rnp->gp_seq != gps) {
1854
1855 /*
1856 * Our bit has already been cleared, or the
1857 * relevant grace period is already over, so done.
1858 */
1859 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1860 return;
1861 }
1862 WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
1863 WARN_ON_ONCE(!rcu_is_leaf_node(rnp) &&
1864 rcu_preempt_blocked_readers_cgp(rnp));
1865 rnp->qsmask &= ~mask;
1866 trace_rcu_quiescent_state_report(rcu_state.name, rnp->gp_seq,
1867 mask, rnp->qsmask, rnp->level,
1868 rnp->grplo, rnp->grphi,
1869 !!rnp->gp_tasks);
1870 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
1871
1872 /* Other bits still set at this level, so done. */
1873 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1874 return;
1875 }
1876 rnp->completedqs = rnp->gp_seq;
1877 mask = rnp->grpmask;
1878 if (rnp->parent == NULL) {
1879
1880 /* No more levels. Exit loop holding root lock. */
1881
1882 break;
1883 }
1884 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1885 rnp_c = rnp;
1886 rnp = rnp->parent;
1887 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1888 oldmask = rnp_c->qsmask;
1889 }
1890
1891 /*
1892 * Get here if we are the last CPU to pass through a quiescent
1893 * state for this grace period. Invoke rcu_report_qs_rsp()
1894 * to clean up and start the next grace period if one is needed.
1895 */
1896 rcu_report_qs_rsp(flags); /* releases rnp->lock. */
1897}
1898
1899/*
1900 * Record a quiescent state for all tasks that were previously queued
1901 * on the specified rcu_node structure and that were blocking the current
1902 * RCU grace period. The caller must hold the corresponding rnp->lock with
1903 * irqs disabled, and this lock is released upon return, but irqs remain
1904 * disabled.
1905 */
1906static void __maybe_unused
1907rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
1908 __releases(rnp->lock)
1909{
1910 unsigned long gps;
1911 unsigned long mask;
1912 struct rcu_node *rnp_p;
1913
1914 raw_lockdep_assert_held_rcu_node(rnp);
1915 if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPTION)) ||
1916 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)) ||
1917 rnp->qsmask != 0) {
1918 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1919 return; /* Still need more quiescent states! */
1920 }
1921
1922 rnp->completedqs = rnp->gp_seq;
1923 rnp_p = rnp->parent;
1924 if (rnp_p == NULL) {
1925 /*
1926 * Only one rcu_node structure in the tree, so don't
1927 * try to report up to its nonexistent parent!
1928 */
1929 rcu_report_qs_rsp(flags);
1930 return;
1931 }
1932
1933 /* Report up the rest of the hierarchy, tracking current ->gp_seq. */
1934 gps = rnp->gp_seq;
1935 mask = rnp->grpmask;
1936 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
1937 raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */
1938 rcu_report_qs_rnp(mask, rnp_p, gps, flags);
1939}
1940
1941/*
1942 * Record a quiescent state for the specified CPU to that CPU's rcu_data
1943 * structure. This must be called from the specified CPU.
1944 */
1945static void
1946rcu_report_qs_rdp(int cpu, struct rcu_data *rdp)
1947{
1948 unsigned long flags;
1949 unsigned long mask;
1950 bool needwake = false;
1951 const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
1952 rcu_segcblist_is_offloaded(&rdp->cblist);
1953 struct rcu_node *rnp;
1954
1955 rnp = rdp->mynode;
1956 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1957 if (rdp->cpu_no_qs.b.norm || rdp->gp_seq != rnp->gp_seq ||
1958 rdp->gpwrap) {
1959
1960 /*
1961 * The grace period in which this quiescent state was
1962 * recorded has ended, so don't report it upwards.
1963 * We will instead need a new quiescent state that lies
1964 * within the current grace period.
1965 */
1966 rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */
1967 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1968 return;
1969 }
1970 mask = rdp->grpmask;
1971 rdp->core_needs_qs = false;
1972 if ((rnp->qsmask & mask) == 0) {
1973 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1974 } else {
1975 /*
1976 * This GP can't end until cpu checks in, so all of our
1977 * callbacks can be processed during the next GP.
1978 */
1979 if (!offloaded)
1980 needwake = rcu_accelerate_cbs(rnp, rdp);
1981
1982 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
1983 /* ^^^ Released rnp->lock */
1984 if (needwake)
1985 rcu_gp_kthread_wake();
1986 }
1987}
1988
1989/*
1990 * Check to see if there is a new grace period of which this CPU
1991 * is not yet aware, and if so, set up local rcu_data state for it.
1992 * Otherwise, see if this CPU has just passed through its first
1993 * quiescent state for this grace period, and record that fact if so.
1994 */
1995static void
1996rcu_check_quiescent_state(struct rcu_data *rdp)
1997{
1998 /* Check for grace-period ends and beginnings. */
1999 note_gp_changes(rdp);
2000
2001 /*
2002 * Does this CPU still need to do its part for current grace period?
2003 * If no, return and let the other CPUs do their part as well.
2004 */
2005 if (!rdp->core_needs_qs)
2006 return;
2007
2008 /*
2009 * Was there a quiescent state since the beginning of the grace
2010 * period? If no, then exit and wait for the next call.
2011 */
2012 if (rdp->cpu_no_qs.b.norm)
2013 return;
2014
2015 /*
2016 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
2017 * judge of that).
2018 */
2019 rcu_report_qs_rdp(rdp->cpu, rdp);
2020}
2021
2022/*
2023 * Near the end of the offline process. Trace the fact that this CPU
2024 * is going offline.
2025 */
2026int rcutree_dying_cpu(unsigned int cpu)
2027{
2028 bool blkd;
2029 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
2030 struct rcu_node *rnp = rdp->mynode;
2031
2032 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2033 return 0;
2034
2035 blkd = !!(rnp->qsmask & rdp->grpmask);
2036 trace_rcu_grace_period(rcu_state.name, rnp->gp_seq,
2037 blkd ? TPS("cpuofl") : TPS("cpuofl-bgp"));
2038 return 0;
2039}
2040
2041/*
2042 * All CPUs for the specified rcu_node structure have gone offline,
2043 * and all tasks that were preempted within an RCU read-side critical
2044 * section while running on one of those CPUs have since exited their RCU
2045 * read-side critical section. Some other CPU is reporting this fact with
2046 * the specified rcu_node structure's ->lock held and interrupts disabled.
2047 * This function therefore goes up the tree of rcu_node structures,
2048 * clearing the corresponding bits in the ->qsmaskinit fields. Note that
2049 * the leaf rcu_node structure's ->qsmaskinit field has already been
2050 * updated.
2051 *
2052 * This function does check that the specified rcu_node structure has
2053 * all CPUs offline and no blocked tasks, so it is OK to invoke it
2054 * prematurely. That said, invoking it after the fact will cost you
2055 * a needless lock acquisition. So once it has done its work, don't
2056 * invoke it again.
2057 */
2058static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
2059{
2060 long mask;
2061 struct rcu_node *rnp = rnp_leaf;
2062
2063 raw_lockdep_assert_held_rcu_node(rnp_leaf);
2064 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
2065 WARN_ON_ONCE(rnp_leaf->qsmaskinit) ||
2066 WARN_ON_ONCE(rcu_preempt_has_tasks(rnp_leaf)))
2067 return;
2068 for (;;) {
2069 mask = rnp->grpmask;
2070 rnp = rnp->parent;
2071 if (!rnp)
2072 break;
2073 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
2074 rnp->qsmaskinit &= ~mask;
2075 /* Between grace periods, so better already be zero! */
2076 WARN_ON_ONCE(rnp->qsmask);
2077 if (rnp->qsmaskinit) {
2078 raw_spin_unlock_rcu_node(rnp);
2079 /* irqs remain disabled. */
2080 return;
2081 }
2082 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2083 }
2084}
2085
2086/*
2087 * The CPU has been completely removed, and some other CPU is reporting
2088 * this fact from process context. Do the remainder of the cleanup.
2089 * There can only be one CPU hotplug operation at a time, so no need for
2090 * explicit locking.
2091 */
2092int rcutree_dead_cpu(unsigned int cpu)
2093{
2094 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
2095 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
2096
2097 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2098 return 0;
2099
2100 /* Adjust any no-longer-needed kthreads. */
2101 rcu_boost_kthread_setaffinity(rnp, -1);
2102 /* Do any needed no-CB deferred wakeups from this CPU. */
2103 do_nocb_deferred_wakeup(per_cpu_ptr(&rcu_data, cpu));
2104 return 0;
2105}
2106
2107/*
2108 * Invoke any RCU callbacks that have made it to the end of their grace
2109 * period. Thottle as specified by rdp->blimit.
2110 */
2111static void rcu_do_batch(struct rcu_data *rdp)
2112{
2113 unsigned long flags;
2114 const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
2115 rcu_segcblist_is_offloaded(&rdp->cblist);
2116 struct rcu_head *rhp;
2117 struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
2118 long bl, count;
2119 long pending, tlimit = 0;
2120
2121 /* If no callbacks are ready, just return. */
2122 if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
2123 trace_rcu_batch_start(rcu_state.name,
2124 rcu_segcblist_n_lazy_cbs(&rdp->cblist),
2125 rcu_segcblist_n_cbs(&rdp->cblist), 0);
2126 trace_rcu_batch_end(rcu_state.name, 0,
2127 !rcu_segcblist_empty(&rdp->cblist),
2128 need_resched(), is_idle_task(current),
2129 rcu_is_callbacks_kthread());
2130 return;
2131 }
2132
2133 /*
2134 * Extract the list of ready callbacks, disabling to prevent
2135 * races with call_rcu() from interrupt handlers. Leave the
2136 * callback counts, as rcu_barrier() needs to be conservative.
2137 */
2138 local_irq_save(flags);
2139 rcu_nocb_lock(rdp);
2140 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2141 pending = rcu_segcblist_n_cbs(&rdp->cblist);
2142 bl = max(rdp->blimit, pending >> rcu_divisor);
2143 if (unlikely(bl > 100))
2144 tlimit = local_clock() + rcu_resched_ns;
2145 trace_rcu_batch_start(rcu_state.name,
2146 rcu_segcblist_n_lazy_cbs(&rdp->cblist),
2147 rcu_segcblist_n_cbs(&rdp->cblist), bl);
2148 rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
2149 if (offloaded)
2150 rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
2151 rcu_nocb_unlock_irqrestore(rdp, flags);
2152
2153 /* Invoke callbacks. */
2154 rhp = rcu_cblist_dequeue(&rcl);
2155 for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
2156 debug_rcu_head_unqueue(rhp);
2157 if (__rcu_reclaim(rcu_state.name, rhp))
2158 rcu_cblist_dequeued_lazy(&rcl);
2159 /*
2160 * Stop only if limit reached and CPU has something to do.
2161 * Note: The rcl structure counts down from zero.
2162 */
2163 if (-rcl.len >= bl && !offloaded &&
2164 (need_resched() ||
2165 (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
2166 break;
2167 if (unlikely(tlimit)) {
2168 /* only call local_clock() every 32 callbacks */
2169 if (likely((-rcl.len & 31) || local_clock() < tlimit))
2170 continue;
2171 /* Exceeded the time limit, so leave. */
2172 break;
2173 }
2174 if (offloaded) {
2175 WARN_ON_ONCE(in_serving_softirq());
2176 local_bh_enable();
2177 lockdep_assert_irqs_enabled();
2178 cond_resched_tasks_rcu_qs();
2179 lockdep_assert_irqs_enabled();
2180 local_bh_disable();
2181 }
2182 }
2183
2184 local_irq_save(flags);
2185 rcu_nocb_lock(rdp);
2186 count = -rcl.len;
2187 trace_rcu_batch_end(rcu_state.name, count, !!rcl.head, need_resched(),
2188 is_idle_task(current), rcu_is_callbacks_kthread());
2189
2190 /* Update counts and requeue any remaining callbacks. */
2191 rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
2192 smp_mb(); /* List handling before counting for rcu_barrier(). */
2193 rcu_segcblist_insert_count(&rdp->cblist, &rcl);
2194
2195 /* Reinstate batch limit if we have worked down the excess. */
2196 count = rcu_segcblist_n_cbs(&rdp->cblist);
2197 if (rdp->blimit >= DEFAULT_MAX_RCU_BLIMIT && count <= qlowmark)
2198 rdp->blimit = blimit;
2199
2200 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2201 if (count == 0 && rdp->qlen_last_fqs_check != 0) {
2202 rdp->qlen_last_fqs_check = 0;
2203 rdp->n_force_qs_snap = rcu_state.n_force_qs;
2204 } else if (count < rdp->qlen_last_fqs_check - qhimark)
2205 rdp->qlen_last_fqs_check = count;
2206
2207 /*
2208 * The following usually indicates a double call_rcu(). To track
2209 * this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.
2210 */
2211 WARN_ON_ONCE(count == 0 && !rcu_segcblist_empty(&rdp->cblist));
2212 WARN_ON_ONCE(!IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
2213 count != 0 && rcu_segcblist_empty(&rdp->cblist));
2214
2215 rcu_nocb_unlock_irqrestore(rdp, flags);
2216
2217 /* Re-invoke RCU core processing if there are callbacks remaining. */
2218 if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist))
2219 invoke_rcu_core();
2220}
2221
2222/*
2223 * This function is invoked from each scheduling-clock interrupt,
2224 * and checks to see if this CPU is in a non-context-switch quiescent
2225 * state, for example, user mode or idle loop. It also schedules RCU
2226 * core processing. If the current grace period has gone on too long,
2227 * it will ask the scheduler to manufacture a context switch for the sole
2228 * purpose of providing a providing the needed quiescent state.
2229 */
2230void rcu_sched_clock_irq(int user)
2231{
2232 trace_rcu_utilization(TPS("Start scheduler-tick"));
2233 raw_cpu_inc(rcu_data.ticks_this_gp);
2234 /* The load-acquire pairs with the store-release setting to true. */
2235 if (smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
2236 /* Idle and userspace execution already are quiescent states. */
2237 if (!rcu_is_cpu_rrupt_from_idle() && !user) {
2238 set_tsk_need_resched(current);
2239 set_preempt_need_resched();
2240 }
2241 __this_cpu_write(rcu_data.rcu_urgent_qs, false);
2242 }
2243 rcu_flavor_sched_clock_irq(user);
2244 if (rcu_pending())
2245 invoke_rcu_core();
2246
2247 trace_rcu_utilization(TPS("End scheduler-tick"));
2248}
2249
2250/*
2251 * Scan the leaf rcu_node structures. For each structure on which all
2252 * CPUs have reported a quiescent state and on which there are tasks
2253 * blocking the current grace period, initiate RCU priority boosting.
2254 * Otherwise, invoke the specified function to check dyntick state for
2255 * each CPU that has not yet reported a quiescent state.
2256 */
2257static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
2258{
2259 int cpu;
2260 unsigned long flags;
2261 unsigned long mask;
2262 struct rcu_node *rnp;
2263
2264 rcu_for_each_leaf_node(rnp) {
2265 cond_resched_tasks_rcu_qs();
2266 mask = 0;
2267 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2268 if (rnp->qsmask == 0) {
2269 if (!IS_ENABLED(CONFIG_PREEMPTION) ||
2270 rcu_preempt_blocked_readers_cgp(rnp)) {
2271 /*
2272 * No point in scanning bits because they
2273 * are all zero. But we might need to
2274 * priority-boost blocked readers.
2275 */
2276 rcu_initiate_boost(rnp, flags);
2277 /* rcu_initiate_boost() releases rnp->lock */
2278 continue;
2279 }
2280 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2281 continue;
2282 }
2283 for_each_leaf_node_possible_cpu(rnp, cpu) {
2284 unsigned long bit = leaf_node_cpu_bit(rnp, cpu);
2285 if ((rnp->qsmask & bit) != 0) {
2286 if (f(per_cpu_ptr(&rcu_data, cpu)))
2287 mask |= bit;
2288 }
2289 }
2290 if (mask != 0) {
2291 /* Idle/offline CPUs, report (releases rnp->lock). */
2292 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
2293 } else {
2294 /* Nothing to do here, so just drop the lock. */
2295 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2296 }
2297 }
2298}
2299
2300/*
2301 * Force quiescent states on reluctant CPUs, and also detect which
2302 * CPUs are in dyntick-idle mode.
2303 */
2304void rcu_force_quiescent_state(void)
2305{
2306 unsigned long flags;
2307 bool ret;
2308 struct rcu_node *rnp;
2309 struct rcu_node *rnp_old = NULL;
2310
2311 /* Funnel through hierarchy to reduce memory contention. */
2312 rnp = __this_cpu_read(rcu_data.mynode);
2313 for (; rnp != NULL; rnp = rnp->parent) {
2314 ret = (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) ||
2315 !raw_spin_trylock(&rnp->fqslock);
2316 if (rnp_old != NULL)
2317 raw_spin_unlock(&rnp_old->fqslock);
2318 if (ret)
2319 return;
2320 rnp_old = rnp;
2321 }
2322 /* rnp_old == rcu_get_root(), rnp == NULL. */
2323
2324 /* Reached the root of the rcu_node tree, acquire lock. */
2325 raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
2326 raw_spin_unlock(&rnp_old->fqslock);
2327 if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) {
2328 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2329 return; /* Someone beat us to it. */
2330 }
2331 WRITE_ONCE(rcu_state.gp_flags,
2332 READ_ONCE(rcu_state.gp_flags) | RCU_GP_FLAG_FQS);
2333 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2334 rcu_gp_kthread_wake();
2335}
2336EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
2337
2338/* Perform RCU core processing work for the current CPU. */
2339static __latent_entropy void rcu_core(void)
2340{
2341 unsigned long flags;
2342 struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
2343 struct rcu_node *rnp = rdp->mynode;
2344 const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
2345 rcu_segcblist_is_offloaded(&rdp->cblist);
2346
2347 if (cpu_is_offline(smp_processor_id()))
2348 return;
2349 trace_rcu_utilization(TPS("Start RCU core"));
2350 WARN_ON_ONCE(!rdp->beenonline);
2351
2352 /* Report any deferred quiescent states if preemption enabled. */
2353 if (!(preempt_count() & PREEMPT_MASK)) {
2354 rcu_preempt_deferred_qs(current);
2355 } else if (rcu_preempt_need_deferred_qs(current)) {
2356 set_tsk_need_resched(current);
2357 set_preempt_need_resched();
2358 }
2359
2360 /* Update RCU state based on any recent quiescent states. */
2361 rcu_check_quiescent_state(rdp);
2362
2363 /* No grace period and unregistered callbacks? */
2364 if (!rcu_gp_in_progress() &&
2365 rcu_segcblist_is_enabled(&rdp->cblist) && !offloaded) {
2366 local_irq_save(flags);
2367 if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
2368 rcu_accelerate_cbs_unlocked(rnp, rdp);
2369 local_irq_restore(flags);
2370 }
2371
2372 rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check());
2373
2374 /* If there are callbacks ready, invoke them. */
2375 if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist) &&
2376 likely(READ_ONCE(rcu_scheduler_fully_active)))
2377 rcu_do_batch(rdp);
2378
2379 /* Do any needed deferred wakeups of rcuo kthreads. */
2380 do_nocb_deferred_wakeup(rdp);
2381 trace_rcu_utilization(TPS("End RCU core"));
2382}
2383
2384static void rcu_core_si(struct softirq_action *h)
2385{
2386 rcu_core();
2387}
2388
2389static void rcu_wake_cond(struct task_struct *t, int status)
2390{
2391 /*
2392 * If the thread is yielding, only wake it when this
2393 * is invoked from idle
2394 */
2395 if (t && (status != RCU_KTHREAD_YIELDING || is_idle_task(current)))
2396 wake_up_process(t);
2397}
2398
2399static void invoke_rcu_core_kthread(void)
2400{
2401 struct task_struct *t;
2402 unsigned long flags;
2403
2404 local_irq_save(flags);
2405 __this_cpu_write(rcu_data.rcu_cpu_has_work, 1);
2406 t = __this_cpu_read(rcu_data.rcu_cpu_kthread_task);
2407 if (t != NULL && t != current)
2408 rcu_wake_cond(t, __this_cpu_read(rcu_data.rcu_cpu_kthread_status));
2409 local_irq_restore(flags);
2410}
2411
2412/*
2413 * Wake up this CPU's rcuc kthread to do RCU core processing.
2414 */
2415static void invoke_rcu_core(void)
2416{
2417 if (!cpu_online(smp_processor_id()))
2418 return;
2419 if (use_softirq)
2420 raise_softirq(RCU_SOFTIRQ);
2421 else
2422 invoke_rcu_core_kthread();
2423}
2424
2425static void rcu_cpu_kthread_park(unsigned int cpu)
2426{
2427 per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
2428}
2429
2430static int rcu_cpu_kthread_should_run(unsigned int cpu)
2431{
2432 return __this_cpu_read(rcu_data.rcu_cpu_has_work);
2433}
2434
2435/*
2436 * Per-CPU kernel thread that invokes RCU callbacks. This replaces
2437 * the RCU softirq used in configurations of RCU that do not support RCU
2438 * priority boosting.
2439 */
2440static void rcu_cpu_kthread(unsigned int cpu)
2441{
2442 unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status);
2443 char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work);
2444 int spincnt;
2445
2446 for (spincnt = 0; spincnt < 10; spincnt++) {
2447 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
2448 local_bh_disable();
2449 *statusp = RCU_KTHREAD_RUNNING;
2450 local_irq_disable();
2451 work = *workp;
2452 *workp = 0;
2453 local_irq_enable();
2454 if (work)
2455 rcu_core();
2456 local_bh_enable();
2457 if (*workp == 0) {
2458 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
2459 *statusp = RCU_KTHREAD_WAITING;
2460 return;
2461 }
2462 }
2463 *statusp = RCU_KTHREAD_YIELDING;
2464 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
2465 schedule_timeout_interruptible(2);
2466 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
2467 *statusp = RCU_KTHREAD_WAITING;
2468}
2469
2470static struct smp_hotplug_thread rcu_cpu_thread_spec = {
2471 .store = &rcu_data.rcu_cpu_kthread_task,
2472 .thread_should_run = rcu_cpu_kthread_should_run,
2473 .thread_fn = rcu_cpu_kthread,
2474 .thread_comm = "rcuc/%u",
2475 .setup = rcu_cpu_kthread_setup,
2476 .park = rcu_cpu_kthread_park,
2477};
2478
2479/*
2480 * Spawn per-CPU RCU core processing kthreads.
2481 */
2482static int __init rcu_spawn_core_kthreads(void)
2483{
2484 int cpu;
2485
2486 for_each_possible_cpu(cpu)
2487 per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0;
2488 if (!IS_ENABLED(CONFIG_RCU_BOOST) && use_softirq)
2489 return 0;
2490 WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec),
2491 "%s: Could not start rcuc kthread, OOM is now expected behavior\n", __func__);
2492 return 0;
2493}
2494early_initcall(rcu_spawn_core_kthreads);
2495
2496/*
2497 * Handle any core-RCU processing required by a call_rcu() invocation.
2498 */
2499static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
2500 unsigned long flags)
2501{
2502 /*
2503 * If called from an extended quiescent state, invoke the RCU
2504 * core in order to force a re-evaluation of RCU's idleness.
2505 */
2506 if (!rcu_is_watching())
2507 invoke_rcu_core();
2508
2509 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2510 if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2511 return;
2512
2513 /*
2514 * Force the grace period if too many callbacks or too long waiting.
2515 * Enforce hysteresis, and don't invoke rcu_force_quiescent_state()
2516 * if some other CPU has recently done so. Also, don't bother
2517 * invoking rcu_force_quiescent_state() if the newly enqueued callback
2518 * is the only one waiting for a grace period to complete.
2519 */
2520 if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
2521 rdp->qlen_last_fqs_check + qhimark)) {
2522
2523 /* Are we ignoring a completed grace period? */
2524 note_gp_changes(rdp);
2525
2526 /* Start a new grace period if one not already started. */
2527 if (!rcu_gp_in_progress()) {
2528 rcu_accelerate_cbs_unlocked(rdp->mynode, rdp);
2529 } else {
2530 /* Give the grace period a kick. */
2531 rdp->blimit = DEFAULT_MAX_RCU_BLIMIT;
2532 if (rcu_state.n_force_qs == rdp->n_force_qs_snap &&
2533 rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
2534 rcu_force_quiescent_state();
2535 rdp->n_force_qs_snap = rcu_state.n_force_qs;
2536 rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
2537 }
2538 }
2539}
2540
2541/*
2542 * RCU callback function to leak a callback.
2543 */
2544static void rcu_leak_callback(struct rcu_head *rhp)
2545{
2546}
2547
2548/*
2549 * Helper function for call_rcu() and friends. The cpu argument will
2550 * normally be -1, indicating "currently running CPU". It may specify
2551 * a CPU only if that CPU is a no-CBs CPU. Currently, only rcu_barrier()
2552 * is expected to specify a CPU.
2553 */
2554static void
2555__call_rcu(struct rcu_head *head, rcu_callback_t func, bool lazy)
2556{
2557 unsigned long flags;
2558 struct rcu_data *rdp;
2559 bool was_alldone;
2560
2561 /* Misaligned rcu_head! */
2562 WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
2563
2564 if (debug_rcu_head_queue(head)) {
2565 /*
2566 * Probable double call_rcu(), so leak the callback.
2567 * Use rcu:rcu_callback trace event to find the previous
2568 * time callback was passed to __call_rcu().
2569 */
2570 WARN_ONCE(1, "__call_rcu(): Double-freed CB %p->%pS()!!!\n",
2571 head, head->func);
2572 WRITE_ONCE(head->func, rcu_leak_callback);
2573 return;
2574 }
2575 head->func = func;
2576 head->next = NULL;
2577 local_irq_save(flags);
2578 rdp = this_cpu_ptr(&rcu_data);
2579
2580 /* Add the callback to our list. */
2581 if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) {
2582 // This can trigger due to call_rcu() from offline CPU:
2583 WARN_ON_ONCE(rcu_scheduler_active != RCU_SCHEDULER_INACTIVE);
2584 WARN_ON_ONCE(!rcu_is_watching());
2585 // Very early boot, before rcu_init(). Initialize if needed
2586 // and then drop through to queue the callback.
2587 if (rcu_segcblist_empty(&rdp->cblist))
2588 rcu_segcblist_init(&rdp->cblist);
2589 }
2590 if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags))
2591 return; // Enqueued onto ->nocb_bypass, so just leave.
2592 /* If we get here, rcu_nocb_try_bypass() acquired ->nocb_lock. */
2593 rcu_segcblist_enqueue(&rdp->cblist, head, lazy);
2594 if (__is_kfree_rcu_offset((unsigned long)func))
2595 trace_rcu_kfree_callback(rcu_state.name, head,
2596 (unsigned long)func,
2597 rcu_segcblist_n_lazy_cbs(&rdp->cblist),
2598 rcu_segcblist_n_cbs(&rdp->cblist));
2599 else
2600 trace_rcu_callback(rcu_state.name, head,
2601 rcu_segcblist_n_lazy_cbs(&rdp->cblist),
2602 rcu_segcblist_n_cbs(&rdp->cblist));
2603
2604 /* Go handle any RCU core processing required. */
2605 if (IS_ENABLED(CONFIG_RCU_NOCB_CPU) &&
2606 unlikely(rcu_segcblist_is_offloaded(&rdp->cblist))) {
2607 __call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
2608 } else {
2609 __call_rcu_core(rdp, head, flags);
2610 local_irq_restore(flags);
2611 }
2612}
2613
2614/**
2615 * call_rcu() - Queue an RCU callback for invocation after a grace period.
2616 * @head: structure to be used for queueing the RCU updates.
2617 * @func: actual callback function to be invoked after the grace period
2618 *
2619 * The callback function will be invoked some time after a full grace
2620 * period elapses, in other words after all pre-existing RCU read-side
2621 * critical sections have completed. However, the callback function
2622 * might well execute concurrently with RCU read-side critical sections
2623 * that started after call_rcu() was invoked. RCU read-side critical
2624 * sections are delimited by rcu_read_lock() and rcu_read_unlock(), and
2625 * may be nested. In addition, regions of code across which interrupts,
2626 * preemption, or softirqs have been disabled also serve as RCU read-side
2627 * critical sections. This includes hardware interrupt handlers, softirq
2628 * handlers, and NMI handlers.
2629 *
2630 * Note that all CPUs must agree that the grace period extended beyond
2631 * all pre-existing RCU read-side critical section. On systems with more
2632 * than one CPU, this means that when "func()" is invoked, each CPU is
2633 * guaranteed to have executed a full memory barrier since the end of its
2634 * last RCU read-side critical section whose beginning preceded the call
2635 * to call_rcu(). It also means that each CPU executing an RCU read-side
2636 * critical section that continues beyond the start of "func()" must have
2637 * executed a memory barrier after the call_rcu() but before the beginning
2638 * of that RCU read-side critical section. Note that these guarantees
2639 * include CPUs that are offline, idle, or executing in user mode, as
2640 * well as CPUs that are executing in the kernel.
2641 *
2642 * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
2643 * resulting RCU callback function "func()", then both CPU A and CPU B are
2644 * guaranteed to execute a full memory barrier during the time interval
2645 * between the call to call_rcu() and the invocation of "func()" -- even
2646 * if CPU A and CPU B are the same CPU (but again only if the system has
2647 * more than one CPU).
2648 */
2649void call_rcu(struct rcu_head *head, rcu_callback_t func)
2650{
2651 __call_rcu(head, func, 0);
2652}
2653EXPORT_SYMBOL_GPL(call_rcu);
2654
2655/*
2656 * Queue an RCU callback for lazy invocation after a grace period.
2657 * This will likely be later named something like "call_rcu_lazy()",
2658 * but this change will require some way of tagging the lazy RCU
2659 * callbacks in the list of pending callbacks. Until then, this
2660 * function may only be called from __kfree_rcu().
2661 */
2662void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
2663{
2664 __call_rcu(head, func, 1);
2665}
2666EXPORT_SYMBOL_GPL(kfree_call_rcu);
2667
2668/*
2669 * During early boot, any blocking grace-period wait automatically
2670 * implies a grace period. Later on, this is never the case for PREEMPT.
2671 *
2672 * Howevr, because a context switch is a grace period for !PREEMPT, any
2673 * blocking grace-period wait automatically implies a grace period if
2674 * there is only one CPU online at any point time during execution of
2675 * either synchronize_rcu() or synchronize_rcu_expedited(). It is OK to
2676 * occasionally incorrectly indicate that there are multiple CPUs online
2677 * when there was in fact only one the whole time, as this just adds some
2678 * overhead: RCU still operates correctly.
2679 */
2680static int rcu_blocking_is_gp(void)
2681{
2682 int ret;
2683
2684 if (IS_ENABLED(CONFIG_PREEMPTION))
2685 return rcu_scheduler_active == RCU_SCHEDULER_INACTIVE;
2686 might_sleep(); /* Check for RCU read-side critical section. */
2687 preempt_disable();
2688 ret = num_online_cpus() <= 1;
2689 preempt_enable();
2690 return ret;
2691}
2692
2693/**
2694 * synchronize_rcu - wait until a grace period has elapsed.
2695 *
2696 * Control will return to the caller some time after a full grace
2697 * period has elapsed, in other words after all currently executing RCU
2698 * read-side critical sections have completed. Note, however, that
2699 * upon return from synchronize_rcu(), the caller might well be executing
2700 * concurrently with new RCU read-side critical sections that began while
2701 * synchronize_rcu() was waiting. RCU read-side critical sections are
2702 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
2703 * In addition, regions of code across which interrupts, preemption, or
2704 * softirqs have been disabled also serve as RCU read-side critical
2705 * sections. This includes hardware interrupt handlers, softirq handlers,
2706 * and NMI handlers.
2707 *
2708 * Note that this guarantee implies further memory-ordering guarantees.
2709 * On systems with more than one CPU, when synchronize_rcu() returns,
2710 * each CPU is guaranteed to have executed a full memory barrier since
2711 * the end of its last RCU read-side critical section whose beginning
2712 * preceded the call to synchronize_rcu(). In addition, each CPU having
2713 * an RCU read-side critical section that extends beyond the return from
2714 * synchronize_rcu() is guaranteed to have executed a full memory barrier
2715 * after the beginning of synchronize_rcu() and before the beginning of
2716 * that RCU read-side critical section. Note that these guarantees include
2717 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
2718 * that are executing in the kernel.
2719 *
2720 * Furthermore, if CPU A invoked synchronize_rcu(), which returned
2721 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
2722 * to have executed a full memory barrier during the execution of
2723 * synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but
2724 * again only if the system has more than one CPU).
2725 */
2726void synchronize_rcu(void)
2727{
2728 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
2729 lock_is_held(&rcu_lock_map) ||
2730 lock_is_held(&rcu_sched_lock_map),
2731 "Illegal synchronize_rcu() in RCU read-side critical section");
2732 if (rcu_blocking_is_gp())
2733 return;
2734 if (rcu_gp_is_expedited())
2735 synchronize_rcu_expedited();
2736 else
2737 wait_rcu_gp(call_rcu);
2738}
2739EXPORT_SYMBOL_GPL(synchronize_rcu);
2740
2741/**
2742 * get_state_synchronize_rcu - Snapshot current RCU state
2743 *
2744 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
2745 * to determine whether or not a full grace period has elapsed in the
2746 * meantime.
2747 */
2748unsigned long get_state_synchronize_rcu(void)
2749{
2750 /*
2751 * Any prior manipulation of RCU-protected data must happen
2752 * before the load from ->gp_seq.
2753 */
2754 smp_mb(); /* ^^^ */
2755 return rcu_seq_snap(&rcu_state.gp_seq);
2756}
2757EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
2758
2759/**
2760 * cond_synchronize_rcu - Conditionally wait for an RCU grace period
2761 *
2762 * @oldstate: return value from earlier call to get_state_synchronize_rcu()
2763 *
2764 * If a full RCU grace period has elapsed since the earlier call to
2765 * get_state_synchronize_rcu(), just return. Otherwise, invoke
2766 * synchronize_rcu() to wait for a full grace period.
2767 *
2768 * Yes, this function does not take counter wrap into account. But
2769 * counter wrap is harmless. If the counter wraps, we have waited for
2770 * more than 2 billion grace periods (and way more on a 64-bit system!),
2771 * so waiting for one additional grace period should be just fine.
2772 */
2773void cond_synchronize_rcu(unsigned long oldstate)
2774{
2775 if (!rcu_seq_done(&rcu_state.gp_seq, oldstate))
2776 synchronize_rcu();
2777 else
2778 smp_mb(); /* Ensure GP ends before subsequent accesses. */
2779}
2780EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
2781
2782/*
2783 * Check to see if there is any immediate RCU-related work to be done by
2784 * the current CPU, returning 1 if so and zero otherwise. The checks are
2785 * in order of increasing expense: checks that can be carried out against
2786 * CPU-local state are performed first. However, we must check for CPU
2787 * stalls first, else we might not get a chance.
2788 */
2789static int rcu_pending(void)
2790{
2791 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
2792 struct rcu_node *rnp = rdp->mynode;
2793
2794 /* Check for CPU stalls, if enabled. */
2795 check_cpu_stall(rdp);
2796
2797 /* Does this CPU need a deferred NOCB wakeup? */
2798 if (rcu_nocb_need_deferred_wakeup(rdp))
2799 return 1;
2800
2801 /* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
2802 if (rcu_nohz_full_cpu())
2803 return 0;
2804
2805 /* Is the RCU core waiting for a quiescent state from this CPU? */
2806 if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm)
2807 return 1;
2808
2809 /* Does this CPU have callbacks ready to invoke? */
2810 if (rcu_segcblist_ready_cbs(&rdp->cblist))
2811 return 1;
2812
2813 /* Has RCU gone idle with this CPU needing another grace period? */
2814 if (!rcu_gp_in_progress() &&
2815 rcu_segcblist_is_enabled(&rdp->cblist) &&
2816 (!IS_ENABLED(CONFIG_RCU_NOCB_CPU) ||
2817 !rcu_segcblist_is_offloaded(&rdp->cblist)) &&
2818 !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
2819 return 1;
2820
2821 /* Have RCU grace period completed or started? */
2822 if (rcu_seq_current(&rnp->gp_seq) != rdp->gp_seq ||
2823 unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */
2824 return 1;
2825
2826 /* nothing to do */
2827 return 0;
2828}
2829
2830/*
2831 * Helper function for rcu_barrier() tracing. If tracing is disabled,
2832 * the compiler is expected to optimize this away.
2833 */
2834static void rcu_barrier_trace(const char *s, int cpu, unsigned long done)
2835{
2836 trace_rcu_barrier(rcu_state.name, s, cpu,
2837 atomic_read(&rcu_state.barrier_cpu_count), done);
2838}
2839
2840/*
2841 * RCU callback function for rcu_barrier(). If we are last, wake
2842 * up the task executing rcu_barrier().
2843 */
2844static void rcu_barrier_callback(struct rcu_head *rhp)
2845{
2846 if (atomic_dec_and_test(&rcu_state.barrier_cpu_count)) {
2847 rcu_barrier_trace(TPS("LastCB"), -1,
2848 rcu_state.barrier_sequence);
2849 complete(&rcu_state.barrier_completion);
2850 } else {
2851 rcu_barrier_trace(TPS("CB"), -1, rcu_state.barrier_sequence);
2852 }
2853}
2854
2855/*
2856 * Called with preemption disabled, and from cross-cpu IRQ context.
2857 */
2858static void rcu_barrier_func(void *unused)
2859{
2860 struct rcu_data *rdp = raw_cpu_ptr(&rcu_data);
2861
2862 rcu_barrier_trace(TPS("IRQ"), -1, rcu_state.barrier_sequence);
2863 rdp->barrier_head.func = rcu_barrier_callback;
2864 debug_rcu_head_queue(&rdp->barrier_head);
2865 rcu_nocb_lock(rdp);
2866 WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies));
2867 if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head, 0)) {
2868 atomic_inc(&rcu_state.barrier_cpu_count);
2869 } else {
2870 debug_rcu_head_unqueue(&rdp->barrier_head);
2871 rcu_barrier_trace(TPS("IRQNQ"), -1,
2872 rcu_state.barrier_sequence);
2873 }
2874 rcu_nocb_unlock(rdp);
2875}
2876
2877/**
2878 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
2879 *
2880 * Note that this primitive does not necessarily wait for an RCU grace period
2881 * to complete. For example, if there are no RCU callbacks queued anywhere
2882 * in the system, then rcu_barrier() is within its rights to return
2883 * immediately, without waiting for anything, much less an RCU grace period.
2884 */
2885void rcu_barrier(void)
2886{
2887 int cpu;
2888 struct rcu_data *rdp;
2889 unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
2890
2891 rcu_barrier_trace(TPS("Begin"), -1, s);
2892
2893 /* Take mutex to serialize concurrent rcu_barrier() requests. */
2894 mutex_lock(&rcu_state.barrier_mutex);
2895
2896 /* Did someone else do our work for us? */
2897 if (rcu_seq_done(&rcu_state.barrier_sequence, s)) {
2898 rcu_barrier_trace(TPS("EarlyExit"), -1,
2899 rcu_state.barrier_sequence);
2900 smp_mb(); /* caller's subsequent code after above check. */
2901 mutex_unlock(&rcu_state.barrier_mutex);
2902 return;
2903 }
2904
2905 /* Mark the start of the barrier operation. */
2906 rcu_seq_start(&rcu_state.barrier_sequence);
2907 rcu_barrier_trace(TPS("Inc1"), -1, rcu_state.barrier_sequence);
2908
2909 /*
2910 * Initialize the count to one rather than to zero in order to
2911 * avoid a too-soon return to zero in case of a short grace period
2912 * (or preemption of this task). Exclude CPU-hotplug operations
2913 * to ensure that no offline CPU has callbacks queued.
2914 */
2915 init_completion(&rcu_state.barrier_completion);
2916 atomic_set(&rcu_state.barrier_cpu_count, 1);
2917 get_online_cpus();
2918
2919 /*
2920 * Force each CPU with callbacks to register a new callback.
2921 * When that callback is invoked, we will know that all of the
2922 * corresponding CPU's preceding callbacks have been invoked.
2923 */
2924 for_each_possible_cpu(cpu) {
2925 rdp = per_cpu_ptr(&rcu_data, cpu);
2926 if (!cpu_online(cpu) &&
2927 !rcu_segcblist_is_offloaded(&rdp->cblist))
2928 continue;
2929 if (rcu_segcblist_n_cbs(&rdp->cblist)) {
2930 rcu_barrier_trace(TPS("OnlineQ"), cpu,
2931 rcu_state.barrier_sequence);
2932 smp_call_function_single(cpu, rcu_barrier_func, NULL, 1);
2933 } else {
2934 rcu_barrier_trace(TPS("OnlineNQ"), cpu,
2935 rcu_state.barrier_sequence);
2936 }
2937 }
2938 put_online_cpus();
2939
2940 /*
2941 * Now that we have an rcu_barrier_callback() callback on each
2942 * CPU, and thus each counted, remove the initial count.
2943 */
2944 if (atomic_dec_and_test(&rcu_state.barrier_cpu_count))
2945 complete(&rcu_state.barrier_completion);
2946
2947 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
2948 wait_for_completion(&rcu_state.barrier_completion);
2949
2950 /* Mark the end of the barrier operation. */
2951 rcu_barrier_trace(TPS("Inc2"), -1, rcu_state.barrier_sequence);
2952 rcu_seq_end(&rcu_state.barrier_sequence);
2953
2954 /* Other rcu_barrier() invocations can now safely proceed. */
2955 mutex_unlock(&rcu_state.barrier_mutex);
2956}
2957EXPORT_SYMBOL_GPL(rcu_barrier);
2958
2959/*
2960 * Propagate ->qsinitmask bits up the rcu_node tree to account for the
2961 * first CPU in a given leaf rcu_node structure coming online. The caller
2962 * must hold the corresponding leaf rcu_node ->lock with interrrupts
2963 * disabled.
2964 */
2965static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
2966{
2967 long mask;
2968 long oldmask;
2969 struct rcu_node *rnp = rnp_leaf;
2970
2971 raw_lockdep_assert_held_rcu_node(rnp_leaf);
2972 WARN_ON_ONCE(rnp->wait_blkd_tasks);
2973 for (;;) {
2974 mask = rnp->grpmask;
2975 rnp = rnp->parent;
2976 if (rnp == NULL)
2977 return;
2978 raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
2979 oldmask = rnp->qsmaskinit;
2980 rnp->qsmaskinit |= mask;
2981 raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
2982 if (oldmask)
2983 return;
2984 }
2985}
2986
2987/*
2988 * Do boot-time initialization of a CPU's per-CPU RCU data.
2989 */
2990static void __init
2991rcu_boot_init_percpu_data(int cpu)
2992{
2993 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
2994
2995 /* Set up local state, ensuring consistent view of global state. */
2996 rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
2997 WARN_ON_ONCE(rdp->dynticks_nesting != 1);
2998 WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp)));
2999 rdp->rcu_ofl_gp_seq = rcu_state.gp_seq;
3000 rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED;
3001 rdp->rcu_onl_gp_seq = rcu_state.gp_seq;
3002 rdp->rcu_onl_gp_flags = RCU_GP_CLEANED;
3003 rdp->cpu = cpu;
3004 rcu_boot_init_nocb_percpu_data(rdp);
3005}
3006
3007/*
3008 * Invoked early in the CPU-online process, when pretty much all services
3009 * are available. The incoming CPU is not present.
3010 *
3011 * Initializes a CPU's per-CPU RCU data. Note that only one online or
3012 * offline event can be happening at a given time. Note also that we can
3013 * accept some slop in the rsp->gp_seq access due to the fact that this
3014 * CPU cannot possibly have any non-offloaded RCU callbacks in flight yet.
3015 * And any offloaded callbacks are being numbered elsewhere.
3016 */
3017int rcutree_prepare_cpu(unsigned int cpu)
3018{
3019 unsigned long flags;
3020 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
3021 struct rcu_node *rnp = rcu_get_root();
3022
3023 /* Set up local state, ensuring consistent view of global state. */
3024 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3025 rdp->qlen_last_fqs_check = 0;
3026 rdp->n_force_qs_snap = rcu_state.n_force_qs;
3027 rdp->blimit = blimit;
3028 if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */
3029 !rcu_segcblist_is_offloaded(&rdp->cblist))
3030 rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
3031 rdp->dynticks_nesting = 1; /* CPU not up, no tearing. */
3032 rcu_dynticks_eqs_online();
3033 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
3034
3035 /*
3036 * Add CPU to leaf rcu_node pending-online bitmask. Any needed
3037 * propagation up the rcu_node tree will happen at the beginning
3038 * of the next grace period.
3039 */
3040 rnp = rdp->mynode;
3041 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
3042 rdp->beenonline = true; /* We have now been online. */
3043 rdp->gp_seq = rnp->gp_seq;
3044 rdp->gp_seq_needed = rnp->gp_seq;
3045 rdp->cpu_no_qs.b.norm = true;
3046 rdp->core_needs_qs = false;
3047 rdp->rcu_iw_pending = false;
3048 rdp->rcu_iw_gp_seq = rnp->gp_seq - 1;
3049 trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl"));
3050 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3051 rcu_prepare_kthreads(cpu);
3052 rcu_spawn_cpu_nocb_kthread(cpu);
3053
3054 return 0;
3055}
3056
3057/*
3058 * Update RCU priority boot kthread affinity for CPU-hotplug changes.
3059 */
3060static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
3061{
3062 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
3063
3064 rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
3065}
3066
3067/*
3068 * Near the end of the CPU-online process. Pretty much all services
3069 * enabled, and the CPU is now very much alive.
3070 */
3071int rcutree_online_cpu(unsigned int cpu)
3072{
3073 unsigned long flags;
3074 struct rcu_data *rdp;
3075 struct rcu_node *rnp;
3076
3077 rdp = per_cpu_ptr(&rcu_data, cpu);
3078 rnp = rdp->mynode;
3079 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3080 rnp->ffmask |= rdp->grpmask;
3081 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3082 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
3083 return 0; /* Too early in boot for scheduler work. */
3084 sync_sched_exp_online_cleanup(cpu);
3085 rcutree_affinity_setting(cpu, -1);
3086 return 0;
3087}
3088
3089/*
3090 * Near the beginning of the process. The CPU is still very much alive
3091 * with pretty much all services enabled.
3092 */
3093int rcutree_offline_cpu(unsigned int cpu)
3094{
3095 unsigned long flags;
3096 struct rcu_data *rdp;
3097 struct rcu_node *rnp;
3098
3099 rdp = per_cpu_ptr(&rcu_data, cpu);
3100 rnp = rdp->mynode;
3101 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3102 rnp->ffmask &= ~rdp->grpmask;
3103 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3104
3105 rcutree_affinity_setting(cpu, cpu);
3106 return 0;
3107}
3108
3109static DEFINE_PER_CPU(int, rcu_cpu_started);
3110
3111/*
3112 * Mark the specified CPU as being online so that subsequent grace periods
3113 * (both expedited and normal) will wait on it. Note that this means that
3114 * incoming CPUs are not allowed to use RCU read-side critical sections
3115 * until this function is called. Failing to observe this restriction
3116 * will result in lockdep splats.
3117 *
3118 * Note that this function is special in that it is invoked directly
3119 * from the incoming CPU rather than from the cpuhp_step mechanism.
3120 * This is because this function must be invoked at a precise location.
3121 */
3122void rcu_cpu_starting(unsigned int cpu)
3123{
3124 unsigned long flags;
3125 unsigned long mask;
3126 int nbits;
3127 unsigned long oldmask;
3128 struct rcu_data *rdp;
3129 struct rcu_node *rnp;
3130
3131 if (per_cpu(rcu_cpu_started, cpu))
3132 return;
3133
3134 per_cpu(rcu_cpu_started, cpu) = 1;
3135
3136 rdp = per_cpu_ptr(&rcu_data, cpu);
3137 rnp = rdp->mynode;
3138 mask = rdp->grpmask;
3139 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3140 rnp->qsmaskinitnext |= mask;
3141 oldmask = rnp->expmaskinitnext;
3142 rnp->expmaskinitnext |= mask;
3143 oldmask ^= rnp->expmaskinitnext;
3144 nbits = bitmap_weight(&oldmask, BITS_PER_LONG);
3145 /* Allow lockless access for expedited grace periods. */
3146 smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + nbits); /* ^^^ */
3147 rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */
3148 rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
3149 rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags);
3150 if (rnp->qsmask & mask) { /* RCU waiting on incoming CPU? */
3151 /* Report QS -after- changing ->qsmaskinitnext! */
3152 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
3153 } else {
3154 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3155 }
3156 smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
3157}
3158
3159#ifdef CONFIG_HOTPLUG_CPU
3160/*
3161 * The outgoing function has no further need of RCU, so remove it from
3162 * the rcu_node tree's ->qsmaskinitnext bit masks.
3163 *
3164 * Note that this function is special in that it is invoked directly
3165 * from the outgoing CPU rather than from the cpuhp_step mechanism.
3166 * This is because this function must be invoked at a precise location.
3167 */
3168void rcu_report_dead(unsigned int cpu)
3169{
3170 unsigned long flags;
3171 unsigned long mask;
3172 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
3173 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
3174
3175 /* QS for any half-done expedited grace period. */
3176 preempt_disable();
3177 rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
3178 preempt_enable();
3179 rcu_preempt_deferred_qs(current);
3180
3181 /* Remove outgoing CPU from mask in the leaf rcu_node structure. */
3182 mask = rdp->grpmask;
3183 raw_spin_lock(&rcu_state.ofl_lock);
3184 raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
3185 rdp->rcu_ofl_gp_seq = READ_ONCE(rcu_state.gp_seq);
3186 rdp->rcu_ofl_gp_flags = READ_ONCE(rcu_state.gp_flags);
3187 if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */
3188 /* Report quiescent state -before- changing ->qsmaskinitnext! */
3189 rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
3190 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3191 }
3192 rnp->qsmaskinitnext &= ~mask;
3193 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3194 raw_spin_unlock(&rcu_state.ofl_lock);
3195
3196 per_cpu(rcu_cpu_started, cpu) = 0;
3197}
3198
3199/*
3200 * The outgoing CPU has just passed through the dying-idle state, and we
3201 * are being invoked from the CPU that was IPIed to continue the offline
3202 * operation. Migrate the outgoing CPU's callbacks to the current CPU.
3203 */
3204void rcutree_migrate_callbacks(int cpu)
3205{
3206 unsigned long flags;
3207 struct rcu_data *my_rdp;
3208 struct rcu_node *my_rnp;
3209 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
3210 bool needwake;
3211
3212 if (rcu_segcblist_is_offloaded(&rdp->cblist) ||
3213 rcu_segcblist_empty(&rdp->cblist))
3214 return; /* No callbacks to migrate. */
3215
3216 local_irq_save(flags);
3217 my_rdp = this_cpu_ptr(&rcu_data);
3218 my_rnp = my_rdp->mynode;
3219 rcu_nocb_lock(my_rdp); /* irqs already disabled. */
3220 WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies));
3221 raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */
3222 /* Leverage recent GPs and set GP for new callbacks. */
3223 needwake = rcu_advance_cbs(my_rnp, rdp) ||
3224 rcu_advance_cbs(my_rnp, my_rdp);
3225 rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
3226 needwake = needwake || rcu_advance_cbs(my_rnp, my_rdp);
3227 rcu_segcblist_disable(&rdp->cblist);
3228 WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) !=
3229 !rcu_segcblist_n_cbs(&my_rdp->cblist));
3230 if (rcu_segcblist_is_offloaded(&my_rdp->cblist)) {
3231 raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */
3232 __call_rcu_nocb_wake(my_rdp, true, flags);
3233 } else {
3234 rcu_nocb_unlock(my_rdp); /* irqs remain disabled. */
3235 raw_spin_unlock_irqrestore_rcu_node(my_rnp, flags);
3236 }
3237 if (needwake)
3238 rcu_gp_kthread_wake();
3239 lockdep_assert_irqs_enabled();
3240 WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
3241 !rcu_segcblist_empty(&rdp->cblist),
3242 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
3243 cpu, rcu_segcblist_n_cbs(&rdp->cblist),
3244 rcu_segcblist_first_cb(&rdp->cblist));
3245}
3246#endif
3247
3248/*
3249 * On non-huge systems, use expedited RCU grace periods to make suspend
3250 * and hibernation run faster.
3251 */
3252static int rcu_pm_notify(struct notifier_block *self,
3253 unsigned long action, void *hcpu)
3254{
3255 switch (action) {
3256 case PM_HIBERNATION_PREPARE:
3257 case PM_SUSPEND_PREPARE:
3258 rcu_expedite_gp();
3259 break;
3260 case PM_POST_HIBERNATION:
3261 case PM_POST_SUSPEND:
3262 rcu_unexpedite_gp();
3263 break;
3264 default:
3265 break;
3266 }
3267 return NOTIFY_OK;
3268}
3269
3270/*
3271 * Spawn the kthreads that handle RCU's grace periods.
3272 */
3273static int __init rcu_spawn_gp_kthread(void)
3274{
3275 unsigned long flags;
3276 int kthread_prio_in = kthread_prio;
3277 struct rcu_node *rnp;
3278 struct sched_param sp;
3279 struct task_struct *t;
3280
3281 /* Force priority into range. */
3282 if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 2
3283 && IS_BUILTIN(CONFIG_RCU_TORTURE_TEST))
3284 kthread_prio = 2;
3285 else if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
3286 kthread_prio = 1;
3287 else if (kthread_prio < 0)
3288 kthread_prio = 0;
3289 else if (kthread_prio > 99)
3290 kthread_prio = 99;
3291
3292 if (kthread_prio != kthread_prio_in)
3293 pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
3294 kthread_prio, kthread_prio_in);
3295
3296 rcu_scheduler_fully_active = 1;
3297 t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name);
3298 if (WARN_ONCE(IS_ERR(t), "%s: Could not start grace-period kthread, OOM is now expected behavior\n", __func__))
3299 return 0;
3300 if (kthread_prio) {
3301 sp.sched_priority = kthread_prio;
3302 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
3303 }
3304 rnp = rcu_get_root();
3305 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3306 rcu_state.gp_kthread = t;
3307 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3308 wake_up_process(t);
3309 rcu_spawn_nocb_kthreads();
3310 rcu_spawn_boost_kthreads();
3311 return 0;
3312}
3313early_initcall(rcu_spawn_gp_kthread);
3314
3315/*
3316 * This function is invoked towards the end of the scheduler's
3317 * initialization process. Before this is called, the idle task might
3318 * contain synchronous grace-period primitives (during which time, this idle
3319 * task is booting the system, and such primitives are no-ops). After this
3320 * function is called, any synchronous grace-period primitives are run as
3321 * expedited, with the requesting task driving the grace period forward.
3322 * A later core_initcall() rcu_set_runtime_mode() will switch to full
3323 * runtime RCU functionality.
3324 */
3325void rcu_scheduler_starting(void)
3326{
3327 WARN_ON(num_online_cpus() != 1);
3328 WARN_ON(nr_context_switches() > 0);
3329 rcu_test_sync_prims();
3330 rcu_scheduler_active = RCU_SCHEDULER_INIT;
3331 rcu_test_sync_prims();
3332}
3333
3334/*
3335 * Helper function for rcu_init() that initializes the rcu_state structure.
3336 */
3337static void __init rcu_init_one(void)
3338{
3339 static const char * const buf[] = RCU_NODE_NAME_INIT;
3340 static const char * const fqs[] = RCU_FQS_NAME_INIT;
3341 static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
3342 static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
3343
3344 int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */
3345 int cpustride = 1;
3346 int i;
3347 int j;
3348 struct rcu_node *rnp;
3349
3350 BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
3351
3352 /* Silence gcc 4.8 false positive about array index out of range. */
3353 if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
3354 panic("rcu_init_one: rcu_num_lvls out of range");
3355
3356 /* Initialize the level-tracking arrays. */
3357
3358 for (i = 1; i < rcu_num_lvls; i++)
3359 rcu_state.level[i] =
3360 rcu_state.level[i - 1] + num_rcu_lvl[i - 1];
3361 rcu_init_levelspread(levelspread, num_rcu_lvl);
3362
3363 /* Initialize the elements themselves, starting from the leaves. */
3364
3365 for (i = rcu_num_lvls - 1; i >= 0; i--) {
3366 cpustride *= levelspread[i];
3367 rnp = rcu_state.level[i];
3368 for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
3369 raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
3370 lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
3371 &rcu_node_class[i], buf[i]);
3372 raw_spin_lock_init(&rnp->fqslock);
3373 lockdep_set_class_and_name(&rnp->fqslock,
3374 &rcu_fqs_class[i], fqs[i]);
3375 rnp->gp_seq = rcu_state.gp_seq;
3376 rnp->gp_seq_needed = rcu_state.gp_seq;
3377 rnp->completedqs = rcu_state.gp_seq;
3378 rnp->qsmask = 0;
3379 rnp->qsmaskinit = 0;
3380 rnp->grplo = j * cpustride;
3381 rnp->grphi = (j + 1) * cpustride - 1;
3382 if (rnp->grphi >= nr_cpu_ids)
3383 rnp->grphi = nr_cpu_ids - 1;
3384 if (i == 0) {
3385 rnp->grpnum = 0;
3386 rnp->grpmask = 0;
3387 rnp->parent = NULL;
3388 } else {
3389 rnp->grpnum = j % levelspread[i - 1];
3390 rnp->grpmask = BIT(rnp->grpnum);
3391 rnp->parent = rcu_state.level[i - 1] +
3392 j / levelspread[i - 1];
3393 }
3394 rnp->level = i;
3395 INIT_LIST_HEAD(&rnp->blkd_tasks);
3396 rcu_init_one_nocb(rnp);
3397 init_waitqueue_head(&rnp->exp_wq[0]);
3398 init_waitqueue_head(&rnp->exp_wq[1]);
3399 init_waitqueue_head(&rnp->exp_wq[2]);
3400 init_waitqueue_head(&rnp->exp_wq[3]);
3401 spin_lock_init(&rnp->exp_lock);
3402 }
3403 }
3404
3405 init_swait_queue_head(&rcu_state.gp_wq);
3406 init_swait_queue_head(&rcu_state.expedited_wq);
3407 rnp = rcu_first_leaf_node();
3408 for_each_possible_cpu(i) {
3409 while (i > rnp->grphi)
3410 rnp++;
3411 per_cpu_ptr(&rcu_data, i)->mynode = rnp;
3412 rcu_boot_init_percpu_data(i);
3413 }
3414}
3415
3416/*
3417 * Compute the rcu_node tree geometry from kernel parameters. This cannot
3418 * replace the definitions in tree.h because those are needed to size
3419 * the ->node array in the rcu_state structure.
3420 */
3421static void __init rcu_init_geometry(void)
3422{
3423 ulong d;
3424 int i;
3425 int rcu_capacity[RCU_NUM_LVLS];
3426
3427 /*
3428 * Initialize any unspecified boot parameters.
3429 * The default values of jiffies_till_first_fqs and
3430 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
3431 * value, which is a function of HZ, then adding one for each
3432 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
3433 */
3434 d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
3435 if (jiffies_till_first_fqs == ULONG_MAX)
3436 jiffies_till_first_fqs = d;
3437 if (jiffies_till_next_fqs == ULONG_MAX)
3438 jiffies_till_next_fqs = d;
3439 adjust_jiffies_till_sched_qs();
3440
3441 /* If the compile-time values are accurate, just leave. */
3442 if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
3443 nr_cpu_ids == NR_CPUS)
3444 return;
3445 pr_info("Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%u\n",
3446 rcu_fanout_leaf, nr_cpu_ids);
3447
3448 /*
3449 * The boot-time rcu_fanout_leaf parameter must be at least two
3450 * and cannot exceed the number of bits in the rcu_node masks.
3451 * Complain and fall back to the compile-time values if this
3452 * limit is exceeded.
3453 */
3454 if (rcu_fanout_leaf < 2 ||
3455 rcu_fanout_leaf > sizeof(unsigned long) * 8) {
3456 rcu_fanout_leaf = RCU_FANOUT_LEAF;
3457 WARN_ON(1);
3458 return;
3459 }
3460
3461 /*
3462 * Compute number of nodes that can be handled an rcu_node tree
3463 * with the given number of levels.
3464 */
3465 rcu_capacity[0] = rcu_fanout_leaf;
3466 for (i = 1; i < RCU_NUM_LVLS; i++)
3467 rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
3468
3469 /*
3470 * The tree must be able to accommodate the configured number of CPUs.
3471 * If this limit is exceeded, fall back to the compile-time values.
3472 */
3473 if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
3474 rcu_fanout_leaf = RCU_FANOUT_LEAF;
3475 WARN_ON(1);
3476 return;
3477 }
3478
3479 /* Calculate the number of levels in the tree. */
3480 for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
3481 }
3482 rcu_num_lvls = i + 1;
3483
3484 /* Calculate the number of rcu_nodes at each level of the tree. */
3485 for (i = 0; i < rcu_num_lvls; i++) {
3486 int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
3487 num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
3488 }
3489
3490 /* Calculate the total number of rcu_node structures. */
3491 rcu_num_nodes = 0;
3492 for (i = 0; i < rcu_num_lvls; i++)
3493 rcu_num_nodes += num_rcu_lvl[i];
3494}
3495
3496/*
3497 * Dump out the structure of the rcu_node combining tree associated
3498 * with the rcu_state structure.
3499 */
3500static void __init rcu_dump_rcu_node_tree(void)
3501{
3502 int level = 0;
3503 struct rcu_node *rnp;
3504
3505 pr_info("rcu_node tree layout dump\n");
3506 pr_info(" ");
3507 rcu_for_each_node_breadth_first(rnp) {
3508 if (rnp->level != level) {
3509 pr_cont("\n");
3510 pr_info(" ");
3511 level = rnp->level;
3512 }
3513 pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum);
3514 }
3515 pr_cont("\n");
3516}
3517
3518struct workqueue_struct *rcu_gp_wq;
3519struct workqueue_struct *rcu_par_gp_wq;
3520
3521void __init rcu_init(void)
3522{
3523 int cpu;
3524
3525 rcu_early_boot_tests();
3526
3527 rcu_bootup_announce();
3528 rcu_init_geometry();
3529 rcu_init_one();
3530 if (dump_tree)
3531 rcu_dump_rcu_node_tree();
3532 if (use_softirq)
3533 open_softirq(RCU_SOFTIRQ, rcu_core_si);
3534
3535 /*
3536 * We don't need protection against CPU-hotplug here because
3537 * this is called early in boot, before either interrupts
3538 * or the scheduler are operational.
3539 */
3540 pm_notifier(rcu_pm_notify, 0);
3541 for_each_online_cpu(cpu) {
3542 rcutree_prepare_cpu(cpu);
3543 rcu_cpu_starting(cpu);
3544 rcutree_online_cpu(cpu);
3545 }
3546
3547 /* Create workqueue for expedited GPs and for Tree SRCU. */
3548 rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
3549 WARN_ON(!rcu_gp_wq);
3550 rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0);
3551 WARN_ON(!rcu_par_gp_wq);
3552 srcu_init();
3553}
3554
3555#include "tree_stall.h"
3556#include "tree_exp.h"
3557#include "tree_plugin.h"
1/*
2 * Read-Copy Update mechanism for mutual exclusion
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, you can access it online at
16 * http://www.gnu.org/licenses/gpl-2.0.html.
17 *
18 * Copyright IBM Corporation, 2008
19 *
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
22 * Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
23 *
24 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
25 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
26 *
27 * For detailed explanation of Read-Copy Update mechanism see -
28 * Documentation/RCU
29 */
30#include <linux/types.h>
31#include <linux/kernel.h>
32#include <linux/init.h>
33#include <linux/spinlock.h>
34#include <linux/smp.h>
35#include <linux/rcupdate_wait.h>
36#include <linux/interrupt.h>
37#include <linux/sched.h>
38#include <linux/sched/debug.h>
39#include <linux/nmi.h>
40#include <linux/atomic.h>
41#include <linux/bitops.h>
42#include <linux/export.h>
43#include <linux/completion.h>
44#include <linux/moduleparam.h>
45#include <linux/percpu.h>
46#include <linux/notifier.h>
47#include <linux/cpu.h>
48#include <linux/mutex.h>
49#include <linux/time.h>
50#include <linux/kernel_stat.h>
51#include <linux/wait.h>
52#include <linux/kthread.h>
53#include <uapi/linux/sched/types.h>
54#include <linux/prefetch.h>
55#include <linux/delay.h>
56#include <linux/stop_machine.h>
57#include <linux/random.h>
58#include <linux/trace_events.h>
59#include <linux/suspend.h>
60#include <linux/ftrace.h>
61
62#include "tree.h"
63#include "rcu.h"
64
65#ifdef MODULE_PARAM_PREFIX
66#undef MODULE_PARAM_PREFIX
67#endif
68#define MODULE_PARAM_PREFIX "rcutree."
69
70/* Data structures. */
71
72/*
73 * In order to export the rcu_state name to the tracing tools, it
74 * needs to be added in the __tracepoint_string section.
75 * This requires defining a separate variable tp_<sname>_varname
76 * that points to the string being used, and this will allow
77 * the tracing userspace tools to be able to decipher the string
78 * address to the matching string.
79 */
80#ifdef CONFIG_TRACING
81# define DEFINE_RCU_TPS(sname) \
82static char sname##_varname[] = #sname; \
83static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname;
84# define RCU_STATE_NAME(sname) sname##_varname
85#else
86# define DEFINE_RCU_TPS(sname)
87# define RCU_STATE_NAME(sname) __stringify(sname)
88#endif
89
90#define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
91DEFINE_RCU_TPS(sname) \
92static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, sname##_data); \
93struct rcu_state sname##_state = { \
94 .level = { &sname##_state.node[0] }, \
95 .rda = &sname##_data, \
96 .call = cr, \
97 .gp_state = RCU_GP_IDLE, \
98 .gpnum = 0UL - 300UL, \
99 .completed = 0UL - 300UL, \
100 .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
101 .name = RCU_STATE_NAME(sname), \
102 .abbr = sabbr, \
103 .exp_mutex = __MUTEX_INITIALIZER(sname##_state.exp_mutex), \
104 .exp_wake_mutex = __MUTEX_INITIALIZER(sname##_state.exp_wake_mutex), \
105}
106
107RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
108RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);
109
110static struct rcu_state *const rcu_state_p;
111LIST_HEAD(rcu_struct_flavors);
112
113/* Dump rcu_node combining tree at boot to verify correct setup. */
114static bool dump_tree;
115module_param(dump_tree, bool, 0444);
116/* Control rcu_node-tree auto-balancing at boot time. */
117static bool rcu_fanout_exact;
118module_param(rcu_fanout_exact, bool, 0444);
119/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
120static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
121module_param(rcu_fanout_leaf, int, 0444);
122int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
123/* Number of rcu_nodes at specified level. */
124int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
125int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
126/* panic() on RCU Stall sysctl. */
127int sysctl_panic_on_rcu_stall __read_mostly;
128
129/*
130 * The rcu_scheduler_active variable is initialized to the value
131 * RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the
132 * first task is spawned. So when this variable is RCU_SCHEDULER_INACTIVE,
133 * RCU can assume that there is but one task, allowing RCU to (for example)
134 * optimize synchronize_rcu() to a simple barrier(). When this variable
135 * is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required
136 * to detect real grace periods. This variable is also used to suppress
137 * boot-time false positives from lockdep-RCU error checking. Finally, it
138 * transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU
139 * is fully initialized, including all of its kthreads having been spawned.
140 */
141int rcu_scheduler_active __read_mostly;
142EXPORT_SYMBOL_GPL(rcu_scheduler_active);
143
144/*
145 * The rcu_scheduler_fully_active variable transitions from zero to one
146 * during the early_initcall() processing, which is after the scheduler
147 * is capable of creating new tasks. So RCU processing (for example,
148 * creating tasks for RCU priority boosting) must be delayed until after
149 * rcu_scheduler_fully_active transitions from zero to one. We also
150 * currently delay invocation of any RCU callbacks until after this point.
151 *
152 * It might later prove better for people registering RCU callbacks during
153 * early boot to take responsibility for these callbacks, but one step at
154 * a time.
155 */
156static int rcu_scheduler_fully_active __read_mostly;
157
158static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
159static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
160static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
161static void invoke_rcu_core(void);
162static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
163static void rcu_report_exp_rdp(struct rcu_state *rsp,
164 struct rcu_data *rdp, bool wake);
165static void sync_sched_exp_online_cleanup(int cpu);
166
167/* rcuc/rcub kthread realtime priority */
168static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
169module_param(kthread_prio, int, 0644);
170
171/* Delay in jiffies for grace-period initialization delays, debug only. */
172
173static int gp_preinit_delay;
174module_param(gp_preinit_delay, int, 0444);
175static int gp_init_delay;
176module_param(gp_init_delay, int, 0444);
177static int gp_cleanup_delay;
178module_param(gp_cleanup_delay, int, 0444);
179
180/*
181 * Number of grace periods between delays, normalized by the duration of
182 * the delay. The longer the delay, the more the grace periods between
183 * each delay. The reason for this normalization is that it means that,
184 * for non-zero delays, the overall slowdown of grace periods is constant
185 * regardless of the duration of the delay. This arrangement balances
186 * the need for long delays to increase some race probabilities with the
187 * need for fast grace periods to increase other race probabilities.
188 */
189#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays. */
190
191/*
192 * Track the rcutorture test sequence number and the update version
193 * number within a given test. The rcutorture_testseq is incremented
194 * on every rcutorture module load and unload, so has an odd value
195 * when a test is running. The rcutorture_vernum is set to zero
196 * when rcutorture starts and is incremented on each rcutorture update.
197 * These variables enable correlating rcutorture output with the
198 * RCU tracing information.
199 */
200unsigned long rcutorture_testseq;
201unsigned long rcutorture_vernum;
202
203/*
204 * Compute the mask of online CPUs for the specified rcu_node structure.
205 * This will not be stable unless the rcu_node structure's ->lock is
206 * held, but the bit corresponding to the current CPU will be stable
207 * in most contexts.
208 */
209unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
210{
211 return READ_ONCE(rnp->qsmaskinitnext);
212}
213
214/*
215 * Return true if an RCU grace period is in progress. The READ_ONCE()s
216 * permit this function to be invoked without holding the root rcu_node
217 * structure's ->lock, but of course results can be subject to change.
218 */
219static int rcu_gp_in_progress(struct rcu_state *rsp)
220{
221 return READ_ONCE(rsp->completed) != READ_ONCE(rsp->gpnum);
222}
223
224/*
225 * Note a quiescent state. Because we do not need to know
226 * how many quiescent states passed, just if there was at least
227 * one since the start of the grace period, this just sets a flag.
228 * The caller must have disabled preemption.
229 */
230void rcu_sched_qs(void)
231{
232 RCU_LOCKDEP_WARN(preemptible(), "rcu_sched_qs() invoked with preemption enabled!!!");
233 if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.s))
234 return;
235 trace_rcu_grace_period(TPS("rcu_sched"),
236 __this_cpu_read(rcu_sched_data.gpnum),
237 TPS("cpuqs"));
238 __this_cpu_write(rcu_sched_data.cpu_no_qs.b.norm, false);
239 if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
240 return;
241 __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, false);
242 rcu_report_exp_rdp(&rcu_sched_state,
243 this_cpu_ptr(&rcu_sched_data), true);
244}
245
246void rcu_bh_qs(void)
247{
248 RCU_LOCKDEP_WARN(preemptible(), "rcu_bh_qs() invoked with preemption enabled!!!");
249 if (__this_cpu_read(rcu_bh_data.cpu_no_qs.s)) {
250 trace_rcu_grace_period(TPS("rcu_bh"),
251 __this_cpu_read(rcu_bh_data.gpnum),
252 TPS("cpuqs"));
253 __this_cpu_write(rcu_bh_data.cpu_no_qs.b.norm, false);
254 }
255}
256
257/*
258 * Steal a bit from the bottom of ->dynticks for idle entry/exit
259 * control. Initially this is for TLB flushing.
260 */
261#define RCU_DYNTICK_CTRL_MASK 0x1
262#define RCU_DYNTICK_CTRL_CTR (RCU_DYNTICK_CTRL_MASK + 1)
263#ifndef rcu_eqs_special_exit
264#define rcu_eqs_special_exit() do { } while (0)
265#endif
266
267static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
268 .dynticks_nesting = 1,
269 .dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
270 .dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR),
271};
272
273/*
274 * Record entry into an extended quiescent state. This is only to be
275 * called when not already in an extended quiescent state.
276 */
277static void rcu_dynticks_eqs_enter(void)
278{
279 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
280 int seq;
281
282 /*
283 * CPUs seeing atomic_add_return() must see prior RCU read-side
284 * critical sections, and we also must force ordering with the
285 * next idle sojourn.
286 */
287 seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
288 /* Better be in an extended quiescent state! */
289 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
290 (seq & RCU_DYNTICK_CTRL_CTR));
291 /* Better not have special action (TLB flush) pending! */
292 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
293 (seq & RCU_DYNTICK_CTRL_MASK));
294}
295
296/*
297 * Record exit from an extended quiescent state. This is only to be
298 * called from an extended quiescent state.
299 */
300static void rcu_dynticks_eqs_exit(void)
301{
302 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
303 int seq;
304
305 /*
306 * CPUs seeing atomic_add_return() must see prior idle sojourns,
307 * and we also must force ordering with the next RCU read-side
308 * critical section.
309 */
310 seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
311 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
312 !(seq & RCU_DYNTICK_CTRL_CTR));
313 if (seq & RCU_DYNTICK_CTRL_MASK) {
314 atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdtp->dynticks);
315 smp_mb__after_atomic(); /* _exit after clearing mask. */
316 /* Prefer duplicate flushes to losing a flush. */
317 rcu_eqs_special_exit();
318 }
319}
320
321/*
322 * Reset the current CPU's ->dynticks counter to indicate that the
323 * newly onlined CPU is no longer in an extended quiescent state.
324 * This will either leave the counter unchanged, or increment it
325 * to the next non-quiescent value.
326 *
327 * The non-atomic test/increment sequence works because the upper bits
328 * of the ->dynticks counter are manipulated only by the corresponding CPU,
329 * or when the corresponding CPU is offline.
330 */
331static void rcu_dynticks_eqs_online(void)
332{
333 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
334
335 if (atomic_read(&rdtp->dynticks) & RCU_DYNTICK_CTRL_CTR)
336 return;
337 atomic_add(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
338}
339
340/*
341 * Is the current CPU in an extended quiescent state?
342 *
343 * No ordering, as we are sampling CPU-local information.
344 */
345bool rcu_dynticks_curr_cpu_in_eqs(void)
346{
347 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
348
349 return !(atomic_read(&rdtp->dynticks) & RCU_DYNTICK_CTRL_CTR);
350}
351
352/*
353 * Snapshot the ->dynticks counter with full ordering so as to allow
354 * stable comparison of this counter with past and future snapshots.
355 */
356int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
357{
358 int snap = atomic_add_return(0, &rdtp->dynticks);
359
360 return snap & ~RCU_DYNTICK_CTRL_MASK;
361}
362
363/*
364 * Return true if the snapshot returned from rcu_dynticks_snap()
365 * indicates that RCU is in an extended quiescent state.
366 */
367static bool rcu_dynticks_in_eqs(int snap)
368{
369 return !(snap & RCU_DYNTICK_CTRL_CTR);
370}
371
372/*
373 * Return true if the CPU corresponding to the specified rcu_dynticks
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_dynticks *rdtp, int snap)
378{
379 return snap != rcu_dynticks_snap(rdtp);
380}
381
382/*
383 * Do a double-increment of the ->dynticks counter to emulate a
384 * momentary idle-CPU quiescent state.
385 */
386static void rcu_dynticks_momentary_idle(void)
387{
388 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
389 int special = atomic_add_return(2 * RCU_DYNTICK_CTRL_CTR,
390 &rdtp->dynticks);
391
392 /* It is illegal to call this from idle state. */
393 WARN_ON_ONCE(!(special & RCU_DYNTICK_CTRL_CTR));
394}
395
396/*
397 * Set the special (bottom) bit of the specified CPU so that it
398 * will take special action (such as flushing its TLB) on the
399 * next exit from an extended quiescent state. Returns true if
400 * the bit was successfully set, or false if the CPU was not in
401 * an extended quiescent state.
402 */
403bool rcu_eqs_special_set(int cpu)
404{
405 int old;
406 int new;
407 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
408
409 do {
410 old = atomic_read(&rdtp->dynticks);
411 if (old & RCU_DYNTICK_CTRL_CTR)
412 return false;
413 new = old | RCU_DYNTICK_CTRL_MASK;
414 } while (atomic_cmpxchg(&rdtp->dynticks, old, new) != old);
415 return true;
416}
417
418/*
419 * Let the RCU core know that this CPU has gone through the scheduler,
420 * which is a quiescent state. This is called when the need for a
421 * quiescent state is urgent, so we burn an atomic operation and full
422 * memory barriers to let the RCU core know about it, regardless of what
423 * this CPU might (or might not) do in the near future.
424 *
425 * We inform the RCU core by emulating a zero-duration dyntick-idle period.
426 *
427 * The caller must have disabled interrupts.
428 */
429static void rcu_momentary_dyntick_idle(void)
430{
431 raw_cpu_write(rcu_dynticks.rcu_need_heavy_qs, false);
432 rcu_dynticks_momentary_idle();
433}
434
435/*
436 * Note a context switch. This is a quiescent state for RCU-sched,
437 * and requires special handling for preemptible RCU.
438 * The caller must have disabled interrupts.
439 */
440void rcu_note_context_switch(bool preempt)
441{
442 barrier(); /* Avoid RCU read-side critical sections leaking down. */
443 trace_rcu_utilization(TPS("Start context switch"));
444 rcu_sched_qs();
445 rcu_preempt_note_context_switch(preempt);
446 /* Load rcu_urgent_qs before other flags. */
447 if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs)))
448 goto out;
449 this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
450 if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs)))
451 rcu_momentary_dyntick_idle();
452 this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
453 if (!preempt)
454 rcu_note_voluntary_context_switch_lite(current);
455out:
456 trace_rcu_utilization(TPS("End context switch"));
457 barrier(); /* Avoid RCU read-side critical sections leaking up. */
458}
459EXPORT_SYMBOL_GPL(rcu_note_context_switch);
460
461/*
462 * Register a quiescent state for all RCU flavors. If there is an
463 * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
464 * dyntick-idle quiescent state visible to other CPUs (but only for those
465 * RCU flavors in desperate need of a quiescent state, which will normally
466 * be none of them). Either way, do a lightweight quiescent state for
467 * all RCU flavors.
468 *
469 * The barrier() calls are redundant in the common case when this is
470 * called externally, but just in case this is called from within this
471 * file.
472 *
473 */
474void rcu_all_qs(void)
475{
476 unsigned long flags;
477
478 if (!raw_cpu_read(rcu_dynticks.rcu_urgent_qs))
479 return;
480 preempt_disable();
481 /* Load rcu_urgent_qs before other flags. */
482 if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) {
483 preempt_enable();
484 return;
485 }
486 this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
487 barrier(); /* Avoid RCU read-side critical sections leaking down. */
488 if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) {
489 local_irq_save(flags);
490 rcu_momentary_dyntick_idle();
491 local_irq_restore(flags);
492 }
493 if (unlikely(raw_cpu_read(rcu_sched_data.cpu_no_qs.b.exp)))
494 rcu_sched_qs();
495 this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
496 barrier(); /* Avoid RCU read-side critical sections leaking up. */
497 preempt_enable();
498}
499EXPORT_SYMBOL_GPL(rcu_all_qs);
500
501#define DEFAULT_RCU_BLIMIT 10 /* Maximum callbacks per rcu_do_batch. */
502static long blimit = DEFAULT_RCU_BLIMIT;
503#define DEFAULT_RCU_QHIMARK 10000 /* If this many pending, ignore blimit. */
504static long qhimark = DEFAULT_RCU_QHIMARK;
505#define DEFAULT_RCU_QLOMARK 100 /* Once only this many pending, use blimit. */
506static long qlowmark = DEFAULT_RCU_QLOMARK;
507
508module_param(blimit, long, 0444);
509module_param(qhimark, long, 0444);
510module_param(qlowmark, long, 0444);
511
512static ulong jiffies_till_first_fqs = ULONG_MAX;
513static ulong jiffies_till_next_fqs = ULONG_MAX;
514static bool rcu_kick_kthreads;
515
516module_param(jiffies_till_first_fqs, ulong, 0644);
517module_param(jiffies_till_next_fqs, ulong, 0644);
518module_param(rcu_kick_kthreads, bool, 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 = HZ / 10;
525module_param(jiffies_till_sched_qs, ulong, 0444);
526
527static bool rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
528 struct rcu_data *rdp);
529static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp));
530static void force_quiescent_state(struct rcu_state *rsp);
531static int rcu_pending(void);
532
533/*
534 * Return the number of RCU batches started thus far for debug & stats.
535 */
536unsigned long rcu_batches_started(void)
537{
538 return rcu_state_p->gpnum;
539}
540EXPORT_SYMBOL_GPL(rcu_batches_started);
541
542/*
543 * Return the number of RCU-sched batches started thus far for debug & stats.
544 */
545unsigned long rcu_batches_started_sched(void)
546{
547 return rcu_sched_state.gpnum;
548}
549EXPORT_SYMBOL_GPL(rcu_batches_started_sched);
550
551/*
552 * Return the number of RCU BH batches started thus far for debug & stats.
553 */
554unsigned long rcu_batches_started_bh(void)
555{
556 return rcu_bh_state.gpnum;
557}
558EXPORT_SYMBOL_GPL(rcu_batches_started_bh);
559
560/*
561 * Return the number of RCU batches completed thus far for debug & stats.
562 */
563unsigned long rcu_batches_completed(void)
564{
565 return rcu_state_p->completed;
566}
567EXPORT_SYMBOL_GPL(rcu_batches_completed);
568
569/*
570 * Return the number of RCU-sched batches completed thus far for debug & stats.
571 */
572unsigned long rcu_batches_completed_sched(void)
573{
574 return rcu_sched_state.completed;
575}
576EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
577
578/*
579 * Return the number of RCU BH batches completed thus far for debug & stats.
580 */
581unsigned long rcu_batches_completed_bh(void)
582{
583 return rcu_bh_state.completed;
584}
585EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
586
587/*
588 * Return the number of RCU expedited batches completed thus far for
589 * debug & stats. Odd numbers mean that a batch is in progress, even
590 * numbers mean idle. The value returned will thus be roughly double
591 * the cumulative batches since boot.
592 */
593unsigned long rcu_exp_batches_completed(void)
594{
595 return rcu_state_p->expedited_sequence;
596}
597EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
598
599/*
600 * Return the number of RCU-sched expedited batches completed thus far
601 * for debug & stats. Similar to rcu_exp_batches_completed().
602 */
603unsigned long rcu_exp_batches_completed_sched(void)
604{
605 return rcu_sched_state.expedited_sequence;
606}
607EXPORT_SYMBOL_GPL(rcu_exp_batches_completed_sched);
608
609/*
610 * Force a quiescent state.
611 */
612void rcu_force_quiescent_state(void)
613{
614 force_quiescent_state(rcu_state_p);
615}
616EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
617
618/*
619 * Force a quiescent state for RCU BH.
620 */
621void rcu_bh_force_quiescent_state(void)
622{
623 force_quiescent_state(&rcu_bh_state);
624}
625EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
626
627/*
628 * Force a quiescent state for RCU-sched.
629 */
630void rcu_sched_force_quiescent_state(void)
631{
632 force_quiescent_state(&rcu_sched_state);
633}
634EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
635
636/*
637 * Show the state of the grace-period kthreads.
638 */
639void show_rcu_gp_kthreads(void)
640{
641 struct rcu_state *rsp;
642
643 for_each_rcu_flavor(rsp) {
644 pr_info("%s: wait state: %d ->state: %#lx\n",
645 rsp->name, rsp->gp_state, rsp->gp_kthread->state);
646 /* sched_show_task(rsp->gp_kthread); */
647 }
648}
649EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
650
651/*
652 * Record the number of times rcutorture tests have been initiated and
653 * terminated. This information allows the debugfs tracing stats to be
654 * correlated to the rcutorture messages, even when the rcutorture module
655 * is being repeatedly loaded and unloaded. In other words, we cannot
656 * store this state in rcutorture itself.
657 */
658void rcutorture_record_test_transition(void)
659{
660 rcutorture_testseq++;
661 rcutorture_vernum = 0;
662}
663EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);
664
665/*
666 * Send along grace-period-related data for rcutorture diagnostics.
667 */
668void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
669 unsigned long *gpnum, unsigned long *completed)
670{
671 struct rcu_state *rsp = NULL;
672
673 switch (test_type) {
674 case RCU_FLAVOR:
675 rsp = rcu_state_p;
676 break;
677 case RCU_BH_FLAVOR:
678 rsp = &rcu_bh_state;
679 break;
680 case RCU_SCHED_FLAVOR:
681 rsp = &rcu_sched_state;
682 break;
683 default:
684 break;
685 }
686 if (rsp == NULL)
687 return;
688 *flags = READ_ONCE(rsp->gp_flags);
689 *gpnum = READ_ONCE(rsp->gpnum);
690 *completed = READ_ONCE(rsp->completed);
691}
692EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
693
694/*
695 * Record the number of writer passes through the current rcutorture test.
696 * This is also used to correlate debugfs tracing stats with the rcutorture
697 * messages.
698 */
699void rcutorture_record_progress(unsigned long vernum)
700{
701 rcutorture_vernum++;
702}
703EXPORT_SYMBOL_GPL(rcutorture_record_progress);
704
705/*
706 * Return the root node of the specified rcu_state structure.
707 */
708static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
709{
710 return &rsp->node[0];
711}
712
713/*
714 * Is there any need for future grace periods?
715 * Interrupts must be disabled. If the caller does not hold the root
716 * rnp_node structure's ->lock, the results are advisory only.
717 */
718static int rcu_future_needs_gp(struct rcu_state *rsp)
719{
720 struct rcu_node *rnp = rcu_get_root(rsp);
721 int idx = (READ_ONCE(rnp->completed) + 1) & 0x1;
722 int *fp = &rnp->need_future_gp[idx];
723
724 lockdep_assert_irqs_disabled();
725 return READ_ONCE(*fp);
726}
727
728/*
729 * Does the current CPU require a not-yet-started grace period?
730 * The caller must have disabled interrupts to prevent races with
731 * normal callback registry.
732 */
733static bool
734cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
735{
736 lockdep_assert_irqs_disabled();
737 if (rcu_gp_in_progress(rsp))
738 return false; /* No, a grace period is already in progress. */
739 if (rcu_future_needs_gp(rsp))
740 return true; /* Yes, a no-CBs CPU needs one. */
741 if (!rcu_segcblist_is_enabled(&rdp->cblist))
742 return false; /* No, this is a no-CBs (or offline) CPU. */
743 if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
744 return true; /* Yes, CPU has newly registered callbacks. */
745 if (rcu_segcblist_future_gp_needed(&rdp->cblist,
746 READ_ONCE(rsp->completed)))
747 return true; /* Yes, CBs for future grace period. */
748 return false; /* No grace period needed. */
749}
750
751/*
752 * Enter an RCU extended quiescent state, which can be either the
753 * idle loop or adaptive-tickless usermode execution.
754 *
755 * We crowbar the ->dynticks_nmi_nesting field to zero to allow for
756 * the possibility of usermode upcalls having messed up our count
757 * of interrupt nesting level during the prior busy period.
758 */
759static void rcu_eqs_enter(bool user)
760{
761 struct rcu_state *rsp;
762 struct rcu_data *rdp;
763 struct rcu_dynticks *rdtp;
764
765 rdtp = this_cpu_ptr(&rcu_dynticks);
766 WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0);
767 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
768 rdtp->dynticks_nesting == 0);
769 if (rdtp->dynticks_nesting != 1) {
770 rdtp->dynticks_nesting--;
771 return;
772 }
773
774 lockdep_assert_irqs_disabled();
775 trace_rcu_dyntick(TPS("Start"), rdtp->dynticks_nesting, 0, rdtp->dynticks);
776 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
777 for_each_rcu_flavor(rsp) {
778 rdp = this_cpu_ptr(rsp->rda);
779 do_nocb_deferred_wakeup(rdp);
780 }
781 rcu_prepare_for_idle();
782 WRITE_ONCE(rdtp->dynticks_nesting, 0); /* Avoid irq-access tearing. */
783 rcu_dynticks_eqs_enter();
784 rcu_dynticks_task_enter();
785}
786
787/**
788 * rcu_idle_enter - inform RCU that current CPU is entering idle
789 *
790 * Enter idle mode, in other words, -leave- the mode in which RCU
791 * read-side critical sections can occur. (Though RCU read-side
792 * critical sections can occur in irq handlers in idle, a possibility
793 * handled by irq_enter() and irq_exit().)
794 *
795 * If you add or remove a call to rcu_idle_enter(), be sure to test with
796 * CONFIG_RCU_EQS_DEBUG=y.
797 */
798void rcu_idle_enter(void)
799{
800 lockdep_assert_irqs_disabled();
801 rcu_eqs_enter(false);
802}
803
804#ifdef CONFIG_NO_HZ_FULL
805/**
806 * rcu_user_enter - inform RCU that we are resuming userspace.
807 *
808 * Enter RCU idle mode right before resuming userspace. No use of RCU
809 * is permitted between this call and rcu_user_exit(). This way the
810 * CPU doesn't need to maintain the tick for RCU maintenance purposes
811 * when the CPU runs in userspace.
812 *
813 * If you add or remove a call to rcu_user_enter(), be sure to test with
814 * CONFIG_RCU_EQS_DEBUG=y.
815 */
816void rcu_user_enter(void)
817{
818 lockdep_assert_irqs_disabled();
819 rcu_eqs_enter(true);
820}
821#endif /* CONFIG_NO_HZ_FULL */
822
823/**
824 * rcu_nmi_exit - inform RCU of exit from NMI context
825 *
826 * If we are returning from the outermost NMI handler that interrupted an
827 * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting
828 * to let the RCU grace-period handling know that the CPU is back to
829 * being RCU-idle.
830 *
831 * If you add or remove a call to rcu_nmi_exit(), be sure to test
832 * with CONFIG_RCU_EQS_DEBUG=y.
833 */
834void rcu_nmi_exit(void)
835{
836 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
837
838 /*
839 * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
840 * (We are exiting an NMI handler, so RCU better be paying attention
841 * to us!)
842 */
843 WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0);
844 WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs());
845
846 /*
847 * If the nesting level is not 1, the CPU wasn't RCU-idle, so
848 * leave it in non-RCU-idle state.
849 */
850 if (rdtp->dynticks_nmi_nesting != 1) {
851 trace_rcu_dyntick(TPS("--="), rdtp->dynticks_nmi_nesting, rdtp->dynticks_nmi_nesting - 2, rdtp->dynticks);
852 WRITE_ONCE(rdtp->dynticks_nmi_nesting, /* No store tearing. */
853 rdtp->dynticks_nmi_nesting - 2);
854 return;
855 }
856
857 /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
858 trace_rcu_dyntick(TPS("Startirq"), rdtp->dynticks_nmi_nesting, 0, rdtp->dynticks);
859 WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
860 rcu_dynticks_eqs_enter();
861}
862
863/**
864 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
865 *
866 * Exit from an interrupt handler, which might possibly result in entering
867 * idle mode, in other words, leaving the mode in which read-side critical
868 * sections can occur. The caller must have disabled interrupts.
869 *
870 * This code assumes that the idle loop never does anything that might
871 * result in unbalanced calls to irq_enter() and irq_exit(). If your
872 * architecture's idle loop violates this assumption, RCU will give you what
873 * you deserve, good and hard. But very infrequently and irreproducibly.
874 *
875 * Use things like work queues to work around this limitation.
876 *
877 * You have been warned.
878 *
879 * If you add or remove a call to rcu_irq_exit(), be sure to test with
880 * CONFIG_RCU_EQS_DEBUG=y.
881 */
882void rcu_irq_exit(void)
883{
884 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
885
886 lockdep_assert_irqs_disabled();
887 if (rdtp->dynticks_nmi_nesting == 1)
888 rcu_prepare_for_idle();
889 rcu_nmi_exit();
890 if (rdtp->dynticks_nmi_nesting == 0)
891 rcu_dynticks_task_enter();
892}
893
894/*
895 * Wrapper for rcu_irq_exit() where interrupts are enabled.
896 *
897 * If you add or remove a call to rcu_irq_exit_irqson(), be sure to test
898 * with CONFIG_RCU_EQS_DEBUG=y.
899 */
900void rcu_irq_exit_irqson(void)
901{
902 unsigned long flags;
903
904 local_irq_save(flags);
905 rcu_irq_exit();
906 local_irq_restore(flags);
907}
908
909/*
910 * Exit an RCU extended quiescent state, which can be either the
911 * idle loop or adaptive-tickless usermode execution.
912 *
913 * We crowbar the ->dynticks_nmi_nesting field to DYNTICK_IRQ_NONIDLE to
914 * allow for the possibility of usermode upcalls messing up our count of
915 * interrupt nesting level during the busy period that is just now starting.
916 */
917static void rcu_eqs_exit(bool user)
918{
919 struct rcu_dynticks *rdtp;
920 long oldval;
921
922 lockdep_assert_irqs_disabled();
923 rdtp = this_cpu_ptr(&rcu_dynticks);
924 oldval = rdtp->dynticks_nesting;
925 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
926 if (oldval) {
927 rdtp->dynticks_nesting++;
928 return;
929 }
930 rcu_dynticks_task_exit();
931 rcu_dynticks_eqs_exit();
932 rcu_cleanup_after_idle();
933 trace_rcu_dyntick(TPS("End"), rdtp->dynticks_nesting, 1, rdtp->dynticks);
934 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
935 WRITE_ONCE(rdtp->dynticks_nesting, 1);
936 WRITE_ONCE(rdtp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE);
937}
938
939/**
940 * rcu_idle_exit - inform RCU that current CPU is leaving idle
941 *
942 * Exit idle mode, in other words, -enter- the mode in which RCU
943 * read-side critical sections can occur.
944 *
945 * If you add or remove a call to rcu_idle_exit(), be sure to test with
946 * CONFIG_RCU_EQS_DEBUG=y.
947 */
948void rcu_idle_exit(void)
949{
950 unsigned long flags;
951
952 local_irq_save(flags);
953 rcu_eqs_exit(false);
954 local_irq_restore(flags);
955}
956
957#ifdef CONFIG_NO_HZ_FULL
958/**
959 * rcu_user_exit - inform RCU that we are exiting userspace.
960 *
961 * Exit RCU idle mode while entering the kernel because it can
962 * run a RCU read side critical section anytime.
963 *
964 * If you add or remove a call to rcu_user_exit(), be sure to test with
965 * CONFIG_RCU_EQS_DEBUG=y.
966 */
967void rcu_user_exit(void)
968{
969 rcu_eqs_exit(1);
970}
971#endif /* CONFIG_NO_HZ_FULL */
972
973/**
974 * rcu_nmi_enter - inform RCU of entry to NMI context
975 *
976 * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and
977 * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know
978 * that the CPU is active. This implementation permits nested NMIs, as
979 * long as the nesting level does not overflow an int. (You will probably
980 * run out of stack space first.)
981 *
982 * If you add or remove a call to rcu_nmi_enter(), be sure to test
983 * with CONFIG_RCU_EQS_DEBUG=y.
984 */
985void rcu_nmi_enter(void)
986{
987 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
988 long incby = 2;
989
990 /* Complain about underflow. */
991 WARN_ON_ONCE(rdtp->dynticks_nmi_nesting < 0);
992
993 /*
994 * If idle from RCU viewpoint, atomically increment ->dynticks
995 * to mark non-idle and increment ->dynticks_nmi_nesting by one.
996 * Otherwise, increment ->dynticks_nmi_nesting by two. This means
997 * if ->dynticks_nmi_nesting is equal to one, we are guaranteed
998 * to be in the outermost NMI handler that interrupted an RCU-idle
999 * period (observation due to Andy Lutomirski).
1000 */
1001 if (rcu_dynticks_curr_cpu_in_eqs()) {
1002 rcu_dynticks_eqs_exit();
1003 incby = 1;
1004 }
1005 trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
1006 rdtp->dynticks_nmi_nesting,
1007 rdtp->dynticks_nmi_nesting + incby, rdtp->dynticks);
1008 WRITE_ONCE(rdtp->dynticks_nmi_nesting, /* Prevent store tearing. */
1009 rdtp->dynticks_nmi_nesting + incby);
1010 barrier();
1011}
1012
1013/**
1014 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
1015 *
1016 * Enter an interrupt handler, which might possibly result in exiting
1017 * idle mode, in other words, entering the mode in which read-side critical
1018 * sections can occur. The caller must have disabled interrupts.
1019 *
1020 * Note that the Linux kernel is fully capable of entering an interrupt
1021 * handler that it never exits, for example when doing upcalls to user mode!
1022 * This code assumes that the idle loop never does upcalls to user mode.
1023 * If your architecture's idle loop does do upcalls to user mode (or does
1024 * anything else that results in unbalanced calls to the irq_enter() and
1025 * irq_exit() functions), RCU will give you what you deserve, good and hard.
1026 * But very infrequently and irreproducibly.
1027 *
1028 * Use things like work queues to work around this limitation.
1029 *
1030 * You have been warned.
1031 *
1032 * If you add or remove a call to rcu_irq_enter(), be sure to test with
1033 * CONFIG_RCU_EQS_DEBUG=y.
1034 */
1035void rcu_irq_enter(void)
1036{
1037 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1038
1039 lockdep_assert_irqs_disabled();
1040 if (rdtp->dynticks_nmi_nesting == 0)
1041 rcu_dynticks_task_exit();
1042 rcu_nmi_enter();
1043 if (rdtp->dynticks_nmi_nesting == 1)
1044 rcu_cleanup_after_idle();
1045}
1046
1047/*
1048 * Wrapper for rcu_irq_enter() where interrupts are enabled.
1049 *
1050 * If you add or remove a call to rcu_irq_enter_irqson(), be sure to test
1051 * with CONFIG_RCU_EQS_DEBUG=y.
1052 */
1053void rcu_irq_enter_irqson(void)
1054{
1055 unsigned long flags;
1056
1057 local_irq_save(flags);
1058 rcu_irq_enter();
1059 local_irq_restore(flags);
1060}
1061
1062/**
1063 * rcu_is_watching - see if RCU thinks that the current CPU is idle
1064 *
1065 * Return true if RCU is watching the running CPU, which means that this
1066 * CPU can safely enter RCU read-side critical sections. In other words,
1067 * if the current CPU is in its idle loop and is neither in an interrupt
1068 * or NMI handler, return true.
1069 */
1070bool notrace rcu_is_watching(void)
1071{
1072 bool ret;
1073
1074 preempt_disable_notrace();
1075 ret = !rcu_dynticks_curr_cpu_in_eqs();
1076 preempt_enable_notrace();
1077 return ret;
1078}
1079EXPORT_SYMBOL_GPL(rcu_is_watching);
1080
1081/*
1082 * If a holdout task is actually running, request an urgent quiescent
1083 * state from its CPU. This is unsynchronized, so migrations can cause
1084 * the request to go to the wrong CPU. Which is OK, all that will happen
1085 * is that the CPU's next context switch will be a bit slower and next
1086 * time around this task will generate another request.
1087 */
1088void rcu_request_urgent_qs_task(struct task_struct *t)
1089{
1090 int cpu;
1091
1092 barrier();
1093 cpu = task_cpu(t);
1094 if (!task_curr(t))
1095 return; /* This task is not running on that CPU. */
1096 smp_store_release(per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, cpu), true);
1097}
1098
1099#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
1100
1101/*
1102 * Is the current CPU online? Disable preemption to avoid false positives
1103 * that could otherwise happen due to the current CPU number being sampled,
1104 * this task being preempted, its old CPU being taken offline, resuming
1105 * on some other CPU, then determining that its old CPU is now offline.
1106 * It is OK to use RCU on an offline processor during initial boot, hence
1107 * the check for rcu_scheduler_fully_active. Note also that it is OK
1108 * for a CPU coming online to use RCU for one jiffy prior to marking itself
1109 * online in the cpu_online_mask. Similarly, it is OK for a CPU going
1110 * offline to continue to use RCU for one jiffy after marking itself
1111 * offline in the cpu_online_mask. This leniency is necessary given the
1112 * non-atomic nature of the online and offline processing, for example,
1113 * the fact that a CPU enters the scheduler after completing the teardown
1114 * of the CPU.
1115 *
1116 * This is also why RCU internally marks CPUs online during in the
1117 * preparation phase and offline after the CPU has been taken down.
1118 *
1119 * Disable checking if in an NMI handler because we cannot safely report
1120 * errors from NMI handlers anyway.
1121 */
1122bool rcu_lockdep_current_cpu_online(void)
1123{
1124 struct rcu_data *rdp;
1125 struct rcu_node *rnp;
1126 bool ret;
1127
1128 if (in_nmi())
1129 return true;
1130 preempt_disable();
1131 rdp = this_cpu_ptr(&rcu_sched_data);
1132 rnp = rdp->mynode;
1133 ret = (rdp->grpmask & rcu_rnp_online_cpus(rnp)) ||
1134 !rcu_scheduler_fully_active;
1135 preempt_enable();
1136 return ret;
1137}
1138EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
1139
1140#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
1141
1142/**
1143 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
1144 *
1145 * If the current CPU is idle or running at a first-level (not nested)
1146 * interrupt from idle, return true. The caller must have at least
1147 * disabled preemption.
1148 */
1149static int rcu_is_cpu_rrupt_from_idle(void)
1150{
1151 return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 0 &&
1152 __this_cpu_read(rcu_dynticks.dynticks_nmi_nesting) <= 1;
1153}
1154
1155/*
1156 * We are reporting a quiescent state on behalf of some other CPU, so
1157 * it is our responsibility to check for and handle potential overflow
1158 * of the rcu_node ->gpnum counter with respect to the rcu_data counters.
1159 * After all, the CPU might be in deep idle state, and thus executing no
1160 * code whatsoever.
1161 */
1162static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
1163{
1164 raw_lockdep_assert_held_rcu_node(rnp);
1165 if (ULONG_CMP_LT(READ_ONCE(rdp->gpnum) + ULONG_MAX / 4, rnp->gpnum))
1166 WRITE_ONCE(rdp->gpwrap, true);
1167 if (ULONG_CMP_LT(rdp->rcu_iw_gpnum + ULONG_MAX / 4, rnp->gpnum))
1168 rdp->rcu_iw_gpnum = rnp->gpnum + ULONG_MAX / 4;
1169}
1170
1171/*
1172 * Snapshot the specified CPU's dynticks counter so that we can later
1173 * credit them with an implicit quiescent state. Return 1 if this CPU
1174 * is in dynticks idle mode, which is an extended quiescent state.
1175 */
1176static int dyntick_save_progress_counter(struct rcu_data *rdp)
1177{
1178 rdp->dynticks_snap = rcu_dynticks_snap(rdp->dynticks);
1179 if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
1180 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
1181 rcu_gpnum_ovf(rdp->mynode, rdp);
1182 return 1;
1183 }
1184 return 0;
1185}
1186
1187/*
1188 * Handler for the irq_work request posted when a grace period has
1189 * gone on for too long, but not yet long enough for an RCU CPU
1190 * stall warning. Set state appropriately, but just complain if
1191 * there is unexpected state on entry.
1192 */
1193static void rcu_iw_handler(struct irq_work *iwp)
1194{
1195 struct rcu_data *rdp;
1196 struct rcu_node *rnp;
1197
1198 rdp = container_of(iwp, struct rcu_data, rcu_iw);
1199 rnp = rdp->mynode;
1200 raw_spin_lock_rcu_node(rnp);
1201 if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
1202 rdp->rcu_iw_gpnum = rnp->gpnum;
1203 rdp->rcu_iw_pending = false;
1204 }
1205 raw_spin_unlock_rcu_node(rnp);
1206}
1207
1208/*
1209 * Return true if the specified CPU has passed through a quiescent
1210 * state by virtue of being in or having passed through an dynticks
1211 * idle state since the last call to dyntick_save_progress_counter()
1212 * for this same CPU, or by virtue of having been offline.
1213 */
1214static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
1215{
1216 unsigned long jtsq;
1217 bool *rnhqp;
1218 bool *ruqp;
1219 struct rcu_node *rnp = rdp->mynode;
1220
1221 /*
1222 * If the CPU passed through or entered a dynticks idle phase with
1223 * no active irq/NMI handlers, then we can safely pretend that the CPU
1224 * already acknowledged the request to pass through a quiescent
1225 * state. Either way, that CPU cannot possibly be in an RCU
1226 * read-side critical section that started before the beginning
1227 * of the current RCU grace period.
1228 */
1229 if (rcu_dynticks_in_eqs_since(rdp->dynticks, rdp->dynticks_snap)) {
1230 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
1231 rdp->dynticks_fqs++;
1232 rcu_gpnum_ovf(rnp, rdp);
1233 return 1;
1234 }
1235
1236 /*
1237 * Has this CPU encountered a cond_resched_rcu_qs() since the
1238 * beginning of the grace period? For this to be the case,
1239 * the CPU has to have noticed the current grace period. This
1240 * might not be the case for nohz_full CPUs looping in the kernel.
1241 */
1242 jtsq = jiffies_till_sched_qs;
1243 ruqp = per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, rdp->cpu);
1244 if (time_after(jiffies, rdp->rsp->gp_start + jtsq) &&
1245 READ_ONCE(rdp->rcu_qs_ctr_snap) != per_cpu(rcu_dynticks.rcu_qs_ctr, rdp->cpu) &&
1246 READ_ONCE(rdp->gpnum) == rnp->gpnum && !rdp->gpwrap) {
1247 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("rqc"));
1248 rcu_gpnum_ovf(rnp, rdp);
1249 return 1;
1250 } else if (time_after(jiffies, rdp->rsp->gp_start + jtsq)) {
1251 /* Load rcu_qs_ctr before store to rcu_urgent_qs. */
1252 smp_store_release(ruqp, true);
1253 }
1254
1255 /* Check for the CPU being offline. */
1256 if (!(rdp->grpmask & rcu_rnp_online_cpus(rnp))) {
1257 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));
1258 rdp->offline_fqs++;
1259 rcu_gpnum_ovf(rnp, rdp);
1260 return 1;
1261 }
1262
1263 /*
1264 * A CPU running for an extended time within the kernel can
1265 * delay RCU grace periods. When the CPU is in NO_HZ_FULL mode,
1266 * even context-switching back and forth between a pair of
1267 * in-kernel CPU-bound tasks cannot advance grace periods.
1268 * So if the grace period is old enough, make the CPU pay attention.
1269 * Note that the unsynchronized assignments to the per-CPU
1270 * rcu_need_heavy_qs variable are safe. Yes, setting of
1271 * bits can be lost, but they will be set again on the next
1272 * force-quiescent-state pass. So lost bit sets do not result
1273 * in incorrect behavior, merely in a grace period lasting
1274 * a few jiffies longer than it might otherwise. Because
1275 * there are at most four threads involved, and because the
1276 * updates are only once every few jiffies, the probability of
1277 * lossage (and thus of slight grace-period extension) is
1278 * quite low.
1279 */
1280 rnhqp = &per_cpu(rcu_dynticks.rcu_need_heavy_qs, rdp->cpu);
1281 if (!READ_ONCE(*rnhqp) &&
1282 (time_after(jiffies, rdp->rsp->gp_start + jtsq) ||
1283 time_after(jiffies, rdp->rsp->jiffies_resched))) {
1284 WRITE_ONCE(*rnhqp, true);
1285 /* Store rcu_need_heavy_qs before rcu_urgent_qs. */
1286 smp_store_release(ruqp, true);
1287 rdp->rsp->jiffies_resched += jtsq; /* Re-enable beating. */
1288 }
1289
1290 /*
1291 * If more than halfway to RCU CPU stall-warning time, do a
1292 * resched_cpu() to try to loosen things up a bit. Also check to
1293 * see if the CPU is getting hammered with interrupts, but only
1294 * once per grace period, just to keep the IPIs down to a dull roar.
1295 */
1296 if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2) {
1297 resched_cpu(rdp->cpu);
1298 if (IS_ENABLED(CONFIG_IRQ_WORK) &&
1299 !rdp->rcu_iw_pending && rdp->rcu_iw_gpnum != rnp->gpnum &&
1300 (rnp->ffmask & rdp->grpmask)) {
1301 init_irq_work(&rdp->rcu_iw, rcu_iw_handler);
1302 rdp->rcu_iw_pending = true;
1303 rdp->rcu_iw_gpnum = rnp->gpnum;
1304 irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
1305 }
1306 }
1307
1308 return 0;
1309}
1310
1311static void record_gp_stall_check_time(struct rcu_state *rsp)
1312{
1313 unsigned long j = jiffies;
1314 unsigned long j1;
1315
1316 rsp->gp_start = j;
1317 smp_wmb(); /* Record start time before stall time. */
1318 j1 = rcu_jiffies_till_stall_check();
1319 WRITE_ONCE(rsp->jiffies_stall, j + j1);
1320 rsp->jiffies_resched = j + j1 / 2;
1321 rsp->n_force_qs_gpstart = READ_ONCE(rsp->n_force_qs);
1322}
1323
1324/*
1325 * Convert a ->gp_state value to a character string.
1326 */
1327static const char *gp_state_getname(short gs)
1328{
1329 if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
1330 return "???";
1331 return gp_state_names[gs];
1332}
1333
1334/*
1335 * Complain about starvation of grace-period kthread.
1336 */
1337static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
1338{
1339 unsigned long gpa;
1340 unsigned long j;
1341
1342 j = jiffies;
1343 gpa = READ_ONCE(rsp->gp_activity);
1344 if (j - gpa > 2 * HZ) {
1345 pr_err("%s kthread starved for %ld jiffies! g%lu c%lu f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
1346 rsp->name, j - gpa,
1347 rsp->gpnum, rsp->completed,
1348 rsp->gp_flags,
1349 gp_state_getname(rsp->gp_state), rsp->gp_state,
1350 rsp->gp_kthread ? rsp->gp_kthread->state : ~0,
1351 rsp->gp_kthread ? task_cpu(rsp->gp_kthread) : -1);
1352 if (rsp->gp_kthread) {
1353 pr_err("RCU grace-period kthread stack dump:\n");
1354 sched_show_task(rsp->gp_kthread);
1355 wake_up_process(rsp->gp_kthread);
1356 }
1357 }
1358}
1359
1360/*
1361 * Dump stacks of all tasks running on stalled CPUs. First try using
1362 * NMIs, but fall back to manual remote stack tracing on architectures
1363 * that don't support NMI-based stack dumps. The NMI-triggered stack
1364 * traces are more accurate because they are printed by the target CPU.
1365 */
1366static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
1367{
1368 int cpu;
1369 unsigned long flags;
1370 struct rcu_node *rnp;
1371
1372 rcu_for_each_leaf_node(rsp, rnp) {
1373 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1374 for_each_leaf_node_possible_cpu(rnp, cpu)
1375 if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
1376 if (!trigger_single_cpu_backtrace(cpu))
1377 dump_cpu_task(cpu);
1378 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1379 }
1380}
1381
1382/*
1383 * If too much time has passed in the current grace period, and if
1384 * so configured, go kick the relevant kthreads.
1385 */
1386static void rcu_stall_kick_kthreads(struct rcu_state *rsp)
1387{
1388 unsigned long j;
1389
1390 if (!rcu_kick_kthreads)
1391 return;
1392 j = READ_ONCE(rsp->jiffies_kick_kthreads);
1393 if (time_after(jiffies, j) && rsp->gp_kthread &&
1394 (rcu_gp_in_progress(rsp) || READ_ONCE(rsp->gp_flags))) {
1395 WARN_ONCE(1, "Kicking %s grace-period kthread\n", rsp->name);
1396 rcu_ftrace_dump(DUMP_ALL);
1397 wake_up_process(rsp->gp_kthread);
1398 WRITE_ONCE(rsp->jiffies_kick_kthreads, j + HZ);
1399 }
1400}
1401
1402static inline void panic_on_rcu_stall(void)
1403{
1404 if (sysctl_panic_on_rcu_stall)
1405 panic("RCU Stall\n");
1406}
1407
1408static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
1409{
1410 int cpu;
1411 long delta;
1412 unsigned long flags;
1413 unsigned long gpa;
1414 unsigned long j;
1415 int ndetected = 0;
1416 struct rcu_node *rnp = rcu_get_root(rsp);
1417 long totqlen = 0;
1418
1419 /* Kick and suppress, if so configured. */
1420 rcu_stall_kick_kthreads(rsp);
1421 if (rcu_cpu_stall_suppress)
1422 return;
1423
1424 /* Only let one CPU complain about others per time interval. */
1425
1426 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1427 delta = jiffies - READ_ONCE(rsp->jiffies_stall);
1428 if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
1429 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1430 return;
1431 }
1432 WRITE_ONCE(rsp->jiffies_stall,
1433 jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
1434 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1435
1436 /*
1437 * OK, time to rat on our buddy...
1438 * See Documentation/RCU/stallwarn.txt for info on how to debug
1439 * RCU CPU stall warnings.
1440 */
1441 pr_err("INFO: %s detected stalls on CPUs/tasks:",
1442 rsp->name);
1443 print_cpu_stall_info_begin();
1444 rcu_for_each_leaf_node(rsp, rnp) {
1445 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1446 ndetected += rcu_print_task_stall(rnp);
1447 if (rnp->qsmask != 0) {
1448 for_each_leaf_node_possible_cpu(rnp, cpu)
1449 if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
1450 print_cpu_stall_info(rsp, cpu);
1451 ndetected++;
1452 }
1453 }
1454 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1455 }
1456
1457 print_cpu_stall_info_end();
1458 for_each_possible_cpu(cpu)
1459 totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
1460 cpu)->cblist);
1461 pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
1462 smp_processor_id(), (long)(jiffies - rsp->gp_start),
1463 (long)rsp->gpnum, (long)rsp->completed, totqlen);
1464 if (ndetected) {
1465 rcu_dump_cpu_stacks(rsp);
1466
1467 /* Complain about tasks blocking the grace period. */
1468 rcu_print_detail_task_stall(rsp);
1469 } else {
1470 if (READ_ONCE(rsp->gpnum) != gpnum ||
1471 READ_ONCE(rsp->completed) == gpnum) {
1472 pr_err("INFO: Stall ended before state dump start\n");
1473 } else {
1474 j = jiffies;
1475 gpa = READ_ONCE(rsp->gp_activity);
1476 pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
1477 rsp->name, j - gpa, j, gpa,
1478 jiffies_till_next_fqs,
1479 rcu_get_root(rsp)->qsmask);
1480 /* In this case, the current CPU might be at fault. */
1481 sched_show_task(current);
1482 }
1483 }
1484
1485 rcu_check_gp_kthread_starvation(rsp);
1486
1487 panic_on_rcu_stall();
1488
1489 force_quiescent_state(rsp); /* Kick them all. */
1490}
1491
1492static void print_cpu_stall(struct rcu_state *rsp)
1493{
1494 int cpu;
1495 unsigned long flags;
1496 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1497 struct rcu_node *rnp = rcu_get_root(rsp);
1498 long totqlen = 0;
1499
1500 /* Kick and suppress, if so configured. */
1501 rcu_stall_kick_kthreads(rsp);
1502 if (rcu_cpu_stall_suppress)
1503 return;
1504
1505 /*
1506 * OK, time to rat on ourselves...
1507 * See Documentation/RCU/stallwarn.txt for info on how to debug
1508 * RCU CPU stall warnings.
1509 */
1510 pr_err("INFO: %s self-detected stall on CPU", rsp->name);
1511 print_cpu_stall_info_begin();
1512 raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
1513 print_cpu_stall_info(rsp, smp_processor_id());
1514 raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
1515 print_cpu_stall_info_end();
1516 for_each_possible_cpu(cpu)
1517 totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
1518 cpu)->cblist);
1519 pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
1520 jiffies - rsp->gp_start,
1521 (long)rsp->gpnum, (long)rsp->completed, totqlen);
1522
1523 rcu_check_gp_kthread_starvation(rsp);
1524
1525 rcu_dump_cpu_stacks(rsp);
1526
1527 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1528 if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall)))
1529 WRITE_ONCE(rsp->jiffies_stall,
1530 jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
1531 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1532
1533 panic_on_rcu_stall();
1534
1535 /*
1536 * Attempt to revive the RCU machinery by forcing a context switch.
1537 *
1538 * A context switch would normally allow the RCU state machine to make
1539 * progress and it could be we're stuck in kernel space without context
1540 * switches for an entirely unreasonable amount of time.
1541 */
1542 resched_cpu(smp_processor_id());
1543}
1544
1545static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
1546{
1547 unsigned long completed;
1548 unsigned long gpnum;
1549 unsigned long gps;
1550 unsigned long j;
1551 unsigned long js;
1552 struct rcu_node *rnp;
1553
1554 if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
1555 !rcu_gp_in_progress(rsp))
1556 return;
1557 rcu_stall_kick_kthreads(rsp);
1558 j = jiffies;
1559
1560 /*
1561 * Lots of memory barriers to reject false positives.
1562 *
1563 * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
1564 * then rsp->gp_start, and finally rsp->completed. These values
1565 * are updated in the opposite order with memory barriers (or
1566 * equivalent) during grace-period initialization and cleanup.
1567 * Now, a false positive can occur if we get an new value of
1568 * rsp->gp_start and a old value of rsp->jiffies_stall. But given
1569 * the memory barriers, the only way that this can happen is if one
1570 * grace period ends and another starts between these two fetches.
1571 * Detect this by comparing rsp->completed with the previous fetch
1572 * from rsp->gpnum.
1573 *
1574 * Given this check, comparisons of jiffies, rsp->jiffies_stall,
1575 * and rsp->gp_start suffice to forestall false positives.
1576 */
1577 gpnum = READ_ONCE(rsp->gpnum);
1578 smp_rmb(); /* Pick up ->gpnum first... */
1579 js = READ_ONCE(rsp->jiffies_stall);
1580 smp_rmb(); /* ...then ->jiffies_stall before the rest... */
1581 gps = READ_ONCE(rsp->gp_start);
1582 smp_rmb(); /* ...and finally ->gp_start before ->completed. */
1583 completed = READ_ONCE(rsp->completed);
1584 if (ULONG_CMP_GE(completed, gpnum) ||
1585 ULONG_CMP_LT(j, js) ||
1586 ULONG_CMP_GE(gps, js))
1587 return; /* No stall or GP completed since entering function. */
1588 rnp = rdp->mynode;
1589 if (rcu_gp_in_progress(rsp) &&
1590 (READ_ONCE(rnp->qsmask) & rdp->grpmask)) {
1591
1592 /* We haven't checked in, so go dump stack. */
1593 print_cpu_stall(rsp);
1594
1595 } else if (rcu_gp_in_progress(rsp) &&
1596 ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
1597
1598 /* They had a few time units to dump stack, so complain. */
1599 print_other_cpu_stall(rsp, gpnum);
1600 }
1601}
1602
1603/**
1604 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
1605 *
1606 * Set the stall-warning timeout way off into the future, thus preventing
1607 * any RCU CPU stall-warning messages from appearing in the current set of
1608 * RCU grace periods.
1609 *
1610 * The caller must disable hard irqs.
1611 */
1612void rcu_cpu_stall_reset(void)
1613{
1614 struct rcu_state *rsp;
1615
1616 for_each_rcu_flavor(rsp)
1617 WRITE_ONCE(rsp->jiffies_stall, jiffies + ULONG_MAX / 2);
1618}
1619
1620/*
1621 * Determine the value that ->completed will have at the end of the
1622 * next subsequent grace period. This is used to tag callbacks so that
1623 * a CPU can invoke callbacks in a timely fashion even if that CPU has
1624 * been dyntick-idle for an extended period with callbacks under the
1625 * influence of RCU_FAST_NO_HZ.
1626 *
1627 * The caller must hold rnp->lock with interrupts disabled.
1628 */
1629static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
1630 struct rcu_node *rnp)
1631{
1632 raw_lockdep_assert_held_rcu_node(rnp);
1633
1634 /*
1635 * If RCU is idle, we just wait for the next grace period.
1636 * But we can only be sure that RCU is idle if we are looking
1637 * at the root rcu_node structure -- otherwise, a new grace
1638 * period might have started, but just not yet gotten around
1639 * to initializing the current non-root rcu_node structure.
1640 */
1641 if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed)
1642 return rnp->completed + 1;
1643
1644 /*
1645 * Otherwise, wait for a possible partial grace period and
1646 * then the subsequent full grace period.
1647 */
1648 return rnp->completed + 2;
1649}
1650
1651/*
1652 * Trace-event helper function for rcu_start_future_gp() and
1653 * rcu_nocb_wait_gp().
1654 */
1655static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1656 unsigned long c, const char *s)
1657{
1658 trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,
1659 rnp->completed, c, rnp->level,
1660 rnp->grplo, rnp->grphi, s);
1661}
1662
1663/*
1664 * Start some future grace period, as needed to handle newly arrived
1665 * callbacks. The required future grace periods are recorded in each
1666 * rcu_node structure's ->need_future_gp field. Returns true if there
1667 * is reason to awaken the grace-period kthread.
1668 *
1669 * The caller must hold the specified rcu_node structure's ->lock.
1670 */
1671static bool __maybe_unused
1672rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1673 unsigned long *c_out)
1674{
1675 unsigned long c;
1676 bool ret = false;
1677 struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
1678
1679 raw_lockdep_assert_held_rcu_node(rnp);
1680
1681 /*
1682 * Pick up grace-period number for new callbacks. If this
1683 * grace period is already marked as needed, return to the caller.
1684 */
1685 c = rcu_cbs_completed(rdp->rsp, rnp);
1686 trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
1687 if (rnp->need_future_gp[c & 0x1]) {
1688 trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
1689 goto out;
1690 }
1691
1692 /*
1693 * If either this rcu_node structure or the root rcu_node structure
1694 * believe that a grace period is in progress, then we must wait
1695 * for the one following, which is in "c". Because our request
1696 * will be noticed at the end of the current grace period, we don't
1697 * need to explicitly start one. We only do the lockless check
1698 * of rnp_root's fields if the current rcu_node structure thinks
1699 * there is no grace period in flight, and because we hold rnp->lock,
1700 * the only possible change is when rnp_root's two fields are
1701 * equal, in which case rnp_root->gpnum might be concurrently
1702 * incremented. But that is OK, as it will just result in our
1703 * doing some extra useless work.
1704 */
1705 if (rnp->gpnum != rnp->completed ||
1706 READ_ONCE(rnp_root->gpnum) != READ_ONCE(rnp_root->completed)) {
1707 rnp->need_future_gp[c & 0x1]++;
1708 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
1709 goto out;
1710 }
1711
1712 /*
1713 * There might be no grace period in progress. If we don't already
1714 * hold it, acquire the root rcu_node structure's lock in order to
1715 * start one (if needed).
1716 */
1717 if (rnp != rnp_root)
1718 raw_spin_lock_rcu_node(rnp_root);
1719
1720 /*
1721 * Get a new grace-period number. If there really is no grace
1722 * period in progress, it will be smaller than the one we obtained
1723 * earlier. Adjust callbacks as needed.
1724 */
1725 c = rcu_cbs_completed(rdp->rsp, rnp_root);
1726 if (!rcu_is_nocb_cpu(rdp->cpu))
1727 (void)rcu_segcblist_accelerate(&rdp->cblist, c);
1728
1729 /*
1730 * If the needed for the required grace period is already
1731 * recorded, trace and leave.
1732 */
1733 if (rnp_root->need_future_gp[c & 0x1]) {
1734 trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
1735 goto unlock_out;
1736 }
1737
1738 /* Record the need for the future grace period. */
1739 rnp_root->need_future_gp[c & 0x1]++;
1740
1741 /* If a grace period is not already in progress, start one. */
1742 if (rnp_root->gpnum != rnp_root->completed) {
1743 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot"));
1744 } else {
1745 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot"));
1746 ret = rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp);
1747 }
1748unlock_out:
1749 if (rnp != rnp_root)
1750 raw_spin_unlock_rcu_node(rnp_root);
1751out:
1752 if (c_out != NULL)
1753 *c_out = c;
1754 return ret;
1755}
1756
1757/*
1758 * Clean up any old requests for the just-ended grace period. Also return
1759 * whether any additional grace periods have been requested.
1760 */
1761static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
1762{
1763 int c = rnp->completed;
1764 int needmore;
1765 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1766
1767 rnp->need_future_gp[c & 0x1] = 0;
1768 needmore = rnp->need_future_gp[(c + 1) & 0x1];
1769 trace_rcu_future_gp(rnp, rdp, c,
1770 needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1771 return needmore;
1772}
1773
1774/*
1775 * Awaken the grace-period kthread for the specified flavor of RCU.
1776 * Don't do a self-awaken, and don't bother awakening when there is
1777 * nothing for the grace-period kthread to do (as in several CPUs
1778 * raced to awaken, and we lost), and finally don't try to awaken
1779 * a kthread that has not yet been created.
1780 */
1781static void rcu_gp_kthread_wake(struct rcu_state *rsp)
1782{
1783 if (current == rsp->gp_kthread ||
1784 !READ_ONCE(rsp->gp_flags) ||
1785 !rsp->gp_kthread)
1786 return;
1787 swake_up(&rsp->gp_wq);
1788}
1789
1790/*
1791 * If there is room, assign a ->completed number to any callbacks on
1792 * this CPU that have not already been assigned. Also accelerate any
1793 * callbacks that were previously assigned a ->completed number that has
1794 * since proven to be too conservative, which can happen if callbacks get
1795 * assigned a ->completed number while RCU is idle, but with reference to
1796 * a non-root rcu_node structure. This function is idempotent, so it does
1797 * not hurt to call it repeatedly. Returns an flag saying that we should
1798 * awaken the RCU grace-period kthread.
1799 *
1800 * The caller must hold rnp->lock with interrupts disabled.
1801 */
1802static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1803 struct rcu_data *rdp)
1804{
1805 bool ret = false;
1806
1807 raw_lockdep_assert_held_rcu_node(rnp);
1808
1809 /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
1810 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1811 return false;
1812
1813 /*
1814 * Callbacks are often registered with incomplete grace-period
1815 * information. Something about the fact that getting exact
1816 * information requires acquiring a global lock... RCU therefore
1817 * makes a conservative estimate of the grace period number at which
1818 * a given callback will become ready to invoke. The following
1819 * code checks this estimate and improves it when possible, thus
1820 * accelerating callback invocation to an earlier grace-period
1821 * number.
1822 */
1823 if (rcu_segcblist_accelerate(&rdp->cblist, rcu_cbs_completed(rsp, rnp)))
1824 ret = rcu_start_future_gp(rnp, rdp, NULL);
1825
1826 /* Trace depending on how much we were able to accelerate. */
1827 if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
1828 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
1829 else
1830 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
1831 return ret;
1832}
1833
1834/*
1835 * Move any callbacks whose grace period has completed to the
1836 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1837 * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
1838 * sublist. This function is idempotent, so it does not hurt to
1839 * invoke it repeatedly. As long as it is not invoked -too- often...
1840 * Returns true if the RCU grace-period kthread needs to be awakened.
1841 *
1842 * The caller must hold rnp->lock with interrupts disabled.
1843 */
1844static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1845 struct rcu_data *rdp)
1846{
1847 raw_lockdep_assert_held_rcu_node(rnp);
1848
1849 /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
1850 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1851 return false;
1852
1853 /*
1854 * Find all callbacks whose ->completed numbers indicate that they
1855 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1856 */
1857 rcu_segcblist_advance(&rdp->cblist, rnp->completed);
1858
1859 /* Classify any remaining callbacks. */
1860 return rcu_accelerate_cbs(rsp, rnp, rdp);
1861}
1862
1863/*
1864 * Update CPU-local rcu_data state to record the beginnings and ends of
1865 * grace periods. The caller must hold the ->lock of the leaf rcu_node
1866 * structure corresponding to the current CPU, and must have irqs disabled.
1867 * Returns true if the grace-period kthread needs to be awakened.
1868 */
1869static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
1870 struct rcu_data *rdp)
1871{
1872 bool ret;
1873 bool need_gp;
1874
1875 raw_lockdep_assert_held_rcu_node(rnp);
1876
1877 /* Handle the ends of any preceding grace periods first. */
1878 if (rdp->completed == rnp->completed &&
1879 !unlikely(READ_ONCE(rdp->gpwrap))) {
1880
1881 /* No grace period end, so just accelerate recent callbacks. */
1882 ret = rcu_accelerate_cbs(rsp, rnp, rdp);
1883
1884 } else {
1885
1886 /* Advance callbacks. */
1887 ret = rcu_advance_cbs(rsp, rnp, rdp);
1888
1889 /* Remember that we saw this grace-period completion. */
1890 rdp->completed = rnp->completed;
1891 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
1892 }
1893
1894 if (rdp->gpnum != rnp->gpnum || unlikely(READ_ONCE(rdp->gpwrap))) {
1895 /*
1896 * If the current grace period is waiting for this CPU,
1897 * set up to detect a quiescent state, otherwise don't
1898 * go looking for one.
1899 */
1900 rdp->gpnum = rnp->gpnum;
1901 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
1902 need_gp = !!(rnp->qsmask & rdp->grpmask);
1903 rdp->cpu_no_qs.b.norm = need_gp;
1904 rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr);
1905 rdp->core_needs_qs = need_gp;
1906 zero_cpu_stall_ticks(rdp);
1907 WRITE_ONCE(rdp->gpwrap, false);
1908 rcu_gpnum_ovf(rnp, rdp);
1909 }
1910 return ret;
1911}
1912
1913static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
1914{
1915 unsigned long flags;
1916 bool needwake;
1917 struct rcu_node *rnp;
1918
1919 local_irq_save(flags);
1920 rnp = rdp->mynode;
1921 if ((rdp->gpnum == READ_ONCE(rnp->gpnum) &&
1922 rdp->completed == READ_ONCE(rnp->completed) &&
1923 !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
1924 !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
1925 local_irq_restore(flags);
1926 return;
1927 }
1928 needwake = __note_gp_changes(rsp, rnp, rdp);
1929 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1930 if (needwake)
1931 rcu_gp_kthread_wake(rsp);
1932}
1933
1934static void rcu_gp_slow(struct rcu_state *rsp, int delay)
1935{
1936 if (delay > 0 &&
1937 !(rsp->gpnum % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
1938 schedule_timeout_uninterruptible(delay);
1939}
1940
1941/*
1942 * Initialize a new grace period. Return false if no grace period required.
1943 */
1944static bool rcu_gp_init(struct rcu_state *rsp)
1945{
1946 unsigned long oldmask;
1947 struct rcu_data *rdp;
1948 struct rcu_node *rnp = rcu_get_root(rsp);
1949
1950 WRITE_ONCE(rsp->gp_activity, jiffies);
1951 raw_spin_lock_irq_rcu_node(rnp);
1952 if (!READ_ONCE(rsp->gp_flags)) {
1953 /* Spurious wakeup, tell caller to go back to sleep. */
1954 raw_spin_unlock_irq_rcu_node(rnp);
1955 return false;
1956 }
1957 WRITE_ONCE(rsp->gp_flags, 0); /* Clear all flags: New grace period. */
1958
1959 if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
1960 /*
1961 * Grace period already in progress, don't start another.
1962 * Not supposed to be able to happen.
1963 */
1964 raw_spin_unlock_irq_rcu_node(rnp);
1965 return false;
1966 }
1967
1968 /* Advance to a new grace period and initialize state. */
1969 record_gp_stall_check_time(rsp);
1970 /* Record GP times before starting GP, hence smp_store_release(). */
1971 smp_store_release(&rsp->gpnum, rsp->gpnum + 1);
1972 trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start"));
1973 raw_spin_unlock_irq_rcu_node(rnp);
1974
1975 /*
1976 * Apply per-leaf buffered online and offline operations to the
1977 * rcu_node tree. Note that this new grace period need not wait
1978 * for subsequent online CPUs, and that quiescent-state forcing
1979 * will handle subsequent offline CPUs.
1980 */
1981 rcu_for_each_leaf_node(rsp, rnp) {
1982 rcu_gp_slow(rsp, gp_preinit_delay);
1983 raw_spin_lock_irq_rcu_node(rnp);
1984 if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
1985 !rnp->wait_blkd_tasks) {
1986 /* Nothing to do on this leaf rcu_node structure. */
1987 raw_spin_unlock_irq_rcu_node(rnp);
1988 continue;
1989 }
1990
1991 /* Record old state, apply changes to ->qsmaskinit field. */
1992 oldmask = rnp->qsmaskinit;
1993 rnp->qsmaskinit = rnp->qsmaskinitnext;
1994
1995 /* If zero-ness of ->qsmaskinit changed, propagate up tree. */
1996 if (!oldmask != !rnp->qsmaskinit) {
1997 if (!oldmask) /* First online CPU for this rcu_node. */
1998 rcu_init_new_rnp(rnp);
1999 else if (rcu_preempt_has_tasks(rnp)) /* blocked tasks */
2000 rnp->wait_blkd_tasks = true;
2001 else /* Last offline CPU and can propagate. */
2002 rcu_cleanup_dead_rnp(rnp);
2003 }
2004
2005 /*
2006 * If all waited-on tasks from prior grace period are
2007 * done, and if all this rcu_node structure's CPUs are
2008 * still offline, propagate up the rcu_node tree and
2009 * clear ->wait_blkd_tasks. Otherwise, if one of this
2010 * rcu_node structure's CPUs has since come back online,
2011 * simply clear ->wait_blkd_tasks (but rcu_cleanup_dead_rnp()
2012 * checks for this, so just call it unconditionally).
2013 */
2014 if (rnp->wait_blkd_tasks &&
2015 (!rcu_preempt_has_tasks(rnp) ||
2016 rnp->qsmaskinit)) {
2017 rnp->wait_blkd_tasks = false;
2018 rcu_cleanup_dead_rnp(rnp);
2019 }
2020
2021 raw_spin_unlock_irq_rcu_node(rnp);
2022 }
2023
2024 /*
2025 * Set the quiescent-state-needed bits in all the rcu_node
2026 * structures for all currently online CPUs in breadth-first order,
2027 * starting from the root rcu_node structure, relying on the layout
2028 * of the tree within the rsp->node[] array. Note that other CPUs
2029 * will access only the leaves of the hierarchy, thus seeing that no
2030 * grace period is in progress, at least until the corresponding
2031 * leaf node has been initialized.
2032 *
2033 * The grace period cannot complete until the initialization
2034 * process finishes, because this kthread handles both.
2035 */
2036 rcu_for_each_node_breadth_first(rsp, rnp) {
2037 rcu_gp_slow(rsp, gp_init_delay);
2038 raw_spin_lock_irq_rcu_node(rnp);
2039 rdp = this_cpu_ptr(rsp->rda);
2040 rcu_preempt_check_blocked_tasks(rnp);
2041 rnp->qsmask = rnp->qsmaskinit;
2042 WRITE_ONCE(rnp->gpnum, rsp->gpnum);
2043 if (WARN_ON_ONCE(rnp->completed != rsp->completed))
2044 WRITE_ONCE(rnp->completed, rsp->completed);
2045 if (rnp == rdp->mynode)
2046 (void)__note_gp_changes(rsp, rnp, rdp);
2047 rcu_preempt_boost_start_gp(rnp);
2048 trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
2049 rnp->level, rnp->grplo,
2050 rnp->grphi, rnp->qsmask);
2051 raw_spin_unlock_irq_rcu_node(rnp);
2052 cond_resched_rcu_qs();
2053 WRITE_ONCE(rsp->gp_activity, jiffies);
2054 }
2055
2056 return true;
2057}
2058
2059/*
2060 * Helper function for swait_event_idle() wakeup at force-quiescent-state
2061 * time.
2062 */
2063static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)
2064{
2065 struct rcu_node *rnp = rcu_get_root(rsp);
2066
2067 /* Someone like call_rcu() requested a force-quiescent-state scan. */
2068 *gfp = READ_ONCE(rsp->gp_flags);
2069 if (*gfp & RCU_GP_FLAG_FQS)
2070 return true;
2071
2072 /* The current grace period has completed. */
2073 if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
2074 return true;
2075
2076 return false;
2077}
2078
2079/*
2080 * Do one round of quiescent-state forcing.
2081 */
2082static void rcu_gp_fqs(struct rcu_state *rsp, bool first_time)
2083{
2084 struct rcu_node *rnp = rcu_get_root(rsp);
2085
2086 WRITE_ONCE(rsp->gp_activity, jiffies);
2087 rsp->n_force_qs++;
2088 if (first_time) {
2089 /* Collect dyntick-idle snapshots. */
2090 force_qs_rnp(rsp, dyntick_save_progress_counter);
2091 } else {
2092 /* Handle dyntick-idle and offline CPUs. */
2093 force_qs_rnp(rsp, rcu_implicit_dynticks_qs);
2094 }
2095 /* Clear flag to prevent immediate re-entry. */
2096 if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
2097 raw_spin_lock_irq_rcu_node(rnp);
2098 WRITE_ONCE(rsp->gp_flags,
2099 READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS);
2100 raw_spin_unlock_irq_rcu_node(rnp);
2101 }
2102}
2103
2104/*
2105 * Clean up after the old grace period.
2106 */
2107static void rcu_gp_cleanup(struct rcu_state *rsp)
2108{
2109 unsigned long gp_duration;
2110 bool needgp = false;
2111 int nocb = 0;
2112 struct rcu_data *rdp;
2113 struct rcu_node *rnp = rcu_get_root(rsp);
2114 struct swait_queue_head *sq;
2115
2116 WRITE_ONCE(rsp->gp_activity, jiffies);
2117 raw_spin_lock_irq_rcu_node(rnp);
2118 gp_duration = jiffies - rsp->gp_start;
2119 if (gp_duration > rsp->gp_max)
2120 rsp->gp_max = gp_duration;
2121
2122 /*
2123 * We know the grace period is complete, but to everyone else
2124 * it appears to still be ongoing. But it is also the case
2125 * that to everyone else it looks like there is nothing that
2126 * they can do to advance the grace period. It is therefore
2127 * safe for us to drop the lock in order to mark the grace
2128 * period as completed in all of the rcu_node structures.
2129 */
2130 raw_spin_unlock_irq_rcu_node(rnp);
2131
2132 /*
2133 * Propagate new ->completed value to rcu_node structures so
2134 * that other CPUs don't have to wait until the start of the next
2135 * grace period to process their callbacks. This also avoids
2136 * some nasty RCU grace-period initialization races by forcing
2137 * the end of the current grace period to be completely recorded in
2138 * all of the rcu_node structures before the beginning of the next
2139 * grace period is recorded in any of the rcu_node structures.
2140 */
2141 rcu_for_each_node_breadth_first(rsp, rnp) {
2142 raw_spin_lock_irq_rcu_node(rnp);
2143 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
2144 WARN_ON_ONCE(rnp->qsmask);
2145 WRITE_ONCE(rnp->completed, rsp->gpnum);
2146 rdp = this_cpu_ptr(rsp->rda);
2147 if (rnp == rdp->mynode)
2148 needgp = __note_gp_changes(rsp, rnp, rdp) || needgp;
2149 /* smp_mb() provided by prior unlock-lock pair. */
2150 nocb += rcu_future_gp_cleanup(rsp, rnp);
2151 sq = rcu_nocb_gp_get(rnp);
2152 raw_spin_unlock_irq_rcu_node(rnp);
2153 rcu_nocb_gp_cleanup(sq);
2154 cond_resched_rcu_qs();
2155 WRITE_ONCE(rsp->gp_activity, jiffies);
2156 rcu_gp_slow(rsp, gp_cleanup_delay);
2157 }
2158 rnp = rcu_get_root(rsp);
2159 raw_spin_lock_irq_rcu_node(rnp); /* Order GP before ->completed update. */
2160 rcu_nocb_gp_set(rnp, nocb);
2161
2162 /* Declare grace period done. */
2163 WRITE_ONCE(rsp->completed, rsp->gpnum);
2164 trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
2165 rsp->gp_state = RCU_GP_IDLE;
2166 rdp = this_cpu_ptr(rsp->rda);
2167 /* Advance CBs to reduce false positives below. */
2168 needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
2169 if (needgp || cpu_needs_another_gp(rsp, rdp)) {
2170 WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
2171 trace_rcu_grace_period(rsp->name,
2172 READ_ONCE(rsp->gpnum),
2173 TPS("newreq"));
2174 }
2175 raw_spin_unlock_irq_rcu_node(rnp);
2176}
2177
2178/*
2179 * Body of kthread that handles grace periods.
2180 */
2181static int __noreturn rcu_gp_kthread(void *arg)
2182{
2183 bool first_gp_fqs;
2184 int gf;
2185 unsigned long j;
2186 int ret;
2187 struct rcu_state *rsp = arg;
2188 struct rcu_node *rnp = rcu_get_root(rsp);
2189
2190 rcu_bind_gp_kthread();
2191 for (;;) {
2192
2193 /* Handle grace-period start. */
2194 for (;;) {
2195 trace_rcu_grace_period(rsp->name,
2196 READ_ONCE(rsp->gpnum),
2197 TPS("reqwait"));
2198 rsp->gp_state = RCU_GP_WAIT_GPS;
2199 swait_event_idle(rsp->gp_wq, READ_ONCE(rsp->gp_flags) &
2200 RCU_GP_FLAG_INIT);
2201 rsp->gp_state = RCU_GP_DONE_GPS;
2202 /* Locking provides needed memory barrier. */
2203 if (rcu_gp_init(rsp))
2204 break;
2205 cond_resched_rcu_qs();
2206 WRITE_ONCE(rsp->gp_activity, jiffies);
2207 WARN_ON(signal_pending(current));
2208 trace_rcu_grace_period(rsp->name,
2209 READ_ONCE(rsp->gpnum),
2210 TPS("reqwaitsig"));
2211 }
2212
2213 /* Handle quiescent-state forcing. */
2214 first_gp_fqs = true;
2215 j = jiffies_till_first_fqs;
2216 if (j > HZ) {
2217 j = HZ;
2218 jiffies_till_first_fqs = HZ;
2219 }
2220 ret = 0;
2221 for (;;) {
2222 if (!ret) {
2223 rsp->jiffies_force_qs = jiffies + j;
2224 WRITE_ONCE(rsp->jiffies_kick_kthreads,
2225 jiffies + 3 * j);
2226 }
2227 trace_rcu_grace_period(rsp->name,
2228 READ_ONCE(rsp->gpnum),
2229 TPS("fqswait"));
2230 rsp->gp_state = RCU_GP_WAIT_FQS;
2231 ret = swait_event_idle_timeout(rsp->gp_wq,
2232 rcu_gp_fqs_check_wake(rsp, &gf), j);
2233 rsp->gp_state = RCU_GP_DOING_FQS;
2234 /* Locking provides needed memory barriers. */
2235 /* If grace period done, leave loop. */
2236 if (!READ_ONCE(rnp->qsmask) &&
2237 !rcu_preempt_blocked_readers_cgp(rnp))
2238 break;
2239 /* If time for quiescent-state forcing, do it. */
2240 if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
2241 (gf & RCU_GP_FLAG_FQS)) {
2242 trace_rcu_grace_period(rsp->name,
2243 READ_ONCE(rsp->gpnum),
2244 TPS("fqsstart"));
2245 rcu_gp_fqs(rsp, first_gp_fqs);
2246 first_gp_fqs = false;
2247 trace_rcu_grace_period(rsp->name,
2248 READ_ONCE(rsp->gpnum),
2249 TPS("fqsend"));
2250 cond_resched_rcu_qs();
2251 WRITE_ONCE(rsp->gp_activity, jiffies);
2252 ret = 0; /* Force full wait till next FQS. */
2253 j = jiffies_till_next_fqs;
2254 if (j > HZ) {
2255 j = HZ;
2256 jiffies_till_next_fqs = HZ;
2257 } else if (j < 1) {
2258 j = 1;
2259 jiffies_till_next_fqs = 1;
2260 }
2261 } else {
2262 /* Deal with stray signal. */
2263 cond_resched_rcu_qs();
2264 WRITE_ONCE(rsp->gp_activity, jiffies);
2265 WARN_ON(signal_pending(current));
2266 trace_rcu_grace_period(rsp->name,
2267 READ_ONCE(rsp->gpnum),
2268 TPS("fqswaitsig"));
2269 ret = 1; /* Keep old FQS timing. */
2270 j = jiffies;
2271 if (time_after(jiffies, rsp->jiffies_force_qs))
2272 j = 1;
2273 else
2274 j = rsp->jiffies_force_qs - j;
2275 }
2276 }
2277
2278 /* Handle grace-period end. */
2279 rsp->gp_state = RCU_GP_CLEANUP;
2280 rcu_gp_cleanup(rsp);
2281 rsp->gp_state = RCU_GP_CLEANED;
2282 }
2283}
2284
2285/*
2286 * Start a new RCU grace period if warranted, re-initializing the hierarchy
2287 * in preparation for detecting the next grace period. The caller must hold
2288 * the root node's ->lock and hard irqs must be disabled.
2289 *
2290 * Note that it is legal for a dying CPU (which is marked as offline) to
2291 * invoke this function. This can happen when the dying CPU reports its
2292 * quiescent state.
2293 *
2294 * Returns true if the grace-period kthread must be awakened.
2295 */
2296static bool
2297rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
2298 struct rcu_data *rdp)
2299{
2300 raw_lockdep_assert_held_rcu_node(rnp);
2301 if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
2302 /*
2303 * Either we have not yet spawned the grace-period
2304 * task, this CPU does not need another grace period,
2305 * or a grace period is already in progress.
2306 * Either way, don't start a new grace period.
2307 */
2308 return false;
2309 }
2310 WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
2311 trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum),
2312 TPS("newreq"));
2313
2314 /*
2315 * We can't do wakeups while holding the rnp->lock, as that
2316 * could cause possible deadlocks with the rq->lock. Defer
2317 * the wakeup to our caller.
2318 */
2319 return true;
2320}
2321
2322/*
2323 * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
2324 * callbacks. Note that rcu_start_gp_advanced() cannot do this because it
2325 * is invoked indirectly from rcu_advance_cbs(), which would result in
2326 * endless recursion -- or would do so if it wasn't for the self-deadlock
2327 * that is encountered beforehand.
2328 *
2329 * Returns true if the grace-period kthread needs to be awakened.
2330 */
2331static bool rcu_start_gp(struct rcu_state *rsp)
2332{
2333 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
2334 struct rcu_node *rnp = rcu_get_root(rsp);
2335 bool ret = false;
2336
2337 /*
2338 * If there is no grace period in progress right now, any
2339 * callbacks we have up to this point will be satisfied by the
2340 * next grace period. Also, advancing the callbacks reduces the
2341 * probability of false positives from cpu_needs_another_gp()
2342 * resulting in pointless grace periods. So, advance callbacks
2343 * then start the grace period!
2344 */
2345 ret = rcu_advance_cbs(rsp, rnp, rdp) || ret;
2346 ret = rcu_start_gp_advanced(rsp, rnp, rdp) || ret;
2347 return ret;
2348}
2349
2350/*
2351 * Report a full set of quiescent states to the specified rcu_state data
2352 * structure. Invoke rcu_gp_kthread_wake() to awaken the grace-period
2353 * kthread if another grace period is required. Whether we wake
2354 * the grace-period kthread or it awakens itself for the next round
2355 * of quiescent-state forcing, that kthread will clean up after the
2356 * just-completed grace period. Note that the caller must hold rnp->lock,
2357 * which is released before return.
2358 */
2359static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
2360 __releases(rcu_get_root(rsp)->lock)
2361{
2362 raw_lockdep_assert_held_rcu_node(rcu_get_root(rsp));
2363 WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
2364 WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
2365 raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags);
2366 rcu_gp_kthread_wake(rsp);
2367}
2368
2369/*
2370 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
2371 * Allows quiescent states for a group of CPUs to be reported at one go
2372 * to the specified rcu_node structure, though all the CPUs in the group
2373 * must be represented by the same rcu_node structure (which need not be a
2374 * leaf rcu_node structure, though it often will be). The gps parameter
2375 * is the grace-period snapshot, which means that the quiescent states
2376 * are valid only if rnp->gpnum is equal to gps. That structure's lock
2377 * must be held upon entry, and it is released before return.
2378 */
2379static void
2380rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
2381 struct rcu_node *rnp, unsigned long gps, unsigned long flags)
2382 __releases(rnp->lock)
2383{
2384 unsigned long oldmask = 0;
2385 struct rcu_node *rnp_c;
2386
2387 raw_lockdep_assert_held_rcu_node(rnp);
2388
2389 /* Walk up the rcu_node hierarchy. */
2390 for (;;) {
2391 if (!(rnp->qsmask & mask) || rnp->gpnum != gps) {
2392
2393 /*
2394 * Our bit has already been cleared, or the
2395 * relevant grace period is already over, so done.
2396 */
2397 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2398 return;
2399 }
2400 WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
2401 WARN_ON_ONCE(rnp->level != rcu_num_lvls - 1 &&
2402 rcu_preempt_blocked_readers_cgp(rnp));
2403 rnp->qsmask &= ~mask;
2404 trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
2405 mask, rnp->qsmask, rnp->level,
2406 rnp->grplo, rnp->grphi,
2407 !!rnp->gp_tasks);
2408 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2409
2410 /* Other bits still set at this level, so done. */
2411 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2412 return;
2413 }
2414 mask = rnp->grpmask;
2415 if (rnp->parent == NULL) {
2416
2417 /* No more levels. Exit loop holding root lock. */
2418
2419 break;
2420 }
2421 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2422 rnp_c = rnp;
2423 rnp = rnp->parent;
2424 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2425 oldmask = rnp_c->qsmask;
2426 }
2427
2428 /*
2429 * Get here if we are the last CPU to pass through a quiescent
2430 * state for this grace period. Invoke rcu_report_qs_rsp()
2431 * to clean up and start the next grace period if one is needed.
2432 */
2433 rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
2434}
2435
2436/*
2437 * Record a quiescent state for all tasks that were previously queued
2438 * on the specified rcu_node structure and that were blocking the current
2439 * RCU grace period. The caller must hold the specified rnp->lock with
2440 * irqs disabled, and this lock is released upon return, but irqs remain
2441 * disabled.
2442 */
2443static void rcu_report_unblock_qs_rnp(struct rcu_state *rsp,
2444 struct rcu_node *rnp, unsigned long flags)
2445 __releases(rnp->lock)
2446{
2447 unsigned long gps;
2448 unsigned long mask;
2449 struct rcu_node *rnp_p;
2450
2451 raw_lockdep_assert_held_rcu_node(rnp);
2452 if (rcu_state_p == &rcu_sched_state || rsp != rcu_state_p ||
2453 rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2454 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2455 return; /* Still need more quiescent states! */
2456 }
2457
2458 rnp_p = rnp->parent;
2459 if (rnp_p == NULL) {
2460 /*
2461 * Only one rcu_node structure in the tree, so don't
2462 * try to report up to its nonexistent parent!
2463 */
2464 rcu_report_qs_rsp(rsp, flags);
2465 return;
2466 }
2467
2468 /* Report up the rest of the hierarchy, tracking current ->gpnum. */
2469 gps = rnp->gpnum;
2470 mask = rnp->grpmask;
2471 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2472 raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */
2473 rcu_report_qs_rnp(mask, rsp, rnp_p, gps, flags);
2474}
2475
2476/*
2477 * Record a quiescent state for the specified CPU to that CPU's rcu_data
2478 * structure. This must be called from the specified CPU.
2479 */
2480static void
2481rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
2482{
2483 unsigned long flags;
2484 unsigned long mask;
2485 bool needwake;
2486 struct rcu_node *rnp;
2487
2488 rnp = rdp->mynode;
2489 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2490 if (rdp->cpu_no_qs.b.norm || rdp->gpnum != rnp->gpnum ||
2491 rnp->completed == rnp->gpnum || rdp->gpwrap) {
2492
2493 /*
2494 * The grace period in which this quiescent state was
2495 * recorded has ended, so don't report it upwards.
2496 * We will instead need a new quiescent state that lies
2497 * within the current grace period.
2498 */
2499 rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */
2500 rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr);
2501 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2502 return;
2503 }
2504 mask = rdp->grpmask;
2505 if ((rnp->qsmask & mask) == 0) {
2506 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2507 } else {
2508 rdp->core_needs_qs = false;
2509
2510 /*
2511 * This GP can't end until cpu checks in, so all of our
2512 * callbacks can be processed during the next GP.
2513 */
2514 needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
2515
2516 rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
2517 /* ^^^ Released rnp->lock */
2518 if (needwake)
2519 rcu_gp_kthread_wake(rsp);
2520 }
2521}
2522
2523/*
2524 * Check to see if there is a new grace period of which this CPU
2525 * is not yet aware, and if so, set up local rcu_data state for it.
2526 * Otherwise, see if this CPU has just passed through its first
2527 * quiescent state for this grace period, and record that fact if so.
2528 */
2529static void
2530rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
2531{
2532 /* Check for grace-period ends and beginnings. */
2533 note_gp_changes(rsp, rdp);
2534
2535 /*
2536 * Does this CPU still need to do its part for current grace period?
2537 * If no, return and let the other CPUs do their part as well.
2538 */
2539 if (!rdp->core_needs_qs)
2540 return;
2541
2542 /*
2543 * Was there a quiescent state since the beginning of the grace
2544 * period? If no, then exit and wait for the next call.
2545 */
2546 if (rdp->cpu_no_qs.b.norm)
2547 return;
2548
2549 /*
2550 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
2551 * judge of that).
2552 */
2553 rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
2554}
2555
2556/*
2557 * Trace the fact that this CPU is going offline.
2558 */
2559static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
2560{
2561 RCU_TRACE(unsigned long mask;)
2562 RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda);)
2563 RCU_TRACE(struct rcu_node *rnp = rdp->mynode;)
2564
2565 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2566 return;
2567
2568 RCU_TRACE(mask = rdp->grpmask;)
2569 trace_rcu_grace_period(rsp->name,
2570 rnp->gpnum + 1 - !!(rnp->qsmask & mask),
2571 TPS("cpuofl"));
2572}
2573
2574/*
2575 * All CPUs for the specified rcu_node structure have gone offline,
2576 * and all tasks that were preempted within an RCU read-side critical
2577 * section while running on one of those CPUs have since exited their RCU
2578 * read-side critical section. Some other CPU is reporting this fact with
2579 * the specified rcu_node structure's ->lock held and interrupts disabled.
2580 * This function therefore goes up the tree of rcu_node structures,
2581 * clearing the corresponding bits in the ->qsmaskinit fields. Note that
2582 * the leaf rcu_node structure's ->qsmaskinit field has already been
2583 * updated
2584 *
2585 * This function does check that the specified rcu_node structure has
2586 * all CPUs offline and no blocked tasks, so it is OK to invoke it
2587 * prematurely. That said, invoking it after the fact will cost you
2588 * a needless lock acquisition. So once it has done its work, don't
2589 * invoke it again.
2590 */
2591static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
2592{
2593 long mask;
2594 struct rcu_node *rnp = rnp_leaf;
2595
2596 raw_lockdep_assert_held_rcu_node(rnp);
2597 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
2598 rnp->qsmaskinit || rcu_preempt_has_tasks(rnp))
2599 return;
2600 for (;;) {
2601 mask = rnp->grpmask;
2602 rnp = rnp->parent;
2603 if (!rnp)
2604 break;
2605 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
2606 rnp->qsmaskinit &= ~mask;
2607 rnp->qsmask &= ~mask;
2608 if (rnp->qsmaskinit) {
2609 raw_spin_unlock_rcu_node(rnp);
2610 /* irqs remain disabled. */
2611 return;
2612 }
2613 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2614 }
2615}
2616
2617/*
2618 * The CPU has been completely removed, and some other CPU is reporting
2619 * this fact from process context. Do the remainder of the cleanup.
2620 * There can only be one CPU hotplug operation at a time, so no need for
2621 * explicit locking.
2622 */
2623static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2624{
2625 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2626 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
2627
2628 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2629 return;
2630
2631 /* Adjust any no-longer-needed kthreads. */
2632 rcu_boost_kthread_setaffinity(rnp, -1);
2633}
2634
2635/*
2636 * Invoke any RCU callbacks that have made it to the end of their grace
2637 * period. Thottle as specified by rdp->blimit.
2638 */
2639static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
2640{
2641 unsigned long flags;
2642 struct rcu_head *rhp;
2643 struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
2644 long bl, count;
2645
2646 /* If no callbacks are ready, just return. */
2647 if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
2648 trace_rcu_batch_start(rsp->name,
2649 rcu_segcblist_n_lazy_cbs(&rdp->cblist),
2650 rcu_segcblist_n_cbs(&rdp->cblist), 0);
2651 trace_rcu_batch_end(rsp->name, 0,
2652 !rcu_segcblist_empty(&rdp->cblist),
2653 need_resched(), is_idle_task(current),
2654 rcu_is_callbacks_kthread());
2655 return;
2656 }
2657
2658 /*
2659 * Extract the list of ready callbacks, disabling to prevent
2660 * races with call_rcu() from interrupt handlers. Leave the
2661 * callback counts, as rcu_barrier() needs to be conservative.
2662 */
2663 local_irq_save(flags);
2664 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2665 bl = rdp->blimit;
2666 trace_rcu_batch_start(rsp->name, rcu_segcblist_n_lazy_cbs(&rdp->cblist),
2667 rcu_segcblist_n_cbs(&rdp->cblist), bl);
2668 rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
2669 local_irq_restore(flags);
2670
2671 /* Invoke callbacks. */
2672 rhp = rcu_cblist_dequeue(&rcl);
2673 for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
2674 debug_rcu_head_unqueue(rhp);
2675 if (__rcu_reclaim(rsp->name, rhp))
2676 rcu_cblist_dequeued_lazy(&rcl);
2677 /*
2678 * Stop only if limit reached and CPU has something to do.
2679 * Note: The rcl structure counts down from zero.
2680 */
2681 if (-rcl.len >= bl &&
2682 (need_resched() ||
2683 (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
2684 break;
2685 }
2686
2687 local_irq_save(flags);
2688 count = -rcl.len;
2689 trace_rcu_batch_end(rsp->name, count, !!rcl.head, need_resched(),
2690 is_idle_task(current), rcu_is_callbacks_kthread());
2691
2692 /* Update counts and requeue any remaining callbacks. */
2693 rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
2694 smp_mb(); /* List handling before counting for rcu_barrier(). */
2695 rcu_segcblist_insert_count(&rdp->cblist, &rcl);
2696
2697 /* Reinstate batch limit if we have worked down the excess. */
2698 count = rcu_segcblist_n_cbs(&rdp->cblist);
2699 if (rdp->blimit == LONG_MAX && count <= qlowmark)
2700 rdp->blimit = blimit;
2701
2702 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2703 if (count == 0 && rdp->qlen_last_fqs_check != 0) {
2704 rdp->qlen_last_fqs_check = 0;
2705 rdp->n_force_qs_snap = rsp->n_force_qs;
2706 } else if (count < rdp->qlen_last_fqs_check - qhimark)
2707 rdp->qlen_last_fqs_check = count;
2708
2709 /*
2710 * The following usually indicates a double call_rcu(). To track
2711 * this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.
2712 */
2713 WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) != (count == 0));
2714
2715 local_irq_restore(flags);
2716
2717 /* Re-invoke RCU core processing if there are callbacks remaining. */
2718 if (rcu_segcblist_ready_cbs(&rdp->cblist))
2719 invoke_rcu_core();
2720}
2721
2722/*
2723 * Check to see if this CPU is in a non-context-switch quiescent state
2724 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
2725 * Also schedule RCU core processing.
2726 *
2727 * This function must be called from hardirq context. It is normally
2728 * invoked from the scheduling-clock interrupt.
2729 */
2730void rcu_check_callbacks(int user)
2731{
2732 trace_rcu_utilization(TPS("Start scheduler-tick"));
2733 increment_cpu_stall_ticks();
2734 if (user || rcu_is_cpu_rrupt_from_idle()) {
2735
2736 /*
2737 * Get here if this CPU took its interrupt from user
2738 * mode or from the idle loop, and if this is not a
2739 * nested interrupt. In this case, the CPU is in
2740 * a quiescent state, so note it.
2741 *
2742 * No memory barrier is required here because both
2743 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
2744 * variables that other CPUs neither access nor modify,
2745 * at least not while the corresponding CPU is online.
2746 */
2747
2748 rcu_sched_qs();
2749 rcu_bh_qs();
2750
2751 } else if (!in_softirq()) {
2752
2753 /*
2754 * Get here if this CPU did not take its interrupt from
2755 * softirq, in other words, if it is not interrupting
2756 * a rcu_bh read-side critical section. This is an _bh
2757 * critical section, so note it.
2758 */
2759
2760 rcu_bh_qs();
2761 }
2762 rcu_preempt_check_callbacks();
2763 if (rcu_pending())
2764 invoke_rcu_core();
2765 if (user)
2766 rcu_note_voluntary_context_switch(current);
2767 trace_rcu_utilization(TPS("End scheduler-tick"));
2768}
2769
2770/*
2771 * Scan the leaf rcu_node structures, processing dyntick state for any that
2772 * have not yet encountered a quiescent state, using the function specified.
2773 * Also initiate boosting for any threads blocked on the root rcu_node.
2774 *
2775 * The caller must have suppressed start of new grace periods.
2776 */
2777static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp))
2778{
2779 int cpu;
2780 unsigned long flags;
2781 unsigned long mask;
2782 struct rcu_node *rnp;
2783
2784 rcu_for_each_leaf_node(rsp, rnp) {
2785 cond_resched_rcu_qs();
2786 mask = 0;
2787 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2788 if (rnp->qsmask == 0) {
2789 if (rcu_state_p == &rcu_sched_state ||
2790 rsp != rcu_state_p ||
2791 rcu_preempt_blocked_readers_cgp(rnp)) {
2792 /*
2793 * No point in scanning bits because they
2794 * are all zero. But we might need to
2795 * priority-boost blocked readers.
2796 */
2797 rcu_initiate_boost(rnp, flags);
2798 /* rcu_initiate_boost() releases rnp->lock */
2799 continue;
2800 }
2801 if (rnp->parent &&
2802 (rnp->parent->qsmask & rnp->grpmask)) {
2803 /*
2804 * Race between grace-period
2805 * initialization and task exiting RCU
2806 * read-side critical section: Report.
2807 */
2808 rcu_report_unblock_qs_rnp(rsp, rnp, flags);
2809 /* rcu_report_unblock_qs_rnp() rlses ->lock */
2810 continue;
2811 }
2812 }
2813 for_each_leaf_node_possible_cpu(rnp, cpu) {
2814 unsigned long bit = leaf_node_cpu_bit(rnp, cpu);
2815 if ((rnp->qsmask & bit) != 0) {
2816 if (f(per_cpu_ptr(rsp->rda, cpu)))
2817 mask |= bit;
2818 }
2819 }
2820 if (mask != 0) {
2821 /* Idle/offline CPUs, report (releases rnp->lock. */
2822 rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags);
2823 } else {
2824 /* Nothing to do here, so just drop the lock. */
2825 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2826 }
2827 }
2828}
2829
2830/*
2831 * Force quiescent states on reluctant CPUs, and also detect which
2832 * CPUs are in dyntick-idle mode.
2833 */
2834static void force_quiescent_state(struct rcu_state *rsp)
2835{
2836 unsigned long flags;
2837 bool ret;
2838 struct rcu_node *rnp;
2839 struct rcu_node *rnp_old = NULL;
2840
2841 /* Funnel through hierarchy to reduce memory contention. */
2842 rnp = __this_cpu_read(rsp->rda->mynode);
2843 for (; rnp != NULL; rnp = rnp->parent) {
2844 ret = (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
2845 !raw_spin_trylock(&rnp->fqslock);
2846 if (rnp_old != NULL)
2847 raw_spin_unlock(&rnp_old->fqslock);
2848 if (ret)
2849 return;
2850 rnp_old = rnp;
2851 }
2852 /* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2853
2854 /* Reached the root of the rcu_node tree, acquire lock. */
2855 raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
2856 raw_spin_unlock(&rnp_old->fqslock);
2857 if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
2858 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2859 return; /* Someone beat us to it. */
2860 }
2861 WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
2862 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2863 rcu_gp_kthread_wake(rsp);
2864}
2865
2866/*
2867 * This does the RCU core processing work for the specified rcu_state
2868 * and rcu_data structures. This may be called only from the CPU to
2869 * whom the rdp belongs.
2870 */
2871static void
2872__rcu_process_callbacks(struct rcu_state *rsp)
2873{
2874 unsigned long flags;
2875 bool needwake;
2876 struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
2877
2878 WARN_ON_ONCE(!rdp->beenonline);
2879
2880 /* Update RCU state based on any recent quiescent states. */
2881 rcu_check_quiescent_state(rsp, rdp);
2882
2883 /* Does this CPU require a not-yet-started grace period? */
2884 local_irq_save(flags);
2885 if (cpu_needs_another_gp(rsp, rdp)) {
2886 raw_spin_lock_rcu_node(rcu_get_root(rsp)); /* irqs disabled. */
2887 needwake = rcu_start_gp(rsp);
2888 raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags);
2889 if (needwake)
2890 rcu_gp_kthread_wake(rsp);
2891 } else {
2892 local_irq_restore(flags);
2893 }
2894
2895 /* If there are callbacks ready, invoke them. */
2896 if (rcu_segcblist_ready_cbs(&rdp->cblist))
2897 invoke_rcu_callbacks(rsp, rdp);
2898
2899 /* Do any needed deferred wakeups of rcuo kthreads. */
2900 do_nocb_deferred_wakeup(rdp);
2901}
2902
2903/*
2904 * Do RCU core processing for the current CPU.
2905 */
2906static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
2907{
2908 struct rcu_state *rsp;
2909
2910 if (cpu_is_offline(smp_processor_id()))
2911 return;
2912 trace_rcu_utilization(TPS("Start RCU core"));
2913 for_each_rcu_flavor(rsp)
2914 __rcu_process_callbacks(rsp);
2915 trace_rcu_utilization(TPS("End RCU core"));
2916}
2917
2918/*
2919 * Schedule RCU callback invocation. If the specified type of RCU
2920 * does not support RCU priority boosting, just do a direct call,
2921 * otherwise wake up the per-CPU kernel kthread. Note that because we
2922 * are running on the current CPU with softirqs disabled, the
2923 * rcu_cpu_kthread_task cannot disappear out from under us.
2924 */
2925static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
2926{
2927 if (unlikely(!READ_ONCE(rcu_scheduler_fully_active)))
2928 return;
2929 if (likely(!rsp->boost)) {
2930 rcu_do_batch(rsp, rdp);
2931 return;
2932 }
2933 invoke_rcu_callbacks_kthread();
2934}
2935
2936static void invoke_rcu_core(void)
2937{
2938 if (cpu_online(smp_processor_id()))
2939 raise_softirq(RCU_SOFTIRQ);
2940}
2941
2942/*
2943 * Handle any core-RCU processing required by a call_rcu() invocation.
2944 */
2945static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
2946 struct rcu_head *head, unsigned long flags)
2947{
2948 bool needwake;
2949
2950 /*
2951 * If called from an extended quiescent state, invoke the RCU
2952 * core in order to force a re-evaluation of RCU's idleness.
2953 */
2954 if (!rcu_is_watching())
2955 invoke_rcu_core();
2956
2957 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2958 if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2959 return;
2960
2961 /*
2962 * Force the grace period if too many callbacks or too long waiting.
2963 * Enforce hysteresis, and don't invoke force_quiescent_state()
2964 * if some other CPU has recently done so. Also, don't bother
2965 * invoking force_quiescent_state() if the newly enqueued callback
2966 * is the only one waiting for a grace period to complete.
2967 */
2968 if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
2969 rdp->qlen_last_fqs_check + qhimark)) {
2970
2971 /* Are we ignoring a completed grace period? */
2972 note_gp_changes(rsp, rdp);
2973
2974 /* Start a new grace period if one not already started. */
2975 if (!rcu_gp_in_progress(rsp)) {
2976 struct rcu_node *rnp_root = rcu_get_root(rsp);
2977
2978 raw_spin_lock_rcu_node(rnp_root);
2979 needwake = rcu_start_gp(rsp);
2980 raw_spin_unlock_rcu_node(rnp_root);
2981 if (needwake)
2982 rcu_gp_kthread_wake(rsp);
2983 } else {
2984 /* Give the grace period a kick. */
2985 rdp->blimit = LONG_MAX;
2986 if (rsp->n_force_qs == rdp->n_force_qs_snap &&
2987 rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
2988 force_quiescent_state(rsp);
2989 rdp->n_force_qs_snap = rsp->n_force_qs;
2990 rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
2991 }
2992 }
2993}
2994
2995/*
2996 * RCU callback function to leak a callback.
2997 */
2998static void rcu_leak_callback(struct rcu_head *rhp)
2999{
3000}
3001
3002/*
3003 * Helper function for call_rcu() and friends. The cpu argument will
3004 * normally be -1, indicating "currently running CPU". It may specify
3005 * a CPU only if that CPU is a no-CBs CPU. Currently, only _rcu_barrier()
3006 * is expected to specify a CPU.
3007 */
3008static void
3009__call_rcu(struct rcu_head *head, rcu_callback_t func,
3010 struct rcu_state *rsp, int cpu, bool lazy)
3011{
3012 unsigned long flags;
3013 struct rcu_data *rdp;
3014
3015 /* Misaligned rcu_head! */
3016 WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
3017
3018 if (debug_rcu_head_queue(head)) {
3019 /*
3020 * Probable double call_rcu(), so leak the callback.
3021 * Use rcu:rcu_callback trace event to find the previous
3022 * time callback was passed to __call_rcu().
3023 */
3024 WARN_ONCE(1, "__call_rcu(): Double-freed CB %p->%pF()!!!\n",
3025 head, head->func);
3026 WRITE_ONCE(head->func, rcu_leak_callback);
3027 return;
3028 }
3029 head->func = func;
3030 head->next = NULL;
3031 local_irq_save(flags);
3032 rdp = this_cpu_ptr(rsp->rda);
3033
3034 /* Add the callback to our list. */
3035 if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist)) || cpu != -1) {
3036 int offline;
3037
3038 if (cpu != -1)
3039 rdp = per_cpu_ptr(rsp->rda, cpu);
3040 if (likely(rdp->mynode)) {
3041 /* Post-boot, so this should be for a no-CBs CPU. */
3042 offline = !__call_rcu_nocb(rdp, head, lazy, flags);
3043 WARN_ON_ONCE(offline);
3044 /* Offline CPU, _call_rcu() illegal, leak callback. */
3045 local_irq_restore(flags);
3046 return;
3047 }
3048 /*
3049 * Very early boot, before rcu_init(). Initialize if needed
3050 * and then drop through to queue the callback.
3051 */
3052 BUG_ON(cpu != -1);
3053 WARN_ON_ONCE(!rcu_is_watching());
3054 if (rcu_segcblist_empty(&rdp->cblist))
3055 rcu_segcblist_init(&rdp->cblist);
3056 }
3057 rcu_segcblist_enqueue(&rdp->cblist, head, lazy);
3058 if (!lazy)
3059 rcu_idle_count_callbacks_posted();
3060
3061 if (__is_kfree_rcu_offset((unsigned long)func))
3062 trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
3063 rcu_segcblist_n_lazy_cbs(&rdp->cblist),
3064 rcu_segcblist_n_cbs(&rdp->cblist));
3065 else
3066 trace_rcu_callback(rsp->name, head,
3067 rcu_segcblist_n_lazy_cbs(&rdp->cblist),
3068 rcu_segcblist_n_cbs(&rdp->cblist));
3069
3070 /* Go handle any RCU core processing required. */
3071 __call_rcu_core(rsp, rdp, head, flags);
3072 local_irq_restore(flags);
3073}
3074
3075/**
3076 * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
3077 * @head: structure to be used for queueing the RCU updates.
3078 * @func: actual callback function to be invoked after the grace period
3079 *
3080 * The callback function will be invoked some time after a full grace
3081 * period elapses, in other words after all currently executing RCU
3082 * read-side critical sections have completed. call_rcu_sched() assumes
3083 * that the read-side critical sections end on enabling of preemption
3084 * or on voluntary preemption.
3085 * RCU read-side critical sections are delimited by:
3086 *
3087 * - rcu_read_lock_sched() and rcu_read_unlock_sched(), OR
3088 * - anything that disables preemption.
3089 *
3090 * These may be nested.
3091 *
3092 * See the description of call_rcu() for more detailed information on
3093 * memory ordering guarantees.
3094 */
3095void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
3096{
3097 __call_rcu(head, func, &rcu_sched_state, -1, 0);
3098}
3099EXPORT_SYMBOL_GPL(call_rcu_sched);
3100
3101/**
3102 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
3103 * @head: structure to be used for queueing the RCU updates.
3104 * @func: actual callback function to be invoked after the grace period
3105 *
3106 * The callback function will be invoked some time after a full grace
3107 * period elapses, in other words after all currently executing RCU
3108 * read-side critical sections have completed. call_rcu_bh() assumes
3109 * that the read-side critical sections end on completion of a softirq
3110 * handler. This means that read-side critical sections in process
3111 * context must not be interrupted by softirqs. This interface is to be
3112 * used when most of the read-side critical sections are in softirq context.
3113 * RCU read-side critical sections are delimited by:
3114 *
3115 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context, OR
3116 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
3117 *
3118 * These may be nested.
3119 *
3120 * See the description of call_rcu() for more detailed information on
3121 * memory ordering guarantees.
3122 */
3123void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
3124{
3125 __call_rcu(head, func, &rcu_bh_state, -1, 0);
3126}
3127EXPORT_SYMBOL_GPL(call_rcu_bh);
3128
3129/*
3130 * Queue an RCU callback for lazy invocation after a grace period.
3131 * This will likely be later named something like "call_rcu_lazy()",
3132 * but this change will require some way of tagging the lazy RCU
3133 * callbacks in the list of pending callbacks. Until then, this
3134 * function may only be called from __kfree_rcu().
3135 */
3136void kfree_call_rcu(struct rcu_head *head,
3137 rcu_callback_t func)
3138{
3139 __call_rcu(head, func, rcu_state_p, -1, 1);
3140}
3141EXPORT_SYMBOL_GPL(kfree_call_rcu);
3142
3143/*
3144 * Because a context switch is a grace period for RCU-sched and RCU-bh,
3145 * any blocking grace-period wait automatically implies a grace period
3146 * if there is only one CPU online at any point time during execution
3147 * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
3148 * occasionally incorrectly indicate that there are multiple CPUs online
3149 * when there was in fact only one the whole time, as this just adds
3150 * some overhead: RCU still operates correctly.
3151 */
3152static inline int rcu_blocking_is_gp(void)
3153{
3154 int ret;
3155
3156 might_sleep(); /* Check for RCU read-side critical section. */
3157 preempt_disable();
3158 ret = num_online_cpus() <= 1;
3159 preempt_enable();
3160 return ret;
3161}
3162
3163/**
3164 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
3165 *
3166 * Control will return to the caller some time after a full rcu-sched
3167 * grace period has elapsed, in other words after all currently executing
3168 * rcu-sched read-side critical sections have completed. These read-side
3169 * critical sections are delimited by rcu_read_lock_sched() and
3170 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
3171 * local_irq_disable(), and so on may be used in place of
3172 * rcu_read_lock_sched().
3173 *
3174 * This means that all preempt_disable code sequences, including NMI and
3175 * non-threaded hardware-interrupt handlers, in progress on entry will
3176 * have completed before this primitive returns. However, this does not
3177 * guarantee that softirq handlers will have completed, since in some
3178 * kernels, these handlers can run in process context, and can block.
3179 *
3180 * Note that this guarantee implies further memory-ordering guarantees.
3181 * On systems with more than one CPU, when synchronize_sched() returns,
3182 * each CPU is guaranteed to have executed a full memory barrier since the
3183 * end of its last RCU-sched read-side critical section whose beginning
3184 * preceded the call to synchronize_sched(). In addition, each CPU having
3185 * an RCU read-side critical section that extends beyond the return from
3186 * synchronize_sched() is guaranteed to have executed a full memory barrier
3187 * after the beginning of synchronize_sched() and before the beginning of
3188 * that RCU read-side critical section. Note that these guarantees include
3189 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
3190 * that are executing in the kernel.
3191 *
3192 * Furthermore, if CPU A invoked synchronize_sched(), which returned
3193 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
3194 * to have executed a full memory barrier during the execution of
3195 * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
3196 * again only if the system has more than one CPU).
3197 */
3198void synchronize_sched(void)
3199{
3200 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
3201 lock_is_held(&rcu_lock_map) ||
3202 lock_is_held(&rcu_sched_lock_map),
3203 "Illegal synchronize_sched() in RCU-sched read-side critical section");
3204 if (rcu_blocking_is_gp())
3205 return;
3206 if (rcu_gp_is_expedited())
3207 synchronize_sched_expedited();
3208 else
3209 wait_rcu_gp(call_rcu_sched);
3210}
3211EXPORT_SYMBOL_GPL(synchronize_sched);
3212
3213/**
3214 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
3215 *
3216 * Control will return to the caller some time after a full rcu_bh grace
3217 * period has elapsed, in other words after all currently executing rcu_bh
3218 * read-side critical sections have completed. RCU read-side critical
3219 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
3220 * and may be nested.
3221 *
3222 * See the description of synchronize_sched() for more detailed information
3223 * on memory ordering guarantees.
3224 */
3225void synchronize_rcu_bh(void)
3226{
3227 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
3228 lock_is_held(&rcu_lock_map) ||
3229 lock_is_held(&rcu_sched_lock_map),
3230 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
3231 if (rcu_blocking_is_gp())
3232 return;
3233 if (rcu_gp_is_expedited())
3234 synchronize_rcu_bh_expedited();
3235 else
3236 wait_rcu_gp(call_rcu_bh);
3237}
3238EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
3239
3240/**
3241 * get_state_synchronize_rcu - Snapshot current RCU state
3242 *
3243 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
3244 * to determine whether or not a full grace period has elapsed in the
3245 * meantime.
3246 */
3247unsigned long get_state_synchronize_rcu(void)
3248{
3249 /*
3250 * Any prior manipulation of RCU-protected data must happen
3251 * before the load from ->gpnum.
3252 */
3253 smp_mb(); /* ^^^ */
3254
3255 /*
3256 * Make sure this load happens before the purportedly
3257 * time-consuming work between get_state_synchronize_rcu()
3258 * and cond_synchronize_rcu().
3259 */
3260 return smp_load_acquire(&rcu_state_p->gpnum);
3261}
3262EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
3263
3264/**
3265 * cond_synchronize_rcu - Conditionally wait for an RCU grace period
3266 *
3267 * @oldstate: return value from earlier call to get_state_synchronize_rcu()
3268 *
3269 * If a full RCU grace period has elapsed since the earlier call to
3270 * get_state_synchronize_rcu(), just return. Otherwise, invoke
3271 * synchronize_rcu() to wait for a full grace period.
3272 *
3273 * Yes, this function does not take counter wrap into account. But
3274 * counter wrap is harmless. If the counter wraps, we have waited for
3275 * more than 2 billion grace periods (and way more on a 64-bit system!),
3276 * so waiting for one additional grace period should be just fine.
3277 */
3278void cond_synchronize_rcu(unsigned long oldstate)
3279{
3280 unsigned long newstate;
3281
3282 /*
3283 * Ensure that this load happens before any RCU-destructive
3284 * actions the caller might carry out after we return.
3285 */
3286 newstate = smp_load_acquire(&rcu_state_p->completed);
3287 if (ULONG_CMP_GE(oldstate, newstate))
3288 synchronize_rcu();
3289}
3290EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
3291
3292/**
3293 * get_state_synchronize_sched - Snapshot current RCU-sched state
3294 *
3295 * Returns a cookie that is used by a later call to cond_synchronize_sched()
3296 * to determine whether or not a full grace period has elapsed in the
3297 * meantime.
3298 */
3299unsigned long get_state_synchronize_sched(void)
3300{
3301 /*
3302 * Any prior manipulation of RCU-protected data must happen
3303 * before the load from ->gpnum.
3304 */
3305 smp_mb(); /* ^^^ */
3306
3307 /*
3308 * Make sure this load happens before the purportedly
3309 * time-consuming work between get_state_synchronize_sched()
3310 * and cond_synchronize_sched().
3311 */
3312 return smp_load_acquire(&rcu_sched_state.gpnum);
3313}
3314EXPORT_SYMBOL_GPL(get_state_synchronize_sched);
3315
3316/**
3317 * cond_synchronize_sched - Conditionally wait for an RCU-sched grace period
3318 *
3319 * @oldstate: return value from earlier call to get_state_synchronize_sched()
3320 *
3321 * If a full RCU-sched grace period has elapsed since the earlier call to
3322 * get_state_synchronize_sched(), just return. Otherwise, invoke
3323 * synchronize_sched() to wait for a full grace period.
3324 *
3325 * Yes, this function does not take counter wrap into account. But
3326 * counter wrap is harmless. If the counter wraps, we have waited for
3327 * more than 2 billion grace periods (and way more on a 64-bit system!),
3328 * so waiting for one additional grace period should be just fine.
3329 */
3330void cond_synchronize_sched(unsigned long oldstate)
3331{
3332 unsigned long newstate;
3333
3334 /*
3335 * Ensure that this load happens before any RCU-destructive
3336 * actions the caller might carry out after we return.
3337 */
3338 newstate = smp_load_acquire(&rcu_sched_state.completed);
3339 if (ULONG_CMP_GE(oldstate, newstate))
3340 synchronize_sched();
3341}
3342EXPORT_SYMBOL_GPL(cond_synchronize_sched);
3343
3344/*
3345 * Check to see if there is any immediate RCU-related work to be done
3346 * by the current CPU, for the specified type of RCU, returning 1 if so.
3347 * The checks are in order of increasing expense: checks that can be
3348 * carried out against CPU-local state are performed first. However,
3349 * we must check for CPU stalls first, else we might not get a chance.
3350 */
3351static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
3352{
3353 struct rcu_node *rnp = rdp->mynode;
3354
3355 /* Check for CPU stalls, if enabled. */
3356 check_cpu_stall(rsp, rdp);
3357
3358 /* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
3359 if (rcu_nohz_full_cpu(rsp))
3360 return 0;
3361
3362 /* Is the RCU core waiting for a quiescent state from this CPU? */
3363 if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm)
3364 return 1;
3365
3366 /* Does this CPU have callbacks ready to invoke? */
3367 if (rcu_segcblist_ready_cbs(&rdp->cblist))
3368 return 1;
3369
3370 /* Has RCU gone idle with this CPU needing another grace period? */
3371 if (cpu_needs_another_gp(rsp, rdp))
3372 return 1;
3373
3374 /* Has another RCU grace period completed? */
3375 if (READ_ONCE(rnp->completed) != rdp->completed) /* outside lock */
3376 return 1;
3377
3378 /* Has a new RCU grace period started? */
3379 if (READ_ONCE(rnp->gpnum) != rdp->gpnum ||
3380 unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */
3381 return 1;
3382
3383 /* Does this CPU need a deferred NOCB wakeup? */
3384 if (rcu_nocb_need_deferred_wakeup(rdp))
3385 return 1;
3386
3387 /* nothing to do */
3388 return 0;
3389}
3390
3391/*
3392 * Check to see if there is any immediate RCU-related work to be done
3393 * by the current CPU, returning 1 if so. This function is part of the
3394 * RCU implementation; it is -not- an exported member of the RCU API.
3395 */
3396static int rcu_pending(void)
3397{
3398 struct rcu_state *rsp;
3399
3400 for_each_rcu_flavor(rsp)
3401 if (__rcu_pending(rsp, this_cpu_ptr(rsp->rda)))
3402 return 1;
3403 return 0;
3404}
3405
3406/*
3407 * Return true if the specified CPU has any callback. If all_lazy is
3408 * non-NULL, store an indication of whether all callbacks are lazy.
3409 * (If there are no callbacks, all of them are deemed to be lazy.)
3410 */
3411static bool __maybe_unused rcu_cpu_has_callbacks(bool *all_lazy)
3412{
3413 bool al = true;
3414 bool hc = false;
3415 struct rcu_data *rdp;
3416 struct rcu_state *rsp;
3417
3418 for_each_rcu_flavor(rsp) {
3419 rdp = this_cpu_ptr(rsp->rda);
3420 if (rcu_segcblist_empty(&rdp->cblist))
3421 continue;
3422 hc = true;
3423 if (rcu_segcblist_n_nonlazy_cbs(&rdp->cblist) || !all_lazy) {
3424 al = false;
3425 break;
3426 }
3427 }
3428 if (all_lazy)
3429 *all_lazy = al;
3430 return hc;
3431}
3432
3433/*
3434 * Helper function for _rcu_barrier() tracing. If tracing is disabled,
3435 * the compiler is expected to optimize this away.
3436 */
3437static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
3438 int cpu, unsigned long done)
3439{
3440 trace_rcu_barrier(rsp->name, s, cpu,
3441 atomic_read(&rsp->barrier_cpu_count), done);
3442}
3443
3444/*
3445 * RCU callback function for _rcu_barrier(). If we are last, wake
3446 * up the task executing _rcu_barrier().
3447 */
3448static void rcu_barrier_callback(struct rcu_head *rhp)
3449{
3450 struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
3451 struct rcu_state *rsp = rdp->rsp;
3452
3453 if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
3454 _rcu_barrier_trace(rsp, TPS("LastCB"), -1,
3455 rsp->barrier_sequence);
3456 complete(&rsp->barrier_completion);
3457 } else {
3458 _rcu_barrier_trace(rsp, TPS("CB"), -1, rsp->barrier_sequence);
3459 }
3460}
3461
3462/*
3463 * Called with preemption disabled, and from cross-cpu IRQ context.
3464 */
3465static void rcu_barrier_func(void *type)
3466{
3467 struct rcu_state *rsp = type;
3468 struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
3469
3470 _rcu_barrier_trace(rsp, TPS("IRQ"), -1, rsp->barrier_sequence);
3471 rdp->barrier_head.func = rcu_barrier_callback;
3472 debug_rcu_head_queue(&rdp->barrier_head);
3473 if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head, 0)) {
3474 atomic_inc(&rsp->barrier_cpu_count);
3475 } else {
3476 debug_rcu_head_unqueue(&rdp->barrier_head);
3477 _rcu_barrier_trace(rsp, TPS("IRQNQ"), -1,
3478 rsp->barrier_sequence);
3479 }
3480}
3481
3482/*
3483 * Orchestrate the specified type of RCU barrier, waiting for all
3484 * RCU callbacks of the specified type to complete.
3485 */
3486static void _rcu_barrier(struct rcu_state *rsp)
3487{
3488 int cpu;
3489 struct rcu_data *rdp;
3490 unsigned long s = rcu_seq_snap(&rsp->barrier_sequence);
3491
3492 _rcu_barrier_trace(rsp, TPS("Begin"), -1, s);
3493
3494 /* Take mutex to serialize concurrent rcu_barrier() requests. */
3495 mutex_lock(&rsp->barrier_mutex);
3496
3497 /* Did someone else do our work for us? */
3498 if (rcu_seq_done(&rsp->barrier_sequence, s)) {
3499 _rcu_barrier_trace(rsp, TPS("EarlyExit"), -1,
3500 rsp->barrier_sequence);
3501 smp_mb(); /* caller's subsequent code after above check. */
3502 mutex_unlock(&rsp->barrier_mutex);
3503 return;
3504 }
3505
3506 /* Mark the start of the barrier operation. */
3507 rcu_seq_start(&rsp->barrier_sequence);
3508 _rcu_barrier_trace(rsp, TPS("Inc1"), -1, rsp->barrier_sequence);
3509
3510 /*
3511 * Initialize the count to one rather than to zero in order to
3512 * avoid a too-soon return to zero in case of a short grace period
3513 * (or preemption of this task). Exclude CPU-hotplug operations
3514 * to ensure that no offline CPU has callbacks queued.
3515 */
3516 init_completion(&rsp->barrier_completion);
3517 atomic_set(&rsp->barrier_cpu_count, 1);
3518 get_online_cpus();
3519
3520 /*
3521 * Force each CPU with callbacks to register a new callback.
3522 * When that callback is invoked, we will know that all of the
3523 * corresponding CPU's preceding callbacks have been invoked.
3524 */
3525 for_each_possible_cpu(cpu) {
3526 if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
3527 continue;
3528 rdp = per_cpu_ptr(rsp->rda, cpu);
3529 if (rcu_is_nocb_cpu(cpu)) {
3530 if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) {
3531 _rcu_barrier_trace(rsp, TPS("OfflineNoCB"), cpu,
3532 rsp->barrier_sequence);
3533 } else {
3534 _rcu_barrier_trace(rsp, TPS("OnlineNoCB"), cpu,
3535 rsp->barrier_sequence);
3536 smp_mb__before_atomic();
3537 atomic_inc(&rsp->barrier_cpu_count);
3538 __call_rcu(&rdp->barrier_head,
3539 rcu_barrier_callback, rsp, cpu, 0);
3540 }
3541 } else if (rcu_segcblist_n_cbs(&rdp->cblist)) {
3542 _rcu_barrier_trace(rsp, TPS("OnlineQ"), cpu,
3543 rsp->barrier_sequence);
3544 smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
3545 } else {
3546 _rcu_barrier_trace(rsp, TPS("OnlineNQ"), cpu,
3547 rsp->barrier_sequence);
3548 }
3549 }
3550 put_online_cpus();
3551
3552 /*
3553 * Now that we have an rcu_barrier_callback() callback on each
3554 * CPU, and thus each counted, remove the initial count.
3555 */
3556 if (atomic_dec_and_test(&rsp->barrier_cpu_count))
3557 complete(&rsp->barrier_completion);
3558
3559 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
3560 wait_for_completion(&rsp->barrier_completion);
3561
3562 /* Mark the end of the barrier operation. */
3563 _rcu_barrier_trace(rsp, TPS("Inc2"), -1, rsp->barrier_sequence);
3564 rcu_seq_end(&rsp->barrier_sequence);
3565
3566 /* Other rcu_barrier() invocations can now safely proceed. */
3567 mutex_unlock(&rsp->barrier_mutex);
3568}
3569
3570/**
3571 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
3572 */
3573void rcu_barrier_bh(void)
3574{
3575 _rcu_barrier(&rcu_bh_state);
3576}
3577EXPORT_SYMBOL_GPL(rcu_barrier_bh);
3578
3579/**
3580 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
3581 */
3582void rcu_barrier_sched(void)
3583{
3584 _rcu_barrier(&rcu_sched_state);
3585}
3586EXPORT_SYMBOL_GPL(rcu_barrier_sched);
3587
3588/*
3589 * Propagate ->qsinitmask bits up the rcu_node tree to account for the
3590 * first CPU in a given leaf rcu_node structure coming online. The caller
3591 * must hold the corresponding leaf rcu_node ->lock with interrrupts
3592 * disabled.
3593 */
3594static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
3595{
3596 long mask;
3597 struct rcu_node *rnp = rnp_leaf;
3598
3599 raw_lockdep_assert_held_rcu_node(rnp);
3600 for (;;) {
3601 mask = rnp->grpmask;
3602 rnp = rnp->parent;
3603 if (rnp == NULL)
3604 return;
3605 raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
3606 rnp->qsmaskinit |= mask;
3607 raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
3608 }
3609}
3610
3611/*
3612 * Do boot-time initialization of a CPU's per-CPU RCU data.
3613 */
3614static void __init
3615rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
3616{
3617 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3618
3619 /* Set up local state, ensuring consistent view of global state. */
3620 rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
3621 rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
3622 WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != 1);
3623 WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp->dynticks)));
3624 rdp->cpu = cpu;
3625 rdp->rsp = rsp;
3626 rcu_boot_init_nocb_percpu_data(rdp);
3627}
3628
3629/*
3630 * Initialize a CPU's per-CPU RCU data. Note that only one online or
3631 * offline event can be happening at a given time. Note also that we
3632 * can accept some slop in the rsp->completed access due to the fact
3633 * that this CPU cannot possibly have any RCU callbacks in flight yet.
3634 */
3635static void
3636rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
3637{
3638 unsigned long flags;
3639 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3640 struct rcu_node *rnp = rcu_get_root(rsp);
3641
3642 /* Set up local state, ensuring consistent view of global state. */
3643 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3644 rdp->qlen_last_fqs_check = 0;
3645 rdp->n_force_qs_snap = rsp->n_force_qs;
3646 rdp->blimit = blimit;
3647 if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */
3648 !init_nocb_callback_list(rdp))
3649 rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
3650 rdp->dynticks->dynticks_nesting = 1; /* CPU not up, no tearing. */
3651 rcu_dynticks_eqs_online();
3652 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
3653
3654 /*
3655 * Add CPU to leaf rcu_node pending-online bitmask. Any needed
3656 * propagation up the rcu_node tree will happen at the beginning
3657 * of the next grace period.
3658 */
3659 rnp = rdp->mynode;
3660 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
3661 rdp->beenonline = true; /* We have now been online. */
3662 rdp->gpnum = rnp->completed; /* Make CPU later note any new GP. */
3663 rdp->completed = rnp->completed;
3664 rdp->cpu_no_qs.b.norm = true;
3665 rdp->rcu_qs_ctr_snap = per_cpu(rcu_dynticks.rcu_qs_ctr, cpu);
3666 rdp->core_needs_qs = false;
3667 rdp->rcu_iw_pending = false;
3668 rdp->rcu_iw_gpnum = rnp->gpnum - 1;
3669 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
3670 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3671}
3672
3673/*
3674 * Invoked early in the CPU-online process, when pretty much all
3675 * services are available. The incoming CPU is not present.
3676 */
3677int rcutree_prepare_cpu(unsigned int cpu)
3678{
3679 struct rcu_state *rsp;
3680
3681 for_each_rcu_flavor(rsp)
3682 rcu_init_percpu_data(cpu, rsp);
3683
3684 rcu_prepare_kthreads(cpu);
3685 rcu_spawn_all_nocb_kthreads(cpu);
3686
3687 return 0;
3688}
3689
3690/*
3691 * Update RCU priority boot kthread affinity for CPU-hotplug changes.
3692 */
3693static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
3694{
3695 struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
3696
3697 rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
3698}
3699
3700/*
3701 * Near the end of the CPU-online process. Pretty much all services
3702 * enabled, and the CPU is now very much alive.
3703 */
3704int rcutree_online_cpu(unsigned int cpu)
3705{
3706 unsigned long flags;
3707 struct rcu_data *rdp;
3708 struct rcu_node *rnp;
3709 struct rcu_state *rsp;
3710
3711 for_each_rcu_flavor(rsp) {
3712 rdp = per_cpu_ptr(rsp->rda, cpu);
3713 rnp = rdp->mynode;
3714 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3715 rnp->ffmask |= rdp->grpmask;
3716 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3717 }
3718 if (IS_ENABLED(CONFIG_TREE_SRCU))
3719 srcu_online_cpu(cpu);
3720 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
3721 return 0; /* Too early in boot for scheduler work. */
3722 sync_sched_exp_online_cleanup(cpu);
3723 rcutree_affinity_setting(cpu, -1);
3724 return 0;
3725}
3726
3727/*
3728 * Near the beginning of the process. The CPU is still very much alive
3729 * with pretty much all services enabled.
3730 */
3731int rcutree_offline_cpu(unsigned int cpu)
3732{
3733 unsigned long flags;
3734 struct rcu_data *rdp;
3735 struct rcu_node *rnp;
3736 struct rcu_state *rsp;
3737
3738 for_each_rcu_flavor(rsp) {
3739 rdp = per_cpu_ptr(rsp->rda, cpu);
3740 rnp = rdp->mynode;
3741 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3742 rnp->ffmask &= ~rdp->grpmask;
3743 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3744 }
3745
3746 rcutree_affinity_setting(cpu, cpu);
3747 if (IS_ENABLED(CONFIG_TREE_SRCU))
3748 srcu_offline_cpu(cpu);
3749 return 0;
3750}
3751
3752/*
3753 * Near the end of the offline process. We do only tracing here.
3754 */
3755int rcutree_dying_cpu(unsigned int cpu)
3756{
3757 struct rcu_state *rsp;
3758
3759 for_each_rcu_flavor(rsp)
3760 rcu_cleanup_dying_cpu(rsp);
3761 return 0;
3762}
3763
3764/*
3765 * The outgoing CPU is gone and we are running elsewhere.
3766 */
3767int rcutree_dead_cpu(unsigned int cpu)
3768{
3769 struct rcu_state *rsp;
3770
3771 for_each_rcu_flavor(rsp) {
3772 rcu_cleanup_dead_cpu(cpu, rsp);
3773 do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu));
3774 }
3775 return 0;
3776}
3777
3778/*
3779 * Mark the specified CPU as being online so that subsequent grace periods
3780 * (both expedited and normal) will wait on it. Note that this means that
3781 * incoming CPUs are not allowed to use RCU read-side critical sections
3782 * until this function is called. Failing to observe this restriction
3783 * will result in lockdep splats.
3784 *
3785 * Note that this function is special in that it is invoked directly
3786 * from the incoming CPU rather than from the cpuhp_step mechanism.
3787 * This is because this function must be invoked at a precise location.
3788 */
3789void rcu_cpu_starting(unsigned int cpu)
3790{
3791 unsigned long flags;
3792 unsigned long mask;
3793 int nbits;
3794 unsigned long oldmask;
3795 struct rcu_data *rdp;
3796 struct rcu_node *rnp;
3797 struct rcu_state *rsp;
3798
3799 for_each_rcu_flavor(rsp) {
3800 rdp = per_cpu_ptr(rsp->rda, cpu);
3801 rnp = rdp->mynode;
3802 mask = rdp->grpmask;
3803 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3804 rnp->qsmaskinitnext |= mask;
3805 oldmask = rnp->expmaskinitnext;
3806 rnp->expmaskinitnext |= mask;
3807 oldmask ^= rnp->expmaskinitnext;
3808 nbits = bitmap_weight(&oldmask, BITS_PER_LONG);
3809 /* Allow lockless access for expedited grace periods. */
3810 smp_store_release(&rsp->ncpus, rsp->ncpus + nbits); /* ^^^ */
3811 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3812 }
3813 smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
3814}
3815
3816#ifdef CONFIG_HOTPLUG_CPU
3817/*
3818 * The CPU is exiting the idle loop into the arch_cpu_idle_dead()
3819 * function. We now remove it from the rcu_node tree's ->qsmaskinit
3820 * bit masks.
3821 */
3822static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp)
3823{
3824 unsigned long flags;
3825 unsigned long mask;
3826 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3827 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
3828
3829 /* Remove outgoing CPU from mask in the leaf rcu_node structure. */
3830 mask = rdp->grpmask;
3831 raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
3832 rnp->qsmaskinitnext &= ~mask;
3833 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3834}
3835
3836/*
3837 * The outgoing function has no further need of RCU, so remove it from
3838 * the list of CPUs that RCU must track.
3839 *
3840 * Note that this function is special in that it is invoked directly
3841 * from the outgoing CPU rather than from the cpuhp_step mechanism.
3842 * This is because this function must be invoked at a precise location.
3843 */
3844void rcu_report_dead(unsigned int cpu)
3845{
3846 struct rcu_state *rsp;
3847
3848 /* QS for any half-done expedited RCU-sched GP. */
3849 preempt_disable();
3850 rcu_report_exp_rdp(&rcu_sched_state,
3851 this_cpu_ptr(rcu_sched_state.rda), true);
3852 preempt_enable();
3853 for_each_rcu_flavor(rsp)
3854 rcu_cleanup_dying_idle_cpu(cpu, rsp);
3855}
3856
3857/* Migrate the dead CPU's callbacks to the current CPU. */
3858static void rcu_migrate_callbacks(int cpu, struct rcu_state *rsp)
3859{
3860 unsigned long flags;
3861 struct rcu_data *my_rdp;
3862 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3863 struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
3864
3865 if (rcu_is_nocb_cpu(cpu) || rcu_segcblist_empty(&rdp->cblist))
3866 return; /* No callbacks to migrate. */
3867
3868 local_irq_save(flags);
3869 my_rdp = this_cpu_ptr(rsp->rda);
3870 if (rcu_nocb_adopt_orphan_cbs(my_rdp, rdp, flags)) {
3871 local_irq_restore(flags);
3872 return;
3873 }
3874 raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
3875 rcu_advance_cbs(rsp, rnp_root, rdp); /* Leverage recent GPs. */
3876 rcu_advance_cbs(rsp, rnp_root, my_rdp); /* Assign GP to pending CBs. */
3877 rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
3878 WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) !=
3879 !rcu_segcblist_n_cbs(&my_rdp->cblist));
3880 raw_spin_unlock_irqrestore_rcu_node(rnp_root, flags);
3881 WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
3882 !rcu_segcblist_empty(&rdp->cblist),
3883 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
3884 cpu, rcu_segcblist_n_cbs(&rdp->cblist),
3885 rcu_segcblist_first_cb(&rdp->cblist));
3886}
3887
3888/*
3889 * The outgoing CPU has just passed through the dying-idle state,
3890 * and we are being invoked from the CPU that was IPIed to continue the
3891 * offline operation. We need to migrate the outgoing CPU's callbacks.
3892 */
3893void rcutree_migrate_callbacks(int cpu)
3894{
3895 struct rcu_state *rsp;
3896
3897 for_each_rcu_flavor(rsp)
3898 rcu_migrate_callbacks(cpu, rsp);
3899}
3900#endif
3901
3902/*
3903 * On non-huge systems, use expedited RCU grace periods to make suspend
3904 * and hibernation run faster.
3905 */
3906static int rcu_pm_notify(struct notifier_block *self,
3907 unsigned long action, void *hcpu)
3908{
3909 switch (action) {
3910 case PM_HIBERNATION_PREPARE:
3911 case PM_SUSPEND_PREPARE:
3912 if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
3913 rcu_expedite_gp();
3914 break;
3915 case PM_POST_HIBERNATION:
3916 case PM_POST_SUSPEND:
3917 if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
3918 rcu_unexpedite_gp();
3919 break;
3920 default:
3921 break;
3922 }
3923 return NOTIFY_OK;
3924}
3925
3926/*
3927 * Spawn the kthreads that handle each RCU flavor's grace periods.
3928 */
3929static int __init rcu_spawn_gp_kthread(void)
3930{
3931 unsigned long flags;
3932 int kthread_prio_in = kthread_prio;
3933 struct rcu_node *rnp;
3934 struct rcu_state *rsp;
3935 struct sched_param sp;
3936 struct task_struct *t;
3937
3938 /* Force priority into range. */
3939 if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
3940 kthread_prio = 1;
3941 else if (kthread_prio < 0)
3942 kthread_prio = 0;
3943 else if (kthread_prio > 99)
3944 kthread_prio = 99;
3945 if (kthread_prio != kthread_prio_in)
3946 pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
3947 kthread_prio, kthread_prio_in);
3948
3949 rcu_scheduler_fully_active = 1;
3950 for_each_rcu_flavor(rsp) {
3951 t = kthread_create(rcu_gp_kthread, rsp, "%s", rsp->name);
3952 BUG_ON(IS_ERR(t));
3953 rnp = rcu_get_root(rsp);
3954 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3955 rsp->gp_kthread = t;
3956 if (kthread_prio) {
3957 sp.sched_priority = kthread_prio;
3958 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
3959 }
3960 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3961 wake_up_process(t);
3962 }
3963 rcu_spawn_nocb_kthreads();
3964 rcu_spawn_boost_kthreads();
3965 return 0;
3966}
3967early_initcall(rcu_spawn_gp_kthread);
3968
3969/*
3970 * This function is invoked towards the end of the scheduler's
3971 * initialization process. Before this is called, the idle task might
3972 * contain synchronous grace-period primitives (during which time, this idle
3973 * task is booting the system, and such primitives are no-ops). After this
3974 * function is called, any synchronous grace-period primitives are run as
3975 * expedited, with the requesting task driving the grace period forward.
3976 * A later core_initcall() rcu_set_runtime_mode() will switch to full
3977 * runtime RCU functionality.
3978 */
3979void rcu_scheduler_starting(void)
3980{
3981 WARN_ON(num_online_cpus() != 1);
3982 WARN_ON(nr_context_switches() > 0);
3983 rcu_test_sync_prims();
3984 rcu_scheduler_active = RCU_SCHEDULER_INIT;
3985 rcu_test_sync_prims();
3986}
3987
3988/*
3989 * Helper function for rcu_init() that initializes one rcu_state structure.
3990 */
3991static void __init rcu_init_one(struct rcu_state *rsp)
3992{
3993 static const char * const buf[] = RCU_NODE_NAME_INIT;
3994 static const char * const fqs[] = RCU_FQS_NAME_INIT;
3995 static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
3996 static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
3997
3998 int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */
3999 int cpustride = 1;
4000 int i;
4001 int j;
4002 struct rcu_node *rnp;
4003
4004 BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
4005
4006 /* Silence gcc 4.8 false positive about array index out of range. */
4007 if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
4008 panic("rcu_init_one: rcu_num_lvls out of range");
4009
4010 /* Initialize the level-tracking arrays. */
4011
4012 for (i = 1; i < rcu_num_lvls; i++)
4013 rsp->level[i] = rsp->level[i - 1] + num_rcu_lvl[i - 1];
4014 rcu_init_levelspread(levelspread, num_rcu_lvl);
4015
4016 /* Initialize the elements themselves, starting from the leaves. */
4017
4018 for (i = rcu_num_lvls - 1; i >= 0; i--) {
4019 cpustride *= levelspread[i];
4020 rnp = rsp->level[i];
4021 for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
4022 raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
4023 lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
4024 &rcu_node_class[i], buf[i]);
4025 raw_spin_lock_init(&rnp->fqslock);
4026 lockdep_set_class_and_name(&rnp->fqslock,
4027 &rcu_fqs_class[i], fqs[i]);
4028 rnp->gpnum = rsp->gpnum;
4029 rnp->completed = rsp->completed;
4030 rnp->qsmask = 0;
4031 rnp->qsmaskinit = 0;
4032 rnp->grplo = j * cpustride;
4033 rnp->grphi = (j + 1) * cpustride - 1;
4034 if (rnp->grphi >= nr_cpu_ids)
4035 rnp->grphi = nr_cpu_ids - 1;
4036 if (i == 0) {
4037 rnp->grpnum = 0;
4038 rnp->grpmask = 0;
4039 rnp->parent = NULL;
4040 } else {
4041 rnp->grpnum = j % levelspread[i - 1];
4042 rnp->grpmask = 1UL << rnp->grpnum;
4043 rnp->parent = rsp->level[i - 1] +
4044 j / levelspread[i - 1];
4045 }
4046 rnp->level = i;
4047 INIT_LIST_HEAD(&rnp->blkd_tasks);
4048 rcu_init_one_nocb(rnp);
4049 init_waitqueue_head(&rnp->exp_wq[0]);
4050 init_waitqueue_head(&rnp->exp_wq[1]);
4051 init_waitqueue_head(&rnp->exp_wq[2]);
4052 init_waitqueue_head(&rnp->exp_wq[3]);
4053 spin_lock_init(&rnp->exp_lock);
4054 }
4055 }
4056
4057 init_swait_queue_head(&rsp->gp_wq);
4058 init_swait_queue_head(&rsp->expedited_wq);
4059 rnp = rsp->level[rcu_num_lvls - 1];
4060 for_each_possible_cpu(i) {
4061 while (i > rnp->grphi)
4062 rnp++;
4063 per_cpu_ptr(rsp->rda, i)->mynode = rnp;
4064 rcu_boot_init_percpu_data(i, rsp);
4065 }
4066 list_add(&rsp->flavors, &rcu_struct_flavors);
4067}
4068
4069/*
4070 * Compute the rcu_node tree geometry from kernel parameters. This cannot
4071 * replace the definitions in tree.h because those are needed to size
4072 * the ->node array in the rcu_state structure.
4073 */
4074static void __init rcu_init_geometry(void)
4075{
4076 ulong d;
4077 int i;
4078 int rcu_capacity[RCU_NUM_LVLS];
4079
4080 /*
4081 * Initialize any unspecified boot parameters.
4082 * The default values of jiffies_till_first_fqs and
4083 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
4084 * value, which is a function of HZ, then adding one for each
4085 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
4086 */
4087 d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
4088 if (jiffies_till_first_fqs == ULONG_MAX)
4089 jiffies_till_first_fqs = d;
4090 if (jiffies_till_next_fqs == ULONG_MAX)
4091 jiffies_till_next_fqs = d;
4092
4093 /* If the compile-time values are accurate, just leave. */
4094 if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
4095 nr_cpu_ids == NR_CPUS)
4096 return;
4097 pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%u\n",
4098 rcu_fanout_leaf, nr_cpu_ids);
4099
4100 /*
4101 * The boot-time rcu_fanout_leaf parameter must be at least two
4102 * and cannot exceed the number of bits in the rcu_node masks.
4103 * Complain and fall back to the compile-time values if this
4104 * limit is exceeded.
4105 */
4106 if (rcu_fanout_leaf < 2 ||
4107 rcu_fanout_leaf > sizeof(unsigned long) * 8) {
4108 rcu_fanout_leaf = RCU_FANOUT_LEAF;
4109 WARN_ON(1);
4110 return;
4111 }
4112
4113 /*
4114 * Compute number of nodes that can be handled an rcu_node tree
4115 * with the given number of levels.
4116 */
4117 rcu_capacity[0] = rcu_fanout_leaf;
4118 for (i = 1; i < RCU_NUM_LVLS; i++)
4119 rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
4120
4121 /*
4122 * The tree must be able to accommodate the configured number of CPUs.
4123 * If this limit is exceeded, fall back to the compile-time values.
4124 */
4125 if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
4126 rcu_fanout_leaf = RCU_FANOUT_LEAF;
4127 WARN_ON(1);
4128 return;
4129 }
4130
4131 /* Calculate the number of levels in the tree. */
4132 for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
4133 }
4134 rcu_num_lvls = i + 1;
4135
4136 /* Calculate the number of rcu_nodes at each level of the tree. */
4137 for (i = 0; i < rcu_num_lvls; i++) {
4138 int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
4139 num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
4140 }
4141
4142 /* Calculate the total number of rcu_node structures. */
4143 rcu_num_nodes = 0;
4144 for (i = 0; i < rcu_num_lvls; i++)
4145 rcu_num_nodes += num_rcu_lvl[i];
4146}
4147
4148/*
4149 * Dump out the structure of the rcu_node combining tree associated
4150 * with the rcu_state structure referenced by rsp.
4151 */
4152static void __init rcu_dump_rcu_node_tree(struct rcu_state *rsp)
4153{
4154 int level = 0;
4155 struct rcu_node *rnp;
4156
4157 pr_info("rcu_node tree layout dump\n");
4158 pr_info(" ");
4159 rcu_for_each_node_breadth_first(rsp, rnp) {
4160 if (rnp->level != level) {
4161 pr_cont("\n");
4162 pr_info(" ");
4163 level = rnp->level;
4164 }
4165 pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum);
4166 }
4167 pr_cont("\n");
4168}
4169
4170struct workqueue_struct *rcu_gp_wq;
4171
4172void __init rcu_init(void)
4173{
4174 int cpu;
4175
4176 rcu_early_boot_tests();
4177
4178 rcu_bootup_announce();
4179 rcu_init_geometry();
4180 rcu_init_one(&rcu_bh_state);
4181 rcu_init_one(&rcu_sched_state);
4182 if (dump_tree)
4183 rcu_dump_rcu_node_tree(&rcu_sched_state);
4184 __rcu_init_preempt();
4185 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
4186
4187 /*
4188 * We don't need protection against CPU-hotplug here because
4189 * this is called early in boot, before either interrupts
4190 * or the scheduler are operational.
4191 */
4192 pm_notifier(rcu_pm_notify, 0);
4193 for_each_online_cpu(cpu) {
4194 rcutree_prepare_cpu(cpu);
4195 rcu_cpu_starting(cpu);
4196 rcutree_online_cpu(cpu);
4197 }
4198
4199 /* Create workqueue for expedited GPs and for Tree SRCU. */
4200 rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
4201 WARN_ON(!rcu_gp_wq);
4202}
4203
4204#include "tree_exp.h"
4205#include "tree_plugin.h"