1 /* SPDX-License-Identifier: GPL-2.0+ */
3 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
4 * Internal non-public definitions that provide either classic
5 * or preemptible semantics.
7 * Copyright Red Hat, 2009
8 * Copyright IBM Corporation, 2009
10 * Author: Ingo Molnar <mingo@elte.hu>
11 * Paul E. McKenney <paulmck@linux.ibm.com>
14 #include "../locking/rtmutex_common.h"
16 #ifdef CONFIG_RCU_NOCB_CPU
17 static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
18 static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
19 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
22 * Check the RCU kernel configuration parameters and print informative
23 * messages about anything out of the ordinary.
25 static void __init rcu_bootup_announce_oddness(void)
27 if (IS_ENABLED(CONFIG_RCU_TRACE))
28 pr_info("\tRCU event tracing is enabled.\n");
29 if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||
30 (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))
31 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d.\n",
34 pr_info("\tHierarchical RCU autobalancing is disabled.\n");
35 if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ))
36 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
37 if (IS_ENABLED(CONFIG_PROVE_RCU))
38 pr_info("\tRCU lockdep checking is enabled.\n");
39 if (RCU_NUM_LVLS >= 4)
40 pr_info("\tFour(or more)-level hierarchy is enabled.\n");
41 if (RCU_FANOUT_LEAF != 16)
42 pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
44 if (rcu_fanout_leaf != RCU_FANOUT_LEAF)
45 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n",
47 if (nr_cpu_ids != NR_CPUS)
48 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%u.\n", NR_CPUS, nr_cpu_ids);
49 #ifdef CONFIG_RCU_BOOST
50 pr_info("\tRCU priority boosting: priority %d delay %d ms.\n",
51 kthread_prio, CONFIG_RCU_BOOST_DELAY);
53 if (blimit != DEFAULT_RCU_BLIMIT)
54 pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit);
55 if (qhimark != DEFAULT_RCU_QHIMARK)
56 pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark);
57 if (qlowmark != DEFAULT_RCU_QLOMARK)
58 pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark);
59 if (jiffies_till_first_fqs != ULONG_MAX)
60 pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs);
61 if (jiffies_till_next_fqs != ULONG_MAX)
62 pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs);
63 if (jiffies_till_sched_qs != ULONG_MAX)
64 pr_info("\tBoot-time adjustment of scheduler-enlistment delay to %ld jiffies.\n", jiffies_till_sched_qs);
65 if (rcu_kick_kthreads)
66 pr_info("\tKick kthreads if too-long grace period.\n");
67 if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD))
68 pr_info("\tRCU callback double-/use-after-free debug enabled.\n");
70 pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay);
72 pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay);
74 pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay);
76 pr_info("\tRCU_SOFTIRQ processing moved to rcuc kthreads.\n");
77 if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))
78 pr_info("\tRCU debug extended QS entry/exit.\n");
79 rcupdate_announce_bootup_oddness();
82 #ifdef CONFIG_PREEMPT_RCU
84 static void rcu_report_exp_rnp(struct rcu_node *rnp, bool wake);
85 static void rcu_read_unlock_special(struct task_struct *t);
88 * Tell them what RCU they are running.
90 static void __init rcu_bootup_announce(void)
92 pr_info("Preemptible hierarchical RCU implementation.\n");
93 rcu_bootup_announce_oddness();
96 /* Flags for rcu_preempt_ctxt_queue() decision table. */
97 #define RCU_GP_TASKS 0x8
98 #define RCU_EXP_TASKS 0x4
99 #define RCU_GP_BLKD 0x2
100 #define RCU_EXP_BLKD 0x1
103 * Queues a task preempted within an RCU-preempt read-side critical
104 * section into the appropriate location within the ->blkd_tasks list,
105 * depending on the states of any ongoing normal and expedited grace
106 * periods. The ->gp_tasks pointer indicates which element the normal
107 * grace period is waiting on (NULL if none), and the ->exp_tasks pointer
108 * indicates which element the expedited grace period is waiting on (again,
109 * NULL if none). If a grace period is waiting on a given element in the
110 * ->blkd_tasks list, it also waits on all subsequent elements. Thus,
111 * adding a task to the tail of the list blocks any grace period that is
112 * already waiting on one of the elements. In contrast, adding a task
113 * to the head of the list won't block any grace period that is already
114 * waiting on one of the elements.
116 * This queuing is imprecise, and can sometimes make an ongoing grace
117 * period wait for a task that is not strictly speaking blocking it.
118 * Given the choice, we needlessly block a normal grace period rather than
119 * blocking an expedited grace period.
121 * Note that an endless sequence of expedited grace periods still cannot
122 * indefinitely postpone a normal grace period. Eventually, all of the
123 * fixed number of preempted tasks blocking the normal grace period that are
124 * not also blocking the expedited grace period will resume and complete
125 * their RCU read-side critical sections. At that point, the ->gp_tasks
126 * pointer will equal the ->exp_tasks pointer, at which point the end of
127 * the corresponding expedited grace period will also be the end of the
128 * normal grace period.
130 static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
131 __releases(rnp->lock) /* But leaves rrupts disabled. */
133 int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) +
134 (rnp->exp_tasks ? RCU_EXP_TASKS : 0) +
135 (rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) +
136 (rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0);
137 struct task_struct *t = current;
139 raw_lockdep_assert_held_rcu_node(rnp);
140 WARN_ON_ONCE(rdp->mynode != rnp);
141 WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
142 /* RCU better not be waiting on newly onlined CPUs! */
143 WARN_ON_ONCE(rnp->qsmaskinitnext & ~rnp->qsmaskinit & rnp->qsmask &
147 * Decide where to queue the newly blocked task. In theory,
148 * this could be an if-statement. In practice, when I tried
149 * that, it was quite messy.
151 switch (blkd_state) {
154 case RCU_EXP_TASKS + RCU_GP_BLKD:
156 case RCU_GP_TASKS + RCU_EXP_TASKS:
159 * Blocking neither GP, or first task blocking the normal
160 * GP but not blocking the already-waiting expedited GP.
161 * Queue at the head of the list to avoid unnecessarily
162 * blocking the already-waiting GPs.
164 list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
169 case RCU_GP_BLKD + RCU_EXP_BLKD:
170 case RCU_GP_TASKS + RCU_EXP_BLKD:
171 case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
172 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
175 * First task arriving that blocks either GP, or first task
176 * arriving that blocks the expedited GP (with the normal
177 * GP already waiting), or a task arriving that blocks
178 * both GPs with both GPs already waiting. Queue at the
179 * tail of the list to avoid any GP waiting on any of the
180 * already queued tasks that are not blocking it.
182 list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);
185 case RCU_EXP_TASKS + RCU_EXP_BLKD:
186 case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
187 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD:
190 * Second or subsequent task blocking the expedited GP.
191 * The task either does not block the normal GP, or is the
192 * first task blocking the normal GP. Queue just after
193 * the first task blocking the expedited GP.
195 list_add(&t->rcu_node_entry, rnp->exp_tasks);
198 case RCU_GP_TASKS + RCU_GP_BLKD:
199 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD:
202 * Second or subsequent task blocking the normal GP.
203 * The task does not block the expedited GP. Queue just
204 * after the first task blocking the normal GP.
206 list_add(&t->rcu_node_entry, rnp->gp_tasks);
211 /* Yet another exercise in excessive paranoia. */
217 * We have now queued the task. If it was the first one to
218 * block either grace period, update the ->gp_tasks and/or
219 * ->exp_tasks pointers, respectively, to reference the newly
222 if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) {
223 WRITE_ONCE(rnp->gp_tasks, &t->rcu_node_entry);
224 WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq);
226 if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
227 rnp->exp_tasks = &t->rcu_node_entry;
228 WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=
229 !(rnp->qsmask & rdp->grpmask));
230 WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) !=
231 !(rnp->expmask & rdp->grpmask));
232 raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */
235 * Report the quiescent state for the expedited GP. This expedited
236 * GP should not be able to end until we report, so there should be
237 * no need to check for a subsequent expedited GP. (Though we are
238 * still in a quiescent state in any case.)
240 if (blkd_state & RCU_EXP_BLKD && rdp->exp_deferred_qs)
241 rcu_report_exp_rdp(rdp);
243 WARN_ON_ONCE(rdp->exp_deferred_qs);
247 * Record a preemptible-RCU quiescent state for the specified CPU.
248 * Note that this does not necessarily mean that the task currently running
249 * on the CPU is in a quiescent state: Instead, it means that the current
250 * grace period need not wait on any RCU read-side critical section that
251 * starts later on this CPU. It also means that if the current task is
252 * in an RCU read-side critical section, it has already added itself to
253 * some leaf rcu_node structure's ->blkd_tasks list. In addition to the
254 * current task, there might be any number of other tasks blocked while
255 * in an RCU read-side critical section.
257 * Callers to this function must disable preemption.
259 static void rcu_qs(void)
261 RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n");
262 if (__this_cpu_read(rcu_data.cpu_no_qs.s)) {
263 trace_rcu_grace_period(TPS("rcu_preempt"),
264 __this_cpu_read(rcu_data.gp_seq),
266 __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
267 barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */
268 WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, false);
273 * We have entered the scheduler, and the current task might soon be
274 * context-switched away from. If this task is in an RCU read-side
275 * critical section, we will no longer be able to rely on the CPU to
276 * record that fact, so we enqueue the task on the blkd_tasks list.
277 * The task will dequeue itself when it exits the outermost enclosing
278 * RCU read-side critical section. Therefore, the current grace period
279 * cannot be permitted to complete until the blkd_tasks list entries
280 * predating the current grace period drain, in other words, until
281 * rnp->gp_tasks becomes NULL.
283 * Caller must disable interrupts.
285 void rcu_note_context_switch(bool preempt)
287 struct task_struct *t = current;
288 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
289 struct rcu_node *rnp;
291 trace_rcu_utilization(TPS("Start context switch"));
292 lockdep_assert_irqs_disabled();
293 WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0);
294 if (t->rcu_read_lock_nesting > 0 &&
295 !t->rcu_read_unlock_special.b.blocked) {
297 /* Possibly blocking in an RCU read-side critical section. */
299 raw_spin_lock_rcu_node(rnp);
300 t->rcu_read_unlock_special.b.blocked = true;
301 t->rcu_blocked_node = rnp;
304 * Verify the CPU's sanity, trace the preemption, and
305 * then queue the task as required based on the states
306 * of any ongoing and expedited grace periods.
308 WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);
309 WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
310 trace_rcu_preempt_task(rcu_state.name,
312 (rnp->qsmask & rdp->grpmask)
314 : rcu_seq_snap(&rnp->gp_seq));
315 rcu_preempt_ctxt_queue(rnp, rdp);
317 rcu_preempt_deferred_qs(t);
321 * Either we were not in an RCU read-side critical section to
322 * begin with, or we have now recorded that critical section
323 * globally. Either way, we can now note a quiescent state
324 * for this CPU. Again, if we were in an RCU read-side critical
325 * section, and if that critical section was blocking the current
326 * grace period, then the fact that the task has been enqueued
327 * means that we continue to block the current grace period.
330 if (rdp->exp_deferred_qs)
331 rcu_report_exp_rdp(rdp);
332 trace_rcu_utilization(TPS("End context switch"));
334 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
337 * Check for preempted RCU readers blocking the current grace period
338 * for the specified rcu_node structure. If the caller needs a reliable
339 * answer, it must hold the rcu_node's ->lock.
341 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
343 return READ_ONCE(rnp->gp_tasks) != NULL;
346 /* Bias and limit values for ->rcu_read_lock_nesting. */
347 #define RCU_NEST_BIAS INT_MAX
348 #define RCU_NEST_NMAX (-INT_MAX / 2)
349 #define RCU_NEST_PMAX (INT_MAX / 2)
352 * Preemptible RCU implementation for rcu_read_lock().
353 * Just increment ->rcu_read_lock_nesting, shared state will be updated
356 void __rcu_read_lock(void)
358 current->rcu_read_lock_nesting++;
359 if (IS_ENABLED(CONFIG_PROVE_LOCKING))
360 WARN_ON_ONCE(current->rcu_read_lock_nesting > RCU_NEST_PMAX);
361 barrier(); /* critical section after entry code. */
363 EXPORT_SYMBOL_GPL(__rcu_read_lock);
366 * Preemptible RCU implementation for rcu_read_unlock().
367 * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
368 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
369 * invoke rcu_read_unlock_special() to clean up after a context switch
370 * in an RCU read-side critical section and other special cases.
372 void __rcu_read_unlock(void)
374 struct task_struct *t = current;
376 if (t->rcu_read_lock_nesting != 1) {
377 --t->rcu_read_lock_nesting;
379 barrier(); /* critical section before exit code. */
380 t->rcu_read_lock_nesting = -RCU_NEST_BIAS;
381 barrier(); /* assign before ->rcu_read_unlock_special load */
382 if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
383 rcu_read_unlock_special(t);
384 barrier(); /* ->rcu_read_unlock_special load before assign */
385 t->rcu_read_lock_nesting = 0;
387 if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
388 int rrln = t->rcu_read_lock_nesting;
390 WARN_ON_ONCE(rrln < 0 && rrln > RCU_NEST_NMAX);
393 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
396 * Advance a ->blkd_tasks-list pointer to the next entry, instead
397 * returning NULL if at the end of the list.
399 static struct list_head *rcu_next_node_entry(struct task_struct *t,
400 struct rcu_node *rnp)
402 struct list_head *np;
404 np = t->rcu_node_entry.next;
405 if (np == &rnp->blkd_tasks)
411 * Return true if the specified rcu_node structure has tasks that were
412 * preempted within an RCU read-side critical section.
414 static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
416 return !list_empty(&rnp->blkd_tasks);
420 * Report deferred quiescent states. The deferral time can
421 * be quite short, for example, in the case of the call from
422 * rcu_read_unlock_special().
425 rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
430 struct list_head *np;
431 bool drop_boost_mutex = false;
432 struct rcu_data *rdp;
433 struct rcu_node *rnp;
434 union rcu_special special;
437 * If RCU core is waiting for this CPU to exit its critical section,
438 * report the fact that it has exited. Because irqs are disabled,
439 * t->rcu_read_unlock_special cannot change.
441 special = t->rcu_read_unlock_special;
442 rdp = this_cpu_ptr(&rcu_data);
443 if (!special.s && !rdp->exp_deferred_qs) {
444 local_irq_restore(flags);
447 t->rcu_read_unlock_special.b.deferred_qs = false;
448 if (special.b.need_qs) {
450 t->rcu_read_unlock_special.b.need_qs = false;
451 if (!t->rcu_read_unlock_special.s && !rdp->exp_deferred_qs) {
452 local_irq_restore(flags);
458 * Respond to a request by an expedited grace period for a
459 * quiescent state from this CPU. Note that requests from
460 * tasks are handled when removing the task from the
461 * blocked-tasks list below.
463 if (rdp->exp_deferred_qs) {
464 rcu_report_exp_rdp(rdp);
465 if (!t->rcu_read_unlock_special.s) {
466 local_irq_restore(flags);
471 /* Clean up if blocked during RCU read-side critical section. */
472 if (special.b.blocked) {
473 t->rcu_read_unlock_special.b.blocked = false;
476 * Remove this task from the list it blocked on. The task
477 * now remains queued on the rcu_node corresponding to the
478 * CPU it first blocked on, so there is no longer any need
479 * to loop. Retain a WARN_ON_ONCE() out of sheer paranoia.
481 rnp = t->rcu_blocked_node;
482 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
483 WARN_ON_ONCE(rnp != t->rcu_blocked_node);
484 WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
485 empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
486 WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq &&
487 (!empty_norm || rnp->qsmask));
488 empty_exp = sync_rcu_preempt_exp_done(rnp);
489 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
490 np = rcu_next_node_entry(t, rnp);
491 list_del_init(&t->rcu_node_entry);
492 t->rcu_blocked_node = NULL;
493 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
494 rnp->gp_seq, t->pid);
495 if (&t->rcu_node_entry == rnp->gp_tasks)
496 WRITE_ONCE(rnp->gp_tasks, np);
497 if (&t->rcu_node_entry == rnp->exp_tasks)
499 if (IS_ENABLED(CONFIG_RCU_BOOST)) {
500 /* Snapshot ->boost_mtx ownership w/rnp->lock held. */
501 drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
502 if (&t->rcu_node_entry == rnp->boost_tasks)
503 rnp->boost_tasks = np;
507 * If this was the last task on the current list, and if
508 * we aren't waiting on any CPUs, report the quiescent state.
509 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
510 * so we must take a snapshot of the expedited state.
512 empty_exp_now = sync_rcu_preempt_exp_done(rnp);
513 if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
514 trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
521 rcu_report_unblock_qs_rnp(rnp, flags);
523 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
526 /* Unboost if we were boosted. */
527 if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
528 rt_mutex_futex_unlock(&rnp->boost_mtx);
531 * If this was the last task on the expedited lists,
532 * then we need to report up the rcu_node hierarchy.
534 if (!empty_exp && empty_exp_now)
535 rcu_report_exp_rnp(rnp, true);
537 local_irq_restore(flags);
542 * Is a deferred quiescent-state pending, and are we also not in
543 * an RCU read-side critical section? It is the caller's responsibility
544 * to ensure it is otherwise safe to report any deferred quiescent
545 * states. The reason for this is that it is safe to report a
546 * quiescent state during context switch even though preemption
547 * is disabled. This function cannot be expected to understand these
548 * nuances, so the caller must handle them.
550 static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
552 return (__this_cpu_read(rcu_data.exp_deferred_qs) ||
553 READ_ONCE(t->rcu_read_unlock_special.s)) &&
554 t->rcu_read_lock_nesting <= 0;
558 * Report a deferred quiescent state if needed and safe to do so.
559 * As with rcu_preempt_need_deferred_qs(), "safe" involves only
560 * not being in an RCU read-side critical section. The caller must
561 * evaluate safety in terms of interrupt, softirq, and preemption
564 static void rcu_preempt_deferred_qs(struct task_struct *t)
567 bool couldrecurse = t->rcu_read_lock_nesting >= 0;
569 if (!rcu_preempt_need_deferred_qs(t))
572 t->rcu_read_lock_nesting -= RCU_NEST_BIAS;
573 local_irq_save(flags);
574 rcu_preempt_deferred_qs_irqrestore(t, flags);
576 t->rcu_read_lock_nesting += RCU_NEST_BIAS;
580 * Minimal handler to give the scheduler a chance to re-evaluate.
582 static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp)
584 struct rcu_data *rdp;
586 rdp = container_of(iwp, struct rcu_data, defer_qs_iw);
587 rdp->defer_qs_iw_pending = false;
591 * Handle special cases during rcu_read_unlock(), such as needing to
592 * notify RCU core processing or task having blocked during the RCU
593 * read-side critical section.
595 static void rcu_read_unlock_special(struct task_struct *t)
598 bool preempt_bh_were_disabled =
599 !!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK));
600 bool irqs_were_disabled;
602 /* NMI handlers cannot block and cannot safely manipulate state. */
606 local_irq_save(flags);
607 irqs_were_disabled = irqs_disabled_flags(flags);
608 if (preempt_bh_were_disabled || irqs_were_disabled) {
610 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
611 struct rcu_node *rnp = rdp->mynode;
613 t->rcu_read_unlock_special.b.exp_hint = false;
614 exp = (t->rcu_blocked_node && t->rcu_blocked_node->exp_tasks) ||
615 (rdp->grpmask & rnp->expmask) ||
616 tick_nohz_full_cpu(rdp->cpu);
617 // Need to defer quiescent state until everything is enabled.
618 if (irqs_were_disabled && use_softirq &&
620 (exp && !t->rcu_read_unlock_special.b.deferred_qs))) {
621 // Using softirq, safe to awaken, and we get
622 // no help from enabling irqs, unlike bh/preempt.
623 raise_softirq_irqoff(RCU_SOFTIRQ);
625 // Enabling BH or preempt does reschedule, so...
626 // Also if no expediting or NO_HZ_FULL, slow is OK.
627 set_tsk_need_resched(current);
628 set_preempt_need_resched();
629 if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled &&
630 !rdp->defer_qs_iw_pending && exp) {
631 // Get scheduler to re-evaluate and call hooks.
632 // If !IRQ_WORK, FQS scan will eventually IPI.
633 init_irq_work(&rdp->defer_qs_iw,
634 rcu_preempt_deferred_qs_handler);
635 rdp->defer_qs_iw_pending = true;
636 irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
639 t->rcu_read_unlock_special.b.deferred_qs = true;
640 local_irq_restore(flags);
643 WRITE_ONCE(t->rcu_read_unlock_special.b.exp_hint, false);
644 rcu_preempt_deferred_qs_irqrestore(t, flags);
648 * Check that the list of blocked tasks for the newly completed grace
649 * period is in fact empty. It is a serious bug to complete a grace
650 * period that still has RCU readers blocked! This function must be
651 * invoked -before- updating this rnp's ->gp_seq, and the rnp's ->lock
652 * must be held by the caller.
654 * Also, if there are blocked tasks on the list, they automatically
655 * block the newly created grace period, so set up ->gp_tasks accordingly.
657 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
659 struct task_struct *t;
661 RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
662 if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
663 dump_blkd_tasks(rnp, 10);
664 if (rcu_preempt_has_tasks(rnp) &&
665 (rnp->qsmaskinit || rnp->wait_blkd_tasks)) {
666 WRITE_ONCE(rnp->gp_tasks, rnp->blkd_tasks.next);
667 t = container_of(rnp->gp_tasks, struct task_struct,
669 trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
670 rnp->gp_seq, t->pid);
672 WARN_ON_ONCE(rnp->qsmask);
676 * Check for a quiescent state from the current CPU, including voluntary
677 * context switches for Tasks RCU. When a task blocks, the task is
678 * recorded in the corresponding CPU's rcu_node structure, which is checked
679 * elsewhere, hence this function need only check for quiescent states
680 * related to the current CPU, not to those related to tasks.
682 static void rcu_flavor_sched_clock_irq(int user)
684 struct task_struct *t = current;
686 if (user || rcu_is_cpu_rrupt_from_idle()) {
687 rcu_note_voluntary_context_switch(current);
689 if (t->rcu_read_lock_nesting > 0 ||
690 (preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) {
691 /* No QS, force context switch if deferred. */
692 if (rcu_preempt_need_deferred_qs(t)) {
693 set_tsk_need_resched(t);
694 set_preempt_need_resched();
696 } else if (rcu_preempt_need_deferred_qs(t)) {
697 rcu_preempt_deferred_qs(t); /* Report deferred QS. */
699 } else if (!t->rcu_read_lock_nesting) {
700 rcu_qs(); /* Report immediate QS. */
704 /* If GP is oldish, ask for help from rcu_read_unlock_special(). */
705 if (t->rcu_read_lock_nesting > 0 &&
706 __this_cpu_read(rcu_data.core_needs_qs) &&
707 __this_cpu_read(rcu_data.cpu_no_qs.b.norm) &&
708 !t->rcu_read_unlock_special.b.need_qs &&
709 time_after(jiffies, rcu_state.gp_start + HZ))
710 t->rcu_read_unlock_special.b.need_qs = true;
714 * Check for a task exiting while in a preemptible-RCU read-side
715 * critical section, clean up if so. No need to issue warnings, as
716 * debug_check_no_locks_held() already does this if lockdep is enabled.
717 * Besides, if this function does anything other than just immediately
718 * return, there was a bug of some sort. Spewing warnings from this
719 * function is like as not to simply obscure important prior warnings.
723 struct task_struct *t = current;
725 if (unlikely(!list_empty(¤t->rcu_node_entry))) {
726 t->rcu_read_lock_nesting = 1;
728 WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true);
729 } else if (unlikely(t->rcu_read_lock_nesting)) {
730 t->rcu_read_lock_nesting = 1;
735 rcu_preempt_deferred_qs(current);
739 * Dump the blocked-tasks state, but limit the list dump to the
740 * specified number of elements.
743 dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
747 struct list_head *lhp;
749 struct rcu_data *rdp;
750 struct rcu_node *rnp1;
752 raw_lockdep_assert_held_rcu_node(rnp);
753 pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
754 __func__, rnp->grplo, rnp->grphi, rnp->level,
755 (long)rnp->gp_seq, (long)rnp->completedqs);
756 for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
757 pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n",
758 __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext);
759 pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n",
760 __func__, READ_ONCE(rnp->gp_tasks), rnp->boost_tasks,
762 pr_info("%s: ->blkd_tasks", __func__);
764 list_for_each(lhp, &rnp->blkd_tasks) {
770 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
771 rdp = per_cpu_ptr(&rcu_data, cpu);
772 onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
773 pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n",
775 (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
776 (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
780 #else /* #ifdef CONFIG_PREEMPT_RCU */
783 * Tell them what RCU they are running.
785 static void __init rcu_bootup_announce(void)
787 pr_info("Hierarchical RCU implementation.\n");
788 rcu_bootup_announce_oddness();
792 * Note a quiescent state for PREEMPT=n. Because we do not need to know
793 * how many quiescent states passed, just if there was at least one since
794 * the start of the grace period, this just sets a flag. The caller must
795 * have disabled preemption.
797 static void rcu_qs(void)
799 RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!");
800 if (!__this_cpu_read(rcu_data.cpu_no_qs.s))
802 trace_rcu_grace_period(TPS("rcu_sched"),
803 __this_cpu_read(rcu_data.gp_seq), TPS("cpuqs"));
804 __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
805 if (!__this_cpu_read(rcu_data.cpu_no_qs.b.exp))
807 __this_cpu_write(rcu_data.cpu_no_qs.b.exp, false);
808 rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
812 * Register an urgently needed quiescent state. If there is an
813 * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
814 * dyntick-idle quiescent state visible to other CPUs, which will in
815 * some cases serve for expedited as well as normal grace periods.
816 * Either way, register a lightweight quiescent state.
818 void rcu_all_qs(void)
822 if (!raw_cpu_read(rcu_data.rcu_urgent_qs))
825 /* Load rcu_urgent_qs before other flags. */
826 if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
830 this_cpu_write(rcu_data.rcu_urgent_qs, false);
831 if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) {
832 local_irq_save(flags);
833 rcu_momentary_dyntick_idle();
834 local_irq_restore(flags);
839 EXPORT_SYMBOL_GPL(rcu_all_qs);
842 * Note a PREEMPT=n context switch. The caller must have disabled interrupts.
844 void rcu_note_context_switch(bool preempt)
846 trace_rcu_utilization(TPS("Start context switch"));
848 /* Load rcu_urgent_qs before other flags. */
849 if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs)))
851 this_cpu_write(rcu_data.rcu_urgent_qs, false);
852 if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs)))
853 rcu_momentary_dyntick_idle();
855 rcu_tasks_qs(current);
857 trace_rcu_utilization(TPS("End context switch"));
859 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
862 * Because preemptible RCU does not exist, there are never any preempted
865 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
871 * Because there is no preemptible RCU, there can be no readers blocked.
873 static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
879 * Because there is no preemptible RCU, there can be no deferred quiescent
882 static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
886 static void rcu_preempt_deferred_qs(struct task_struct *t) { }
889 * Because there is no preemptible RCU, there can be no readers blocked,
890 * so there is no need to check for blocked tasks. So check only for
891 * bogus qsmask values.
893 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
895 WARN_ON_ONCE(rnp->qsmask);
899 * Check to see if this CPU is in a non-context-switch quiescent state,
900 * namely user mode and idle loop.
902 static void rcu_flavor_sched_clock_irq(int user)
904 if (user || rcu_is_cpu_rrupt_from_idle()) {
907 * Get here if this CPU took its interrupt from user
908 * mode or from the idle loop, and if this is not a
909 * nested interrupt. In this case, the CPU is in
910 * a quiescent state, so note it.
912 * No memory barrier is required here because rcu_qs()
913 * references only CPU-local variables that other CPUs
914 * neither access nor modify, at least not while the
915 * corresponding CPU is online.
923 * Because preemptible RCU does not exist, tasks cannot possibly exit
924 * while in preemptible RCU read-side critical sections.
931 * Dump the guaranteed-empty blocked-tasks state. Trust but verify.
934 dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
936 WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));
939 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
942 * If boosting, set rcuc kthreads to realtime priority.
944 static void rcu_cpu_kthread_setup(unsigned int cpu)
946 #ifdef CONFIG_RCU_BOOST
947 struct sched_param sp;
949 sp.sched_priority = kthread_prio;
950 sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
951 #endif /* #ifdef CONFIG_RCU_BOOST */
954 #ifdef CONFIG_RCU_BOOST
957 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
958 * or ->boost_tasks, advancing the pointer to the next task in the
961 * Note that irqs must be enabled: boosting the task can block.
962 * Returns 1 if there are more tasks needing to be boosted.
964 static int rcu_boost(struct rcu_node *rnp)
967 struct task_struct *t;
968 struct list_head *tb;
970 if (READ_ONCE(rnp->exp_tasks) == NULL &&
971 READ_ONCE(rnp->boost_tasks) == NULL)
972 return 0; /* Nothing left to boost. */
974 raw_spin_lock_irqsave_rcu_node(rnp, flags);
977 * Recheck under the lock: all tasks in need of boosting
978 * might exit their RCU read-side critical sections on their own.
980 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
981 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
986 * Preferentially boost tasks blocking expedited grace periods.
987 * This cannot starve the normal grace periods because a second
988 * expedited grace period must boost all blocked tasks, including
989 * those blocking the pre-existing normal grace period.
991 if (rnp->exp_tasks != NULL)
994 tb = rnp->boost_tasks;
997 * We boost task t by manufacturing an rt_mutex that appears to
998 * be held by task t. We leave a pointer to that rt_mutex where
999 * task t can find it, and task t will release the mutex when it
1000 * exits its outermost RCU read-side critical section. Then
1001 * simply acquiring this artificial rt_mutex will boost task
1002 * t's priority. (Thanks to tglx for suggesting this approach!)
1004 * Note that task t must acquire rnp->lock to remove itself from
1005 * the ->blkd_tasks list, which it will do from exit() if from
1006 * nowhere else. We therefore are guaranteed that task t will
1007 * stay around at least until we drop rnp->lock. Note that
1008 * rnp->lock also resolves races between our priority boosting
1009 * and task t's exiting its outermost RCU read-side critical
1012 t = container_of(tb, struct task_struct, rcu_node_entry);
1013 rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
1014 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1015 /* Lock only for side effect: boosts task t's priority. */
1016 rt_mutex_lock(&rnp->boost_mtx);
1017 rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
1019 return READ_ONCE(rnp->exp_tasks) != NULL ||
1020 READ_ONCE(rnp->boost_tasks) != NULL;
1024 * Priority-boosting kthread, one per leaf rcu_node.
1026 static int rcu_boost_kthread(void *arg)
1028 struct rcu_node *rnp = (struct rcu_node *)arg;
1032 trace_rcu_utilization(TPS("Start boost kthread@init"));
1034 rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1035 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1036 rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1037 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1038 rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1039 more2boost = rcu_boost(rnp);
1045 rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1046 trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1047 schedule_timeout_interruptible(2);
1048 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1053 trace_rcu_utilization(TPS("End boost kthread@notreached"));
1058 * Check to see if it is time to start boosting RCU readers that are
1059 * blocking the current grace period, and, if so, tell the per-rcu_node
1060 * kthread to start boosting them. If there is an expedited grace
1061 * period in progress, it is always time to boost.
1063 * The caller must hold rnp->lock, which this function releases.
1064 * The ->boost_kthread_task is immortal, so we don't need to worry
1065 * about it going away.
1067 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1068 __releases(rnp->lock)
1070 raw_lockdep_assert_held_rcu_node(rnp);
1071 if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1072 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1075 if (rnp->exp_tasks != NULL ||
1076 (rnp->gp_tasks != NULL &&
1077 rnp->boost_tasks == NULL &&
1079 ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1080 if (rnp->exp_tasks == NULL)
1081 rnp->boost_tasks = rnp->gp_tasks;
1082 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1083 rcu_wake_cond(rnp->boost_kthread_task,
1084 rnp->boost_kthread_status);
1086 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1091 * Is the current CPU running the RCU-callbacks kthread?
1092 * Caller must have preemption disabled.
1094 static bool rcu_is_callbacks_kthread(void)
1096 return __this_cpu_read(rcu_data.rcu_cpu_kthread_task) == current;
1099 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1102 * Do priority-boost accounting for the start of a new grace period.
1104 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1106 rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1110 * Create an RCU-boost kthread for the specified node if one does not
1111 * already exist. We only create this kthread for preemptible RCU.
1112 * Returns zero if all is well, a negated errno otherwise.
1114 static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
1116 int rnp_index = rnp - rcu_get_root();
1117 unsigned long flags;
1118 struct sched_param sp;
1119 struct task_struct *t;
1121 if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
1124 if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
1127 rcu_state.boost = 1;
1129 if (rnp->boost_kthread_task != NULL)
1132 t = kthread_create(rcu_boost_kthread, (void *)rnp,
1133 "rcub/%d", rnp_index);
1134 if (WARN_ON_ONCE(IS_ERR(t)))
1137 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1138 rnp->boost_kthread_task = t;
1139 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1140 sp.sched_priority = kthread_prio;
1141 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1142 wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1146 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1147 * served by the rcu_node in question. The CPU hotplug lock is still
1148 * held, so the value of rnp->qsmaskinit will be stable.
1150 * We don't include outgoingcpu in the affinity set, use -1 if there is
1151 * no outgoing CPU. If there are no CPUs left in the affinity set,
1152 * this function allows the kthread to execute on any CPU.
1154 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1156 struct task_struct *t = rnp->boost_kthread_task;
1157 unsigned long mask = rcu_rnp_online_cpus(rnp);
1163 if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1165 for_each_leaf_node_possible_cpu(rnp, cpu)
1166 if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
1168 cpumask_set_cpu(cpu, cm);
1169 if (cpumask_weight(cm) == 0)
1171 set_cpus_allowed_ptr(t, cm);
1172 free_cpumask_var(cm);
1176 * Spawn boost kthreads -- called as soon as the scheduler is running.
1178 static void __init rcu_spawn_boost_kthreads(void)
1180 struct rcu_node *rnp;
1182 rcu_for_each_leaf_node(rnp)
1183 rcu_spawn_one_boost_kthread(rnp);
1186 static void rcu_prepare_kthreads(int cpu)
1188 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
1189 struct rcu_node *rnp = rdp->mynode;
1191 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1192 if (rcu_scheduler_fully_active)
1193 rcu_spawn_one_boost_kthread(rnp);
1196 #else /* #ifdef CONFIG_RCU_BOOST */
1198 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1199 __releases(rnp->lock)
1201 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1204 static bool rcu_is_callbacks_kthread(void)
1209 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1213 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1217 static void __init rcu_spawn_boost_kthreads(void)
1221 static void rcu_prepare_kthreads(int cpu)
1225 #endif /* #else #ifdef CONFIG_RCU_BOOST */
1227 #if !defined(CONFIG_RCU_FAST_NO_HZ)
1230 * Check to see if any future non-offloaded RCU-related work will need
1231 * to be done by the current CPU, even if none need be done immediately,
1232 * returning 1 if so. This function is part of the RCU implementation;
1233 * it is -not- an exported member of the RCU API.
1235 * Because we not have RCU_FAST_NO_HZ, just check whether or not this
1236 * CPU has RCU callbacks queued.
1238 int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1240 *nextevt = KTIME_MAX;
1241 return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) &&
1242 !rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist);
1246 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1249 static void rcu_cleanup_after_idle(void)
1254 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1257 static void rcu_prepare_for_idle(void)
1261 #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1264 * This code is invoked when a CPU goes idle, at which point we want
1265 * to have the CPU do everything required for RCU so that it can enter
1266 * the energy-efficient dyntick-idle mode. This is handled by a
1267 * state machine implemented by rcu_prepare_for_idle() below.
1269 * The following three proprocessor symbols control this state machine:
1271 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1272 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1273 * is sized to be roughly one RCU grace period. Those energy-efficiency
1274 * benchmarkers who might otherwise be tempted to set this to a large
1275 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1276 * system. And if you are -that- concerned about energy efficiency,
1277 * just power the system down and be done with it!
1278 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1279 * permitted to sleep in dyntick-idle mode with only lazy RCU
1280 * callbacks pending. Setting this too high can OOM your system.
1282 * The values below work well in practice. If future workloads require
1283 * adjustment, they can be converted into kernel config parameters, though
1284 * making the state machine smarter might be a better option.
1286 #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1287 #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1289 static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
1290 module_param(rcu_idle_gp_delay, int, 0644);
1291 static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
1292 module_param(rcu_idle_lazy_gp_delay, int, 0644);
1295 * Try to advance callbacks on the current CPU, but only if it has been
1296 * awhile since the last time we did so. Afterwards, if there are any
1297 * callbacks ready for immediate invocation, return true.
1299 static bool __maybe_unused rcu_try_advance_all_cbs(void)
1301 bool cbs_ready = false;
1302 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1303 struct rcu_node *rnp;
1305 /* Exit early if we advanced recently. */
1306 if (jiffies == rdp->last_advance_all)
1308 rdp->last_advance_all = jiffies;
1313 * Don't bother checking unless a grace period has
1314 * completed since we last checked and there are
1315 * callbacks not yet ready to invoke.
1317 if ((rcu_seq_completed_gp(rdp->gp_seq,
1318 rcu_seq_current(&rnp->gp_seq)) ||
1319 unlikely(READ_ONCE(rdp->gpwrap))) &&
1320 rcu_segcblist_pend_cbs(&rdp->cblist))
1321 note_gp_changes(rdp);
1323 if (rcu_segcblist_ready_cbs(&rdp->cblist))
1329 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1330 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1331 * caller to set the timeout based on whether or not there are non-lazy
1334 * The caller must have disabled interrupts.
1336 int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1338 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1341 lockdep_assert_irqs_disabled();
1343 /* If no non-offloaded callbacks, RCU doesn't need the CPU. */
1344 if (rcu_segcblist_empty(&rdp->cblist) ||
1345 rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist)) {
1346 *nextevt = KTIME_MAX;
1350 /* Attempt to advance callbacks. */
1351 if (rcu_try_advance_all_cbs()) {
1352 /* Some ready to invoke, so initiate later invocation. */
1356 rdp->last_accelerate = jiffies;
1358 /* Request timer delay depending on laziness, and round. */
1359 rdp->all_lazy = !rcu_segcblist_n_nonlazy_cbs(&rdp->cblist);
1360 if (rdp->all_lazy) {
1361 dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1363 dj = round_up(rcu_idle_gp_delay + jiffies,
1364 rcu_idle_gp_delay) - jiffies;
1366 *nextevt = basemono + dj * TICK_NSEC;
1371 * Prepare a CPU for idle from an RCU perspective. The first major task
1372 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1373 * The second major task is to check to see if a non-lazy callback has
1374 * arrived at a CPU that previously had only lazy callbacks. The third
1375 * major task is to accelerate (that is, assign grace-period numbers to)
1376 * any recently arrived callbacks.
1378 * The caller must have disabled interrupts.
1380 static void rcu_prepare_for_idle(void)
1383 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1384 struct rcu_node *rnp;
1387 lockdep_assert_irqs_disabled();
1388 if (rcu_segcblist_is_offloaded(&rdp->cblist))
1391 /* Handle nohz enablement switches conservatively. */
1392 tne = READ_ONCE(tick_nohz_active);
1393 if (tne != rdp->tick_nohz_enabled_snap) {
1394 if (!rcu_segcblist_empty(&rdp->cblist))
1395 invoke_rcu_core(); /* force nohz to see update. */
1396 rdp->tick_nohz_enabled_snap = tne;
1403 * If a non-lazy callback arrived at a CPU having only lazy
1404 * callbacks, invoke RCU core for the side-effect of recalculating
1405 * idle duration on re-entry to idle.
1407 if (rdp->all_lazy && rcu_segcblist_n_nonlazy_cbs(&rdp->cblist)) {
1408 rdp->all_lazy = false;
1414 * If we have not yet accelerated this jiffy, accelerate all
1415 * callbacks on this CPU.
1417 if (rdp->last_accelerate == jiffies)
1419 rdp->last_accelerate = jiffies;
1420 if (rcu_segcblist_pend_cbs(&rdp->cblist)) {
1422 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
1423 needwake = rcu_accelerate_cbs(rnp, rdp);
1424 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
1426 rcu_gp_kthread_wake();
1431 * Clean up for exit from idle. Attempt to advance callbacks based on
1432 * any grace periods that elapsed while the CPU was idle, and if any
1433 * callbacks are now ready to invoke, initiate invocation.
1435 static void rcu_cleanup_after_idle(void)
1437 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1439 lockdep_assert_irqs_disabled();
1440 if (rcu_segcblist_is_offloaded(&rdp->cblist))
1442 if (rcu_try_advance_all_cbs())
1446 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1448 #ifdef CONFIG_RCU_NOCB_CPU
1451 * Offload callback processing from the boot-time-specified set of CPUs
1452 * specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads
1453 * created that pull the callbacks from the corresponding CPU, wait for
1454 * a grace period to elapse, and invoke the callbacks. These kthreads
1455 * are organized into GP kthreads, which manage incoming callbacks, wait for
1456 * grace periods, and awaken CB kthreads, and the CB kthreads, which only
1457 * invoke callbacks. Each GP kthread invokes its own CBs. The no-CBs CPUs
1458 * do a wake_up() on their GP kthread when they insert a callback into any
1459 * empty list, unless the rcu_nocb_poll boot parameter has been specified,
1460 * in which case each kthread actively polls its CPU. (Which isn't so great
1461 * for energy efficiency, but which does reduce RCU's overhead on that CPU.)
1463 * This is intended to be used in conjunction with Frederic Weisbecker's
1464 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
1465 * running CPU-bound user-mode computations.
1467 * Offloading of callbacks can also be used as an energy-efficiency
1468 * measure because CPUs with no RCU callbacks queued are more aggressive
1469 * about entering dyntick-idle mode.
1474 * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters.
1475 * The string after the "rcu_nocbs=" is either "all" for all CPUs, or a
1476 * comma-separated list of CPUs and/or CPU ranges. If an invalid list is
1477 * given, a warning is emitted and all CPUs are offloaded.
1479 static int __init rcu_nocb_setup(char *str)
1481 alloc_bootmem_cpumask_var(&rcu_nocb_mask);
1482 if (!strcasecmp(str, "all"))
1483 cpumask_setall(rcu_nocb_mask);
1485 if (cpulist_parse(str, rcu_nocb_mask)) {
1486 pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
1487 cpumask_setall(rcu_nocb_mask);
1491 __setup("rcu_nocbs=", rcu_nocb_setup);
1493 static int __init parse_rcu_nocb_poll(char *arg)
1495 rcu_nocb_poll = true;
1498 early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
1501 * Don't bother bypassing ->cblist if the call_rcu() rate is low.
1502 * After all, the main point of bypassing is to avoid lock contention
1503 * on ->nocb_lock, which only can happen at high call_rcu() rates.
1505 int nocb_nobypass_lim_per_jiffy = 16 * 1000 / HZ;
1506 module_param(nocb_nobypass_lim_per_jiffy, int, 0);
1509 * Acquire the specified rcu_data structure's ->nocb_bypass_lock. If the
1510 * lock isn't immediately available, increment ->nocb_lock_contended to
1511 * flag the contention.
1513 static void rcu_nocb_bypass_lock(struct rcu_data *rdp)
1515 lockdep_assert_irqs_disabled();
1516 if (raw_spin_trylock(&rdp->nocb_bypass_lock))
1518 atomic_inc(&rdp->nocb_lock_contended);
1519 WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
1520 smp_mb__after_atomic(); /* atomic_inc() before lock. */
1521 raw_spin_lock(&rdp->nocb_bypass_lock);
1522 smp_mb__before_atomic(); /* atomic_dec() after lock. */
1523 atomic_dec(&rdp->nocb_lock_contended);
1527 * Spinwait until the specified rcu_data structure's ->nocb_lock is
1528 * not contended. Please note that this is extremely special-purpose,
1529 * relying on the fact that at most two kthreads and one CPU contend for
1530 * this lock, and also that the two kthreads are guaranteed to have frequent
1531 * grace-period-duration time intervals between successive acquisitions
1532 * of the lock. This allows us to use an extremely simple throttling
1533 * mechanism, and further to apply it only to the CPU doing floods of
1534 * call_rcu() invocations. Don't try this at home!
1536 static void rcu_nocb_wait_contended(struct rcu_data *rdp)
1538 WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
1539 while (WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended)))
1544 * Conditionally acquire the specified rcu_data structure's
1545 * ->nocb_bypass_lock.
1547 static bool rcu_nocb_bypass_trylock(struct rcu_data *rdp)
1549 lockdep_assert_irqs_disabled();
1550 return raw_spin_trylock(&rdp->nocb_bypass_lock);
1554 * Release the specified rcu_data structure's ->nocb_bypass_lock.
1556 static void rcu_nocb_bypass_unlock(struct rcu_data *rdp)
1558 lockdep_assert_irqs_disabled();
1559 raw_spin_unlock(&rdp->nocb_bypass_lock);
1563 * Acquire the specified rcu_data structure's ->nocb_lock, but only
1564 * if it corresponds to a no-CBs CPU.
1566 static void rcu_nocb_lock(struct rcu_data *rdp)
1568 lockdep_assert_irqs_disabled();
1569 if (!rcu_segcblist_is_offloaded(&rdp->cblist))
1571 raw_spin_lock(&rdp->nocb_lock);
1575 * Release the specified rcu_data structure's ->nocb_lock, but only
1576 * if it corresponds to a no-CBs CPU.
1578 static void rcu_nocb_unlock(struct rcu_data *rdp)
1580 if (rcu_segcblist_is_offloaded(&rdp->cblist)) {
1581 lockdep_assert_irqs_disabled();
1582 raw_spin_unlock(&rdp->nocb_lock);
1587 * Release the specified rcu_data structure's ->nocb_lock and restore
1588 * interrupts, but only if it corresponds to a no-CBs CPU.
1590 static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
1591 unsigned long flags)
1593 if (rcu_segcblist_is_offloaded(&rdp->cblist)) {
1594 lockdep_assert_irqs_disabled();
1595 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1597 local_irq_restore(flags);
1601 /* Lockdep check that ->cblist may be safely accessed. */
1602 static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
1604 lockdep_assert_irqs_disabled();
1605 if (rcu_segcblist_is_offloaded(&rdp->cblist) &&
1606 cpu_online(rdp->cpu))
1607 lockdep_assert_held(&rdp->nocb_lock);
1611 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
1614 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
1619 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
1621 return &rnp->nocb_gp_wq[rcu_seq_ctr(rnp->gp_seq) & 0x1];
1624 static void rcu_init_one_nocb(struct rcu_node *rnp)
1626 init_swait_queue_head(&rnp->nocb_gp_wq[0]);
1627 init_swait_queue_head(&rnp->nocb_gp_wq[1]);
1630 /* Is the specified CPU a no-CBs CPU? */
1631 bool rcu_is_nocb_cpu(int cpu)
1633 if (cpumask_available(rcu_nocb_mask))
1634 return cpumask_test_cpu(cpu, rcu_nocb_mask);
1639 * Kick the GP kthread for this NOCB group. Caller holds ->nocb_lock
1640 * and this function releases it.
1642 static void wake_nocb_gp(struct rcu_data *rdp, bool force,
1643 unsigned long flags)
1644 __releases(rdp->nocb_lock)
1646 bool needwake = false;
1647 struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
1649 lockdep_assert_held(&rdp->nocb_lock);
1650 if (!READ_ONCE(rdp_gp->nocb_gp_kthread)) {
1651 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1652 TPS("AlreadyAwake"));
1653 rcu_nocb_unlock_irqrestore(rdp, flags);
1656 del_timer(&rdp->nocb_timer);
1657 rcu_nocb_unlock_irqrestore(rdp, flags);
1658 raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
1659 if (force || READ_ONCE(rdp_gp->nocb_gp_sleep)) {
1660 WRITE_ONCE(rdp_gp->nocb_gp_sleep, false);
1662 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DoWake"));
1664 raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
1666 wake_up_process(rdp_gp->nocb_gp_kthread);
1670 * Arrange to wake the GP kthread for this NOCB group at some future
1671 * time when it is safe to do so.
1673 static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
1676 if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
1677 mod_timer(&rdp->nocb_timer, jiffies + 1);
1678 if (rdp->nocb_defer_wakeup < waketype)
1679 WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
1680 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason);
1684 * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
1685 * However, if there is a callback to be enqueued and if ->nocb_bypass
1686 * proves to be initially empty, just return false because the no-CB GP
1687 * kthread may need to be awakened in this case.
1689 * Note that this function always returns true if rhp is NULL.
1691 static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
1694 struct rcu_cblist rcl;
1696 WARN_ON_ONCE(!rcu_segcblist_is_offloaded(&rdp->cblist));
1697 rcu_lockdep_assert_cblist_protected(rdp);
1698 lockdep_assert_held(&rdp->nocb_bypass_lock);
1699 if (rhp && !rcu_cblist_n_cbs(&rdp->nocb_bypass)) {
1700 raw_spin_unlock(&rdp->nocb_bypass_lock);
1703 /* Note: ->cblist.len already accounts for ->nocb_bypass contents. */
1705 rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
1706 rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp);
1707 rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl);
1708 WRITE_ONCE(rdp->nocb_bypass_first, j);
1709 rcu_nocb_bypass_unlock(rdp);
1714 * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
1715 * However, if there is a callback to be enqueued and if ->nocb_bypass
1716 * proves to be initially empty, just return false because the no-CB GP
1717 * kthread may need to be awakened in this case.
1719 * Note that this function always returns true if rhp is NULL.
1721 static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
1724 if (!rcu_segcblist_is_offloaded(&rdp->cblist))
1726 rcu_lockdep_assert_cblist_protected(rdp);
1727 rcu_nocb_bypass_lock(rdp);
1728 return rcu_nocb_do_flush_bypass(rdp, rhp, j);
1732 * If the ->nocb_bypass_lock is immediately available, flush the
1733 * ->nocb_bypass queue into ->cblist.
1735 static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j)
1737 rcu_lockdep_assert_cblist_protected(rdp);
1738 if (!rcu_segcblist_is_offloaded(&rdp->cblist) ||
1739 !rcu_nocb_bypass_trylock(rdp))
1741 WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j));
1745 * See whether it is appropriate to use the ->nocb_bypass list in order
1746 * to control contention on ->nocb_lock. A limited number of direct
1747 * enqueues are permitted into ->cblist per jiffy. If ->nocb_bypass
1748 * is non-empty, further callbacks must be placed into ->nocb_bypass,
1749 * otherwise rcu_barrier() breaks. Use rcu_nocb_flush_bypass() to switch
1750 * back to direct use of ->cblist. However, ->nocb_bypass should not be
1751 * used if ->cblist is empty, because otherwise callbacks can be stranded
1752 * on ->nocb_bypass because we cannot count on the current CPU ever again
1753 * invoking call_rcu(). The general rule is that if ->nocb_bypass is
1754 * non-empty, the corresponding no-CBs grace-period kthread must not be
1755 * in an indefinite sleep state.
1757 * Finally, it is not permitted to use the bypass during early boot,
1758 * as doing so would confuse the auto-initialization code. Besides
1759 * which, there is no point in worrying about lock contention while
1760 * there is only one CPU in operation.
1762 static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
1763 bool *was_alldone, unsigned long flags)
1766 unsigned long cur_gp_seq;
1767 unsigned long j = jiffies;
1768 long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
1770 if (!rcu_segcblist_is_offloaded(&rdp->cblist)) {
1771 *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
1772 return false; /* Not offloaded, no bypassing. */
1774 lockdep_assert_irqs_disabled();
1776 // Don't use ->nocb_bypass during early boot.
1777 if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING) {
1779 WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
1780 *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
1784 // If we have advanced to a new jiffy, reset counts to allow
1785 // moving back from ->nocb_bypass to ->cblist.
1786 if (j == rdp->nocb_nobypass_last) {
1787 c = rdp->nocb_nobypass_count + 1;
1789 WRITE_ONCE(rdp->nocb_nobypass_last, j);
1790 c = rdp->nocb_nobypass_count - nocb_nobypass_lim_per_jiffy;
1791 if (ULONG_CMP_LT(rdp->nocb_nobypass_count,
1792 nocb_nobypass_lim_per_jiffy))
1794 else if (c > nocb_nobypass_lim_per_jiffy)
1795 c = nocb_nobypass_lim_per_jiffy;
1797 WRITE_ONCE(rdp->nocb_nobypass_count, c);
1799 // If there hasn't yet been all that many ->cblist enqueues
1800 // this jiffy, tell the caller to enqueue onto ->cblist. But flush
1801 // ->nocb_bypass first.
1802 if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy) {
1804 *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
1806 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1808 WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j));
1809 WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
1810 return false; // Caller must enqueue the callback.
1813 // If ->nocb_bypass has been used too long or is too full,
1814 // flush ->nocb_bypass to ->cblist.
1815 if ((ncbs && j != READ_ONCE(rdp->nocb_bypass_first)) ||
1818 if (!rcu_nocb_flush_bypass(rdp, rhp, j)) {
1819 *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
1821 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1823 WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
1824 return false; // Caller must enqueue the callback.
1826 if (j != rdp->nocb_gp_adv_time &&
1827 rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
1828 rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
1829 rcu_advance_cbs_nowake(rdp->mynode, rdp);
1830 rdp->nocb_gp_adv_time = j;
1832 rcu_nocb_unlock_irqrestore(rdp, flags);
1833 return true; // Callback already enqueued.
1836 // We need to use the bypass.
1837 rcu_nocb_wait_contended(rdp);
1838 rcu_nocb_bypass_lock(rdp);
1839 ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
1840 rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
1841 rcu_cblist_enqueue(&rdp->nocb_bypass, rhp);
1843 WRITE_ONCE(rdp->nocb_bypass_first, j);
1844 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstBQ"));
1846 rcu_nocb_bypass_unlock(rdp);
1847 smp_mb(); /* Order enqueue before wake. */
1849 local_irq_restore(flags);
1851 // No-CBs GP kthread might be indefinitely asleep, if so, wake.
1852 rcu_nocb_lock(rdp); // Rare during call_rcu() flood.
1853 if (!rcu_segcblist_pend_cbs(&rdp->cblist)) {
1854 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1855 TPS("FirstBQwake"));
1856 __call_rcu_nocb_wake(rdp, true, flags);
1858 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1859 TPS("FirstBQnoWake"));
1860 rcu_nocb_unlock_irqrestore(rdp, flags);
1863 return true; // Callback already enqueued.
1867 * Awaken the no-CBs grace-period kthead if needed, either due to it
1868 * legitimately being asleep or due to overload conditions.
1870 * If warranted, also wake up the kthread servicing this CPUs queues.
1872 static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
1873 unsigned long flags)
1874 __releases(rdp->nocb_lock)
1876 unsigned long cur_gp_seq;
1879 struct task_struct *t;
1881 // If we are being polled or there is no kthread, just leave.
1882 t = READ_ONCE(rdp->nocb_gp_kthread);
1883 if (rcu_nocb_poll || !t) {
1884 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1885 TPS("WakeNotPoll"));
1886 rcu_nocb_unlock_irqrestore(rdp, flags);
1889 // Need to actually to a wakeup.
1890 len = rcu_segcblist_n_cbs(&rdp->cblist);
1892 rdp->qlen_last_fqs_check = len;
1893 if (!irqs_disabled_flags(flags)) {
1894 /* ... if queue was empty ... */
1895 wake_nocb_gp(rdp, false, flags);
1896 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1899 wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE,
1900 TPS("WakeEmptyIsDeferred"));
1901 rcu_nocb_unlock_irqrestore(rdp, flags);
1903 } else if (len > rdp->qlen_last_fqs_check + qhimark) {
1904 /* ... or if many callbacks queued. */
1905 rdp->qlen_last_fqs_check = len;
1907 if (j != rdp->nocb_gp_adv_time &&
1908 rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
1909 rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
1910 rcu_advance_cbs_nowake(rdp->mynode, rdp);
1911 rdp->nocb_gp_adv_time = j;
1913 smp_mb(); /* Enqueue before timer_pending(). */
1914 if ((rdp->nocb_cb_sleep ||
1915 !rcu_segcblist_ready_cbs(&rdp->cblist)) &&
1916 !timer_pending(&rdp->nocb_bypass_timer))
1917 wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
1918 TPS("WakeOvfIsDeferred"));
1919 rcu_nocb_unlock_irqrestore(rdp, flags);
1921 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
1922 rcu_nocb_unlock_irqrestore(rdp, flags);
1927 /* Wake up the no-CBs GP kthread to flush ->nocb_bypass. */
1928 static void do_nocb_bypass_wakeup_timer(struct timer_list *t)
1930 unsigned long flags;
1931 struct rcu_data *rdp = from_timer(rdp, t, nocb_bypass_timer);
1933 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Timer"));
1934 rcu_nocb_lock_irqsave(rdp, flags);
1935 smp_mb__after_spinlock(); /* Timer expire before wakeup. */
1936 __call_rcu_nocb_wake(rdp, true, flags);
1940 * No-CBs GP kthreads come here to wait for additional callbacks to show up
1941 * or for grace periods to end.
1943 static void nocb_gp_wait(struct rcu_data *my_rdp)
1945 bool bypass = false;
1947 int __maybe_unused cpu = my_rdp->cpu;
1948 unsigned long cur_gp_seq;
1949 unsigned long flags;
1950 bool gotcbs = false;
1951 unsigned long j = jiffies;
1952 bool needwait_gp = false; // This prevents actual uninitialized use.
1955 struct rcu_data *rdp;
1956 struct rcu_node *rnp;
1957 unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning.
1960 * Each pass through the following loop checks for CBs and for the
1961 * nearest grace period (if any) to wait for next. The CB kthreads
1962 * and the global grace-period kthread are awakened if needed.
1964 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_cb_rdp) {
1965 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check"));
1966 rcu_nocb_lock_irqsave(rdp, flags);
1967 bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
1969 (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) ||
1970 bypass_ncbs > 2 * qhimark)) {
1971 // Bypass full or old, so flush it.
1972 (void)rcu_nocb_try_flush_bypass(rdp, j);
1973 bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
1974 } else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) {
1975 rcu_nocb_unlock_irqrestore(rdp, flags);
1976 continue; /* No callbacks here, try next. */
1979 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1984 if (bypass) { // Avoid race with first bypass CB.
1985 WRITE_ONCE(my_rdp->nocb_defer_wakeup,
1987 del_timer(&my_rdp->nocb_timer);
1989 // Advance callbacks if helpful and low contention.
1990 needwake_gp = false;
1991 if (!rcu_segcblist_restempty(&rdp->cblist,
1992 RCU_NEXT_READY_TAIL) ||
1993 (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
1994 rcu_seq_done(&rnp->gp_seq, cur_gp_seq))) {
1995 raw_spin_lock_rcu_node(rnp); /* irqs disabled. */
1996 needwake_gp = rcu_advance_cbs(rnp, rdp);
1997 raw_spin_unlock_rcu_node(rnp); /* irqs disabled. */
1999 // Need to wait on some grace period?
2000 WARN_ON_ONCE(!rcu_segcblist_restempty(&rdp->cblist,
2001 RCU_NEXT_READY_TAIL));
2002 if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq)) {
2004 ULONG_CMP_LT(cur_gp_seq, wait_gp_seq))
2005 wait_gp_seq = cur_gp_seq;
2007 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
2010 if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
2011 needwake = rdp->nocb_cb_sleep;
2012 WRITE_ONCE(rdp->nocb_cb_sleep, false);
2013 smp_mb(); /* CB invocation -after- GP end. */
2017 rcu_nocb_unlock_irqrestore(rdp, flags);
2019 swake_up_one(&rdp->nocb_cb_wq);
2023 rcu_gp_kthread_wake();
2026 my_rdp->nocb_gp_bypass = bypass;
2027 my_rdp->nocb_gp_gp = needwait_gp;
2028 my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;
2029 if (bypass && !rcu_nocb_poll) {
2030 // At least one child with non-empty ->nocb_bypass, so set
2031 // timer in order to avoid stranding its callbacks.
2032 raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
2033 mod_timer(&my_rdp->nocb_bypass_timer, j + 2);
2034 raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
2036 if (rcu_nocb_poll) {
2037 /* Polling, so trace if first poll in the series. */
2039 trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
2040 schedule_timeout_interruptible(1);
2041 } else if (!needwait_gp) {
2042 /* Wait for callbacks to appear. */
2043 trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
2044 swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq,
2045 !READ_ONCE(my_rdp->nocb_gp_sleep));
2046 trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep"));
2048 rnp = my_rdp->mynode;
2049 trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("StartWait"));
2050 swait_event_interruptible_exclusive(
2051 rnp->nocb_gp_wq[rcu_seq_ctr(wait_gp_seq) & 0x1],
2052 rcu_seq_done(&rnp->gp_seq, wait_gp_seq) ||
2053 !READ_ONCE(my_rdp->nocb_gp_sleep));
2054 trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("EndWait"));
2056 if (!rcu_nocb_poll) {
2057 raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
2059 del_timer(&my_rdp->nocb_bypass_timer);
2060 WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
2061 raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
2063 my_rdp->nocb_gp_seq = -1;
2064 WARN_ON(signal_pending(current));
2068 * No-CBs grace-period-wait kthread. There is one of these per group
2069 * of CPUs, but only once at least one CPU in that group has come online
2070 * at least once since boot. This kthread checks for newly posted
2071 * callbacks from any of the CPUs it is responsible for, waits for a
2072 * grace period, then awakens all of the rcu_nocb_cb_kthread() instances
2073 * that then have callback-invocation work to do.
2075 static int rcu_nocb_gp_kthread(void *arg)
2077 struct rcu_data *rdp = arg;
2080 WRITE_ONCE(rdp->nocb_gp_loops, rdp->nocb_gp_loops + 1);
2082 cond_resched_tasks_rcu_qs();
2088 * Invoke any ready callbacks from the corresponding no-CBs CPU,
2089 * then, if there are no more, wait for more to appear.
2091 static void nocb_cb_wait(struct rcu_data *rdp)
2093 unsigned long cur_gp_seq;
2094 unsigned long flags;
2095 bool needwake_gp = false;
2096 struct rcu_node *rnp = rdp->mynode;
2098 local_irq_save(flags);
2099 rcu_momentary_dyntick_idle();
2100 local_irq_restore(flags);
2104 lockdep_assert_irqs_enabled();
2105 rcu_nocb_lock_irqsave(rdp, flags);
2106 if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
2107 rcu_seq_done(&rnp->gp_seq, cur_gp_seq) &&
2108 raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */
2109 needwake_gp = rcu_advance_cbs(rdp->mynode, rdp);
2110 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2112 if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
2113 rcu_nocb_unlock_irqrestore(rdp, flags);
2115 rcu_gp_kthread_wake();
2119 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("CBSleep"));
2120 WRITE_ONCE(rdp->nocb_cb_sleep, true);
2121 rcu_nocb_unlock_irqrestore(rdp, flags);
2123 rcu_gp_kthread_wake();
2124 swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
2125 !READ_ONCE(rdp->nocb_cb_sleep));
2126 if (!smp_load_acquire(&rdp->nocb_cb_sleep)) { /* VVV */
2127 /* ^^^ Ensure CB invocation follows _sleep test. */
2130 WARN_ON(signal_pending(current));
2131 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty"));
2135 * Per-rcu_data kthread, but only for no-CBs CPUs. Repeatedly invoke
2136 * nocb_cb_wait() to do the dirty work.
2138 static int rcu_nocb_cb_kthread(void *arg)
2140 struct rcu_data *rdp = arg;
2142 // Each pass through this loop does one callback batch, and,
2143 // if there are no more ready callbacks, waits for them.
2146 cond_resched_tasks_rcu_qs();
2151 /* Is a deferred wakeup of rcu_nocb_kthread() required? */
2152 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2154 return READ_ONCE(rdp->nocb_defer_wakeup);
2157 /* Do a deferred wakeup of rcu_nocb_kthread(). */
2158 static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
2160 unsigned long flags;
2163 rcu_nocb_lock_irqsave(rdp, flags);
2164 if (!rcu_nocb_need_deferred_wakeup(rdp)) {
2165 rcu_nocb_unlock_irqrestore(rdp, flags);
2168 ndw = READ_ONCE(rdp->nocb_defer_wakeup);
2169 WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
2170 wake_nocb_gp(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
2171 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DeferredWake"));
2174 /* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
2175 static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
2177 struct rcu_data *rdp = from_timer(rdp, t, nocb_timer);
2179 do_nocb_deferred_wakeup_common(rdp);
2183 * Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
2184 * This means we do an inexact common-case check. Note that if
2185 * we miss, ->nocb_timer will eventually clean things up.
2187 static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2189 if (rcu_nocb_need_deferred_wakeup(rdp))
2190 do_nocb_deferred_wakeup_common(rdp);
2193 void __init rcu_init_nohz(void)
2196 bool need_rcu_nocb_mask = false;
2197 struct rcu_data *rdp;
2199 #if defined(CONFIG_NO_HZ_FULL)
2200 if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
2201 need_rcu_nocb_mask = true;
2202 #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2204 if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) {
2205 if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
2206 pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
2210 if (!cpumask_available(rcu_nocb_mask))
2213 #if defined(CONFIG_NO_HZ_FULL)
2214 if (tick_nohz_full_running)
2215 cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
2216 #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2218 if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
2219 pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
2220 cpumask_and(rcu_nocb_mask, cpu_possible_mask,
2223 if (cpumask_empty(rcu_nocb_mask))
2224 pr_info("\tOffload RCU callbacks from CPUs: (none).\n");
2226 pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
2227 cpumask_pr_args(rcu_nocb_mask));
2229 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
2231 for_each_cpu(cpu, rcu_nocb_mask) {
2232 rdp = per_cpu_ptr(&rcu_data, cpu);
2233 if (rcu_segcblist_empty(&rdp->cblist))
2234 rcu_segcblist_init(&rdp->cblist);
2235 rcu_segcblist_offload(&rdp->cblist);
2237 rcu_organize_nocb_kthreads();
2240 /* Initialize per-rcu_data variables for no-CBs CPUs. */
2241 static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2243 init_swait_queue_head(&rdp->nocb_cb_wq);
2244 init_swait_queue_head(&rdp->nocb_gp_wq);
2245 raw_spin_lock_init(&rdp->nocb_lock);
2246 raw_spin_lock_init(&rdp->nocb_bypass_lock);
2247 raw_spin_lock_init(&rdp->nocb_gp_lock);
2248 timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
2249 timer_setup(&rdp->nocb_bypass_timer, do_nocb_bypass_wakeup_timer, 0);
2250 rcu_cblist_init(&rdp->nocb_bypass);
2254 * If the specified CPU is a no-CBs CPU that does not already have its
2255 * rcuo CB kthread, spawn it. Additionally, if the rcuo GP kthread
2256 * for this CPU's group has not yet been created, spawn it as well.
2258 static void rcu_spawn_one_nocb_kthread(int cpu)
2260 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
2261 struct rcu_data *rdp_gp;
2262 struct task_struct *t;
2265 * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
2266 * then nothing to do.
2268 if (!rcu_is_nocb_cpu(cpu) || rdp->nocb_cb_kthread)
2271 /* If we didn't spawn the GP kthread first, reorganize! */
2272 rdp_gp = rdp->nocb_gp_rdp;
2273 if (!rdp_gp->nocb_gp_kthread) {
2274 t = kthread_run(rcu_nocb_gp_kthread, rdp_gp,
2275 "rcuog/%d", rdp_gp->cpu);
2276 if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__))
2278 WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);
2281 /* Spawn the kthread for this CPU. */
2282 t = kthread_run(rcu_nocb_cb_kthread, rdp,
2283 "rcuo%c/%d", rcu_state.abbr, cpu);
2284 if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__))
2286 WRITE_ONCE(rdp->nocb_cb_kthread, t);
2287 WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread);
2291 * If the specified CPU is a no-CBs CPU that does not already have its
2292 * rcuo kthread, spawn it.
2294 static void rcu_spawn_cpu_nocb_kthread(int cpu)
2296 if (rcu_scheduler_fully_active)
2297 rcu_spawn_one_nocb_kthread(cpu);
2301 * Once the scheduler is running, spawn rcuo kthreads for all online
2302 * no-CBs CPUs. This assumes that the early_initcall()s happen before
2303 * non-boot CPUs come online -- if this changes, we will need to add
2304 * some mutual exclusion.
2306 static void __init rcu_spawn_nocb_kthreads(void)
2310 for_each_online_cpu(cpu)
2311 rcu_spawn_cpu_nocb_kthread(cpu);
2314 /* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */
2315 static int rcu_nocb_gp_stride = -1;
2316 module_param(rcu_nocb_gp_stride, int, 0444);
2319 * Initialize GP-CB relationships for all no-CBs CPU.
2321 static void __init rcu_organize_nocb_kthreads(void)
2324 bool firsttime = true;
2325 int ls = rcu_nocb_gp_stride;
2326 int nl = 0; /* Next GP kthread. */
2327 struct rcu_data *rdp;
2328 struct rcu_data *rdp_gp = NULL; /* Suppress misguided gcc warn. */
2329 struct rcu_data *rdp_prev = NULL;
2331 if (!cpumask_available(rcu_nocb_mask))
2334 ls = nr_cpu_ids / int_sqrt(nr_cpu_ids);
2335 rcu_nocb_gp_stride = ls;
2339 * Each pass through this loop sets up one rcu_data structure.
2340 * Should the corresponding CPU come online in the future, then
2341 * we will spawn the needed set of rcu_nocb_kthread() kthreads.
2343 for_each_cpu(cpu, rcu_nocb_mask) {
2344 rdp = per_cpu_ptr(&rcu_data, cpu);
2345 if (rdp->cpu >= nl) {
2346 /* New GP kthread, set up for CBs & next GP. */
2347 nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
2348 rdp->nocb_gp_rdp = rdp;
2350 if (!firsttime && dump_tree)
2353 pr_alert("%s: No-CB GP kthread CPU %d:", __func__, cpu);
2355 /* Another CB kthread, link to previous GP kthread. */
2356 rdp->nocb_gp_rdp = rdp_gp;
2357 rdp_prev->nocb_next_cb_rdp = rdp;
2358 pr_alert(" %d", cpu);
2365 * Bind the current task to the offloaded CPUs. If there are no offloaded
2366 * CPUs, leave the task unbound. Splat if the bind attempt fails.
2368 void rcu_bind_current_to_nocb(void)
2370 if (cpumask_available(rcu_nocb_mask) && cpumask_weight(rcu_nocb_mask))
2371 WARN_ON(sched_setaffinity(current->pid, rcu_nocb_mask));
2373 EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb);
2376 * Dump out nocb grace-period kthread state for the specified rcu_data
2379 static void show_rcu_nocb_gp_state(struct rcu_data *rdp)
2381 struct rcu_node *rnp = rdp->mynode;
2383 pr_info("nocb GP %d %c%c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu\n",
2385 "kK"[!!rdp->nocb_gp_kthread],
2386 "lL"[raw_spin_is_locked(&rdp->nocb_gp_lock)],
2387 "dD"[!!rdp->nocb_defer_wakeup],
2388 "tT"[timer_pending(&rdp->nocb_timer)],
2389 "bB"[timer_pending(&rdp->nocb_bypass_timer)],
2390 "sS"[!!rdp->nocb_gp_sleep],
2391 ".W"[swait_active(&rdp->nocb_gp_wq)],
2392 ".W"[swait_active(&rnp->nocb_gp_wq[0])],
2393 ".W"[swait_active(&rnp->nocb_gp_wq[1])],
2394 ".B"[!!rdp->nocb_gp_bypass],
2395 ".G"[!!rdp->nocb_gp_gp],
2396 (long)rdp->nocb_gp_seq,
2397 rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops));
2400 /* Dump out nocb kthread state for the specified rcu_data structure. */
2401 static void show_rcu_nocb_state(struct rcu_data *rdp)
2403 struct rcu_segcblist *rsclp = &rdp->cblist;
2408 if (rdp->nocb_gp_rdp == rdp)
2409 show_rcu_nocb_gp_state(rdp);
2411 pr_info(" CB %d->%d %c%c%c%c%c%c F%ld L%ld C%d %c%c%c%c%c q%ld\n",
2412 rdp->cpu, rdp->nocb_gp_rdp->cpu,
2413 "kK"[!!rdp->nocb_cb_kthread],
2414 "bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)],
2415 "cC"[!!atomic_read(&rdp->nocb_lock_contended)],
2416 "lL"[raw_spin_is_locked(&rdp->nocb_lock)],
2417 "sS"[!!rdp->nocb_cb_sleep],
2418 ".W"[swait_active(&rdp->nocb_cb_wq)],
2419 jiffies - rdp->nocb_bypass_first,
2420 jiffies - rdp->nocb_nobypass_last,
2421 rdp->nocb_nobypass_count,
2422 ".D"[rcu_segcblist_ready_cbs(rsclp)],
2423 ".W"[!rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL)],
2424 ".R"[!rcu_segcblist_restempty(rsclp, RCU_WAIT_TAIL)],
2425 ".N"[!rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL)],
2426 ".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)],
2427 rcu_segcblist_n_cbs(&rdp->cblist));
2429 /* It is OK for GP kthreads to have GP state. */
2430 if (rdp->nocb_gp_rdp == rdp)
2433 waslocked = raw_spin_is_locked(&rdp->nocb_gp_lock);
2434 wastimer = timer_pending(&rdp->nocb_timer);
2435 wassleep = swait_active(&rdp->nocb_gp_wq);
2436 if (!rdp->nocb_defer_wakeup && !rdp->nocb_gp_sleep &&
2437 !waslocked && !wastimer && !wassleep)
2438 return; /* Nothing untowards. */
2440 pr_info(" !!! %c%c%c%c %c\n",
2442 "dD"[!!rdp->nocb_defer_wakeup],
2444 "sS"[!!rdp->nocb_gp_sleep],
2448 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
2450 /* No ->nocb_lock to acquire. */
2451 static void rcu_nocb_lock(struct rcu_data *rdp)
2455 /* No ->nocb_lock to release. */
2456 static void rcu_nocb_unlock(struct rcu_data *rdp)
2460 /* No ->nocb_lock to release. */
2461 static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
2462 unsigned long flags)
2464 local_irq_restore(flags);
2467 /* Lockdep check that ->cblist may be safely accessed. */
2468 static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
2470 lockdep_assert_irqs_disabled();
2473 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
2477 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
2482 static void rcu_init_one_nocb(struct rcu_node *rnp)
2486 static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
2492 static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
2493 bool *was_alldone, unsigned long flags)
2498 static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
2499 unsigned long flags)
2501 WARN_ON_ONCE(1); /* Should be dead code! */
2504 static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2508 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2513 static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2517 static void rcu_spawn_cpu_nocb_kthread(int cpu)
2521 static void __init rcu_spawn_nocb_kthreads(void)
2525 static void show_rcu_nocb_state(struct rcu_data *rdp)
2529 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2532 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
2533 * grace-period kthread will do force_quiescent_state() processing?
2534 * The idea is to avoid waking up RCU core processing on such a
2535 * CPU unless the grace period has extended for too long.
2537 * This code relies on the fact that all NO_HZ_FULL CPUs are also
2538 * CONFIG_RCU_NOCB_CPU CPUs.
2540 static bool rcu_nohz_full_cpu(void)
2542 #ifdef CONFIG_NO_HZ_FULL
2543 if (tick_nohz_full_cpu(smp_processor_id()) &&
2544 (!rcu_gp_in_progress() ||
2545 ULONG_CMP_LT(jiffies, READ_ONCE(rcu_state.gp_start) + HZ)))
2547 #endif /* #ifdef CONFIG_NO_HZ_FULL */
2552 * Bind the RCU grace-period kthreads to the housekeeping CPU.
2554 static void rcu_bind_gp_kthread(void)
2556 if (!tick_nohz_full_enabled())
2558 housekeeping_affine(current, HK_FLAG_RCU);
2561 /* Record the current task on dyntick-idle entry. */
2562 static void rcu_dynticks_task_enter(void)
2564 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2565 WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
2566 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
2569 /* Record no current task on dyntick-idle exit. */
2570 static void rcu_dynticks_task_exit(void)
2572 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2573 WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
2574 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */