2 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
3 * Internal non-public definitions that provide either classic
4 * or preemptible semantics.
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, you can access it online at
18 * http://www.gnu.org/licenses/gpl-2.0.html.
20 * Copyright Red Hat, 2009
21 * Copyright IBM Corporation, 2009
23 * Author: Ingo Molnar <mingo@elte.hu>
24 * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
27 #include <linux/delay.h>
28 #include <linux/gfp.h>
29 #include <linux/oom.h>
30 #include <linux/sched/debug.h>
31 #include <linux/smpboot.h>
32 #include <linux/sched/isolation.h>
33 #include <uapi/linux/sched/types.h>
34 #include "../time/tick-internal.h"
36 #ifdef CONFIG_RCU_BOOST
38 #include "../locking/rtmutex_common.h"
41 * Control variables for per-CPU and per-rcu_node kthreads. These
42 * handle all flavors of RCU.
44 static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
45 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
46 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
47 DEFINE_PER_CPU(char, rcu_cpu_has_work);
49 #else /* #ifdef CONFIG_RCU_BOOST */
52 * Some architectures do not define rt_mutexes, but if !CONFIG_RCU_BOOST,
53 * all uses are in dead code. Provide a definition to keep the compiler
54 * happy, but add WARN_ON_ONCE() to complain if used in the wrong place.
55 * This probably needs to be excluded from -rt builds.
57 #define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; })
58 #define rt_mutex_futex_unlock(x) WARN_ON_ONCE(1)
60 #endif /* #else #ifdef CONFIG_RCU_BOOST */
62 #ifdef CONFIG_RCU_NOCB_CPU
63 static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
64 static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
65 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
68 * Check the RCU kernel configuration parameters and print informative
69 * messages about anything out of the ordinary.
71 static void __init rcu_bootup_announce_oddness(void)
73 if (IS_ENABLED(CONFIG_RCU_TRACE))
74 pr_info("\tRCU event tracing is enabled.\n");
75 if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||
76 (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))
77 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d.\n",
80 pr_info("\tHierarchical RCU autobalancing is disabled.\n");
81 if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ))
82 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
83 if (IS_ENABLED(CONFIG_PROVE_RCU))
84 pr_info("\tRCU lockdep checking is enabled.\n");
85 if (RCU_NUM_LVLS >= 4)
86 pr_info("\tFour(or more)-level hierarchy is enabled.\n");
87 if (RCU_FANOUT_LEAF != 16)
88 pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
90 if (rcu_fanout_leaf != RCU_FANOUT_LEAF)
91 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n",
93 if (nr_cpu_ids != NR_CPUS)
94 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%u.\n", NR_CPUS, nr_cpu_ids);
95 #ifdef CONFIG_RCU_BOOST
96 pr_info("\tRCU priority boosting: priority %d delay %d ms.\n",
97 kthread_prio, CONFIG_RCU_BOOST_DELAY);
99 if (blimit != DEFAULT_RCU_BLIMIT)
100 pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit);
101 if (qhimark != DEFAULT_RCU_QHIMARK)
102 pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark);
103 if (qlowmark != DEFAULT_RCU_QLOMARK)
104 pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark);
105 if (jiffies_till_first_fqs != ULONG_MAX)
106 pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs);
107 if (jiffies_till_next_fqs != ULONG_MAX)
108 pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs);
109 if (rcu_kick_kthreads)
110 pr_info("\tKick kthreads if too-long grace period.\n");
111 if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD))
112 pr_info("\tRCU callback double-/use-after-free debug enabled.\n");
113 if (gp_preinit_delay)
114 pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay);
116 pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay);
117 if (gp_cleanup_delay)
118 pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay);
119 if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))
120 pr_info("\tRCU debug extended QS entry/exit.\n");
121 rcupdate_announce_bootup_oddness();
124 #ifdef CONFIG_PREEMPT_RCU
126 RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
127 static struct rcu_state *const rcu_state_p = &rcu_preempt_state;
128 static struct rcu_data __percpu *const rcu_data_p = &rcu_preempt_data;
130 static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
132 static void rcu_read_unlock_special(struct task_struct *t);
135 * Tell them what RCU they are running.
137 static void __init rcu_bootup_announce(void)
139 pr_info("Preemptible hierarchical RCU implementation.\n");
140 rcu_bootup_announce_oddness();
143 /* Flags for rcu_preempt_ctxt_queue() decision table. */
144 #define RCU_GP_TASKS 0x8
145 #define RCU_EXP_TASKS 0x4
146 #define RCU_GP_BLKD 0x2
147 #define RCU_EXP_BLKD 0x1
150 * Queues a task preempted within an RCU-preempt read-side critical
151 * section into the appropriate location within the ->blkd_tasks list,
152 * depending on the states of any ongoing normal and expedited grace
153 * periods. The ->gp_tasks pointer indicates which element the normal
154 * grace period is waiting on (NULL if none), and the ->exp_tasks pointer
155 * indicates which element the expedited grace period is waiting on (again,
156 * NULL if none). If a grace period is waiting on a given element in the
157 * ->blkd_tasks list, it also waits on all subsequent elements. Thus,
158 * adding a task to the tail of the list blocks any grace period that is
159 * already waiting on one of the elements. In contrast, adding a task
160 * to the head of the list won't block any grace period that is already
161 * waiting on one of the elements.
163 * This queuing is imprecise, and can sometimes make an ongoing grace
164 * period wait for a task that is not strictly speaking blocking it.
165 * Given the choice, we needlessly block a normal grace period rather than
166 * blocking an expedited grace period.
168 * Note that an endless sequence of expedited grace periods still cannot
169 * indefinitely postpone a normal grace period. Eventually, all of the
170 * fixed number of preempted tasks blocking the normal grace period that are
171 * not also blocking the expedited grace period will resume and complete
172 * their RCU read-side critical sections. At that point, the ->gp_tasks
173 * pointer will equal the ->exp_tasks pointer, at which point the end of
174 * the corresponding expedited grace period will also be the end of the
175 * normal grace period.
177 static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
178 __releases(rnp->lock) /* But leaves rrupts disabled. */
180 int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) +
181 (rnp->exp_tasks ? RCU_EXP_TASKS : 0) +
182 (rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) +
183 (rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0);
184 struct task_struct *t = current;
186 raw_lockdep_assert_held_rcu_node(rnp);
187 WARN_ON_ONCE(rdp->mynode != rnp);
188 WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
189 /* RCU better not be waiting on newly onlined CPUs! */
190 WARN_ON_ONCE(rnp->qsmaskinitnext & ~rnp->qsmaskinit & rnp->qsmask &
194 * Decide where to queue the newly blocked task. In theory,
195 * this could be an if-statement. In practice, when I tried
196 * that, it was quite messy.
198 switch (blkd_state) {
201 case RCU_EXP_TASKS + RCU_GP_BLKD:
203 case RCU_GP_TASKS + RCU_EXP_TASKS:
206 * Blocking neither GP, or first task blocking the normal
207 * GP but not blocking the already-waiting expedited GP.
208 * Queue at the head of the list to avoid unnecessarily
209 * blocking the already-waiting GPs.
211 list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
216 case RCU_GP_BLKD + RCU_EXP_BLKD:
217 case RCU_GP_TASKS + RCU_EXP_BLKD:
218 case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
219 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
222 * First task arriving that blocks either GP, or first task
223 * arriving that blocks the expedited GP (with the normal
224 * GP already waiting), or a task arriving that blocks
225 * both GPs with both GPs already waiting. Queue at the
226 * tail of the list to avoid any GP waiting on any of the
227 * already queued tasks that are not blocking it.
229 list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);
232 case RCU_EXP_TASKS + RCU_EXP_BLKD:
233 case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
234 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD:
237 * Second or subsequent task blocking the expedited GP.
238 * The task either does not block the normal GP, or is the
239 * first task blocking the normal GP. Queue just after
240 * the first task blocking the expedited GP.
242 list_add(&t->rcu_node_entry, rnp->exp_tasks);
245 case RCU_GP_TASKS + RCU_GP_BLKD:
246 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD:
249 * Second or subsequent task blocking the normal GP.
250 * The task does not block the expedited GP. Queue just
251 * after the first task blocking the normal GP.
253 list_add(&t->rcu_node_entry, rnp->gp_tasks);
258 /* Yet another exercise in excessive paranoia. */
264 * We have now queued the task. If it was the first one to
265 * block either grace period, update the ->gp_tasks and/or
266 * ->exp_tasks pointers, respectively, to reference the newly
269 if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) {
270 rnp->gp_tasks = &t->rcu_node_entry;
271 WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq);
273 if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
274 rnp->exp_tasks = &t->rcu_node_entry;
275 WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=
276 !(rnp->qsmask & rdp->grpmask));
277 WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) !=
278 !(rnp->expmask & rdp->grpmask));
279 raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */
282 * Report the quiescent state for the expedited GP. This expedited
283 * GP should not be able to end until we report, so there should be
284 * no need to check for a subsequent expedited GP. (Though we are
285 * still in a quiescent state in any case.)
287 if (blkd_state & RCU_EXP_BLKD &&
288 t->rcu_read_unlock_special.b.exp_need_qs) {
289 t->rcu_read_unlock_special.b.exp_need_qs = false;
290 rcu_report_exp_rdp(rdp->rsp, rdp, true);
292 WARN_ON_ONCE(t->rcu_read_unlock_special.b.exp_need_qs);
297 * Record a preemptible-RCU quiescent state for the specified CPU.
298 * Note that this does not necessarily mean that the task currently running
299 * on the CPU is in a quiescent state: Instead, it means that the current
300 * grace period need not wait on any RCU read-side critical section that
301 * starts later on this CPU. It also means that if the current task is
302 * in an RCU read-side critical section, it has already added itself to
303 * some leaf rcu_node structure's ->blkd_tasks list. In addition to the
304 * current task, there might be any number of other tasks blocked while
305 * in an RCU read-side critical section.
307 * Callers to this function must disable preemption.
309 static void rcu_preempt_qs(void)
311 RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_qs() invoked with preemption enabled!!!\n");
312 if (__this_cpu_read(rcu_data_p->cpu_no_qs.s)) {
313 trace_rcu_grace_period(TPS("rcu_preempt"),
314 __this_cpu_read(rcu_data_p->gp_seq),
316 __this_cpu_write(rcu_data_p->cpu_no_qs.b.norm, false);
317 barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
318 current->rcu_read_unlock_special.b.need_qs = false;
323 * We have entered the scheduler, and the current task might soon be
324 * context-switched away from. If this task is in an RCU read-side
325 * critical section, we will no longer be able to rely on the CPU to
326 * record that fact, so we enqueue the task on the blkd_tasks list.
327 * The task will dequeue itself when it exits the outermost enclosing
328 * RCU read-side critical section. Therefore, the current grace period
329 * cannot be permitted to complete until the blkd_tasks list entries
330 * predating the current grace period drain, in other words, until
331 * rnp->gp_tasks becomes NULL.
333 * Caller must disable interrupts.
335 static void rcu_preempt_note_context_switch(bool preempt)
337 struct task_struct *t = current;
338 struct rcu_data *rdp;
339 struct rcu_node *rnp;
341 lockdep_assert_irqs_disabled();
342 WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0);
343 if (t->rcu_read_lock_nesting > 0 &&
344 !t->rcu_read_unlock_special.b.blocked) {
346 /* Possibly blocking in an RCU read-side critical section. */
347 rdp = this_cpu_ptr(rcu_state_p->rda);
349 raw_spin_lock_rcu_node(rnp);
350 t->rcu_read_unlock_special.b.blocked = true;
351 t->rcu_blocked_node = rnp;
354 * Verify the CPU's sanity, trace the preemption, and
355 * then queue the task as required based on the states
356 * of any ongoing and expedited grace periods.
358 WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);
359 WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
360 trace_rcu_preempt_task(rdp->rsp->name,
362 (rnp->qsmask & rdp->grpmask)
364 : rcu_seq_snap(&rnp->gp_seq));
365 rcu_preempt_ctxt_queue(rnp, rdp);
366 } else if (t->rcu_read_lock_nesting < 0 &&
367 t->rcu_read_unlock_special.s) {
370 * Complete exit from RCU read-side critical section on
371 * behalf of preempted instance of __rcu_read_unlock().
373 rcu_read_unlock_special(t);
377 * Either we were not in an RCU read-side critical section to
378 * begin with, or we have now recorded that critical section
379 * globally. Either way, we can now note a quiescent state
380 * for this CPU. Again, if we were in an RCU read-side critical
381 * section, and if that critical section was blocking the current
382 * grace period, then the fact that the task has been enqueued
383 * means that we continue to block the current grace period.
389 * Check for preempted RCU readers blocking the current grace period
390 * for the specified rcu_node structure. If the caller needs a reliable
391 * answer, it must hold the rcu_node's ->lock.
393 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
395 return rnp->gp_tasks != NULL;
399 * Preemptible RCU implementation for rcu_read_lock().
400 * Just increment ->rcu_read_lock_nesting, shared state will be updated
403 void __rcu_read_lock(void)
405 current->rcu_read_lock_nesting++;
406 barrier(); /* critical section after entry code. */
408 EXPORT_SYMBOL_GPL(__rcu_read_lock);
411 * Preemptible RCU implementation for rcu_read_unlock().
412 * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
413 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
414 * invoke rcu_read_unlock_special() to clean up after a context switch
415 * in an RCU read-side critical section and other special cases.
417 void __rcu_read_unlock(void)
419 struct task_struct *t = current;
421 if (t->rcu_read_lock_nesting != 1) {
422 --t->rcu_read_lock_nesting;
424 barrier(); /* critical section before exit code. */
425 t->rcu_read_lock_nesting = INT_MIN;
426 barrier(); /* assign before ->rcu_read_unlock_special load */
427 if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
428 rcu_read_unlock_special(t);
429 barrier(); /* ->rcu_read_unlock_special load before assign */
430 t->rcu_read_lock_nesting = 0;
432 #ifdef CONFIG_PROVE_LOCKING
434 int rrln = READ_ONCE(t->rcu_read_lock_nesting);
436 WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
438 #endif /* #ifdef CONFIG_PROVE_LOCKING */
440 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
443 * Advance a ->blkd_tasks-list pointer to the next entry, instead
444 * returning NULL if at the end of the list.
446 static struct list_head *rcu_next_node_entry(struct task_struct *t,
447 struct rcu_node *rnp)
449 struct list_head *np;
451 np = t->rcu_node_entry.next;
452 if (np == &rnp->blkd_tasks)
458 * Return true if the specified rcu_node structure has tasks that were
459 * preempted within an RCU read-side critical section.
461 static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
463 return !list_empty(&rnp->blkd_tasks);
467 * Handle special cases during rcu_read_unlock(), such as needing to
468 * notify RCU core processing or task having blocked during the RCU
469 * read-side critical section.
471 static void rcu_read_unlock_special(struct task_struct *t)
477 struct list_head *np;
478 bool drop_boost_mutex = false;
479 struct rcu_data *rdp;
480 struct rcu_node *rnp;
481 union rcu_special special;
483 /* NMI handlers cannot block and cannot safely manipulate state. */
487 local_irq_save(flags);
490 * If RCU core is waiting for this CPU to exit its critical section,
491 * report the fact that it has exited. Because irqs are disabled,
492 * t->rcu_read_unlock_special cannot change.
494 special = t->rcu_read_unlock_special;
495 if (special.b.need_qs) {
497 t->rcu_read_unlock_special.b.need_qs = false;
498 if (!t->rcu_read_unlock_special.s) {
499 local_irq_restore(flags);
505 * Respond to a request for an expedited grace period, but only if
506 * we were not preempted, meaning that we were running on the same
507 * CPU throughout. If we were preempted, the exp_need_qs flag
508 * would have been cleared at the time of the first preemption,
509 * and the quiescent state would be reported when we were dequeued.
511 if (special.b.exp_need_qs) {
512 WARN_ON_ONCE(special.b.blocked);
513 t->rcu_read_unlock_special.b.exp_need_qs = false;
514 rdp = this_cpu_ptr(rcu_state_p->rda);
515 rcu_report_exp_rdp(rcu_state_p, rdp, true);
516 if (!t->rcu_read_unlock_special.s) {
517 local_irq_restore(flags);
522 /* Hardware IRQ handlers cannot block, complain if they get here. */
523 if (in_irq() || in_serving_softirq()) {
524 lockdep_rcu_suspicious(__FILE__, __LINE__,
525 "rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n");
526 pr_alert("->rcu_read_unlock_special: %#x (b: %d, enq: %d nq: %d)\n",
527 t->rcu_read_unlock_special.s,
528 t->rcu_read_unlock_special.b.blocked,
529 t->rcu_read_unlock_special.b.exp_need_qs,
530 t->rcu_read_unlock_special.b.need_qs);
531 local_irq_restore(flags);
535 /* Clean up if blocked during RCU read-side critical section. */
536 if (special.b.blocked) {
537 t->rcu_read_unlock_special.b.blocked = false;
540 * Remove this task from the list it blocked on. The task
541 * now remains queued on the rcu_node corresponding to the
542 * CPU it first blocked on, so there is no longer any need
543 * to loop. Retain a WARN_ON_ONCE() out of sheer paranoia.
545 rnp = t->rcu_blocked_node;
546 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
547 WARN_ON_ONCE(rnp != t->rcu_blocked_node);
548 WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
549 empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
550 WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq &&
551 (!empty_norm || rnp->qsmask));
552 empty_exp = sync_rcu_preempt_exp_done(rnp);
553 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
554 np = rcu_next_node_entry(t, rnp);
555 list_del_init(&t->rcu_node_entry);
556 t->rcu_blocked_node = NULL;
557 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
558 rnp->gp_seq, t->pid);
559 if (&t->rcu_node_entry == rnp->gp_tasks)
561 if (&t->rcu_node_entry == rnp->exp_tasks)
563 if (IS_ENABLED(CONFIG_RCU_BOOST)) {
564 /* Snapshot ->boost_mtx ownership w/rnp->lock held. */
565 drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
566 if (&t->rcu_node_entry == rnp->boost_tasks)
567 rnp->boost_tasks = np;
571 * If this was the last task on the current list, and if
572 * we aren't waiting on any CPUs, report the quiescent state.
573 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
574 * so we must take a snapshot of the expedited state.
576 empty_exp_now = sync_rcu_preempt_exp_done(rnp);
577 if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
578 trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
585 rcu_report_unblock_qs_rnp(rcu_state_p, rnp, flags);
587 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
590 /* Unboost if we were boosted. */
591 if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
592 rt_mutex_futex_unlock(&rnp->boost_mtx);
595 * If this was the last task on the expedited lists,
596 * then we need to report up the rcu_node hierarchy.
598 if (!empty_exp && empty_exp_now)
599 rcu_report_exp_rnp(rcu_state_p, rnp, true);
601 local_irq_restore(flags);
606 * Dump detailed information for all tasks blocking the current RCU
607 * grace period on the specified rcu_node structure.
609 static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
612 struct task_struct *t;
614 raw_spin_lock_irqsave_rcu_node(rnp, flags);
615 if (!rcu_preempt_blocked_readers_cgp(rnp)) {
616 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
619 t = list_entry(rnp->gp_tasks->prev,
620 struct task_struct, rcu_node_entry);
621 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
623 * We could be printing a lot while holding a spinlock.
624 * Avoid triggering hard lockup.
626 touch_nmi_watchdog();
629 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
633 * Dump detailed information for all tasks blocking the current RCU
636 static void rcu_print_detail_task_stall(struct rcu_state *rsp)
638 struct rcu_node *rnp = rcu_get_root(rsp);
640 rcu_print_detail_task_stall_rnp(rnp);
641 rcu_for_each_leaf_node(rsp, rnp)
642 rcu_print_detail_task_stall_rnp(rnp);
645 static void rcu_print_task_stall_begin(struct rcu_node *rnp)
647 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
648 rnp->level, rnp->grplo, rnp->grphi);
651 static void rcu_print_task_stall_end(void)
657 * Scan the current list of tasks blocked within RCU read-side critical
658 * sections, printing out the tid of each.
660 static int rcu_print_task_stall(struct rcu_node *rnp)
662 struct task_struct *t;
665 if (!rcu_preempt_blocked_readers_cgp(rnp))
667 rcu_print_task_stall_begin(rnp);
668 t = list_entry(rnp->gp_tasks->prev,
669 struct task_struct, rcu_node_entry);
670 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
671 pr_cont(" P%d", t->pid);
674 rcu_print_task_stall_end();
679 * Scan the current list of tasks blocked within RCU read-side critical
680 * sections, printing out the tid of each that is blocking the current
681 * expedited grace period.
683 static int rcu_print_task_exp_stall(struct rcu_node *rnp)
685 struct task_struct *t;
690 t = list_entry(rnp->exp_tasks->prev,
691 struct task_struct, rcu_node_entry);
692 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
693 pr_cont(" P%d", t->pid);
700 * Check that the list of blocked tasks for the newly completed grace
701 * period is in fact empty. It is a serious bug to complete a grace
702 * period that still has RCU readers blocked! This function must be
703 * invoked -before- updating this rnp's ->gp_seq, and the rnp's ->lock
704 * must be held by the caller.
706 * Also, if there are blocked tasks on the list, they automatically
707 * block the newly created grace period, so set up ->gp_tasks accordingly.
710 rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp)
712 struct task_struct *t;
714 RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
715 if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
716 dump_blkd_tasks(rsp, rnp, 10);
717 if (rcu_preempt_has_tasks(rnp) &&
718 (rnp->qsmaskinit || rnp->wait_blkd_tasks)) {
719 rnp->gp_tasks = rnp->blkd_tasks.next;
720 t = container_of(rnp->gp_tasks, struct task_struct,
722 trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
723 rnp->gp_seq, t->pid);
725 WARN_ON_ONCE(rnp->qsmask);
729 * Check for a quiescent state from the current CPU. When a task blocks,
730 * the task is recorded in the corresponding CPU's rcu_node structure,
731 * which is checked elsewhere.
733 * Caller must disable hard irqs.
735 static void rcu_preempt_check_callbacks(void)
737 struct rcu_state *rsp = &rcu_preempt_state;
738 struct task_struct *t = current;
740 if (t->rcu_read_lock_nesting == 0) {
744 if (t->rcu_read_lock_nesting > 0 &&
745 __this_cpu_read(rcu_data_p->core_needs_qs) &&
746 __this_cpu_read(rcu_data_p->cpu_no_qs.b.norm) &&
747 !t->rcu_read_unlock_special.b.need_qs &&
748 time_after(jiffies, rsp->gp_start + HZ))
749 t->rcu_read_unlock_special.b.need_qs = true;
753 * call_rcu() - Queue an RCU callback for invocation after a grace period.
754 * @head: structure to be used for queueing the RCU updates.
755 * @func: actual callback function to be invoked after the grace period
757 * The callback function will be invoked some time after a full grace
758 * period elapses, in other words after all pre-existing RCU read-side
759 * critical sections have completed. However, the callback function
760 * might well execute concurrently with RCU read-side critical sections
761 * that started after call_rcu() was invoked. RCU read-side critical
762 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
765 * Note that all CPUs must agree that the grace period extended beyond
766 * all pre-existing RCU read-side critical section. On systems with more
767 * than one CPU, this means that when "func()" is invoked, each CPU is
768 * guaranteed to have executed a full memory barrier since the end of its
769 * last RCU read-side critical section whose beginning preceded the call
770 * to call_rcu(). It also means that each CPU executing an RCU read-side
771 * critical section that continues beyond the start of "func()" must have
772 * executed a memory barrier after the call_rcu() but before the beginning
773 * of that RCU read-side critical section. Note that these guarantees
774 * include CPUs that are offline, idle, or executing in user mode, as
775 * well as CPUs that are executing in the kernel.
777 * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
778 * resulting RCU callback function "func()", then both CPU A and CPU B are
779 * guaranteed to execute a full memory barrier during the time interval
780 * between the call to call_rcu() and the invocation of "func()" -- even
781 * if CPU A and CPU B are the same CPU (but again only if the system has
782 * more than one CPU).
784 void call_rcu(struct rcu_head *head, rcu_callback_t func)
786 __call_rcu(head, func, rcu_state_p, -1, 0);
788 EXPORT_SYMBOL_GPL(call_rcu);
791 * synchronize_rcu - wait until a grace period has elapsed.
793 * Control will return to the caller some time after a full grace
794 * period has elapsed, in other words after all currently executing RCU
795 * read-side critical sections have completed. Note, however, that
796 * upon return from synchronize_rcu(), the caller might well be executing
797 * concurrently with new RCU read-side critical sections that began while
798 * synchronize_rcu() was waiting. RCU read-side critical sections are
799 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
801 * See the description of synchronize_sched() for more detailed
802 * information on memory-ordering guarantees. However, please note
803 * that -only- the memory-ordering guarantees apply. For example,
804 * synchronize_rcu() is -not- guaranteed to wait on things like code
805 * protected by preempt_disable(), instead, synchronize_rcu() is -only-
806 * guaranteed to wait on RCU read-side critical sections, that is, sections
807 * of code protected by rcu_read_lock().
809 void synchronize_rcu(void)
811 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
812 lock_is_held(&rcu_lock_map) ||
813 lock_is_held(&rcu_sched_lock_map),
814 "Illegal synchronize_rcu() in RCU read-side critical section");
815 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
817 if (rcu_gp_is_expedited())
818 synchronize_rcu_expedited();
820 wait_rcu_gp(call_rcu);
822 EXPORT_SYMBOL_GPL(synchronize_rcu);
825 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
827 * Note that this primitive does not necessarily wait for an RCU grace period
828 * to complete. For example, if there are no RCU callbacks queued anywhere
829 * in the system, then rcu_barrier() is within its rights to return
830 * immediately, without waiting for anything, much less an RCU grace period.
832 void rcu_barrier(void)
834 _rcu_barrier(rcu_state_p);
836 EXPORT_SYMBOL_GPL(rcu_barrier);
839 * Initialize preemptible RCU's state structures.
841 static void __init __rcu_init_preempt(void)
843 rcu_init_one(rcu_state_p);
847 * Check for a task exiting while in a preemptible-RCU read-side
848 * critical section, clean up if so. No need to issue warnings,
849 * as debug_check_no_locks_held() already does this if lockdep
854 struct task_struct *t = current;
856 if (likely(list_empty(¤t->rcu_node_entry)))
858 t->rcu_read_lock_nesting = 1;
860 t->rcu_read_unlock_special.b.blocked = true;
865 * Dump the blocked-tasks state, but limit the list dump to the
866 * specified number of elements.
869 dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, int ncheck)
873 struct list_head *lhp;
875 struct rcu_data *rdp;
876 struct rcu_node *rnp1;
878 raw_lockdep_assert_held_rcu_node(rnp);
879 pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
880 __func__, rnp->grplo, rnp->grphi, rnp->level,
881 (long)rnp->gp_seq, (long)rnp->completedqs);
882 for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
883 pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n",
884 __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext);
885 pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n",
886 __func__, rnp->gp_tasks, rnp->boost_tasks, rnp->exp_tasks);
887 pr_info("%s: ->blkd_tasks", __func__);
889 list_for_each(lhp, &rnp->blkd_tasks) {
895 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
896 rdp = per_cpu_ptr(rsp->rda, cpu);
897 onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
898 pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n",
900 (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
901 (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
905 #else /* #ifdef CONFIG_PREEMPT_RCU */
907 static struct rcu_state *const rcu_state_p = &rcu_sched_state;
910 * Tell them what RCU they are running.
912 static void __init rcu_bootup_announce(void)
914 pr_info("Hierarchical RCU implementation.\n");
915 rcu_bootup_announce_oddness();
919 * Because preemptible RCU does not exist, we never have to check for
920 * CPUs being in quiescent states.
922 static void rcu_preempt_note_context_switch(bool preempt)
927 * Because preemptible RCU does not exist, there are never any preempted
930 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
936 * Because there is no preemptible RCU, there can be no readers blocked.
938 static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
944 * Because preemptible RCU does not exist, we never have to check for
945 * tasks blocked within RCU read-side critical sections.
947 static void rcu_print_detail_task_stall(struct rcu_state *rsp)
952 * Because preemptible RCU does not exist, we never have to check for
953 * tasks blocked within RCU read-side critical sections.
955 static int rcu_print_task_stall(struct rcu_node *rnp)
961 * Because preemptible RCU does not exist, we never have to check for
962 * tasks blocked within RCU read-side critical sections that are
963 * blocking the current expedited grace period.
965 static int rcu_print_task_exp_stall(struct rcu_node *rnp)
971 * Because there is no preemptible RCU, there can be no readers blocked,
972 * so there is no need to check for blocked tasks. So check only for
973 * bogus qsmask values.
976 rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp)
978 WARN_ON_ONCE(rnp->qsmask);
982 * Because preemptible RCU does not exist, it never has any callbacks
985 static void rcu_preempt_check_callbacks(void)
990 * Because preemptible RCU does not exist, rcu_barrier() is just
991 * another name for rcu_barrier_sched().
993 void rcu_barrier(void)
997 EXPORT_SYMBOL_GPL(rcu_barrier);
1000 * Because preemptible RCU does not exist, it need not be initialized.
1002 static void __init __rcu_init_preempt(void)
1007 * Because preemptible RCU does not exist, tasks cannot possibly exit
1008 * while in preemptible RCU read-side critical sections.
1015 * Dump the guaranteed-empty blocked-tasks state. Trust but verify.
1018 dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, int ncheck)
1020 WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));
1023 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
1025 #ifdef CONFIG_RCU_BOOST
1027 static void rcu_wake_cond(struct task_struct *t, int status)
1030 * If the thread is yielding, only wake it when this
1031 * is invoked from idle
1033 if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
1038 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
1039 * or ->boost_tasks, advancing the pointer to the next task in the
1040 * ->blkd_tasks list.
1042 * Note that irqs must be enabled: boosting the task can block.
1043 * Returns 1 if there are more tasks needing to be boosted.
1045 static int rcu_boost(struct rcu_node *rnp)
1047 unsigned long flags;
1048 struct task_struct *t;
1049 struct list_head *tb;
1051 if (READ_ONCE(rnp->exp_tasks) == NULL &&
1052 READ_ONCE(rnp->boost_tasks) == NULL)
1053 return 0; /* Nothing left to boost. */
1055 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1058 * Recheck under the lock: all tasks in need of boosting
1059 * might exit their RCU read-side critical sections on their own.
1061 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
1062 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1067 * Preferentially boost tasks blocking expedited grace periods.
1068 * This cannot starve the normal grace periods because a second
1069 * expedited grace period must boost all blocked tasks, including
1070 * those blocking the pre-existing normal grace period.
1072 if (rnp->exp_tasks != NULL)
1073 tb = rnp->exp_tasks;
1075 tb = rnp->boost_tasks;
1078 * We boost task t by manufacturing an rt_mutex that appears to
1079 * be held by task t. We leave a pointer to that rt_mutex where
1080 * task t can find it, and task t will release the mutex when it
1081 * exits its outermost RCU read-side critical section. Then
1082 * simply acquiring this artificial rt_mutex will boost task
1083 * t's priority. (Thanks to tglx for suggesting this approach!)
1085 * Note that task t must acquire rnp->lock to remove itself from
1086 * the ->blkd_tasks list, which it will do from exit() if from
1087 * nowhere else. We therefore are guaranteed that task t will
1088 * stay around at least until we drop rnp->lock. Note that
1089 * rnp->lock also resolves races between our priority boosting
1090 * and task t's exiting its outermost RCU read-side critical
1093 t = container_of(tb, struct task_struct, rcu_node_entry);
1094 rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
1095 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1096 /* Lock only for side effect: boosts task t's priority. */
1097 rt_mutex_lock(&rnp->boost_mtx);
1098 rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
1100 return READ_ONCE(rnp->exp_tasks) != NULL ||
1101 READ_ONCE(rnp->boost_tasks) != NULL;
1105 * Priority-boosting kthread, one per leaf rcu_node.
1107 static int rcu_boost_kthread(void *arg)
1109 struct rcu_node *rnp = (struct rcu_node *)arg;
1113 trace_rcu_utilization(TPS("Start boost kthread@init"));
1115 rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1116 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1117 rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1118 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1119 rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1120 more2boost = rcu_boost(rnp);
1126 rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1127 trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1128 schedule_timeout_interruptible(2);
1129 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1134 trace_rcu_utilization(TPS("End boost kthread@notreached"));
1139 * Check to see if it is time to start boosting RCU readers that are
1140 * blocking the current grace period, and, if so, tell the per-rcu_node
1141 * kthread to start boosting them. If there is an expedited grace
1142 * period in progress, it is always time to boost.
1144 * The caller must hold rnp->lock, which this function releases.
1145 * The ->boost_kthread_task is immortal, so we don't need to worry
1146 * about it going away.
1148 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1149 __releases(rnp->lock)
1151 struct task_struct *t;
1153 raw_lockdep_assert_held_rcu_node(rnp);
1154 if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1155 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1158 if (rnp->exp_tasks != NULL ||
1159 (rnp->gp_tasks != NULL &&
1160 rnp->boost_tasks == NULL &&
1162 ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1163 if (rnp->exp_tasks == NULL)
1164 rnp->boost_tasks = rnp->gp_tasks;
1165 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1166 t = rnp->boost_kthread_task;
1168 rcu_wake_cond(t, rnp->boost_kthread_status);
1170 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1175 * Wake up the per-CPU kthread to invoke RCU callbacks.
1177 static void invoke_rcu_callbacks_kthread(void)
1179 unsigned long flags;
1181 local_irq_save(flags);
1182 __this_cpu_write(rcu_cpu_has_work, 1);
1183 if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
1184 current != __this_cpu_read(rcu_cpu_kthread_task)) {
1185 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
1186 __this_cpu_read(rcu_cpu_kthread_status));
1188 local_irq_restore(flags);
1192 * Is the current CPU running the RCU-callbacks kthread?
1193 * Caller must have preemption disabled.
1195 static bool rcu_is_callbacks_kthread(void)
1197 return __this_cpu_read(rcu_cpu_kthread_task) == current;
1200 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1203 * Do priority-boost accounting for the start of a new grace period.
1205 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1207 rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1211 * Create an RCU-boost kthread for the specified node if one does not
1212 * already exist. We only create this kthread for preemptible RCU.
1213 * Returns zero if all is well, a negated errno otherwise.
1215 static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
1216 struct rcu_node *rnp)
1218 int rnp_index = rnp - &rsp->node[0];
1219 unsigned long flags;
1220 struct sched_param sp;
1221 struct task_struct *t;
1223 if (rcu_state_p != rsp)
1226 if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
1230 if (rnp->boost_kthread_task != NULL)
1232 t = kthread_create(rcu_boost_kthread, (void *)rnp,
1233 "rcub/%d", rnp_index);
1236 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1237 rnp->boost_kthread_task = t;
1238 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1239 sp.sched_priority = kthread_prio;
1240 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1241 wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1245 static void rcu_kthread_do_work(void)
1247 rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
1248 rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
1249 rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
1252 static void rcu_cpu_kthread_setup(unsigned int cpu)
1254 struct sched_param sp;
1256 sp.sched_priority = kthread_prio;
1257 sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
1260 static void rcu_cpu_kthread_park(unsigned int cpu)
1262 per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1265 static int rcu_cpu_kthread_should_run(unsigned int cpu)
1267 return __this_cpu_read(rcu_cpu_has_work);
1271 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
1272 * RCU softirq used in flavors and configurations of RCU that do not
1273 * support RCU priority boosting.
1275 static void rcu_cpu_kthread(unsigned int cpu)
1277 unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
1278 char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
1281 for (spincnt = 0; spincnt < 10; spincnt++) {
1282 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1284 *statusp = RCU_KTHREAD_RUNNING;
1285 this_cpu_inc(rcu_cpu_kthread_loops);
1286 local_irq_disable();
1291 rcu_kthread_do_work();
1294 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1295 *statusp = RCU_KTHREAD_WAITING;
1299 *statusp = RCU_KTHREAD_YIELDING;
1300 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1301 schedule_timeout_interruptible(2);
1302 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1303 *statusp = RCU_KTHREAD_WAITING;
1307 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1308 * served by the rcu_node in question. The CPU hotplug lock is still
1309 * held, so the value of rnp->qsmaskinit will be stable.
1311 * We don't include outgoingcpu in the affinity set, use -1 if there is
1312 * no outgoing CPU. If there are no CPUs left in the affinity set,
1313 * this function allows the kthread to execute on any CPU.
1315 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1317 struct task_struct *t = rnp->boost_kthread_task;
1318 unsigned long mask = rcu_rnp_online_cpus(rnp);
1324 if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1326 for_each_leaf_node_possible_cpu(rnp, cpu)
1327 if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
1329 cpumask_set_cpu(cpu, cm);
1330 if (cpumask_weight(cm) == 0)
1332 set_cpus_allowed_ptr(t, cm);
1333 free_cpumask_var(cm);
1336 static struct smp_hotplug_thread rcu_cpu_thread_spec = {
1337 .store = &rcu_cpu_kthread_task,
1338 .thread_should_run = rcu_cpu_kthread_should_run,
1339 .thread_fn = rcu_cpu_kthread,
1340 .thread_comm = "rcuc/%u",
1341 .setup = rcu_cpu_kthread_setup,
1342 .park = rcu_cpu_kthread_park,
1346 * Spawn boost kthreads -- called as soon as the scheduler is running.
1348 static void __init rcu_spawn_boost_kthreads(void)
1350 struct rcu_node *rnp;
1353 for_each_possible_cpu(cpu)
1354 per_cpu(rcu_cpu_has_work, cpu) = 0;
1355 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
1356 rcu_for_each_leaf_node(rcu_state_p, rnp)
1357 (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1360 static void rcu_prepare_kthreads(int cpu)
1362 struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
1363 struct rcu_node *rnp = rdp->mynode;
1365 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1366 if (rcu_scheduler_fully_active)
1367 (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1370 #else /* #ifdef CONFIG_RCU_BOOST */
1372 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1373 __releases(rnp->lock)
1375 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1378 static void invoke_rcu_callbacks_kthread(void)
1383 static bool rcu_is_callbacks_kthread(void)
1388 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1392 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1396 static void __init rcu_spawn_boost_kthreads(void)
1400 static void rcu_prepare_kthreads(int cpu)
1404 #endif /* #else #ifdef CONFIG_RCU_BOOST */
1406 #if !defined(CONFIG_RCU_FAST_NO_HZ)
1409 * Check to see if any future RCU-related work will need to be done
1410 * by the current CPU, even if none need be done immediately, returning
1411 * 1 if so. This function is part of the RCU implementation; it is -not-
1412 * an exported member of the RCU API.
1414 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1415 * any flavor of RCU.
1417 int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1419 *nextevt = KTIME_MAX;
1420 return rcu_cpu_has_callbacks(NULL);
1424 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1427 static void rcu_cleanup_after_idle(void)
1432 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1435 static void rcu_prepare_for_idle(void)
1440 * Don't bother keeping a running count of the number of RCU callbacks
1441 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1443 static void rcu_idle_count_callbacks_posted(void)
1447 #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1450 * This code is invoked when a CPU goes idle, at which point we want
1451 * to have the CPU do everything required for RCU so that it can enter
1452 * the energy-efficient dyntick-idle mode. This is handled by a
1453 * state machine implemented by rcu_prepare_for_idle() below.
1455 * The following three proprocessor symbols control this state machine:
1457 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1458 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1459 * is sized to be roughly one RCU grace period. Those energy-efficiency
1460 * benchmarkers who might otherwise be tempted to set this to a large
1461 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1462 * system. And if you are -that- concerned about energy efficiency,
1463 * just power the system down and be done with it!
1464 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1465 * permitted to sleep in dyntick-idle mode with only lazy RCU
1466 * callbacks pending. Setting this too high can OOM your system.
1468 * The values below work well in practice. If future workloads require
1469 * adjustment, they can be converted into kernel config parameters, though
1470 * making the state machine smarter might be a better option.
1472 #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1473 #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1475 static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
1476 module_param(rcu_idle_gp_delay, int, 0644);
1477 static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
1478 module_param(rcu_idle_lazy_gp_delay, int, 0644);
1481 * Try to advance callbacks for all flavors of RCU on the current CPU, but
1482 * only if it has been awhile since the last time we did so. Afterwards,
1483 * if there are any callbacks ready for immediate invocation, return true.
1485 static bool __maybe_unused rcu_try_advance_all_cbs(void)
1487 bool cbs_ready = false;
1488 struct rcu_data *rdp;
1489 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1490 struct rcu_node *rnp;
1491 struct rcu_state *rsp;
1493 /* Exit early if we advanced recently. */
1494 if (jiffies == rdtp->last_advance_all)
1496 rdtp->last_advance_all = jiffies;
1498 for_each_rcu_flavor(rsp) {
1499 rdp = this_cpu_ptr(rsp->rda);
1503 * Don't bother checking unless a grace period has
1504 * completed since we last checked and there are
1505 * callbacks not yet ready to invoke.
1507 if ((rcu_seq_completed_gp(rdp->gp_seq,
1508 rcu_seq_current(&rnp->gp_seq)) ||
1509 unlikely(READ_ONCE(rdp->gpwrap))) &&
1510 rcu_segcblist_pend_cbs(&rdp->cblist))
1511 note_gp_changes(rsp, rdp);
1513 if (rcu_segcblist_ready_cbs(&rdp->cblist))
1520 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1521 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1522 * caller to set the timeout based on whether or not there are non-lazy
1525 * The caller must have disabled interrupts.
1527 int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1529 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1532 lockdep_assert_irqs_disabled();
1534 /* Snapshot to detect later posting of non-lazy callback. */
1535 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1537 /* If no callbacks, RCU doesn't need the CPU. */
1538 if (!rcu_cpu_has_callbacks(&rdtp->all_lazy)) {
1539 *nextevt = KTIME_MAX;
1543 /* Attempt to advance callbacks. */
1544 if (rcu_try_advance_all_cbs()) {
1545 /* Some ready to invoke, so initiate later invocation. */
1549 rdtp->last_accelerate = jiffies;
1551 /* Request timer delay depending on laziness, and round. */
1552 if (!rdtp->all_lazy) {
1553 dj = round_up(rcu_idle_gp_delay + jiffies,
1554 rcu_idle_gp_delay) - jiffies;
1556 dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1558 *nextevt = basemono + dj * TICK_NSEC;
1563 * Prepare a CPU for idle from an RCU perspective. The first major task
1564 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1565 * The second major task is to check to see if a non-lazy callback has
1566 * arrived at a CPU that previously had only lazy callbacks. The third
1567 * major task is to accelerate (that is, assign grace-period numbers to)
1568 * any recently arrived callbacks.
1570 * The caller must have disabled interrupts.
1572 static void rcu_prepare_for_idle(void)
1575 struct rcu_data *rdp;
1576 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1577 struct rcu_node *rnp;
1578 struct rcu_state *rsp;
1581 lockdep_assert_irqs_disabled();
1582 if (rcu_is_nocb_cpu(smp_processor_id()))
1585 /* Handle nohz enablement switches conservatively. */
1586 tne = READ_ONCE(tick_nohz_active);
1587 if (tne != rdtp->tick_nohz_enabled_snap) {
1588 if (rcu_cpu_has_callbacks(NULL))
1589 invoke_rcu_core(); /* force nohz to see update. */
1590 rdtp->tick_nohz_enabled_snap = tne;
1597 * If a non-lazy callback arrived at a CPU having only lazy
1598 * callbacks, invoke RCU core for the side-effect of recalculating
1599 * idle duration on re-entry to idle.
1601 if (rdtp->all_lazy &&
1602 rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
1603 rdtp->all_lazy = false;
1604 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1610 * If we have not yet accelerated this jiffy, accelerate all
1611 * callbacks on this CPU.
1613 if (rdtp->last_accelerate == jiffies)
1615 rdtp->last_accelerate = jiffies;
1616 for_each_rcu_flavor(rsp) {
1617 rdp = this_cpu_ptr(rsp->rda);
1618 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1621 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
1622 needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
1623 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
1625 rcu_gp_kthread_wake(rsp);
1630 * Clean up for exit from idle. Attempt to advance callbacks based on
1631 * any grace periods that elapsed while the CPU was idle, and if any
1632 * callbacks are now ready to invoke, initiate invocation.
1634 static void rcu_cleanup_after_idle(void)
1636 lockdep_assert_irqs_disabled();
1637 if (rcu_is_nocb_cpu(smp_processor_id()))
1639 if (rcu_try_advance_all_cbs())
1644 * Keep a running count of the number of non-lazy callbacks posted
1645 * on this CPU. This running counter (which is never decremented) allows
1646 * rcu_prepare_for_idle() to detect when something out of the idle loop
1647 * posts a callback, even if an equal number of callbacks are invoked.
1648 * Of course, callbacks should only be posted from within a trace event
1649 * designed to be called from idle or from within RCU_NONIDLE().
1651 static void rcu_idle_count_callbacks_posted(void)
1653 __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
1657 * Data for flushing lazy RCU callbacks at OOM time.
1659 static atomic_t oom_callback_count;
1660 static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
1663 * RCU OOM callback -- decrement the outstanding count and deliver the
1664 * wake-up if we are the last one.
1666 static void rcu_oom_callback(struct rcu_head *rhp)
1668 if (atomic_dec_and_test(&oom_callback_count))
1669 wake_up(&oom_callback_wq);
1673 * Post an rcu_oom_notify callback on the current CPU if it has at
1674 * least one lazy callback. This will unnecessarily post callbacks
1675 * to CPUs that already have a non-lazy callback at the end of their
1676 * callback list, but this is an infrequent operation, so accept some
1677 * extra overhead to keep things simple.
1679 static void rcu_oom_notify_cpu(void *unused)
1681 struct rcu_state *rsp;
1682 struct rcu_data *rdp;
1684 for_each_rcu_flavor(rsp) {
1685 rdp = raw_cpu_ptr(rsp->rda);
1686 if (rcu_segcblist_n_lazy_cbs(&rdp->cblist)) {
1687 atomic_inc(&oom_callback_count);
1688 rsp->call(&rdp->oom_head, rcu_oom_callback);
1694 * If low on memory, ensure that each CPU has a non-lazy callback.
1695 * This will wake up CPUs that have only lazy callbacks, in turn
1696 * ensuring that they free up the corresponding memory in a timely manner.
1697 * Because an uncertain amount of memory will be freed in some uncertain
1698 * timeframe, we do not claim to have freed anything.
1700 static int rcu_oom_notify(struct notifier_block *self,
1701 unsigned long notused, void *nfreed)
1705 /* Wait for callbacks from earlier instance to complete. */
1706 wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
1707 smp_mb(); /* Ensure callback reuse happens after callback invocation. */
1710 * Prevent premature wakeup: ensure that all increments happen
1711 * before there is a chance of the counter reaching zero.
1713 atomic_set(&oom_callback_count, 1);
1715 for_each_online_cpu(cpu) {
1716 smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
1717 cond_resched_tasks_rcu_qs();
1720 /* Unconditionally decrement: no need to wake ourselves up. */
1721 atomic_dec(&oom_callback_count);
1726 static struct notifier_block rcu_oom_nb = {
1727 .notifier_call = rcu_oom_notify
1730 static int __init rcu_register_oom_notifier(void)
1732 register_oom_notifier(&rcu_oom_nb);
1735 early_initcall(rcu_register_oom_notifier);
1737 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1739 #ifdef CONFIG_RCU_FAST_NO_HZ
1741 static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1743 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1744 unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
1746 sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1747 rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
1749 rdtp->all_lazy ? 'L' : '.',
1750 rdtp->tick_nohz_enabled_snap ? '.' : 'D');
1753 #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1755 static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1760 #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1762 /* Initiate the stall-info list. */
1763 static void print_cpu_stall_info_begin(void)
1769 * Print out diagnostic information for the specified stalled CPU.
1771 * If the specified CPU is aware of the current RCU grace period
1772 * (flavor specified by rsp), then print the number of scheduling
1773 * clock interrupts the CPU has taken during the time that it has
1774 * been aware. Otherwise, print the number of RCU grace periods
1775 * that this CPU is ignorant of, for example, "1" if the CPU was
1776 * aware of the previous grace period.
1778 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1780 static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1782 unsigned long delta;
1783 char fast_no_hz[72];
1784 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1785 struct rcu_dynticks *rdtp = rdp->dynticks;
1787 unsigned long ticks_value;
1790 * We could be printing a lot while holding a spinlock. Avoid
1791 * triggering hard lockup.
1793 touch_nmi_watchdog();
1795 ticks_value = rcu_seq_ctr(rsp->gp_seq - rdp->gp_seq);
1797 ticks_title = "GPs behind";
1799 ticks_title = "ticks this GP";
1800 ticks_value = rdp->ticks_this_gp;
1802 print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
1803 delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
1804 pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n",
1806 "O."[!!cpu_online(cpu)],
1807 "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
1808 "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
1809 !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
1810 rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
1812 ticks_value, ticks_title,
1813 rcu_dynticks_snap(rdtp) & 0xfff,
1814 rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
1815 rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
1816 READ_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart,
1820 /* Terminate the stall-info list. */
1821 static void print_cpu_stall_info_end(void)
1826 /* Zero ->ticks_this_gp for all flavors of RCU. */
1827 static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1829 rdp->ticks_this_gp = 0;
1830 rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
1833 /* Increment ->ticks_this_gp for all flavors of RCU. */
1834 static void increment_cpu_stall_ticks(void)
1836 struct rcu_state *rsp;
1838 for_each_rcu_flavor(rsp)
1839 raw_cpu_inc(rsp->rda->ticks_this_gp);
1842 #ifdef CONFIG_RCU_NOCB_CPU
1845 * Offload callback processing from the boot-time-specified set of CPUs
1846 * specified by rcu_nocb_mask. For each CPU in the set, there is a
1847 * kthread created that pulls the callbacks from the corresponding CPU,
1848 * waits for a grace period to elapse, and invokes the callbacks.
1849 * The no-CBs CPUs do a wake_up() on their kthread when they insert
1850 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
1851 * has been specified, in which case each kthread actively polls its
1852 * CPU. (Which isn't so great for energy efficiency, but which does
1853 * reduce RCU's overhead on that CPU.)
1855 * This is intended to be used in conjunction with Frederic Weisbecker's
1856 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
1857 * running CPU-bound user-mode computations.
1859 * Offloading of callback processing could also in theory be used as
1860 * an energy-efficiency measure because CPUs with no RCU callbacks
1861 * queued are more aggressive about entering dyntick-idle mode.
1865 /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
1866 static int __init rcu_nocb_setup(char *str)
1868 alloc_bootmem_cpumask_var(&rcu_nocb_mask);
1869 cpulist_parse(str, rcu_nocb_mask);
1872 __setup("rcu_nocbs=", rcu_nocb_setup);
1874 static int __init parse_rcu_nocb_poll(char *arg)
1876 rcu_nocb_poll = true;
1879 early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
1882 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
1885 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
1890 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
1892 return &rnp->nocb_gp_wq[rcu_seq_ctr(rnp->gp_seq) & 0x1];
1895 static void rcu_init_one_nocb(struct rcu_node *rnp)
1897 init_swait_queue_head(&rnp->nocb_gp_wq[0]);
1898 init_swait_queue_head(&rnp->nocb_gp_wq[1]);
1901 /* Is the specified CPU a no-CBs CPU? */
1902 bool rcu_is_nocb_cpu(int cpu)
1904 if (cpumask_available(rcu_nocb_mask))
1905 return cpumask_test_cpu(cpu, rcu_nocb_mask);
1910 * Kick the leader kthread for this NOCB group. Caller holds ->nocb_lock
1911 * and this function releases it.
1913 static void __wake_nocb_leader(struct rcu_data *rdp, bool force,
1914 unsigned long flags)
1915 __releases(rdp->nocb_lock)
1917 struct rcu_data *rdp_leader = rdp->nocb_leader;
1919 lockdep_assert_held(&rdp->nocb_lock);
1920 if (!READ_ONCE(rdp_leader->nocb_kthread)) {
1921 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1924 if (rdp_leader->nocb_leader_sleep || force) {
1925 /* Prior smp_mb__after_atomic() orders against prior enqueue. */
1926 WRITE_ONCE(rdp_leader->nocb_leader_sleep, false);
1927 del_timer(&rdp->nocb_timer);
1928 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1929 smp_mb(); /* ->nocb_leader_sleep before swake_up_one(). */
1930 swake_up_one(&rdp_leader->nocb_wq);
1932 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1937 * Kick the leader kthread for this NOCB group, but caller has not
1940 static void wake_nocb_leader(struct rcu_data *rdp, bool force)
1942 unsigned long flags;
1944 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
1945 __wake_nocb_leader(rdp, force, flags);
1949 * Arrange to wake the leader kthread for this NOCB group at some
1950 * future time when it is safe to do so.
1952 static void wake_nocb_leader_defer(struct rcu_data *rdp, int waketype,
1955 unsigned long flags;
1957 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
1958 if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
1959 mod_timer(&rdp->nocb_timer, jiffies + 1);
1960 WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
1961 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, reason);
1962 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1966 * Does the specified CPU need an RCU callback for the specified flavor
1969 static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
1971 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1973 #ifdef CONFIG_PROVE_RCU
1974 struct rcu_head *rhp;
1975 #endif /* #ifdef CONFIG_PROVE_RCU */
1978 * Check count of all no-CBs callbacks awaiting invocation.
1979 * There needs to be a barrier before this function is called,
1980 * but associated with a prior determination that no more
1981 * callbacks would be posted. In the worst case, the first
1982 * barrier in _rcu_barrier() suffices (but the caller cannot
1983 * necessarily rely on this, not a substitute for the caller
1984 * getting the concurrency design right!). There must also be
1985 * a barrier between the following load an posting of a callback
1986 * (if a callback is in fact needed). This is associated with an
1987 * atomic_inc() in the caller.
1989 ret = atomic_long_read(&rdp->nocb_q_count);
1991 #ifdef CONFIG_PROVE_RCU
1992 rhp = READ_ONCE(rdp->nocb_head);
1994 rhp = READ_ONCE(rdp->nocb_gp_head);
1996 rhp = READ_ONCE(rdp->nocb_follower_head);
1998 /* Having no rcuo kthread but CBs after scheduler starts is bad! */
1999 if (!READ_ONCE(rdp->nocb_kthread) && rhp &&
2000 rcu_scheduler_fully_active) {
2001 /* RCU callback enqueued before CPU first came online??? */
2002 pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
2006 #endif /* #ifdef CONFIG_PROVE_RCU */
2012 * Enqueue the specified string of rcu_head structures onto the specified
2013 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
2014 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
2015 * counts are supplied by rhcount and rhcount_lazy.
2017 * If warranted, also wake up the kthread servicing this CPUs queues.
2019 static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
2020 struct rcu_head *rhp,
2021 struct rcu_head **rhtp,
2022 int rhcount, int rhcount_lazy,
2023 unsigned long flags)
2026 struct rcu_head **old_rhpp;
2027 struct task_struct *t;
2029 /* Enqueue the callback on the nocb list and update counts. */
2030 atomic_long_add(rhcount, &rdp->nocb_q_count);
2031 /* rcu_barrier() relies on ->nocb_q_count add before xchg. */
2032 old_rhpp = xchg(&rdp->nocb_tail, rhtp);
2033 WRITE_ONCE(*old_rhpp, rhp);
2034 atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
2035 smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
2037 /* If we are not being polled and there is a kthread, awaken it ... */
2038 t = READ_ONCE(rdp->nocb_kthread);
2039 if (rcu_nocb_poll || !t) {
2040 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2041 TPS("WakeNotPoll"));
2044 len = atomic_long_read(&rdp->nocb_q_count);
2045 if (old_rhpp == &rdp->nocb_head) {
2046 if (!irqs_disabled_flags(flags)) {
2047 /* ... if queue was empty ... */
2048 wake_nocb_leader(rdp, false);
2049 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2052 wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE,
2053 TPS("WakeEmptyIsDeferred"));
2055 rdp->qlen_last_fqs_check = 0;
2056 } else if (len > rdp->qlen_last_fqs_check + qhimark) {
2057 /* ... or if many callbacks queued. */
2058 if (!irqs_disabled_flags(flags)) {
2059 wake_nocb_leader(rdp, true);
2060 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2063 wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE_FORCE,
2064 TPS("WakeOvfIsDeferred"));
2066 rdp->qlen_last_fqs_check = LONG_MAX / 2;
2068 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
2074 * This is a helper for __call_rcu(), which invokes this when the normal
2075 * callback queue is inoperable. If this is not a no-CBs CPU, this
2076 * function returns failure back to __call_rcu(), which can complain
2079 * Otherwise, this function queues the callback where the corresponding
2080 * "rcuo" kthread can find it.
2082 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2083 bool lazy, unsigned long flags)
2086 if (!rcu_is_nocb_cpu(rdp->cpu))
2088 __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
2089 if (__is_kfree_rcu_offset((unsigned long)rhp->func))
2090 trace_rcu_kfree_callback(rdp->rsp->name, rhp,
2091 (unsigned long)rhp->func,
2092 -atomic_long_read(&rdp->nocb_q_count_lazy),
2093 -atomic_long_read(&rdp->nocb_q_count));
2095 trace_rcu_callback(rdp->rsp->name, rhp,
2096 -atomic_long_read(&rdp->nocb_q_count_lazy),
2097 -atomic_long_read(&rdp->nocb_q_count));
2100 * If called from an extended quiescent state with interrupts
2101 * disabled, invoke the RCU core in order to allow the idle-entry
2102 * deferred-wakeup check to function.
2104 if (irqs_disabled_flags(flags) &&
2105 !rcu_is_watching() &&
2106 cpu_online(smp_processor_id()))
2113 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2116 static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
2117 struct rcu_data *rdp,
2118 unsigned long flags)
2120 lockdep_assert_irqs_disabled();
2121 if (!rcu_is_nocb_cpu(smp_processor_id()))
2122 return false; /* Not NOCBs CPU, caller must migrate CBs. */
2123 __call_rcu_nocb_enqueue(my_rdp, rcu_segcblist_head(&rdp->cblist),
2124 rcu_segcblist_tail(&rdp->cblist),
2125 rcu_segcblist_n_cbs(&rdp->cblist),
2126 rcu_segcblist_n_lazy_cbs(&rdp->cblist), flags);
2127 rcu_segcblist_init(&rdp->cblist);
2128 rcu_segcblist_disable(&rdp->cblist);
2133 * If necessary, kick off a new grace period, and either way wait
2134 * for a subsequent grace period to complete.
2136 static void rcu_nocb_wait_gp(struct rcu_data *rdp)
2140 unsigned long flags;
2142 struct rcu_node *rnp = rdp->mynode;
2144 local_irq_save(flags);
2145 c = rcu_seq_snap(&rdp->rsp->gp_seq);
2146 if (!rdp->gpwrap && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {
2147 local_irq_restore(flags);
2149 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
2150 needwake = rcu_start_this_gp(rnp, rdp, c);
2151 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2153 rcu_gp_kthread_wake(rdp->rsp);
2157 * Wait for the grace period. Do so interruptibly to avoid messing
2158 * up the load average.
2160 trace_rcu_this_gp(rnp, rdp, c, TPS("StartWait"));
2162 swait_event_interruptible_exclusive(
2163 rnp->nocb_gp_wq[rcu_seq_ctr(c) & 0x1],
2164 (d = rcu_seq_done(&rnp->gp_seq, c)));
2167 WARN_ON(signal_pending(current));
2168 trace_rcu_this_gp(rnp, rdp, c, TPS("ResumeWait"));
2170 trace_rcu_this_gp(rnp, rdp, c, TPS("EndWait"));
2171 smp_mb(); /* Ensure that CB invocation happens after GP end. */
2175 * Leaders come here to wait for additional callbacks to show up.
2176 * This function does not return until callbacks appear.
2178 static void nocb_leader_wait(struct rcu_data *my_rdp)
2180 bool firsttime = true;
2181 unsigned long flags;
2183 struct rcu_data *rdp;
2184 struct rcu_head **tail;
2188 /* Wait for callbacks to appear. */
2189 if (!rcu_nocb_poll) {
2190 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, TPS("Sleep"));
2191 swait_event_interruptible_exclusive(my_rdp->nocb_wq,
2192 !READ_ONCE(my_rdp->nocb_leader_sleep));
2193 raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags);
2194 my_rdp->nocb_leader_sleep = true;
2195 WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
2196 del_timer(&my_rdp->nocb_timer);
2197 raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags);
2198 } else if (firsttime) {
2199 firsttime = false; /* Don't drown trace log with "Poll"! */
2200 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, TPS("Poll"));
2204 * Each pass through the following loop checks a follower for CBs.
2205 * We are our own first follower. Any CBs found are moved to
2206 * nocb_gp_head, where they await a grace period.
2209 smp_mb(); /* wakeup and _sleep before ->nocb_head reads. */
2210 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
2211 rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head);
2212 if (!rdp->nocb_gp_head)
2213 continue; /* No CBs here, try next follower. */
2215 /* Move callbacks to wait-for-GP list, which is empty. */
2216 WRITE_ONCE(rdp->nocb_head, NULL);
2217 rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
2221 /* No callbacks? Sleep a bit if polling, and go retry. */
2222 if (unlikely(!gotcbs)) {
2223 WARN_ON(signal_pending(current));
2224 if (rcu_nocb_poll) {
2225 schedule_timeout_interruptible(1);
2227 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
2233 /* Wait for one grace period. */
2234 rcu_nocb_wait_gp(my_rdp);
2236 /* Each pass through the following loop wakes a follower, if needed. */
2237 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
2238 if (!rcu_nocb_poll &&
2239 READ_ONCE(rdp->nocb_head) &&
2240 READ_ONCE(my_rdp->nocb_leader_sleep)) {
2241 raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags);
2242 my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/
2243 raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags);
2245 if (!rdp->nocb_gp_head)
2246 continue; /* No CBs, so no need to wake follower. */
2248 /* Append callbacks to follower's "done" list. */
2249 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
2250 tail = rdp->nocb_follower_tail;
2251 rdp->nocb_follower_tail = rdp->nocb_gp_tail;
2252 *tail = rdp->nocb_gp_head;
2253 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
2254 if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
2255 /* List was empty, so wake up the follower. */
2256 swake_up_one(&rdp->nocb_wq);
2260 /* If we (the leader) don't have CBs, go wait some more. */
2261 if (!my_rdp->nocb_follower_head)
2266 * Followers come here to wait for additional callbacks to show up.
2267 * This function does not return until callbacks appear.
2269 static void nocb_follower_wait(struct rcu_data *rdp)
2272 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("FollowerSleep"));
2273 swait_event_interruptible_exclusive(rdp->nocb_wq,
2274 READ_ONCE(rdp->nocb_follower_head));
2275 if (smp_load_acquire(&rdp->nocb_follower_head)) {
2276 /* ^^^ Ensure CB invocation follows _head test. */
2279 WARN_ON(signal_pending(current));
2280 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeEmpty"));
2285 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
2286 * callbacks queued by the corresponding no-CBs CPU, however, there is
2287 * an optional leader-follower relationship so that the grace-period
2288 * kthreads don't have to do quite so many wakeups.
2290 static int rcu_nocb_kthread(void *arg)
2293 unsigned long flags;
2294 struct rcu_head *list;
2295 struct rcu_head *next;
2296 struct rcu_head **tail;
2297 struct rcu_data *rdp = arg;
2299 /* Each pass through this loop invokes one batch of callbacks */
2301 /* Wait for callbacks. */
2302 if (rdp->nocb_leader == rdp)
2303 nocb_leader_wait(rdp);
2305 nocb_follower_wait(rdp);
2307 /* Pull the ready-to-invoke callbacks onto local list. */
2308 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
2309 list = rdp->nocb_follower_head;
2310 rdp->nocb_follower_head = NULL;
2311 tail = rdp->nocb_follower_tail;
2312 rdp->nocb_follower_tail = &rdp->nocb_follower_head;
2313 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
2315 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeNonEmpty"));
2317 /* Each pass through the following loop invokes a callback. */
2318 trace_rcu_batch_start(rdp->rsp->name,
2319 atomic_long_read(&rdp->nocb_q_count_lazy),
2320 atomic_long_read(&rdp->nocb_q_count), -1);
2324 /* Wait for enqueuing to complete, if needed. */
2325 while (next == NULL && &list->next != tail) {
2326 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2328 schedule_timeout_interruptible(1);
2329 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2333 debug_rcu_head_unqueue(list);
2335 if (__rcu_reclaim(rdp->rsp->name, list))
2339 cond_resched_tasks_rcu_qs();
2342 trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
2343 smp_mb__before_atomic(); /* _add after CB invocation. */
2344 atomic_long_add(-c, &rdp->nocb_q_count);
2345 atomic_long_add(-cl, &rdp->nocb_q_count_lazy);
2350 /* Is a deferred wakeup of rcu_nocb_kthread() required? */
2351 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2353 return READ_ONCE(rdp->nocb_defer_wakeup);
2356 /* Do a deferred wakeup of rcu_nocb_kthread(). */
2357 static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
2359 unsigned long flags;
2362 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
2363 if (!rcu_nocb_need_deferred_wakeup(rdp)) {
2364 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
2367 ndw = READ_ONCE(rdp->nocb_defer_wakeup);
2368 WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
2369 __wake_nocb_leader(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
2370 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake"));
2373 /* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
2374 static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
2376 struct rcu_data *rdp = from_timer(rdp, t, nocb_timer);
2378 do_nocb_deferred_wakeup_common(rdp);
2382 * Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
2383 * This means we do an inexact common-case check. Note that if
2384 * we miss, ->nocb_timer will eventually clean things up.
2386 static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2388 if (rcu_nocb_need_deferred_wakeup(rdp))
2389 do_nocb_deferred_wakeup_common(rdp);
2392 void __init rcu_init_nohz(void)
2395 bool need_rcu_nocb_mask = false;
2396 struct rcu_state *rsp;
2398 #if defined(CONFIG_NO_HZ_FULL)
2399 if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
2400 need_rcu_nocb_mask = true;
2401 #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2403 if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) {
2404 if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
2405 pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
2409 if (!cpumask_available(rcu_nocb_mask))
2412 #if defined(CONFIG_NO_HZ_FULL)
2413 if (tick_nohz_full_running)
2414 cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
2415 #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2417 if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
2418 pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
2419 cpumask_and(rcu_nocb_mask, cpu_possible_mask,
2422 if (cpumask_empty(rcu_nocb_mask))
2423 pr_info("\tOffload RCU callbacks from CPUs: (none).\n");
2425 pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
2426 cpumask_pr_args(rcu_nocb_mask));
2428 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
2430 for_each_rcu_flavor(rsp) {
2431 for_each_cpu(cpu, rcu_nocb_mask)
2432 init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu));
2433 rcu_organize_nocb_kthreads(rsp);
2437 /* Initialize per-rcu_data variables for no-CBs CPUs. */
2438 static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2440 rdp->nocb_tail = &rdp->nocb_head;
2441 init_swait_queue_head(&rdp->nocb_wq);
2442 rdp->nocb_follower_tail = &rdp->nocb_follower_head;
2443 raw_spin_lock_init(&rdp->nocb_lock);
2444 timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
2448 * If the specified CPU is a no-CBs CPU that does not already have its
2449 * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are
2450 * brought online out of order, this can require re-organizing the
2451 * leader-follower relationships.
2453 static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu)
2455 struct rcu_data *rdp;
2456 struct rcu_data *rdp_last;
2457 struct rcu_data *rdp_old_leader;
2458 struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu);
2459 struct task_struct *t;
2462 * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
2463 * then nothing to do.
2465 if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread)
2468 /* If we didn't spawn the leader first, reorganize! */
2469 rdp_old_leader = rdp_spawn->nocb_leader;
2470 if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) {
2472 rdp = rdp_old_leader;
2474 rdp->nocb_leader = rdp_spawn;
2475 if (rdp_last && rdp != rdp_spawn)
2476 rdp_last->nocb_next_follower = rdp;
2477 if (rdp == rdp_spawn) {
2478 rdp = rdp->nocb_next_follower;
2481 rdp = rdp->nocb_next_follower;
2482 rdp_last->nocb_next_follower = NULL;
2485 rdp_spawn->nocb_next_follower = rdp_old_leader;
2488 /* Spawn the kthread for this CPU and RCU flavor. */
2489 t = kthread_run(rcu_nocb_kthread, rdp_spawn,
2490 "rcuo%c/%d", rsp->abbr, cpu);
2492 WRITE_ONCE(rdp_spawn->nocb_kthread, t);
2496 * If the specified CPU is a no-CBs CPU that does not already have its
2497 * rcuo kthreads, spawn them.
2499 static void rcu_spawn_all_nocb_kthreads(int cpu)
2501 struct rcu_state *rsp;
2503 if (rcu_scheduler_fully_active)
2504 for_each_rcu_flavor(rsp)
2505 rcu_spawn_one_nocb_kthread(rsp, cpu);
2509 * Once the scheduler is running, spawn rcuo kthreads for all online
2510 * no-CBs CPUs. This assumes that the early_initcall()s happen before
2511 * non-boot CPUs come online -- if this changes, we will need to add
2512 * some mutual exclusion.
2514 static void __init rcu_spawn_nocb_kthreads(void)
2518 for_each_online_cpu(cpu)
2519 rcu_spawn_all_nocb_kthreads(cpu);
2522 /* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */
2523 static int rcu_nocb_leader_stride = -1;
2524 module_param(rcu_nocb_leader_stride, int, 0444);
2527 * Initialize leader-follower relationships for all no-CBs CPU.
2529 static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp)
2532 int ls = rcu_nocb_leader_stride;
2533 int nl = 0; /* Next leader. */
2534 struct rcu_data *rdp;
2535 struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */
2536 struct rcu_data *rdp_prev = NULL;
2538 if (!cpumask_available(rcu_nocb_mask))
2541 ls = int_sqrt(nr_cpu_ids);
2542 rcu_nocb_leader_stride = ls;
2546 * Each pass through this loop sets up one rcu_data structure.
2547 * Should the corresponding CPU come online in the future, then
2548 * we will spawn the needed set of rcu_nocb_kthread() kthreads.
2550 for_each_cpu(cpu, rcu_nocb_mask) {
2551 rdp = per_cpu_ptr(rsp->rda, cpu);
2552 if (rdp->cpu >= nl) {
2553 /* New leader, set up for followers & next leader. */
2554 nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
2555 rdp->nocb_leader = rdp;
2558 /* Another follower, link to previous leader. */
2559 rdp->nocb_leader = rdp_leader;
2560 rdp_prev->nocb_next_follower = rdp;
2566 /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2567 static bool init_nocb_callback_list(struct rcu_data *rdp)
2569 if (!rcu_is_nocb_cpu(rdp->cpu))
2572 /* If there are early-boot callbacks, move them to nocb lists. */
2573 if (!rcu_segcblist_empty(&rdp->cblist)) {
2574 rdp->nocb_head = rcu_segcblist_head(&rdp->cblist);
2575 rdp->nocb_tail = rcu_segcblist_tail(&rdp->cblist);
2576 atomic_long_set(&rdp->nocb_q_count,
2577 rcu_segcblist_n_cbs(&rdp->cblist));
2578 atomic_long_set(&rdp->nocb_q_count_lazy,
2579 rcu_segcblist_n_lazy_cbs(&rdp->cblist));
2580 rcu_segcblist_init(&rdp->cblist);
2582 rcu_segcblist_disable(&rdp->cblist);
2586 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
2588 static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
2590 WARN_ON_ONCE(1); /* Should be dead code. */
2594 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
2598 static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
2603 static void rcu_init_one_nocb(struct rcu_node *rnp)
2607 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2608 bool lazy, unsigned long flags)
2613 static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
2614 struct rcu_data *rdp,
2615 unsigned long flags)
2620 static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2624 static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2629 static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2633 static void rcu_spawn_all_nocb_kthreads(int cpu)
2637 static void __init rcu_spawn_nocb_kthreads(void)
2641 static bool init_nocb_callback_list(struct rcu_data *rdp)
2646 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2649 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
2650 * grace-period kthread will do force_quiescent_state() processing?
2651 * The idea is to avoid waking up RCU core processing on such a
2652 * CPU unless the grace period has extended for too long.
2654 * This code relies on the fact that all NO_HZ_FULL CPUs are also
2655 * CONFIG_RCU_NOCB_CPU CPUs.
2657 static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
2659 #ifdef CONFIG_NO_HZ_FULL
2660 if (tick_nohz_full_cpu(smp_processor_id()) &&
2661 (!rcu_gp_in_progress(rsp) ||
2662 ULONG_CMP_LT(jiffies, READ_ONCE(rsp->gp_start) + HZ)))
2664 #endif /* #ifdef CONFIG_NO_HZ_FULL */
2669 * Bind the RCU grace-period kthreads to the housekeeping CPU.
2671 static void rcu_bind_gp_kthread(void)
2673 if (!tick_nohz_full_enabled())
2675 housekeeping_affine(current, HK_FLAG_RCU);
2678 /* Record the current task on dyntick-idle entry. */
2679 static void rcu_dynticks_task_enter(void)
2681 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2682 WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
2683 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
2686 /* Record no current task on dyntick-idle exit. */
2687 static void rcu_dynticks_task_exit(void)
2689 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2690 WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
2691 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */