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, write to the Free Software
18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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/smpboot.h>
31 #include "../time/tick-internal.h"
33 #define RCU_KTHREAD_PRIO 1
35 #ifdef CONFIG_RCU_BOOST
36 #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
38 #define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
41 #ifdef CONFIG_RCU_NOCB_CPU
42 static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
43 static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */
44 static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
45 static char __initdata nocb_buf[NR_CPUS * 5];
46 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
49 * Check the RCU kernel configuration parameters and print informative
50 * messages about anything out of the ordinary. If you like #ifdef, you
51 * will love this function.
53 static void __init rcu_bootup_announce_oddness(void)
55 #ifdef CONFIG_RCU_TRACE
56 pr_info("\tRCU debugfs-based tracing is enabled.\n");
58 #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
59 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
62 #ifdef CONFIG_RCU_FANOUT_EXACT
63 pr_info("\tHierarchical RCU autobalancing is disabled.\n");
65 #ifdef CONFIG_RCU_FAST_NO_HZ
66 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
68 #ifdef CONFIG_PROVE_RCU
69 pr_info("\tRCU lockdep checking is enabled.\n");
71 #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
72 pr_info("\tRCU torture testing starts during boot.\n");
74 #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
75 pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n");
77 #if defined(CONFIG_RCU_CPU_STALL_INFO)
78 pr_info("\tAdditional per-CPU info printed with stalls.\n");
80 #if NUM_RCU_LVL_4 != 0
81 pr_info("\tFour-level hierarchy is enabled.\n");
83 if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
84 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
85 if (nr_cpu_ids != NR_CPUS)
86 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
87 #ifdef CONFIG_RCU_NOCB_CPU
88 #ifndef CONFIG_RCU_NOCB_CPU_NONE
89 if (!have_rcu_nocb_mask) {
90 zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
91 have_rcu_nocb_mask = true;
93 #ifdef CONFIG_RCU_NOCB_CPU_ZERO
94 pr_info("\tOffload RCU callbacks from CPU 0\n");
95 cpumask_set_cpu(0, rcu_nocb_mask);
96 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
97 #ifdef CONFIG_RCU_NOCB_CPU_ALL
98 pr_info("\tOffload RCU callbacks from all CPUs\n");
99 cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
100 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
101 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
102 if (have_rcu_nocb_mask) {
103 if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
104 pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
105 cpumask_and(rcu_nocb_mask, cpu_possible_mask,
108 cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
109 pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
111 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
113 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
116 #ifdef CONFIG_TREE_PREEMPT_RCU
118 RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
119 static struct rcu_state *rcu_state = &rcu_preempt_state;
121 static int rcu_preempted_readers_exp(struct rcu_node *rnp);
124 * Tell them what RCU they are running.
126 static void __init rcu_bootup_announce(void)
128 pr_info("Preemptible hierarchical RCU implementation.\n");
129 rcu_bootup_announce_oddness();
133 * Return the number of RCU-preempt batches processed thus far
134 * for debug and statistics.
136 long rcu_batches_completed_preempt(void)
138 return rcu_preempt_state.completed;
140 EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
143 * Return the number of RCU batches processed thus far for debug & stats.
145 long rcu_batches_completed(void)
147 return rcu_batches_completed_preempt();
149 EXPORT_SYMBOL_GPL(rcu_batches_completed);
152 * Force a quiescent state for preemptible RCU.
154 void rcu_force_quiescent_state(void)
156 force_quiescent_state(&rcu_preempt_state);
158 EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
161 * Record a preemptible-RCU quiescent state for the specified CPU. Note
162 * that this just means that the task currently running on the CPU is
163 * not in a quiescent state. There might be any number of tasks blocked
164 * while in an RCU read-side critical section.
166 * Unlike the other rcu_*_qs() functions, callers to this function
167 * must disable irqs in order to protect the assignment to
168 * ->rcu_read_unlock_special.
170 static void rcu_preempt_qs(int cpu)
172 struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
174 if (rdp->passed_quiesce == 0)
175 trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs"));
176 rdp->passed_quiesce = 1;
177 current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
181 * We have entered the scheduler, and the current task might soon be
182 * context-switched away from. If this task is in an RCU read-side
183 * critical section, we will no longer be able to rely on the CPU to
184 * record that fact, so we enqueue the task on the blkd_tasks list.
185 * The task will dequeue itself when it exits the outermost enclosing
186 * RCU read-side critical section. Therefore, the current grace period
187 * cannot be permitted to complete until the blkd_tasks list entries
188 * predating the current grace period drain, in other words, until
189 * rnp->gp_tasks becomes NULL.
191 * Caller must disable preemption.
193 static void rcu_preempt_note_context_switch(int cpu)
195 struct task_struct *t = current;
197 struct rcu_data *rdp;
198 struct rcu_node *rnp;
200 if (t->rcu_read_lock_nesting > 0 &&
201 (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
203 /* Possibly blocking in an RCU read-side critical section. */
204 rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
206 raw_spin_lock_irqsave(&rnp->lock, flags);
207 smp_mb__after_unlock_lock();
208 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
209 t->rcu_blocked_node = rnp;
212 * If this CPU has already checked in, then this task
213 * will hold up the next grace period rather than the
214 * current grace period. Queue the task accordingly.
215 * If the task is queued for the current grace period
216 * (i.e., this CPU has not yet passed through a quiescent
217 * state for the current grace period), then as long
218 * as that task remains queued, the current grace period
219 * cannot end. Note that there is some uncertainty as
220 * to exactly when the current grace period started.
221 * We take a conservative approach, which can result
222 * in unnecessarily waiting on tasks that started very
223 * slightly after the current grace period began. C'est
226 * But first, note that the current CPU must still be
229 WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
230 WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
231 if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
232 list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
233 rnp->gp_tasks = &t->rcu_node_entry;
234 #ifdef CONFIG_RCU_BOOST
235 if (rnp->boost_tasks != NULL)
236 rnp->boost_tasks = rnp->gp_tasks;
237 #endif /* #ifdef CONFIG_RCU_BOOST */
239 list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
240 if (rnp->qsmask & rdp->grpmask)
241 rnp->gp_tasks = &t->rcu_node_entry;
243 trace_rcu_preempt_task(rdp->rsp->name,
245 (rnp->qsmask & rdp->grpmask)
248 raw_spin_unlock_irqrestore(&rnp->lock, flags);
249 } else if (t->rcu_read_lock_nesting < 0 &&
250 t->rcu_read_unlock_special) {
253 * Complete exit from RCU read-side critical section on
254 * behalf of preempted instance of __rcu_read_unlock().
256 rcu_read_unlock_special(t);
260 * Either we were not in an RCU read-side critical section to
261 * begin with, or we have now recorded that critical section
262 * globally. Either way, we can now note a quiescent state
263 * for this CPU. Again, if we were in an RCU read-side critical
264 * section, and if that critical section was blocking the current
265 * grace period, then the fact that the task has been enqueued
266 * means that we continue to block the current grace period.
268 local_irq_save(flags);
270 local_irq_restore(flags);
274 * Check for preempted RCU readers blocking the current grace period
275 * for the specified rcu_node structure. If the caller needs a reliable
276 * answer, it must hold the rcu_node's ->lock.
278 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
280 return rnp->gp_tasks != NULL;
284 * Record a quiescent state for all tasks that were previously queued
285 * on the specified rcu_node structure and that were blocking the current
286 * RCU grace period. The caller must hold the specified rnp->lock with
287 * irqs disabled, and this lock is released upon return, but irqs remain
290 static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
291 __releases(rnp->lock)
294 struct rcu_node *rnp_p;
296 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
297 raw_spin_unlock_irqrestore(&rnp->lock, flags);
298 return; /* Still need more quiescent states! */
304 * Either there is only one rcu_node in the tree,
305 * or tasks were kicked up to root rcu_node due to
306 * CPUs going offline.
308 rcu_report_qs_rsp(&rcu_preempt_state, flags);
312 /* Report up the rest of the hierarchy. */
314 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
315 raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */
316 smp_mb__after_unlock_lock();
317 rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
321 * Advance a ->blkd_tasks-list pointer to the next entry, instead
322 * returning NULL if at the end of the list.
324 static struct list_head *rcu_next_node_entry(struct task_struct *t,
325 struct rcu_node *rnp)
327 struct list_head *np;
329 np = t->rcu_node_entry.next;
330 if (np == &rnp->blkd_tasks)
336 * Handle special cases during rcu_read_unlock(), such as needing to
337 * notify RCU core processing or task having blocked during the RCU
338 * read-side critical section.
340 void rcu_read_unlock_special(struct task_struct *t)
346 struct list_head *np;
347 #ifdef CONFIG_RCU_BOOST
348 struct rt_mutex *rbmp = NULL;
349 #endif /* #ifdef CONFIG_RCU_BOOST */
350 struct rcu_node *rnp;
353 /* NMI handlers cannot block and cannot safely manipulate state. */
357 local_irq_save(flags);
360 * If RCU core is waiting for this CPU to exit critical section,
361 * let it know that we have done so.
363 special = t->rcu_read_unlock_special;
364 if (special & RCU_READ_UNLOCK_NEED_QS) {
365 rcu_preempt_qs(smp_processor_id());
368 /* Hardware IRQ handlers cannot block. */
369 if (in_irq() || in_serving_softirq()) {
370 local_irq_restore(flags);
374 /* Clean up if blocked during RCU read-side critical section. */
375 if (special & RCU_READ_UNLOCK_BLOCKED) {
376 t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
379 * Remove this task from the list it blocked on. The
380 * task can migrate while we acquire the lock, but at
381 * most one time. So at most two passes through loop.
384 rnp = t->rcu_blocked_node;
385 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
386 smp_mb__after_unlock_lock();
387 if (rnp == t->rcu_blocked_node)
389 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
391 empty = !rcu_preempt_blocked_readers_cgp(rnp);
392 empty_exp = !rcu_preempted_readers_exp(rnp);
393 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
394 np = rcu_next_node_entry(t, rnp);
395 list_del_init(&t->rcu_node_entry);
396 t->rcu_blocked_node = NULL;
397 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
399 if (&t->rcu_node_entry == rnp->gp_tasks)
401 if (&t->rcu_node_entry == rnp->exp_tasks)
403 #ifdef CONFIG_RCU_BOOST
404 if (&t->rcu_node_entry == rnp->boost_tasks)
405 rnp->boost_tasks = np;
406 /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
407 if (t->rcu_boost_mutex) {
408 rbmp = t->rcu_boost_mutex;
409 t->rcu_boost_mutex = NULL;
411 #endif /* #ifdef CONFIG_RCU_BOOST */
414 * If this was the last task on the current list, and if
415 * we aren't waiting on any CPUs, report the quiescent state.
416 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
417 * so we must take a snapshot of the expedited state.
419 empty_exp_now = !rcu_preempted_readers_exp(rnp);
420 if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
421 trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
428 rcu_report_unblock_qs_rnp(rnp, flags);
430 raw_spin_unlock_irqrestore(&rnp->lock, flags);
433 #ifdef CONFIG_RCU_BOOST
434 /* Unboost if we were boosted. */
436 rt_mutex_unlock(rbmp);
437 #endif /* #ifdef CONFIG_RCU_BOOST */
440 * If this was the last task on the expedited lists,
441 * then we need to report up the rcu_node hierarchy.
443 if (!empty_exp && empty_exp_now)
444 rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
446 local_irq_restore(flags);
450 #ifdef CONFIG_RCU_CPU_STALL_VERBOSE
453 * Dump detailed information for all tasks blocking the current RCU
454 * grace period on the specified rcu_node structure.
456 static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
459 struct task_struct *t;
461 raw_spin_lock_irqsave(&rnp->lock, flags);
462 if (!rcu_preempt_blocked_readers_cgp(rnp)) {
463 raw_spin_unlock_irqrestore(&rnp->lock, flags);
466 t = list_entry(rnp->gp_tasks,
467 struct task_struct, rcu_node_entry);
468 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
470 raw_spin_unlock_irqrestore(&rnp->lock, flags);
474 * Dump detailed information for all tasks blocking the current RCU
477 static void rcu_print_detail_task_stall(struct rcu_state *rsp)
479 struct rcu_node *rnp = rcu_get_root(rsp);
481 rcu_print_detail_task_stall_rnp(rnp);
482 rcu_for_each_leaf_node(rsp, rnp)
483 rcu_print_detail_task_stall_rnp(rnp);
486 #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
488 static void rcu_print_detail_task_stall(struct rcu_state *rsp)
492 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
494 #ifdef CONFIG_RCU_CPU_STALL_INFO
496 static void rcu_print_task_stall_begin(struct rcu_node *rnp)
498 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
499 rnp->level, rnp->grplo, rnp->grphi);
502 static void rcu_print_task_stall_end(void)
507 #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
509 static void rcu_print_task_stall_begin(struct rcu_node *rnp)
513 static void rcu_print_task_stall_end(void)
517 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
520 * Scan the current list of tasks blocked within RCU read-side critical
521 * sections, printing out the tid of each.
523 static int rcu_print_task_stall(struct rcu_node *rnp)
525 struct task_struct *t;
528 if (!rcu_preempt_blocked_readers_cgp(rnp))
530 rcu_print_task_stall_begin(rnp);
531 t = list_entry(rnp->gp_tasks,
532 struct task_struct, rcu_node_entry);
533 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
534 pr_cont(" P%d", t->pid);
537 rcu_print_task_stall_end();
542 * Check that the list of blocked tasks for the newly completed grace
543 * period is in fact empty. It is a serious bug to complete a grace
544 * period that still has RCU readers blocked! This function must be
545 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
546 * must be held by the caller.
548 * Also, if there are blocked tasks on the list, they automatically
549 * block the newly created grace period, so set up ->gp_tasks accordingly.
551 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
553 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
554 if (!list_empty(&rnp->blkd_tasks))
555 rnp->gp_tasks = rnp->blkd_tasks.next;
556 WARN_ON_ONCE(rnp->qsmask);
559 #ifdef CONFIG_HOTPLUG_CPU
562 * Handle tasklist migration for case in which all CPUs covered by the
563 * specified rcu_node have gone offline. Move them up to the root
564 * rcu_node. The reason for not just moving them to the immediate
565 * parent is to remove the need for rcu_read_unlock_special() to
566 * make more than two attempts to acquire the target rcu_node's lock.
567 * Returns true if there were tasks blocking the current RCU grace
570 * Returns 1 if there was previously a task blocking the current grace
571 * period on the specified rcu_node structure.
573 * The caller must hold rnp->lock with irqs disabled.
575 static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
576 struct rcu_node *rnp,
577 struct rcu_data *rdp)
579 struct list_head *lp;
580 struct list_head *lp_root;
582 struct rcu_node *rnp_root = rcu_get_root(rsp);
583 struct task_struct *t;
585 if (rnp == rnp_root) {
586 WARN_ONCE(1, "Last CPU thought to be offlined?");
587 return 0; /* Shouldn't happen: at least one CPU online. */
590 /* If we are on an internal node, complain bitterly. */
591 WARN_ON_ONCE(rnp != rdp->mynode);
594 * Move tasks up to root rcu_node. Don't try to get fancy for
595 * this corner-case operation -- just put this node's tasks
596 * at the head of the root node's list, and update the root node's
597 * ->gp_tasks and ->exp_tasks pointers to those of this node's,
598 * if non-NULL. This might result in waiting for more tasks than
599 * absolutely necessary, but this is a good performance/complexity
602 if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
603 retval |= RCU_OFL_TASKS_NORM_GP;
604 if (rcu_preempted_readers_exp(rnp))
605 retval |= RCU_OFL_TASKS_EXP_GP;
606 lp = &rnp->blkd_tasks;
607 lp_root = &rnp_root->blkd_tasks;
608 while (!list_empty(lp)) {
609 t = list_entry(lp->next, typeof(*t), rcu_node_entry);
610 raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
611 smp_mb__after_unlock_lock();
612 list_del(&t->rcu_node_entry);
613 t->rcu_blocked_node = rnp_root;
614 list_add(&t->rcu_node_entry, lp_root);
615 if (&t->rcu_node_entry == rnp->gp_tasks)
616 rnp_root->gp_tasks = rnp->gp_tasks;
617 if (&t->rcu_node_entry == rnp->exp_tasks)
618 rnp_root->exp_tasks = rnp->exp_tasks;
619 #ifdef CONFIG_RCU_BOOST
620 if (&t->rcu_node_entry == rnp->boost_tasks)
621 rnp_root->boost_tasks = rnp->boost_tasks;
622 #endif /* #ifdef CONFIG_RCU_BOOST */
623 raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
626 rnp->gp_tasks = NULL;
627 rnp->exp_tasks = NULL;
628 #ifdef CONFIG_RCU_BOOST
629 rnp->boost_tasks = NULL;
631 * In case root is being boosted and leaf was not. Make sure
632 * that we boost the tasks blocking the current grace period
635 raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
636 smp_mb__after_unlock_lock();
637 if (rnp_root->boost_tasks != NULL &&
638 rnp_root->boost_tasks != rnp_root->gp_tasks &&
639 rnp_root->boost_tasks != rnp_root->exp_tasks)
640 rnp_root->boost_tasks = rnp_root->gp_tasks;
641 raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
642 #endif /* #ifdef CONFIG_RCU_BOOST */
647 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
650 * Check for a quiescent state from the current CPU. When a task blocks,
651 * the task is recorded in the corresponding CPU's rcu_node structure,
652 * which is checked elsewhere.
654 * Caller must disable hard irqs.
656 static void rcu_preempt_check_callbacks(int cpu)
658 struct task_struct *t = current;
660 if (t->rcu_read_lock_nesting == 0) {
664 if (t->rcu_read_lock_nesting > 0 &&
665 per_cpu(rcu_preempt_data, cpu).qs_pending)
666 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
669 #ifdef CONFIG_RCU_BOOST
671 static void rcu_preempt_do_callbacks(void)
673 rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
676 #endif /* #ifdef CONFIG_RCU_BOOST */
679 * Queue a preemptible-RCU callback for invocation after a grace period.
681 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
683 __call_rcu(head, func, &rcu_preempt_state, -1, 0);
685 EXPORT_SYMBOL_GPL(call_rcu);
688 * Queue an RCU callback for lazy invocation after a grace period.
689 * This will likely be later named something like "call_rcu_lazy()",
690 * but this change will require some way of tagging the lazy RCU
691 * callbacks in the list of pending callbacks. Until then, this
692 * function may only be called from __kfree_rcu().
694 void kfree_call_rcu(struct rcu_head *head,
695 void (*func)(struct rcu_head *rcu))
697 __call_rcu(head, func, &rcu_preempt_state, -1, 1);
699 EXPORT_SYMBOL_GPL(kfree_call_rcu);
702 * synchronize_rcu - wait until a grace period has elapsed.
704 * Control will return to the caller some time after a full grace
705 * period has elapsed, in other words after all currently executing RCU
706 * read-side critical sections have completed. Note, however, that
707 * upon return from synchronize_rcu(), the caller might well be executing
708 * concurrently with new RCU read-side critical sections that began while
709 * synchronize_rcu() was waiting. RCU read-side critical sections are
710 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
712 * See the description of synchronize_sched() for more detailed information
713 * on memory ordering guarantees.
715 void synchronize_rcu(void)
717 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
718 !lock_is_held(&rcu_lock_map) &&
719 !lock_is_held(&rcu_sched_lock_map),
720 "Illegal synchronize_rcu() in RCU read-side critical section");
721 if (!rcu_scheduler_active)
724 synchronize_rcu_expedited();
726 wait_rcu_gp(call_rcu);
728 EXPORT_SYMBOL_GPL(synchronize_rcu);
730 static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
731 static unsigned long sync_rcu_preempt_exp_count;
732 static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
735 * Return non-zero if there are any tasks in RCU read-side critical
736 * sections blocking the current preemptible-RCU expedited grace period.
737 * If there is no preemptible-RCU expedited grace period currently in
738 * progress, returns zero unconditionally.
740 static int rcu_preempted_readers_exp(struct rcu_node *rnp)
742 return rnp->exp_tasks != NULL;
746 * return non-zero if there is no RCU expedited grace period in progress
747 * for the specified rcu_node structure, in other words, if all CPUs and
748 * tasks covered by the specified rcu_node structure have done their bit
749 * for the current expedited grace period. Works only for preemptible
750 * RCU -- other RCU implementation use other means.
752 * Caller must hold sync_rcu_preempt_exp_mutex.
754 static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
756 return !rcu_preempted_readers_exp(rnp) &&
757 ACCESS_ONCE(rnp->expmask) == 0;
761 * Report the exit from RCU read-side critical section for the last task
762 * that queued itself during or before the current expedited preemptible-RCU
763 * grace period. This event is reported either to the rcu_node structure on
764 * which the task was queued or to one of that rcu_node structure's ancestors,
765 * recursively up the tree. (Calm down, calm down, we do the recursion
768 * Most callers will set the "wake" flag, but the task initiating the
769 * expedited grace period need not wake itself.
771 * Caller must hold sync_rcu_preempt_exp_mutex.
773 static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
779 raw_spin_lock_irqsave(&rnp->lock, flags);
780 smp_mb__after_unlock_lock();
782 if (!sync_rcu_preempt_exp_done(rnp)) {
783 raw_spin_unlock_irqrestore(&rnp->lock, flags);
786 if (rnp->parent == NULL) {
787 raw_spin_unlock_irqrestore(&rnp->lock, flags);
789 wake_up(&sync_rcu_preempt_exp_wq);
793 raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
795 raw_spin_lock(&rnp->lock); /* irqs already disabled */
796 smp_mb__after_unlock_lock();
797 rnp->expmask &= ~mask;
802 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
803 * grace period for the specified rcu_node structure. If there are no such
804 * tasks, report it up the rcu_node hierarchy.
806 * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
807 * CPU hotplug operations.
810 sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
815 raw_spin_lock_irqsave(&rnp->lock, flags);
816 smp_mb__after_unlock_lock();
817 if (list_empty(&rnp->blkd_tasks)) {
818 raw_spin_unlock_irqrestore(&rnp->lock, flags);
820 rnp->exp_tasks = rnp->blkd_tasks.next;
821 rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
825 rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
829 * synchronize_rcu_expedited - Brute-force RCU grace period
831 * Wait for an RCU-preempt grace period, but expedite it. The basic
832 * idea is to invoke synchronize_sched_expedited() to push all the tasks to
833 * the ->blkd_tasks lists and wait for this list to drain. This consumes
834 * significant time on all CPUs and is unfriendly to real-time workloads,
835 * so is thus not recommended for any sort of common-case code.
836 * In fact, if you are using synchronize_rcu_expedited() in a loop,
837 * please restructure your code to batch your updates, and then Use a
838 * single synchronize_rcu() instead.
840 * Note that it is illegal to call this function while holding any lock
841 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
842 * to call this function from a CPU-hotplug notifier. Failing to observe
843 * these restriction will result in deadlock.
845 void synchronize_rcu_expedited(void)
848 struct rcu_node *rnp;
849 struct rcu_state *rsp = &rcu_preempt_state;
853 smp_mb(); /* Caller's modifications seen first by other CPUs. */
854 snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
855 smp_mb(); /* Above access cannot bleed into critical section. */
858 * Block CPU-hotplug operations. This means that any CPU-hotplug
859 * operation that finds an rcu_node structure with tasks in the
860 * process of being boosted will know that all tasks blocking
861 * this expedited grace period will already be in the process of
862 * being boosted. This simplifies the process of moving tasks
863 * from leaf to root rcu_node structures.
868 * Acquire lock, falling back to synchronize_rcu() if too many
869 * lock-acquisition failures. Of course, if someone does the
870 * expedited grace period for us, just leave.
872 while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
873 if (ULONG_CMP_LT(snap,
874 ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
876 goto mb_ret; /* Others did our work for us. */
878 if (trycount++ < 10) {
879 udelay(trycount * num_online_cpus());
882 wait_rcu_gp(call_rcu);
886 if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
888 goto unlock_mb_ret; /* Others did our work for us. */
891 /* force all RCU readers onto ->blkd_tasks lists. */
892 synchronize_sched_expedited();
894 /* Initialize ->expmask for all non-leaf rcu_node structures. */
895 rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
896 raw_spin_lock_irqsave(&rnp->lock, flags);
897 smp_mb__after_unlock_lock();
898 rnp->expmask = rnp->qsmaskinit;
899 raw_spin_unlock_irqrestore(&rnp->lock, flags);
902 /* Snapshot current state of ->blkd_tasks lists. */
903 rcu_for_each_leaf_node(rsp, rnp)
904 sync_rcu_preempt_exp_init(rsp, rnp);
905 if (NUM_RCU_NODES > 1)
906 sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
910 /* Wait for snapshotted ->blkd_tasks lists to drain. */
911 rnp = rcu_get_root(rsp);
912 wait_event(sync_rcu_preempt_exp_wq,
913 sync_rcu_preempt_exp_done(rnp));
915 /* Clean up and exit. */
916 smp_mb(); /* ensure expedited GP seen before counter increment. */
917 ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
919 mutex_unlock(&sync_rcu_preempt_exp_mutex);
921 smp_mb(); /* ensure subsequent action seen after grace period. */
923 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
926 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
928 * Note that this primitive does not necessarily wait for an RCU grace period
929 * to complete. For example, if there are no RCU callbacks queued anywhere
930 * in the system, then rcu_barrier() is within its rights to return
931 * immediately, without waiting for anything, much less an RCU grace period.
933 void rcu_barrier(void)
935 _rcu_barrier(&rcu_preempt_state);
937 EXPORT_SYMBOL_GPL(rcu_barrier);
940 * Initialize preemptible RCU's state structures.
942 static void __init __rcu_init_preempt(void)
944 rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
948 * Check for a task exiting while in a preemptible-RCU read-side
949 * critical section, clean up if so. No need to issue warnings,
950 * as debug_check_no_locks_held() already does this if lockdep
955 struct task_struct *t = current;
957 if (likely(list_empty(¤t->rcu_node_entry)))
959 t->rcu_read_lock_nesting = 1;
961 t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
965 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
967 static struct rcu_state *rcu_state = &rcu_sched_state;
970 * Tell them what RCU they are running.
972 static void __init rcu_bootup_announce(void)
974 pr_info("Hierarchical RCU implementation.\n");
975 rcu_bootup_announce_oddness();
979 * Return the number of RCU batches processed thus far for debug & stats.
981 long rcu_batches_completed(void)
983 return rcu_batches_completed_sched();
985 EXPORT_SYMBOL_GPL(rcu_batches_completed);
988 * Force a quiescent state for RCU, which, because there is no preemptible
989 * RCU, becomes the same as rcu-sched.
991 void rcu_force_quiescent_state(void)
993 rcu_sched_force_quiescent_state();
995 EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
998 * Because preemptible RCU does not exist, we never have to check for
999 * CPUs being in quiescent states.
1001 static void rcu_preempt_note_context_switch(int cpu)
1006 * Because preemptible RCU does not exist, there are never any preempted
1009 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
1014 #ifdef CONFIG_HOTPLUG_CPU
1016 /* Because preemptible RCU does not exist, no quieting of tasks. */
1017 static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
1019 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1022 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1025 * Because preemptible RCU does not exist, we never have to check for
1026 * tasks blocked within RCU read-side critical sections.
1028 static void rcu_print_detail_task_stall(struct rcu_state *rsp)
1033 * Because preemptible RCU does not exist, we never have to check for
1034 * tasks blocked within RCU read-side critical sections.
1036 static int rcu_print_task_stall(struct rcu_node *rnp)
1042 * Because there is no preemptible RCU, there can be no readers blocked,
1043 * so there is no need to check for blocked tasks. So check only for
1044 * bogus qsmask values.
1046 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
1048 WARN_ON_ONCE(rnp->qsmask);
1051 #ifdef CONFIG_HOTPLUG_CPU
1054 * Because preemptible RCU does not exist, it never needs to migrate
1055 * tasks that were blocked within RCU read-side critical sections, and
1056 * such non-existent tasks cannot possibly have been blocking the current
1059 static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
1060 struct rcu_node *rnp,
1061 struct rcu_data *rdp)
1066 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1069 * Because preemptible RCU does not exist, it never has any callbacks
1072 static void rcu_preempt_check_callbacks(int cpu)
1077 * Queue an RCU callback for lazy invocation after a grace period.
1078 * This will likely be later named something like "call_rcu_lazy()",
1079 * but this change will require some way of tagging the lazy RCU
1080 * callbacks in the list of pending callbacks. Until then, this
1081 * function may only be called from __kfree_rcu().
1083 * Because there is no preemptible RCU, we use RCU-sched instead.
1085 void kfree_call_rcu(struct rcu_head *head,
1086 void (*func)(struct rcu_head *rcu))
1088 __call_rcu(head, func, &rcu_sched_state, -1, 1);
1090 EXPORT_SYMBOL_GPL(kfree_call_rcu);
1093 * Wait for an rcu-preempt grace period, but make it happen quickly.
1094 * But because preemptible RCU does not exist, map to rcu-sched.
1096 void synchronize_rcu_expedited(void)
1098 synchronize_sched_expedited();
1100 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
1102 #ifdef CONFIG_HOTPLUG_CPU
1105 * Because preemptible RCU does not exist, there is never any need to
1106 * report on tasks preempted in RCU read-side critical sections during
1107 * expedited RCU grace periods.
1109 static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
1114 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1117 * Because preemptible RCU does not exist, rcu_barrier() is just
1118 * another name for rcu_barrier_sched().
1120 void rcu_barrier(void)
1122 rcu_barrier_sched();
1124 EXPORT_SYMBOL_GPL(rcu_barrier);
1127 * Because preemptible RCU does not exist, it need not be initialized.
1129 static void __init __rcu_init_preempt(void)
1134 * Because preemptible RCU does not exist, tasks cannot possibly exit
1135 * while in preemptible RCU read-side critical sections.
1141 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1143 #ifdef CONFIG_RCU_BOOST
1145 #include "../locking/rtmutex_common.h"
1147 #ifdef CONFIG_RCU_TRACE
1149 static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1151 if (list_empty(&rnp->blkd_tasks))
1152 rnp->n_balk_blkd_tasks++;
1153 else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
1154 rnp->n_balk_exp_gp_tasks++;
1155 else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
1156 rnp->n_balk_boost_tasks++;
1157 else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
1158 rnp->n_balk_notblocked++;
1159 else if (rnp->gp_tasks != NULL &&
1160 ULONG_CMP_LT(jiffies, rnp->boost_time))
1161 rnp->n_balk_notyet++;
1166 #else /* #ifdef CONFIG_RCU_TRACE */
1168 static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1172 #endif /* #else #ifdef CONFIG_RCU_TRACE */
1174 static void rcu_wake_cond(struct task_struct *t, int status)
1177 * If the thread is yielding, only wake it when this
1178 * is invoked from idle
1180 if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
1185 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
1186 * or ->boost_tasks, advancing the pointer to the next task in the
1187 * ->blkd_tasks list.
1189 * Note that irqs must be enabled: boosting the task can block.
1190 * Returns 1 if there are more tasks needing to be boosted.
1192 static int rcu_boost(struct rcu_node *rnp)
1194 unsigned long flags;
1195 struct rt_mutex mtx;
1196 struct task_struct *t;
1197 struct list_head *tb;
1199 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
1200 return 0; /* Nothing left to boost. */
1202 raw_spin_lock_irqsave(&rnp->lock, flags);
1203 smp_mb__after_unlock_lock();
1206 * Recheck under the lock: all tasks in need of boosting
1207 * might exit their RCU read-side critical sections on their own.
1209 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
1210 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1215 * Preferentially boost tasks blocking expedited grace periods.
1216 * This cannot starve the normal grace periods because a second
1217 * expedited grace period must boost all blocked tasks, including
1218 * those blocking the pre-existing normal grace period.
1220 if (rnp->exp_tasks != NULL) {
1221 tb = rnp->exp_tasks;
1222 rnp->n_exp_boosts++;
1224 tb = rnp->boost_tasks;
1225 rnp->n_normal_boosts++;
1227 rnp->n_tasks_boosted++;
1230 * We boost task t by manufacturing an rt_mutex that appears to
1231 * be held by task t. We leave a pointer to that rt_mutex where
1232 * task t can find it, and task t will release the mutex when it
1233 * exits its outermost RCU read-side critical section. Then
1234 * simply acquiring this artificial rt_mutex will boost task
1235 * t's priority. (Thanks to tglx for suggesting this approach!)
1237 * Note that task t must acquire rnp->lock to remove itself from
1238 * the ->blkd_tasks list, which it will do from exit() if from
1239 * nowhere else. We therefore are guaranteed that task t will
1240 * stay around at least until we drop rnp->lock. Note that
1241 * rnp->lock also resolves races between our priority boosting
1242 * and task t's exiting its outermost RCU read-side critical
1245 t = container_of(tb, struct task_struct, rcu_node_entry);
1246 rt_mutex_init_proxy_locked(&mtx, t);
1247 t->rcu_boost_mutex = &mtx;
1248 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1249 rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */
1250 rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
1252 return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
1253 ACCESS_ONCE(rnp->boost_tasks) != NULL;
1257 * Priority-boosting kthread. One per leaf rcu_node and one for the
1260 static int rcu_boost_kthread(void *arg)
1262 struct rcu_node *rnp = (struct rcu_node *)arg;
1266 trace_rcu_utilization(TPS("Start boost kthread@init"));
1268 rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1269 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1270 rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1271 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1272 rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1273 more2boost = rcu_boost(rnp);
1279 rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1280 trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1281 schedule_timeout_interruptible(2);
1282 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1287 trace_rcu_utilization(TPS("End boost kthread@notreached"));
1292 * Check to see if it is time to start boosting RCU readers that are
1293 * blocking the current grace period, and, if so, tell the per-rcu_node
1294 * kthread to start boosting them. If there is an expedited grace
1295 * period in progress, it is always time to boost.
1297 * The caller must hold rnp->lock, which this function releases.
1298 * The ->boost_kthread_task is immortal, so we don't need to worry
1299 * about it going away.
1301 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1303 struct task_struct *t;
1305 if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1306 rnp->n_balk_exp_gp_tasks++;
1307 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1310 if (rnp->exp_tasks != NULL ||
1311 (rnp->gp_tasks != NULL &&
1312 rnp->boost_tasks == NULL &&
1314 ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1315 if (rnp->exp_tasks == NULL)
1316 rnp->boost_tasks = rnp->gp_tasks;
1317 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1318 t = rnp->boost_kthread_task;
1320 rcu_wake_cond(t, rnp->boost_kthread_status);
1322 rcu_initiate_boost_trace(rnp);
1323 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1328 * Wake up the per-CPU kthread to invoke RCU callbacks.
1330 static void invoke_rcu_callbacks_kthread(void)
1332 unsigned long flags;
1334 local_irq_save(flags);
1335 __this_cpu_write(rcu_cpu_has_work, 1);
1336 if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
1337 current != __this_cpu_read(rcu_cpu_kthread_task)) {
1338 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
1339 __this_cpu_read(rcu_cpu_kthread_status));
1341 local_irq_restore(flags);
1345 * Is the current CPU running the RCU-callbacks kthread?
1346 * Caller must have preemption disabled.
1348 static bool rcu_is_callbacks_kthread(void)
1350 return __this_cpu_read(rcu_cpu_kthread_task) == current;
1353 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1356 * Do priority-boost accounting for the start of a new grace period.
1358 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1360 rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1364 * Create an RCU-boost kthread for the specified node if one does not
1365 * already exist. We only create this kthread for preemptible RCU.
1366 * Returns zero if all is well, a negated errno otherwise.
1368 static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
1369 struct rcu_node *rnp)
1371 int rnp_index = rnp - &rsp->node[0];
1372 unsigned long flags;
1373 struct sched_param sp;
1374 struct task_struct *t;
1376 if (&rcu_preempt_state != rsp)
1379 if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
1383 if (rnp->boost_kthread_task != NULL)
1385 t = kthread_create(rcu_boost_kthread, (void *)rnp,
1386 "rcub/%d", rnp_index);
1389 raw_spin_lock_irqsave(&rnp->lock, flags);
1390 smp_mb__after_unlock_lock();
1391 rnp->boost_kthread_task = t;
1392 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1393 sp.sched_priority = RCU_BOOST_PRIO;
1394 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1395 wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1399 static void rcu_kthread_do_work(void)
1401 rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
1402 rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
1403 rcu_preempt_do_callbacks();
1406 static void rcu_cpu_kthread_setup(unsigned int cpu)
1408 struct sched_param sp;
1410 sp.sched_priority = RCU_KTHREAD_PRIO;
1411 sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
1414 static void rcu_cpu_kthread_park(unsigned int cpu)
1416 per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1419 static int rcu_cpu_kthread_should_run(unsigned int cpu)
1421 return __this_cpu_read(rcu_cpu_has_work);
1425 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
1426 * RCU softirq used in flavors and configurations of RCU that do not
1427 * support RCU priority boosting.
1429 static void rcu_cpu_kthread(unsigned int cpu)
1431 unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
1432 char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
1435 for (spincnt = 0; spincnt < 10; spincnt++) {
1436 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1438 *statusp = RCU_KTHREAD_RUNNING;
1439 this_cpu_inc(rcu_cpu_kthread_loops);
1440 local_irq_disable();
1445 rcu_kthread_do_work();
1448 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1449 *statusp = RCU_KTHREAD_WAITING;
1453 *statusp = RCU_KTHREAD_YIELDING;
1454 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1455 schedule_timeout_interruptible(2);
1456 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1457 *statusp = RCU_KTHREAD_WAITING;
1461 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1462 * served by the rcu_node in question. The CPU hotplug lock is still
1463 * held, so the value of rnp->qsmaskinit will be stable.
1465 * We don't include outgoingcpu in the affinity set, use -1 if there is
1466 * no outgoing CPU. If there are no CPUs left in the affinity set,
1467 * this function allows the kthread to execute on any CPU.
1469 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1471 struct task_struct *t = rnp->boost_kthread_task;
1472 unsigned long mask = rnp->qsmaskinit;
1478 if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1480 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
1481 if ((mask & 0x1) && cpu != outgoingcpu)
1482 cpumask_set_cpu(cpu, cm);
1483 if (cpumask_weight(cm) == 0) {
1485 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
1486 cpumask_clear_cpu(cpu, cm);
1487 WARN_ON_ONCE(cpumask_weight(cm) == 0);
1489 set_cpus_allowed_ptr(t, cm);
1490 free_cpumask_var(cm);
1493 static struct smp_hotplug_thread rcu_cpu_thread_spec = {
1494 .store = &rcu_cpu_kthread_task,
1495 .thread_should_run = rcu_cpu_kthread_should_run,
1496 .thread_fn = rcu_cpu_kthread,
1497 .thread_comm = "rcuc/%u",
1498 .setup = rcu_cpu_kthread_setup,
1499 .park = rcu_cpu_kthread_park,
1503 * Spawn all kthreads -- called as soon as the scheduler is running.
1505 static int __init rcu_spawn_kthreads(void)
1507 struct rcu_node *rnp;
1510 rcu_scheduler_fully_active = 1;
1511 for_each_possible_cpu(cpu)
1512 per_cpu(rcu_cpu_has_work, cpu) = 0;
1513 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
1514 rnp = rcu_get_root(rcu_state);
1515 (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1516 if (NUM_RCU_NODES > 1) {
1517 rcu_for_each_leaf_node(rcu_state, rnp)
1518 (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1522 early_initcall(rcu_spawn_kthreads);
1524 static void rcu_prepare_kthreads(int cpu)
1526 struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
1527 struct rcu_node *rnp = rdp->mynode;
1529 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1530 if (rcu_scheduler_fully_active)
1531 (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1534 #else /* #ifdef CONFIG_RCU_BOOST */
1536 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1538 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1541 static void invoke_rcu_callbacks_kthread(void)
1546 static bool rcu_is_callbacks_kthread(void)
1551 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1555 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1559 static int __init rcu_scheduler_really_started(void)
1561 rcu_scheduler_fully_active = 1;
1564 early_initcall(rcu_scheduler_really_started);
1566 static void rcu_prepare_kthreads(int cpu)
1570 #endif /* #else #ifdef CONFIG_RCU_BOOST */
1572 #if !defined(CONFIG_RCU_FAST_NO_HZ)
1575 * Check to see if any future RCU-related work will need to be done
1576 * by the current CPU, even if none need be done immediately, returning
1577 * 1 if so. This function is part of the RCU implementation; it is -not-
1578 * an exported member of the RCU API.
1580 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1581 * any flavor of RCU.
1583 int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
1585 *delta_jiffies = ULONG_MAX;
1586 return rcu_cpu_has_callbacks(cpu, NULL);
1590 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1593 static void rcu_cleanup_after_idle(int cpu)
1598 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1601 static void rcu_prepare_for_idle(int cpu)
1606 * Don't bother keeping a running count of the number of RCU callbacks
1607 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1609 static void rcu_idle_count_callbacks_posted(void)
1613 #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1616 * This code is invoked when a CPU goes idle, at which point we want
1617 * to have the CPU do everything required for RCU so that it can enter
1618 * the energy-efficient dyntick-idle mode. This is handled by a
1619 * state machine implemented by rcu_prepare_for_idle() below.
1621 * The following three proprocessor symbols control this state machine:
1623 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1624 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1625 * is sized to be roughly one RCU grace period. Those energy-efficiency
1626 * benchmarkers who might otherwise be tempted to set this to a large
1627 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1628 * system. And if you are -that- concerned about energy efficiency,
1629 * just power the system down and be done with it!
1630 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1631 * permitted to sleep in dyntick-idle mode with only lazy RCU
1632 * callbacks pending. Setting this too high can OOM your system.
1634 * The values below work well in practice. If future workloads require
1635 * adjustment, they can be converted into kernel config parameters, though
1636 * making the state machine smarter might be a better option.
1638 #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1639 #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1641 static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
1642 module_param(rcu_idle_gp_delay, int, 0644);
1643 static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
1644 module_param(rcu_idle_lazy_gp_delay, int, 0644);
1646 extern int tick_nohz_active;
1649 * Try to advance callbacks for all flavors of RCU on the current CPU, but
1650 * only if it has been awhile since the last time we did so. Afterwards,
1651 * if there are any callbacks ready for immediate invocation, return true.
1653 static bool rcu_try_advance_all_cbs(void)
1655 bool cbs_ready = false;
1656 struct rcu_data *rdp;
1657 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1658 struct rcu_node *rnp;
1659 struct rcu_state *rsp;
1661 /* Exit early if we advanced recently. */
1662 if (jiffies == rdtp->last_advance_all)
1664 rdtp->last_advance_all = jiffies;
1666 for_each_rcu_flavor(rsp) {
1667 rdp = this_cpu_ptr(rsp->rda);
1671 * Don't bother checking unless a grace period has
1672 * completed since we last checked and there are
1673 * callbacks not yet ready to invoke.
1675 if (rdp->completed != rnp->completed &&
1676 rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
1677 note_gp_changes(rsp, rdp);
1679 if (cpu_has_callbacks_ready_to_invoke(rdp))
1686 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1687 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1688 * caller to set the timeout based on whether or not there are non-lazy
1691 * The caller must have disabled interrupts.
1693 int rcu_needs_cpu(int cpu, unsigned long *dj)
1695 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1697 /* Snapshot to detect later posting of non-lazy callback. */
1698 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1700 /* If no callbacks, RCU doesn't need the CPU. */
1701 if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) {
1706 /* Attempt to advance callbacks. */
1707 if (rcu_try_advance_all_cbs()) {
1708 /* Some ready to invoke, so initiate later invocation. */
1712 rdtp->last_accelerate = jiffies;
1714 /* Request timer delay depending on laziness, and round. */
1715 if (!rdtp->all_lazy) {
1716 *dj = round_up(rcu_idle_gp_delay + jiffies,
1717 rcu_idle_gp_delay) - jiffies;
1719 *dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1725 * Prepare a CPU for idle from an RCU perspective. The first major task
1726 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1727 * The second major task is to check to see if a non-lazy callback has
1728 * arrived at a CPU that previously had only lazy callbacks. The third
1729 * major task is to accelerate (that is, assign grace-period numbers to)
1730 * any recently arrived callbacks.
1732 * The caller must have disabled interrupts.
1734 static void rcu_prepare_for_idle(int cpu)
1736 struct rcu_data *rdp;
1737 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1738 struct rcu_node *rnp;
1739 struct rcu_state *rsp;
1742 /* Handle nohz enablement switches conservatively. */
1743 tne = ACCESS_ONCE(tick_nohz_active);
1744 if (tne != rdtp->tick_nohz_enabled_snap) {
1745 if (rcu_cpu_has_callbacks(cpu, NULL))
1746 invoke_rcu_core(); /* force nohz to see update. */
1747 rdtp->tick_nohz_enabled_snap = tne;
1753 /* If this is a no-CBs CPU, no callbacks, just return. */
1754 if (rcu_is_nocb_cpu(cpu))
1758 * If a non-lazy callback arrived at a CPU having only lazy
1759 * callbacks, invoke RCU core for the side-effect of recalculating
1760 * idle duration on re-entry to idle.
1762 if (rdtp->all_lazy &&
1763 rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
1764 rdtp->all_lazy = false;
1765 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1771 * If we have not yet accelerated this jiffy, accelerate all
1772 * callbacks on this CPU.
1774 if (rdtp->last_accelerate == jiffies)
1776 rdtp->last_accelerate = jiffies;
1777 for_each_rcu_flavor(rsp) {
1778 rdp = per_cpu_ptr(rsp->rda, cpu);
1779 if (!*rdp->nxttail[RCU_DONE_TAIL])
1782 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
1783 smp_mb__after_unlock_lock();
1784 rcu_accelerate_cbs(rsp, rnp, rdp);
1785 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1790 * Clean up for exit from idle. Attempt to advance callbacks based on
1791 * any grace periods that elapsed while the CPU was idle, and if any
1792 * callbacks are now ready to invoke, initiate invocation.
1794 static void rcu_cleanup_after_idle(int cpu)
1797 if (rcu_is_nocb_cpu(cpu))
1799 if (rcu_try_advance_all_cbs())
1804 * Keep a running count of the number of non-lazy callbacks posted
1805 * on this CPU. This running counter (which is never decremented) allows
1806 * rcu_prepare_for_idle() to detect when something out of the idle loop
1807 * posts a callback, even if an equal number of callbacks are invoked.
1808 * Of course, callbacks should only be posted from within a trace event
1809 * designed to be called from idle or from within RCU_NONIDLE().
1811 static void rcu_idle_count_callbacks_posted(void)
1813 __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
1817 * Data for flushing lazy RCU callbacks at OOM time.
1819 static atomic_t oom_callback_count;
1820 static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
1823 * RCU OOM callback -- decrement the outstanding count and deliver the
1824 * wake-up if we are the last one.
1826 static void rcu_oom_callback(struct rcu_head *rhp)
1828 if (atomic_dec_and_test(&oom_callback_count))
1829 wake_up(&oom_callback_wq);
1833 * Post an rcu_oom_notify callback on the current CPU if it has at
1834 * least one lazy callback. This will unnecessarily post callbacks
1835 * to CPUs that already have a non-lazy callback at the end of their
1836 * callback list, but this is an infrequent operation, so accept some
1837 * extra overhead to keep things simple.
1839 static void rcu_oom_notify_cpu(void *unused)
1841 struct rcu_state *rsp;
1842 struct rcu_data *rdp;
1844 for_each_rcu_flavor(rsp) {
1845 rdp = __this_cpu_ptr(rsp->rda);
1846 if (rdp->qlen_lazy != 0) {
1847 atomic_inc(&oom_callback_count);
1848 rsp->call(&rdp->oom_head, rcu_oom_callback);
1854 * If low on memory, ensure that each CPU has a non-lazy callback.
1855 * This will wake up CPUs that have only lazy callbacks, in turn
1856 * ensuring that they free up the corresponding memory in a timely manner.
1857 * Because an uncertain amount of memory will be freed in some uncertain
1858 * timeframe, we do not claim to have freed anything.
1860 static int rcu_oom_notify(struct notifier_block *self,
1861 unsigned long notused, void *nfreed)
1865 /* Wait for callbacks from earlier instance to complete. */
1866 wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
1869 * Prevent premature wakeup: ensure that all increments happen
1870 * before there is a chance of the counter reaching zero.
1872 atomic_set(&oom_callback_count, 1);
1875 for_each_online_cpu(cpu) {
1876 smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
1881 /* Unconditionally decrement: no need to wake ourselves up. */
1882 atomic_dec(&oom_callback_count);
1887 static struct notifier_block rcu_oom_nb = {
1888 .notifier_call = rcu_oom_notify
1891 static int __init rcu_register_oom_notifier(void)
1893 register_oom_notifier(&rcu_oom_nb);
1896 early_initcall(rcu_register_oom_notifier);
1898 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1900 #ifdef CONFIG_RCU_CPU_STALL_INFO
1902 #ifdef CONFIG_RCU_FAST_NO_HZ
1904 static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1906 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1907 unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
1909 sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1910 rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
1912 rdtp->all_lazy ? 'L' : '.',
1913 rdtp->tick_nohz_enabled_snap ? '.' : 'D');
1916 #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1918 static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1923 #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1925 /* Initiate the stall-info list. */
1926 static void print_cpu_stall_info_begin(void)
1932 * Print out diagnostic information for the specified stalled CPU.
1934 * If the specified CPU is aware of the current RCU grace period
1935 * (flavor specified by rsp), then print the number of scheduling
1936 * clock interrupts the CPU has taken during the time that it has
1937 * been aware. Otherwise, print the number of RCU grace periods
1938 * that this CPU is ignorant of, for example, "1" if the CPU was
1939 * aware of the previous grace period.
1941 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1943 static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1945 char fast_no_hz[72];
1946 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1947 struct rcu_dynticks *rdtp = rdp->dynticks;
1949 unsigned long ticks_value;
1951 if (rsp->gpnum == rdp->gpnum) {
1952 ticks_title = "ticks this GP";
1953 ticks_value = rdp->ticks_this_gp;
1955 ticks_title = "GPs behind";
1956 ticks_value = rsp->gpnum - rdp->gpnum;
1958 print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
1959 pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
1960 cpu, ticks_value, ticks_title,
1961 atomic_read(&rdtp->dynticks) & 0xfff,
1962 rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
1963 rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
1967 /* Terminate the stall-info list. */
1968 static void print_cpu_stall_info_end(void)
1973 /* Zero ->ticks_this_gp for all flavors of RCU. */
1974 static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1976 rdp->ticks_this_gp = 0;
1977 rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
1980 /* Increment ->ticks_this_gp for all flavors of RCU. */
1981 static void increment_cpu_stall_ticks(void)
1983 struct rcu_state *rsp;
1985 for_each_rcu_flavor(rsp)
1986 __this_cpu_ptr(rsp->rda)->ticks_this_gp++;
1989 #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
1991 static void print_cpu_stall_info_begin(void)
1996 static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1998 pr_cont(" %d", cpu);
2001 static void print_cpu_stall_info_end(void)
2006 static void zero_cpu_stall_ticks(struct rcu_data *rdp)
2010 static void increment_cpu_stall_ticks(void)
2014 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
2016 #ifdef CONFIG_RCU_NOCB_CPU
2019 * Offload callback processing from the boot-time-specified set of CPUs
2020 * specified by rcu_nocb_mask. For each CPU in the set, there is a
2021 * kthread created that pulls the callbacks from the corresponding CPU,
2022 * waits for a grace period to elapse, and invokes the callbacks.
2023 * The no-CBs CPUs do a wake_up() on their kthread when they insert
2024 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
2025 * has been specified, in which case each kthread actively polls its
2026 * CPU. (Which isn't so great for energy efficiency, but which does
2027 * reduce RCU's overhead on that CPU.)
2029 * This is intended to be used in conjunction with Frederic Weisbecker's
2030 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
2031 * running CPU-bound user-mode computations.
2033 * Offloading of callback processing could also in theory be used as
2034 * an energy-efficiency measure because CPUs with no RCU callbacks
2035 * queued are more aggressive about entering dyntick-idle mode.
2039 /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
2040 static int __init rcu_nocb_setup(char *str)
2042 alloc_bootmem_cpumask_var(&rcu_nocb_mask);
2043 have_rcu_nocb_mask = true;
2044 cpulist_parse(str, rcu_nocb_mask);
2047 __setup("rcu_nocbs=", rcu_nocb_setup);
2049 static int __init parse_rcu_nocb_poll(char *arg)
2054 early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
2057 * Do any no-CBs CPUs need another grace period?
2059 * Interrupts must be disabled. If the caller does not hold the root
2060 * rnp_node structure's ->lock, the results are advisory only.
2062 static int rcu_nocb_needs_gp(struct rcu_state *rsp)
2064 struct rcu_node *rnp = rcu_get_root(rsp);
2066 return rnp->need_future_gp[(ACCESS_ONCE(rnp->completed) + 1) & 0x1];
2070 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
2073 static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2075 wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
2079 * Set the root rcu_node structure's ->need_future_gp field
2080 * based on the sum of those of all rcu_node structures. This does
2081 * double-count the root rcu_node structure's requests, but this
2082 * is necessary to handle the possibility of a rcu_nocb_kthread()
2083 * having awakened during the time that the rcu_node structures
2084 * were being updated for the end of the previous grace period.
2086 static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2088 rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
2091 static void rcu_init_one_nocb(struct rcu_node *rnp)
2093 init_waitqueue_head(&rnp->nocb_gp_wq[0]);
2094 init_waitqueue_head(&rnp->nocb_gp_wq[1]);
2097 /* Is the specified CPU a no-CPUs CPU? */
2098 bool rcu_is_nocb_cpu(int cpu)
2100 if (have_rcu_nocb_mask)
2101 return cpumask_test_cpu(cpu, rcu_nocb_mask);
2106 * Enqueue the specified string of rcu_head structures onto the specified
2107 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
2108 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
2109 * counts are supplied by rhcount and rhcount_lazy.
2111 * If warranted, also wake up the kthread servicing this CPUs queues.
2113 static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
2114 struct rcu_head *rhp,
2115 struct rcu_head **rhtp,
2116 int rhcount, int rhcount_lazy)
2119 struct rcu_head **old_rhpp;
2120 struct task_struct *t;
2122 /* Enqueue the callback on the nocb list and update counts. */
2123 old_rhpp = xchg(&rdp->nocb_tail, rhtp);
2124 ACCESS_ONCE(*old_rhpp) = rhp;
2125 atomic_long_add(rhcount, &rdp->nocb_q_count);
2126 atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
2128 /* If we are not being polled and there is a kthread, awaken it ... */
2129 t = ACCESS_ONCE(rdp->nocb_kthread);
2130 if (rcu_nocb_poll || !t) {
2131 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2132 TPS("WakeNotPoll"));
2135 len = atomic_long_read(&rdp->nocb_q_count);
2136 if (old_rhpp == &rdp->nocb_head) {
2137 wake_up(&rdp->nocb_wq); /* ... only if queue was empty ... */
2138 rdp->qlen_last_fqs_check = 0;
2139 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeEmpty"));
2140 } else if (len > rdp->qlen_last_fqs_check + qhimark) {
2141 wake_up_process(t); /* ... or if many callbacks queued. */
2142 rdp->qlen_last_fqs_check = LONG_MAX / 2;
2143 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf"));
2145 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
2151 * This is a helper for __call_rcu(), which invokes this when the normal
2152 * callback queue is inoperable. If this is not a no-CBs CPU, this
2153 * function returns failure back to __call_rcu(), which can complain
2156 * Otherwise, this function queues the callback where the corresponding
2157 * "rcuo" kthread can find it.
2159 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2163 if (!rcu_is_nocb_cpu(rdp->cpu))
2165 __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy);
2166 if (__is_kfree_rcu_offset((unsigned long)rhp->func))
2167 trace_rcu_kfree_callback(rdp->rsp->name, rhp,
2168 (unsigned long)rhp->func,
2169 -atomic_long_read(&rdp->nocb_q_count_lazy),
2170 -atomic_long_read(&rdp->nocb_q_count));
2172 trace_rcu_callback(rdp->rsp->name, rhp,
2173 -atomic_long_read(&rdp->nocb_q_count_lazy),
2174 -atomic_long_read(&rdp->nocb_q_count));
2179 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2182 static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2183 struct rcu_data *rdp)
2185 long ql = rsp->qlen;
2186 long qll = rsp->qlen_lazy;
2188 /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
2189 if (!rcu_is_nocb_cpu(smp_processor_id()))
2194 /* First, enqueue the donelist, if any. This preserves CB ordering. */
2195 if (rsp->orphan_donelist != NULL) {
2196 __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
2197 rsp->orphan_donetail, ql, qll);
2199 rsp->orphan_donelist = NULL;
2200 rsp->orphan_donetail = &rsp->orphan_donelist;
2202 if (rsp->orphan_nxtlist != NULL) {
2203 __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
2204 rsp->orphan_nxttail, ql, qll);
2206 rsp->orphan_nxtlist = NULL;
2207 rsp->orphan_nxttail = &rsp->orphan_nxtlist;
2213 * If necessary, kick off a new grace period, and either way wait
2214 * for a subsequent grace period to complete.
2216 static void rcu_nocb_wait_gp(struct rcu_data *rdp)
2220 unsigned long flags;
2221 struct rcu_node *rnp = rdp->mynode;
2223 raw_spin_lock_irqsave(&rnp->lock, flags);
2224 smp_mb__after_unlock_lock();
2225 c = rcu_start_future_gp(rnp, rdp);
2226 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2229 * Wait for the grace period. Do so interruptibly to avoid messing
2230 * up the load average.
2232 trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
2234 wait_event_interruptible(
2235 rnp->nocb_gp_wq[c & 0x1],
2236 (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
2239 flush_signals(current);
2240 trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
2242 trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
2243 smp_mb(); /* Ensure that CB invocation happens after GP end. */
2247 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
2248 * callbacks queued by the corresponding no-CBs CPU.
2250 static int rcu_nocb_kthread(void *arg)
2254 struct rcu_head *list;
2255 struct rcu_head *next;
2256 struct rcu_head **tail;
2257 struct rcu_data *rdp = arg;
2259 /* Each pass through this loop invokes one batch of callbacks */
2261 /* If not polling, wait for next batch of callbacks. */
2262 if (!rcu_nocb_poll) {
2263 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2265 wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
2266 } else if (firsttime) {
2268 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2271 list = ACCESS_ONCE(rdp->nocb_head);
2274 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2276 schedule_timeout_interruptible(1);
2277 flush_signals(current);
2281 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2282 TPS("WokeNonEmpty"));
2285 * Extract queued callbacks, update counts, and wait
2286 * for a grace period to elapse.
2288 ACCESS_ONCE(rdp->nocb_head) = NULL;
2289 tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
2290 c = atomic_long_xchg(&rdp->nocb_q_count, 0);
2291 cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0);
2292 ACCESS_ONCE(rdp->nocb_p_count) += c;
2293 ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl;
2294 rcu_nocb_wait_gp(rdp);
2296 /* Each pass through the following loop invokes a callback. */
2297 trace_rcu_batch_start(rdp->rsp->name, cl, c, -1);
2301 /* Wait for enqueuing to complete, if needed. */
2302 while (next == NULL && &list->next != tail) {
2303 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2305 schedule_timeout_interruptible(1);
2306 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2310 debug_rcu_head_unqueue(list);
2312 if (__rcu_reclaim(rdp->rsp->name, list))
2318 trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
2319 ACCESS_ONCE(rdp->nocb_p_count) -= c;
2320 ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl;
2321 rdp->n_nocbs_invoked += c;
2326 /* Initialize per-rcu_data variables for no-CBs CPUs. */
2327 static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2329 rdp->nocb_tail = &rdp->nocb_head;
2330 init_waitqueue_head(&rdp->nocb_wq);
2333 /* Create a kthread for each RCU flavor for each no-CBs CPU. */
2334 static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
2337 struct rcu_data *rdp;
2338 struct task_struct *t;
2340 if (rcu_nocb_mask == NULL)
2342 for_each_cpu(cpu, rcu_nocb_mask) {
2343 rdp = per_cpu_ptr(rsp->rda, cpu);
2344 t = kthread_run(rcu_nocb_kthread, rdp,
2345 "rcuo%c/%d", rsp->abbr, cpu);
2347 ACCESS_ONCE(rdp->nocb_kthread) = t;
2351 /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2352 static bool init_nocb_callback_list(struct rcu_data *rdp)
2354 if (rcu_nocb_mask == NULL ||
2355 !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
2357 rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2361 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
2363 static int rcu_nocb_needs_gp(struct rcu_state *rsp)
2368 static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2372 static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2376 static void rcu_init_one_nocb(struct rcu_node *rnp)
2380 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2386 static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2387 struct rcu_data *rdp)
2392 static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2396 static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
2400 static bool init_nocb_callback_list(struct rcu_data *rdp)
2405 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2408 * An adaptive-ticks CPU can potentially execute in kernel mode for an
2409 * arbitrarily long period of time with the scheduling-clock tick turned
2410 * off. RCU will be paying attention to this CPU because it is in the
2411 * kernel, but the CPU cannot be guaranteed to be executing the RCU state
2412 * machine because the scheduling-clock tick has been disabled. Therefore,
2413 * if an adaptive-ticks CPU is failing to respond to the current grace
2414 * period and has not be idle from an RCU perspective, kick it.
2416 static void rcu_kick_nohz_cpu(int cpu)
2418 #ifdef CONFIG_NO_HZ_FULL
2419 if (tick_nohz_full_cpu(cpu))
2420 smp_send_reschedule(cpu);
2421 #endif /* #ifdef CONFIG_NO_HZ_FULL */
2425 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
2428 * Define RCU flavor that holds sysidle state. This needs to be the
2429 * most active flavor of RCU.
2431 #ifdef CONFIG_PREEMPT_RCU
2432 static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state;
2433 #else /* #ifdef CONFIG_PREEMPT_RCU */
2434 static struct rcu_state *rcu_sysidle_state = &rcu_sched_state;
2435 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
2437 static int full_sysidle_state; /* Current system-idle state. */
2438 #define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */
2439 #define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */
2440 #define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */
2441 #define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */
2442 #define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */
2445 * Invoked to note exit from irq or task transition to idle. Note that
2446 * usermode execution does -not- count as idle here! After all, we want
2447 * to detect full-system idle states, not RCU quiescent states and grace
2448 * periods. The caller must have disabled interrupts.
2450 static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
2454 /* Adjust nesting, check for fully idle. */
2456 rdtp->dynticks_idle_nesting--;
2457 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
2458 if (rdtp->dynticks_idle_nesting != 0)
2459 return; /* Still not fully idle. */
2461 if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) ==
2462 DYNTICK_TASK_NEST_VALUE) {
2463 rdtp->dynticks_idle_nesting = 0;
2465 rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE;
2466 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
2467 return; /* Still not fully idle. */
2471 /* Record start of fully idle period. */
2473 ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j;
2474 smp_mb__before_atomic_inc();
2475 atomic_inc(&rdtp->dynticks_idle);
2476 smp_mb__after_atomic_inc();
2477 WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
2481 * Unconditionally force exit from full system-idle state. This is
2482 * invoked when a normal CPU exits idle, but must be called separately
2483 * for the timekeeping CPU (tick_do_timer_cpu). The reason for this
2484 * is that the timekeeping CPU is permitted to take scheduling-clock
2485 * interrupts while the system is in system-idle state, and of course
2486 * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
2487 * interrupt from any other type of interrupt.
2489 void rcu_sysidle_force_exit(void)
2491 int oldstate = ACCESS_ONCE(full_sysidle_state);
2495 * Each pass through the following loop attempts to exit full
2496 * system-idle state. If contention proves to be a problem,
2497 * a trylock-based contention tree could be used here.
2499 while (oldstate > RCU_SYSIDLE_SHORT) {
2500 newoldstate = cmpxchg(&full_sysidle_state,
2501 oldstate, RCU_SYSIDLE_NOT);
2502 if (oldstate == newoldstate &&
2503 oldstate == RCU_SYSIDLE_FULL_NOTED) {
2504 rcu_kick_nohz_cpu(tick_do_timer_cpu);
2505 return; /* We cleared it, done! */
2507 oldstate = newoldstate;
2509 smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
2513 * Invoked to note entry to irq or task transition from idle. Note that
2514 * usermode execution does -not- count as idle here! The caller must
2515 * have disabled interrupts.
2517 static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
2519 /* Adjust nesting, check for already non-idle. */
2521 rdtp->dynticks_idle_nesting++;
2522 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
2523 if (rdtp->dynticks_idle_nesting != 1)
2524 return; /* Already non-idle. */
2527 * Allow for irq misnesting. Yes, it really is possible
2528 * to enter an irq handler then never leave it, and maybe
2529 * also vice versa. Handle both possibilities.
2531 if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) {
2532 rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE;
2533 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
2534 return; /* Already non-idle. */
2536 rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE;
2540 /* Record end of idle period. */
2541 smp_mb__before_atomic_inc();
2542 atomic_inc(&rdtp->dynticks_idle);
2543 smp_mb__after_atomic_inc();
2544 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
2547 * If we are the timekeeping CPU, we are permitted to be non-idle
2548 * during a system-idle state. This must be the case, because
2549 * the timekeeping CPU has to take scheduling-clock interrupts
2550 * during the time that the system is transitioning to full
2551 * system-idle state. This means that the timekeeping CPU must
2552 * invoke rcu_sysidle_force_exit() directly if it does anything
2553 * more than take a scheduling-clock interrupt.
2555 if (smp_processor_id() == tick_do_timer_cpu)
2558 /* Update system-idle state: We are clearly no longer fully idle! */
2559 rcu_sysidle_force_exit();
2563 * Check to see if the current CPU is idle. Note that usermode execution
2564 * does not count as idle. The caller must have disabled interrupts.
2566 static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
2567 unsigned long *maxj)
2571 struct rcu_dynticks *rdtp = rdp->dynticks;
2574 * If some other CPU has already reported non-idle, if this is
2575 * not the flavor of RCU that tracks sysidle state, or if this
2576 * is an offline or the timekeeping CPU, nothing to do.
2578 if (!*isidle || rdp->rsp != rcu_sysidle_state ||
2579 cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
2581 if (rcu_gp_in_progress(rdp->rsp))
2582 WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
2584 /* Pick up current idle and NMI-nesting counter and check. */
2585 cur = atomic_read(&rdtp->dynticks_idle);
2587 *isidle = false; /* We are not idle! */
2590 smp_mb(); /* Read counters before timestamps. */
2592 /* Pick up timestamps. */
2593 j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies);
2594 /* If this CPU entered idle more recently, update maxj timestamp. */
2595 if (ULONG_CMP_LT(*maxj, j))
2600 * Is this the flavor of RCU that is handling full-system idle?
2602 static bool is_sysidle_rcu_state(struct rcu_state *rsp)
2604 return rsp == rcu_sysidle_state;
2608 * Bind the grace-period kthread for the sysidle flavor of RCU to the
2611 static void rcu_bind_gp_kthread(void)
2613 int cpu = ACCESS_ONCE(tick_do_timer_cpu);
2615 if (cpu < 0 || cpu >= nr_cpu_ids)
2617 if (raw_smp_processor_id() != cpu)
2618 set_cpus_allowed_ptr(current, cpumask_of(cpu));
2622 * Return a delay in jiffies based on the number of CPUs, rcu_node
2623 * leaf fanout, and jiffies tick rate. The idea is to allow larger
2624 * systems more time to transition to full-idle state in order to
2625 * avoid the cache thrashing that otherwise occur on the state variable.
2626 * Really small systems (less than a couple of tens of CPUs) should
2627 * instead use a single global atomically incremented counter, and later
2628 * versions of this will automatically reconfigure themselves accordingly.
2630 static unsigned long rcu_sysidle_delay(void)
2632 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
2634 return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000);
2638 * Advance the full-system-idle state. This is invoked when all of
2639 * the non-timekeeping CPUs are idle.
2641 static void rcu_sysidle(unsigned long j)
2643 /* Check the current state. */
2644 switch (ACCESS_ONCE(full_sysidle_state)) {
2645 case RCU_SYSIDLE_NOT:
2647 /* First time all are idle, so note a short idle period. */
2648 ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT;
2651 case RCU_SYSIDLE_SHORT:
2654 * Idle for a bit, time to advance to next state?
2655 * cmpxchg failure means race with non-idle, let them win.
2657 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
2658 (void)cmpxchg(&full_sysidle_state,
2659 RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG);
2662 case RCU_SYSIDLE_LONG:
2665 * Do an additional check pass before advancing to full.
2666 * cmpxchg failure means race with non-idle, let them win.
2668 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
2669 (void)cmpxchg(&full_sysidle_state,
2670 RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL);
2679 * Found a non-idle non-timekeeping CPU, so kick the system-idle state
2680 * back to the beginning.
2682 static void rcu_sysidle_cancel(void)
2685 ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT;
2689 * Update the sysidle state based on the results of a force-quiescent-state
2690 * scan of the CPUs' dyntick-idle state.
2692 static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
2693 unsigned long maxj, bool gpkt)
2695 if (rsp != rcu_sysidle_state)
2696 return; /* Wrong flavor, ignore. */
2697 if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
2698 return; /* Running state machine from timekeeping CPU. */
2700 rcu_sysidle(maxj); /* More idle! */
2702 rcu_sysidle_cancel(); /* Idle is over. */
2706 * Wrapper for rcu_sysidle_report() when called from the grace-period
2707 * kthread's context.
2709 static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
2712 rcu_sysidle_report(rsp, isidle, maxj, true);
2715 /* Callback and function for forcing an RCU grace period. */
2716 struct rcu_sysidle_head {
2721 static void rcu_sysidle_cb(struct rcu_head *rhp)
2723 struct rcu_sysidle_head *rshp;
2726 * The following memory barrier is needed to replace the
2727 * memory barriers that would normally be in the memory
2730 smp_mb(); /* grace period precedes setting inuse. */
2732 rshp = container_of(rhp, struct rcu_sysidle_head, rh);
2733 ACCESS_ONCE(rshp->inuse) = 0;
2737 * Check to see if the system is fully idle, other than the timekeeping CPU.
2738 * The caller must have disabled interrupts.
2740 bool rcu_sys_is_idle(void)
2742 static struct rcu_sysidle_head rsh;
2743 int rss = ACCESS_ONCE(full_sysidle_state);
2745 if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu))
2748 /* Handle small-system case by doing a full scan of CPUs. */
2749 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) {
2750 int oldrss = rss - 1;
2753 * One pass to advance to each state up to _FULL.
2754 * Give up if any pass fails to advance the state.
2756 while (rss < RCU_SYSIDLE_FULL && oldrss < rss) {
2759 unsigned long maxj = jiffies - ULONG_MAX / 4;
2760 struct rcu_data *rdp;
2762 /* Scan all the CPUs looking for nonidle CPUs. */
2763 for_each_possible_cpu(cpu) {
2764 rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu);
2765 rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
2769 rcu_sysidle_report(rcu_sysidle_state,
2770 isidle, maxj, false);
2772 rss = ACCESS_ONCE(full_sysidle_state);
2776 /* If this is the first observation of an idle period, record it. */
2777 if (rss == RCU_SYSIDLE_FULL) {
2778 rss = cmpxchg(&full_sysidle_state,
2779 RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED);
2780 return rss == RCU_SYSIDLE_FULL;
2783 smp_mb(); /* ensure rss load happens before later caller actions. */
2785 /* If already fully idle, tell the caller (in case of races). */
2786 if (rss == RCU_SYSIDLE_FULL_NOTED)
2790 * If we aren't there yet, and a grace period is not in flight,
2791 * initiate a grace period. Either way, tell the caller that
2792 * we are not there yet. We use an xchg() rather than an assignment
2793 * to make up for the memory barriers that would otherwise be
2794 * provided by the memory allocator.
2796 if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
2797 !rcu_gp_in_progress(rcu_sysidle_state) &&
2798 !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
2799 call_rcu(&rsh.rh, rcu_sysidle_cb);
2804 * Initialize dynticks sysidle state for CPUs coming online.
2806 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
2808 rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE;
2811 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
2813 static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
2817 static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
2821 static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
2822 unsigned long *maxj)
2826 static bool is_sysidle_rcu_state(struct rcu_state *rsp)
2831 static void rcu_bind_gp_kthread(void)
2835 static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
2840 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
2844 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */