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 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
208 t->rcu_blocked_node = rnp;
211 * If this CPU has already checked in, then this task
212 * will hold up the next grace period rather than the
213 * current grace period. Queue the task accordingly.
214 * If the task is queued for the current grace period
215 * (i.e., this CPU has not yet passed through a quiescent
216 * state for the current grace period), then as long
217 * as that task remains queued, the current grace period
218 * cannot end. Note that there is some uncertainty as
219 * to exactly when the current grace period started.
220 * We take a conservative approach, which can result
221 * in unnecessarily waiting on tasks that started very
222 * slightly after the current grace period began. C'est
225 * But first, note that the current CPU must still be
228 WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
229 WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
230 if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
231 list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
232 rnp->gp_tasks = &t->rcu_node_entry;
233 #ifdef CONFIG_RCU_BOOST
234 if (rnp->boost_tasks != NULL)
235 rnp->boost_tasks = rnp->gp_tasks;
236 #endif /* #ifdef CONFIG_RCU_BOOST */
238 list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
239 if (rnp->qsmask & rdp->grpmask)
240 rnp->gp_tasks = &t->rcu_node_entry;
242 trace_rcu_preempt_task(rdp->rsp->name,
244 (rnp->qsmask & rdp->grpmask)
247 raw_spin_unlock_irqrestore(&rnp->lock, flags);
248 } else if (t->rcu_read_lock_nesting < 0 &&
249 t->rcu_read_unlock_special) {
252 * Complete exit from RCU read-side critical section on
253 * behalf of preempted instance of __rcu_read_unlock().
255 rcu_read_unlock_special(t);
259 * Either we were not in an RCU read-side critical section to
260 * begin with, or we have now recorded that critical section
261 * globally. Either way, we can now note a quiescent state
262 * for this CPU. Again, if we were in an RCU read-side critical
263 * section, and if that critical section was blocking the current
264 * grace period, then the fact that the task has been enqueued
265 * means that we continue to block the current grace period.
267 local_irq_save(flags);
269 local_irq_restore(flags);
273 * Check for preempted RCU readers blocking the current grace period
274 * for the specified rcu_node structure. If the caller needs a reliable
275 * answer, it must hold the rcu_node's ->lock.
277 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
279 return rnp->gp_tasks != NULL;
283 * Record a quiescent state for all tasks that were previously queued
284 * on the specified rcu_node structure and that were blocking the current
285 * RCU grace period. The caller must hold the specified rnp->lock with
286 * irqs disabled, and this lock is released upon return, but irqs remain
289 static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
290 __releases(rnp->lock)
293 struct rcu_node *rnp_p;
295 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
296 raw_spin_unlock_irqrestore(&rnp->lock, flags);
297 return; /* Still need more quiescent states! */
303 * Either there is only one rcu_node in the tree,
304 * or tasks were kicked up to root rcu_node due to
305 * CPUs going offline.
307 rcu_report_qs_rsp(&rcu_preempt_state, flags);
311 /* Report up the rest of the hierarchy. */
313 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
314 raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */
315 rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
319 * Advance a ->blkd_tasks-list pointer to the next entry, instead
320 * returning NULL if at the end of the list.
322 static struct list_head *rcu_next_node_entry(struct task_struct *t,
323 struct rcu_node *rnp)
325 struct list_head *np;
327 np = t->rcu_node_entry.next;
328 if (np == &rnp->blkd_tasks)
334 * Handle special cases during rcu_read_unlock(), such as needing to
335 * notify RCU core processing or task having blocked during the RCU
336 * read-side critical section.
338 void rcu_read_unlock_special(struct task_struct *t)
344 struct list_head *np;
345 #ifdef CONFIG_RCU_BOOST
346 struct rt_mutex *rbmp = NULL;
347 #endif /* #ifdef CONFIG_RCU_BOOST */
348 struct rcu_node *rnp;
351 /* NMI handlers cannot block and cannot safely manipulate state. */
355 local_irq_save(flags);
358 * If RCU core is waiting for this CPU to exit critical section,
359 * let it know that we have done so.
361 special = t->rcu_read_unlock_special;
362 if (special & RCU_READ_UNLOCK_NEED_QS) {
363 rcu_preempt_qs(smp_processor_id());
366 /* Hardware IRQ handlers cannot block. */
367 if (in_irq() || in_serving_softirq()) {
368 local_irq_restore(flags);
372 /* Clean up if blocked during RCU read-side critical section. */
373 if (special & RCU_READ_UNLOCK_BLOCKED) {
374 t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
377 * Remove this task from the list it blocked on. The
378 * task can migrate while we acquire the lock, but at
379 * most one time. So at most two passes through loop.
382 rnp = t->rcu_blocked_node;
383 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
384 if (rnp == t->rcu_blocked_node)
386 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
388 empty = !rcu_preempt_blocked_readers_cgp(rnp);
389 empty_exp = !rcu_preempted_readers_exp(rnp);
390 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
391 np = rcu_next_node_entry(t, rnp);
392 list_del_init(&t->rcu_node_entry);
393 t->rcu_blocked_node = NULL;
394 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
396 if (&t->rcu_node_entry == rnp->gp_tasks)
398 if (&t->rcu_node_entry == rnp->exp_tasks)
400 #ifdef CONFIG_RCU_BOOST
401 if (&t->rcu_node_entry == rnp->boost_tasks)
402 rnp->boost_tasks = np;
403 /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
404 if (t->rcu_boost_mutex) {
405 rbmp = t->rcu_boost_mutex;
406 t->rcu_boost_mutex = NULL;
408 #endif /* #ifdef CONFIG_RCU_BOOST */
411 * If this was the last task on the current list, and if
412 * we aren't waiting on any CPUs, report the quiescent state.
413 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
414 * so we must take a snapshot of the expedited state.
416 empty_exp_now = !rcu_preempted_readers_exp(rnp);
417 if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
418 trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
425 rcu_report_unblock_qs_rnp(rnp, flags);
427 raw_spin_unlock_irqrestore(&rnp->lock, flags);
430 #ifdef CONFIG_RCU_BOOST
431 /* Unboost if we were boosted. */
433 rt_mutex_unlock(rbmp);
434 #endif /* #ifdef CONFIG_RCU_BOOST */
437 * If this was the last task on the expedited lists,
438 * then we need to report up the rcu_node hierarchy.
440 if (!empty_exp && empty_exp_now)
441 rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
443 local_irq_restore(flags);
447 #ifdef CONFIG_RCU_CPU_STALL_VERBOSE
450 * Dump detailed information for all tasks blocking the current RCU
451 * grace period on the specified rcu_node structure.
453 static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
456 struct task_struct *t;
458 raw_spin_lock_irqsave(&rnp->lock, flags);
459 if (!rcu_preempt_blocked_readers_cgp(rnp)) {
460 raw_spin_unlock_irqrestore(&rnp->lock, flags);
463 t = list_entry(rnp->gp_tasks,
464 struct task_struct, rcu_node_entry);
465 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
467 raw_spin_unlock_irqrestore(&rnp->lock, flags);
471 * Dump detailed information for all tasks blocking the current RCU
474 static void rcu_print_detail_task_stall(struct rcu_state *rsp)
476 struct rcu_node *rnp = rcu_get_root(rsp);
478 rcu_print_detail_task_stall_rnp(rnp);
479 rcu_for_each_leaf_node(rsp, rnp)
480 rcu_print_detail_task_stall_rnp(rnp);
483 #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
485 static void rcu_print_detail_task_stall(struct rcu_state *rsp)
489 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
491 #ifdef CONFIG_RCU_CPU_STALL_INFO
493 static void rcu_print_task_stall_begin(struct rcu_node *rnp)
495 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
496 rnp->level, rnp->grplo, rnp->grphi);
499 static void rcu_print_task_stall_end(void)
504 #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
506 static void rcu_print_task_stall_begin(struct rcu_node *rnp)
510 static void rcu_print_task_stall_end(void)
514 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
517 * Scan the current list of tasks blocked within RCU read-side critical
518 * sections, printing out the tid of each.
520 static int rcu_print_task_stall(struct rcu_node *rnp)
522 struct task_struct *t;
525 if (!rcu_preempt_blocked_readers_cgp(rnp))
527 rcu_print_task_stall_begin(rnp);
528 t = list_entry(rnp->gp_tasks,
529 struct task_struct, rcu_node_entry);
530 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
531 pr_cont(" P%d", t->pid);
534 rcu_print_task_stall_end();
539 * Check that the list of blocked tasks for the newly completed grace
540 * period is in fact empty. It is a serious bug to complete a grace
541 * period that still has RCU readers blocked! This function must be
542 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
543 * must be held by the caller.
545 * Also, if there are blocked tasks on the list, they automatically
546 * block the newly created grace period, so set up ->gp_tasks accordingly.
548 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
550 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
551 if (!list_empty(&rnp->blkd_tasks))
552 rnp->gp_tasks = rnp->blkd_tasks.next;
553 WARN_ON_ONCE(rnp->qsmask);
556 #ifdef CONFIG_HOTPLUG_CPU
559 * Handle tasklist migration for case in which all CPUs covered by the
560 * specified rcu_node have gone offline. Move them up to the root
561 * rcu_node. The reason for not just moving them to the immediate
562 * parent is to remove the need for rcu_read_unlock_special() to
563 * make more than two attempts to acquire the target rcu_node's lock.
564 * Returns true if there were tasks blocking the current RCU grace
567 * Returns 1 if there was previously a task blocking the current grace
568 * period on the specified rcu_node structure.
570 * The caller must hold rnp->lock with irqs disabled.
572 static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
573 struct rcu_node *rnp,
574 struct rcu_data *rdp)
576 struct list_head *lp;
577 struct list_head *lp_root;
579 struct rcu_node *rnp_root = rcu_get_root(rsp);
580 struct task_struct *t;
582 if (rnp == rnp_root) {
583 WARN_ONCE(1, "Last CPU thought to be offlined?");
584 return 0; /* Shouldn't happen: at least one CPU online. */
587 /* If we are on an internal node, complain bitterly. */
588 WARN_ON_ONCE(rnp != rdp->mynode);
591 * Move tasks up to root rcu_node. Don't try to get fancy for
592 * this corner-case operation -- just put this node's tasks
593 * at the head of the root node's list, and update the root node's
594 * ->gp_tasks and ->exp_tasks pointers to those of this node's,
595 * if non-NULL. This might result in waiting for more tasks than
596 * absolutely necessary, but this is a good performance/complexity
599 if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
600 retval |= RCU_OFL_TASKS_NORM_GP;
601 if (rcu_preempted_readers_exp(rnp))
602 retval |= RCU_OFL_TASKS_EXP_GP;
603 lp = &rnp->blkd_tasks;
604 lp_root = &rnp_root->blkd_tasks;
605 while (!list_empty(lp)) {
606 t = list_entry(lp->next, typeof(*t), rcu_node_entry);
607 raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
608 list_del(&t->rcu_node_entry);
609 t->rcu_blocked_node = rnp_root;
610 list_add(&t->rcu_node_entry, lp_root);
611 if (&t->rcu_node_entry == rnp->gp_tasks)
612 rnp_root->gp_tasks = rnp->gp_tasks;
613 if (&t->rcu_node_entry == rnp->exp_tasks)
614 rnp_root->exp_tasks = rnp->exp_tasks;
615 #ifdef CONFIG_RCU_BOOST
616 if (&t->rcu_node_entry == rnp->boost_tasks)
617 rnp_root->boost_tasks = rnp->boost_tasks;
618 #endif /* #ifdef CONFIG_RCU_BOOST */
619 raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
622 rnp->gp_tasks = NULL;
623 rnp->exp_tasks = NULL;
624 #ifdef CONFIG_RCU_BOOST
625 rnp->boost_tasks = NULL;
627 * In case root is being boosted and leaf was not. Make sure
628 * that we boost the tasks blocking the current grace period
631 raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
632 if (rnp_root->boost_tasks != NULL &&
633 rnp_root->boost_tasks != rnp_root->gp_tasks &&
634 rnp_root->boost_tasks != rnp_root->exp_tasks)
635 rnp_root->boost_tasks = rnp_root->gp_tasks;
636 raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
637 #endif /* #ifdef CONFIG_RCU_BOOST */
642 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
645 * Check for a quiescent state from the current CPU. When a task blocks,
646 * the task is recorded in the corresponding CPU's rcu_node structure,
647 * which is checked elsewhere.
649 * Caller must disable hard irqs.
651 static void rcu_preempt_check_callbacks(int cpu)
653 struct task_struct *t = current;
655 if (t->rcu_read_lock_nesting == 0) {
659 if (t->rcu_read_lock_nesting > 0 &&
660 per_cpu(rcu_preempt_data, cpu).qs_pending)
661 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
664 #ifdef CONFIG_RCU_BOOST
666 static void rcu_preempt_do_callbacks(void)
668 rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
671 #endif /* #ifdef CONFIG_RCU_BOOST */
674 * Queue a preemptible-RCU callback for invocation after a grace period.
676 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
678 __call_rcu(head, func, &rcu_preempt_state, -1, 0);
680 EXPORT_SYMBOL_GPL(call_rcu);
683 * Queue an RCU callback for lazy invocation after a grace period.
684 * This will likely be later named something like "call_rcu_lazy()",
685 * but this change will require some way of tagging the lazy RCU
686 * callbacks in the list of pending callbacks. Until then, this
687 * function may only be called from __kfree_rcu().
689 void kfree_call_rcu(struct rcu_head *head,
690 void (*func)(struct rcu_head *rcu))
692 __call_rcu(head, func, &rcu_preempt_state, -1, 1);
694 EXPORT_SYMBOL_GPL(kfree_call_rcu);
697 * synchronize_rcu - wait until a grace period has elapsed.
699 * Control will return to the caller some time after a full grace
700 * period has elapsed, in other words after all currently executing RCU
701 * read-side critical sections have completed. Note, however, that
702 * upon return from synchronize_rcu(), the caller might well be executing
703 * concurrently with new RCU read-side critical sections that began while
704 * synchronize_rcu() was waiting. RCU read-side critical sections are
705 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
707 * See the description of synchronize_sched() for more detailed information
708 * on memory ordering guarantees.
710 void synchronize_rcu(void)
712 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
713 !lock_is_held(&rcu_lock_map) &&
714 !lock_is_held(&rcu_sched_lock_map),
715 "Illegal synchronize_rcu() in RCU read-side critical section");
716 if (!rcu_scheduler_active)
719 synchronize_rcu_expedited();
721 wait_rcu_gp(call_rcu);
723 EXPORT_SYMBOL_GPL(synchronize_rcu);
725 static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
726 static unsigned long sync_rcu_preempt_exp_count;
727 static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
730 * Return non-zero if there are any tasks in RCU read-side critical
731 * sections blocking the current preemptible-RCU expedited grace period.
732 * If there is no preemptible-RCU expedited grace period currently in
733 * progress, returns zero unconditionally.
735 static int rcu_preempted_readers_exp(struct rcu_node *rnp)
737 return rnp->exp_tasks != NULL;
741 * return non-zero if there is no RCU expedited grace period in progress
742 * for the specified rcu_node structure, in other words, if all CPUs and
743 * tasks covered by the specified rcu_node structure have done their bit
744 * for the current expedited grace period. Works only for preemptible
745 * RCU -- other RCU implementation use other means.
747 * Caller must hold sync_rcu_preempt_exp_mutex.
749 static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
751 return !rcu_preempted_readers_exp(rnp) &&
752 ACCESS_ONCE(rnp->expmask) == 0;
756 * Report the exit from RCU read-side critical section for the last task
757 * that queued itself during or before the current expedited preemptible-RCU
758 * grace period. This event is reported either to the rcu_node structure on
759 * which the task was queued or to one of that rcu_node structure's ancestors,
760 * recursively up the tree. (Calm down, calm down, we do the recursion
763 * Most callers will set the "wake" flag, but the task initiating the
764 * expedited grace period need not wake itself.
766 * Caller must hold sync_rcu_preempt_exp_mutex.
768 static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
774 raw_spin_lock_irqsave(&rnp->lock, flags);
776 if (!sync_rcu_preempt_exp_done(rnp)) {
777 raw_spin_unlock_irqrestore(&rnp->lock, flags);
780 if (rnp->parent == NULL) {
781 raw_spin_unlock_irqrestore(&rnp->lock, flags);
783 smp_mb(); /* EGP done before wake_up(). */
784 wake_up(&sync_rcu_preempt_exp_wq);
789 raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
791 raw_spin_lock(&rnp->lock); /* irqs already disabled */
792 rnp->expmask &= ~mask;
797 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
798 * grace period for the specified rcu_node structure. If there are no such
799 * tasks, report it up the rcu_node hierarchy.
801 * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
802 * CPU hotplug operations.
805 sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
810 raw_spin_lock_irqsave(&rnp->lock, flags);
811 if (list_empty(&rnp->blkd_tasks)) {
812 raw_spin_unlock_irqrestore(&rnp->lock, flags);
814 rnp->exp_tasks = rnp->blkd_tasks.next;
815 rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
819 rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
823 * synchronize_rcu_expedited - Brute-force RCU grace period
825 * Wait for an RCU-preempt grace period, but expedite it. The basic
826 * idea is to invoke synchronize_sched_expedited() to push all the tasks to
827 * the ->blkd_tasks lists and wait for this list to drain. This consumes
828 * significant time on all CPUs and is unfriendly to real-time workloads,
829 * so is thus not recommended for any sort of common-case code.
830 * In fact, if you are using synchronize_rcu_expedited() in a loop,
831 * please restructure your code to batch your updates, and then Use a
832 * single synchronize_rcu() instead.
834 * Note that it is illegal to call this function while holding any lock
835 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
836 * to call this function from a CPU-hotplug notifier. Failing to observe
837 * these restriction will result in deadlock.
839 void synchronize_rcu_expedited(void)
842 struct rcu_node *rnp;
843 struct rcu_state *rsp = &rcu_preempt_state;
847 smp_mb(); /* Caller's modifications seen first by other CPUs. */
848 snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
849 smp_mb(); /* Above access cannot bleed into critical section. */
852 * Block CPU-hotplug operations. This means that any CPU-hotplug
853 * operation that finds an rcu_node structure with tasks in the
854 * process of being boosted will know that all tasks blocking
855 * this expedited grace period will already be in the process of
856 * being boosted. This simplifies the process of moving tasks
857 * from leaf to root rcu_node structures.
862 * Acquire lock, falling back to synchronize_rcu() if too many
863 * lock-acquisition failures. Of course, if someone does the
864 * expedited grace period for us, just leave.
866 while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
867 if (ULONG_CMP_LT(snap,
868 ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
870 goto mb_ret; /* Others did our work for us. */
872 if (trycount++ < 10) {
873 udelay(trycount * num_online_cpus());
876 wait_rcu_gp(call_rcu);
880 if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
882 goto unlock_mb_ret; /* Others did our work for us. */
885 /* force all RCU readers onto ->blkd_tasks lists. */
886 synchronize_sched_expedited();
888 /* Initialize ->expmask for all non-leaf rcu_node structures. */
889 rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
890 raw_spin_lock_irqsave(&rnp->lock, flags);
891 rnp->expmask = rnp->qsmaskinit;
892 raw_spin_unlock_irqrestore(&rnp->lock, flags);
895 /* Snapshot current state of ->blkd_tasks lists. */
896 rcu_for_each_leaf_node(rsp, rnp)
897 sync_rcu_preempt_exp_init(rsp, rnp);
898 if (NUM_RCU_NODES > 1)
899 sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
903 /* Wait for snapshotted ->blkd_tasks lists to drain. */
904 rnp = rcu_get_root(rsp);
905 wait_event(sync_rcu_preempt_exp_wq,
906 sync_rcu_preempt_exp_done(rnp));
908 /* Clean up and exit. */
909 smp_mb(); /* ensure expedited GP seen before counter increment. */
910 ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
912 mutex_unlock(&sync_rcu_preempt_exp_mutex);
914 smp_mb(); /* ensure subsequent action seen after grace period. */
916 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
919 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
921 * Note that this primitive does not necessarily wait for an RCU grace period
922 * to complete. For example, if there are no RCU callbacks queued anywhere
923 * in the system, then rcu_barrier() is within its rights to return
924 * immediately, without waiting for anything, much less an RCU grace period.
926 void rcu_barrier(void)
928 _rcu_barrier(&rcu_preempt_state);
930 EXPORT_SYMBOL_GPL(rcu_barrier);
933 * Initialize preemptible RCU's state structures.
935 static void __init __rcu_init_preempt(void)
937 rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
941 * Check for a task exiting while in a preemptible-RCU read-side
942 * critical section, clean up if so. No need to issue warnings,
943 * as debug_check_no_locks_held() already does this if lockdep
948 struct task_struct *t = current;
950 if (likely(list_empty(¤t->rcu_node_entry)))
952 t->rcu_read_lock_nesting = 1;
954 t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
958 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
960 static struct rcu_state *rcu_state = &rcu_sched_state;
963 * Tell them what RCU they are running.
965 static void __init rcu_bootup_announce(void)
967 pr_info("Hierarchical RCU implementation.\n");
968 rcu_bootup_announce_oddness();
972 * Return the number of RCU batches processed thus far for debug & stats.
974 long rcu_batches_completed(void)
976 return rcu_batches_completed_sched();
978 EXPORT_SYMBOL_GPL(rcu_batches_completed);
981 * Force a quiescent state for RCU, which, because there is no preemptible
982 * RCU, becomes the same as rcu-sched.
984 void rcu_force_quiescent_state(void)
986 rcu_sched_force_quiescent_state();
988 EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
991 * Because preemptible RCU does not exist, we never have to check for
992 * CPUs being in quiescent states.
994 static void rcu_preempt_note_context_switch(int cpu)
999 * Because preemptible RCU does not exist, there are never any preempted
1002 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
1007 #ifdef CONFIG_HOTPLUG_CPU
1009 /* Because preemptible RCU does not exist, no quieting of tasks. */
1010 static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
1012 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1015 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1018 * Because preemptible RCU does not exist, we never have to check for
1019 * tasks blocked within RCU read-side critical sections.
1021 static void rcu_print_detail_task_stall(struct rcu_state *rsp)
1026 * Because preemptible RCU does not exist, we never have to check for
1027 * tasks blocked within RCU read-side critical sections.
1029 static int rcu_print_task_stall(struct rcu_node *rnp)
1035 * Because there is no preemptible RCU, there can be no readers blocked,
1036 * so there is no need to check for blocked tasks. So check only for
1037 * bogus qsmask values.
1039 static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
1041 WARN_ON_ONCE(rnp->qsmask);
1044 #ifdef CONFIG_HOTPLUG_CPU
1047 * Because preemptible RCU does not exist, it never needs to migrate
1048 * tasks that were blocked within RCU read-side critical sections, and
1049 * such non-existent tasks cannot possibly have been blocking the current
1052 static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
1053 struct rcu_node *rnp,
1054 struct rcu_data *rdp)
1059 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1062 * Because preemptible RCU does not exist, it never has any callbacks
1065 static void rcu_preempt_check_callbacks(int cpu)
1070 * Queue an RCU callback for lazy invocation after a grace period.
1071 * This will likely be later named something like "call_rcu_lazy()",
1072 * but this change will require some way of tagging the lazy RCU
1073 * callbacks in the list of pending callbacks. Until then, this
1074 * function may only be called from __kfree_rcu().
1076 * Because there is no preemptible RCU, we use RCU-sched instead.
1078 void kfree_call_rcu(struct rcu_head *head,
1079 void (*func)(struct rcu_head *rcu))
1081 __call_rcu(head, func, &rcu_sched_state, -1, 1);
1083 EXPORT_SYMBOL_GPL(kfree_call_rcu);
1086 * Wait for an rcu-preempt grace period, but make it happen quickly.
1087 * But because preemptible RCU does not exist, map to rcu-sched.
1089 void synchronize_rcu_expedited(void)
1091 synchronize_sched_expedited();
1093 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
1095 #ifdef CONFIG_HOTPLUG_CPU
1098 * Because preemptible RCU does not exist, there is never any need to
1099 * report on tasks preempted in RCU read-side critical sections during
1100 * expedited RCU grace periods.
1102 static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
1107 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1110 * Because preemptible RCU does not exist, rcu_barrier() is just
1111 * another name for rcu_barrier_sched().
1113 void rcu_barrier(void)
1115 rcu_barrier_sched();
1117 EXPORT_SYMBOL_GPL(rcu_barrier);
1120 * Because preemptible RCU does not exist, it need not be initialized.
1122 static void __init __rcu_init_preempt(void)
1127 * Because preemptible RCU does not exist, tasks cannot possibly exit
1128 * while in preemptible RCU read-side critical sections.
1134 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1136 #ifdef CONFIG_RCU_BOOST
1138 #include "../locking/rtmutex_common.h"
1140 #ifdef CONFIG_RCU_TRACE
1142 static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1144 if (list_empty(&rnp->blkd_tasks))
1145 rnp->n_balk_blkd_tasks++;
1146 else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
1147 rnp->n_balk_exp_gp_tasks++;
1148 else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
1149 rnp->n_balk_boost_tasks++;
1150 else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
1151 rnp->n_balk_notblocked++;
1152 else if (rnp->gp_tasks != NULL &&
1153 ULONG_CMP_LT(jiffies, rnp->boost_time))
1154 rnp->n_balk_notyet++;
1159 #else /* #ifdef CONFIG_RCU_TRACE */
1161 static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1165 #endif /* #else #ifdef CONFIG_RCU_TRACE */
1167 static void rcu_wake_cond(struct task_struct *t, int status)
1170 * If the thread is yielding, only wake it when this
1171 * is invoked from idle
1173 if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
1178 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
1179 * or ->boost_tasks, advancing the pointer to the next task in the
1180 * ->blkd_tasks list.
1182 * Note that irqs must be enabled: boosting the task can block.
1183 * Returns 1 if there are more tasks needing to be boosted.
1185 static int rcu_boost(struct rcu_node *rnp)
1187 unsigned long flags;
1188 struct rt_mutex mtx;
1189 struct task_struct *t;
1190 struct list_head *tb;
1192 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
1193 return 0; /* Nothing left to boost. */
1195 raw_spin_lock_irqsave(&rnp->lock, flags);
1198 * Recheck under the lock: all tasks in need of boosting
1199 * might exit their RCU read-side critical sections on their own.
1201 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
1202 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1207 * Preferentially boost tasks blocking expedited grace periods.
1208 * This cannot starve the normal grace periods because a second
1209 * expedited grace period must boost all blocked tasks, including
1210 * those blocking the pre-existing normal grace period.
1212 if (rnp->exp_tasks != NULL) {
1213 tb = rnp->exp_tasks;
1214 rnp->n_exp_boosts++;
1216 tb = rnp->boost_tasks;
1217 rnp->n_normal_boosts++;
1219 rnp->n_tasks_boosted++;
1222 * We boost task t by manufacturing an rt_mutex that appears to
1223 * be held by task t. We leave a pointer to that rt_mutex where
1224 * task t can find it, and task t will release the mutex when it
1225 * exits its outermost RCU read-side critical section. Then
1226 * simply acquiring this artificial rt_mutex will boost task
1227 * t's priority. (Thanks to tglx for suggesting this approach!)
1229 * Note that task t must acquire rnp->lock to remove itself from
1230 * the ->blkd_tasks list, which it will do from exit() if from
1231 * nowhere else. We therefore are guaranteed that task t will
1232 * stay around at least until we drop rnp->lock. Note that
1233 * rnp->lock also resolves races between our priority boosting
1234 * and task t's exiting its outermost RCU read-side critical
1237 t = container_of(tb, struct task_struct, rcu_node_entry);
1238 rt_mutex_init_proxy_locked(&mtx, t);
1239 t->rcu_boost_mutex = &mtx;
1240 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1241 rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */
1242 rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
1244 return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
1245 ACCESS_ONCE(rnp->boost_tasks) != NULL;
1249 * Priority-boosting kthread. One per leaf rcu_node and one for the
1252 static int rcu_boost_kthread(void *arg)
1254 struct rcu_node *rnp = (struct rcu_node *)arg;
1258 trace_rcu_utilization(TPS("Start boost kthread@init"));
1260 rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1261 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1262 rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1263 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1264 rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1265 more2boost = rcu_boost(rnp);
1271 rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1272 trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1273 schedule_timeout_interruptible(2);
1274 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1279 trace_rcu_utilization(TPS("End boost kthread@notreached"));
1284 * Check to see if it is time to start boosting RCU readers that are
1285 * blocking the current grace period, and, if so, tell the per-rcu_node
1286 * kthread to start boosting them. If there is an expedited grace
1287 * period in progress, it is always time to boost.
1289 * The caller must hold rnp->lock, which this function releases.
1290 * The ->boost_kthread_task is immortal, so we don't need to worry
1291 * about it going away.
1293 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1295 struct task_struct *t;
1297 if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1298 rnp->n_balk_exp_gp_tasks++;
1299 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1302 if (rnp->exp_tasks != NULL ||
1303 (rnp->gp_tasks != NULL &&
1304 rnp->boost_tasks == NULL &&
1306 ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1307 if (rnp->exp_tasks == NULL)
1308 rnp->boost_tasks = rnp->gp_tasks;
1309 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1310 t = rnp->boost_kthread_task;
1312 rcu_wake_cond(t, rnp->boost_kthread_status);
1314 rcu_initiate_boost_trace(rnp);
1315 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1320 * Wake up the per-CPU kthread to invoke RCU callbacks.
1322 static void invoke_rcu_callbacks_kthread(void)
1324 unsigned long flags;
1326 local_irq_save(flags);
1327 __this_cpu_write(rcu_cpu_has_work, 1);
1328 if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
1329 current != __this_cpu_read(rcu_cpu_kthread_task)) {
1330 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
1331 __this_cpu_read(rcu_cpu_kthread_status));
1333 local_irq_restore(flags);
1337 * Is the current CPU running the RCU-callbacks kthread?
1338 * Caller must have preemption disabled.
1340 static bool rcu_is_callbacks_kthread(void)
1342 return __this_cpu_read(rcu_cpu_kthread_task) == current;
1345 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1348 * Do priority-boost accounting for the start of a new grace period.
1350 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1352 rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1356 * Create an RCU-boost kthread for the specified node if one does not
1357 * already exist. We only create this kthread for preemptible RCU.
1358 * Returns zero if all is well, a negated errno otherwise.
1360 static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
1361 struct rcu_node *rnp)
1363 int rnp_index = rnp - &rsp->node[0];
1364 unsigned long flags;
1365 struct sched_param sp;
1366 struct task_struct *t;
1368 if (&rcu_preempt_state != rsp)
1371 if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
1375 if (rnp->boost_kthread_task != NULL)
1377 t = kthread_create(rcu_boost_kthread, (void *)rnp,
1378 "rcub/%d", rnp_index);
1381 raw_spin_lock_irqsave(&rnp->lock, flags);
1382 rnp->boost_kthread_task = t;
1383 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1384 sp.sched_priority = RCU_BOOST_PRIO;
1385 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1386 wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1390 static void rcu_kthread_do_work(void)
1392 rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
1393 rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
1394 rcu_preempt_do_callbacks();
1397 static void rcu_cpu_kthread_setup(unsigned int cpu)
1399 struct sched_param sp;
1401 sp.sched_priority = RCU_KTHREAD_PRIO;
1402 sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
1405 static void rcu_cpu_kthread_park(unsigned int cpu)
1407 per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1410 static int rcu_cpu_kthread_should_run(unsigned int cpu)
1412 return __this_cpu_read(rcu_cpu_has_work);
1416 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
1417 * RCU softirq used in flavors and configurations of RCU that do not
1418 * support RCU priority boosting.
1420 static void rcu_cpu_kthread(unsigned int cpu)
1422 unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
1423 char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
1426 for (spincnt = 0; spincnt < 10; spincnt++) {
1427 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1429 *statusp = RCU_KTHREAD_RUNNING;
1430 this_cpu_inc(rcu_cpu_kthread_loops);
1431 local_irq_disable();
1436 rcu_kthread_do_work();
1439 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1440 *statusp = RCU_KTHREAD_WAITING;
1444 *statusp = RCU_KTHREAD_YIELDING;
1445 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1446 schedule_timeout_interruptible(2);
1447 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1448 *statusp = RCU_KTHREAD_WAITING;
1452 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1453 * served by the rcu_node in question. The CPU hotplug lock is still
1454 * held, so the value of rnp->qsmaskinit will be stable.
1456 * We don't include outgoingcpu in the affinity set, use -1 if there is
1457 * no outgoing CPU. If there are no CPUs left in the affinity set,
1458 * this function allows the kthread to execute on any CPU.
1460 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1462 struct task_struct *t = rnp->boost_kthread_task;
1463 unsigned long mask = rnp->qsmaskinit;
1469 if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1471 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
1472 if ((mask & 0x1) && cpu != outgoingcpu)
1473 cpumask_set_cpu(cpu, cm);
1474 if (cpumask_weight(cm) == 0) {
1476 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
1477 cpumask_clear_cpu(cpu, cm);
1478 WARN_ON_ONCE(cpumask_weight(cm) == 0);
1480 set_cpus_allowed_ptr(t, cm);
1481 free_cpumask_var(cm);
1484 static struct smp_hotplug_thread rcu_cpu_thread_spec = {
1485 .store = &rcu_cpu_kthread_task,
1486 .thread_should_run = rcu_cpu_kthread_should_run,
1487 .thread_fn = rcu_cpu_kthread,
1488 .thread_comm = "rcuc/%u",
1489 .setup = rcu_cpu_kthread_setup,
1490 .park = rcu_cpu_kthread_park,
1494 * Spawn all kthreads -- called as soon as the scheduler is running.
1496 static int __init rcu_spawn_kthreads(void)
1498 struct rcu_node *rnp;
1501 rcu_scheduler_fully_active = 1;
1502 for_each_possible_cpu(cpu)
1503 per_cpu(rcu_cpu_has_work, cpu) = 0;
1504 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
1505 rnp = rcu_get_root(rcu_state);
1506 (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1507 if (NUM_RCU_NODES > 1) {
1508 rcu_for_each_leaf_node(rcu_state, rnp)
1509 (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1513 early_initcall(rcu_spawn_kthreads);
1515 static void rcu_prepare_kthreads(int cpu)
1517 struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
1518 struct rcu_node *rnp = rdp->mynode;
1520 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1521 if (rcu_scheduler_fully_active)
1522 (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1525 #else /* #ifdef CONFIG_RCU_BOOST */
1527 static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1529 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1532 static void invoke_rcu_callbacks_kthread(void)
1537 static bool rcu_is_callbacks_kthread(void)
1542 static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1546 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1550 static int __init rcu_scheduler_really_started(void)
1552 rcu_scheduler_fully_active = 1;
1555 early_initcall(rcu_scheduler_really_started);
1557 static void rcu_prepare_kthreads(int cpu)
1561 #endif /* #else #ifdef CONFIG_RCU_BOOST */
1563 #if !defined(CONFIG_RCU_FAST_NO_HZ)
1566 * Check to see if any future RCU-related work will need to be done
1567 * by the current CPU, even if none need be done immediately, returning
1568 * 1 if so. This function is part of the RCU implementation; it is -not-
1569 * an exported member of the RCU API.
1571 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1572 * any flavor of RCU.
1574 int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
1576 *delta_jiffies = ULONG_MAX;
1577 return rcu_cpu_has_callbacks(cpu, NULL);
1581 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1584 static void rcu_cleanup_after_idle(int cpu)
1589 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1592 static void rcu_prepare_for_idle(int cpu)
1597 * Don't bother keeping a running count of the number of RCU callbacks
1598 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1600 static void rcu_idle_count_callbacks_posted(void)
1604 #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1607 * This code is invoked when a CPU goes idle, at which point we want
1608 * to have the CPU do everything required for RCU so that it can enter
1609 * the energy-efficient dyntick-idle mode. This is handled by a
1610 * state machine implemented by rcu_prepare_for_idle() below.
1612 * The following three proprocessor symbols control this state machine:
1614 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1615 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1616 * is sized to be roughly one RCU grace period. Those energy-efficiency
1617 * benchmarkers who might otherwise be tempted to set this to a large
1618 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1619 * system. And if you are -that- concerned about energy efficiency,
1620 * just power the system down and be done with it!
1621 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1622 * permitted to sleep in dyntick-idle mode with only lazy RCU
1623 * callbacks pending. Setting this too high can OOM your system.
1625 * The values below work well in practice. If future workloads require
1626 * adjustment, they can be converted into kernel config parameters, though
1627 * making the state machine smarter might be a better option.
1629 #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1630 #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1632 static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
1633 module_param(rcu_idle_gp_delay, int, 0644);
1634 static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
1635 module_param(rcu_idle_lazy_gp_delay, int, 0644);
1637 extern int tick_nohz_enabled;
1640 * Try to advance callbacks for all flavors of RCU on the current CPU, but
1641 * only if it has been awhile since the last time we did so. Afterwards,
1642 * if there are any callbacks ready for immediate invocation, return true.
1644 static bool rcu_try_advance_all_cbs(void)
1646 bool cbs_ready = false;
1647 struct rcu_data *rdp;
1648 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1649 struct rcu_node *rnp;
1650 struct rcu_state *rsp;
1652 /* Exit early if we advanced recently. */
1653 if (jiffies == rdtp->last_advance_all)
1655 rdtp->last_advance_all = jiffies;
1657 for_each_rcu_flavor(rsp) {
1658 rdp = this_cpu_ptr(rsp->rda);
1662 * Don't bother checking unless a grace period has
1663 * completed since we last checked and there are
1664 * callbacks not yet ready to invoke.
1666 if (rdp->completed != rnp->completed &&
1667 rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
1668 note_gp_changes(rsp, rdp);
1670 if (cpu_has_callbacks_ready_to_invoke(rdp))
1677 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1678 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1679 * caller to set the timeout based on whether or not there are non-lazy
1682 * The caller must have disabled interrupts.
1684 int rcu_needs_cpu(int cpu, unsigned long *dj)
1686 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1688 /* Snapshot to detect later posting of non-lazy callback. */
1689 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1691 /* If no callbacks, RCU doesn't need the CPU. */
1692 if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) {
1697 /* Attempt to advance callbacks. */
1698 if (rcu_try_advance_all_cbs()) {
1699 /* Some ready to invoke, so initiate later invocation. */
1703 rdtp->last_accelerate = jiffies;
1705 /* Request timer delay depending on laziness, and round. */
1706 if (!rdtp->all_lazy) {
1707 *dj = round_up(rcu_idle_gp_delay + jiffies,
1708 rcu_idle_gp_delay) - jiffies;
1710 *dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1716 * Prepare a CPU for idle from an RCU perspective. The first major task
1717 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1718 * The second major task is to check to see if a non-lazy callback has
1719 * arrived at a CPU that previously had only lazy callbacks. The third
1720 * major task is to accelerate (that is, assign grace-period numbers to)
1721 * any recently arrived callbacks.
1723 * The caller must have disabled interrupts.
1725 static void rcu_prepare_for_idle(int cpu)
1727 struct rcu_data *rdp;
1728 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1729 struct rcu_node *rnp;
1730 struct rcu_state *rsp;
1733 /* Handle nohz enablement switches conservatively. */
1734 tne = ACCESS_ONCE(tick_nohz_enabled);
1735 if (tne != rdtp->tick_nohz_enabled_snap) {
1736 if (rcu_cpu_has_callbacks(cpu, NULL))
1737 invoke_rcu_core(); /* force nohz to see update. */
1738 rdtp->tick_nohz_enabled_snap = tne;
1744 /* If this is a no-CBs CPU, no callbacks, just return. */
1745 if (rcu_is_nocb_cpu(cpu))
1749 * If a non-lazy callback arrived at a CPU having only lazy
1750 * callbacks, invoke RCU core for the side-effect of recalculating
1751 * idle duration on re-entry to idle.
1753 if (rdtp->all_lazy &&
1754 rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
1755 rdtp->all_lazy = false;
1756 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1762 * If we have not yet accelerated this jiffy, accelerate all
1763 * callbacks on this CPU.
1765 if (rdtp->last_accelerate == jiffies)
1767 rdtp->last_accelerate = jiffies;
1768 for_each_rcu_flavor(rsp) {
1769 rdp = per_cpu_ptr(rsp->rda, cpu);
1770 if (!*rdp->nxttail[RCU_DONE_TAIL])
1773 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
1774 rcu_accelerate_cbs(rsp, rnp, rdp);
1775 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1780 * Clean up for exit from idle. Attempt to advance callbacks based on
1781 * any grace periods that elapsed while the CPU was idle, and if any
1782 * callbacks are now ready to invoke, initiate invocation.
1784 static void rcu_cleanup_after_idle(int cpu)
1787 if (rcu_is_nocb_cpu(cpu))
1789 if (rcu_try_advance_all_cbs())
1794 * Keep a running count of the number of non-lazy callbacks posted
1795 * on this CPU. This running counter (which is never decremented) allows
1796 * rcu_prepare_for_idle() to detect when something out of the idle loop
1797 * posts a callback, even if an equal number of callbacks are invoked.
1798 * Of course, callbacks should only be posted from within a trace event
1799 * designed to be called from idle or from within RCU_NONIDLE().
1801 static void rcu_idle_count_callbacks_posted(void)
1803 __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
1807 * Data for flushing lazy RCU callbacks at OOM time.
1809 static atomic_t oom_callback_count;
1810 static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
1813 * RCU OOM callback -- decrement the outstanding count and deliver the
1814 * wake-up if we are the last one.
1816 static void rcu_oom_callback(struct rcu_head *rhp)
1818 if (atomic_dec_and_test(&oom_callback_count))
1819 wake_up(&oom_callback_wq);
1823 * Post an rcu_oom_notify callback on the current CPU if it has at
1824 * least one lazy callback. This will unnecessarily post callbacks
1825 * to CPUs that already have a non-lazy callback at the end of their
1826 * callback list, but this is an infrequent operation, so accept some
1827 * extra overhead to keep things simple.
1829 static void rcu_oom_notify_cpu(void *unused)
1831 struct rcu_state *rsp;
1832 struct rcu_data *rdp;
1834 for_each_rcu_flavor(rsp) {
1835 rdp = __this_cpu_ptr(rsp->rda);
1836 if (rdp->qlen_lazy != 0) {
1837 atomic_inc(&oom_callback_count);
1838 rsp->call(&rdp->oom_head, rcu_oom_callback);
1844 * If low on memory, ensure that each CPU has a non-lazy callback.
1845 * This will wake up CPUs that have only lazy callbacks, in turn
1846 * ensuring that they free up the corresponding memory in a timely manner.
1847 * Because an uncertain amount of memory will be freed in some uncertain
1848 * timeframe, we do not claim to have freed anything.
1850 static int rcu_oom_notify(struct notifier_block *self,
1851 unsigned long notused, void *nfreed)
1855 /* Wait for callbacks from earlier instance to complete. */
1856 wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
1857 smp_mb(); /* Ensure callback reuse happens after callback invocation. */
1860 * Prevent premature wakeup: ensure that all increments happen
1861 * before there is a chance of the counter reaching zero.
1863 atomic_set(&oom_callback_count, 1);
1866 for_each_online_cpu(cpu) {
1867 smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
1872 /* Unconditionally decrement: no need to wake ourselves up. */
1873 atomic_dec(&oom_callback_count);
1878 static struct notifier_block rcu_oom_nb = {
1879 .notifier_call = rcu_oom_notify
1882 static int __init rcu_register_oom_notifier(void)
1884 register_oom_notifier(&rcu_oom_nb);
1887 early_initcall(rcu_register_oom_notifier);
1889 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1891 #ifdef CONFIG_RCU_CPU_STALL_INFO
1893 #ifdef CONFIG_RCU_FAST_NO_HZ
1895 static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1897 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1898 unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
1900 sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1901 rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
1903 rdtp->all_lazy ? 'L' : '.',
1904 rdtp->tick_nohz_enabled_snap ? '.' : 'D');
1907 #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1909 static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1914 #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1916 /* Initiate the stall-info list. */
1917 static void print_cpu_stall_info_begin(void)
1923 * Print out diagnostic information for the specified stalled CPU.
1925 * If the specified CPU is aware of the current RCU grace period
1926 * (flavor specified by rsp), then print the number of scheduling
1927 * clock interrupts the CPU has taken during the time that it has
1928 * been aware. Otherwise, print the number of RCU grace periods
1929 * that this CPU is ignorant of, for example, "1" if the CPU was
1930 * aware of the previous grace period.
1932 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1934 static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1936 char fast_no_hz[72];
1937 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1938 struct rcu_dynticks *rdtp = rdp->dynticks;
1940 unsigned long ticks_value;
1942 if (rsp->gpnum == rdp->gpnum) {
1943 ticks_title = "ticks this GP";
1944 ticks_value = rdp->ticks_this_gp;
1946 ticks_title = "GPs behind";
1947 ticks_value = rsp->gpnum - rdp->gpnum;
1949 print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
1950 pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
1951 cpu, ticks_value, ticks_title,
1952 atomic_read(&rdtp->dynticks) & 0xfff,
1953 rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
1954 rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
1958 /* Terminate the stall-info list. */
1959 static void print_cpu_stall_info_end(void)
1964 /* Zero ->ticks_this_gp for all flavors of RCU. */
1965 static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1967 rdp->ticks_this_gp = 0;
1968 rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
1971 /* Increment ->ticks_this_gp for all flavors of RCU. */
1972 static void increment_cpu_stall_ticks(void)
1974 struct rcu_state *rsp;
1976 for_each_rcu_flavor(rsp)
1977 __this_cpu_ptr(rsp->rda)->ticks_this_gp++;
1980 #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
1982 static void print_cpu_stall_info_begin(void)
1987 static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1989 pr_cont(" %d", cpu);
1992 static void print_cpu_stall_info_end(void)
1997 static void zero_cpu_stall_ticks(struct rcu_data *rdp)
2001 static void increment_cpu_stall_ticks(void)
2005 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
2007 #ifdef CONFIG_RCU_NOCB_CPU
2010 * Offload callback processing from the boot-time-specified set of CPUs
2011 * specified by rcu_nocb_mask. For each CPU in the set, there is a
2012 * kthread created that pulls the callbacks from the corresponding CPU,
2013 * waits for a grace period to elapse, and invokes the callbacks.
2014 * The no-CBs CPUs do a wake_up() on their kthread when they insert
2015 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
2016 * has been specified, in which case each kthread actively polls its
2017 * CPU. (Which isn't so great for energy efficiency, but which does
2018 * reduce RCU's overhead on that CPU.)
2020 * This is intended to be used in conjunction with Frederic Weisbecker's
2021 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
2022 * running CPU-bound user-mode computations.
2024 * Offloading of callback processing could also in theory be used as
2025 * an energy-efficiency measure because CPUs with no RCU callbacks
2026 * queued are more aggressive about entering dyntick-idle mode.
2030 /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
2031 static int __init rcu_nocb_setup(char *str)
2033 alloc_bootmem_cpumask_var(&rcu_nocb_mask);
2034 have_rcu_nocb_mask = true;
2035 cpulist_parse(str, rcu_nocb_mask);
2038 __setup("rcu_nocbs=", rcu_nocb_setup);
2040 static int __init parse_rcu_nocb_poll(char *arg)
2045 early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
2048 * Do any no-CBs CPUs need another grace period?
2050 * Interrupts must be disabled. If the caller does not hold the root
2051 * rnp_node structure's ->lock, the results are advisory only.
2053 static int rcu_nocb_needs_gp(struct rcu_state *rsp)
2055 struct rcu_node *rnp = rcu_get_root(rsp);
2057 return rnp->need_future_gp[(ACCESS_ONCE(rnp->completed) + 1) & 0x1];
2061 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
2064 static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2066 wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
2070 * Set the root rcu_node structure's ->need_future_gp field
2071 * based on the sum of those of all rcu_node structures. This does
2072 * double-count the root rcu_node structure's requests, but this
2073 * is necessary to handle the possibility of a rcu_nocb_kthread()
2074 * having awakened during the time that the rcu_node structures
2075 * were being updated for the end of the previous grace period.
2077 static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2079 rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
2082 static void rcu_init_one_nocb(struct rcu_node *rnp)
2084 init_waitqueue_head(&rnp->nocb_gp_wq[0]);
2085 init_waitqueue_head(&rnp->nocb_gp_wq[1]);
2088 /* Is the specified CPU a no-CPUs CPU? */
2089 bool rcu_is_nocb_cpu(int cpu)
2091 if (have_rcu_nocb_mask)
2092 return cpumask_test_cpu(cpu, rcu_nocb_mask);
2097 * Enqueue the specified string of rcu_head structures onto the specified
2098 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
2099 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
2100 * counts are supplied by rhcount and rhcount_lazy.
2102 * If warranted, also wake up the kthread servicing this CPUs queues.
2104 static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
2105 struct rcu_head *rhp,
2106 struct rcu_head **rhtp,
2107 int rhcount, int rhcount_lazy,
2108 unsigned long flags)
2111 struct rcu_head **old_rhpp;
2112 struct task_struct *t;
2114 /* Enqueue the callback on the nocb list and update counts. */
2115 old_rhpp = xchg(&rdp->nocb_tail, rhtp);
2116 ACCESS_ONCE(*old_rhpp) = rhp;
2117 atomic_long_add(rhcount, &rdp->nocb_q_count);
2118 atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
2120 /* If we are not being polled and there is a kthread, awaken it ... */
2121 t = ACCESS_ONCE(rdp->nocb_kthread);
2122 if (rcu_nocb_poll || !t) {
2123 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2124 TPS("WakeNotPoll"));
2127 len = atomic_long_read(&rdp->nocb_q_count);
2128 if (old_rhpp == &rdp->nocb_head) {
2129 if (!irqs_disabled_flags(flags)) {
2130 wake_up(&rdp->nocb_wq); /* ... if queue was empty ... */
2131 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2134 rdp->nocb_defer_wakeup = true;
2135 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2136 TPS("WakeEmptyIsDeferred"));
2138 rdp->qlen_last_fqs_check = 0;
2139 } else if (len > rdp->qlen_last_fqs_check + qhimark) {
2140 wake_up_process(t); /* ... or if many callbacks queued. */
2141 rdp->qlen_last_fqs_check = LONG_MAX / 2;
2142 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf"));
2144 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
2150 * This is a helper for __call_rcu(), which invokes this when the normal
2151 * callback queue is inoperable. If this is not a no-CBs CPU, this
2152 * function returns failure back to __call_rcu(), which can complain
2155 * Otherwise, this function queues the callback where the corresponding
2156 * "rcuo" kthread can find it.
2158 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2159 bool lazy, unsigned long flags)
2162 if (!rcu_is_nocb_cpu(rdp->cpu))
2164 __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
2165 if (__is_kfree_rcu_offset((unsigned long)rhp->func))
2166 trace_rcu_kfree_callback(rdp->rsp->name, rhp,
2167 (unsigned long)rhp->func,
2168 -atomic_long_read(&rdp->nocb_q_count_lazy),
2169 -atomic_long_read(&rdp->nocb_q_count));
2171 trace_rcu_callback(rdp->rsp->name, rhp,
2172 -atomic_long_read(&rdp->nocb_q_count_lazy),
2173 -atomic_long_read(&rdp->nocb_q_count));
2178 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2181 static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2182 struct rcu_data *rdp,
2183 unsigned long flags)
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, flags);
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, flags);
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 c = rcu_start_future_gp(rnp, rdp);
2225 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2228 * Wait for the grace period. Do so interruptibly to avoid messing
2229 * up the load average.
2231 trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
2233 wait_event_interruptible(
2234 rnp->nocb_gp_wq[c & 0x1],
2235 (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
2238 flush_signals(current);
2239 trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
2241 trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
2242 smp_mb(); /* Ensure that CB invocation happens after GP end. */
2246 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
2247 * callbacks queued by the corresponding no-CBs CPU.
2249 static int rcu_nocb_kthread(void *arg)
2253 struct rcu_head *list;
2254 struct rcu_head *next;
2255 struct rcu_head **tail;
2256 struct rcu_data *rdp = arg;
2258 /* Each pass through this loop invokes one batch of callbacks */
2260 /* If not polling, wait for next batch of callbacks. */
2261 if (!rcu_nocb_poll) {
2262 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2264 wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
2265 /* Memory barrier provide by xchg() below. */
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 /* Is a deferred wakeup of rcu_nocb_kthread() required? */
2327 static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2329 return ACCESS_ONCE(rdp->nocb_defer_wakeup);
2332 /* Do a deferred wakeup of rcu_nocb_kthread(). */
2333 static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2335 if (!rcu_nocb_need_deferred_wakeup(rdp))
2337 ACCESS_ONCE(rdp->nocb_defer_wakeup) = false;
2338 wake_up(&rdp->nocb_wq);
2339 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWakeEmpty"));
2342 /* Initialize per-rcu_data variables for no-CBs CPUs. */
2343 static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2345 rdp->nocb_tail = &rdp->nocb_head;
2346 init_waitqueue_head(&rdp->nocb_wq);
2349 /* Create a kthread for each RCU flavor for each no-CBs CPU. */
2350 static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
2353 struct rcu_data *rdp;
2354 struct task_struct *t;
2356 if (rcu_nocb_mask == NULL)
2358 for_each_cpu(cpu, rcu_nocb_mask) {
2359 rdp = per_cpu_ptr(rsp->rda, cpu);
2360 t = kthread_run(rcu_nocb_kthread, rdp,
2361 "rcuo%c/%d", rsp->abbr, cpu);
2363 ACCESS_ONCE(rdp->nocb_kthread) = t;
2367 /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2368 static bool init_nocb_callback_list(struct rcu_data *rdp)
2370 if (rcu_nocb_mask == NULL ||
2371 !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
2373 rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2377 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
2379 static int rcu_nocb_needs_gp(struct rcu_state *rsp)
2384 static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2388 static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2392 static void rcu_init_one_nocb(struct rcu_node *rnp)
2396 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2397 bool lazy, unsigned long flags)
2402 static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2403 struct rcu_data *rdp,
2404 unsigned long flags)
2409 static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2413 static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2418 static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2422 static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
2426 static bool init_nocb_callback_list(struct rcu_data *rdp)
2431 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2434 * An adaptive-ticks CPU can potentially execute in kernel mode for an
2435 * arbitrarily long period of time with the scheduling-clock tick turned
2436 * off. RCU will be paying attention to this CPU because it is in the
2437 * kernel, but the CPU cannot be guaranteed to be executing the RCU state
2438 * machine because the scheduling-clock tick has been disabled. Therefore,
2439 * if an adaptive-ticks CPU is failing to respond to the current grace
2440 * period and has not be idle from an RCU perspective, kick it.
2442 static void rcu_kick_nohz_cpu(int cpu)
2444 #ifdef CONFIG_NO_HZ_FULL
2445 if (tick_nohz_full_cpu(cpu))
2446 smp_send_reschedule(cpu);
2447 #endif /* #ifdef CONFIG_NO_HZ_FULL */
2451 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
2454 * Define RCU flavor that holds sysidle state. This needs to be the
2455 * most active flavor of RCU.
2457 #ifdef CONFIG_PREEMPT_RCU
2458 static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state;
2459 #else /* #ifdef CONFIG_PREEMPT_RCU */
2460 static struct rcu_state *rcu_sysidle_state = &rcu_sched_state;
2461 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
2463 static int full_sysidle_state; /* Current system-idle state. */
2464 #define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */
2465 #define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */
2466 #define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */
2467 #define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */
2468 #define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */
2471 * Invoked to note exit from irq or task transition to idle. Note that
2472 * usermode execution does -not- count as idle here! After all, we want
2473 * to detect full-system idle states, not RCU quiescent states and grace
2474 * periods. The caller must have disabled interrupts.
2476 static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
2480 /* Adjust nesting, check for fully idle. */
2482 rdtp->dynticks_idle_nesting--;
2483 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
2484 if (rdtp->dynticks_idle_nesting != 0)
2485 return; /* Still not fully idle. */
2487 if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) ==
2488 DYNTICK_TASK_NEST_VALUE) {
2489 rdtp->dynticks_idle_nesting = 0;
2491 rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE;
2492 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
2493 return; /* Still not fully idle. */
2497 /* Record start of fully idle period. */
2499 ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j;
2500 smp_mb__before_atomic_inc();
2501 atomic_inc(&rdtp->dynticks_idle);
2502 smp_mb__after_atomic_inc();
2503 WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
2507 * Unconditionally force exit from full system-idle state. This is
2508 * invoked when a normal CPU exits idle, but must be called separately
2509 * for the timekeeping CPU (tick_do_timer_cpu). The reason for this
2510 * is that the timekeeping CPU is permitted to take scheduling-clock
2511 * interrupts while the system is in system-idle state, and of course
2512 * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
2513 * interrupt from any other type of interrupt.
2515 void rcu_sysidle_force_exit(void)
2517 int oldstate = ACCESS_ONCE(full_sysidle_state);
2521 * Each pass through the following loop attempts to exit full
2522 * system-idle state. If contention proves to be a problem,
2523 * a trylock-based contention tree could be used here.
2525 while (oldstate > RCU_SYSIDLE_SHORT) {
2526 newoldstate = cmpxchg(&full_sysidle_state,
2527 oldstate, RCU_SYSIDLE_NOT);
2528 if (oldstate == newoldstate &&
2529 oldstate == RCU_SYSIDLE_FULL_NOTED) {
2530 rcu_kick_nohz_cpu(tick_do_timer_cpu);
2531 return; /* We cleared it, done! */
2533 oldstate = newoldstate;
2535 smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
2539 * Invoked to note entry to irq or task transition from idle. Note that
2540 * usermode execution does -not- count as idle here! The caller must
2541 * have disabled interrupts.
2543 static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
2545 /* Adjust nesting, check for already non-idle. */
2547 rdtp->dynticks_idle_nesting++;
2548 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
2549 if (rdtp->dynticks_idle_nesting != 1)
2550 return; /* Already non-idle. */
2553 * Allow for irq misnesting. Yes, it really is possible
2554 * to enter an irq handler then never leave it, and maybe
2555 * also vice versa. Handle both possibilities.
2557 if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) {
2558 rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE;
2559 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
2560 return; /* Already non-idle. */
2562 rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE;
2566 /* Record end of idle period. */
2567 smp_mb__before_atomic_inc();
2568 atomic_inc(&rdtp->dynticks_idle);
2569 smp_mb__after_atomic_inc();
2570 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
2573 * If we are the timekeeping CPU, we are permitted to be non-idle
2574 * during a system-idle state. This must be the case, because
2575 * the timekeeping CPU has to take scheduling-clock interrupts
2576 * during the time that the system is transitioning to full
2577 * system-idle state. This means that the timekeeping CPU must
2578 * invoke rcu_sysidle_force_exit() directly if it does anything
2579 * more than take a scheduling-clock interrupt.
2581 if (smp_processor_id() == tick_do_timer_cpu)
2584 /* Update system-idle state: We are clearly no longer fully idle! */
2585 rcu_sysidle_force_exit();
2589 * Check to see if the current CPU is idle. Note that usermode execution
2590 * does not count as idle. The caller must have disabled interrupts.
2592 static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
2593 unsigned long *maxj)
2597 struct rcu_dynticks *rdtp = rdp->dynticks;
2600 * If some other CPU has already reported non-idle, if this is
2601 * not the flavor of RCU that tracks sysidle state, or if this
2602 * is an offline or the timekeeping CPU, nothing to do.
2604 if (!*isidle || rdp->rsp != rcu_sysidle_state ||
2605 cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
2607 if (rcu_gp_in_progress(rdp->rsp))
2608 WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
2610 /* Pick up current idle and NMI-nesting counter and check. */
2611 cur = atomic_read(&rdtp->dynticks_idle);
2613 *isidle = false; /* We are not idle! */
2616 smp_mb(); /* Read counters before timestamps. */
2618 /* Pick up timestamps. */
2619 j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies);
2620 /* If this CPU entered idle more recently, update maxj timestamp. */
2621 if (ULONG_CMP_LT(*maxj, j))
2626 * Is this the flavor of RCU that is handling full-system idle?
2628 static bool is_sysidle_rcu_state(struct rcu_state *rsp)
2630 return rsp == rcu_sysidle_state;
2634 * Bind the grace-period kthread for the sysidle flavor of RCU to the
2637 static void rcu_bind_gp_kthread(void)
2639 int cpu = ACCESS_ONCE(tick_do_timer_cpu);
2641 if (cpu < 0 || cpu >= nr_cpu_ids)
2643 if (raw_smp_processor_id() != cpu)
2644 set_cpus_allowed_ptr(current, cpumask_of(cpu));
2648 * Return a delay in jiffies based on the number of CPUs, rcu_node
2649 * leaf fanout, and jiffies tick rate. The idea is to allow larger
2650 * systems more time to transition to full-idle state in order to
2651 * avoid the cache thrashing that otherwise occur on the state variable.
2652 * Really small systems (less than a couple of tens of CPUs) should
2653 * instead use a single global atomically incremented counter, and later
2654 * versions of this will automatically reconfigure themselves accordingly.
2656 static unsigned long rcu_sysidle_delay(void)
2658 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
2660 return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000);
2664 * Advance the full-system-idle state. This is invoked when all of
2665 * the non-timekeeping CPUs are idle.
2667 static void rcu_sysidle(unsigned long j)
2669 /* Check the current state. */
2670 switch (ACCESS_ONCE(full_sysidle_state)) {
2671 case RCU_SYSIDLE_NOT:
2673 /* First time all are idle, so note a short idle period. */
2674 ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT;
2677 case RCU_SYSIDLE_SHORT:
2680 * Idle for a bit, time to advance to next state?
2681 * cmpxchg failure means race with non-idle, let them win.
2683 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
2684 (void)cmpxchg(&full_sysidle_state,
2685 RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG);
2688 case RCU_SYSIDLE_LONG:
2691 * Do an additional check pass before advancing to full.
2692 * cmpxchg failure means race with non-idle, let them win.
2694 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
2695 (void)cmpxchg(&full_sysidle_state,
2696 RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL);
2705 * Found a non-idle non-timekeeping CPU, so kick the system-idle state
2706 * back to the beginning.
2708 static void rcu_sysidle_cancel(void)
2711 ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT;
2715 * Update the sysidle state based on the results of a force-quiescent-state
2716 * scan of the CPUs' dyntick-idle state.
2718 static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
2719 unsigned long maxj, bool gpkt)
2721 if (rsp != rcu_sysidle_state)
2722 return; /* Wrong flavor, ignore. */
2723 if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
2724 return; /* Running state machine from timekeeping CPU. */
2726 rcu_sysidle(maxj); /* More idle! */
2728 rcu_sysidle_cancel(); /* Idle is over. */
2732 * Wrapper for rcu_sysidle_report() when called from the grace-period
2733 * kthread's context.
2735 static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
2738 rcu_sysidle_report(rsp, isidle, maxj, true);
2741 /* Callback and function for forcing an RCU grace period. */
2742 struct rcu_sysidle_head {
2747 static void rcu_sysidle_cb(struct rcu_head *rhp)
2749 struct rcu_sysidle_head *rshp;
2752 * The following memory barrier is needed to replace the
2753 * memory barriers that would normally be in the memory
2756 smp_mb(); /* grace period precedes setting inuse. */
2758 rshp = container_of(rhp, struct rcu_sysidle_head, rh);
2759 ACCESS_ONCE(rshp->inuse) = 0;
2763 * Check to see if the system is fully idle, other than the timekeeping CPU.
2764 * The caller must have disabled interrupts.
2766 bool rcu_sys_is_idle(void)
2768 static struct rcu_sysidle_head rsh;
2769 int rss = ACCESS_ONCE(full_sysidle_state);
2771 if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu))
2774 /* Handle small-system case by doing a full scan of CPUs. */
2775 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) {
2776 int oldrss = rss - 1;
2779 * One pass to advance to each state up to _FULL.
2780 * Give up if any pass fails to advance the state.
2782 while (rss < RCU_SYSIDLE_FULL && oldrss < rss) {
2785 unsigned long maxj = jiffies - ULONG_MAX / 4;
2786 struct rcu_data *rdp;
2788 /* Scan all the CPUs looking for nonidle CPUs. */
2789 for_each_possible_cpu(cpu) {
2790 rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu);
2791 rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
2795 rcu_sysidle_report(rcu_sysidle_state,
2796 isidle, maxj, false);
2798 rss = ACCESS_ONCE(full_sysidle_state);
2802 /* If this is the first observation of an idle period, record it. */
2803 if (rss == RCU_SYSIDLE_FULL) {
2804 rss = cmpxchg(&full_sysidle_state,
2805 RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED);
2806 return rss == RCU_SYSIDLE_FULL;
2809 smp_mb(); /* ensure rss load happens before later caller actions. */
2811 /* If already fully idle, tell the caller (in case of races). */
2812 if (rss == RCU_SYSIDLE_FULL_NOTED)
2816 * If we aren't there yet, and a grace period is not in flight,
2817 * initiate a grace period. Either way, tell the caller that
2818 * we are not there yet. We use an xchg() rather than an assignment
2819 * to make up for the memory barriers that would otherwise be
2820 * provided by the memory allocator.
2822 if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
2823 !rcu_gp_in_progress(rcu_sysidle_state) &&
2824 !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
2825 call_rcu(&rsh.rh, rcu_sysidle_cb);
2830 * Initialize dynticks sysidle state for CPUs coming online.
2832 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
2834 rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE;
2837 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
2839 static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
2843 static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
2847 static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
2848 unsigned long *maxj)
2852 static bool is_sysidle_rcu_state(struct rcu_state *rsp)
2857 static void rcu_bind_gp_kthread(void)
2861 static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
2866 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
2870 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */