2 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
3 * Internal non-public definitions that provide either classic
4 * or preemptible semantics.
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, you can access it online at
18 * http://www.gnu.org/licenses/gpl-2.0.html.
20 * Copyright Red Hat, 2009
21 * Copyright IBM Corporation, 2009
23 * Author: Ingo Molnar <mingo@elte.hu>
24 * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
27 #include <linux/delay.h>
28 #include <linux/gfp.h>
29 #include <linux/oom.h>
30 #include <linux/smpboot.h>
31 #include "../time/tick-internal.h"
33 #ifdef CONFIG_RCU_BOOST
35 #include "../locking/rtmutex_common.h"
37 /* rcuc/rcub kthread realtime priority */
38 static int kthread_prio
= CONFIG_RCU_KTHREAD_PRIO
;
39 module_param(kthread_prio
, int, 0644);
42 * Control variables for per-CPU and per-rcu_node kthreads. These
43 * handle all flavors of RCU.
45 static DEFINE_PER_CPU(struct task_struct
*, rcu_cpu_kthread_task
);
46 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status
);
47 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops
);
48 DEFINE_PER_CPU(char, rcu_cpu_has_work
);
50 #endif /* #ifdef CONFIG_RCU_BOOST */
52 #ifdef CONFIG_RCU_NOCB_CPU
53 static cpumask_var_t rcu_nocb_mask
; /* CPUs to have callbacks offloaded. */
54 static bool have_rcu_nocb_mask
; /* Was rcu_nocb_mask allocated? */
55 static bool __read_mostly rcu_nocb_poll
; /* Offload kthread are to poll. */
56 static char __initdata nocb_buf
[NR_CPUS
* 5];
57 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
60 * Check the RCU kernel configuration parameters and print informative
61 * messages about anything out of the ordinary. If you like #ifdef, you
62 * will love this function.
64 static void __init
rcu_bootup_announce_oddness(void)
66 #ifdef CONFIG_RCU_TRACE
67 pr_info("\tRCU debugfs-based tracing is enabled.\n");
69 #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
70 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
73 #ifdef CONFIG_RCU_FANOUT_EXACT
74 pr_info("\tHierarchical RCU autobalancing is disabled.\n");
76 #ifdef CONFIG_RCU_FAST_NO_HZ
77 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
79 #ifdef CONFIG_PROVE_RCU
80 pr_info("\tRCU lockdep checking is enabled.\n");
82 #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
83 pr_info("\tRCU torture testing starts during boot.\n");
85 #if defined(CONFIG_RCU_CPU_STALL_INFO)
86 pr_info("\tAdditional per-CPU info printed with stalls.\n");
88 #if NUM_RCU_LVL_4 != 0
89 pr_info("\tFour-level hierarchy is enabled.\n");
91 if (rcu_fanout_leaf
!= CONFIG_RCU_FANOUT_LEAF
)
92 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf
);
93 if (nr_cpu_ids
!= NR_CPUS
)
94 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS
, nr_cpu_ids
);
95 #ifdef CONFIG_RCU_BOOST
96 pr_info("\tRCU kthread priority: %d.\n", kthread_prio
);
100 #ifdef CONFIG_PREEMPT_RCU
102 RCU_STATE_INITIALIZER(rcu_preempt
, 'p', call_rcu
);
103 static struct rcu_state
*rcu_state_p
= &rcu_preempt_state
;
105 static int rcu_preempted_readers_exp(struct rcu_node
*rnp
);
106 static void rcu_report_exp_rnp(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
110 * Tell them what RCU they are running.
112 static void __init
rcu_bootup_announce(void)
114 pr_info("Preemptible hierarchical RCU implementation.\n");
115 rcu_bootup_announce_oddness();
119 * Return the number of RCU-preempt batches processed thus far
120 * for debug and statistics.
122 static long rcu_batches_completed_preempt(void)
124 return rcu_preempt_state
.completed
;
126 EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt
);
129 * Return the number of RCU batches processed thus far for debug & stats.
131 long rcu_batches_completed(void)
133 return rcu_batches_completed_preempt();
135 EXPORT_SYMBOL_GPL(rcu_batches_completed
);
138 * Record a preemptible-RCU quiescent state for the specified CPU. Note
139 * that this just means that the task currently running on the CPU is
140 * not in a quiescent state. There might be any number of tasks blocked
141 * while in an RCU read-side critical section.
143 * As with the other rcu_*_qs() functions, callers to this function
144 * must disable preemption.
146 static void rcu_preempt_qs(void)
148 if (!__this_cpu_read(rcu_preempt_data
.passed_quiesce
)) {
149 trace_rcu_grace_period(TPS("rcu_preempt"),
150 __this_cpu_read(rcu_preempt_data
.gpnum
),
152 __this_cpu_write(rcu_preempt_data
.passed_quiesce
, 1);
153 barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
154 current
->rcu_read_unlock_special
.b
.need_qs
= false;
159 * We have entered the scheduler, and the current task might soon be
160 * context-switched away from. If this task is in an RCU read-side
161 * critical section, we will no longer be able to rely on the CPU to
162 * record that fact, so we enqueue the task on the blkd_tasks list.
163 * The task will dequeue itself when it exits the outermost enclosing
164 * RCU read-side critical section. Therefore, the current grace period
165 * cannot be permitted to complete until the blkd_tasks list entries
166 * predating the current grace period drain, in other words, until
167 * rnp->gp_tasks becomes NULL.
169 * Caller must disable preemption.
171 static void rcu_preempt_note_context_switch(void)
173 struct task_struct
*t
= current
;
175 struct rcu_data
*rdp
;
176 struct rcu_node
*rnp
;
178 if (t
->rcu_read_lock_nesting
> 0 &&
179 !t
->rcu_read_unlock_special
.b
.blocked
) {
181 /* Possibly blocking in an RCU read-side critical section. */
182 rdp
= this_cpu_ptr(rcu_preempt_state
.rda
);
184 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
185 smp_mb__after_unlock_lock();
186 t
->rcu_read_unlock_special
.b
.blocked
= true;
187 t
->rcu_blocked_node
= rnp
;
190 * If this CPU has already checked in, then this task
191 * will hold up the next grace period rather than the
192 * current grace period. Queue the task accordingly.
193 * If the task is queued for the current grace period
194 * (i.e., this CPU has not yet passed through a quiescent
195 * state for the current grace period), then as long
196 * as that task remains queued, the current grace period
197 * cannot end. Note that there is some uncertainty as
198 * to exactly when the current grace period started.
199 * We take a conservative approach, which can result
200 * in unnecessarily waiting on tasks that started very
201 * slightly after the current grace period began. C'est
204 * But first, note that the current CPU must still be
207 WARN_ON_ONCE((rdp
->grpmask
& rnp
->qsmaskinit
) == 0);
208 WARN_ON_ONCE(!list_empty(&t
->rcu_node_entry
));
209 if ((rnp
->qsmask
& rdp
->grpmask
) && rnp
->gp_tasks
!= NULL
) {
210 list_add(&t
->rcu_node_entry
, rnp
->gp_tasks
->prev
);
211 rnp
->gp_tasks
= &t
->rcu_node_entry
;
212 #ifdef CONFIG_RCU_BOOST
213 if (rnp
->boost_tasks
!= NULL
)
214 rnp
->boost_tasks
= rnp
->gp_tasks
;
215 #endif /* #ifdef CONFIG_RCU_BOOST */
217 list_add(&t
->rcu_node_entry
, &rnp
->blkd_tasks
);
218 if (rnp
->qsmask
& rdp
->grpmask
)
219 rnp
->gp_tasks
= &t
->rcu_node_entry
;
221 trace_rcu_preempt_task(rdp
->rsp
->name
,
223 (rnp
->qsmask
& rdp
->grpmask
)
226 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
227 } else if (t
->rcu_read_lock_nesting
< 0 &&
228 t
->rcu_read_unlock_special
.s
) {
231 * Complete exit from RCU read-side critical section on
232 * behalf of preempted instance of __rcu_read_unlock().
234 rcu_read_unlock_special(t
);
238 * Either we were not in an RCU read-side critical section to
239 * begin with, or we have now recorded that critical section
240 * globally. Either way, we can now note a quiescent state
241 * for this CPU. Again, if we were in an RCU read-side critical
242 * section, and if that critical section was blocking the current
243 * grace period, then the fact that the task has been enqueued
244 * means that we continue to block the current grace period.
250 * Check for preempted RCU readers blocking the current grace period
251 * for the specified rcu_node structure. If the caller needs a reliable
252 * answer, it must hold the rcu_node's ->lock.
254 static int rcu_preempt_blocked_readers_cgp(struct rcu_node
*rnp
)
256 return rnp
->gp_tasks
!= NULL
;
260 * Record a quiescent state for all tasks that were previously queued
261 * on the specified rcu_node structure and that were blocking the current
262 * RCU grace period. The caller must hold the specified rnp->lock with
263 * irqs disabled, and this lock is released upon return, but irqs remain
266 static void rcu_report_unblock_qs_rnp(struct rcu_node
*rnp
, unsigned long flags
)
267 __releases(rnp
->lock
)
270 struct rcu_node
*rnp_p
;
272 if (rnp
->qsmask
!= 0 || rcu_preempt_blocked_readers_cgp(rnp
)) {
273 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
274 return; /* Still need more quiescent states! */
280 * Either there is only one rcu_node in the tree,
281 * or tasks were kicked up to root rcu_node due to
282 * CPUs going offline.
284 rcu_report_qs_rsp(&rcu_preempt_state
, flags
);
288 /* Report up the rest of the hierarchy. */
290 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
291 raw_spin_lock(&rnp_p
->lock
); /* irqs already disabled. */
292 smp_mb__after_unlock_lock();
293 rcu_report_qs_rnp(mask
, &rcu_preempt_state
, rnp_p
, flags
);
297 * Advance a ->blkd_tasks-list pointer to the next entry, instead
298 * returning NULL if at the end of the list.
300 static struct list_head
*rcu_next_node_entry(struct task_struct
*t
,
301 struct rcu_node
*rnp
)
303 struct list_head
*np
;
305 np
= t
->rcu_node_entry
.next
;
306 if (np
== &rnp
->blkd_tasks
)
312 * Return true if the specified rcu_node structure has tasks that were
313 * preempted within an RCU read-side critical section.
315 static bool rcu_preempt_has_tasks(struct rcu_node
*rnp
)
317 return !list_empty(&rnp
->blkd_tasks
);
321 * Handle special cases during rcu_read_unlock(), such as needing to
322 * notify RCU core processing or task having blocked during the RCU
323 * read-side critical section.
325 void rcu_read_unlock_special(struct task_struct
*t
)
332 struct list_head
*np
;
333 #ifdef CONFIG_RCU_BOOST
334 bool drop_boost_mutex
= false;
335 #endif /* #ifdef CONFIG_RCU_BOOST */
336 struct rcu_node
*rnp
;
337 union rcu_special special
;
339 /* NMI handlers cannot block and cannot safely manipulate state. */
343 local_irq_save(flags
);
346 * If RCU core is waiting for this CPU to exit critical section,
347 * let it know that we have done so. Because irqs are disabled,
348 * t->rcu_read_unlock_special cannot change.
350 special
= t
->rcu_read_unlock_special
;
351 if (special
.b
.need_qs
) {
353 if (!t
->rcu_read_unlock_special
.s
) {
354 local_irq_restore(flags
);
359 /* Hardware IRQ handlers cannot block, complain if they get here. */
360 if (WARN_ON_ONCE(in_irq() || in_serving_softirq())) {
361 local_irq_restore(flags
);
365 /* Clean up if blocked during RCU read-side critical section. */
366 if (special
.b
.blocked
) {
367 t
->rcu_read_unlock_special
.b
.blocked
= false;
370 * Remove this task from the list it blocked on. The
371 * task can migrate while we acquire the lock, but at
372 * most one time. So at most two passes through loop.
375 rnp
= t
->rcu_blocked_node
;
376 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
377 smp_mb__after_unlock_lock();
378 if (rnp
== t
->rcu_blocked_node
)
380 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
382 empty
= !rcu_preempt_has_tasks(rnp
);
383 empty_norm
= !rcu_preempt_blocked_readers_cgp(rnp
);
384 empty_exp
= !rcu_preempted_readers_exp(rnp
);
385 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
386 np
= rcu_next_node_entry(t
, rnp
);
387 list_del_init(&t
->rcu_node_entry
);
388 t
->rcu_blocked_node
= NULL
;
389 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
391 if (&t
->rcu_node_entry
== rnp
->gp_tasks
)
393 if (&t
->rcu_node_entry
== rnp
->exp_tasks
)
395 #ifdef CONFIG_RCU_BOOST
396 if (&t
->rcu_node_entry
== rnp
->boost_tasks
)
397 rnp
->boost_tasks
= np
;
398 /* Snapshot ->boost_mtx ownership with rcu_node lock held. */
399 drop_boost_mutex
= rt_mutex_owner(&rnp
->boost_mtx
) == t
;
400 #endif /* #ifdef CONFIG_RCU_BOOST */
403 * If this was the last task on the list, go see if we
404 * need to propagate ->qsmaskinit bit clearing up the
407 if (!empty
&& !rcu_preempt_has_tasks(rnp
))
408 rcu_cleanup_dead_rnp(rnp
);
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_norm
&& !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. */
432 if (drop_boost_mutex
) {
433 rt_mutex_unlock(&rnp
->boost_mtx
);
434 complete(&rnp
->boost_completion
);
436 #endif /* #ifdef CONFIG_RCU_BOOST */
439 * If this was the last task on the expedited lists,
440 * then we need to report up the rcu_node hierarchy.
442 if (!empty_exp
&& empty_exp_now
)
443 rcu_report_exp_rnp(&rcu_preempt_state
, rnp
, true);
445 local_irq_restore(flags
);
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 #ifdef CONFIG_RCU_CPU_STALL_INFO
485 static void rcu_print_task_stall_begin(struct rcu_node
*rnp
)
487 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
488 rnp
->level
, rnp
->grplo
, rnp
->grphi
);
491 static void rcu_print_task_stall_end(void)
496 #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
498 static void rcu_print_task_stall_begin(struct rcu_node
*rnp
)
502 static void rcu_print_task_stall_end(void)
506 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
509 * Scan the current list of tasks blocked within RCU read-side critical
510 * sections, printing out the tid of each.
512 static int rcu_print_task_stall(struct rcu_node
*rnp
)
514 struct task_struct
*t
;
517 if (!rcu_preempt_blocked_readers_cgp(rnp
))
519 rcu_print_task_stall_begin(rnp
);
520 t
= list_entry(rnp
->gp_tasks
,
521 struct task_struct
, rcu_node_entry
);
522 list_for_each_entry_continue(t
, &rnp
->blkd_tasks
, rcu_node_entry
) {
523 pr_cont(" P%d", t
->pid
);
526 rcu_print_task_stall_end();
531 * Check that the list of blocked tasks for the newly completed grace
532 * period is in fact empty. It is a serious bug to complete a grace
533 * period that still has RCU readers blocked! This function must be
534 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
535 * must be held by the caller.
537 * Also, if there are blocked tasks on the list, they automatically
538 * block the newly created grace period, so set up ->gp_tasks accordingly.
540 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
542 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp
));
543 if (rcu_preempt_has_tasks(rnp
))
544 rnp
->gp_tasks
= rnp
->blkd_tasks
.next
;
545 WARN_ON_ONCE(rnp
->qsmask
);
548 #ifdef CONFIG_HOTPLUG_CPU
550 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
553 * Check for a quiescent state from the current CPU. When a task blocks,
554 * the task is recorded in the corresponding CPU's rcu_node structure,
555 * which is checked elsewhere.
557 * Caller must disable hard irqs.
559 static void rcu_preempt_check_callbacks(void)
561 struct task_struct
*t
= current
;
563 if (t
->rcu_read_lock_nesting
== 0) {
567 if (t
->rcu_read_lock_nesting
> 0 &&
568 __this_cpu_read(rcu_preempt_data
.qs_pending
) &&
569 !__this_cpu_read(rcu_preempt_data
.passed_quiesce
))
570 t
->rcu_read_unlock_special
.b
.need_qs
= true;
573 #ifdef CONFIG_RCU_BOOST
575 static void rcu_preempt_do_callbacks(void)
577 rcu_do_batch(&rcu_preempt_state
, this_cpu_ptr(&rcu_preempt_data
));
580 #endif /* #ifdef CONFIG_RCU_BOOST */
583 * Queue a preemptible-RCU callback for invocation after a grace period.
585 void call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
587 __call_rcu(head
, func
, &rcu_preempt_state
, -1, 0);
589 EXPORT_SYMBOL_GPL(call_rcu
);
592 * synchronize_rcu - wait until a grace period has elapsed.
594 * Control will return to the caller some time after a full grace
595 * period has elapsed, in other words after all currently executing RCU
596 * read-side critical sections have completed. Note, however, that
597 * upon return from synchronize_rcu(), the caller might well be executing
598 * concurrently with new RCU read-side critical sections that began while
599 * synchronize_rcu() was waiting. RCU read-side critical sections are
600 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
602 * See the description of synchronize_sched() for more detailed information
603 * on memory ordering guarantees.
605 void synchronize_rcu(void)
607 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
608 !lock_is_held(&rcu_lock_map
) &&
609 !lock_is_held(&rcu_sched_lock_map
),
610 "Illegal synchronize_rcu() in RCU read-side critical section");
611 if (!rcu_scheduler_active
)
614 synchronize_rcu_expedited();
616 wait_rcu_gp(call_rcu
);
618 EXPORT_SYMBOL_GPL(synchronize_rcu
);
620 static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq
);
621 static unsigned long sync_rcu_preempt_exp_count
;
622 static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex
);
625 * Return non-zero if there are any tasks in RCU read-side critical
626 * sections blocking the current preemptible-RCU expedited grace period.
627 * If there is no preemptible-RCU expedited grace period currently in
628 * progress, returns zero unconditionally.
630 static int rcu_preempted_readers_exp(struct rcu_node
*rnp
)
632 return rnp
->exp_tasks
!= NULL
;
636 * return non-zero if there is no RCU expedited grace period in progress
637 * for the specified rcu_node structure, in other words, if all CPUs and
638 * tasks covered by the specified rcu_node structure have done their bit
639 * for the current expedited grace period. Works only for preemptible
640 * RCU -- other RCU implementation use other means.
642 * Caller must hold sync_rcu_preempt_exp_mutex.
644 static int sync_rcu_preempt_exp_done(struct rcu_node
*rnp
)
646 return !rcu_preempted_readers_exp(rnp
) &&
647 ACCESS_ONCE(rnp
->expmask
) == 0;
651 * Report the exit from RCU read-side critical section for the last task
652 * that queued itself during or before the current expedited preemptible-RCU
653 * grace period. This event is reported either to the rcu_node structure on
654 * which the task was queued or to one of that rcu_node structure's ancestors,
655 * recursively up the tree. (Calm down, calm down, we do the recursion
658 * Most callers will set the "wake" flag, but the task initiating the
659 * expedited grace period need not wake itself.
661 * Caller must hold sync_rcu_preempt_exp_mutex.
663 static void rcu_report_exp_rnp(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
669 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
670 smp_mb__after_unlock_lock();
672 if (!sync_rcu_preempt_exp_done(rnp
)) {
673 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
676 if (rnp
->parent
== NULL
) {
677 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
679 smp_mb(); /* EGP done before wake_up(). */
680 wake_up(&sync_rcu_preempt_exp_wq
);
685 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
687 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
688 smp_mb__after_unlock_lock();
689 rnp
->expmask
&= ~mask
;
694 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
695 * grace period for the specified rcu_node structure. If there are no such
696 * tasks, report it up the rcu_node hierarchy.
698 * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
699 * CPU hotplug operations.
702 sync_rcu_preempt_exp_init(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
707 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
708 smp_mb__after_unlock_lock();
709 if (!rcu_preempt_has_tasks(rnp
)) {
710 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
712 rnp
->exp_tasks
= rnp
->blkd_tasks
.next
;
713 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock */
717 rcu_report_exp_rnp(rsp
, rnp
, false); /* Don't wake self. */
721 * synchronize_rcu_expedited - Brute-force RCU grace period
723 * Wait for an RCU-preempt grace period, but expedite it. The basic
724 * idea is to invoke synchronize_sched_expedited() to push all the tasks to
725 * the ->blkd_tasks lists and wait for this list to drain. This consumes
726 * significant time on all CPUs and is unfriendly to real-time workloads,
727 * so is thus not recommended for any sort of common-case code.
728 * In fact, if you are using synchronize_rcu_expedited() in a loop,
729 * please restructure your code to batch your updates, and then Use a
730 * single synchronize_rcu() instead.
732 void synchronize_rcu_expedited(void)
735 struct rcu_node
*rnp
;
736 struct rcu_state
*rsp
= &rcu_preempt_state
;
740 smp_mb(); /* Caller's modifications seen first by other CPUs. */
741 snap
= ACCESS_ONCE(sync_rcu_preempt_exp_count
) + 1;
742 smp_mb(); /* Above access cannot bleed into critical section. */
745 * Block CPU-hotplug operations. This means that any CPU-hotplug
746 * operation that finds an rcu_node structure with tasks in the
747 * process of being boosted will know that all tasks blocking
748 * this expedited grace period will already be in the process of
749 * being boosted. This simplifies the process of moving tasks
750 * from leaf to root rcu_node structures.
752 if (!try_get_online_cpus()) {
753 /* CPU-hotplug operation in flight, fall back to normal GP. */
754 wait_rcu_gp(call_rcu
);
759 * Acquire lock, falling back to synchronize_rcu() if too many
760 * lock-acquisition failures. Of course, if someone does the
761 * expedited grace period for us, just leave.
763 while (!mutex_trylock(&sync_rcu_preempt_exp_mutex
)) {
764 if (ULONG_CMP_LT(snap
,
765 ACCESS_ONCE(sync_rcu_preempt_exp_count
))) {
767 goto mb_ret
; /* Others did our work for us. */
769 if (trycount
++ < 10) {
770 udelay(trycount
* num_online_cpus());
773 wait_rcu_gp(call_rcu
);
777 if (ULONG_CMP_LT(snap
, ACCESS_ONCE(sync_rcu_preempt_exp_count
))) {
779 goto unlock_mb_ret
; /* Others did our work for us. */
782 /* force all RCU readers onto ->blkd_tasks lists. */
783 synchronize_sched_expedited();
785 /* Initialize ->expmask for all non-leaf rcu_node structures. */
786 rcu_for_each_nonleaf_node_breadth_first(rsp
, rnp
) {
787 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
788 smp_mb__after_unlock_lock();
789 rnp
->expmask
= rnp
->qsmaskinit
;
790 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
793 /* Snapshot current state of ->blkd_tasks lists. */
794 rcu_for_each_leaf_node(rsp
, rnp
)
795 sync_rcu_preempt_exp_init(rsp
, rnp
);
796 if (NUM_RCU_NODES
> 1)
797 sync_rcu_preempt_exp_init(rsp
, rcu_get_root(rsp
));
801 /* Wait for snapshotted ->blkd_tasks lists to drain. */
802 rnp
= rcu_get_root(rsp
);
803 wait_event(sync_rcu_preempt_exp_wq
,
804 sync_rcu_preempt_exp_done(rnp
));
806 /* Clean up and exit. */
807 smp_mb(); /* ensure expedited GP seen before counter increment. */
808 ACCESS_ONCE(sync_rcu_preempt_exp_count
) =
809 sync_rcu_preempt_exp_count
+ 1;
811 mutex_unlock(&sync_rcu_preempt_exp_mutex
);
813 smp_mb(); /* ensure subsequent action seen after grace period. */
815 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited
);
818 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
820 * Note that this primitive does not necessarily wait for an RCU grace period
821 * to complete. For example, if there are no RCU callbacks queued anywhere
822 * in the system, then rcu_barrier() is within its rights to return
823 * immediately, without waiting for anything, much less an RCU grace period.
825 void rcu_barrier(void)
827 _rcu_barrier(&rcu_preempt_state
);
829 EXPORT_SYMBOL_GPL(rcu_barrier
);
832 * Initialize preemptible RCU's state structures.
834 static void __init
__rcu_init_preempt(void)
836 rcu_init_one(&rcu_preempt_state
, &rcu_preempt_data
);
840 * Check for a task exiting while in a preemptible-RCU read-side
841 * critical section, clean up if so. No need to issue warnings,
842 * as debug_check_no_locks_held() already does this if lockdep
847 struct task_struct
*t
= current
;
849 if (likely(list_empty(¤t
->rcu_node_entry
)))
851 t
->rcu_read_lock_nesting
= 1;
853 t
->rcu_read_unlock_special
.b
.blocked
= true;
857 #else /* #ifdef CONFIG_PREEMPT_RCU */
859 static struct rcu_state
*rcu_state_p
= &rcu_sched_state
;
862 * Tell them what RCU they are running.
864 static void __init
rcu_bootup_announce(void)
866 pr_info("Hierarchical RCU implementation.\n");
867 rcu_bootup_announce_oddness();
871 * Return the number of RCU batches processed thus far for debug & stats.
873 long rcu_batches_completed(void)
875 return rcu_batches_completed_sched();
877 EXPORT_SYMBOL_GPL(rcu_batches_completed
);
880 * Because preemptible RCU does not exist, we never have to check for
881 * CPUs being in quiescent states.
883 static void rcu_preempt_note_context_switch(void)
888 * Because preemptible RCU does not exist, there are never any preempted
891 static int rcu_preempt_blocked_readers_cgp(struct rcu_node
*rnp
)
896 #ifdef CONFIG_HOTPLUG_CPU
899 * Because there is no preemptible RCU, there can be no readers blocked.
901 static bool rcu_preempt_has_tasks(struct rcu_node
*rnp
)
906 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
909 * Because preemptible RCU does not exist, we never have to check for
910 * tasks blocked within RCU read-side critical sections.
912 static void rcu_print_detail_task_stall(struct rcu_state
*rsp
)
917 * Because preemptible RCU does not exist, we never have to check for
918 * tasks blocked within RCU read-side critical sections.
920 static int rcu_print_task_stall(struct rcu_node
*rnp
)
926 * Because there is no preemptible RCU, there can be no readers blocked,
927 * so there is no need to check for blocked tasks. So check only for
928 * bogus qsmask values.
930 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
932 WARN_ON_ONCE(rnp
->qsmask
);
936 * Because preemptible RCU does not exist, it never has any callbacks
939 static void rcu_preempt_check_callbacks(void)
944 * Wait for an rcu-preempt grace period, but make it happen quickly.
945 * But because preemptible RCU does not exist, map to rcu-sched.
947 void synchronize_rcu_expedited(void)
949 synchronize_sched_expedited();
951 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited
);
954 * Because preemptible RCU does not exist, rcu_barrier() is just
955 * another name for rcu_barrier_sched().
957 void rcu_barrier(void)
961 EXPORT_SYMBOL_GPL(rcu_barrier
);
964 * Because preemptible RCU does not exist, it need not be initialized.
966 static void __init
__rcu_init_preempt(void)
971 * Because preemptible RCU does not exist, tasks cannot possibly exit
972 * while in preemptible RCU read-side critical sections.
978 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
980 #ifdef CONFIG_RCU_BOOST
982 #include "../locking/rtmutex_common.h"
984 #ifdef CONFIG_RCU_TRACE
986 static void rcu_initiate_boost_trace(struct rcu_node
*rnp
)
988 if (!rcu_preempt_has_tasks(rnp
))
989 rnp
->n_balk_blkd_tasks
++;
990 else if (rnp
->exp_tasks
== NULL
&& rnp
->gp_tasks
== NULL
)
991 rnp
->n_balk_exp_gp_tasks
++;
992 else if (rnp
->gp_tasks
!= NULL
&& rnp
->boost_tasks
!= NULL
)
993 rnp
->n_balk_boost_tasks
++;
994 else if (rnp
->gp_tasks
!= NULL
&& rnp
->qsmask
!= 0)
995 rnp
->n_balk_notblocked
++;
996 else if (rnp
->gp_tasks
!= NULL
&&
997 ULONG_CMP_LT(jiffies
, rnp
->boost_time
))
998 rnp
->n_balk_notyet
++;
1003 #else /* #ifdef CONFIG_RCU_TRACE */
1005 static void rcu_initiate_boost_trace(struct rcu_node
*rnp
)
1009 #endif /* #else #ifdef CONFIG_RCU_TRACE */
1011 static void rcu_wake_cond(struct task_struct
*t
, int status
)
1014 * If the thread is yielding, only wake it when this
1015 * is invoked from idle
1017 if (status
!= RCU_KTHREAD_YIELDING
|| is_idle_task(current
))
1022 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
1023 * or ->boost_tasks, advancing the pointer to the next task in the
1024 * ->blkd_tasks list.
1026 * Note that irqs must be enabled: boosting the task can block.
1027 * Returns 1 if there are more tasks needing to be boosted.
1029 static int rcu_boost(struct rcu_node
*rnp
)
1031 unsigned long flags
;
1032 struct task_struct
*t
;
1033 struct list_head
*tb
;
1035 if (ACCESS_ONCE(rnp
->exp_tasks
) == NULL
&&
1036 ACCESS_ONCE(rnp
->boost_tasks
) == NULL
)
1037 return 0; /* Nothing left to boost. */
1039 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1040 smp_mb__after_unlock_lock();
1043 * Recheck under the lock: all tasks in need of boosting
1044 * might exit their RCU read-side critical sections on their own.
1046 if (rnp
->exp_tasks
== NULL
&& rnp
->boost_tasks
== NULL
) {
1047 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1052 * Preferentially boost tasks blocking expedited grace periods.
1053 * This cannot starve the normal grace periods because a second
1054 * expedited grace period must boost all blocked tasks, including
1055 * those blocking the pre-existing normal grace period.
1057 if (rnp
->exp_tasks
!= NULL
) {
1058 tb
= rnp
->exp_tasks
;
1059 rnp
->n_exp_boosts
++;
1061 tb
= rnp
->boost_tasks
;
1062 rnp
->n_normal_boosts
++;
1064 rnp
->n_tasks_boosted
++;
1067 * We boost task t by manufacturing an rt_mutex that appears to
1068 * be held by task t. We leave a pointer to that rt_mutex where
1069 * task t can find it, and task t will release the mutex when it
1070 * exits its outermost RCU read-side critical section. Then
1071 * simply acquiring this artificial rt_mutex will boost task
1072 * t's priority. (Thanks to tglx for suggesting this approach!)
1074 * Note that task t must acquire rnp->lock to remove itself from
1075 * the ->blkd_tasks list, which it will do from exit() if from
1076 * nowhere else. We therefore are guaranteed that task t will
1077 * stay around at least until we drop rnp->lock. Note that
1078 * rnp->lock also resolves races between our priority boosting
1079 * and task t's exiting its outermost RCU read-side critical
1082 t
= container_of(tb
, struct task_struct
, rcu_node_entry
);
1083 rt_mutex_init_proxy_locked(&rnp
->boost_mtx
, t
);
1084 init_completion(&rnp
->boost_completion
);
1085 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1086 /* Lock only for side effect: boosts task t's priority. */
1087 rt_mutex_lock(&rnp
->boost_mtx
);
1088 rt_mutex_unlock(&rnp
->boost_mtx
); /* Then keep lockdep happy. */
1090 /* Wait for boostee to be done w/boost_mtx before reinitializing. */
1091 wait_for_completion(&rnp
->boost_completion
);
1093 return ACCESS_ONCE(rnp
->exp_tasks
) != NULL
||
1094 ACCESS_ONCE(rnp
->boost_tasks
) != NULL
;
1098 * Priority-boosting kthread. One per leaf rcu_node and one for the
1101 static int rcu_boost_kthread(void *arg
)
1103 struct rcu_node
*rnp
= (struct rcu_node
*)arg
;
1107 trace_rcu_utilization(TPS("Start boost kthread@init"));
1109 rnp
->boost_kthread_status
= RCU_KTHREAD_WAITING
;
1110 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1111 rcu_wait(rnp
->boost_tasks
|| rnp
->exp_tasks
);
1112 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1113 rnp
->boost_kthread_status
= RCU_KTHREAD_RUNNING
;
1114 more2boost
= rcu_boost(rnp
);
1120 rnp
->boost_kthread_status
= RCU_KTHREAD_YIELDING
;
1121 trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1122 schedule_timeout_interruptible(2);
1123 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1128 trace_rcu_utilization(TPS("End boost kthread@notreached"));
1133 * Check to see if it is time to start boosting RCU readers that are
1134 * blocking the current grace period, and, if so, tell the per-rcu_node
1135 * kthread to start boosting them. If there is an expedited grace
1136 * period in progress, it is always time to boost.
1138 * The caller must hold rnp->lock, which this function releases.
1139 * The ->boost_kthread_task is immortal, so we don't need to worry
1140 * about it going away.
1142 static void rcu_initiate_boost(struct rcu_node
*rnp
, unsigned long flags
)
1143 __releases(rnp
->lock
)
1145 struct task_struct
*t
;
1147 if (!rcu_preempt_blocked_readers_cgp(rnp
) && rnp
->exp_tasks
== NULL
) {
1148 rnp
->n_balk_exp_gp_tasks
++;
1149 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1152 if (rnp
->exp_tasks
!= NULL
||
1153 (rnp
->gp_tasks
!= NULL
&&
1154 rnp
->boost_tasks
== NULL
&&
1156 ULONG_CMP_GE(jiffies
, rnp
->boost_time
))) {
1157 if (rnp
->exp_tasks
== NULL
)
1158 rnp
->boost_tasks
= rnp
->gp_tasks
;
1159 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1160 t
= rnp
->boost_kthread_task
;
1162 rcu_wake_cond(t
, rnp
->boost_kthread_status
);
1164 rcu_initiate_boost_trace(rnp
);
1165 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1170 * Wake up the per-CPU kthread to invoke RCU callbacks.
1172 static void invoke_rcu_callbacks_kthread(void)
1174 unsigned long flags
;
1176 local_irq_save(flags
);
1177 __this_cpu_write(rcu_cpu_has_work
, 1);
1178 if (__this_cpu_read(rcu_cpu_kthread_task
) != NULL
&&
1179 current
!= __this_cpu_read(rcu_cpu_kthread_task
)) {
1180 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task
),
1181 __this_cpu_read(rcu_cpu_kthread_status
));
1183 local_irq_restore(flags
);
1187 * Is the current CPU running the RCU-callbacks kthread?
1188 * Caller must have preemption disabled.
1190 static bool rcu_is_callbacks_kthread(void)
1192 return __this_cpu_read(rcu_cpu_kthread_task
) == current
;
1195 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1198 * Do priority-boost accounting for the start of a new grace period.
1200 static void rcu_preempt_boost_start_gp(struct rcu_node
*rnp
)
1202 rnp
->boost_time
= jiffies
+ RCU_BOOST_DELAY_JIFFIES
;
1206 * Create an RCU-boost kthread for the specified node if one does not
1207 * already exist. We only create this kthread for preemptible RCU.
1208 * Returns zero if all is well, a negated errno otherwise.
1210 static int rcu_spawn_one_boost_kthread(struct rcu_state
*rsp
,
1211 struct rcu_node
*rnp
)
1213 int rnp_index
= rnp
- &rsp
->node
[0];
1214 unsigned long flags
;
1215 struct sched_param sp
;
1216 struct task_struct
*t
;
1218 if (&rcu_preempt_state
!= rsp
)
1221 if (!rcu_scheduler_fully_active
|| rnp
->qsmaskinit
== 0)
1225 if (rnp
->boost_kthread_task
!= NULL
)
1227 t
= kthread_create(rcu_boost_kthread
, (void *)rnp
,
1228 "rcub/%d", rnp_index
);
1231 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1232 smp_mb__after_unlock_lock();
1233 rnp
->boost_kthread_task
= t
;
1234 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1235 sp
.sched_priority
= kthread_prio
;
1236 sched_setscheduler_nocheck(t
, SCHED_FIFO
, &sp
);
1237 wake_up_process(t
); /* get to TASK_INTERRUPTIBLE quickly. */
1241 static void rcu_kthread_do_work(void)
1243 rcu_do_batch(&rcu_sched_state
, this_cpu_ptr(&rcu_sched_data
));
1244 rcu_do_batch(&rcu_bh_state
, this_cpu_ptr(&rcu_bh_data
));
1245 rcu_preempt_do_callbacks();
1248 static void rcu_cpu_kthread_setup(unsigned int cpu
)
1250 struct sched_param sp
;
1252 sp
.sched_priority
= kthread_prio
;
1253 sched_setscheduler_nocheck(current
, SCHED_FIFO
, &sp
);
1256 static void rcu_cpu_kthread_park(unsigned int cpu
)
1258 per_cpu(rcu_cpu_kthread_status
, cpu
) = RCU_KTHREAD_OFFCPU
;
1261 static int rcu_cpu_kthread_should_run(unsigned int cpu
)
1263 return __this_cpu_read(rcu_cpu_has_work
);
1267 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
1268 * RCU softirq used in flavors and configurations of RCU that do not
1269 * support RCU priority boosting.
1271 static void rcu_cpu_kthread(unsigned int cpu
)
1273 unsigned int *statusp
= this_cpu_ptr(&rcu_cpu_kthread_status
);
1274 char work
, *workp
= this_cpu_ptr(&rcu_cpu_has_work
);
1277 for (spincnt
= 0; spincnt
< 10; spincnt
++) {
1278 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1280 *statusp
= RCU_KTHREAD_RUNNING
;
1281 this_cpu_inc(rcu_cpu_kthread_loops
);
1282 local_irq_disable();
1287 rcu_kthread_do_work();
1290 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1291 *statusp
= RCU_KTHREAD_WAITING
;
1295 *statusp
= RCU_KTHREAD_YIELDING
;
1296 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1297 schedule_timeout_interruptible(2);
1298 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1299 *statusp
= RCU_KTHREAD_WAITING
;
1303 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1304 * served by the rcu_node in question. The CPU hotplug lock is still
1305 * held, so the value of rnp->qsmaskinit will be stable.
1307 * We don't include outgoingcpu in the affinity set, use -1 if there is
1308 * no outgoing CPU. If there are no CPUs left in the affinity set,
1309 * this function allows the kthread to execute on any CPU.
1311 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
)
1313 struct task_struct
*t
= rnp
->boost_kthread_task
;
1314 unsigned long mask
= rnp
->qsmaskinit
;
1320 if (!zalloc_cpumask_var(&cm
, GFP_KERNEL
))
1322 for (cpu
= rnp
->grplo
; cpu
<= rnp
->grphi
; cpu
++, mask
>>= 1)
1323 if ((mask
& 0x1) && cpu
!= outgoingcpu
)
1324 cpumask_set_cpu(cpu
, cm
);
1325 if (cpumask_weight(cm
) == 0)
1327 set_cpus_allowed_ptr(t
, cm
);
1328 free_cpumask_var(cm
);
1331 static struct smp_hotplug_thread rcu_cpu_thread_spec
= {
1332 .store
= &rcu_cpu_kthread_task
,
1333 .thread_should_run
= rcu_cpu_kthread_should_run
,
1334 .thread_fn
= rcu_cpu_kthread
,
1335 .thread_comm
= "rcuc/%u",
1336 .setup
= rcu_cpu_kthread_setup
,
1337 .park
= rcu_cpu_kthread_park
,
1341 * Spawn boost kthreads -- called as soon as the scheduler is running.
1343 static void __init
rcu_spawn_boost_kthreads(void)
1345 struct rcu_node
*rnp
;
1348 for_each_possible_cpu(cpu
)
1349 per_cpu(rcu_cpu_has_work
, cpu
) = 0;
1350 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec
));
1351 rcu_for_each_leaf_node(rcu_state_p
, rnp
)
1352 (void)rcu_spawn_one_boost_kthread(rcu_state_p
, rnp
);
1355 static void rcu_prepare_kthreads(int cpu
)
1357 struct rcu_data
*rdp
= per_cpu_ptr(rcu_state_p
->rda
, cpu
);
1358 struct rcu_node
*rnp
= rdp
->mynode
;
1360 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1361 if (rcu_scheduler_fully_active
)
1362 (void)rcu_spawn_one_boost_kthread(rcu_state_p
, rnp
);
1365 #else /* #ifdef CONFIG_RCU_BOOST */
1367 static void rcu_initiate_boost(struct rcu_node
*rnp
, unsigned long flags
)
1368 __releases(rnp
->lock
)
1370 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1373 static void invoke_rcu_callbacks_kthread(void)
1378 static bool rcu_is_callbacks_kthread(void)
1383 static void rcu_preempt_boost_start_gp(struct rcu_node
*rnp
)
1387 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
)
1391 static void __init
rcu_spawn_boost_kthreads(void)
1395 static void rcu_prepare_kthreads(int cpu
)
1399 #endif /* #else #ifdef CONFIG_RCU_BOOST */
1401 #if !defined(CONFIG_RCU_FAST_NO_HZ)
1404 * Check to see if any future RCU-related work will need to be done
1405 * by the current CPU, even if none need be done immediately, returning
1406 * 1 if so. This function is part of the RCU implementation; it is -not-
1407 * an exported member of the RCU API.
1409 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1410 * any flavor of RCU.
1412 #ifndef CONFIG_RCU_NOCB_CPU_ALL
1413 int rcu_needs_cpu(unsigned long *delta_jiffies
)
1415 *delta_jiffies
= ULONG_MAX
;
1416 return rcu_cpu_has_callbacks(NULL
);
1418 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1421 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1424 static void rcu_cleanup_after_idle(void)
1429 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1432 static void rcu_prepare_for_idle(void)
1437 * Don't bother keeping a running count of the number of RCU callbacks
1438 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1440 static void rcu_idle_count_callbacks_posted(void)
1444 #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1447 * This code is invoked when a CPU goes idle, at which point we want
1448 * to have the CPU do everything required for RCU so that it can enter
1449 * the energy-efficient dyntick-idle mode. This is handled by a
1450 * state machine implemented by rcu_prepare_for_idle() below.
1452 * The following three proprocessor symbols control this state machine:
1454 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1455 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1456 * is sized to be roughly one RCU grace period. Those energy-efficiency
1457 * benchmarkers who might otherwise be tempted to set this to a large
1458 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1459 * system. And if you are -that- concerned about energy efficiency,
1460 * just power the system down and be done with it!
1461 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1462 * permitted to sleep in dyntick-idle mode with only lazy RCU
1463 * callbacks pending. Setting this too high can OOM your system.
1465 * The values below work well in practice. If future workloads require
1466 * adjustment, they can be converted into kernel config parameters, though
1467 * making the state machine smarter might be a better option.
1469 #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1470 #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1472 static int rcu_idle_gp_delay
= RCU_IDLE_GP_DELAY
;
1473 module_param(rcu_idle_gp_delay
, int, 0644);
1474 static int rcu_idle_lazy_gp_delay
= RCU_IDLE_LAZY_GP_DELAY
;
1475 module_param(rcu_idle_lazy_gp_delay
, int, 0644);
1477 extern int tick_nohz_active
;
1480 * Try to advance callbacks for all flavors of RCU on the current CPU, but
1481 * only if it has been awhile since the last time we did so. Afterwards,
1482 * if there are any callbacks ready for immediate invocation, return true.
1484 static bool __maybe_unused
rcu_try_advance_all_cbs(void)
1486 bool cbs_ready
= false;
1487 struct rcu_data
*rdp
;
1488 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
1489 struct rcu_node
*rnp
;
1490 struct rcu_state
*rsp
;
1492 /* Exit early if we advanced recently. */
1493 if (jiffies
== rdtp
->last_advance_all
)
1495 rdtp
->last_advance_all
= jiffies
;
1497 for_each_rcu_flavor(rsp
) {
1498 rdp
= this_cpu_ptr(rsp
->rda
);
1502 * Don't bother checking unless a grace period has
1503 * completed since we last checked and there are
1504 * callbacks not yet ready to invoke.
1506 if (rdp
->completed
!= rnp
->completed
&&
1507 rdp
->nxttail
[RCU_DONE_TAIL
] != rdp
->nxttail
[RCU_NEXT_TAIL
])
1508 note_gp_changes(rsp
, rdp
);
1510 if (cpu_has_callbacks_ready_to_invoke(rdp
))
1517 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1518 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1519 * caller to set the timeout based on whether or not there are non-lazy
1522 * The caller must have disabled interrupts.
1524 #ifndef CONFIG_RCU_NOCB_CPU_ALL
1525 int rcu_needs_cpu(unsigned long *dj
)
1527 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
1529 /* Snapshot to detect later posting of non-lazy callback. */
1530 rdtp
->nonlazy_posted_snap
= rdtp
->nonlazy_posted
;
1532 /* If no callbacks, RCU doesn't need the CPU. */
1533 if (!rcu_cpu_has_callbacks(&rdtp
->all_lazy
)) {
1538 /* Attempt to advance callbacks. */
1539 if (rcu_try_advance_all_cbs()) {
1540 /* Some ready to invoke, so initiate later invocation. */
1544 rdtp
->last_accelerate
= jiffies
;
1546 /* Request timer delay depending on laziness, and round. */
1547 if (!rdtp
->all_lazy
) {
1548 *dj
= round_up(rcu_idle_gp_delay
+ jiffies
,
1549 rcu_idle_gp_delay
) - jiffies
;
1551 *dj
= round_jiffies(rcu_idle_lazy_gp_delay
+ jiffies
) - jiffies
;
1555 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1558 * Prepare a CPU for idle from an RCU perspective. The first major task
1559 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1560 * The second major task is to check to see if a non-lazy callback has
1561 * arrived at a CPU that previously had only lazy callbacks. The third
1562 * major task is to accelerate (that is, assign grace-period numbers to)
1563 * any recently arrived callbacks.
1565 * The caller must have disabled interrupts.
1567 static void rcu_prepare_for_idle(void)
1569 #ifndef CONFIG_RCU_NOCB_CPU_ALL
1571 struct rcu_data
*rdp
;
1572 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
1573 struct rcu_node
*rnp
;
1574 struct rcu_state
*rsp
;
1577 /* Handle nohz enablement switches conservatively. */
1578 tne
= ACCESS_ONCE(tick_nohz_active
);
1579 if (tne
!= rdtp
->tick_nohz_enabled_snap
) {
1580 if (rcu_cpu_has_callbacks(NULL
))
1581 invoke_rcu_core(); /* force nohz to see update. */
1582 rdtp
->tick_nohz_enabled_snap
= tne
;
1588 /* If this is a no-CBs CPU, no callbacks, just return. */
1589 if (rcu_is_nocb_cpu(smp_processor_id()))
1593 * If a non-lazy callback arrived at a CPU having only lazy
1594 * callbacks, invoke RCU core for the side-effect of recalculating
1595 * idle duration on re-entry to idle.
1597 if (rdtp
->all_lazy
&&
1598 rdtp
->nonlazy_posted
!= rdtp
->nonlazy_posted_snap
) {
1599 rdtp
->all_lazy
= false;
1600 rdtp
->nonlazy_posted_snap
= rdtp
->nonlazy_posted
;
1606 * If we have not yet accelerated this jiffy, accelerate all
1607 * callbacks on this CPU.
1609 if (rdtp
->last_accelerate
== jiffies
)
1611 rdtp
->last_accelerate
= jiffies
;
1612 for_each_rcu_flavor(rsp
) {
1613 rdp
= this_cpu_ptr(rsp
->rda
);
1614 if (!*rdp
->nxttail
[RCU_DONE_TAIL
])
1617 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1618 smp_mb__after_unlock_lock();
1619 needwake
= rcu_accelerate_cbs(rsp
, rnp
, rdp
);
1620 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1622 rcu_gp_kthread_wake(rsp
);
1624 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1628 * Clean up for exit from idle. Attempt to advance callbacks based on
1629 * any grace periods that elapsed while the CPU was idle, and if any
1630 * callbacks are now ready to invoke, initiate invocation.
1632 static void rcu_cleanup_after_idle(void)
1634 #ifndef CONFIG_RCU_NOCB_CPU_ALL
1635 if (rcu_is_nocb_cpu(smp_processor_id()))
1637 if (rcu_try_advance_all_cbs())
1639 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1643 * Keep a running count of the number of non-lazy callbacks posted
1644 * on this CPU. This running counter (which is never decremented) allows
1645 * rcu_prepare_for_idle() to detect when something out of the idle loop
1646 * posts a callback, even if an equal number of callbacks are invoked.
1647 * Of course, callbacks should only be posted from within a trace event
1648 * designed to be called from idle or from within RCU_NONIDLE().
1650 static void rcu_idle_count_callbacks_posted(void)
1652 __this_cpu_add(rcu_dynticks
.nonlazy_posted
, 1);
1656 * Data for flushing lazy RCU callbacks at OOM time.
1658 static atomic_t oom_callback_count
;
1659 static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq
);
1662 * RCU OOM callback -- decrement the outstanding count and deliver the
1663 * wake-up if we are the last one.
1665 static void rcu_oom_callback(struct rcu_head
*rhp
)
1667 if (atomic_dec_and_test(&oom_callback_count
))
1668 wake_up(&oom_callback_wq
);
1672 * Post an rcu_oom_notify callback on the current CPU if it has at
1673 * least one lazy callback. This will unnecessarily post callbacks
1674 * to CPUs that already have a non-lazy callback at the end of their
1675 * callback list, but this is an infrequent operation, so accept some
1676 * extra overhead to keep things simple.
1678 static void rcu_oom_notify_cpu(void *unused
)
1680 struct rcu_state
*rsp
;
1681 struct rcu_data
*rdp
;
1683 for_each_rcu_flavor(rsp
) {
1684 rdp
= raw_cpu_ptr(rsp
->rda
);
1685 if (rdp
->qlen_lazy
!= 0) {
1686 atomic_inc(&oom_callback_count
);
1687 rsp
->call(&rdp
->oom_head
, rcu_oom_callback
);
1693 * If low on memory, ensure that each CPU has a non-lazy callback.
1694 * This will wake up CPUs that have only lazy callbacks, in turn
1695 * ensuring that they free up the corresponding memory in a timely manner.
1696 * Because an uncertain amount of memory will be freed in some uncertain
1697 * timeframe, we do not claim to have freed anything.
1699 static int rcu_oom_notify(struct notifier_block
*self
,
1700 unsigned long notused
, void *nfreed
)
1704 /* Wait for callbacks from earlier instance to complete. */
1705 wait_event(oom_callback_wq
, atomic_read(&oom_callback_count
) == 0);
1706 smp_mb(); /* Ensure callback reuse happens after callback invocation. */
1709 * Prevent premature wakeup: ensure that all increments happen
1710 * before there is a chance of the counter reaching zero.
1712 atomic_set(&oom_callback_count
, 1);
1715 for_each_online_cpu(cpu
) {
1716 smp_call_function_single(cpu
, rcu_oom_notify_cpu
, NULL
, 1);
1717 cond_resched_rcu_qs();
1721 /* Unconditionally decrement: no need to wake ourselves up. */
1722 atomic_dec(&oom_callback_count
);
1727 static struct notifier_block rcu_oom_nb
= {
1728 .notifier_call
= rcu_oom_notify
1731 static int __init
rcu_register_oom_notifier(void)
1733 register_oom_notifier(&rcu_oom_nb
);
1736 early_initcall(rcu_register_oom_notifier
);
1738 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1740 #ifdef CONFIG_RCU_CPU_STALL_INFO
1742 #ifdef CONFIG_RCU_FAST_NO_HZ
1744 static void print_cpu_stall_fast_no_hz(char *cp
, int cpu
)
1746 struct rcu_dynticks
*rdtp
= &per_cpu(rcu_dynticks
, cpu
);
1747 unsigned long nlpd
= rdtp
->nonlazy_posted
- rdtp
->nonlazy_posted_snap
;
1749 sprintf(cp
, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1750 rdtp
->last_accelerate
& 0xffff, jiffies
& 0xffff,
1752 rdtp
->all_lazy
? 'L' : '.',
1753 rdtp
->tick_nohz_enabled_snap
? '.' : 'D');
1756 #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1758 static void print_cpu_stall_fast_no_hz(char *cp
, int cpu
)
1763 #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1765 /* Initiate the stall-info list. */
1766 static void print_cpu_stall_info_begin(void)
1772 * Print out diagnostic information for the specified stalled CPU.
1774 * If the specified CPU is aware of the current RCU grace period
1775 * (flavor specified by rsp), then print the number of scheduling
1776 * clock interrupts the CPU has taken during the time that it has
1777 * been aware. Otherwise, print the number of RCU grace periods
1778 * that this CPU is ignorant of, for example, "1" if the CPU was
1779 * aware of the previous grace period.
1781 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1783 static void print_cpu_stall_info(struct rcu_state
*rsp
, int cpu
)
1785 char fast_no_hz
[72];
1786 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1787 struct rcu_dynticks
*rdtp
= rdp
->dynticks
;
1789 unsigned long ticks_value
;
1791 if (rsp
->gpnum
== rdp
->gpnum
) {
1792 ticks_title
= "ticks this GP";
1793 ticks_value
= rdp
->ticks_this_gp
;
1795 ticks_title
= "GPs behind";
1796 ticks_value
= rsp
->gpnum
- rdp
->gpnum
;
1798 print_cpu_stall_fast_no_hz(fast_no_hz
, cpu
);
1799 pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
1800 cpu
, ticks_value
, ticks_title
,
1801 atomic_read(&rdtp
->dynticks
) & 0xfff,
1802 rdtp
->dynticks_nesting
, rdtp
->dynticks_nmi_nesting
,
1803 rdp
->softirq_snap
, kstat_softirqs_cpu(RCU_SOFTIRQ
, cpu
),
1807 /* Terminate the stall-info list. */
1808 static void print_cpu_stall_info_end(void)
1813 /* Zero ->ticks_this_gp for all flavors of RCU. */
1814 static void zero_cpu_stall_ticks(struct rcu_data
*rdp
)
1816 rdp
->ticks_this_gp
= 0;
1817 rdp
->softirq_snap
= kstat_softirqs_cpu(RCU_SOFTIRQ
, smp_processor_id());
1820 /* Increment ->ticks_this_gp for all flavors of RCU. */
1821 static void increment_cpu_stall_ticks(void)
1823 struct rcu_state
*rsp
;
1825 for_each_rcu_flavor(rsp
)
1826 raw_cpu_inc(rsp
->rda
->ticks_this_gp
);
1829 #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
1831 static void print_cpu_stall_info_begin(void)
1836 static void print_cpu_stall_info(struct rcu_state
*rsp
, int cpu
)
1838 pr_cont(" %d", cpu
);
1841 static void print_cpu_stall_info_end(void)
1846 static void zero_cpu_stall_ticks(struct rcu_data
*rdp
)
1850 static void increment_cpu_stall_ticks(void)
1854 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
1856 #ifdef CONFIG_RCU_NOCB_CPU
1859 * Offload callback processing from the boot-time-specified set of CPUs
1860 * specified by rcu_nocb_mask. For each CPU in the set, there is a
1861 * kthread created that pulls the callbacks from the corresponding CPU,
1862 * waits for a grace period to elapse, and invokes the callbacks.
1863 * The no-CBs CPUs do a wake_up() on their kthread when they insert
1864 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
1865 * has been specified, in which case each kthread actively polls its
1866 * CPU. (Which isn't so great for energy efficiency, but which does
1867 * reduce RCU's overhead on that CPU.)
1869 * This is intended to be used in conjunction with Frederic Weisbecker's
1870 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
1871 * running CPU-bound user-mode computations.
1873 * Offloading of callback processing could also in theory be used as
1874 * an energy-efficiency measure because CPUs with no RCU callbacks
1875 * queued are more aggressive about entering dyntick-idle mode.
1879 /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
1880 static int __init
rcu_nocb_setup(char *str
)
1882 alloc_bootmem_cpumask_var(&rcu_nocb_mask
);
1883 have_rcu_nocb_mask
= true;
1884 cpulist_parse(str
, rcu_nocb_mask
);
1887 __setup("rcu_nocbs=", rcu_nocb_setup
);
1889 static int __init
parse_rcu_nocb_poll(char *arg
)
1894 early_param("rcu_nocb_poll", parse_rcu_nocb_poll
);
1897 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
1900 static void rcu_nocb_gp_cleanup(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
1902 wake_up_all(&rnp
->nocb_gp_wq
[rnp
->completed
& 0x1]);
1906 * Set the root rcu_node structure's ->need_future_gp field
1907 * based on the sum of those of all rcu_node structures. This does
1908 * double-count the root rcu_node structure's requests, but this
1909 * is necessary to handle the possibility of a rcu_nocb_kthread()
1910 * having awakened during the time that the rcu_node structures
1911 * were being updated for the end of the previous grace period.
1913 static void rcu_nocb_gp_set(struct rcu_node
*rnp
, int nrq
)
1915 rnp
->need_future_gp
[(rnp
->completed
+ 1) & 0x1] += nrq
;
1918 static void rcu_init_one_nocb(struct rcu_node
*rnp
)
1920 init_waitqueue_head(&rnp
->nocb_gp_wq
[0]);
1921 init_waitqueue_head(&rnp
->nocb_gp_wq
[1]);
1924 #ifndef CONFIG_RCU_NOCB_CPU_ALL
1925 /* Is the specified CPU a no-CBs CPU? */
1926 bool rcu_is_nocb_cpu(int cpu
)
1928 if (have_rcu_nocb_mask
)
1929 return cpumask_test_cpu(cpu
, rcu_nocb_mask
);
1932 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1935 * Kick the leader kthread for this NOCB group.
1937 static void wake_nocb_leader(struct rcu_data
*rdp
, bool force
)
1939 struct rcu_data
*rdp_leader
= rdp
->nocb_leader
;
1941 if (!ACCESS_ONCE(rdp_leader
->nocb_kthread
))
1943 if (ACCESS_ONCE(rdp_leader
->nocb_leader_sleep
) || force
) {
1944 /* Prior smp_mb__after_atomic() orders against prior enqueue. */
1945 ACCESS_ONCE(rdp_leader
->nocb_leader_sleep
) = false;
1946 wake_up(&rdp_leader
->nocb_wq
);
1951 * Does the specified CPU need an RCU callback for the specified flavor
1954 static bool rcu_nocb_cpu_needs_barrier(struct rcu_state
*rsp
, int cpu
)
1956 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1957 struct rcu_head
*rhp
;
1959 /* No-CBs CPUs might have callbacks on any of three lists. */
1960 rhp
= ACCESS_ONCE(rdp
->nocb_head
);
1962 rhp
= ACCESS_ONCE(rdp
->nocb_gp_head
);
1964 rhp
= ACCESS_ONCE(rdp
->nocb_follower_head
);
1966 /* Having no rcuo kthread but CBs after scheduler starts is bad! */
1967 if (!ACCESS_ONCE(rdp
->nocb_kthread
) && rhp
) {
1968 /* RCU callback enqueued before CPU first came online??? */
1969 pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
1978 * Enqueue the specified string of rcu_head structures onto the specified
1979 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
1980 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
1981 * counts are supplied by rhcount and rhcount_lazy.
1983 * If warranted, also wake up the kthread servicing this CPUs queues.
1985 static void __call_rcu_nocb_enqueue(struct rcu_data
*rdp
,
1986 struct rcu_head
*rhp
,
1987 struct rcu_head
**rhtp
,
1988 int rhcount
, int rhcount_lazy
,
1989 unsigned long flags
)
1992 struct rcu_head
**old_rhpp
;
1993 struct task_struct
*t
;
1995 /* Enqueue the callback on the nocb list and update counts. */
1996 old_rhpp
= xchg(&rdp
->nocb_tail
, rhtp
);
1997 ACCESS_ONCE(*old_rhpp
) = rhp
;
1998 atomic_long_add(rhcount
, &rdp
->nocb_q_count
);
1999 atomic_long_add(rhcount_lazy
, &rdp
->nocb_q_count_lazy
);
2000 smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
2002 /* If we are not being polled and there is a kthread, awaken it ... */
2003 t
= ACCESS_ONCE(rdp
->nocb_kthread
);
2004 if (rcu_nocb_poll
|| !t
) {
2005 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2006 TPS("WakeNotPoll"));
2009 len
= atomic_long_read(&rdp
->nocb_q_count
);
2010 if (old_rhpp
== &rdp
->nocb_head
) {
2011 if (!irqs_disabled_flags(flags
)) {
2012 /* ... if queue was empty ... */
2013 wake_nocb_leader(rdp
, false);
2014 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2017 rdp
->nocb_defer_wakeup
= RCU_NOGP_WAKE
;
2018 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2019 TPS("WakeEmptyIsDeferred"));
2021 rdp
->qlen_last_fqs_check
= 0;
2022 } else if (len
> rdp
->qlen_last_fqs_check
+ qhimark
) {
2023 /* ... or if many callbacks queued. */
2024 if (!irqs_disabled_flags(flags
)) {
2025 wake_nocb_leader(rdp
, true);
2026 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2029 rdp
->nocb_defer_wakeup
= RCU_NOGP_WAKE_FORCE
;
2030 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2031 TPS("WakeOvfIsDeferred"));
2033 rdp
->qlen_last_fqs_check
= LONG_MAX
/ 2;
2035 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, TPS("WakeNot"));
2041 * This is a helper for __call_rcu(), which invokes this when the normal
2042 * callback queue is inoperable. If this is not a no-CBs CPU, this
2043 * function returns failure back to __call_rcu(), which can complain
2046 * Otherwise, this function queues the callback where the corresponding
2047 * "rcuo" kthread can find it.
2049 static bool __call_rcu_nocb(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
2050 bool lazy
, unsigned long flags
)
2053 if (!rcu_is_nocb_cpu(rdp
->cpu
))
2055 __call_rcu_nocb_enqueue(rdp
, rhp
, &rhp
->next
, 1, lazy
, flags
);
2056 if (__is_kfree_rcu_offset((unsigned long)rhp
->func
))
2057 trace_rcu_kfree_callback(rdp
->rsp
->name
, rhp
,
2058 (unsigned long)rhp
->func
,
2059 -atomic_long_read(&rdp
->nocb_q_count_lazy
),
2060 -atomic_long_read(&rdp
->nocb_q_count
));
2062 trace_rcu_callback(rdp
->rsp
->name
, rhp
,
2063 -atomic_long_read(&rdp
->nocb_q_count_lazy
),
2064 -atomic_long_read(&rdp
->nocb_q_count
));
2067 * If called from an extended quiescent state with interrupts
2068 * disabled, invoke the RCU core in order to allow the idle-entry
2069 * deferred-wakeup check to function.
2071 if (irqs_disabled_flags(flags
) &&
2072 !rcu_is_watching() &&
2073 cpu_online(smp_processor_id()))
2080 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2083 static bool __maybe_unused
rcu_nocb_adopt_orphan_cbs(struct rcu_state
*rsp
,
2084 struct rcu_data
*rdp
,
2085 unsigned long flags
)
2087 long ql
= rsp
->qlen
;
2088 long qll
= rsp
->qlen_lazy
;
2090 /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
2091 if (!rcu_is_nocb_cpu(smp_processor_id()))
2096 /* First, enqueue the donelist, if any. This preserves CB ordering. */
2097 if (rsp
->orphan_donelist
!= NULL
) {
2098 __call_rcu_nocb_enqueue(rdp
, rsp
->orphan_donelist
,
2099 rsp
->orphan_donetail
, ql
, qll
, flags
);
2101 rsp
->orphan_donelist
= NULL
;
2102 rsp
->orphan_donetail
= &rsp
->orphan_donelist
;
2104 if (rsp
->orphan_nxtlist
!= NULL
) {
2105 __call_rcu_nocb_enqueue(rdp
, rsp
->orphan_nxtlist
,
2106 rsp
->orphan_nxttail
, ql
, qll
, flags
);
2108 rsp
->orphan_nxtlist
= NULL
;
2109 rsp
->orphan_nxttail
= &rsp
->orphan_nxtlist
;
2115 * If necessary, kick off a new grace period, and either way wait
2116 * for a subsequent grace period to complete.
2118 static void rcu_nocb_wait_gp(struct rcu_data
*rdp
)
2122 unsigned long flags
;
2124 struct rcu_node
*rnp
= rdp
->mynode
;
2126 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2127 smp_mb__after_unlock_lock();
2128 needwake
= rcu_start_future_gp(rnp
, rdp
, &c
);
2129 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2131 rcu_gp_kthread_wake(rdp
->rsp
);
2134 * Wait for the grace period. Do so interruptibly to avoid messing
2135 * up the load average.
2137 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("StartWait"));
2139 wait_event_interruptible(
2140 rnp
->nocb_gp_wq
[c
& 0x1],
2141 (d
= ULONG_CMP_GE(ACCESS_ONCE(rnp
->completed
), c
)));
2144 WARN_ON(signal_pending(current
));
2145 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("ResumeWait"));
2147 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("EndWait"));
2148 smp_mb(); /* Ensure that CB invocation happens after GP end. */
2152 * Leaders come here to wait for additional callbacks to show up.
2153 * This function does not return until callbacks appear.
2155 static void nocb_leader_wait(struct rcu_data
*my_rdp
)
2157 bool firsttime
= true;
2159 struct rcu_data
*rdp
;
2160 struct rcu_head
**tail
;
2164 /* Wait for callbacks to appear. */
2165 if (!rcu_nocb_poll
) {
2166 trace_rcu_nocb_wake(my_rdp
->rsp
->name
, my_rdp
->cpu
, "Sleep");
2167 wait_event_interruptible(my_rdp
->nocb_wq
,
2168 !ACCESS_ONCE(my_rdp
->nocb_leader_sleep
));
2169 /* Memory barrier handled by smp_mb() calls below and repoll. */
2170 } else if (firsttime
) {
2171 firsttime
= false; /* Don't drown trace log with "Poll"! */
2172 trace_rcu_nocb_wake(my_rdp
->rsp
->name
, my_rdp
->cpu
, "Poll");
2176 * Each pass through the following loop checks a follower for CBs.
2177 * We are our own first follower. Any CBs found are moved to
2178 * nocb_gp_head, where they await a grace period.
2181 for (rdp
= my_rdp
; rdp
; rdp
= rdp
->nocb_next_follower
) {
2182 rdp
->nocb_gp_head
= ACCESS_ONCE(rdp
->nocb_head
);
2183 if (!rdp
->nocb_gp_head
)
2184 continue; /* No CBs here, try next follower. */
2186 /* Move callbacks to wait-for-GP list, which is empty. */
2187 ACCESS_ONCE(rdp
->nocb_head
) = NULL
;
2188 rdp
->nocb_gp_tail
= xchg(&rdp
->nocb_tail
, &rdp
->nocb_head
);
2189 rdp
->nocb_gp_count
= atomic_long_xchg(&rdp
->nocb_q_count
, 0);
2190 rdp
->nocb_gp_count_lazy
=
2191 atomic_long_xchg(&rdp
->nocb_q_count_lazy
, 0);
2196 * If there were no callbacks, sleep a bit, rescan after a
2197 * memory barrier, and go retry.
2199 if (unlikely(!gotcbs
)) {
2201 trace_rcu_nocb_wake(my_rdp
->rsp
->name
, my_rdp
->cpu
,
2203 WARN_ON(signal_pending(current
));
2204 schedule_timeout_interruptible(1);
2206 /* Rescan in case we were a victim of memory ordering. */
2207 my_rdp
->nocb_leader_sleep
= true;
2208 smp_mb(); /* Ensure _sleep true before scan. */
2209 for (rdp
= my_rdp
; rdp
; rdp
= rdp
->nocb_next_follower
)
2210 if (ACCESS_ONCE(rdp
->nocb_head
)) {
2211 /* Found CB, so short-circuit next wait. */
2212 my_rdp
->nocb_leader_sleep
= false;
2218 /* Wait for one grace period. */
2219 rcu_nocb_wait_gp(my_rdp
);
2222 * We left ->nocb_leader_sleep unset to reduce cache thrashing.
2223 * We set it now, but recheck for new callbacks while
2224 * traversing our follower list.
2226 my_rdp
->nocb_leader_sleep
= true;
2227 smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */
2229 /* Each pass through the following loop wakes a follower, if needed. */
2230 for (rdp
= my_rdp
; rdp
; rdp
= rdp
->nocb_next_follower
) {
2231 if (ACCESS_ONCE(rdp
->nocb_head
))
2232 my_rdp
->nocb_leader_sleep
= false;/* No need to sleep.*/
2233 if (!rdp
->nocb_gp_head
)
2234 continue; /* No CBs, so no need to wake follower. */
2236 /* Append callbacks to follower's "done" list. */
2237 tail
= xchg(&rdp
->nocb_follower_tail
, rdp
->nocb_gp_tail
);
2238 *tail
= rdp
->nocb_gp_head
;
2239 atomic_long_add(rdp
->nocb_gp_count
, &rdp
->nocb_follower_count
);
2240 atomic_long_add(rdp
->nocb_gp_count_lazy
,
2241 &rdp
->nocb_follower_count_lazy
);
2242 smp_mb__after_atomic(); /* Store *tail before wakeup. */
2243 if (rdp
!= my_rdp
&& tail
== &rdp
->nocb_follower_head
) {
2245 * List was empty, wake up the follower.
2246 * Memory barriers supplied by atomic_long_add().
2248 wake_up(&rdp
->nocb_wq
);
2252 /* If we (the leader) don't have CBs, go wait some more. */
2253 if (!my_rdp
->nocb_follower_head
)
2258 * Followers come here to wait for additional callbacks to show up.
2259 * This function does not return until callbacks appear.
2261 static void nocb_follower_wait(struct rcu_data
*rdp
)
2263 bool firsttime
= true;
2266 if (!rcu_nocb_poll
) {
2267 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2269 wait_event_interruptible(rdp
->nocb_wq
,
2270 ACCESS_ONCE(rdp
->nocb_follower_head
));
2271 } else if (firsttime
) {
2272 /* Don't drown trace log with "Poll"! */
2274 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, "Poll");
2276 if (smp_load_acquire(&rdp
->nocb_follower_head
)) {
2277 /* ^^^ Ensure CB invocation follows _head test. */
2281 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2283 WARN_ON(signal_pending(current
));
2284 schedule_timeout_interruptible(1);
2289 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
2290 * callbacks queued by the corresponding no-CBs CPU, however, there is
2291 * an optional leader-follower relationship so that the grace-period
2292 * kthreads don't have to do quite so many wakeups.
2294 static int rcu_nocb_kthread(void *arg
)
2297 struct rcu_head
*list
;
2298 struct rcu_head
*next
;
2299 struct rcu_head
**tail
;
2300 struct rcu_data
*rdp
= arg
;
2302 /* Each pass through this loop invokes one batch of callbacks */
2304 /* Wait for callbacks. */
2305 if (rdp
->nocb_leader
== rdp
)
2306 nocb_leader_wait(rdp
);
2308 nocb_follower_wait(rdp
);
2310 /* Pull the ready-to-invoke callbacks onto local list. */
2311 list
= ACCESS_ONCE(rdp
->nocb_follower_head
);
2313 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, "WokeNonEmpty");
2314 ACCESS_ONCE(rdp
->nocb_follower_head
) = NULL
;
2315 tail
= xchg(&rdp
->nocb_follower_tail
, &rdp
->nocb_follower_head
);
2316 c
= atomic_long_xchg(&rdp
->nocb_follower_count
, 0);
2317 cl
= atomic_long_xchg(&rdp
->nocb_follower_count_lazy
, 0);
2318 rdp
->nocb_p_count
+= c
;
2319 rdp
->nocb_p_count_lazy
+= cl
;
2321 /* Each pass through the following loop invokes a callback. */
2322 trace_rcu_batch_start(rdp
->rsp
->name
, cl
, c
, -1);
2326 /* Wait for enqueuing to complete, if needed. */
2327 while (next
== NULL
&& &list
->next
!= tail
) {
2328 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2330 schedule_timeout_interruptible(1);
2331 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2335 debug_rcu_head_unqueue(list
);
2337 if (__rcu_reclaim(rdp
->rsp
->name
, list
))
2343 trace_rcu_batch_end(rdp
->rsp
->name
, c
, !!list
, 0, 0, 1);
2344 ACCESS_ONCE(rdp
->nocb_p_count
) = rdp
->nocb_p_count
- c
;
2345 ACCESS_ONCE(rdp
->nocb_p_count_lazy
) =
2346 rdp
->nocb_p_count_lazy
- cl
;
2347 rdp
->n_nocbs_invoked
+= c
;
2352 /* Is a deferred wakeup of rcu_nocb_kthread() required? */
2353 static int rcu_nocb_need_deferred_wakeup(struct rcu_data
*rdp
)
2355 return ACCESS_ONCE(rdp
->nocb_defer_wakeup
);
2358 /* Do a deferred wakeup of rcu_nocb_kthread(). */
2359 static void do_nocb_deferred_wakeup(struct rcu_data
*rdp
)
2363 if (!rcu_nocb_need_deferred_wakeup(rdp
))
2365 ndw
= ACCESS_ONCE(rdp
->nocb_defer_wakeup
);
2366 ACCESS_ONCE(rdp
->nocb_defer_wakeup
) = RCU_NOGP_WAKE_NOT
;
2367 wake_nocb_leader(rdp
, ndw
== RCU_NOGP_WAKE_FORCE
);
2368 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, TPS("DeferredWake"));
2371 void __init
rcu_init_nohz(void)
2374 bool need_rcu_nocb_mask
= true;
2375 struct rcu_state
*rsp
;
2377 #ifdef CONFIG_RCU_NOCB_CPU_NONE
2378 need_rcu_nocb_mask
= false;
2379 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
2381 #if defined(CONFIG_NO_HZ_FULL)
2382 if (tick_nohz_full_running
&& cpumask_weight(tick_nohz_full_mask
))
2383 need_rcu_nocb_mask
= true;
2384 #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2386 if (!have_rcu_nocb_mask
&& need_rcu_nocb_mask
) {
2387 if (!zalloc_cpumask_var(&rcu_nocb_mask
, GFP_KERNEL
)) {
2388 pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
2391 have_rcu_nocb_mask
= true;
2393 if (!have_rcu_nocb_mask
)
2396 #ifdef CONFIG_RCU_NOCB_CPU_ZERO
2397 pr_info("\tOffload RCU callbacks from CPU 0\n");
2398 cpumask_set_cpu(0, rcu_nocb_mask
);
2399 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
2400 #ifdef CONFIG_RCU_NOCB_CPU_ALL
2401 pr_info("\tOffload RCU callbacks from all CPUs\n");
2402 cpumask_copy(rcu_nocb_mask
, cpu_possible_mask
);
2403 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
2404 #if defined(CONFIG_NO_HZ_FULL)
2405 if (tick_nohz_full_running
)
2406 cpumask_or(rcu_nocb_mask
, rcu_nocb_mask
, tick_nohz_full_mask
);
2407 #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2409 if (!cpumask_subset(rcu_nocb_mask
, cpu_possible_mask
)) {
2410 pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
2411 cpumask_and(rcu_nocb_mask
, cpu_possible_mask
,
2414 cpulist_scnprintf(nocb_buf
, sizeof(nocb_buf
), rcu_nocb_mask
);
2415 pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf
);
2417 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
2419 for_each_rcu_flavor(rsp
) {
2420 for_each_cpu(cpu
, rcu_nocb_mask
) {
2421 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2424 * If there are early callbacks, they will need
2425 * to be moved to the nocb lists.
2427 WARN_ON_ONCE(rdp
->nxttail
[RCU_NEXT_TAIL
] !=
2429 rdp
->nxttail
[RCU_NEXT_TAIL
] != NULL
);
2430 init_nocb_callback_list(rdp
);
2432 rcu_organize_nocb_kthreads(rsp
);
2436 /* Initialize per-rcu_data variables for no-CBs CPUs. */
2437 static void __init
rcu_boot_init_nocb_percpu_data(struct rcu_data
*rdp
)
2439 rdp
->nocb_tail
= &rdp
->nocb_head
;
2440 init_waitqueue_head(&rdp
->nocb_wq
);
2441 rdp
->nocb_follower_tail
= &rdp
->nocb_follower_head
;
2445 * If the specified CPU is a no-CBs CPU that does not already have its
2446 * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are
2447 * brought online out of order, this can require re-organizing the
2448 * leader-follower relationships.
2450 static void rcu_spawn_one_nocb_kthread(struct rcu_state
*rsp
, int cpu
)
2452 struct rcu_data
*rdp
;
2453 struct rcu_data
*rdp_last
;
2454 struct rcu_data
*rdp_old_leader
;
2455 struct rcu_data
*rdp_spawn
= per_cpu_ptr(rsp
->rda
, cpu
);
2456 struct task_struct
*t
;
2459 * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
2460 * then nothing to do.
2462 if (!rcu_is_nocb_cpu(cpu
) || rdp_spawn
->nocb_kthread
)
2465 /* If we didn't spawn the leader first, reorganize! */
2466 rdp_old_leader
= rdp_spawn
->nocb_leader
;
2467 if (rdp_old_leader
!= rdp_spawn
&& !rdp_old_leader
->nocb_kthread
) {
2469 rdp
= rdp_old_leader
;
2471 rdp
->nocb_leader
= rdp_spawn
;
2472 if (rdp_last
&& rdp
!= rdp_spawn
)
2473 rdp_last
->nocb_next_follower
= rdp
;
2474 if (rdp
== rdp_spawn
) {
2475 rdp
= rdp
->nocb_next_follower
;
2478 rdp
= rdp
->nocb_next_follower
;
2479 rdp_last
->nocb_next_follower
= NULL
;
2482 rdp_spawn
->nocb_next_follower
= rdp_old_leader
;
2485 /* Spawn the kthread for this CPU and RCU flavor. */
2486 t
= kthread_run(rcu_nocb_kthread
, rdp_spawn
,
2487 "rcuo%c/%d", rsp
->abbr
, cpu
);
2489 ACCESS_ONCE(rdp_spawn
->nocb_kthread
) = t
;
2493 * If the specified CPU is a no-CBs CPU that does not already have its
2494 * rcuo kthreads, spawn them.
2496 static void rcu_spawn_all_nocb_kthreads(int cpu
)
2498 struct rcu_state
*rsp
;
2500 if (rcu_scheduler_fully_active
)
2501 for_each_rcu_flavor(rsp
)
2502 rcu_spawn_one_nocb_kthread(rsp
, cpu
);
2506 * Once the scheduler is running, spawn rcuo kthreads for all online
2507 * no-CBs CPUs. This assumes that the early_initcall()s happen before
2508 * non-boot CPUs come online -- if this changes, we will need to add
2509 * some mutual exclusion.
2511 static void __init
rcu_spawn_nocb_kthreads(void)
2515 for_each_online_cpu(cpu
)
2516 rcu_spawn_all_nocb_kthreads(cpu
);
2519 /* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */
2520 static int rcu_nocb_leader_stride
= -1;
2521 module_param(rcu_nocb_leader_stride
, int, 0444);
2524 * Initialize leader-follower relationships for all no-CBs CPU.
2526 static void __init
rcu_organize_nocb_kthreads(struct rcu_state
*rsp
)
2529 int ls
= rcu_nocb_leader_stride
;
2530 int nl
= 0; /* Next leader. */
2531 struct rcu_data
*rdp
;
2532 struct rcu_data
*rdp_leader
= NULL
; /* Suppress misguided gcc warn. */
2533 struct rcu_data
*rdp_prev
= NULL
;
2535 if (!have_rcu_nocb_mask
)
2538 ls
= int_sqrt(nr_cpu_ids
);
2539 rcu_nocb_leader_stride
= ls
;
2543 * Each pass through this loop sets up one rcu_data structure and
2544 * spawns one rcu_nocb_kthread().
2546 for_each_cpu(cpu
, rcu_nocb_mask
) {
2547 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2548 if (rdp
->cpu
>= nl
) {
2549 /* New leader, set up for followers & next leader. */
2550 nl
= DIV_ROUND_UP(rdp
->cpu
+ 1, ls
) * ls
;
2551 rdp
->nocb_leader
= rdp
;
2554 /* Another follower, link to previous leader. */
2555 rdp
->nocb_leader
= rdp_leader
;
2556 rdp_prev
->nocb_next_follower
= rdp
;
2562 /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2563 static bool init_nocb_callback_list(struct rcu_data
*rdp
)
2565 if (!rcu_is_nocb_cpu(rdp
->cpu
))
2568 rdp
->nxttail
[RCU_NEXT_TAIL
] = NULL
;
2572 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
2574 static bool rcu_nocb_cpu_needs_barrier(struct rcu_state
*rsp
, int cpu
)
2576 WARN_ON_ONCE(1); /* Should be dead code. */
2580 static void rcu_nocb_gp_cleanup(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
2584 static void rcu_nocb_gp_set(struct rcu_node
*rnp
, int nrq
)
2588 static void rcu_init_one_nocb(struct rcu_node
*rnp
)
2592 static bool __call_rcu_nocb(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
2593 bool lazy
, unsigned long flags
)
2598 static bool __maybe_unused
rcu_nocb_adopt_orphan_cbs(struct rcu_state
*rsp
,
2599 struct rcu_data
*rdp
,
2600 unsigned long flags
)
2605 static void __init
rcu_boot_init_nocb_percpu_data(struct rcu_data
*rdp
)
2609 static int rcu_nocb_need_deferred_wakeup(struct rcu_data
*rdp
)
2614 static void do_nocb_deferred_wakeup(struct rcu_data
*rdp
)
2618 static void rcu_spawn_all_nocb_kthreads(int cpu
)
2622 static void __init
rcu_spawn_nocb_kthreads(void)
2626 static bool init_nocb_callback_list(struct rcu_data
*rdp
)
2631 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2634 * An adaptive-ticks CPU can potentially execute in kernel mode for an
2635 * arbitrarily long period of time with the scheduling-clock tick turned
2636 * off. RCU will be paying attention to this CPU because it is in the
2637 * kernel, but the CPU cannot be guaranteed to be executing the RCU state
2638 * machine because the scheduling-clock tick has been disabled. Therefore,
2639 * if an adaptive-ticks CPU is failing to respond to the current grace
2640 * period and has not be idle from an RCU perspective, kick it.
2642 static void __maybe_unused
rcu_kick_nohz_cpu(int cpu
)
2644 #ifdef CONFIG_NO_HZ_FULL
2645 if (tick_nohz_full_cpu(cpu
))
2646 smp_send_reschedule(cpu
);
2647 #endif /* #ifdef CONFIG_NO_HZ_FULL */
2651 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
2653 static int full_sysidle_state
; /* Current system-idle state. */
2654 #define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */
2655 #define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */
2656 #define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */
2657 #define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */
2658 #define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */
2661 * Invoked to note exit from irq or task transition to idle. Note that
2662 * usermode execution does -not- count as idle here! After all, we want
2663 * to detect full-system idle states, not RCU quiescent states and grace
2664 * periods. The caller must have disabled interrupts.
2666 static void rcu_sysidle_enter(int irq
)
2669 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
2671 /* If there are no nohz_full= CPUs, no need to track this. */
2672 if (!tick_nohz_full_enabled())
2675 /* Adjust nesting, check for fully idle. */
2677 rdtp
->dynticks_idle_nesting
--;
2678 WARN_ON_ONCE(rdtp
->dynticks_idle_nesting
< 0);
2679 if (rdtp
->dynticks_idle_nesting
!= 0)
2680 return; /* Still not fully idle. */
2682 if ((rdtp
->dynticks_idle_nesting
& DYNTICK_TASK_NEST_MASK
) ==
2683 DYNTICK_TASK_NEST_VALUE
) {
2684 rdtp
->dynticks_idle_nesting
= 0;
2686 rdtp
->dynticks_idle_nesting
-= DYNTICK_TASK_NEST_VALUE
;
2687 WARN_ON_ONCE(rdtp
->dynticks_idle_nesting
< 0);
2688 return; /* Still not fully idle. */
2692 /* Record start of fully idle period. */
2694 ACCESS_ONCE(rdtp
->dynticks_idle_jiffies
) = j
;
2695 smp_mb__before_atomic();
2696 atomic_inc(&rdtp
->dynticks_idle
);
2697 smp_mb__after_atomic();
2698 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks_idle
) & 0x1);
2702 * Unconditionally force exit from full system-idle state. This is
2703 * invoked when a normal CPU exits idle, but must be called separately
2704 * for the timekeeping CPU (tick_do_timer_cpu). The reason for this
2705 * is that the timekeeping CPU is permitted to take scheduling-clock
2706 * interrupts while the system is in system-idle state, and of course
2707 * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
2708 * interrupt from any other type of interrupt.
2710 void rcu_sysidle_force_exit(void)
2712 int oldstate
= ACCESS_ONCE(full_sysidle_state
);
2716 * Each pass through the following loop attempts to exit full
2717 * system-idle state. If contention proves to be a problem,
2718 * a trylock-based contention tree could be used here.
2720 while (oldstate
> RCU_SYSIDLE_SHORT
) {
2721 newoldstate
= cmpxchg(&full_sysidle_state
,
2722 oldstate
, RCU_SYSIDLE_NOT
);
2723 if (oldstate
== newoldstate
&&
2724 oldstate
== RCU_SYSIDLE_FULL_NOTED
) {
2725 rcu_kick_nohz_cpu(tick_do_timer_cpu
);
2726 return; /* We cleared it, done! */
2728 oldstate
= newoldstate
;
2730 smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
2734 * Invoked to note entry to irq or task transition from idle. Note that
2735 * usermode execution does -not- count as idle here! The caller must
2736 * have disabled interrupts.
2738 static void rcu_sysidle_exit(int irq
)
2740 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
2742 /* If there are no nohz_full= CPUs, no need to track this. */
2743 if (!tick_nohz_full_enabled())
2746 /* Adjust nesting, check for already non-idle. */
2748 rdtp
->dynticks_idle_nesting
++;
2749 WARN_ON_ONCE(rdtp
->dynticks_idle_nesting
<= 0);
2750 if (rdtp
->dynticks_idle_nesting
!= 1)
2751 return; /* Already non-idle. */
2754 * Allow for irq misnesting. Yes, it really is possible
2755 * to enter an irq handler then never leave it, and maybe
2756 * also vice versa. Handle both possibilities.
2758 if (rdtp
->dynticks_idle_nesting
& DYNTICK_TASK_NEST_MASK
) {
2759 rdtp
->dynticks_idle_nesting
+= DYNTICK_TASK_NEST_VALUE
;
2760 WARN_ON_ONCE(rdtp
->dynticks_idle_nesting
<= 0);
2761 return; /* Already non-idle. */
2763 rdtp
->dynticks_idle_nesting
= DYNTICK_TASK_EXIT_IDLE
;
2767 /* Record end of idle period. */
2768 smp_mb__before_atomic();
2769 atomic_inc(&rdtp
->dynticks_idle
);
2770 smp_mb__after_atomic();
2771 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks_idle
) & 0x1));
2774 * If we are the timekeeping CPU, we are permitted to be non-idle
2775 * during a system-idle state. This must be the case, because
2776 * the timekeeping CPU has to take scheduling-clock interrupts
2777 * during the time that the system is transitioning to full
2778 * system-idle state. This means that the timekeeping CPU must
2779 * invoke rcu_sysidle_force_exit() directly if it does anything
2780 * more than take a scheduling-clock interrupt.
2782 if (smp_processor_id() == tick_do_timer_cpu
)
2785 /* Update system-idle state: We are clearly no longer fully idle! */
2786 rcu_sysidle_force_exit();
2790 * Check to see if the current CPU is idle. Note that usermode execution
2791 * does not count as idle. The caller must have disabled interrupts.
2793 static void rcu_sysidle_check_cpu(struct rcu_data
*rdp
, bool *isidle
,
2794 unsigned long *maxj
)
2798 struct rcu_dynticks
*rdtp
= rdp
->dynticks
;
2800 /* If there are no nohz_full= CPUs, don't check system-wide idleness. */
2801 if (!tick_nohz_full_enabled())
2805 * If some other CPU has already reported non-idle, if this is
2806 * not the flavor of RCU that tracks sysidle state, or if this
2807 * is an offline or the timekeeping CPU, nothing to do.
2809 if (!*isidle
|| rdp
->rsp
!= rcu_state_p
||
2810 cpu_is_offline(rdp
->cpu
) || rdp
->cpu
== tick_do_timer_cpu
)
2812 if (rcu_gp_in_progress(rdp
->rsp
))
2813 WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu
);
2815 /* Pick up current idle and NMI-nesting counter and check. */
2816 cur
= atomic_read(&rdtp
->dynticks_idle
);
2818 *isidle
= false; /* We are not idle! */
2821 smp_mb(); /* Read counters before timestamps. */
2823 /* Pick up timestamps. */
2824 j
= ACCESS_ONCE(rdtp
->dynticks_idle_jiffies
);
2825 /* If this CPU entered idle more recently, update maxj timestamp. */
2826 if (ULONG_CMP_LT(*maxj
, j
))
2831 * Is this the flavor of RCU that is handling full-system idle?
2833 static bool is_sysidle_rcu_state(struct rcu_state
*rsp
)
2835 return rsp
== rcu_state_p
;
2839 * Return a delay in jiffies based on the number of CPUs, rcu_node
2840 * leaf fanout, and jiffies tick rate. The idea is to allow larger
2841 * systems more time to transition to full-idle state in order to
2842 * avoid the cache thrashing that otherwise occur on the state variable.
2843 * Really small systems (less than a couple of tens of CPUs) should
2844 * instead use a single global atomically incremented counter, and later
2845 * versions of this will automatically reconfigure themselves accordingly.
2847 static unsigned long rcu_sysidle_delay(void)
2849 if (nr_cpu_ids
<= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
)
2851 return DIV_ROUND_UP(nr_cpu_ids
* HZ
, rcu_fanout_leaf
* 1000);
2855 * Advance the full-system-idle state. This is invoked when all of
2856 * the non-timekeeping CPUs are idle.
2858 static void rcu_sysidle(unsigned long j
)
2860 /* Check the current state. */
2861 switch (ACCESS_ONCE(full_sysidle_state
)) {
2862 case RCU_SYSIDLE_NOT
:
2864 /* First time all are idle, so note a short idle period. */
2865 ACCESS_ONCE(full_sysidle_state
) = RCU_SYSIDLE_SHORT
;
2868 case RCU_SYSIDLE_SHORT
:
2871 * Idle for a bit, time to advance to next state?
2872 * cmpxchg failure means race with non-idle, let them win.
2874 if (ULONG_CMP_GE(jiffies
, j
+ rcu_sysidle_delay()))
2875 (void)cmpxchg(&full_sysidle_state
,
2876 RCU_SYSIDLE_SHORT
, RCU_SYSIDLE_LONG
);
2879 case RCU_SYSIDLE_LONG
:
2882 * Do an additional check pass before advancing to full.
2883 * cmpxchg failure means race with non-idle, let them win.
2885 if (ULONG_CMP_GE(jiffies
, j
+ rcu_sysidle_delay()))
2886 (void)cmpxchg(&full_sysidle_state
,
2887 RCU_SYSIDLE_LONG
, RCU_SYSIDLE_FULL
);
2896 * Found a non-idle non-timekeeping CPU, so kick the system-idle state
2897 * back to the beginning.
2899 static void rcu_sysidle_cancel(void)
2902 if (full_sysidle_state
> RCU_SYSIDLE_SHORT
)
2903 ACCESS_ONCE(full_sysidle_state
) = RCU_SYSIDLE_NOT
;
2907 * Update the sysidle state based on the results of a force-quiescent-state
2908 * scan of the CPUs' dyntick-idle state.
2910 static void rcu_sysidle_report(struct rcu_state
*rsp
, int isidle
,
2911 unsigned long maxj
, bool gpkt
)
2913 if (rsp
!= rcu_state_p
)
2914 return; /* Wrong flavor, ignore. */
2915 if (gpkt
&& nr_cpu_ids
<= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
)
2916 return; /* Running state machine from timekeeping CPU. */
2918 rcu_sysidle(maxj
); /* More idle! */
2920 rcu_sysidle_cancel(); /* Idle is over. */
2924 * Wrapper for rcu_sysidle_report() when called from the grace-period
2925 * kthread's context.
2927 static void rcu_sysidle_report_gp(struct rcu_state
*rsp
, int isidle
,
2930 /* If there are no nohz_full= CPUs, no need to track this. */
2931 if (!tick_nohz_full_enabled())
2934 rcu_sysidle_report(rsp
, isidle
, maxj
, true);
2937 /* Callback and function for forcing an RCU grace period. */
2938 struct rcu_sysidle_head
{
2943 static void rcu_sysidle_cb(struct rcu_head
*rhp
)
2945 struct rcu_sysidle_head
*rshp
;
2948 * The following memory barrier is needed to replace the
2949 * memory barriers that would normally be in the memory
2952 smp_mb(); /* grace period precedes setting inuse. */
2954 rshp
= container_of(rhp
, struct rcu_sysidle_head
, rh
);
2955 ACCESS_ONCE(rshp
->inuse
) = 0;
2959 * Check to see if the system is fully idle, other than the timekeeping CPU.
2960 * The caller must have disabled interrupts. This is not intended to be
2961 * called unless tick_nohz_full_enabled().
2963 bool rcu_sys_is_idle(void)
2965 static struct rcu_sysidle_head rsh
;
2966 int rss
= ACCESS_ONCE(full_sysidle_state
);
2968 if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu
))
2971 /* Handle small-system case by doing a full scan of CPUs. */
2972 if (nr_cpu_ids
<= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
) {
2973 int oldrss
= rss
- 1;
2976 * One pass to advance to each state up to _FULL.
2977 * Give up if any pass fails to advance the state.
2979 while (rss
< RCU_SYSIDLE_FULL
&& oldrss
< rss
) {
2982 unsigned long maxj
= jiffies
- ULONG_MAX
/ 4;
2983 struct rcu_data
*rdp
;
2985 /* Scan all the CPUs looking for nonidle CPUs. */
2986 for_each_possible_cpu(cpu
) {
2987 rdp
= per_cpu_ptr(rcu_state_p
->rda
, cpu
);
2988 rcu_sysidle_check_cpu(rdp
, &isidle
, &maxj
);
2992 rcu_sysidle_report(rcu_state_p
, isidle
, maxj
, false);
2994 rss
= ACCESS_ONCE(full_sysidle_state
);
2998 /* If this is the first observation of an idle period, record it. */
2999 if (rss
== RCU_SYSIDLE_FULL
) {
3000 rss
= cmpxchg(&full_sysidle_state
,
3001 RCU_SYSIDLE_FULL
, RCU_SYSIDLE_FULL_NOTED
);
3002 return rss
== RCU_SYSIDLE_FULL
;
3005 smp_mb(); /* ensure rss load happens before later caller actions. */
3007 /* If already fully idle, tell the caller (in case of races). */
3008 if (rss
== RCU_SYSIDLE_FULL_NOTED
)
3012 * If we aren't there yet, and a grace period is not in flight,
3013 * initiate a grace period. Either way, tell the caller that
3014 * we are not there yet. We use an xchg() rather than an assignment
3015 * to make up for the memory barriers that would otherwise be
3016 * provided by the memory allocator.
3018 if (nr_cpu_ids
> CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
&&
3019 !rcu_gp_in_progress(rcu_state_p
) &&
3020 !rsh
.inuse
&& xchg(&rsh
.inuse
, 1) == 0)
3021 call_rcu(&rsh
.rh
, rcu_sysidle_cb
);
3026 * Initialize dynticks sysidle state for CPUs coming online.
3028 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks
*rdtp
)
3030 rdtp
->dynticks_idle_nesting
= DYNTICK_TASK_NEST_VALUE
;
3033 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3035 static void rcu_sysidle_enter(int irq
)
3039 static void rcu_sysidle_exit(int irq
)
3043 static void rcu_sysidle_check_cpu(struct rcu_data
*rdp
, bool *isidle
,
3044 unsigned long *maxj
)
3048 static bool is_sysidle_rcu_state(struct rcu_state
*rsp
)
3053 static void rcu_sysidle_report_gp(struct rcu_state
*rsp
, int isidle
,
3058 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks
*rdtp
)
3062 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3065 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
3066 * grace-period kthread will do force_quiescent_state() processing?
3067 * The idea is to avoid waking up RCU core processing on such a
3068 * CPU unless the grace period has extended for too long.
3070 * This code relies on the fact that all NO_HZ_FULL CPUs are also
3071 * CONFIG_RCU_NOCB_CPU CPUs.
3073 static bool rcu_nohz_full_cpu(struct rcu_state
*rsp
)
3075 #ifdef CONFIG_NO_HZ_FULL
3076 if (tick_nohz_full_cpu(smp_processor_id()) &&
3077 (!rcu_gp_in_progress(rsp
) ||
3078 ULONG_CMP_LT(jiffies
, ACCESS_ONCE(rsp
->gp_start
) + HZ
)))
3080 #endif /* #ifdef CONFIG_NO_HZ_FULL */
3085 * Bind the grace-period kthread for the sysidle flavor of RCU to the
3088 static void rcu_bind_gp_kthread(void)
3090 int __maybe_unused cpu
;
3092 if (!tick_nohz_full_enabled())
3094 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
3095 cpu
= tick_do_timer_cpu
;
3096 if (cpu
>= 0 && cpu
< nr_cpu_ids
&& raw_smp_processor_id() != cpu
)
3097 set_cpus_allowed_ptr(current
, cpumask_of(cpu
));
3098 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3099 if (!is_housekeeping_cpu(raw_smp_processor_id()))
3100 housekeeping_affine(current
);
3101 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3104 /* Record the current task on dyntick-idle entry. */
3105 static void rcu_dynticks_task_enter(void)
3107 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
3108 ACCESS_ONCE(current
->rcu_tasks_idle_cpu
) = smp_processor_id();
3109 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
3112 /* Record no current task on dyntick-idle exit. */
3113 static void rcu_dynticks_task_exit(void)
3115 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
3116 ACCESS_ONCE(current
->rcu_tasks_idle_cpu
) = -1;
3117 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */