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"
38 * Control variables for per-CPU and per-rcu_node kthreads. These
39 * handle all flavors of RCU.
41 static DEFINE_PER_CPU(struct task_struct
*, rcu_cpu_kthread_task
);
42 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status
);
43 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops
);
44 DEFINE_PER_CPU(char, rcu_cpu_has_work
);
46 #endif /* #ifdef CONFIG_RCU_BOOST */
48 #ifdef CONFIG_RCU_NOCB_CPU
49 static cpumask_var_t rcu_nocb_mask
; /* CPUs to have callbacks offloaded. */
50 static bool have_rcu_nocb_mask
; /* Was rcu_nocb_mask allocated? */
51 static bool __read_mostly rcu_nocb_poll
; /* Offload kthread are to poll. */
52 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
55 * Check the RCU kernel configuration parameters and print informative
56 * messages about anything out of the ordinary. If you like #ifdef, you
57 * will love this function.
59 static void __init
rcu_bootup_announce_oddness(void)
61 #ifdef CONFIG_RCU_TRACE
62 pr_info("\tRCU debugfs-based tracing is enabled.\n");
64 #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
65 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
68 #ifdef CONFIG_RCU_FANOUT_EXACT
69 pr_info("\tHierarchical RCU autobalancing is disabled.\n");
71 #ifdef CONFIG_RCU_FAST_NO_HZ
72 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
74 #ifdef CONFIG_PROVE_RCU
75 pr_info("\tRCU lockdep checking is enabled.\n");
77 #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
78 pr_info("\tRCU torture testing starts during boot.\n");
80 #if defined(CONFIG_RCU_CPU_STALL_INFO)
81 pr_info("\tAdditional per-CPU info printed with stalls.\n");
83 #if NUM_RCU_LVL_4 != 0
84 pr_info("\tFour-level hierarchy is enabled.\n");
86 if (rcu_fanout_leaf
!= CONFIG_RCU_FANOUT_LEAF
)
87 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf
);
88 if (nr_cpu_ids
!= NR_CPUS
)
89 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS
, nr_cpu_ids
);
90 #ifdef CONFIG_RCU_BOOST
91 pr_info("\tRCU kthread priority: %d.\n", kthread_prio
);
95 #ifdef CONFIG_PREEMPT_RCU
97 RCU_STATE_INITIALIZER(rcu_preempt
, 'p', call_rcu
);
98 static struct rcu_state
*rcu_state_p
= &rcu_preempt_state
;
100 static int rcu_preempted_readers_exp(struct rcu_node
*rnp
);
101 static void rcu_report_exp_rnp(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
105 * Tell them what RCU they are running.
107 static void __init
rcu_bootup_announce(void)
109 pr_info("Preemptible hierarchical RCU implementation.\n");
110 rcu_bootup_announce_oddness();
114 * Record a preemptible-RCU quiescent state for the specified CPU. Note
115 * that this just means that the task currently running on the CPU is
116 * not in a quiescent state. There might be any number of tasks blocked
117 * while in an RCU read-side critical section.
119 * As with the other rcu_*_qs() functions, callers to this function
120 * must disable preemption.
122 static void rcu_preempt_qs(void)
124 if (!__this_cpu_read(rcu_preempt_data
.passed_quiesce
)) {
125 trace_rcu_grace_period(TPS("rcu_preempt"),
126 __this_cpu_read(rcu_preempt_data
.gpnum
),
128 __this_cpu_write(rcu_preempt_data
.passed_quiesce
, 1);
129 barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
130 current
->rcu_read_unlock_special
.b
.need_qs
= false;
135 * We have entered the scheduler, and the current task might soon be
136 * context-switched away from. If this task is in an RCU read-side
137 * critical section, we will no longer be able to rely on the CPU to
138 * record that fact, so we enqueue the task on the blkd_tasks list.
139 * The task will dequeue itself when it exits the outermost enclosing
140 * RCU read-side critical section. Therefore, the current grace period
141 * cannot be permitted to complete until the blkd_tasks list entries
142 * predating the current grace period drain, in other words, until
143 * rnp->gp_tasks becomes NULL.
145 * Caller must disable preemption.
147 static void rcu_preempt_note_context_switch(void)
149 struct task_struct
*t
= current
;
151 struct rcu_data
*rdp
;
152 struct rcu_node
*rnp
;
154 if (t
->rcu_read_lock_nesting
> 0 &&
155 !t
->rcu_read_unlock_special
.b
.blocked
) {
157 /* Possibly blocking in an RCU read-side critical section. */
158 rdp
= this_cpu_ptr(rcu_preempt_state
.rda
);
160 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
161 smp_mb__after_unlock_lock();
162 t
->rcu_read_unlock_special
.b
.blocked
= true;
163 t
->rcu_blocked_node
= rnp
;
166 * If this CPU has already checked in, then this task
167 * will hold up the next grace period rather than the
168 * current grace period. Queue the task accordingly.
169 * If the task is queued for the current grace period
170 * (i.e., this CPU has not yet passed through a quiescent
171 * state for the current grace period), then as long
172 * as that task remains queued, the current grace period
173 * cannot end. Note that there is some uncertainty as
174 * to exactly when the current grace period started.
175 * We take a conservative approach, which can result
176 * in unnecessarily waiting on tasks that started very
177 * slightly after the current grace period began. C'est
180 * But first, note that the current CPU must still be
183 WARN_ON_ONCE((rdp
->grpmask
& rcu_rnp_online_cpus(rnp
)) == 0);
184 WARN_ON_ONCE(!list_empty(&t
->rcu_node_entry
));
185 if ((rnp
->qsmask
& rdp
->grpmask
) && rnp
->gp_tasks
!= NULL
) {
186 list_add(&t
->rcu_node_entry
, rnp
->gp_tasks
->prev
);
187 rnp
->gp_tasks
= &t
->rcu_node_entry
;
188 #ifdef CONFIG_RCU_BOOST
189 if (rnp
->boost_tasks
!= NULL
)
190 rnp
->boost_tasks
= rnp
->gp_tasks
;
191 #endif /* #ifdef CONFIG_RCU_BOOST */
193 list_add(&t
->rcu_node_entry
, &rnp
->blkd_tasks
);
194 if (rnp
->qsmask
& rdp
->grpmask
)
195 rnp
->gp_tasks
= &t
->rcu_node_entry
;
197 trace_rcu_preempt_task(rdp
->rsp
->name
,
199 (rnp
->qsmask
& rdp
->grpmask
)
202 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
203 } else if (t
->rcu_read_lock_nesting
< 0 &&
204 t
->rcu_read_unlock_special
.s
) {
207 * Complete exit from RCU read-side critical section on
208 * behalf of preempted instance of __rcu_read_unlock().
210 rcu_read_unlock_special(t
);
214 * Either we were not in an RCU read-side critical section to
215 * begin with, or we have now recorded that critical section
216 * globally. Either way, we can now note a quiescent state
217 * for this CPU. Again, if we were in an RCU read-side critical
218 * section, and if that critical section was blocking the current
219 * grace period, then the fact that the task has been enqueued
220 * means that we continue to block the current grace period.
226 * Check for preempted RCU readers blocking the current grace period
227 * for the specified rcu_node structure. If the caller needs a reliable
228 * answer, it must hold the rcu_node's ->lock.
230 static int rcu_preempt_blocked_readers_cgp(struct rcu_node
*rnp
)
232 return rnp
->gp_tasks
!= NULL
;
236 * Advance a ->blkd_tasks-list pointer to the next entry, instead
237 * returning NULL if at the end of the list.
239 static struct list_head
*rcu_next_node_entry(struct task_struct
*t
,
240 struct rcu_node
*rnp
)
242 struct list_head
*np
;
244 np
= t
->rcu_node_entry
.next
;
245 if (np
== &rnp
->blkd_tasks
)
251 * Return true if the specified rcu_node structure has tasks that were
252 * preempted within an RCU read-side critical section.
254 static bool rcu_preempt_has_tasks(struct rcu_node
*rnp
)
256 return !list_empty(&rnp
->blkd_tasks
);
260 * Handle special cases during rcu_read_unlock(), such as needing to
261 * notify RCU core processing or task having blocked during the RCU
262 * read-side critical section.
264 void rcu_read_unlock_special(struct task_struct
*t
)
270 struct list_head
*np
;
271 #ifdef CONFIG_RCU_BOOST
272 bool drop_boost_mutex
= false;
273 #endif /* #ifdef CONFIG_RCU_BOOST */
274 struct rcu_node
*rnp
;
275 union rcu_special special
;
277 /* NMI handlers cannot block and cannot safely manipulate state. */
281 local_irq_save(flags
);
284 * If RCU core is waiting for this CPU to exit critical section,
285 * let it know that we have done so. Because irqs are disabled,
286 * t->rcu_read_unlock_special cannot change.
288 special
= t
->rcu_read_unlock_special
;
289 if (special
.b
.need_qs
) {
291 t
->rcu_read_unlock_special
.b
.need_qs
= false;
292 if (!t
->rcu_read_unlock_special
.s
) {
293 local_irq_restore(flags
);
298 /* Hardware IRQ handlers cannot block, complain if they get here. */
299 if (WARN_ON_ONCE(in_irq() || in_serving_softirq())) {
300 local_irq_restore(flags
);
304 /* Clean up if blocked during RCU read-side critical section. */
305 if (special
.b
.blocked
) {
306 t
->rcu_read_unlock_special
.b
.blocked
= false;
309 * Remove this task from the list it blocked on. The
310 * task can migrate while we acquire the lock, but at
311 * most one time. So at most two passes through loop.
314 rnp
= t
->rcu_blocked_node
;
315 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
316 smp_mb__after_unlock_lock();
317 if (rnp
== t
->rcu_blocked_node
)
319 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
321 empty_norm
= !rcu_preempt_blocked_readers_cgp(rnp
);
322 empty_exp
= !rcu_preempted_readers_exp(rnp
);
323 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
324 np
= rcu_next_node_entry(t
, rnp
);
325 list_del_init(&t
->rcu_node_entry
);
326 t
->rcu_blocked_node
= NULL
;
327 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
329 if (&t
->rcu_node_entry
== rnp
->gp_tasks
)
331 if (&t
->rcu_node_entry
== rnp
->exp_tasks
)
333 #ifdef CONFIG_RCU_BOOST
334 if (&t
->rcu_node_entry
== rnp
->boost_tasks
)
335 rnp
->boost_tasks
= np
;
336 /* Snapshot ->boost_mtx ownership with rcu_node lock held. */
337 drop_boost_mutex
= rt_mutex_owner(&rnp
->boost_mtx
) == t
;
338 #endif /* #ifdef CONFIG_RCU_BOOST */
341 * If this was the last task on the current list, and if
342 * we aren't waiting on any CPUs, report the quiescent state.
343 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
344 * so we must take a snapshot of the expedited state.
346 empty_exp_now
= !rcu_preempted_readers_exp(rnp
);
347 if (!empty_norm
&& !rcu_preempt_blocked_readers_cgp(rnp
)) {
348 trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
355 rcu_report_unblock_qs_rnp(&rcu_preempt_state
,
358 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
361 #ifdef CONFIG_RCU_BOOST
362 /* Unboost if we were boosted. */
363 if (drop_boost_mutex
)
364 rt_mutex_unlock(&rnp
->boost_mtx
);
365 #endif /* #ifdef CONFIG_RCU_BOOST */
368 * If this was the last task on the expedited lists,
369 * then we need to report up the rcu_node hierarchy.
371 if (!empty_exp
&& empty_exp_now
)
372 rcu_report_exp_rnp(&rcu_preempt_state
, rnp
, true);
374 local_irq_restore(flags
);
379 * Dump detailed information for all tasks blocking the current RCU
380 * grace period on the specified rcu_node structure.
382 static void rcu_print_detail_task_stall_rnp(struct rcu_node
*rnp
)
385 struct task_struct
*t
;
387 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
388 if (!rcu_preempt_blocked_readers_cgp(rnp
)) {
389 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
392 t
= list_entry(rnp
->gp_tasks
,
393 struct task_struct
, rcu_node_entry
);
394 list_for_each_entry_continue(t
, &rnp
->blkd_tasks
, rcu_node_entry
)
396 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
400 * Dump detailed information for all tasks blocking the current RCU
403 static void rcu_print_detail_task_stall(struct rcu_state
*rsp
)
405 struct rcu_node
*rnp
= rcu_get_root(rsp
);
407 rcu_print_detail_task_stall_rnp(rnp
);
408 rcu_for_each_leaf_node(rsp
, rnp
)
409 rcu_print_detail_task_stall_rnp(rnp
);
412 #ifdef CONFIG_RCU_CPU_STALL_INFO
414 static void rcu_print_task_stall_begin(struct rcu_node
*rnp
)
416 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
417 rnp
->level
, rnp
->grplo
, rnp
->grphi
);
420 static void rcu_print_task_stall_end(void)
425 #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
427 static void rcu_print_task_stall_begin(struct rcu_node
*rnp
)
431 static void rcu_print_task_stall_end(void)
435 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
438 * Scan the current list of tasks blocked within RCU read-side critical
439 * sections, printing out the tid of each.
441 static int rcu_print_task_stall(struct rcu_node
*rnp
)
443 struct task_struct
*t
;
446 if (!rcu_preempt_blocked_readers_cgp(rnp
))
448 rcu_print_task_stall_begin(rnp
);
449 t
= list_entry(rnp
->gp_tasks
,
450 struct task_struct
, rcu_node_entry
);
451 list_for_each_entry_continue(t
, &rnp
->blkd_tasks
, rcu_node_entry
) {
452 pr_cont(" P%d", t
->pid
);
455 rcu_print_task_stall_end();
460 * Check that the list of blocked tasks for the newly completed grace
461 * period is in fact empty. It is a serious bug to complete a grace
462 * period that still has RCU readers blocked! This function must be
463 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
464 * must be held by the caller.
466 * Also, if there are blocked tasks on the list, they automatically
467 * block the newly created grace period, so set up ->gp_tasks accordingly.
469 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
471 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp
));
472 if (rcu_preempt_has_tasks(rnp
))
473 rnp
->gp_tasks
= rnp
->blkd_tasks
.next
;
474 WARN_ON_ONCE(rnp
->qsmask
);
478 * Check for a quiescent state from the current CPU. When a task blocks,
479 * the task is recorded in the corresponding CPU's rcu_node structure,
480 * which is checked elsewhere.
482 * Caller must disable hard irqs.
484 static void rcu_preempt_check_callbacks(void)
486 struct task_struct
*t
= current
;
488 if (t
->rcu_read_lock_nesting
== 0) {
492 if (t
->rcu_read_lock_nesting
> 0 &&
493 __this_cpu_read(rcu_preempt_data
.qs_pending
) &&
494 !__this_cpu_read(rcu_preempt_data
.passed_quiesce
))
495 t
->rcu_read_unlock_special
.b
.need_qs
= true;
498 #ifdef CONFIG_RCU_BOOST
500 static void rcu_preempt_do_callbacks(void)
502 rcu_do_batch(&rcu_preempt_state
, this_cpu_ptr(&rcu_preempt_data
));
505 #endif /* #ifdef CONFIG_RCU_BOOST */
508 * Queue a preemptible-RCU callback for invocation after a grace period.
510 void call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
512 __call_rcu(head
, func
, &rcu_preempt_state
, -1, 0);
514 EXPORT_SYMBOL_GPL(call_rcu
);
517 * synchronize_rcu - wait until a grace period has elapsed.
519 * Control will return to the caller some time after a full grace
520 * period has elapsed, in other words after all currently executing RCU
521 * read-side critical sections have completed. Note, however, that
522 * upon return from synchronize_rcu(), the caller might well be executing
523 * concurrently with new RCU read-side critical sections that began while
524 * synchronize_rcu() was waiting. RCU read-side critical sections are
525 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
527 * See the description of synchronize_sched() for more detailed information
528 * on memory ordering guarantees.
530 void synchronize_rcu(void)
532 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
533 !lock_is_held(&rcu_lock_map
) &&
534 !lock_is_held(&rcu_sched_lock_map
),
535 "Illegal synchronize_rcu() in RCU read-side critical section");
536 if (!rcu_scheduler_active
)
539 synchronize_rcu_expedited();
541 wait_rcu_gp(call_rcu
);
543 EXPORT_SYMBOL_GPL(synchronize_rcu
);
545 static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq
);
546 static unsigned long sync_rcu_preempt_exp_count
;
547 static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex
);
550 * Return non-zero if there are any tasks in RCU read-side critical
551 * sections blocking the current preemptible-RCU expedited grace period.
552 * If there is no preemptible-RCU expedited grace period currently in
553 * progress, returns zero unconditionally.
555 static int rcu_preempted_readers_exp(struct rcu_node
*rnp
)
557 return rnp
->exp_tasks
!= NULL
;
561 * return non-zero if there is no RCU expedited grace period in progress
562 * for the specified rcu_node structure, in other words, if all CPUs and
563 * tasks covered by the specified rcu_node structure have done their bit
564 * for the current expedited grace period. Works only for preemptible
565 * RCU -- other RCU implementation use other means.
567 * Caller must hold sync_rcu_preempt_exp_mutex.
569 static int sync_rcu_preempt_exp_done(struct rcu_node
*rnp
)
571 return !rcu_preempted_readers_exp(rnp
) &&
572 ACCESS_ONCE(rnp
->expmask
) == 0;
576 * Report the exit from RCU read-side critical section for the last task
577 * that queued itself during or before the current expedited preemptible-RCU
578 * grace period. This event is reported either to the rcu_node structure on
579 * which the task was queued or to one of that rcu_node structure's ancestors,
580 * recursively up the tree. (Calm down, calm down, we do the recursion
583 * Caller must hold sync_rcu_preempt_exp_mutex.
585 static void rcu_report_exp_rnp(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
591 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
592 smp_mb__after_unlock_lock();
594 if (!sync_rcu_preempt_exp_done(rnp
)) {
595 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
598 if (rnp
->parent
== NULL
) {
599 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
601 smp_mb(); /* EGP done before wake_up(). */
602 wake_up(&sync_rcu_preempt_exp_wq
);
607 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
609 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
610 smp_mb__after_unlock_lock();
611 rnp
->expmask
&= ~mask
;
616 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
617 * grace period for the specified rcu_node structure, phase 1. If there
618 * are such tasks, set the ->expmask bits up the rcu_node tree and also
619 * set the ->expmask bits on the leaf rcu_node structures to tell phase 2
620 * that work is needed here.
622 * Caller must hold sync_rcu_preempt_exp_mutex.
625 sync_rcu_preempt_exp_init1(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
629 struct rcu_node
*rnp_up
;
631 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
632 smp_mb__after_unlock_lock();
633 WARN_ON_ONCE(rnp
->expmask
);
634 WARN_ON_ONCE(rnp
->exp_tasks
);
635 if (!rcu_preempt_has_tasks(rnp
)) {
636 /* No blocked tasks, nothing to do. */
637 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
640 /* Call for Phase 2 and propagate ->expmask bits up the tree. */
643 while (rnp_up
->parent
) {
644 mask
= rnp_up
->grpmask
;
645 rnp_up
= rnp_up
->parent
;
646 if (rnp_up
->expmask
& mask
)
648 raw_spin_lock(&rnp_up
->lock
); /* irqs already off */
649 smp_mb__after_unlock_lock();
650 rnp_up
->expmask
|= mask
;
651 raw_spin_unlock(&rnp_up
->lock
); /* irqs still off */
653 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
657 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
658 * grace period for the specified rcu_node structure, phase 2. If the
659 * leaf rcu_node structure has its ->expmask field set, check for tasks.
660 * If there are some, clear ->expmask and set ->exp_tasks accordingly,
661 * then initiate RCU priority boosting. Otherwise, clear ->expmask and
662 * invoke rcu_report_exp_rnp() to clear out the upper-level ->expmask bits,
663 * enabling rcu_read_unlock_special() to do the bit-clearing.
665 * Caller must hold sync_rcu_preempt_exp_mutex.
668 sync_rcu_preempt_exp_init2(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
672 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
673 smp_mb__after_unlock_lock();
675 /* Phase 1 didn't do anything, so Phase 2 doesn't either. */
676 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
680 /* Phase 1 is over. */
684 * If there are still blocked tasks, set up ->exp_tasks so that
685 * rcu_read_unlock_special() will wake us and then boost them.
687 if (rcu_preempt_has_tasks(rnp
)) {
688 rnp
->exp_tasks
= rnp
->blkd_tasks
.next
;
689 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock */
693 /* No longer any blocked tasks, so undo bit setting. */
694 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
695 rcu_report_exp_rnp(rsp
, rnp
, false);
699 * synchronize_rcu_expedited - Brute-force RCU grace period
701 * Wait for an RCU-preempt grace period, but expedite it. The basic
702 * idea is to invoke synchronize_sched_expedited() to push all the tasks to
703 * the ->blkd_tasks lists and wait for this list to drain. This consumes
704 * significant time on all CPUs and is unfriendly to real-time workloads,
705 * so is thus not recommended for any sort of common-case code.
706 * In fact, if you are using synchronize_rcu_expedited() in a loop,
707 * please restructure your code to batch your updates, and then Use a
708 * single synchronize_rcu() instead.
710 void synchronize_rcu_expedited(void)
712 struct rcu_node
*rnp
;
713 struct rcu_state
*rsp
= &rcu_preempt_state
;
717 smp_mb(); /* Caller's modifications seen first by other CPUs. */
718 snap
= ACCESS_ONCE(sync_rcu_preempt_exp_count
) + 1;
719 smp_mb(); /* Above access cannot bleed into critical section. */
722 * Block CPU-hotplug operations. This means that any CPU-hotplug
723 * operation that finds an rcu_node structure with tasks in the
724 * process of being boosted will know that all tasks blocking
725 * this expedited grace period will already be in the process of
726 * being boosted. This simplifies the process of moving tasks
727 * from leaf to root rcu_node structures.
729 if (!try_get_online_cpus()) {
730 /* CPU-hotplug operation in flight, fall back to normal GP. */
731 wait_rcu_gp(call_rcu
);
736 * Acquire lock, falling back to synchronize_rcu() if too many
737 * lock-acquisition failures. Of course, if someone does the
738 * expedited grace period for us, just leave.
740 while (!mutex_trylock(&sync_rcu_preempt_exp_mutex
)) {
741 if (ULONG_CMP_LT(snap
,
742 ACCESS_ONCE(sync_rcu_preempt_exp_count
))) {
744 goto mb_ret
; /* Others did our work for us. */
746 if (trycount
++ < 10) {
747 udelay(trycount
* num_online_cpus());
750 wait_rcu_gp(call_rcu
);
754 if (ULONG_CMP_LT(snap
, ACCESS_ONCE(sync_rcu_preempt_exp_count
))) {
756 goto unlock_mb_ret
; /* Others did our work for us. */
759 /* force all RCU readers onto ->blkd_tasks lists. */
760 synchronize_sched_expedited();
763 * Snapshot current state of ->blkd_tasks lists into ->expmask.
764 * Phase 1 sets bits and phase 2 permits rcu_read_unlock_special()
765 * to start clearing them. Doing this in one phase leads to
766 * strange races between setting and clearing bits, so just say "no"!
768 rcu_for_each_leaf_node(rsp
, rnp
)
769 sync_rcu_preempt_exp_init1(rsp
, rnp
);
770 rcu_for_each_leaf_node(rsp
, rnp
)
771 sync_rcu_preempt_exp_init2(rsp
, rnp
);
775 /* Wait for snapshotted ->blkd_tasks lists to drain. */
776 rnp
= rcu_get_root(rsp
);
777 wait_event(sync_rcu_preempt_exp_wq
,
778 sync_rcu_preempt_exp_done(rnp
));
780 /* Clean up and exit. */
781 smp_mb(); /* ensure expedited GP seen before counter increment. */
782 ACCESS_ONCE(sync_rcu_preempt_exp_count
) =
783 sync_rcu_preempt_exp_count
+ 1;
785 mutex_unlock(&sync_rcu_preempt_exp_mutex
);
787 smp_mb(); /* ensure subsequent action seen after grace period. */
789 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited
);
792 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
794 * Note that this primitive does not necessarily wait for an RCU grace period
795 * to complete. For example, if there are no RCU callbacks queued anywhere
796 * in the system, then rcu_barrier() is within its rights to return
797 * immediately, without waiting for anything, much less an RCU grace period.
799 void rcu_barrier(void)
801 _rcu_barrier(&rcu_preempt_state
);
803 EXPORT_SYMBOL_GPL(rcu_barrier
);
806 * Initialize preemptible RCU's state structures.
808 static void __init
__rcu_init_preempt(void)
810 rcu_init_one(&rcu_preempt_state
, &rcu_preempt_data
);
814 * Check for a task exiting while in a preemptible-RCU read-side
815 * critical section, clean up if so. No need to issue warnings,
816 * as debug_check_no_locks_held() already does this if lockdep
821 struct task_struct
*t
= current
;
823 if (likely(list_empty(¤t
->rcu_node_entry
)))
825 t
->rcu_read_lock_nesting
= 1;
827 t
->rcu_read_unlock_special
.b
.blocked
= true;
831 #else /* #ifdef CONFIG_PREEMPT_RCU */
833 static struct rcu_state
*rcu_state_p
= &rcu_sched_state
;
836 * Tell them what RCU they are running.
838 static void __init
rcu_bootup_announce(void)
840 pr_info("Hierarchical RCU implementation.\n");
841 rcu_bootup_announce_oddness();
845 * Because preemptible RCU does not exist, we never have to check for
846 * CPUs being in quiescent states.
848 static void rcu_preempt_note_context_switch(void)
853 * Because preemptible RCU does not exist, there are never any preempted
856 static int rcu_preempt_blocked_readers_cgp(struct rcu_node
*rnp
)
862 * Because there is no preemptible RCU, there can be no readers blocked.
864 static bool rcu_preempt_has_tasks(struct rcu_node
*rnp
)
870 * Because preemptible RCU does not exist, we never have to check for
871 * tasks blocked within RCU read-side critical sections.
873 static void rcu_print_detail_task_stall(struct rcu_state
*rsp
)
878 * Because preemptible RCU does not exist, we never have to check for
879 * tasks blocked within RCU read-side critical sections.
881 static int rcu_print_task_stall(struct rcu_node
*rnp
)
887 * Because there is no preemptible RCU, there can be no readers blocked,
888 * so there is no need to check for blocked tasks. So check only for
889 * bogus qsmask values.
891 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
893 WARN_ON_ONCE(rnp
->qsmask
);
897 * Because preemptible RCU does not exist, it never has any callbacks
900 static void rcu_preempt_check_callbacks(void)
905 * Wait for an rcu-preempt grace period, but make it happen quickly.
906 * But because preemptible RCU does not exist, map to rcu-sched.
908 void synchronize_rcu_expedited(void)
910 synchronize_sched_expedited();
912 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited
);
915 * Because preemptible RCU does not exist, rcu_barrier() is just
916 * another name for rcu_barrier_sched().
918 void rcu_barrier(void)
922 EXPORT_SYMBOL_GPL(rcu_barrier
);
925 * Because preemptible RCU does not exist, it need not be initialized.
927 static void __init
__rcu_init_preempt(void)
932 * Because preemptible RCU does not exist, tasks cannot possibly exit
933 * while in preemptible RCU read-side critical sections.
939 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
941 #ifdef CONFIG_RCU_BOOST
943 #include "../locking/rtmutex_common.h"
945 #ifdef CONFIG_RCU_TRACE
947 static void rcu_initiate_boost_trace(struct rcu_node
*rnp
)
949 if (!rcu_preempt_has_tasks(rnp
))
950 rnp
->n_balk_blkd_tasks
++;
951 else if (rnp
->exp_tasks
== NULL
&& rnp
->gp_tasks
== NULL
)
952 rnp
->n_balk_exp_gp_tasks
++;
953 else if (rnp
->gp_tasks
!= NULL
&& rnp
->boost_tasks
!= NULL
)
954 rnp
->n_balk_boost_tasks
++;
955 else if (rnp
->gp_tasks
!= NULL
&& rnp
->qsmask
!= 0)
956 rnp
->n_balk_notblocked
++;
957 else if (rnp
->gp_tasks
!= NULL
&&
958 ULONG_CMP_LT(jiffies
, rnp
->boost_time
))
959 rnp
->n_balk_notyet
++;
964 #else /* #ifdef CONFIG_RCU_TRACE */
966 static void rcu_initiate_boost_trace(struct rcu_node
*rnp
)
970 #endif /* #else #ifdef CONFIG_RCU_TRACE */
972 static void rcu_wake_cond(struct task_struct
*t
, int status
)
975 * If the thread is yielding, only wake it when this
976 * is invoked from idle
978 if (status
!= RCU_KTHREAD_YIELDING
|| is_idle_task(current
))
983 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
984 * or ->boost_tasks, advancing the pointer to the next task in the
987 * Note that irqs must be enabled: boosting the task can block.
988 * Returns 1 if there are more tasks needing to be boosted.
990 static int rcu_boost(struct rcu_node
*rnp
)
993 struct task_struct
*t
;
994 struct list_head
*tb
;
996 if (ACCESS_ONCE(rnp
->exp_tasks
) == NULL
&&
997 ACCESS_ONCE(rnp
->boost_tasks
) == NULL
)
998 return 0; /* Nothing left to boost. */
1000 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1001 smp_mb__after_unlock_lock();
1004 * Recheck under the lock: all tasks in need of boosting
1005 * might exit their RCU read-side critical sections on their own.
1007 if (rnp
->exp_tasks
== NULL
&& rnp
->boost_tasks
== NULL
) {
1008 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1013 * Preferentially boost tasks blocking expedited grace periods.
1014 * This cannot starve the normal grace periods because a second
1015 * expedited grace period must boost all blocked tasks, including
1016 * those blocking the pre-existing normal grace period.
1018 if (rnp
->exp_tasks
!= NULL
) {
1019 tb
= rnp
->exp_tasks
;
1020 rnp
->n_exp_boosts
++;
1022 tb
= rnp
->boost_tasks
;
1023 rnp
->n_normal_boosts
++;
1025 rnp
->n_tasks_boosted
++;
1028 * We boost task t by manufacturing an rt_mutex that appears to
1029 * be held by task t. We leave a pointer to that rt_mutex where
1030 * task t can find it, and task t will release the mutex when it
1031 * exits its outermost RCU read-side critical section. Then
1032 * simply acquiring this artificial rt_mutex will boost task
1033 * t's priority. (Thanks to tglx for suggesting this approach!)
1035 * Note that task t must acquire rnp->lock to remove itself from
1036 * the ->blkd_tasks list, which it will do from exit() if from
1037 * nowhere else. We therefore are guaranteed that task t will
1038 * stay around at least until we drop rnp->lock. Note that
1039 * rnp->lock also resolves races between our priority boosting
1040 * and task t's exiting its outermost RCU read-side critical
1043 t
= container_of(tb
, struct task_struct
, rcu_node_entry
);
1044 rt_mutex_init_proxy_locked(&rnp
->boost_mtx
, t
);
1045 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1046 /* Lock only for side effect: boosts task t's priority. */
1047 rt_mutex_lock(&rnp
->boost_mtx
);
1048 rt_mutex_unlock(&rnp
->boost_mtx
); /* Then keep lockdep happy. */
1050 return ACCESS_ONCE(rnp
->exp_tasks
) != NULL
||
1051 ACCESS_ONCE(rnp
->boost_tasks
) != NULL
;
1055 * Priority-boosting kthread. One per leaf rcu_node and one for the
1058 static int rcu_boost_kthread(void *arg
)
1060 struct rcu_node
*rnp
= (struct rcu_node
*)arg
;
1064 trace_rcu_utilization(TPS("Start boost kthread@init"));
1066 rnp
->boost_kthread_status
= RCU_KTHREAD_WAITING
;
1067 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1068 rcu_wait(rnp
->boost_tasks
|| rnp
->exp_tasks
);
1069 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1070 rnp
->boost_kthread_status
= RCU_KTHREAD_RUNNING
;
1071 more2boost
= rcu_boost(rnp
);
1077 rnp
->boost_kthread_status
= RCU_KTHREAD_YIELDING
;
1078 trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1079 schedule_timeout_interruptible(2);
1080 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1085 trace_rcu_utilization(TPS("End boost kthread@notreached"));
1090 * Check to see if it is time to start boosting RCU readers that are
1091 * blocking the current grace period, and, if so, tell the per-rcu_node
1092 * kthread to start boosting them. If there is an expedited grace
1093 * period in progress, it is always time to boost.
1095 * The caller must hold rnp->lock, which this function releases.
1096 * The ->boost_kthread_task is immortal, so we don't need to worry
1097 * about it going away.
1099 static void rcu_initiate_boost(struct rcu_node
*rnp
, unsigned long flags
)
1100 __releases(rnp
->lock
)
1102 struct task_struct
*t
;
1104 if (!rcu_preempt_blocked_readers_cgp(rnp
) && rnp
->exp_tasks
== NULL
) {
1105 rnp
->n_balk_exp_gp_tasks
++;
1106 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1109 if (rnp
->exp_tasks
!= NULL
||
1110 (rnp
->gp_tasks
!= NULL
&&
1111 rnp
->boost_tasks
== NULL
&&
1113 ULONG_CMP_GE(jiffies
, rnp
->boost_time
))) {
1114 if (rnp
->exp_tasks
== NULL
)
1115 rnp
->boost_tasks
= rnp
->gp_tasks
;
1116 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1117 t
= rnp
->boost_kthread_task
;
1119 rcu_wake_cond(t
, rnp
->boost_kthread_status
);
1121 rcu_initiate_boost_trace(rnp
);
1122 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1127 * Wake up the per-CPU kthread to invoke RCU callbacks.
1129 static void invoke_rcu_callbacks_kthread(void)
1131 unsigned long flags
;
1133 local_irq_save(flags
);
1134 __this_cpu_write(rcu_cpu_has_work
, 1);
1135 if (__this_cpu_read(rcu_cpu_kthread_task
) != NULL
&&
1136 current
!= __this_cpu_read(rcu_cpu_kthread_task
)) {
1137 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task
),
1138 __this_cpu_read(rcu_cpu_kthread_status
));
1140 local_irq_restore(flags
);
1144 * Is the current CPU running the RCU-callbacks kthread?
1145 * Caller must have preemption disabled.
1147 static bool rcu_is_callbacks_kthread(void)
1149 return __this_cpu_read(rcu_cpu_kthread_task
) == current
;
1152 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1155 * Do priority-boost accounting for the start of a new grace period.
1157 static void rcu_preempt_boost_start_gp(struct rcu_node
*rnp
)
1159 rnp
->boost_time
= jiffies
+ RCU_BOOST_DELAY_JIFFIES
;
1163 * Create an RCU-boost kthread for the specified node if one does not
1164 * already exist. We only create this kthread for preemptible RCU.
1165 * Returns zero if all is well, a negated errno otherwise.
1167 static int rcu_spawn_one_boost_kthread(struct rcu_state
*rsp
,
1168 struct rcu_node
*rnp
)
1170 int rnp_index
= rnp
- &rsp
->node
[0];
1171 unsigned long flags
;
1172 struct sched_param sp
;
1173 struct task_struct
*t
;
1175 if (&rcu_preempt_state
!= rsp
)
1178 if (!rcu_scheduler_fully_active
|| rcu_rnp_online_cpus(rnp
) == 0)
1182 if (rnp
->boost_kthread_task
!= NULL
)
1184 t
= kthread_create(rcu_boost_kthread
, (void *)rnp
,
1185 "rcub/%d", rnp_index
);
1188 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1189 smp_mb__after_unlock_lock();
1190 rnp
->boost_kthread_task
= t
;
1191 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1192 sp
.sched_priority
= kthread_prio
;
1193 sched_setscheduler_nocheck(t
, SCHED_FIFO
, &sp
);
1194 wake_up_process(t
); /* get to TASK_INTERRUPTIBLE quickly. */
1198 static void rcu_kthread_do_work(void)
1200 rcu_do_batch(&rcu_sched_state
, this_cpu_ptr(&rcu_sched_data
));
1201 rcu_do_batch(&rcu_bh_state
, this_cpu_ptr(&rcu_bh_data
));
1202 rcu_preempt_do_callbacks();
1205 static void rcu_cpu_kthread_setup(unsigned int cpu
)
1207 struct sched_param sp
;
1209 sp
.sched_priority
= kthread_prio
;
1210 sched_setscheduler_nocheck(current
, SCHED_FIFO
, &sp
);
1213 static void rcu_cpu_kthread_park(unsigned int cpu
)
1215 per_cpu(rcu_cpu_kthread_status
, cpu
) = RCU_KTHREAD_OFFCPU
;
1218 static int rcu_cpu_kthread_should_run(unsigned int cpu
)
1220 return __this_cpu_read(rcu_cpu_has_work
);
1224 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
1225 * RCU softirq used in flavors and configurations of RCU that do not
1226 * support RCU priority boosting.
1228 static void rcu_cpu_kthread(unsigned int cpu
)
1230 unsigned int *statusp
= this_cpu_ptr(&rcu_cpu_kthread_status
);
1231 char work
, *workp
= this_cpu_ptr(&rcu_cpu_has_work
);
1234 for (spincnt
= 0; spincnt
< 10; spincnt
++) {
1235 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1237 *statusp
= RCU_KTHREAD_RUNNING
;
1238 this_cpu_inc(rcu_cpu_kthread_loops
);
1239 local_irq_disable();
1244 rcu_kthread_do_work();
1247 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1248 *statusp
= RCU_KTHREAD_WAITING
;
1252 *statusp
= RCU_KTHREAD_YIELDING
;
1253 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1254 schedule_timeout_interruptible(2);
1255 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1256 *statusp
= RCU_KTHREAD_WAITING
;
1260 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1261 * served by the rcu_node in question. The CPU hotplug lock is still
1262 * held, so the value of rnp->qsmaskinit will be stable.
1264 * We don't include outgoingcpu in the affinity set, use -1 if there is
1265 * no outgoing CPU. If there are no CPUs left in the affinity set,
1266 * this function allows the kthread to execute on any CPU.
1268 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
)
1270 struct task_struct
*t
= rnp
->boost_kthread_task
;
1271 unsigned long mask
= rcu_rnp_online_cpus(rnp
);
1277 if (!zalloc_cpumask_var(&cm
, GFP_KERNEL
))
1279 for (cpu
= rnp
->grplo
; cpu
<= rnp
->grphi
; cpu
++, mask
>>= 1)
1280 if ((mask
& 0x1) && cpu
!= outgoingcpu
)
1281 cpumask_set_cpu(cpu
, cm
);
1282 if (cpumask_weight(cm
) == 0)
1284 set_cpus_allowed_ptr(t
, cm
);
1285 free_cpumask_var(cm
);
1288 static struct smp_hotplug_thread rcu_cpu_thread_spec
= {
1289 .store
= &rcu_cpu_kthread_task
,
1290 .thread_should_run
= rcu_cpu_kthread_should_run
,
1291 .thread_fn
= rcu_cpu_kthread
,
1292 .thread_comm
= "rcuc/%u",
1293 .setup
= rcu_cpu_kthread_setup
,
1294 .park
= rcu_cpu_kthread_park
,
1298 * Spawn boost kthreads -- called as soon as the scheduler is running.
1300 static void __init
rcu_spawn_boost_kthreads(void)
1302 struct rcu_node
*rnp
;
1305 for_each_possible_cpu(cpu
)
1306 per_cpu(rcu_cpu_has_work
, cpu
) = 0;
1307 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec
));
1308 rcu_for_each_leaf_node(rcu_state_p
, rnp
)
1309 (void)rcu_spawn_one_boost_kthread(rcu_state_p
, rnp
);
1312 static void rcu_prepare_kthreads(int cpu
)
1314 struct rcu_data
*rdp
= per_cpu_ptr(rcu_state_p
->rda
, cpu
);
1315 struct rcu_node
*rnp
= rdp
->mynode
;
1317 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1318 if (rcu_scheduler_fully_active
)
1319 (void)rcu_spawn_one_boost_kthread(rcu_state_p
, rnp
);
1322 #else /* #ifdef CONFIG_RCU_BOOST */
1324 static void rcu_initiate_boost(struct rcu_node
*rnp
, unsigned long flags
)
1325 __releases(rnp
->lock
)
1327 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1330 static void invoke_rcu_callbacks_kthread(void)
1335 static bool rcu_is_callbacks_kthread(void)
1340 static void rcu_preempt_boost_start_gp(struct rcu_node
*rnp
)
1344 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
)
1348 static void __init
rcu_spawn_boost_kthreads(void)
1352 static void rcu_prepare_kthreads(int cpu
)
1356 #endif /* #else #ifdef CONFIG_RCU_BOOST */
1358 #if !defined(CONFIG_RCU_FAST_NO_HZ)
1361 * Check to see if any future RCU-related work will need to be done
1362 * by the current CPU, even if none need be done immediately, returning
1363 * 1 if so. This function is part of the RCU implementation; it is -not-
1364 * an exported member of the RCU API.
1366 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1367 * any flavor of RCU.
1369 #ifndef CONFIG_RCU_NOCB_CPU_ALL
1370 int rcu_needs_cpu(unsigned long *delta_jiffies
)
1372 *delta_jiffies
= ULONG_MAX
;
1373 return rcu_cpu_has_callbacks(NULL
);
1375 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1378 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1381 static void rcu_cleanup_after_idle(void)
1386 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1389 static void rcu_prepare_for_idle(void)
1394 * Don't bother keeping a running count of the number of RCU callbacks
1395 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1397 static void rcu_idle_count_callbacks_posted(void)
1401 #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1404 * This code is invoked when a CPU goes idle, at which point we want
1405 * to have the CPU do everything required for RCU so that it can enter
1406 * the energy-efficient dyntick-idle mode. This is handled by a
1407 * state machine implemented by rcu_prepare_for_idle() below.
1409 * The following three proprocessor symbols control this state machine:
1411 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1412 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1413 * is sized to be roughly one RCU grace period. Those energy-efficiency
1414 * benchmarkers who might otherwise be tempted to set this to a large
1415 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1416 * system. And if you are -that- concerned about energy efficiency,
1417 * just power the system down and be done with it!
1418 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1419 * permitted to sleep in dyntick-idle mode with only lazy RCU
1420 * callbacks pending. Setting this too high can OOM your system.
1422 * The values below work well in practice. If future workloads require
1423 * adjustment, they can be converted into kernel config parameters, though
1424 * making the state machine smarter might be a better option.
1426 #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1427 #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1429 static int rcu_idle_gp_delay
= RCU_IDLE_GP_DELAY
;
1430 module_param(rcu_idle_gp_delay
, int, 0644);
1431 static int rcu_idle_lazy_gp_delay
= RCU_IDLE_LAZY_GP_DELAY
;
1432 module_param(rcu_idle_lazy_gp_delay
, int, 0644);
1434 extern int tick_nohz_active
;
1437 * Try to advance callbacks for all flavors of RCU on the current CPU, but
1438 * only if it has been awhile since the last time we did so. Afterwards,
1439 * if there are any callbacks ready for immediate invocation, return true.
1441 static bool __maybe_unused
rcu_try_advance_all_cbs(void)
1443 bool cbs_ready
= false;
1444 struct rcu_data
*rdp
;
1445 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
1446 struct rcu_node
*rnp
;
1447 struct rcu_state
*rsp
;
1449 /* Exit early if we advanced recently. */
1450 if (jiffies
== rdtp
->last_advance_all
)
1452 rdtp
->last_advance_all
= jiffies
;
1454 for_each_rcu_flavor(rsp
) {
1455 rdp
= this_cpu_ptr(rsp
->rda
);
1459 * Don't bother checking unless a grace period has
1460 * completed since we last checked and there are
1461 * callbacks not yet ready to invoke.
1463 if ((rdp
->completed
!= rnp
->completed
||
1464 unlikely(ACCESS_ONCE(rdp
->gpwrap
))) &&
1465 rdp
->nxttail
[RCU_DONE_TAIL
] != rdp
->nxttail
[RCU_NEXT_TAIL
])
1466 note_gp_changes(rsp
, rdp
);
1468 if (cpu_has_callbacks_ready_to_invoke(rdp
))
1475 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1476 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1477 * caller to set the timeout based on whether or not there are non-lazy
1480 * The caller must have disabled interrupts.
1482 #ifndef CONFIG_RCU_NOCB_CPU_ALL
1483 int rcu_needs_cpu(unsigned long *dj
)
1485 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
1487 /* Snapshot to detect later posting of non-lazy callback. */
1488 rdtp
->nonlazy_posted_snap
= rdtp
->nonlazy_posted
;
1490 /* If no callbacks, RCU doesn't need the CPU. */
1491 if (!rcu_cpu_has_callbacks(&rdtp
->all_lazy
)) {
1496 /* Attempt to advance callbacks. */
1497 if (rcu_try_advance_all_cbs()) {
1498 /* Some ready to invoke, so initiate later invocation. */
1502 rdtp
->last_accelerate
= jiffies
;
1504 /* Request timer delay depending on laziness, and round. */
1505 if (!rdtp
->all_lazy
) {
1506 *dj
= round_up(rcu_idle_gp_delay
+ jiffies
,
1507 rcu_idle_gp_delay
) - jiffies
;
1509 *dj
= round_jiffies(rcu_idle_lazy_gp_delay
+ jiffies
) - jiffies
;
1513 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1516 * Prepare a CPU for idle from an RCU perspective. The first major task
1517 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1518 * The second major task is to check to see if a non-lazy callback has
1519 * arrived at a CPU that previously had only lazy callbacks. The third
1520 * major task is to accelerate (that is, assign grace-period numbers to)
1521 * any recently arrived callbacks.
1523 * The caller must have disabled interrupts.
1525 static void rcu_prepare_for_idle(void)
1527 #ifndef CONFIG_RCU_NOCB_CPU_ALL
1529 struct rcu_data
*rdp
;
1530 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
1531 struct rcu_node
*rnp
;
1532 struct rcu_state
*rsp
;
1535 /* Handle nohz enablement switches conservatively. */
1536 tne
= ACCESS_ONCE(tick_nohz_active
);
1537 if (tne
!= rdtp
->tick_nohz_enabled_snap
) {
1538 if (rcu_cpu_has_callbacks(NULL
))
1539 invoke_rcu_core(); /* force nohz to see update. */
1540 rdtp
->tick_nohz_enabled_snap
= tne
;
1546 /* If this is a no-CBs CPU, no callbacks, just return. */
1547 if (rcu_is_nocb_cpu(smp_processor_id()))
1551 * If a non-lazy callback arrived at a CPU having only lazy
1552 * callbacks, invoke RCU core for the side-effect of recalculating
1553 * idle duration on re-entry to idle.
1555 if (rdtp
->all_lazy
&&
1556 rdtp
->nonlazy_posted
!= rdtp
->nonlazy_posted_snap
) {
1557 rdtp
->all_lazy
= false;
1558 rdtp
->nonlazy_posted_snap
= rdtp
->nonlazy_posted
;
1564 * If we have not yet accelerated this jiffy, accelerate all
1565 * callbacks on this CPU.
1567 if (rdtp
->last_accelerate
== jiffies
)
1569 rdtp
->last_accelerate
= jiffies
;
1570 for_each_rcu_flavor(rsp
) {
1571 rdp
= this_cpu_ptr(rsp
->rda
);
1572 if (!*rdp
->nxttail
[RCU_DONE_TAIL
])
1575 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1576 smp_mb__after_unlock_lock();
1577 needwake
= rcu_accelerate_cbs(rsp
, rnp
, rdp
);
1578 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1580 rcu_gp_kthread_wake(rsp
);
1582 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1586 * Clean up for exit from idle. Attempt to advance callbacks based on
1587 * any grace periods that elapsed while the CPU was idle, and if any
1588 * callbacks are now ready to invoke, initiate invocation.
1590 static void rcu_cleanup_after_idle(void)
1592 #ifndef CONFIG_RCU_NOCB_CPU_ALL
1593 if (rcu_is_nocb_cpu(smp_processor_id()))
1595 if (rcu_try_advance_all_cbs())
1597 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1601 * Keep a running count of the number of non-lazy callbacks posted
1602 * on this CPU. This running counter (which is never decremented) allows
1603 * rcu_prepare_for_idle() to detect when something out of the idle loop
1604 * posts a callback, even if an equal number of callbacks are invoked.
1605 * Of course, callbacks should only be posted from within a trace event
1606 * designed to be called from idle or from within RCU_NONIDLE().
1608 static void rcu_idle_count_callbacks_posted(void)
1610 __this_cpu_add(rcu_dynticks
.nonlazy_posted
, 1);
1614 * Data for flushing lazy RCU callbacks at OOM time.
1616 static atomic_t oom_callback_count
;
1617 static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq
);
1620 * RCU OOM callback -- decrement the outstanding count and deliver the
1621 * wake-up if we are the last one.
1623 static void rcu_oom_callback(struct rcu_head
*rhp
)
1625 if (atomic_dec_and_test(&oom_callback_count
))
1626 wake_up(&oom_callback_wq
);
1630 * Post an rcu_oom_notify callback on the current CPU if it has at
1631 * least one lazy callback. This will unnecessarily post callbacks
1632 * to CPUs that already have a non-lazy callback at the end of their
1633 * callback list, but this is an infrequent operation, so accept some
1634 * extra overhead to keep things simple.
1636 static void rcu_oom_notify_cpu(void *unused
)
1638 struct rcu_state
*rsp
;
1639 struct rcu_data
*rdp
;
1641 for_each_rcu_flavor(rsp
) {
1642 rdp
= raw_cpu_ptr(rsp
->rda
);
1643 if (rdp
->qlen_lazy
!= 0) {
1644 atomic_inc(&oom_callback_count
);
1645 rsp
->call(&rdp
->oom_head
, rcu_oom_callback
);
1651 * If low on memory, ensure that each CPU has a non-lazy callback.
1652 * This will wake up CPUs that have only lazy callbacks, in turn
1653 * ensuring that they free up the corresponding memory in a timely manner.
1654 * Because an uncertain amount of memory will be freed in some uncertain
1655 * timeframe, we do not claim to have freed anything.
1657 static int rcu_oom_notify(struct notifier_block
*self
,
1658 unsigned long notused
, void *nfreed
)
1662 /* Wait for callbacks from earlier instance to complete. */
1663 wait_event(oom_callback_wq
, atomic_read(&oom_callback_count
) == 0);
1664 smp_mb(); /* Ensure callback reuse happens after callback invocation. */
1667 * Prevent premature wakeup: ensure that all increments happen
1668 * before there is a chance of the counter reaching zero.
1670 atomic_set(&oom_callback_count
, 1);
1673 for_each_online_cpu(cpu
) {
1674 smp_call_function_single(cpu
, rcu_oom_notify_cpu
, NULL
, 1);
1675 cond_resched_rcu_qs();
1679 /* Unconditionally decrement: no need to wake ourselves up. */
1680 atomic_dec(&oom_callback_count
);
1685 static struct notifier_block rcu_oom_nb
= {
1686 .notifier_call
= rcu_oom_notify
1689 static int __init
rcu_register_oom_notifier(void)
1691 register_oom_notifier(&rcu_oom_nb
);
1694 early_initcall(rcu_register_oom_notifier
);
1696 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1698 #ifdef CONFIG_RCU_CPU_STALL_INFO
1700 #ifdef CONFIG_RCU_FAST_NO_HZ
1702 static void print_cpu_stall_fast_no_hz(char *cp
, int cpu
)
1704 struct rcu_dynticks
*rdtp
= &per_cpu(rcu_dynticks
, cpu
);
1705 unsigned long nlpd
= rdtp
->nonlazy_posted
- rdtp
->nonlazy_posted_snap
;
1707 sprintf(cp
, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1708 rdtp
->last_accelerate
& 0xffff, jiffies
& 0xffff,
1710 rdtp
->all_lazy
? 'L' : '.',
1711 rdtp
->tick_nohz_enabled_snap
? '.' : 'D');
1714 #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1716 static void print_cpu_stall_fast_no_hz(char *cp
, int cpu
)
1721 #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1723 /* Initiate the stall-info list. */
1724 static void print_cpu_stall_info_begin(void)
1730 * Print out diagnostic information for the specified stalled CPU.
1732 * If the specified CPU is aware of the current RCU grace period
1733 * (flavor specified by rsp), then print the number of scheduling
1734 * clock interrupts the CPU has taken during the time that it has
1735 * been aware. Otherwise, print the number of RCU grace periods
1736 * that this CPU is ignorant of, for example, "1" if the CPU was
1737 * aware of the previous grace period.
1739 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1741 static void print_cpu_stall_info(struct rcu_state
*rsp
, int cpu
)
1743 char fast_no_hz
[72];
1744 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1745 struct rcu_dynticks
*rdtp
= rdp
->dynticks
;
1747 unsigned long ticks_value
;
1749 if (rsp
->gpnum
== rdp
->gpnum
) {
1750 ticks_title
= "ticks this GP";
1751 ticks_value
= rdp
->ticks_this_gp
;
1753 ticks_title
= "GPs behind";
1754 ticks_value
= rsp
->gpnum
- rdp
->gpnum
;
1756 print_cpu_stall_fast_no_hz(fast_no_hz
, cpu
);
1757 pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s\n",
1758 cpu
, ticks_value
, ticks_title
,
1759 atomic_read(&rdtp
->dynticks
) & 0xfff,
1760 rdtp
->dynticks_nesting
, rdtp
->dynticks_nmi_nesting
,
1761 rdp
->softirq_snap
, kstat_softirqs_cpu(RCU_SOFTIRQ
, cpu
),
1762 ACCESS_ONCE(rsp
->n_force_qs
) - rsp
->n_force_qs_gpstart
,
1766 /* Terminate the stall-info list. */
1767 static void print_cpu_stall_info_end(void)
1772 /* Zero ->ticks_this_gp for all flavors of RCU. */
1773 static void zero_cpu_stall_ticks(struct rcu_data
*rdp
)
1775 rdp
->ticks_this_gp
= 0;
1776 rdp
->softirq_snap
= kstat_softirqs_cpu(RCU_SOFTIRQ
, smp_processor_id());
1779 /* Increment ->ticks_this_gp for all flavors of RCU. */
1780 static void increment_cpu_stall_ticks(void)
1782 struct rcu_state
*rsp
;
1784 for_each_rcu_flavor(rsp
)
1785 raw_cpu_inc(rsp
->rda
->ticks_this_gp
);
1788 #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
1790 static void print_cpu_stall_info_begin(void)
1795 static void print_cpu_stall_info(struct rcu_state
*rsp
, int cpu
)
1797 pr_cont(" %d", cpu
);
1800 static void print_cpu_stall_info_end(void)
1805 static void zero_cpu_stall_ticks(struct rcu_data
*rdp
)
1809 static void increment_cpu_stall_ticks(void)
1813 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
1815 #ifdef CONFIG_RCU_NOCB_CPU
1818 * Offload callback processing from the boot-time-specified set of CPUs
1819 * specified by rcu_nocb_mask. For each CPU in the set, there is a
1820 * kthread created that pulls the callbacks from the corresponding CPU,
1821 * waits for a grace period to elapse, and invokes the callbacks.
1822 * The no-CBs CPUs do a wake_up() on their kthread when they insert
1823 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
1824 * has been specified, in which case each kthread actively polls its
1825 * CPU. (Which isn't so great for energy efficiency, but which does
1826 * reduce RCU's overhead on that CPU.)
1828 * This is intended to be used in conjunction with Frederic Weisbecker's
1829 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
1830 * running CPU-bound user-mode computations.
1832 * Offloading of callback processing could also in theory be used as
1833 * an energy-efficiency measure because CPUs with no RCU callbacks
1834 * queued are more aggressive about entering dyntick-idle mode.
1838 /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
1839 static int __init
rcu_nocb_setup(char *str
)
1841 alloc_bootmem_cpumask_var(&rcu_nocb_mask
);
1842 have_rcu_nocb_mask
= true;
1843 cpulist_parse(str
, rcu_nocb_mask
);
1846 __setup("rcu_nocbs=", rcu_nocb_setup
);
1848 static int __init
parse_rcu_nocb_poll(char *arg
)
1853 early_param("rcu_nocb_poll", parse_rcu_nocb_poll
);
1856 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
1859 static void rcu_nocb_gp_cleanup(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
1861 wake_up_all(&rnp
->nocb_gp_wq
[rnp
->completed
& 0x1]);
1865 * Set the root rcu_node structure's ->need_future_gp field
1866 * based on the sum of those of all rcu_node structures. This does
1867 * double-count the root rcu_node structure's requests, but this
1868 * is necessary to handle the possibility of a rcu_nocb_kthread()
1869 * having awakened during the time that the rcu_node structures
1870 * were being updated for the end of the previous grace period.
1872 static void rcu_nocb_gp_set(struct rcu_node
*rnp
, int nrq
)
1874 rnp
->need_future_gp
[(rnp
->completed
+ 1) & 0x1] += nrq
;
1877 static void rcu_init_one_nocb(struct rcu_node
*rnp
)
1879 init_waitqueue_head(&rnp
->nocb_gp_wq
[0]);
1880 init_waitqueue_head(&rnp
->nocb_gp_wq
[1]);
1883 #ifndef CONFIG_RCU_NOCB_CPU_ALL
1884 /* Is the specified CPU a no-CBs CPU? */
1885 bool rcu_is_nocb_cpu(int cpu
)
1887 if (have_rcu_nocb_mask
)
1888 return cpumask_test_cpu(cpu
, rcu_nocb_mask
);
1891 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1894 * Kick the leader kthread for this NOCB group.
1896 static void wake_nocb_leader(struct rcu_data
*rdp
, bool force
)
1898 struct rcu_data
*rdp_leader
= rdp
->nocb_leader
;
1900 if (!ACCESS_ONCE(rdp_leader
->nocb_kthread
))
1902 if (ACCESS_ONCE(rdp_leader
->nocb_leader_sleep
) || force
) {
1903 /* Prior smp_mb__after_atomic() orders against prior enqueue. */
1904 ACCESS_ONCE(rdp_leader
->nocb_leader_sleep
) = false;
1905 wake_up(&rdp_leader
->nocb_wq
);
1910 * Does the specified CPU need an RCU callback for the specified flavor
1913 static bool rcu_nocb_cpu_needs_barrier(struct rcu_state
*rsp
, int cpu
)
1915 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1917 #ifdef CONFIG_PROVE_RCU
1918 struct rcu_head
*rhp
;
1919 #endif /* #ifdef CONFIG_PROVE_RCU */
1922 * Check count of all no-CBs callbacks awaiting invocation.
1923 * There needs to be a barrier before this function is called,
1924 * but associated with a prior determination that no more
1925 * callbacks would be posted. In the worst case, the first
1926 * barrier in _rcu_barrier() suffices (but the caller cannot
1927 * necessarily rely on this, not a substitute for the caller
1928 * getting the concurrency design right!). There must also be
1929 * a barrier between the following load an posting of a callback
1930 * (if a callback is in fact needed). This is associated with an
1931 * atomic_inc() in the caller.
1933 ret
= atomic_long_read(&rdp
->nocb_q_count
);
1935 #ifdef CONFIG_PROVE_RCU
1936 rhp
= ACCESS_ONCE(rdp
->nocb_head
);
1938 rhp
= ACCESS_ONCE(rdp
->nocb_gp_head
);
1940 rhp
= ACCESS_ONCE(rdp
->nocb_follower_head
);
1942 /* Having no rcuo kthread but CBs after scheduler starts is bad! */
1943 if (!ACCESS_ONCE(rdp
->nocb_kthread
) && rhp
) {
1944 /* RCU callback enqueued before CPU first came online??? */
1945 pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
1949 #endif /* #ifdef CONFIG_PROVE_RCU */
1955 * Enqueue the specified string of rcu_head structures onto the specified
1956 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
1957 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
1958 * counts are supplied by rhcount and rhcount_lazy.
1960 * If warranted, also wake up the kthread servicing this CPUs queues.
1962 static void __call_rcu_nocb_enqueue(struct rcu_data
*rdp
,
1963 struct rcu_head
*rhp
,
1964 struct rcu_head
**rhtp
,
1965 int rhcount
, int rhcount_lazy
,
1966 unsigned long flags
)
1969 struct rcu_head
**old_rhpp
;
1970 struct task_struct
*t
;
1972 /* Enqueue the callback on the nocb list and update counts. */
1973 atomic_long_add(rhcount
, &rdp
->nocb_q_count
);
1974 /* rcu_barrier() relies on ->nocb_q_count add before xchg. */
1975 old_rhpp
= xchg(&rdp
->nocb_tail
, rhtp
);
1976 ACCESS_ONCE(*old_rhpp
) = rhp
;
1977 atomic_long_add(rhcount_lazy
, &rdp
->nocb_q_count_lazy
);
1978 smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
1980 /* If we are not being polled and there is a kthread, awaken it ... */
1981 t
= ACCESS_ONCE(rdp
->nocb_kthread
);
1982 if (rcu_nocb_poll
|| !t
) {
1983 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
1984 TPS("WakeNotPoll"));
1987 len
= atomic_long_read(&rdp
->nocb_q_count
);
1988 if (old_rhpp
== &rdp
->nocb_head
) {
1989 if (!irqs_disabled_flags(flags
)) {
1990 /* ... if queue was empty ... */
1991 wake_nocb_leader(rdp
, false);
1992 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
1995 rdp
->nocb_defer_wakeup
= RCU_NOGP_WAKE
;
1996 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
1997 TPS("WakeEmptyIsDeferred"));
1999 rdp
->qlen_last_fqs_check
= 0;
2000 } else if (len
> rdp
->qlen_last_fqs_check
+ qhimark
) {
2001 /* ... or if many callbacks queued. */
2002 if (!irqs_disabled_flags(flags
)) {
2003 wake_nocb_leader(rdp
, true);
2004 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2007 rdp
->nocb_defer_wakeup
= RCU_NOGP_WAKE_FORCE
;
2008 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2009 TPS("WakeOvfIsDeferred"));
2011 rdp
->qlen_last_fqs_check
= LONG_MAX
/ 2;
2013 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, TPS("WakeNot"));
2019 * This is a helper for __call_rcu(), which invokes this when the normal
2020 * callback queue is inoperable. If this is not a no-CBs CPU, this
2021 * function returns failure back to __call_rcu(), which can complain
2024 * Otherwise, this function queues the callback where the corresponding
2025 * "rcuo" kthread can find it.
2027 static bool __call_rcu_nocb(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
2028 bool lazy
, unsigned long flags
)
2031 if (!rcu_is_nocb_cpu(rdp
->cpu
))
2033 __call_rcu_nocb_enqueue(rdp
, rhp
, &rhp
->next
, 1, lazy
, flags
);
2034 if (__is_kfree_rcu_offset((unsigned long)rhp
->func
))
2035 trace_rcu_kfree_callback(rdp
->rsp
->name
, rhp
,
2036 (unsigned long)rhp
->func
,
2037 -atomic_long_read(&rdp
->nocb_q_count_lazy
),
2038 -atomic_long_read(&rdp
->nocb_q_count
));
2040 trace_rcu_callback(rdp
->rsp
->name
, rhp
,
2041 -atomic_long_read(&rdp
->nocb_q_count_lazy
),
2042 -atomic_long_read(&rdp
->nocb_q_count
));
2045 * If called from an extended quiescent state with interrupts
2046 * disabled, invoke the RCU core in order to allow the idle-entry
2047 * deferred-wakeup check to function.
2049 if (irqs_disabled_flags(flags
) &&
2050 !rcu_is_watching() &&
2051 cpu_online(smp_processor_id()))
2058 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2061 static bool __maybe_unused
rcu_nocb_adopt_orphan_cbs(struct rcu_state
*rsp
,
2062 struct rcu_data
*rdp
,
2063 unsigned long flags
)
2065 long ql
= rsp
->qlen
;
2066 long qll
= rsp
->qlen_lazy
;
2068 /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
2069 if (!rcu_is_nocb_cpu(smp_processor_id()))
2074 /* First, enqueue the donelist, if any. This preserves CB ordering. */
2075 if (rsp
->orphan_donelist
!= NULL
) {
2076 __call_rcu_nocb_enqueue(rdp
, rsp
->orphan_donelist
,
2077 rsp
->orphan_donetail
, ql
, qll
, flags
);
2079 rsp
->orphan_donelist
= NULL
;
2080 rsp
->orphan_donetail
= &rsp
->orphan_donelist
;
2082 if (rsp
->orphan_nxtlist
!= NULL
) {
2083 __call_rcu_nocb_enqueue(rdp
, rsp
->orphan_nxtlist
,
2084 rsp
->orphan_nxttail
, ql
, qll
, flags
);
2086 rsp
->orphan_nxtlist
= NULL
;
2087 rsp
->orphan_nxttail
= &rsp
->orphan_nxtlist
;
2093 * If necessary, kick off a new grace period, and either way wait
2094 * for a subsequent grace period to complete.
2096 static void rcu_nocb_wait_gp(struct rcu_data
*rdp
)
2100 unsigned long flags
;
2102 struct rcu_node
*rnp
= rdp
->mynode
;
2104 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2105 smp_mb__after_unlock_lock();
2106 needwake
= rcu_start_future_gp(rnp
, rdp
, &c
);
2107 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2109 rcu_gp_kthread_wake(rdp
->rsp
);
2112 * Wait for the grace period. Do so interruptibly to avoid messing
2113 * up the load average.
2115 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("StartWait"));
2117 wait_event_interruptible(
2118 rnp
->nocb_gp_wq
[c
& 0x1],
2119 (d
= ULONG_CMP_GE(ACCESS_ONCE(rnp
->completed
), c
)));
2122 WARN_ON(signal_pending(current
));
2123 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("ResumeWait"));
2125 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("EndWait"));
2126 smp_mb(); /* Ensure that CB invocation happens after GP end. */
2130 * Leaders come here to wait for additional callbacks to show up.
2131 * This function does not return until callbacks appear.
2133 static void nocb_leader_wait(struct rcu_data
*my_rdp
)
2135 bool firsttime
= true;
2137 struct rcu_data
*rdp
;
2138 struct rcu_head
**tail
;
2142 /* Wait for callbacks to appear. */
2143 if (!rcu_nocb_poll
) {
2144 trace_rcu_nocb_wake(my_rdp
->rsp
->name
, my_rdp
->cpu
, "Sleep");
2145 wait_event_interruptible(my_rdp
->nocb_wq
,
2146 !ACCESS_ONCE(my_rdp
->nocb_leader_sleep
));
2147 /* Memory barrier handled by smp_mb() calls below and repoll. */
2148 } else if (firsttime
) {
2149 firsttime
= false; /* Don't drown trace log with "Poll"! */
2150 trace_rcu_nocb_wake(my_rdp
->rsp
->name
, my_rdp
->cpu
, "Poll");
2154 * Each pass through the following loop checks a follower for CBs.
2155 * We are our own first follower. Any CBs found are moved to
2156 * nocb_gp_head, where they await a grace period.
2159 for (rdp
= my_rdp
; rdp
; rdp
= rdp
->nocb_next_follower
) {
2160 rdp
->nocb_gp_head
= ACCESS_ONCE(rdp
->nocb_head
);
2161 if (!rdp
->nocb_gp_head
)
2162 continue; /* No CBs here, try next follower. */
2164 /* Move callbacks to wait-for-GP list, which is empty. */
2165 ACCESS_ONCE(rdp
->nocb_head
) = NULL
;
2166 rdp
->nocb_gp_tail
= xchg(&rdp
->nocb_tail
, &rdp
->nocb_head
);
2171 * If there were no callbacks, sleep a bit, rescan after a
2172 * memory barrier, and go retry.
2174 if (unlikely(!gotcbs
)) {
2176 trace_rcu_nocb_wake(my_rdp
->rsp
->name
, my_rdp
->cpu
,
2178 WARN_ON(signal_pending(current
));
2179 schedule_timeout_interruptible(1);
2181 /* Rescan in case we were a victim of memory ordering. */
2182 my_rdp
->nocb_leader_sleep
= true;
2183 smp_mb(); /* Ensure _sleep true before scan. */
2184 for (rdp
= my_rdp
; rdp
; rdp
= rdp
->nocb_next_follower
)
2185 if (ACCESS_ONCE(rdp
->nocb_head
)) {
2186 /* Found CB, so short-circuit next wait. */
2187 my_rdp
->nocb_leader_sleep
= false;
2193 /* Wait for one grace period. */
2194 rcu_nocb_wait_gp(my_rdp
);
2197 * We left ->nocb_leader_sleep unset to reduce cache thrashing.
2198 * We set it now, but recheck for new callbacks while
2199 * traversing our follower list.
2201 my_rdp
->nocb_leader_sleep
= true;
2202 smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */
2204 /* Each pass through the following loop wakes a follower, if needed. */
2205 for (rdp
= my_rdp
; rdp
; rdp
= rdp
->nocb_next_follower
) {
2206 if (ACCESS_ONCE(rdp
->nocb_head
))
2207 my_rdp
->nocb_leader_sleep
= false;/* No need to sleep.*/
2208 if (!rdp
->nocb_gp_head
)
2209 continue; /* No CBs, so no need to wake follower. */
2211 /* Append callbacks to follower's "done" list. */
2212 tail
= xchg(&rdp
->nocb_follower_tail
, rdp
->nocb_gp_tail
);
2213 *tail
= rdp
->nocb_gp_head
;
2214 smp_mb__after_atomic(); /* Store *tail before wakeup. */
2215 if (rdp
!= my_rdp
&& tail
== &rdp
->nocb_follower_head
) {
2217 * List was empty, wake up the follower.
2218 * Memory barriers supplied by atomic_long_add().
2220 wake_up(&rdp
->nocb_wq
);
2224 /* If we (the leader) don't have CBs, go wait some more. */
2225 if (!my_rdp
->nocb_follower_head
)
2230 * Followers come here to wait for additional callbacks to show up.
2231 * This function does not return until callbacks appear.
2233 static void nocb_follower_wait(struct rcu_data
*rdp
)
2235 bool firsttime
= true;
2238 if (!rcu_nocb_poll
) {
2239 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2241 wait_event_interruptible(rdp
->nocb_wq
,
2242 ACCESS_ONCE(rdp
->nocb_follower_head
));
2243 } else if (firsttime
) {
2244 /* Don't drown trace log with "Poll"! */
2246 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, "Poll");
2248 if (smp_load_acquire(&rdp
->nocb_follower_head
)) {
2249 /* ^^^ Ensure CB invocation follows _head test. */
2253 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2255 WARN_ON(signal_pending(current
));
2256 schedule_timeout_interruptible(1);
2261 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
2262 * callbacks queued by the corresponding no-CBs CPU, however, there is
2263 * an optional leader-follower relationship so that the grace-period
2264 * kthreads don't have to do quite so many wakeups.
2266 static int rcu_nocb_kthread(void *arg
)
2269 struct rcu_head
*list
;
2270 struct rcu_head
*next
;
2271 struct rcu_head
**tail
;
2272 struct rcu_data
*rdp
= arg
;
2274 /* Each pass through this loop invokes one batch of callbacks */
2276 /* Wait for callbacks. */
2277 if (rdp
->nocb_leader
== rdp
)
2278 nocb_leader_wait(rdp
);
2280 nocb_follower_wait(rdp
);
2282 /* Pull the ready-to-invoke callbacks onto local list. */
2283 list
= ACCESS_ONCE(rdp
->nocb_follower_head
);
2285 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, "WokeNonEmpty");
2286 ACCESS_ONCE(rdp
->nocb_follower_head
) = NULL
;
2287 tail
= xchg(&rdp
->nocb_follower_tail
, &rdp
->nocb_follower_head
);
2289 /* Each pass through the following loop invokes a callback. */
2290 trace_rcu_batch_start(rdp
->rsp
->name
,
2291 atomic_long_read(&rdp
->nocb_q_count_lazy
),
2292 atomic_long_read(&rdp
->nocb_q_count
), -1);
2296 /* Wait for enqueuing to complete, if needed. */
2297 while (next
== NULL
&& &list
->next
!= tail
) {
2298 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2300 schedule_timeout_interruptible(1);
2301 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2305 debug_rcu_head_unqueue(list
);
2307 if (__rcu_reclaim(rdp
->rsp
->name
, list
))
2313 trace_rcu_batch_end(rdp
->rsp
->name
, c
, !!list
, 0, 0, 1);
2314 smp_mb__before_atomic(); /* _add after CB invocation. */
2315 atomic_long_add(-c
, &rdp
->nocb_q_count
);
2316 atomic_long_add(-cl
, &rdp
->nocb_q_count_lazy
);
2317 rdp
->n_nocbs_invoked
+= c
;
2322 /* Is a deferred wakeup of rcu_nocb_kthread() required? */
2323 static int rcu_nocb_need_deferred_wakeup(struct rcu_data
*rdp
)
2325 return ACCESS_ONCE(rdp
->nocb_defer_wakeup
);
2328 /* Do a deferred wakeup of rcu_nocb_kthread(). */
2329 static void do_nocb_deferred_wakeup(struct rcu_data
*rdp
)
2333 if (!rcu_nocb_need_deferred_wakeup(rdp
))
2335 ndw
= ACCESS_ONCE(rdp
->nocb_defer_wakeup
);
2336 ACCESS_ONCE(rdp
->nocb_defer_wakeup
) = RCU_NOGP_WAKE_NOT
;
2337 wake_nocb_leader(rdp
, ndw
== RCU_NOGP_WAKE_FORCE
);
2338 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, TPS("DeferredWake"));
2341 void __init
rcu_init_nohz(void)
2344 bool need_rcu_nocb_mask
= true;
2345 struct rcu_state
*rsp
;
2347 #ifdef CONFIG_RCU_NOCB_CPU_NONE
2348 need_rcu_nocb_mask
= false;
2349 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
2351 #if defined(CONFIG_NO_HZ_FULL)
2352 if (tick_nohz_full_running
&& cpumask_weight(tick_nohz_full_mask
))
2353 need_rcu_nocb_mask
= true;
2354 #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2356 if (!have_rcu_nocb_mask
&& need_rcu_nocb_mask
) {
2357 if (!zalloc_cpumask_var(&rcu_nocb_mask
, GFP_KERNEL
)) {
2358 pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
2361 have_rcu_nocb_mask
= true;
2363 if (!have_rcu_nocb_mask
)
2366 #ifdef CONFIG_RCU_NOCB_CPU_ZERO
2367 pr_info("\tOffload RCU callbacks from CPU 0\n");
2368 cpumask_set_cpu(0, rcu_nocb_mask
);
2369 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
2370 #ifdef CONFIG_RCU_NOCB_CPU_ALL
2371 pr_info("\tOffload RCU callbacks from all CPUs\n");
2372 cpumask_copy(rcu_nocb_mask
, cpu_possible_mask
);
2373 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
2374 #if defined(CONFIG_NO_HZ_FULL)
2375 if (tick_nohz_full_running
)
2376 cpumask_or(rcu_nocb_mask
, rcu_nocb_mask
, tick_nohz_full_mask
);
2377 #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2379 if (!cpumask_subset(rcu_nocb_mask
, cpu_possible_mask
)) {
2380 pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
2381 cpumask_and(rcu_nocb_mask
, cpu_possible_mask
,
2384 pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
2385 cpumask_pr_args(rcu_nocb_mask
));
2387 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
2389 for_each_rcu_flavor(rsp
) {
2390 for_each_cpu(cpu
, rcu_nocb_mask
) {
2391 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2394 * If there are early callbacks, they will need
2395 * to be moved to the nocb lists.
2397 WARN_ON_ONCE(rdp
->nxttail
[RCU_NEXT_TAIL
] !=
2399 rdp
->nxttail
[RCU_NEXT_TAIL
] != NULL
);
2400 init_nocb_callback_list(rdp
);
2402 rcu_organize_nocb_kthreads(rsp
);
2406 /* Initialize per-rcu_data variables for no-CBs CPUs. */
2407 static void __init
rcu_boot_init_nocb_percpu_data(struct rcu_data
*rdp
)
2409 rdp
->nocb_tail
= &rdp
->nocb_head
;
2410 init_waitqueue_head(&rdp
->nocb_wq
);
2411 rdp
->nocb_follower_tail
= &rdp
->nocb_follower_head
;
2415 * If the specified CPU is a no-CBs CPU that does not already have its
2416 * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are
2417 * brought online out of order, this can require re-organizing the
2418 * leader-follower relationships.
2420 static void rcu_spawn_one_nocb_kthread(struct rcu_state
*rsp
, int cpu
)
2422 struct rcu_data
*rdp
;
2423 struct rcu_data
*rdp_last
;
2424 struct rcu_data
*rdp_old_leader
;
2425 struct rcu_data
*rdp_spawn
= per_cpu_ptr(rsp
->rda
, cpu
);
2426 struct task_struct
*t
;
2429 * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
2430 * then nothing to do.
2432 if (!rcu_is_nocb_cpu(cpu
) || rdp_spawn
->nocb_kthread
)
2435 /* If we didn't spawn the leader first, reorganize! */
2436 rdp_old_leader
= rdp_spawn
->nocb_leader
;
2437 if (rdp_old_leader
!= rdp_spawn
&& !rdp_old_leader
->nocb_kthread
) {
2439 rdp
= rdp_old_leader
;
2441 rdp
->nocb_leader
= rdp_spawn
;
2442 if (rdp_last
&& rdp
!= rdp_spawn
)
2443 rdp_last
->nocb_next_follower
= rdp
;
2444 if (rdp
== rdp_spawn
) {
2445 rdp
= rdp
->nocb_next_follower
;
2448 rdp
= rdp
->nocb_next_follower
;
2449 rdp_last
->nocb_next_follower
= NULL
;
2452 rdp_spawn
->nocb_next_follower
= rdp_old_leader
;
2455 /* Spawn the kthread for this CPU and RCU flavor. */
2456 t
= kthread_run(rcu_nocb_kthread
, rdp_spawn
,
2457 "rcuo%c/%d", rsp
->abbr
, cpu
);
2459 ACCESS_ONCE(rdp_spawn
->nocb_kthread
) = t
;
2463 * If the specified CPU is a no-CBs CPU that does not already have its
2464 * rcuo kthreads, spawn them.
2466 static void rcu_spawn_all_nocb_kthreads(int cpu
)
2468 struct rcu_state
*rsp
;
2470 if (rcu_scheduler_fully_active
)
2471 for_each_rcu_flavor(rsp
)
2472 rcu_spawn_one_nocb_kthread(rsp
, cpu
);
2476 * Once the scheduler is running, spawn rcuo kthreads for all online
2477 * no-CBs CPUs. This assumes that the early_initcall()s happen before
2478 * non-boot CPUs come online -- if this changes, we will need to add
2479 * some mutual exclusion.
2481 static void __init
rcu_spawn_nocb_kthreads(void)
2485 for_each_online_cpu(cpu
)
2486 rcu_spawn_all_nocb_kthreads(cpu
);
2489 /* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */
2490 static int rcu_nocb_leader_stride
= -1;
2491 module_param(rcu_nocb_leader_stride
, int, 0444);
2494 * Initialize leader-follower relationships for all no-CBs CPU.
2496 static void __init
rcu_organize_nocb_kthreads(struct rcu_state
*rsp
)
2499 int ls
= rcu_nocb_leader_stride
;
2500 int nl
= 0; /* Next leader. */
2501 struct rcu_data
*rdp
;
2502 struct rcu_data
*rdp_leader
= NULL
; /* Suppress misguided gcc warn. */
2503 struct rcu_data
*rdp_prev
= NULL
;
2505 if (!have_rcu_nocb_mask
)
2508 ls
= int_sqrt(nr_cpu_ids
);
2509 rcu_nocb_leader_stride
= ls
;
2513 * Each pass through this loop sets up one rcu_data structure and
2514 * spawns one rcu_nocb_kthread().
2516 for_each_cpu(cpu
, rcu_nocb_mask
) {
2517 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2518 if (rdp
->cpu
>= nl
) {
2519 /* New leader, set up for followers & next leader. */
2520 nl
= DIV_ROUND_UP(rdp
->cpu
+ 1, ls
) * ls
;
2521 rdp
->nocb_leader
= rdp
;
2524 /* Another follower, link to previous leader. */
2525 rdp
->nocb_leader
= rdp_leader
;
2526 rdp_prev
->nocb_next_follower
= rdp
;
2532 /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2533 static bool init_nocb_callback_list(struct rcu_data
*rdp
)
2535 if (!rcu_is_nocb_cpu(rdp
->cpu
))
2538 rdp
->nxttail
[RCU_NEXT_TAIL
] = NULL
;
2542 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
2544 static bool rcu_nocb_cpu_needs_barrier(struct rcu_state
*rsp
, int cpu
)
2546 WARN_ON_ONCE(1); /* Should be dead code. */
2550 static void rcu_nocb_gp_cleanup(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
2554 static void rcu_nocb_gp_set(struct rcu_node
*rnp
, int nrq
)
2558 static void rcu_init_one_nocb(struct rcu_node
*rnp
)
2562 static bool __call_rcu_nocb(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
2563 bool lazy
, unsigned long flags
)
2568 static bool __maybe_unused
rcu_nocb_adopt_orphan_cbs(struct rcu_state
*rsp
,
2569 struct rcu_data
*rdp
,
2570 unsigned long flags
)
2575 static void __init
rcu_boot_init_nocb_percpu_data(struct rcu_data
*rdp
)
2579 static int rcu_nocb_need_deferred_wakeup(struct rcu_data
*rdp
)
2584 static void do_nocb_deferred_wakeup(struct rcu_data
*rdp
)
2588 static void rcu_spawn_all_nocb_kthreads(int cpu
)
2592 static void __init
rcu_spawn_nocb_kthreads(void)
2596 static bool init_nocb_callback_list(struct rcu_data
*rdp
)
2601 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2604 * An adaptive-ticks CPU can potentially execute in kernel mode for an
2605 * arbitrarily long period of time with the scheduling-clock tick turned
2606 * off. RCU will be paying attention to this CPU because it is in the
2607 * kernel, but the CPU cannot be guaranteed to be executing the RCU state
2608 * machine because the scheduling-clock tick has been disabled. Therefore,
2609 * if an adaptive-ticks CPU is failing to respond to the current grace
2610 * period and has not be idle from an RCU perspective, kick it.
2612 static void __maybe_unused
rcu_kick_nohz_cpu(int cpu
)
2614 #ifdef CONFIG_NO_HZ_FULL
2615 if (tick_nohz_full_cpu(cpu
))
2616 smp_send_reschedule(cpu
);
2617 #endif /* #ifdef CONFIG_NO_HZ_FULL */
2621 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
2623 static int full_sysidle_state
; /* Current system-idle state. */
2624 #define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */
2625 #define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */
2626 #define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */
2627 #define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */
2628 #define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */
2631 * Invoked to note exit from irq or task transition to idle. Note that
2632 * usermode execution does -not- count as idle here! After all, we want
2633 * to detect full-system idle states, not RCU quiescent states and grace
2634 * periods. The caller must have disabled interrupts.
2636 static void rcu_sysidle_enter(int irq
)
2639 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
2641 /* If there are no nohz_full= CPUs, no need to track this. */
2642 if (!tick_nohz_full_enabled())
2645 /* Adjust nesting, check for fully idle. */
2647 rdtp
->dynticks_idle_nesting
--;
2648 WARN_ON_ONCE(rdtp
->dynticks_idle_nesting
< 0);
2649 if (rdtp
->dynticks_idle_nesting
!= 0)
2650 return; /* Still not fully idle. */
2652 if ((rdtp
->dynticks_idle_nesting
& DYNTICK_TASK_NEST_MASK
) ==
2653 DYNTICK_TASK_NEST_VALUE
) {
2654 rdtp
->dynticks_idle_nesting
= 0;
2656 rdtp
->dynticks_idle_nesting
-= DYNTICK_TASK_NEST_VALUE
;
2657 WARN_ON_ONCE(rdtp
->dynticks_idle_nesting
< 0);
2658 return; /* Still not fully idle. */
2662 /* Record start of fully idle period. */
2664 ACCESS_ONCE(rdtp
->dynticks_idle_jiffies
) = j
;
2665 smp_mb__before_atomic();
2666 atomic_inc(&rdtp
->dynticks_idle
);
2667 smp_mb__after_atomic();
2668 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks_idle
) & 0x1);
2672 * Unconditionally force exit from full system-idle state. This is
2673 * invoked when a normal CPU exits idle, but must be called separately
2674 * for the timekeeping CPU (tick_do_timer_cpu). The reason for this
2675 * is that the timekeeping CPU is permitted to take scheduling-clock
2676 * interrupts while the system is in system-idle state, and of course
2677 * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
2678 * interrupt from any other type of interrupt.
2680 void rcu_sysidle_force_exit(void)
2682 int oldstate
= ACCESS_ONCE(full_sysidle_state
);
2686 * Each pass through the following loop attempts to exit full
2687 * system-idle state. If contention proves to be a problem,
2688 * a trylock-based contention tree could be used here.
2690 while (oldstate
> RCU_SYSIDLE_SHORT
) {
2691 newoldstate
= cmpxchg(&full_sysidle_state
,
2692 oldstate
, RCU_SYSIDLE_NOT
);
2693 if (oldstate
== newoldstate
&&
2694 oldstate
== RCU_SYSIDLE_FULL_NOTED
) {
2695 rcu_kick_nohz_cpu(tick_do_timer_cpu
);
2696 return; /* We cleared it, done! */
2698 oldstate
= newoldstate
;
2700 smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
2704 * Invoked to note entry to irq or task transition from idle. Note that
2705 * usermode execution does -not- count as idle here! The caller must
2706 * have disabled interrupts.
2708 static void rcu_sysidle_exit(int irq
)
2710 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
2712 /* If there are no nohz_full= CPUs, no need to track this. */
2713 if (!tick_nohz_full_enabled())
2716 /* Adjust nesting, check for already non-idle. */
2718 rdtp
->dynticks_idle_nesting
++;
2719 WARN_ON_ONCE(rdtp
->dynticks_idle_nesting
<= 0);
2720 if (rdtp
->dynticks_idle_nesting
!= 1)
2721 return; /* Already non-idle. */
2724 * Allow for irq misnesting. Yes, it really is possible
2725 * to enter an irq handler then never leave it, and maybe
2726 * also vice versa. Handle both possibilities.
2728 if (rdtp
->dynticks_idle_nesting
& DYNTICK_TASK_NEST_MASK
) {
2729 rdtp
->dynticks_idle_nesting
+= DYNTICK_TASK_NEST_VALUE
;
2730 WARN_ON_ONCE(rdtp
->dynticks_idle_nesting
<= 0);
2731 return; /* Already non-idle. */
2733 rdtp
->dynticks_idle_nesting
= DYNTICK_TASK_EXIT_IDLE
;
2737 /* Record end of idle period. */
2738 smp_mb__before_atomic();
2739 atomic_inc(&rdtp
->dynticks_idle
);
2740 smp_mb__after_atomic();
2741 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks_idle
) & 0x1));
2744 * If we are the timekeeping CPU, we are permitted to be non-idle
2745 * during a system-idle state. This must be the case, because
2746 * the timekeeping CPU has to take scheduling-clock interrupts
2747 * during the time that the system is transitioning to full
2748 * system-idle state. This means that the timekeeping CPU must
2749 * invoke rcu_sysidle_force_exit() directly if it does anything
2750 * more than take a scheduling-clock interrupt.
2752 if (smp_processor_id() == tick_do_timer_cpu
)
2755 /* Update system-idle state: We are clearly no longer fully idle! */
2756 rcu_sysidle_force_exit();
2760 * Check to see if the current CPU is idle. Note that usermode execution
2761 * does not count as idle. The caller must have disabled interrupts.
2763 static void rcu_sysidle_check_cpu(struct rcu_data
*rdp
, bool *isidle
,
2764 unsigned long *maxj
)
2768 struct rcu_dynticks
*rdtp
= rdp
->dynticks
;
2770 /* If there are no nohz_full= CPUs, don't check system-wide idleness. */
2771 if (!tick_nohz_full_enabled())
2775 * If some other CPU has already reported non-idle, if this is
2776 * not the flavor of RCU that tracks sysidle state, or if this
2777 * is an offline or the timekeeping CPU, nothing to do.
2779 if (!*isidle
|| rdp
->rsp
!= rcu_state_p
||
2780 cpu_is_offline(rdp
->cpu
) || rdp
->cpu
== tick_do_timer_cpu
)
2782 if (rcu_gp_in_progress(rdp
->rsp
))
2783 WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu
);
2785 /* Pick up current idle and NMI-nesting counter and check. */
2786 cur
= atomic_read(&rdtp
->dynticks_idle
);
2788 *isidle
= false; /* We are not idle! */
2791 smp_mb(); /* Read counters before timestamps. */
2793 /* Pick up timestamps. */
2794 j
= ACCESS_ONCE(rdtp
->dynticks_idle_jiffies
);
2795 /* If this CPU entered idle more recently, update maxj timestamp. */
2796 if (ULONG_CMP_LT(*maxj
, j
))
2801 * Is this the flavor of RCU that is handling full-system idle?
2803 static bool is_sysidle_rcu_state(struct rcu_state
*rsp
)
2805 return rsp
== rcu_state_p
;
2809 * Return a delay in jiffies based on the number of CPUs, rcu_node
2810 * leaf fanout, and jiffies tick rate. The idea is to allow larger
2811 * systems more time to transition to full-idle state in order to
2812 * avoid the cache thrashing that otherwise occur on the state variable.
2813 * Really small systems (less than a couple of tens of CPUs) should
2814 * instead use a single global atomically incremented counter, and later
2815 * versions of this will automatically reconfigure themselves accordingly.
2817 static unsigned long rcu_sysidle_delay(void)
2819 if (nr_cpu_ids
<= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
)
2821 return DIV_ROUND_UP(nr_cpu_ids
* HZ
, rcu_fanout_leaf
* 1000);
2825 * Advance the full-system-idle state. This is invoked when all of
2826 * the non-timekeeping CPUs are idle.
2828 static void rcu_sysidle(unsigned long j
)
2830 /* Check the current state. */
2831 switch (ACCESS_ONCE(full_sysidle_state
)) {
2832 case RCU_SYSIDLE_NOT
:
2834 /* First time all are idle, so note a short idle period. */
2835 ACCESS_ONCE(full_sysidle_state
) = RCU_SYSIDLE_SHORT
;
2838 case RCU_SYSIDLE_SHORT
:
2841 * Idle for a bit, time to advance to next state?
2842 * cmpxchg failure means race with non-idle, let them win.
2844 if (ULONG_CMP_GE(jiffies
, j
+ rcu_sysidle_delay()))
2845 (void)cmpxchg(&full_sysidle_state
,
2846 RCU_SYSIDLE_SHORT
, RCU_SYSIDLE_LONG
);
2849 case RCU_SYSIDLE_LONG
:
2852 * Do an additional check pass before advancing to full.
2853 * cmpxchg failure means race with non-idle, let them win.
2855 if (ULONG_CMP_GE(jiffies
, j
+ rcu_sysidle_delay()))
2856 (void)cmpxchg(&full_sysidle_state
,
2857 RCU_SYSIDLE_LONG
, RCU_SYSIDLE_FULL
);
2866 * Found a non-idle non-timekeeping CPU, so kick the system-idle state
2867 * back to the beginning.
2869 static void rcu_sysidle_cancel(void)
2872 if (full_sysidle_state
> RCU_SYSIDLE_SHORT
)
2873 ACCESS_ONCE(full_sysidle_state
) = RCU_SYSIDLE_NOT
;
2877 * Update the sysidle state based on the results of a force-quiescent-state
2878 * scan of the CPUs' dyntick-idle state.
2880 static void rcu_sysidle_report(struct rcu_state
*rsp
, int isidle
,
2881 unsigned long maxj
, bool gpkt
)
2883 if (rsp
!= rcu_state_p
)
2884 return; /* Wrong flavor, ignore. */
2885 if (gpkt
&& nr_cpu_ids
<= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
)
2886 return; /* Running state machine from timekeeping CPU. */
2888 rcu_sysidle(maxj
); /* More idle! */
2890 rcu_sysidle_cancel(); /* Idle is over. */
2894 * Wrapper for rcu_sysidle_report() when called from the grace-period
2895 * kthread's context.
2897 static void rcu_sysidle_report_gp(struct rcu_state
*rsp
, int isidle
,
2900 /* If there are no nohz_full= CPUs, no need to track this. */
2901 if (!tick_nohz_full_enabled())
2904 rcu_sysidle_report(rsp
, isidle
, maxj
, true);
2907 /* Callback and function for forcing an RCU grace period. */
2908 struct rcu_sysidle_head
{
2913 static void rcu_sysidle_cb(struct rcu_head
*rhp
)
2915 struct rcu_sysidle_head
*rshp
;
2918 * The following memory barrier is needed to replace the
2919 * memory barriers that would normally be in the memory
2922 smp_mb(); /* grace period precedes setting inuse. */
2924 rshp
= container_of(rhp
, struct rcu_sysidle_head
, rh
);
2925 ACCESS_ONCE(rshp
->inuse
) = 0;
2929 * Check to see if the system is fully idle, other than the timekeeping CPU.
2930 * The caller must have disabled interrupts. This is not intended to be
2931 * called unless tick_nohz_full_enabled().
2933 bool rcu_sys_is_idle(void)
2935 static struct rcu_sysidle_head rsh
;
2936 int rss
= ACCESS_ONCE(full_sysidle_state
);
2938 if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu
))
2941 /* Handle small-system case by doing a full scan of CPUs. */
2942 if (nr_cpu_ids
<= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
) {
2943 int oldrss
= rss
- 1;
2946 * One pass to advance to each state up to _FULL.
2947 * Give up if any pass fails to advance the state.
2949 while (rss
< RCU_SYSIDLE_FULL
&& oldrss
< rss
) {
2952 unsigned long maxj
= jiffies
- ULONG_MAX
/ 4;
2953 struct rcu_data
*rdp
;
2955 /* Scan all the CPUs looking for nonidle CPUs. */
2956 for_each_possible_cpu(cpu
) {
2957 rdp
= per_cpu_ptr(rcu_state_p
->rda
, cpu
);
2958 rcu_sysidle_check_cpu(rdp
, &isidle
, &maxj
);
2962 rcu_sysidle_report(rcu_state_p
, isidle
, maxj
, false);
2964 rss
= ACCESS_ONCE(full_sysidle_state
);
2968 /* If this is the first observation of an idle period, record it. */
2969 if (rss
== RCU_SYSIDLE_FULL
) {
2970 rss
= cmpxchg(&full_sysidle_state
,
2971 RCU_SYSIDLE_FULL
, RCU_SYSIDLE_FULL_NOTED
);
2972 return rss
== RCU_SYSIDLE_FULL
;
2975 smp_mb(); /* ensure rss load happens before later caller actions. */
2977 /* If already fully idle, tell the caller (in case of races). */
2978 if (rss
== RCU_SYSIDLE_FULL_NOTED
)
2982 * If we aren't there yet, and a grace period is not in flight,
2983 * initiate a grace period. Either way, tell the caller that
2984 * we are not there yet. We use an xchg() rather than an assignment
2985 * to make up for the memory barriers that would otherwise be
2986 * provided by the memory allocator.
2988 if (nr_cpu_ids
> CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
&&
2989 !rcu_gp_in_progress(rcu_state_p
) &&
2990 !rsh
.inuse
&& xchg(&rsh
.inuse
, 1) == 0)
2991 call_rcu(&rsh
.rh
, rcu_sysidle_cb
);
2996 * Initialize dynticks sysidle state for CPUs coming online.
2998 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks
*rdtp
)
3000 rdtp
->dynticks_idle_nesting
= DYNTICK_TASK_NEST_VALUE
;
3003 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3005 static void rcu_sysidle_enter(int irq
)
3009 static void rcu_sysidle_exit(int irq
)
3013 static void rcu_sysidle_check_cpu(struct rcu_data
*rdp
, bool *isidle
,
3014 unsigned long *maxj
)
3018 static bool is_sysidle_rcu_state(struct rcu_state
*rsp
)
3023 static void rcu_sysidle_report_gp(struct rcu_state
*rsp
, int isidle
,
3028 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks
*rdtp
)
3032 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3035 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
3036 * grace-period kthread will do force_quiescent_state() processing?
3037 * The idea is to avoid waking up RCU core processing on such a
3038 * CPU unless the grace period has extended for too long.
3040 * This code relies on the fact that all NO_HZ_FULL CPUs are also
3041 * CONFIG_RCU_NOCB_CPU CPUs.
3043 static bool rcu_nohz_full_cpu(struct rcu_state
*rsp
)
3045 #ifdef CONFIG_NO_HZ_FULL
3046 if (tick_nohz_full_cpu(smp_processor_id()) &&
3047 (!rcu_gp_in_progress(rsp
) ||
3048 ULONG_CMP_LT(jiffies
, ACCESS_ONCE(rsp
->gp_start
) + HZ
)))
3050 #endif /* #ifdef CONFIG_NO_HZ_FULL */
3055 * Bind the grace-period kthread for the sysidle flavor of RCU to the
3058 static void rcu_bind_gp_kthread(void)
3060 int __maybe_unused cpu
;
3062 if (!tick_nohz_full_enabled())
3064 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
3065 cpu
= tick_do_timer_cpu
;
3066 if (cpu
>= 0 && cpu
< nr_cpu_ids
&& raw_smp_processor_id() != cpu
)
3067 set_cpus_allowed_ptr(current
, cpumask_of(cpu
));
3068 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3069 if (!is_housekeeping_cpu(raw_smp_processor_id()))
3070 housekeeping_affine(current
);
3071 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3074 /* Record the current task on dyntick-idle entry. */
3075 static void rcu_dynticks_task_enter(void)
3077 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
3078 ACCESS_ONCE(current
->rcu_tasks_idle_cpu
) = smp_processor_id();
3079 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
3082 /* Record no current task on dyntick-idle exit. */
3083 static void rcu_dynticks_task_exit(void)
3085 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
3086 ACCESS_ONCE(current
->rcu_tasks_idle_cpu
) = -1;
3087 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */