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 if (IS_ENABLED(CONFIG_RCU_TRACE
))
62 pr_info("\tRCU debugfs-based tracing is enabled.\n");
63 if ((IS_ENABLED(CONFIG_64BIT
) && CONFIG_RCU_FANOUT
!= 64) ||
64 (!IS_ENABLED(CONFIG_64BIT
) && CONFIG_RCU_FANOUT
!= 32))
65 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
67 if (IS_ENABLED(CONFIG_RCU_FANOUT_EXACT
))
68 pr_info("\tHierarchical RCU autobalancing is disabled.\n");
69 if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ
))
70 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
71 if (IS_ENABLED(CONFIG_PROVE_RCU
))
72 pr_info("\tRCU lockdep checking is enabled.\n");
73 if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_RUNNABLE
))
74 pr_info("\tRCU torture testing starts during boot.\n");
75 if (IS_ENABLED(CONFIG_RCU_CPU_STALL_INFO
))
76 pr_info("\tAdditional per-CPU info printed with stalls.\n");
77 if (NUM_RCU_LVL_4
!= 0)
78 pr_info("\tFour-level hierarchy is enabled.\n");
79 if (CONFIG_RCU_FANOUT_LEAF
!= 16)
80 pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
81 CONFIG_RCU_FANOUT_LEAF
);
82 if (rcu_fanout_leaf
!= CONFIG_RCU_FANOUT_LEAF
)
83 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf
);
84 if (nr_cpu_ids
!= NR_CPUS
)
85 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS
, nr_cpu_ids
);
86 if (IS_ENABLED(CONFIG_RCU_BOOST
))
87 pr_info("\tRCU kthread priority: %d.\n", kthread_prio
);
90 #ifdef CONFIG_PREEMPT_RCU
92 RCU_STATE_INITIALIZER(rcu_preempt
, 'p', call_rcu
);
93 static struct rcu_state
*rcu_state_p
= &rcu_preempt_state
;
95 static int rcu_preempted_readers_exp(struct rcu_node
*rnp
);
96 static void rcu_report_exp_rnp(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
100 * Tell them what RCU they are running.
102 static void __init
rcu_bootup_announce(void)
104 pr_info("Preemptible hierarchical RCU implementation.\n");
105 rcu_bootup_announce_oddness();
109 * Record a preemptible-RCU quiescent state for the specified CPU. Note
110 * that this just means that the task currently running on the CPU is
111 * not in a quiescent state. There might be any number of tasks blocked
112 * while in an RCU read-side critical section.
114 * As with the other rcu_*_qs() functions, callers to this function
115 * must disable preemption.
117 static void rcu_preempt_qs(void)
119 if (!__this_cpu_read(rcu_preempt_data
.passed_quiesce
)) {
120 trace_rcu_grace_period(TPS("rcu_preempt"),
121 __this_cpu_read(rcu_preempt_data
.gpnum
),
123 __this_cpu_write(rcu_preempt_data
.passed_quiesce
, 1);
124 barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
125 current
->rcu_read_unlock_special
.b
.need_qs
= false;
130 * We have entered the scheduler, and the current task might soon be
131 * context-switched away from. If this task is in an RCU read-side
132 * critical section, we will no longer be able to rely on the CPU to
133 * record that fact, so we enqueue the task on the blkd_tasks list.
134 * The task will dequeue itself when it exits the outermost enclosing
135 * RCU read-side critical section. Therefore, the current grace period
136 * cannot be permitted to complete until the blkd_tasks list entries
137 * predating the current grace period drain, in other words, until
138 * rnp->gp_tasks becomes NULL.
140 * Caller must disable preemption.
142 static void rcu_preempt_note_context_switch(void)
144 struct task_struct
*t
= current
;
146 struct rcu_data
*rdp
;
147 struct rcu_node
*rnp
;
149 if (t
->rcu_read_lock_nesting
> 0 &&
150 !t
->rcu_read_unlock_special
.b
.blocked
) {
152 /* Possibly blocking in an RCU read-side critical section. */
153 rdp
= this_cpu_ptr(rcu_preempt_state
.rda
);
155 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
156 smp_mb__after_unlock_lock();
157 t
->rcu_read_unlock_special
.b
.blocked
= true;
158 t
->rcu_blocked_node
= rnp
;
161 * If this CPU has already checked in, then this task
162 * will hold up the next grace period rather than the
163 * current grace period. Queue the task accordingly.
164 * If the task is queued for the current grace period
165 * (i.e., this CPU has not yet passed through a quiescent
166 * state for the current grace period), then as long
167 * as that task remains queued, the current grace period
168 * cannot end. Note that there is some uncertainty as
169 * to exactly when the current grace period started.
170 * We take a conservative approach, which can result
171 * in unnecessarily waiting on tasks that started very
172 * slightly after the current grace period began. C'est
175 * But first, note that the current CPU must still be
178 WARN_ON_ONCE((rdp
->grpmask
& rcu_rnp_online_cpus(rnp
)) == 0);
179 WARN_ON_ONCE(!list_empty(&t
->rcu_node_entry
));
180 if ((rnp
->qsmask
& rdp
->grpmask
) && rnp
->gp_tasks
!= NULL
) {
181 list_add(&t
->rcu_node_entry
, rnp
->gp_tasks
->prev
);
182 rnp
->gp_tasks
= &t
->rcu_node_entry
;
183 #ifdef CONFIG_RCU_BOOST
184 if (rnp
->boost_tasks
!= NULL
)
185 rnp
->boost_tasks
= rnp
->gp_tasks
;
186 #endif /* #ifdef CONFIG_RCU_BOOST */
188 list_add(&t
->rcu_node_entry
, &rnp
->blkd_tasks
);
189 if (rnp
->qsmask
& rdp
->grpmask
)
190 rnp
->gp_tasks
= &t
->rcu_node_entry
;
192 trace_rcu_preempt_task(rdp
->rsp
->name
,
194 (rnp
->qsmask
& rdp
->grpmask
)
197 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
198 } else if (t
->rcu_read_lock_nesting
< 0 &&
199 t
->rcu_read_unlock_special
.s
) {
202 * Complete exit from RCU read-side critical section on
203 * behalf of preempted instance of __rcu_read_unlock().
205 rcu_read_unlock_special(t
);
209 * Either we were not in an RCU read-side critical section to
210 * begin with, or we have now recorded that critical section
211 * globally. Either way, we can now note a quiescent state
212 * for this CPU. Again, if we were in an RCU read-side critical
213 * section, and if that critical section was blocking the current
214 * grace period, then the fact that the task has been enqueued
215 * means that we continue to block the current grace period.
221 * Check for preempted RCU readers blocking the current grace period
222 * for the specified rcu_node structure. If the caller needs a reliable
223 * answer, it must hold the rcu_node's ->lock.
225 static int rcu_preempt_blocked_readers_cgp(struct rcu_node
*rnp
)
227 return rnp
->gp_tasks
!= NULL
;
231 * Advance a ->blkd_tasks-list pointer to the next entry, instead
232 * returning NULL if at the end of the list.
234 static struct list_head
*rcu_next_node_entry(struct task_struct
*t
,
235 struct rcu_node
*rnp
)
237 struct list_head
*np
;
239 np
= t
->rcu_node_entry
.next
;
240 if (np
== &rnp
->blkd_tasks
)
246 * Return true if the specified rcu_node structure has tasks that were
247 * preempted within an RCU read-side critical section.
249 static bool rcu_preempt_has_tasks(struct rcu_node
*rnp
)
251 return !list_empty(&rnp
->blkd_tasks
);
255 * Handle special cases during rcu_read_unlock(), such as needing to
256 * notify RCU core processing or task having blocked during the RCU
257 * read-side critical section.
259 void rcu_read_unlock_special(struct task_struct
*t
)
265 struct list_head
*np
;
266 #ifdef CONFIG_RCU_BOOST
267 bool drop_boost_mutex
= false;
268 #endif /* #ifdef CONFIG_RCU_BOOST */
269 struct rcu_node
*rnp
;
270 union rcu_special special
;
272 /* NMI handlers cannot block and cannot safely manipulate state. */
276 local_irq_save(flags
);
279 * If RCU core is waiting for this CPU to exit critical section,
280 * let it know that we have done so. Because irqs are disabled,
281 * t->rcu_read_unlock_special cannot change.
283 special
= t
->rcu_read_unlock_special
;
284 if (special
.b
.need_qs
) {
286 t
->rcu_read_unlock_special
.b
.need_qs
= false;
287 if (!t
->rcu_read_unlock_special
.s
) {
288 local_irq_restore(flags
);
293 /* Hardware IRQ handlers cannot block, complain if they get here. */
294 if (in_irq() || in_serving_softirq()) {
295 lockdep_rcu_suspicious(__FILE__
, __LINE__
,
296 "rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n");
297 pr_alert("->rcu_read_unlock_special: %#x (b: %d, nq: %d)\n",
298 t
->rcu_read_unlock_special
.s
,
299 t
->rcu_read_unlock_special
.b
.blocked
,
300 t
->rcu_read_unlock_special
.b
.need_qs
);
301 local_irq_restore(flags
);
305 /* Clean up if blocked during RCU read-side critical section. */
306 if (special
.b
.blocked
) {
307 t
->rcu_read_unlock_special
.b
.blocked
= false;
310 * Remove this task from the list it blocked on. The
311 * task can migrate while we acquire the lock, but at
312 * most one time. So at most two passes through loop.
315 rnp
= t
->rcu_blocked_node
;
316 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
317 smp_mb__after_unlock_lock();
318 if (rnp
== t
->rcu_blocked_node
)
320 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
322 empty_norm
= !rcu_preempt_blocked_readers_cgp(rnp
);
323 empty_exp
= !rcu_preempted_readers_exp(rnp
);
324 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
325 np
= rcu_next_node_entry(t
, rnp
);
326 list_del_init(&t
->rcu_node_entry
);
327 t
->rcu_blocked_node
= NULL
;
328 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
330 if (&t
->rcu_node_entry
== rnp
->gp_tasks
)
332 if (&t
->rcu_node_entry
== rnp
->exp_tasks
)
334 #ifdef CONFIG_RCU_BOOST
335 if (&t
->rcu_node_entry
== rnp
->boost_tasks
)
336 rnp
->boost_tasks
= np
;
337 /* Snapshot ->boost_mtx ownership with rcu_node lock held. */
338 drop_boost_mutex
= rt_mutex_owner(&rnp
->boost_mtx
) == t
;
339 #endif /* #ifdef CONFIG_RCU_BOOST */
342 * If this was the last task on the current list, and if
343 * we aren't waiting on any CPUs, report the quiescent state.
344 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
345 * so we must take a snapshot of the expedited state.
347 empty_exp_now
= !rcu_preempted_readers_exp(rnp
);
348 if (!empty_norm
&& !rcu_preempt_blocked_readers_cgp(rnp
)) {
349 trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
356 rcu_report_unblock_qs_rnp(&rcu_preempt_state
,
359 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
362 #ifdef CONFIG_RCU_BOOST
363 /* Unboost if we were boosted. */
364 if (drop_boost_mutex
)
365 rt_mutex_unlock(&rnp
->boost_mtx
);
366 #endif /* #ifdef CONFIG_RCU_BOOST */
369 * If this was the last task on the expedited lists,
370 * then we need to report up the rcu_node hierarchy.
372 if (!empty_exp
&& empty_exp_now
)
373 rcu_report_exp_rnp(&rcu_preempt_state
, rnp
, true);
375 local_irq_restore(flags
);
380 * Dump detailed information for all tasks blocking the current RCU
381 * grace period on the specified rcu_node structure.
383 static void rcu_print_detail_task_stall_rnp(struct rcu_node
*rnp
)
386 struct task_struct
*t
;
388 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
389 if (!rcu_preempt_blocked_readers_cgp(rnp
)) {
390 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
393 t
= list_entry(rnp
->gp_tasks
,
394 struct task_struct
, rcu_node_entry
);
395 list_for_each_entry_continue(t
, &rnp
->blkd_tasks
, rcu_node_entry
)
397 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
401 * Dump detailed information for all tasks blocking the current RCU
404 static void rcu_print_detail_task_stall(struct rcu_state
*rsp
)
406 struct rcu_node
*rnp
= rcu_get_root(rsp
);
408 rcu_print_detail_task_stall_rnp(rnp
);
409 rcu_for_each_leaf_node(rsp
, rnp
)
410 rcu_print_detail_task_stall_rnp(rnp
);
413 #ifdef CONFIG_RCU_CPU_STALL_INFO
415 static void rcu_print_task_stall_begin(struct rcu_node
*rnp
)
417 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
418 rnp
->level
, rnp
->grplo
, rnp
->grphi
);
421 static void rcu_print_task_stall_end(void)
426 #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
428 static void rcu_print_task_stall_begin(struct rcu_node
*rnp
)
432 static void rcu_print_task_stall_end(void)
436 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
439 * Scan the current list of tasks blocked within RCU read-side critical
440 * sections, printing out the tid of each.
442 static int rcu_print_task_stall(struct rcu_node
*rnp
)
444 struct task_struct
*t
;
447 if (!rcu_preempt_blocked_readers_cgp(rnp
))
449 rcu_print_task_stall_begin(rnp
);
450 t
= list_entry(rnp
->gp_tasks
,
451 struct task_struct
, rcu_node_entry
);
452 list_for_each_entry_continue(t
, &rnp
->blkd_tasks
, rcu_node_entry
) {
453 pr_cont(" P%d", t
->pid
);
456 rcu_print_task_stall_end();
461 * Check that the list of blocked tasks for the newly completed grace
462 * period is in fact empty. It is a serious bug to complete a grace
463 * period that still has RCU readers blocked! This function must be
464 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
465 * must be held by the caller.
467 * Also, if there are blocked tasks on the list, they automatically
468 * block the newly created grace period, so set up ->gp_tasks accordingly.
470 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
472 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp
));
473 if (rcu_preempt_has_tasks(rnp
))
474 rnp
->gp_tasks
= rnp
->blkd_tasks
.next
;
475 WARN_ON_ONCE(rnp
->qsmask
);
479 * Check for a quiescent state from the current CPU. When a task blocks,
480 * the task is recorded in the corresponding CPU's rcu_node structure,
481 * which is checked elsewhere.
483 * Caller must disable hard irqs.
485 static void rcu_preempt_check_callbacks(void)
487 struct task_struct
*t
= current
;
489 if (t
->rcu_read_lock_nesting
== 0) {
493 if (t
->rcu_read_lock_nesting
> 0 &&
494 __this_cpu_read(rcu_preempt_data
.qs_pending
) &&
495 !__this_cpu_read(rcu_preempt_data
.passed_quiesce
))
496 t
->rcu_read_unlock_special
.b
.need_qs
= true;
499 #ifdef CONFIG_RCU_BOOST
501 static void rcu_preempt_do_callbacks(void)
503 rcu_do_batch(&rcu_preempt_state
, this_cpu_ptr(&rcu_preempt_data
));
506 #endif /* #ifdef CONFIG_RCU_BOOST */
509 * Queue a preemptible-RCU callback for invocation after a grace period.
511 void call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
513 __call_rcu(head
, func
, &rcu_preempt_state
, -1, 0);
515 EXPORT_SYMBOL_GPL(call_rcu
);
518 * synchronize_rcu - wait until a grace period has elapsed.
520 * Control will return to the caller some time after a full grace
521 * period has elapsed, in other words after all currently executing RCU
522 * read-side critical sections have completed. Note, however, that
523 * upon return from synchronize_rcu(), the caller might well be executing
524 * concurrently with new RCU read-side critical sections that began while
525 * synchronize_rcu() was waiting. RCU read-side critical sections are
526 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
528 * See the description of synchronize_sched() for more detailed information
529 * on memory ordering guarantees.
531 void synchronize_rcu(void)
533 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
534 !lock_is_held(&rcu_lock_map
) &&
535 !lock_is_held(&rcu_sched_lock_map
),
536 "Illegal synchronize_rcu() in RCU read-side critical section");
537 if (!rcu_scheduler_active
)
539 if (rcu_gp_is_expedited())
540 synchronize_rcu_expedited();
542 wait_rcu_gp(call_rcu
);
544 EXPORT_SYMBOL_GPL(synchronize_rcu
);
546 static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq
);
547 static unsigned long sync_rcu_preempt_exp_count
;
548 static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex
);
551 * Return non-zero if there are any tasks in RCU read-side critical
552 * sections blocking the current preemptible-RCU expedited grace period.
553 * If there is no preemptible-RCU expedited grace period currently in
554 * progress, returns zero unconditionally.
556 static int rcu_preempted_readers_exp(struct rcu_node
*rnp
)
558 return rnp
->exp_tasks
!= NULL
;
562 * return non-zero if there is no RCU expedited grace period in progress
563 * for the specified rcu_node structure, in other words, if all CPUs and
564 * tasks covered by the specified rcu_node structure have done their bit
565 * for the current expedited grace period. Works only for preemptible
566 * RCU -- other RCU implementation use other means.
568 * Caller must hold sync_rcu_preempt_exp_mutex.
570 static int sync_rcu_preempt_exp_done(struct rcu_node
*rnp
)
572 return !rcu_preempted_readers_exp(rnp
) &&
573 READ_ONCE(rnp
->expmask
) == 0;
577 * Report the exit from RCU read-side critical section for the last task
578 * that queued itself during or before the current expedited preemptible-RCU
579 * grace period. This event is reported either to the rcu_node structure on
580 * which the task was queued or to one of that rcu_node structure's ancestors,
581 * recursively up the tree. (Calm down, calm down, we do the recursion
584 * Caller must hold sync_rcu_preempt_exp_mutex.
586 static void rcu_report_exp_rnp(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
592 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
593 smp_mb__after_unlock_lock();
595 if (!sync_rcu_preempt_exp_done(rnp
)) {
596 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
599 if (rnp
->parent
== NULL
) {
600 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
602 smp_mb(); /* EGP done before wake_up(). */
603 wake_up(&sync_rcu_preempt_exp_wq
);
608 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
610 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
611 smp_mb__after_unlock_lock();
612 rnp
->expmask
&= ~mask
;
617 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
618 * grace period for the specified rcu_node structure, phase 1. If there
619 * are such tasks, set the ->expmask bits up the rcu_node tree and also
620 * set the ->expmask bits on the leaf rcu_node structures to tell phase 2
621 * that work is needed here.
623 * Caller must hold sync_rcu_preempt_exp_mutex.
626 sync_rcu_preempt_exp_init1(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
630 struct rcu_node
*rnp_up
;
632 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
633 smp_mb__after_unlock_lock();
634 WARN_ON_ONCE(rnp
->expmask
);
635 WARN_ON_ONCE(rnp
->exp_tasks
);
636 if (!rcu_preempt_has_tasks(rnp
)) {
637 /* No blocked tasks, nothing to do. */
638 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
641 /* Call for Phase 2 and propagate ->expmask bits up the tree. */
644 while (rnp_up
->parent
) {
645 mask
= rnp_up
->grpmask
;
646 rnp_up
= rnp_up
->parent
;
647 if (rnp_up
->expmask
& mask
)
649 raw_spin_lock(&rnp_up
->lock
); /* irqs already off */
650 smp_mb__after_unlock_lock();
651 rnp_up
->expmask
|= mask
;
652 raw_spin_unlock(&rnp_up
->lock
); /* irqs still off */
654 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
658 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
659 * grace period for the specified rcu_node structure, phase 2. If the
660 * leaf rcu_node structure has its ->expmask field set, check for tasks.
661 * If there are some, clear ->expmask and set ->exp_tasks accordingly,
662 * then initiate RCU priority boosting. Otherwise, clear ->expmask and
663 * invoke rcu_report_exp_rnp() to clear out the upper-level ->expmask bits,
664 * enabling rcu_read_unlock_special() to do the bit-clearing.
666 * Caller must hold sync_rcu_preempt_exp_mutex.
669 sync_rcu_preempt_exp_init2(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
673 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
674 smp_mb__after_unlock_lock();
676 /* Phase 1 didn't do anything, so Phase 2 doesn't either. */
677 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
681 /* Phase 1 is over. */
685 * If there are still blocked tasks, set up ->exp_tasks so that
686 * rcu_read_unlock_special() will wake us and then boost them.
688 if (rcu_preempt_has_tasks(rnp
)) {
689 rnp
->exp_tasks
= rnp
->blkd_tasks
.next
;
690 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock */
694 /* No longer any blocked tasks, so undo bit setting. */
695 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
696 rcu_report_exp_rnp(rsp
, rnp
, false);
700 * synchronize_rcu_expedited - Brute-force RCU grace period
702 * Wait for an RCU-preempt grace period, but expedite it. The basic
703 * idea is to invoke synchronize_sched_expedited() to push all the tasks to
704 * the ->blkd_tasks lists and wait for this list to drain. This consumes
705 * significant time on all CPUs and is unfriendly to real-time workloads,
706 * so is thus not recommended for any sort of common-case code.
707 * In fact, if you are using synchronize_rcu_expedited() in a loop,
708 * please restructure your code to batch your updates, and then Use a
709 * single synchronize_rcu() instead.
711 void synchronize_rcu_expedited(void)
713 struct rcu_node
*rnp
;
714 struct rcu_state
*rsp
= &rcu_preempt_state
;
718 smp_mb(); /* Caller's modifications seen first by other CPUs. */
719 snap
= READ_ONCE(sync_rcu_preempt_exp_count
) + 1;
720 smp_mb(); /* Above access cannot bleed into critical section. */
723 * Block CPU-hotplug operations. This means that any CPU-hotplug
724 * operation that finds an rcu_node structure with tasks in the
725 * process of being boosted will know that all tasks blocking
726 * this expedited grace period will already be in the process of
727 * being boosted. This simplifies the process of moving tasks
728 * from leaf to root rcu_node structures.
730 if (!try_get_online_cpus()) {
731 /* CPU-hotplug operation in flight, fall back to normal GP. */
732 wait_rcu_gp(call_rcu
);
737 * Acquire lock, falling back to synchronize_rcu() if too many
738 * lock-acquisition failures. Of course, if someone does the
739 * expedited grace period for us, just leave.
741 while (!mutex_trylock(&sync_rcu_preempt_exp_mutex
)) {
742 if (ULONG_CMP_LT(snap
,
743 READ_ONCE(sync_rcu_preempt_exp_count
))) {
745 goto mb_ret
; /* Others did our work for us. */
747 if (trycount
++ < 10) {
748 udelay(trycount
* num_online_cpus());
751 wait_rcu_gp(call_rcu
);
755 if (ULONG_CMP_LT(snap
, READ_ONCE(sync_rcu_preempt_exp_count
))) {
757 goto unlock_mb_ret
; /* Others did our work for us. */
760 /* force all RCU readers onto ->blkd_tasks lists. */
761 synchronize_sched_expedited();
764 * Snapshot current state of ->blkd_tasks lists into ->expmask.
765 * Phase 1 sets bits and phase 2 permits rcu_read_unlock_special()
766 * to start clearing them. Doing this in one phase leads to
767 * strange races between setting and clearing bits, so just say "no"!
769 rcu_for_each_leaf_node(rsp
, rnp
)
770 sync_rcu_preempt_exp_init1(rsp
, rnp
);
771 rcu_for_each_leaf_node(rsp
, rnp
)
772 sync_rcu_preempt_exp_init2(rsp
, rnp
);
776 /* Wait for snapshotted ->blkd_tasks lists to drain. */
777 rnp
= rcu_get_root(rsp
);
778 wait_event(sync_rcu_preempt_exp_wq
,
779 sync_rcu_preempt_exp_done(rnp
));
781 /* Clean up and exit. */
782 smp_mb(); /* ensure expedited GP seen before counter increment. */
783 WRITE_ONCE(sync_rcu_preempt_exp_count
, 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 (READ_ONCE(rnp
->exp_tasks
) == NULL
&&
997 READ_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 READ_ONCE(rnp
->exp_tasks
) != NULL
||
1051 READ_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(READ_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
= READ_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 READ_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 (!READ_ONCE(rdp_leader
->nocb_kthread
))
1902 if (READ_ONCE(rdp_leader
->nocb_leader_sleep
) || force
) {
1903 /* Prior smp_mb__after_atomic() orders against prior enqueue. */
1904 WRITE_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
= READ_ONCE(rdp
->nocb_head
);
1938 rhp
= READ_ONCE(rdp
->nocb_gp_head
);
1940 rhp
= READ_ONCE(rdp
->nocb_follower_head
);
1942 /* Having no rcuo kthread but CBs after scheduler starts is bad! */
1943 if (!READ_ONCE(rdp
->nocb_kthread
) && rhp
&&
1944 rcu_scheduler_fully_active
) {
1945 /* RCU callback enqueued before CPU first came online??? */
1946 pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
1950 #endif /* #ifdef CONFIG_PROVE_RCU */
1956 * Enqueue the specified string of rcu_head structures onto the specified
1957 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
1958 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
1959 * counts are supplied by rhcount and rhcount_lazy.
1961 * If warranted, also wake up the kthread servicing this CPUs queues.
1963 static void __call_rcu_nocb_enqueue(struct rcu_data
*rdp
,
1964 struct rcu_head
*rhp
,
1965 struct rcu_head
**rhtp
,
1966 int rhcount
, int rhcount_lazy
,
1967 unsigned long flags
)
1970 struct rcu_head
**old_rhpp
;
1971 struct task_struct
*t
;
1973 /* Enqueue the callback on the nocb list and update counts. */
1974 atomic_long_add(rhcount
, &rdp
->nocb_q_count
);
1975 /* rcu_barrier() relies on ->nocb_q_count add before xchg. */
1976 old_rhpp
= xchg(&rdp
->nocb_tail
, rhtp
);
1977 WRITE_ONCE(*old_rhpp
, rhp
);
1978 atomic_long_add(rhcount_lazy
, &rdp
->nocb_q_count_lazy
);
1979 smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
1981 /* If we are not being polled and there is a kthread, awaken it ... */
1982 t
= READ_ONCE(rdp
->nocb_kthread
);
1983 if (rcu_nocb_poll
|| !t
) {
1984 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
1985 TPS("WakeNotPoll"));
1988 len
= atomic_long_read(&rdp
->nocb_q_count
);
1989 if (old_rhpp
== &rdp
->nocb_head
) {
1990 if (!irqs_disabled_flags(flags
)) {
1991 /* ... if queue was empty ... */
1992 wake_nocb_leader(rdp
, false);
1993 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
1996 rdp
->nocb_defer_wakeup
= RCU_NOGP_WAKE
;
1997 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
1998 TPS("WakeEmptyIsDeferred"));
2000 rdp
->qlen_last_fqs_check
= 0;
2001 } else if (len
> rdp
->qlen_last_fqs_check
+ qhimark
) {
2002 /* ... or if many callbacks queued. */
2003 if (!irqs_disabled_flags(flags
)) {
2004 wake_nocb_leader(rdp
, true);
2005 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2008 rdp
->nocb_defer_wakeup
= RCU_NOGP_WAKE_FORCE
;
2009 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2010 TPS("WakeOvfIsDeferred"));
2012 rdp
->qlen_last_fqs_check
= LONG_MAX
/ 2;
2014 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, TPS("WakeNot"));
2020 * This is a helper for __call_rcu(), which invokes this when the normal
2021 * callback queue is inoperable. If this is not a no-CBs CPU, this
2022 * function returns failure back to __call_rcu(), which can complain
2025 * Otherwise, this function queues the callback where the corresponding
2026 * "rcuo" kthread can find it.
2028 static bool __call_rcu_nocb(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
2029 bool lazy
, unsigned long flags
)
2032 if (!rcu_is_nocb_cpu(rdp
->cpu
))
2034 __call_rcu_nocb_enqueue(rdp
, rhp
, &rhp
->next
, 1, lazy
, flags
);
2035 if (__is_kfree_rcu_offset((unsigned long)rhp
->func
))
2036 trace_rcu_kfree_callback(rdp
->rsp
->name
, rhp
,
2037 (unsigned long)rhp
->func
,
2038 -atomic_long_read(&rdp
->nocb_q_count_lazy
),
2039 -atomic_long_read(&rdp
->nocb_q_count
));
2041 trace_rcu_callback(rdp
->rsp
->name
, rhp
,
2042 -atomic_long_read(&rdp
->nocb_q_count_lazy
),
2043 -atomic_long_read(&rdp
->nocb_q_count
));
2046 * If called from an extended quiescent state with interrupts
2047 * disabled, invoke the RCU core in order to allow the idle-entry
2048 * deferred-wakeup check to function.
2050 if (irqs_disabled_flags(flags
) &&
2051 !rcu_is_watching() &&
2052 cpu_online(smp_processor_id()))
2059 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2062 static bool __maybe_unused
rcu_nocb_adopt_orphan_cbs(struct rcu_state
*rsp
,
2063 struct rcu_data
*rdp
,
2064 unsigned long flags
)
2066 long ql
= rsp
->qlen
;
2067 long qll
= rsp
->qlen_lazy
;
2069 /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
2070 if (!rcu_is_nocb_cpu(smp_processor_id()))
2075 /* First, enqueue the donelist, if any. This preserves CB ordering. */
2076 if (rsp
->orphan_donelist
!= NULL
) {
2077 __call_rcu_nocb_enqueue(rdp
, rsp
->orphan_donelist
,
2078 rsp
->orphan_donetail
, ql
, qll
, flags
);
2080 rsp
->orphan_donelist
= NULL
;
2081 rsp
->orphan_donetail
= &rsp
->orphan_donelist
;
2083 if (rsp
->orphan_nxtlist
!= NULL
) {
2084 __call_rcu_nocb_enqueue(rdp
, rsp
->orphan_nxtlist
,
2085 rsp
->orphan_nxttail
, ql
, qll
, flags
);
2087 rsp
->orphan_nxtlist
= NULL
;
2088 rsp
->orphan_nxttail
= &rsp
->orphan_nxtlist
;
2094 * If necessary, kick off a new grace period, and either way wait
2095 * for a subsequent grace period to complete.
2097 static void rcu_nocb_wait_gp(struct rcu_data
*rdp
)
2101 unsigned long flags
;
2103 struct rcu_node
*rnp
= rdp
->mynode
;
2105 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2106 smp_mb__after_unlock_lock();
2107 needwake
= rcu_start_future_gp(rnp
, rdp
, &c
);
2108 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2110 rcu_gp_kthread_wake(rdp
->rsp
);
2113 * Wait for the grace period. Do so interruptibly to avoid messing
2114 * up the load average.
2116 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("StartWait"));
2118 wait_event_interruptible(
2119 rnp
->nocb_gp_wq
[c
& 0x1],
2120 (d
= ULONG_CMP_GE(READ_ONCE(rnp
->completed
), c
)));
2123 WARN_ON(signal_pending(current
));
2124 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("ResumeWait"));
2126 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("EndWait"));
2127 smp_mb(); /* Ensure that CB invocation happens after GP end. */
2131 * Leaders come here to wait for additional callbacks to show up.
2132 * This function does not return until callbacks appear.
2134 static void nocb_leader_wait(struct rcu_data
*my_rdp
)
2136 bool firsttime
= true;
2138 struct rcu_data
*rdp
;
2139 struct rcu_head
**tail
;
2143 /* Wait for callbacks to appear. */
2144 if (!rcu_nocb_poll
) {
2145 trace_rcu_nocb_wake(my_rdp
->rsp
->name
, my_rdp
->cpu
, "Sleep");
2146 wait_event_interruptible(my_rdp
->nocb_wq
,
2147 !READ_ONCE(my_rdp
->nocb_leader_sleep
));
2148 /* Memory barrier handled by smp_mb() calls below and repoll. */
2149 } else if (firsttime
) {
2150 firsttime
= false; /* Don't drown trace log with "Poll"! */
2151 trace_rcu_nocb_wake(my_rdp
->rsp
->name
, my_rdp
->cpu
, "Poll");
2155 * Each pass through the following loop checks a follower for CBs.
2156 * We are our own first follower. Any CBs found are moved to
2157 * nocb_gp_head, where they await a grace period.
2160 for (rdp
= my_rdp
; rdp
; rdp
= rdp
->nocb_next_follower
) {
2161 rdp
->nocb_gp_head
= READ_ONCE(rdp
->nocb_head
);
2162 if (!rdp
->nocb_gp_head
)
2163 continue; /* No CBs here, try next follower. */
2165 /* Move callbacks to wait-for-GP list, which is empty. */
2166 WRITE_ONCE(rdp
->nocb_head
, NULL
);
2167 rdp
->nocb_gp_tail
= xchg(&rdp
->nocb_tail
, &rdp
->nocb_head
);
2172 * If there were no callbacks, sleep a bit, rescan after a
2173 * memory barrier, and go retry.
2175 if (unlikely(!gotcbs
)) {
2177 trace_rcu_nocb_wake(my_rdp
->rsp
->name
, my_rdp
->cpu
,
2179 WARN_ON(signal_pending(current
));
2180 schedule_timeout_interruptible(1);
2182 /* Rescan in case we were a victim of memory ordering. */
2183 my_rdp
->nocb_leader_sleep
= true;
2184 smp_mb(); /* Ensure _sleep true before scan. */
2185 for (rdp
= my_rdp
; rdp
; rdp
= rdp
->nocb_next_follower
)
2186 if (READ_ONCE(rdp
->nocb_head
)) {
2187 /* Found CB, so short-circuit next wait. */
2188 my_rdp
->nocb_leader_sleep
= false;
2194 /* Wait for one grace period. */
2195 rcu_nocb_wait_gp(my_rdp
);
2198 * We left ->nocb_leader_sleep unset to reduce cache thrashing.
2199 * We set it now, but recheck for new callbacks while
2200 * traversing our follower list.
2202 my_rdp
->nocb_leader_sleep
= true;
2203 smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */
2205 /* Each pass through the following loop wakes a follower, if needed. */
2206 for (rdp
= my_rdp
; rdp
; rdp
= rdp
->nocb_next_follower
) {
2207 if (READ_ONCE(rdp
->nocb_head
))
2208 my_rdp
->nocb_leader_sleep
= false;/* No need to sleep.*/
2209 if (!rdp
->nocb_gp_head
)
2210 continue; /* No CBs, so no need to wake follower. */
2212 /* Append callbacks to follower's "done" list. */
2213 tail
= xchg(&rdp
->nocb_follower_tail
, rdp
->nocb_gp_tail
);
2214 *tail
= rdp
->nocb_gp_head
;
2215 smp_mb__after_atomic(); /* Store *tail before wakeup. */
2216 if (rdp
!= my_rdp
&& tail
== &rdp
->nocb_follower_head
) {
2218 * List was empty, wake up the follower.
2219 * Memory barriers supplied by atomic_long_add().
2221 wake_up(&rdp
->nocb_wq
);
2225 /* If we (the leader) don't have CBs, go wait some more. */
2226 if (!my_rdp
->nocb_follower_head
)
2231 * Followers come here to wait for additional callbacks to show up.
2232 * This function does not return until callbacks appear.
2234 static void nocb_follower_wait(struct rcu_data
*rdp
)
2236 bool firsttime
= true;
2239 if (!rcu_nocb_poll
) {
2240 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2242 wait_event_interruptible(rdp
->nocb_wq
,
2243 READ_ONCE(rdp
->nocb_follower_head
));
2244 } else if (firsttime
) {
2245 /* Don't drown trace log with "Poll"! */
2247 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, "Poll");
2249 if (smp_load_acquire(&rdp
->nocb_follower_head
)) {
2250 /* ^^^ Ensure CB invocation follows _head test. */
2254 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2256 WARN_ON(signal_pending(current
));
2257 schedule_timeout_interruptible(1);
2262 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
2263 * callbacks queued by the corresponding no-CBs CPU, however, there is
2264 * an optional leader-follower relationship so that the grace-period
2265 * kthreads don't have to do quite so many wakeups.
2267 static int rcu_nocb_kthread(void *arg
)
2270 struct rcu_head
*list
;
2271 struct rcu_head
*next
;
2272 struct rcu_head
**tail
;
2273 struct rcu_data
*rdp
= arg
;
2275 /* Each pass through this loop invokes one batch of callbacks */
2277 /* Wait for callbacks. */
2278 if (rdp
->nocb_leader
== rdp
)
2279 nocb_leader_wait(rdp
);
2281 nocb_follower_wait(rdp
);
2283 /* Pull the ready-to-invoke callbacks onto local list. */
2284 list
= READ_ONCE(rdp
->nocb_follower_head
);
2286 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, "WokeNonEmpty");
2287 WRITE_ONCE(rdp
->nocb_follower_head
, NULL
);
2288 tail
= xchg(&rdp
->nocb_follower_tail
, &rdp
->nocb_follower_head
);
2290 /* Each pass through the following loop invokes a callback. */
2291 trace_rcu_batch_start(rdp
->rsp
->name
,
2292 atomic_long_read(&rdp
->nocb_q_count_lazy
),
2293 atomic_long_read(&rdp
->nocb_q_count
), -1);
2297 /* Wait for enqueuing to complete, if needed. */
2298 while (next
== NULL
&& &list
->next
!= tail
) {
2299 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2301 schedule_timeout_interruptible(1);
2302 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2306 debug_rcu_head_unqueue(list
);
2308 if (__rcu_reclaim(rdp
->rsp
->name
, list
))
2314 trace_rcu_batch_end(rdp
->rsp
->name
, c
, !!list
, 0, 0, 1);
2315 smp_mb__before_atomic(); /* _add after CB invocation. */
2316 atomic_long_add(-c
, &rdp
->nocb_q_count
);
2317 atomic_long_add(-cl
, &rdp
->nocb_q_count_lazy
);
2318 rdp
->n_nocbs_invoked
+= c
;
2323 /* Is a deferred wakeup of rcu_nocb_kthread() required? */
2324 static int rcu_nocb_need_deferred_wakeup(struct rcu_data
*rdp
)
2326 return READ_ONCE(rdp
->nocb_defer_wakeup
);
2329 /* Do a deferred wakeup of rcu_nocb_kthread(). */
2330 static void do_nocb_deferred_wakeup(struct rcu_data
*rdp
)
2334 if (!rcu_nocb_need_deferred_wakeup(rdp
))
2336 ndw
= READ_ONCE(rdp
->nocb_defer_wakeup
);
2337 WRITE_ONCE(rdp
->nocb_defer_wakeup
, RCU_NOGP_WAKE_NOT
);
2338 wake_nocb_leader(rdp
, ndw
== RCU_NOGP_WAKE_FORCE
);
2339 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, TPS("DeferredWake"));
2342 void __init
rcu_init_nohz(void)
2345 bool need_rcu_nocb_mask
= true;
2346 struct rcu_state
*rsp
;
2348 #ifdef CONFIG_RCU_NOCB_CPU_NONE
2349 need_rcu_nocb_mask
= false;
2350 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
2352 #if defined(CONFIG_NO_HZ_FULL)
2353 if (tick_nohz_full_running
&& cpumask_weight(tick_nohz_full_mask
))
2354 need_rcu_nocb_mask
= true;
2355 #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2357 if (!have_rcu_nocb_mask
&& need_rcu_nocb_mask
) {
2358 if (!zalloc_cpumask_var(&rcu_nocb_mask
, GFP_KERNEL
)) {
2359 pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
2362 have_rcu_nocb_mask
= true;
2364 if (!have_rcu_nocb_mask
)
2367 #ifdef CONFIG_RCU_NOCB_CPU_ZERO
2368 pr_info("\tOffload RCU callbacks from CPU 0\n");
2369 cpumask_set_cpu(0, rcu_nocb_mask
);
2370 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
2371 #ifdef CONFIG_RCU_NOCB_CPU_ALL
2372 pr_info("\tOffload RCU callbacks from all CPUs\n");
2373 cpumask_copy(rcu_nocb_mask
, cpu_possible_mask
);
2374 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
2375 #if defined(CONFIG_NO_HZ_FULL)
2376 if (tick_nohz_full_running
)
2377 cpumask_or(rcu_nocb_mask
, rcu_nocb_mask
, tick_nohz_full_mask
);
2378 #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2380 if (!cpumask_subset(rcu_nocb_mask
, cpu_possible_mask
)) {
2381 pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
2382 cpumask_and(rcu_nocb_mask
, cpu_possible_mask
,
2385 pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
2386 cpumask_pr_args(rcu_nocb_mask
));
2388 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
2390 for_each_rcu_flavor(rsp
) {
2391 for_each_cpu(cpu
, rcu_nocb_mask
)
2392 init_nocb_callback_list(per_cpu_ptr(rsp
->rda
, cpu
));
2393 rcu_organize_nocb_kthreads(rsp
);
2397 /* Initialize per-rcu_data variables for no-CBs CPUs. */
2398 static void __init
rcu_boot_init_nocb_percpu_data(struct rcu_data
*rdp
)
2400 rdp
->nocb_tail
= &rdp
->nocb_head
;
2401 init_waitqueue_head(&rdp
->nocb_wq
);
2402 rdp
->nocb_follower_tail
= &rdp
->nocb_follower_head
;
2406 * If the specified CPU is a no-CBs CPU that does not already have its
2407 * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are
2408 * brought online out of order, this can require re-organizing the
2409 * leader-follower relationships.
2411 static void rcu_spawn_one_nocb_kthread(struct rcu_state
*rsp
, int cpu
)
2413 struct rcu_data
*rdp
;
2414 struct rcu_data
*rdp_last
;
2415 struct rcu_data
*rdp_old_leader
;
2416 struct rcu_data
*rdp_spawn
= per_cpu_ptr(rsp
->rda
, cpu
);
2417 struct task_struct
*t
;
2420 * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
2421 * then nothing to do.
2423 if (!rcu_is_nocb_cpu(cpu
) || rdp_spawn
->nocb_kthread
)
2426 /* If we didn't spawn the leader first, reorganize! */
2427 rdp_old_leader
= rdp_spawn
->nocb_leader
;
2428 if (rdp_old_leader
!= rdp_spawn
&& !rdp_old_leader
->nocb_kthread
) {
2430 rdp
= rdp_old_leader
;
2432 rdp
->nocb_leader
= rdp_spawn
;
2433 if (rdp_last
&& rdp
!= rdp_spawn
)
2434 rdp_last
->nocb_next_follower
= rdp
;
2435 if (rdp
== rdp_spawn
) {
2436 rdp
= rdp
->nocb_next_follower
;
2439 rdp
= rdp
->nocb_next_follower
;
2440 rdp_last
->nocb_next_follower
= NULL
;
2443 rdp_spawn
->nocb_next_follower
= rdp_old_leader
;
2446 /* Spawn the kthread for this CPU and RCU flavor. */
2447 t
= kthread_run(rcu_nocb_kthread
, rdp_spawn
,
2448 "rcuo%c/%d", rsp
->abbr
, cpu
);
2450 WRITE_ONCE(rdp_spawn
->nocb_kthread
, t
);
2454 * If the specified CPU is a no-CBs CPU that does not already have its
2455 * rcuo kthreads, spawn them.
2457 static void rcu_spawn_all_nocb_kthreads(int cpu
)
2459 struct rcu_state
*rsp
;
2461 if (rcu_scheduler_fully_active
)
2462 for_each_rcu_flavor(rsp
)
2463 rcu_spawn_one_nocb_kthread(rsp
, cpu
);
2467 * Once the scheduler is running, spawn rcuo kthreads for all online
2468 * no-CBs CPUs. This assumes that the early_initcall()s happen before
2469 * non-boot CPUs come online -- if this changes, we will need to add
2470 * some mutual exclusion.
2472 static void __init
rcu_spawn_nocb_kthreads(void)
2476 for_each_online_cpu(cpu
)
2477 rcu_spawn_all_nocb_kthreads(cpu
);
2480 /* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */
2481 static int rcu_nocb_leader_stride
= -1;
2482 module_param(rcu_nocb_leader_stride
, int, 0444);
2485 * Initialize leader-follower relationships for all no-CBs CPU.
2487 static void __init
rcu_organize_nocb_kthreads(struct rcu_state
*rsp
)
2490 int ls
= rcu_nocb_leader_stride
;
2491 int nl
= 0; /* Next leader. */
2492 struct rcu_data
*rdp
;
2493 struct rcu_data
*rdp_leader
= NULL
; /* Suppress misguided gcc warn. */
2494 struct rcu_data
*rdp_prev
= NULL
;
2496 if (!have_rcu_nocb_mask
)
2499 ls
= int_sqrt(nr_cpu_ids
);
2500 rcu_nocb_leader_stride
= ls
;
2504 * Each pass through this loop sets up one rcu_data structure and
2505 * spawns one rcu_nocb_kthread().
2507 for_each_cpu(cpu
, rcu_nocb_mask
) {
2508 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2509 if (rdp
->cpu
>= nl
) {
2510 /* New leader, set up for followers & next leader. */
2511 nl
= DIV_ROUND_UP(rdp
->cpu
+ 1, ls
) * ls
;
2512 rdp
->nocb_leader
= rdp
;
2515 /* Another follower, link to previous leader. */
2516 rdp
->nocb_leader
= rdp_leader
;
2517 rdp_prev
->nocb_next_follower
= rdp
;
2523 /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2524 static bool init_nocb_callback_list(struct rcu_data
*rdp
)
2526 if (!rcu_is_nocb_cpu(rdp
->cpu
))
2529 /* If there are early-boot callbacks, move them to nocb lists. */
2531 rdp
->nocb_head
= rdp
->nxtlist
;
2532 rdp
->nocb_tail
= rdp
->nxttail
[RCU_NEXT_TAIL
];
2533 atomic_long_set(&rdp
->nocb_q_count
, rdp
->qlen
);
2534 atomic_long_set(&rdp
->nocb_q_count_lazy
, rdp
->qlen_lazy
);
2535 rdp
->nxtlist
= NULL
;
2539 rdp
->nxttail
[RCU_NEXT_TAIL
] = NULL
;
2543 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
2545 static bool rcu_nocb_cpu_needs_barrier(struct rcu_state
*rsp
, int cpu
)
2547 WARN_ON_ONCE(1); /* Should be dead code. */
2551 static void rcu_nocb_gp_cleanup(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
2555 static void rcu_nocb_gp_set(struct rcu_node
*rnp
, int nrq
)
2559 static void rcu_init_one_nocb(struct rcu_node
*rnp
)
2563 static bool __call_rcu_nocb(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
2564 bool lazy
, unsigned long flags
)
2569 static bool __maybe_unused
rcu_nocb_adopt_orphan_cbs(struct rcu_state
*rsp
,
2570 struct rcu_data
*rdp
,
2571 unsigned long flags
)
2576 static void __init
rcu_boot_init_nocb_percpu_data(struct rcu_data
*rdp
)
2580 static int rcu_nocb_need_deferred_wakeup(struct rcu_data
*rdp
)
2585 static void do_nocb_deferred_wakeup(struct rcu_data
*rdp
)
2589 static void rcu_spawn_all_nocb_kthreads(int cpu
)
2593 static void __init
rcu_spawn_nocb_kthreads(void)
2597 static bool init_nocb_callback_list(struct rcu_data
*rdp
)
2602 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2605 * An adaptive-ticks CPU can potentially execute in kernel mode for an
2606 * arbitrarily long period of time with the scheduling-clock tick turned
2607 * off. RCU will be paying attention to this CPU because it is in the
2608 * kernel, but the CPU cannot be guaranteed to be executing the RCU state
2609 * machine because the scheduling-clock tick has been disabled. Therefore,
2610 * if an adaptive-ticks CPU is failing to respond to the current grace
2611 * period and has not be idle from an RCU perspective, kick it.
2613 static void __maybe_unused
rcu_kick_nohz_cpu(int cpu
)
2615 #ifdef CONFIG_NO_HZ_FULL
2616 if (tick_nohz_full_cpu(cpu
))
2617 smp_send_reschedule(cpu
);
2618 #endif /* #ifdef CONFIG_NO_HZ_FULL */
2622 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
2624 static int full_sysidle_state
; /* Current system-idle state. */
2625 #define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */
2626 #define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */
2627 #define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */
2628 #define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */
2629 #define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */
2632 * Invoked to note exit from irq or task transition to idle. Note that
2633 * usermode execution does -not- count as idle here! After all, we want
2634 * to detect full-system idle states, not RCU quiescent states and grace
2635 * periods. The caller must have disabled interrupts.
2637 static void rcu_sysidle_enter(int irq
)
2640 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
2642 /* If there are no nohz_full= CPUs, no need to track this. */
2643 if (!tick_nohz_full_enabled())
2646 /* Adjust nesting, check for fully idle. */
2648 rdtp
->dynticks_idle_nesting
--;
2649 WARN_ON_ONCE(rdtp
->dynticks_idle_nesting
< 0);
2650 if (rdtp
->dynticks_idle_nesting
!= 0)
2651 return; /* Still not fully idle. */
2653 if ((rdtp
->dynticks_idle_nesting
& DYNTICK_TASK_NEST_MASK
) ==
2654 DYNTICK_TASK_NEST_VALUE
) {
2655 rdtp
->dynticks_idle_nesting
= 0;
2657 rdtp
->dynticks_idle_nesting
-= DYNTICK_TASK_NEST_VALUE
;
2658 WARN_ON_ONCE(rdtp
->dynticks_idle_nesting
< 0);
2659 return; /* Still not fully idle. */
2663 /* Record start of fully idle period. */
2665 WRITE_ONCE(rdtp
->dynticks_idle_jiffies
, j
);
2666 smp_mb__before_atomic();
2667 atomic_inc(&rdtp
->dynticks_idle
);
2668 smp_mb__after_atomic();
2669 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks_idle
) & 0x1);
2673 * Unconditionally force exit from full system-idle state. This is
2674 * invoked when a normal CPU exits idle, but must be called separately
2675 * for the timekeeping CPU (tick_do_timer_cpu). The reason for this
2676 * is that the timekeeping CPU is permitted to take scheduling-clock
2677 * interrupts while the system is in system-idle state, and of course
2678 * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
2679 * interrupt from any other type of interrupt.
2681 void rcu_sysidle_force_exit(void)
2683 int oldstate
= READ_ONCE(full_sysidle_state
);
2687 * Each pass through the following loop attempts to exit full
2688 * system-idle state. If contention proves to be a problem,
2689 * a trylock-based contention tree could be used here.
2691 while (oldstate
> RCU_SYSIDLE_SHORT
) {
2692 newoldstate
= cmpxchg(&full_sysidle_state
,
2693 oldstate
, RCU_SYSIDLE_NOT
);
2694 if (oldstate
== newoldstate
&&
2695 oldstate
== RCU_SYSIDLE_FULL_NOTED
) {
2696 rcu_kick_nohz_cpu(tick_do_timer_cpu
);
2697 return; /* We cleared it, done! */
2699 oldstate
= newoldstate
;
2701 smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
2705 * Invoked to note entry to irq or task transition from idle. Note that
2706 * usermode execution does -not- count as idle here! The caller must
2707 * have disabled interrupts.
2709 static void rcu_sysidle_exit(int irq
)
2711 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
2713 /* If there are no nohz_full= CPUs, no need to track this. */
2714 if (!tick_nohz_full_enabled())
2717 /* Adjust nesting, check for already non-idle. */
2719 rdtp
->dynticks_idle_nesting
++;
2720 WARN_ON_ONCE(rdtp
->dynticks_idle_nesting
<= 0);
2721 if (rdtp
->dynticks_idle_nesting
!= 1)
2722 return; /* Already non-idle. */
2725 * Allow for irq misnesting. Yes, it really is possible
2726 * to enter an irq handler then never leave it, and maybe
2727 * also vice versa. Handle both possibilities.
2729 if (rdtp
->dynticks_idle_nesting
& DYNTICK_TASK_NEST_MASK
) {
2730 rdtp
->dynticks_idle_nesting
+= DYNTICK_TASK_NEST_VALUE
;
2731 WARN_ON_ONCE(rdtp
->dynticks_idle_nesting
<= 0);
2732 return; /* Already non-idle. */
2734 rdtp
->dynticks_idle_nesting
= DYNTICK_TASK_EXIT_IDLE
;
2738 /* Record end of idle period. */
2739 smp_mb__before_atomic();
2740 atomic_inc(&rdtp
->dynticks_idle
);
2741 smp_mb__after_atomic();
2742 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks_idle
) & 0x1));
2745 * If we are the timekeeping CPU, we are permitted to be non-idle
2746 * during a system-idle state. This must be the case, because
2747 * the timekeeping CPU has to take scheduling-clock interrupts
2748 * during the time that the system is transitioning to full
2749 * system-idle state. This means that the timekeeping CPU must
2750 * invoke rcu_sysidle_force_exit() directly if it does anything
2751 * more than take a scheduling-clock interrupt.
2753 if (smp_processor_id() == tick_do_timer_cpu
)
2756 /* Update system-idle state: We are clearly no longer fully idle! */
2757 rcu_sysidle_force_exit();
2761 * Check to see if the current CPU is idle. Note that usermode execution
2762 * does not count as idle. The caller must have disabled interrupts,
2763 * and must be running on tick_do_timer_cpu.
2765 static void rcu_sysidle_check_cpu(struct rcu_data
*rdp
, bool *isidle
,
2766 unsigned long *maxj
)
2770 struct rcu_dynticks
*rdtp
= rdp
->dynticks
;
2772 /* If there are no nohz_full= CPUs, don't check system-wide idleness. */
2773 if (!tick_nohz_full_enabled())
2777 * If some other CPU has already reported non-idle, if this is
2778 * not the flavor of RCU that tracks sysidle state, or if this
2779 * is an offline or the timekeeping CPU, nothing to do.
2781 if (!*isidle
|| rdp
->rsp
!= rcu_state_p
||
2782 cpu_is_offline(rdp
->cpu
) || rdp
->cpu
== tick_do_timer_cpu
)
2784 /* Verify affinity of current kthread. */
2785 WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu
);
2787 /* Pick up current idle and NMI-nesting counter and check. */
2788 cur
= atomic_read(&rdtp
->dynticks_idle
);
2790 *isidle
= false; /* We are not idle! */
2793 smp_mb(); /* Read counters before timestamps. */
2795 /* Pick up timestamps. */
2796 j
= READ_ONCE(rdtp
->dynticks_idle_jiffies
);
2797 /* If this CPU entered idle more recently, update maxj timestamp. */
2798 if (ULONG_CMP_LT(*maxj
, j
))
2803 * Is this the flavor of RCU that is handling full-system idle?
2805 static bool is_sysidle_rcu_state(struct rcu_state
*rsp
)
2807 return rsp
== rcu_state_p
;
2811 * Return a delay in jiffies based on the number of CPUs, rcu_node
2812 * leaf fanout, and jiffies tick rate. The idea is to allow larger
2813 * systems more time to transition to full-idle state in order to
2814 * avoid the cache thrashing that otherwise occur on the state variable.
2815 * Really small systems (less than a couple of tens of CPUs) should
2816 * instead use a single global atomically incremented counter, and later
2817 * versions of this will automatically reconfigure themselves accordingly.
2819 static unsigned long rcu_sysidle_delay(void)
2821 if (nr_cpu_ids
<= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
)
2823 return DIV_ROUND_UP(nr_cpu_ids
* HZ
, rcu_fanout_leaf
* 1000);
2827 * Advance the full-system-idle state. This is invoked when all of
2828 * the non-timekeeping CPUs are idle.
2830 static void rcu_sysidle(unsigned long j
)
2832 /* Check the current state. */
2833 switch (READ_ONCE(full_sysidle_state
)) {
2834 case RCU_SYSIDLE_NOT
:
2836 /* First time all are idle, so note a short idle period. */
2837 WRITE_ONCE(full_sysidle_state
, RCU_SYSIDLE_SHORT
);
2840 case RCU_SYSIDLE_SHORT
:
2843 * Idle for a bit, time to advance to next state?
2844 * cmpxchg failure means race with non-idle, let them win.
2846 if (ULONG_CMP_GE(jiffies
, j
+ rcu_sysidle_delay()))
2847 (void)cmpxchg(&full_sysidle_state
,
2848 RCU_SYSIDLE_SHORT
, RCU_SYSIDLE_LONG
);
2851 case RCU_SYSIDLE_LONG
:
2854 * Do an additional check pass before advancing to full.
2855 * cmpxchg failure means race with non-idle, let them win.
2857 if (ULONG_CMP_GE(jiffies
, j
+ rcu_sysidle_delay()))
2858 (void)cmpxchg(&full_sysidle_state
,
2859 RCU_SYSIDLE_LONG
, RCU_SYSIDLE_FULL
);
2868 * Found a non-idle non-timekeeping CPU, so kick the system-idle state
2869 * back to the beginning.
2871 static void rcu_sysidle_cancel(void)
2874 if (full_sysidle_state
> RCU_SYSIDLE_SHORT
)
2875 WRITE_ONCE(full_sysidle_state
, RCU_SYSIDLE_NOT
);
2879 * Update the sysidle state based on the results of a force-quiescent-state
2880 * scan of the CPUs' dyntick-idle state.
2882 static void rcu_sysidle_report(struct rcu_state
*rsp
, int isidle
,
2883 unsigned long maxj
, bool gpkt
)
2885 if (rsp
!= rcu_state_p
)
2886 return; /* Wrong flavor, ignore. */
2887 if (gpkt
&& nr_cpu_ids
<= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
)
2888 return; /* Running state machine from timekeeping CPU. */
2890 rcu_sysidle(maxj
); /* More idle! */
2892 rcu_sysidle_cancel(); /* Idle is over. */
2896 * Wrapper for rcu_sysidle_report() when called from the grace-period
2897 * kthread's context.
2899 static void rcu_sysidle_report_gp(struct rcu_state
*rsp
, int isidle
,
2902 /* If there are no nohz_full= CPUs, no need to track this. */
2903 if (!tick_nohz_full_enabled())
2906 rcu_sysidle_report(rsp
, isidle
, maxj
, true);
2909 /* Callback and function for forcing an RCU grace period. */
2910 struct rcu_sysidle_head
{
2915 static void rcu_sysidle_cb(struct rcu_head
*rhp
)
2917 struct rcu_sysidle_head
*rshp
;
2920 * The following memory barrier is needed to replace the
2921 * memory barriers that would normally be in the memory
2924 smp_mb(); /* grace period precedes setting inuse. */
2926 rshp
= container_of(rhp
, struct rcu_sysidle_head
, rh
);
2927 WRITE_ONCE(rshp
->inuse
, 0);
2931 * Check to see if the system is fully idle, other than the timekeeping CPU.
2932 * The caller must have disabled interrupts. This is not intended to be
2933 * called unless tick_nohz_full_enabled().
2935 bool rcu_sys_is_idle(void)
2937 static struct rcu_sysidle_head rsh
;
2938 int rss
= READ_ONCE(full_sysidle_state
);
2940 if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu
))
2943 /* Handle small-system case by doing a full scan of CPUs. */
2944 if (nr_cpu_ids
<= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
) {
2945 int oldrss
= rss
- 1;
2948 * One pass to advance to each state up to _FULL.
2949 * Give up if any pass fails to advance the state.
2951 while (rss
< RCU_SYSIDLE_FULL
&& oldrss
< rss
) {
2954 unsigned long maxj
= jiffies
- ULONG_MAX
/ 4;
2955 struct rcu_data
*rdp
;
2957 /* Scan all the CPUs looking for nonidle CPUs. */
2958 for_each_possible_cpu(cpu
) {
2959 rdp
= per_cpu_ptr(rcu_state_p
->rda
, cpu
);
2960 rcu_sysidle_check_cpu(rdp
, &isidle
, &maxj
);
2964 rcu_sysidle_report(rcu_state_p
, isidle
, maxj
, false);
2966 rss
= READ_ONCE(full_sysidle_state
);
2970 /* If this is the first observation of an idle period, record it. */
2971 if (rss
== RCU_SYSIDLE_FULL
) {
2972 rss
= cmpxchg(&full_sysidle_state
,
2973 RCU_SYSIDLE_FULL
, RCU_SYSIDLE_FULL_NOTED
);
2974 return rss
== RCU_SYSIDLE_FULL
;
2977 smp_mb(); /* ensure rss load happens before later caller actions. */
2979 /* If already fully idle, tell the caller (in case of races). */
2980 if (rss
== RCU_SYSIDLE_FULL_NOTED
)
2984 * If we aren't there yet, and a grace period is not in flight,
2985 * initiate a grace period. Either way, tell the caller that
2986 * we are not there yet. We use an xchg() rather than an assignment
2987 * to make up for the memory barriers that would otherwise be
2988 * provided by the memory allocator.
2990 if (nr_cpu_ids
> CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
&&
2991 !rcu_gp_in_progress(rcu_state_p
) &&
2992 !rsh
.inuse
&& xchg(&rsh
.inuse
, 1) == 0)
2993 call_rcu(&rsh
.rh
, rcu_sysidle_cb
);
2998 * Initialize dynticks sysidle state for CPUs coming online.
3000 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks
*rdtp
)
3002 rdtp
->dynticks_idle_nesting
= DYNTICK_TASK_NEST_VALUE
;
3005 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3007 static void rcu_sysidle_enter(int irq
)
3011 static void rcu_sysidle_exit(int irq
)
3015 static void rcu_sysidle_check_cpu(struct rcu_data
*rdp
, bool *isidle
,
3016 unsigned long *maxj
)
3020 static bool is_sysidle_rcu_state(struct rcu_state
*rsp
)
3025 static void rcu_sysidle_report_gp(struct rcu_state
*rsp
, int isidle
,
3030 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks
*rdtp
)
3034 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3037 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
3038 * grace-period kthread will do force_quiescent_state() processing?
3039 * The idea is to avoid waking up RCU core processing on such a
3040 * CPU unless the grace period has extended for too long.
3042 * This code relies on the fact that all NO_HZ_FULL CPUs are also
3043 * CONFIG_RCU_NOCB_CPU CPUs.
3045 static bool rcu_nohz_full_cpu(struct rcu_state
*rsp
)
3047 #ifdef CONFIG_NO_HZ_FULL
3048 if (tick_nohz_full_cpu(smp_processor_id()) &&
3049 (!rcu_gp_in_progress(rsp
) ||
3050 ULONG_CMP_LT(jiffies
, READ_ONCE(rsp
->gp_start
) + HZ
)))
3052 #endif /* #ifdef CONFIG_NO_HZ_FULL */
3057 * Bind the grace-period kthread for the sysidle flavor of RCU to the
3060 static void rcu_bind_gp_kthread(void)
3062 int __maybe_unused cpu
;
3064 if (!tick_nohz_full_enabled())
3066 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
3067 cpu
= tick_do_timer_cpu
;
3068 if (cpu
>= 0 && cpu
< nr_cpu_ids
)
3069 set_cpus_allowed_ptr(current
, cpumask_of(cpu
));
3070 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3071 housekeeping_affine(current
);
3072 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
3075 /* Record the current task on dyntick-idle entry. */
3076 static void rcu_dynticks_task_enter(void)
3078 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
3079 WRITE_ONCE(current
->rcu_tasks_idle_cpu
, smp_processor_id());
3080 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
3083 /* Record no current task on dyntick-idle exit. */
3084 static void rcu_dynticks_task_exit(void)
3086 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
3087 WRITE_ONCE(current
->rcu_tasks_idle_cpu
, -1);
3088 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */