2 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
3 * Internal non-public definitions that provide either classic
4 * or preemptible semantics.
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
20 * Copyright Red Hat, 2009
21 * Copyright IBM Corporation, 2009
23 * Author: Ingo Molnar <mingo@elte.hu>
24 * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
27 #include <linux/delay.h>
28 #include <linux/stop_machine.h>
30 #define RCU_KTHREAD_PRIO 1
32 #ifdef CONFIG_RCU_BOOST
33 #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
35 #define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
39 * Check the RCU kernel configuration parameters and print informative
40 * messages about anything out of the ordinary. If you like #ifdef, you
41 * will love this function.
43 static void __init
rcu_bootup_announce_oddness(void)
45 #ifdef CONFIG_RCU_TRACE
46 printk(KERN_INFO
"\tRCU debugfs-based tracing is enabled.\n");
48 #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
49 printk(KERN_INFO
"\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
52 #ifdef CONFIG_RCU_FANOUT_EXACT
53 printk(KERN_INFO
"\tHierarchical RCU autobalancing is disabled.\n");
55 #ifdef CONFIG_RCU_FAST_NO_HZ
57 "\tRCU dyntick-idle grace-period acceleration is enabled.\n");
59 #ifdef CONFIG_PROVE_RCU
60 printk(KERN_INFO
"\tRCU lockdep checking is enabled.\n");
62 #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
63 printk(KERN_INFO
"\tRCU torture testing starts during boot.\n");
65 #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
66 printk(KERN_INFO
"\tVerbose stalled-CPUs detection is disabled.\n");
68 #if NUM_RCU_LVL_4 != 0
69 printk(KERN_INFO
"\tExperimental four-level hierarchy is enabled.\n");
73 #ifdef CONFIG_TREE_PREEMPT_RCU
75 struct rcu_state rcu_preempt_state
= RCU_STATE_INITIALIZER(rcu_preempt
);
76 DEFINE_PER_CPU(struct rcu_data
, rcu_preempt_data
);
77 static struct rcu_state
*rcu_state
= &rcu_preempt_state
;
79 static void rcu_read_unlock_special(struct task_struct
*t
);
80 static int rcu_preempted_readers_exp(struct rcu_node
*rnp
);
83 * Tell them what RCU they are running.
85 static void __init
rcu_bootup_announce(void)
87 printk(KERN_INFO
"Preemptible hierarchical RCU implementation.\n");
88 rcu_bootup_announce_oddness();
92 * Return the number of RCU-preempt batches processed thus far
93 * for debug and statistics.
95 long rcu_batches_completed_preempt(void)
97 return rcu_preempt_state
.completed
;
99 EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt
);
102 * Return the number of RCU batches processed thus far for debug & stats.
104 long rcu_batches_completed(void)
106 return rcu_batches_completed_preempt();
108 EXPORT_SYMBOL_GPL(rcu_batches_completed
);
111 * Force a quiescent state for preemptible RCU.
113 void rcu_force_quiescent_state(void)
115 force_quiescent_state(&rcu_preempt_state
, 0);
117 EXPORT_SYMBOL_GPL(rcu_force_quiescent_state
);
120 * Record a preemptible-RCU quiescent state for the specified CPU. Note
121 * that this just means that the task currently running on the CPU is
122 * not in a quiescent state. There might be any number of tasks blocked
123 * while in an RCU read-side critical section.
125 * Unlike the other rcu_*_qs() functions, callers to this function
126 * must disable irqs in order to protect the assignment to
127 * ->rcu_read_unlock_special.
129 static void rcu_preempt_qs(int cpu
)
131 struct rcu_data
*rdp
= &per_cpu(rcu_preempt_data
, cpu
);
133 rdp
->passed_quiesce_gpnum
= rdp
->gpnum
;
135 if (rdp
->passed_quiesce
== 0)
136 trace_rcu_grace_period("rcu_preempt", rdp
->gpnum
, "cpuqs");
137 rdp
->passed_quiesce
= 1;
138 current
->rcu_read_unlock_special
&= ~RCU_READ_UNLOCK_NEED_QS
;
142 * We have entered the scheduler, and the current task might soon be
143 * context-switched away from. If this task is in an RCU read-side
144 * critical section, we will no longer be able to rely on the CPU to
145 * record that fact, so we enqueue the task on the blkd_tasks list.
146 * The task will dequeue itself when it exits the outermost enclosing
147 * RCU read-side critical section. Therefore, the current grace period
148 * cannot be permitted to complete until the blkd_tasks list entries
149 * predating the current grace period drain, in other words, until
150 * rnp->gp_tasks becomes NULL.
152 * Caller must disable preemption.
154 static void rcu_preempt_note_context_switch(int cpu
)
156 struct task_struct
*t
= current
;
158 struct rcu_data
*rdp
;
159 struct rcu_node
*rnp
;
161 if (t
->rcu_read_lock_nesting
> 0 &&
162 (t
->rcu_read_unlock_special
& RCU_READ_UNLOCK_BLOCKED
) == 0) {
164 /* Possibly blocking in an RCU read-side critical section. */
165 rdp
= per_cpu_ptr(rcu_preempt_state
.rda
, cpu
);
167 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
168 t
->rcu_read_unlock_special
|= RCU_READ_UNLOCK_BLOCKED
;
169 t
->rcu_blocked_node
= rnp
;
172 * If this CPU has already checked in, then this task
173 * will hold up the next grace period rather than the
174 * current grace period. Queue the task accordingly.
175 * If the task is queued for the current grace period
176 * (i.e., this CPU has not yet passed through a quiescent
177 * state for the current grace period), then as long
178 * as that task remains queued, the current grace period
179 * cannot end. Note that there is some uncertainty as
180 * to exactly when the current grace period started.
181 * We take a conservative approach, which can result
182 * in unnecessarily waiting on tasks that started very
183 * slightly after the current grace period began. C'est
186 * But first, note that the current CPU must still be
189 WARN_ON_ONCE((rdp
->grpmask
& rnp
->qsmaskinit
) == 0);
190 WARN_ON_ONCE(!list_empty(&t
->rcu_node_entry
));
191 if ((rnp
->qsmask
& rdp
->grpmask
) && rnp
->gp_tasks
!= NULL
) {
192 list_add(&t
->rcu_node_entry
, rnp
->gp_tasks
->prev
);
193 rnp
->gp_tasks
= &t
->rcu_node_entry
;
194 #ifdef CONFIG_RCU_BOOST
195 if (rnp
->boost_tasks
!= NULL
)
196 rnp
->boost_tasks
= rnp
->gp_tasks
;
197 #endif /* #ifdef CONFIG_RCU_BOOST */
199 list_add(&t
->rcu_node_entry
, &rnp
->blkd_tasks
);
200 if (rnp
->qsmask
& rdp
->grpmask
)
201 rnp
->gp_tasks
= &t
->rcu_node_entry
;
203 trace_rcu_preempt_task(rdp
->rsp
->name
,
205 (rnp
->qsmask
& rdp
->grpmask
)
208 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
209 } else if (t
->rcu_read_lock_nesting
< 0 &&
210 t
->rcu_read_unlock_special
) {
213 * Complete exit from RCU read-side critical section on
214 * behalf of preempted instance of __rcu_read_unlock().
216 rcu_read_unlock_special(t
);
220 * Either we were not in an RCU read-side critical section to
221 * begin with, or we have now recorded that critical section
222 * globally. Either way, we can now note a quiescent state
223 * for this CPU. Again, if we were in an RCU read-side critical
224 * section, and if that critical section was blocking the current
225 * grace period, then the fact that the task has been enqueued
226 * means that we continue to block the current grace period.
228 local_irq_save(flags
);
230 local_irq_restore(flags
);
234 * Tree-preemptible RCU implementation for rcu_read_lock().
235 * Just increment ->rcu_read_lock_nesting, shared state will be updated
238 void __rcu_read_lock(void)
240 current
->rcu_read_lock_nesting
++;
241 barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */
243 EXPORT_SYMBOL_GPL(__rcu_read_lock
);
246 * Check for preempted RCU readers blocking the current grace period
247 * for the specified rcu_node structure. If the caller needs a reliable
248 * answer, it must hold the rcu_node's ->lock.
250 static int rcu_preempt_blocked_readers_cgp(struct rcu_node
*rnp
)
252 return rnp
->gp_tasks
!= NULL
;
256 * Record a quiescent state for all tasks that were previously queued
257 * on the specified rcu_node structure and that were blocking the current
258 * RCU grace period. The caller must hold the specified rnp->lock with
259 * irqs disabled, and this lock is released upon return, but irqs remain
262 static void rcu_report_unblock_qs_rnp(struct rcu_node
*rnp
, unsigned long flags
)
263 __releases(rnp
->lock
)
266 struct rcu_node
*rnp_p
;
268 if (rnp
->qsmask
!= 0 || rcu_preempt_blocked_readers_cgp(rnp
)) {
269 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
270 return; /* Still need more quiescent states! */
276 * Either there is only one rcu_node in the tree,
277 * or tasks were kicked up to root rcu_node due to
278 * CPUs going offline.
280 rcu_report_qs_rsp(&rcu_preempt_state
, flags
);
284 /* Report up the rest of the hierarchy. */
286 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
287 raw_spin_lock(&rnp_p
->lock
); /* irqs already disabled. */
288 rcu_report_qs_rnp(mask
, &rcu_preempt_state
, rnp_p
, flags
);
292 * Advance a ->blkd_tasks-list pointer to the next entry, instead
293 * returning NULL if at the end of the list.
295 static struct list_head
*rcu_next_node_entry(struct task_struct
*t
,
296 struct rcu_node
*rnp
)
298 struct list_head
*np
;
300 np
= t
->rcu_node_entry
.next
;
301 if (np
== &rnp
->blkd_tasks
)
307 * Handle special cases during rcu_read_unlock(), such as needing to
308 * notify RCU core processing or task having blocked during the RCU
309 * read-side critical section.
311 static noinline
void rcu_read_unlock_special(struct task_struct
*t
)
317 struct list_head
*np
;
318 #ifdef CONFIG_RCU_BOOST
319 struct rt_mutex
*rbmp
= NULL
;
320 #endif /* #ifdef CONFIG_RCU_BOOST */
321 struct rcu_node
*rnp
;
324 /* NMI handlers cannot block and cannot safely manipulate state. */
328 local_irq_save(flags
);
331 * If RCU core is waiting for this CPU to exit critical section,
332 * let it know that we have done so.
334 special
= t
->rcu_read_unlock_special
;
335 if (special
& RCU_READ_UNLOCK_NEED_QS
) {
336 rcu_preempt_qs(smp_processor_id());
339 /* Hardware IRQ handlers cannot block. */
340 if (in_irq() || in_serving_softirq()) {
341 local_irq_restore(flags
);
345 /* Clean up if blocked during RCU read-side critical section. */
346 if (special
& RCU_READ_UNLOCK_BLOCKED
) {
347 t
->rcu_read_unlock_special
&= ~RCU_READ_UNLOCK_BLOCKED
;
350 * Remove this task from the list it blocked on. The
351 * task can migrate while we acquire the lock, but at
352 * most one time. So at most two passes through loop.
355 rnp
= t
->rcu_blocked_node
;
356 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
357 if (rnp
== t
->rcu_blocked_node
)
359 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
361 empty
= !rcu_preempt_blocked_readers_cgp(rnp
);
362 empty_exp
= !rcu_preempted_readers_exp(rnp
);
363 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
364 np
= rcu_next_node_entry(t
, rnp
);
365 list_del_init(&t
->rcu_node_entry
);
366 t
->rcu_blocked_node
= NULL
;
367 trace_rcu_unlock_preempted_task("rcu_preempt",
369 if (&t
->rcu_node_entry
== rnp
->gp_tasks
)
371 if (&t
->rcu_node_entry
== rnp
->exp_tasks
)
373 #ifdef CONFIG_RCU_BOOST
374 if (&t
->rcu_node_entry
== rnp
->boost_tasks
)
375 rnp
->boost_tasks
= np
;
376 /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
377 if (t
->rcu_boost_mutex
) {
378 rbmp
= t
->rcu_boost_mutex
;
379 t
->rcu_boost_mutex
= NULL
;
381 #endif /* #ifdef CONFIG_RCU_BOOST */
384 * If this was the last task on the current list, and if
385 * we aren't waiting on any CPUs, report the quiescent state.
386 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
387 * so we must take a snapshot of the expedited state.
389 empty_exp_now
= !rcu_preempted_readers_exp(rnp
);
390 if (!empty
&& !rcu_preempt_blocked_readers_cgp(rnp
)) {
391 trace_rcu_quiescent_state_report("preempt_rcu",
398 rcu_report_unblock_qs_rnp(rnp
, flags
);
400 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
402 #ifdef CONFIG_RCU_BOOST
403 /* Unboost if we were boosted. */
405 rt_mutex_unlock(rbmp
);
406 #endif /* #ifdef CONFIG_RCU_BOOST */
409 * If this was the last task on the expedited lists,
410 * then we need to report up the rcu_node hierarchy.
412 if (!empty_exp
&& empty_exp_now
)
413 rcu_report_exp_rnp(&rcu_preempt_state
, rnp
, true);
415 local_irq_restore(flags
);
420 * Tree-preemptible RCU implementation for rcu_read_unlock().
421 * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
422 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
423 * invoke rcu_read_unlock_special() to clean up after a context switch
424 * in an RCU read-side critical section and other special cases.
426 void __rcu_read_unlock(void)
428 struct task_struct
*t
= current
;
430 if (t
->rcu_read_lock_nesting
!= 1)
431 --t
->rcu_read_lock_nesting
;
433 barrier(); /* critical section before exit code. */
434 t
->rcu_read_lock_nesting
= INT_MIN
;
435 barrier(); /* assign before ->rcu_read_unlock_special load */
436 if (unlikely(ACCESS_ONCE(t
->rcu_read_unlock_special
)))
437 rcu_read_unlock_special(t
);
438 barrier(); /* ->rcu_read_unlock_special load before assign */
439 t
->rcu_read_lock_nesting
= 0;
441 #ifdef CONFIG_PROVE_LOCKING
443 int rrln
= ACCESS_ONCE(t
->rcu_read_lock_nesting
);
445 WARN_ON_ONCE(rrln
< 0 && rrln
> INT_MIN
/ 2);
447 #endif /* #ifdef CONFIG_PROVE_LOCKING */
449 EXPORT_SYMBOL_GPL(__rcu_read_unlock
);
451 #ifdef CONFIG_RCU_CPU_STALL_VERBOSE
454 * Dump detailed information for all tasks blocking the current RCU
455 * grace period on the specified rcu_node structure.
457 static void rcu_print_detail_task_stall_rnp(struct rcu_node
*rnp
)
460 struct task_struct
*t
;
462 if (!rcu_preempt_blocked_readers_cgp(rnp
))
464 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
465 t
= list_entry(rnp
->gp_tasks
,
466 struct task_struct
, rcu_node_entry
);
467 list_for_each_entry_continue(t
, &rnp
->blkd_tasks
, rcu_node_entry
)
469 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
473 * Dump detailed information for all tasks blocking the current RCU
476 static void rcu_print_detail_task_stall(struct rcu_state
*rsp
)
478 struct rcu_node
*rnp
= rcu_get_root(rsp
);
480 rcu_print_detail_task_stall_rnp(rnp
);
481 rcu_for_each_leaf_node(rsp
, rnp
)
482 rcu_print_detail_task_stall_rnp(rnp
);
485 #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
487 static void rcu_print_detail_task_stall(struct rcu_state
*rsp
)
491 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
494 * Scan the current list of tasks blocked within RCU read-side critical
495 * sections, printing out the tid of each.
497 static int rcu_print_task_stall(struct rcu_node
*rnp
)
499 struct task_struct
*t
;
502 if (!rcu_preempt_blocked_readers_cgp(rnp
))
504 t
= list_entry(rnp
->gp_tasks
,
505 struct task_struct
, rcu_node_entry
);
506 list_for_each_entry_continue(t
, &rnp
->blkd_tasks
, rcu_node_entry
) {
507 printk(" P%d", t
->pid
);
514 * Suppress preemptible RCU's CPU stall warnings by pushing the
515 * time of the next stall-warning message comfortably far into the
518 static void rcu_preempt_stall_reset(void)
520 rcu_preempt_state
.jiffies_stall
= jiffies
+ ULONG_MAX
/ 2;
524 * Check that the list of blocked tasks for the newly completed grace
525 * period is in fact empty. It is a serious bug to complete a grace
526 * period that still has RCU readers blocked! This function must be
527 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
528 * must be held by the caller.
530 * Also, if there are blocked tasks on the list, they automatically
531 * block the newly created grace period, so set up ->gp_tasks accordingly.
533 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
535 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp
));
536 if (!list_empty(&rnp
->blkd_tasks
))
537 rnp
->gp_tasks
= rnp
->blkd_tasks
.next
;
538 WARN_ON_ONCE(rnp
->qsmask
);
541 #ifdef CONFIG_HOTPLUG_CPU
544 * Handle tasklist migration for case in which all CPUs covered by the
545 * specified rcu_node have gone offline. Move them up to the root
546 * rcu_node. The reason for not just moving them to the immediate
547 * parent is to remove the need for rcu_read_unlock_special() to
548 * make more than two attempts to acquire the target rcu_node's lock.
549 * Returns true if there were tasks blocking the current RCU grace
552 * Returns 1 if there was previously a task blocking the current grace
553 * period on the specified rcu_node structure.
555 * The caller must hold rnp->lock with irqs disabled.
557 static int rcu_preempt_offline_tasks(struct rcu_state
*rsp
,
558 struct rcu_node
*rnp
,
559 struct rcu_data
*rdp
)
561 struct list_head
*lp
;
562 struct list_head
*lp_root
;
564 struct rcu_node
*rnp_root
= rcu_get_root(rsp
);
565 struct task_struct
*t
;
567 if (rnp
== rnp_root
) {
568 WARN_ONCE(1, "Last CPU thought to be offlined?");
569 return 0; /* Shouldn't happen: at least one CPU online. */
572 /* If we are on an internal node, complain bitterly. */
573 WARN_ON_ONCE(rnp
!= rdp
->mynode
);
576 * Move tasks up to root rcu_node. Don't try to get fancy for
577 * this corner-case operation -- just put this node's tasks
578 * at the head of the root node's list, and update the root node's
579 * ->gp_tasks and ->exp_tasks pointers to those of this node's,
580 * if non-NULL. This might result in waiting for more tasks than
581 * absolutely necessary, but this is a good performance/complexity
584 if (rcu_preempt_blocked_readers_cgp(rnp
))
585 retval
|= RCU_OFL_TASKS_NORM_GP
;
586 if (rcu_preempted_readers_exp(rnp
))
587 retval
|= RCU_OFL_TASKS_EXP_GP
;
588 lp
= &rnp
->blkd_tasks
;
589 lp_root
= &rnp_root
->blkd_tasks
;
590 while (!list_empty(lp
)) {
591 t
= list_entry(lp
->next
, typeof(*t
), rcu_node_entry
);
592 raw_spin_lock(&rnp_root
->lock
); /* irqs already disabled */
593 list_del(&t
->rcu_node_entry
);
594 t
->rcu_blocked_node
= rnp_root
;
595 list_add(&t
->rcu_node_entry
, lp_root
);
596 if (&t
->rcu_node_entry
== rnp
->gp_tasks
)
597 rnp_root
->gp_tasks
= rnp
->gp_tasks
;
598 if (&t
->rcu_node_entry
== rnp
->exp_tasks
)
599 rnp_root
->exp_tasks
= rnp
->exp_tasks
;
600 #ifdef CONFIG_RCU_BOOST
601 if (&t
->rcu_node_entry
== rnp
->boost_tasks
)
602 rnp_root
->boost_tasks
= rnp
->boost_tasks
;
603 #endif /* #ifdef CONFIG_RCU_BOOST */
604 raw_spin_unlock(&rnp_root
->lock
); /* irqs still disabled */
607 #ifdef CONFIG_RCU_BOOST
608 /* In case root is being boosted and leaf is not. */
609 raw_spin_lock(&rnp_root
->lock
); /* irqs already disabled */
610 if (rnp_root
->boost_tasks
!= NULL
&&
611 rnp_root
->boost_tasks
!= rnp_root
->gp_tasks
)
612 rnp_root
->boost_tasks
= rnp_root
->gp_tasks
;
613 raw_spin_unlock(&rnp_root
->lock
); /* irqs still disabled */
614 #endif /* #ifdef CONFIG_RCU_BOOST */
616 rnp
->gp_tasks
= NULL
;
617 rnp
->exp_tasks
= NULL
;
622 * Do CPU-offline processing for preemptible RCU.
624 static void rcu_preempt_offline_cpu(int cpu
)
626 __rcu_offline_cpu(cpu
, &rcu_preempt_state
);
629 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
632 * Check for a quiescent state from the current CPU. When a task blocks,
633 * the task is recorded in the corresponding CPU's rcu_node structure,
634 * which is checked elsewhere.
636 * Caller must disable hard irqs.
638 static void rcu_preempt_check_callbacks(int cpu
)
640 struct task_struct
*t
= current
;
642 if (t
->rcu_read_lock_nesting
== 0) {
646 if (t
->rcu_read_lock_nesting
> 0 &&
647 per_cpu(rcu_preempt_data
, cpu
).qs_pending
)
648 t
->rcu_read_unlock_special
|= RCU_READ_UNLOCK_NEED_QS
;
652 * Process callbacks for preemptible RCU.
654 static void rcu_preempt_process_callbacks(void)
656 __rcu_process_callbacks(&rcu_preempt_state
,
657 &__get_cpu_var(rcu_preempt_data
));
660 #ifdef CONFIG_RCU_BOOST
662 static void rcu_preempt_do_callbacks(void)
664 rcu_do_batch(&rcu_preempt_state
, &__get_cpu_var(rcu_preempt_data
));
667 #endif /* #ifdef CONFIG_RCU_BOOST */
670 * Queue a preemptible-RCU callback for invocation after a grace period.
672 void call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
674 __call_rcu(head
, func
, &rcu_preempt_state
);
676 EXPORT_SYMBOL_GPL(call_rcu
);
679 * synchronize_rcu - wait until a grace period has elapsed.
681 * Control will return to the caller some time after a full grace
682 * period has elapsed, in other words after all currently executing RCU
683 * read-side critical sections have completed. Note, however, that
684 * upon return from synchronize_rcu(), the caller might well be executing
685 * concurrently with new RCU read-side critical sections that began while
686 * synchronize_rcu() was waiting. RCU read-side critical sections are
687 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
689 void synchronize_rcu(void)
691 if (!rcu_scheduler_active
)
693 wait_rcu_gp(call_rcu
);
695 EXPORT_SYMBOL_GPL(synchronize_rcu
);
697 static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq
);
698 static long sync_rcu_preempt_exp_count
;
699 static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex
);
702 * Return non-zero if there are any tasks in RCU read-side critical
703 * sections blocking the current preemptible-RCU expedited grace period.
704 * If there is no preemptible-RCU expedited grace period currently in
705 * progress, returns zero unconditionally.
707 static int rcu_preempted_readers_exp(struct rcu_node
*rnp
)
709 return rnp
->exp_tasks
!= NULL
;
713 * return non-zero if there is no RCU expedited grace period in progress
714 * for the specified rcu_node structure, in other words, if all CPUs and
715 * tasks covered by the specified rcu_node structure have done their bit
716 * for the current expedited grace period. Works only for preemptible
717 * RCU -- other RCU implementation use other means.
719 * Caller must hold sync_rcu_preempt_exp_mutex.
721 static int sync_rcu_preempt_exp_done(struct rcu_node
*rnp
)
723 return !rcu_preempted_readers_exp(rnp
) &&
724 ACCESS_ONCE(rnp
->expmask
) == 0;
728 * Report the exit from RCU read-side critical section for the last task
729 * that queued itself during or before the current expedited preemptible-RCU
730 * grace period. This event is reported either to the rcu_node structure on
731 * which the task was queued or to one of that rcu_node structure's ancestors,
732 * recursively up the tree. (Calm down, calm down, we do the recursion
735 * Most callers will set the "wake" flag, but the task initiating the
736 * expedited grace period need not wake itself.
738 * Caller must hold sync_rcu_preempt_exp_mutex.
740 static void rcu_report_exp_rnp(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
746 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
748 if (!sync_rcu_preempt_exp_done(rnp
)) {
749 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
752 if (rnp
->parent
== NULL
) {
753 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
755 wake_up(&sync_rcu_preempt_exp_wq
);
759 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
761 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
762 rnp
->expmask
&= ~mask
;
767 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
768 * grace period for the specified rcu_node structure. If there are no such
769 * tasks, report it up the rcu_node hierarchy.
771 * Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock.
774 sync_rcu_preempt_exp_init(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
779 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
780 if (list_empty(&rnp
->blkd_tasks
))
781 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
783 rnp
->exp_tasks
= rnp
->blkd_tasks
.next
;
784 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock */
788 rcu_report_exp_rnp(rsp
, rnp
, false); /* Don't wake self. */
792 * Wait for an rcu-preempt grace period, but expedite it. The basic idea
793 * is to invoke synchronize_sched_expedited() to push all the tasks to
794 * the ->blkd_tasks lists and wait for this list to drain.
796 void synchronize_rcu_expedited(void)
799 struct rcu_node
*rnp
;
800 struct rcu_state
*rsp
= &rcu_preempt_state
;
804 smp_mb(); /* Caller's modifications seen first by other CPUs. */
805 snap
= ACCESS_ONCE(sync_rcu_preempt_exp_count
) + 1;
806 smp_mb(); /* Above access cannot bleed into critical section. */
809 * Acquire lock, falling back to synchronize_rcu() if too many
810 * lock-acquisition failures. Of course, if someone does the
811 * expedited grace period for us, just leave.
813 while (!mutex_trylock(&sync_rcu_preempt_exp_mutex
)) {
815 udelay(trycount
* num_online_cpus());
820 if ((ACCESS_ONCE(sync_rcu_preempt_exp_count
) - snap
) > 0)
821 goto mb_ret
; /* Others did our work for us. */
823 if ((ACCESS_ONCE(sync_rcu_preempt_exp_count
) - snap
) > 0)
824 goto unlock_mb_ret
; /* Others did our work for us. */
826 /* force all RCU readers onto ->blkd_tasks lists. */
827 synchronize_sched_expedited();
829 raw_spin_lock_irqsave(&rsp
->onofflock
, flags
);
831 /* Initialize ->expmask for all non-leaf rcu_node structures. */
832 rcu_for_each_nonleaf_node_breadth_first(rsp
, rnp
) {
833 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
834 rnp
->expmask
= rnp
->qsmaskinit
;
835 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
838 /* Snapshot current state of ->blkd_tasks lists. */
839 rcu_for_each_leaf_node(rsp
, rnp
)
840 sync_rcu_preempt_exp_init(rsp
, rnp
);
841 if (NUM_RCU_NODES
> 1)
842 sync_rcu_preempt_exp_init(rsp
, rcu_get_root(rsp
));
844 raw_spin_unlock_irqrestore(&rsp
->onofflock
, flags
);
846 /* Wait for snapshotted ->blkd_tasks lists to drain. */
847 rnp
= rcu_get_root(rsp
);
848 wait_event(sync_rcu_preempt_exp_wq
,
849 sync_rcu_preempt_exp_done(rnp
));
851 /* Clean up and exit. */
852 smp_mb(); /* ensure expedited GP seen before counter increment. */
853 ACCESS_ONCE(sync_rcu_preempt_exp_count
)++;
855 mutex_unlock(&sync_rcu_preempt_exp_mutex
);
857 smp_mb(); /* ensure subsequent action seen after grace period. */
859 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited
);
862 * Check to see if there is any immediate preemptible-RCU-related work
865 static int rcu_preempt_pending(int cpu
)
867 return __rcu_pending(&rcu_preempt_state
,
868 &per_cpu(rcu_preempt_data
, cpu
));
872 * Does preemptible RCU need the CPU to stay out of dynticks mode?
874 static int rcu_preempt_needs_cpu(int cpu
)
876 return !!per_cpu(rcu_preempt_data
, cpu
).nxtlist
;
880 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
882 void rcu_barrier(void)
884 _rcu_barrier(&rcu_preempt_state
, call_rcu
);
886 EXPORT_SYMBOL_GPL(rcu_barrier
);
889 * Initialize preemptible RCU's per-CPU data.
891 static void __cpuinit
rcu_preempt_init_percpu_data(int cpu
)
893 rcu_init_percpu_data(cpu
, &rcu_preempt_state
, 1);
897 * Move preemptible RCU's callbacks from dying CPU to other online CPU.
899 static void rcu_preempt_send_cbs_to_online(void)
901 rcu_send_cbs_to_online(&rcu_preempt_state
);
905 * Initialize preemptible RCU's state structures.
907 static void __init
__rcu_init_preempt(void)
909 rcu_init_one(&rcu_preempt_state
, &rcu_preempt_data
);
913 * Check for a task exiting while in a preemptible-RCU read-side
914 * critical section, clean up if so. No need to issue warnings,
915 * as debug_check_no_locks_held() already does this if lockdep
920 struct task_struct
*t
= current
;
922 if (t
->rcu_read_lock_nesting
== 0)
924 t
->rcu_read_lock_nesting
= 1;
928 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
930 static struct rcu_state
*rcu_state
= &rcu_sched_state
;
933 * Tell them what RCU they are running.
935 static void __init
rcu_bootup_announce(void)
937 printk(KERN_INFO
"Hierarchical RCU implementation.\n");
938 rcu_bootup_announce_oddness();
942 * Return the number of RCU batches processed thus far for debug & stats.
944 long rcu_batches_completed(void)
946 return rcu_batches_completed_sched();
948 EXPORT_SYMBOL_GPL(rcu_batches_completed
);
951 * Force a quiescent state for RCU, which, because there is no preemptible
952 * RCU, becomes the same as rcu-sched.
954 void rcu_force_quiescent_state(void)
956 rcu_sched_force_quiescent_state();
958 EXPORT_SYMBOL_GPL(rcu_force_quiescent_state
);
961 * Because preemptible RCU does not exist, we never have to check for
962 * CPUs being in quiescent states.
964 static void rcu_preempt_note_context_switch(int cpu
)
969 * Because preemptible RCU does not exist, there are never any preempted
972 static int rcu_preempt_blocked_readers_cgp(struct rcu_node
*rnp
)
977 #ifdef CONFIG_HOTPLUG_CPU
979 /* Because preemptible RCU does not exist, no quieting of tasks. */
980 static void rcu_report_unblock_qs_rnp(struct rcu_node
*rnp
, unsigned long flags
)
982 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
985 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
988 * Because preemptible RCU does not exist, we never have to check for
989 * tasks blocked within RCU read-side critical sections.
991 static void rcu_print_detail_task_stall(struct rcu_state
*rsp
)
996 * Because preemptible RCU does not exist, we never have to check for
997 * tasks blocked within RCU read-side critical sections.
999 static int rcu_print_task_stall(struct rcu_node
*rnp
)
1005 * Because preemptible RCU does not exist, there is no need to suppress
1006 * its CPU stall warnings.
1008 static void rcu_preempt_stall_reset(void)
1013 * Because there is no preemptible RCU, there can be no readers blocked,
1014 * so there is no need to check for blocked tasks. So check only for
1015 * bogus qsmask values.
1017 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
1019 WARN_ON_ONCE(rnp
->qsmask
);
1022 #ifdef CONFIG_HOTPLUG_CPU
1025 * Because preemptible RCU does not exist, it never needs to migrate
1026 * tasks that were blocked within RCU read-side critical sections, and
1027 * such non-existent tasks cannot possibly have been blocking the current
1030 static int rcu_preempt_offline_tasks(struct rcu_state
*rsp
,
1031 struct rcu_node
*rnp
,
1032 struct rcu_data
*rdp
)
1038 * Because preemptible RCU does not exist, it never needs CPU-offline
1041 static void rcu_preempt_offline_cpu(int cpu
)
1045 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1048 * Because preemptible RCU does not exist, it never has any callbacks
1051 static void rcu_preempt_check_callbacks(int cpu
)
1056 * Because preemptible RCU does not exist, it never has any callbacks
1059 static void rcu_preempt_process_callbacks(void)
1064 * Wait for an rcu-preempt grace period, but make it happen quickly.
1065 * But because preemptible RCU does not exist, map to rcu-sched.
1067 void synchronize_rcu_expedited(void)
1069 synchronize_sched_expedited();
1071 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited
);
1073 #ifdef CONFIG_HOTPLUG_CPU
1076 * Because preemptible RCU does not exist, there is never any need to
1077 * report on tasks preempted in RCU read-side critical sections during
1078 * expedited RCU grace periods.
1080 static void rcu_report_exp_rnp(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
1085 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1088 * Because preemptible RCU does not exist, it never has any work to do.
1090 static int rcu_preempt_pending(int cpu
)
1096 * Because preemptible RCU does not exist, it never needs any CPU.
1098 static int rcu_preempt_needs_cpu(int cpu
)
1104 * Because preemptible RCU does not exist, rcu_barrier() is just
1105 * another name for rcu_barrier_sched().
1107 void rcu_barrier(void)
1109 rcu_barrier_sched();
1111 EXPORT_SYMBOL_GPL(rcu_barrier
);
1114 * Because preemptible RCU does not exist, there is no per-CPU
1115 * data to initialize.
1117 static void __cpuinit
rcu_preempt_init_percpu_data(int cpu
)
1122 * Because there is no preemptible RCU, there are no callbacks to move.
1124 static void rcu_preempt_send_cbs_to_online(void)
1129 * Because preemptible RCU does not exist, it need not be initialized.
1131 static void __init
__rcu_init_preempt(void)
1135 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1137 #ifdef CONFIG_RCU_BOOST
1139 #include "rtmutex_common.h"
1141 #ifdef CONFIG_RCU_TRACE
1143 static void rcu_initiate_boost_trace(struct rcu_node
*rnp
)
1145 if (list_empty(&rnp
->blkd_tasks
))
1146 rnp
->n_balk_blkd_tasks
++;
1147 else if (rnp
->exp_tasks
== NULL
&& rnp
->gp_tasks
== NULL
)
1148 rnp
->n_balk_exp_gp_tasks
++;
1149 else if (rnp
->gp_tasks
!= NULL
&& rnp
->boost_tasks
!= NULL
)
1150 rnp
->n_balk_boost_tasks
++;
1151 else if (rnp
->gp_tasks
!= NULL
&& rnp
->qsmask
!= 0)
1152 rnp
->n_balk_notblocked
++;
1153 else if (rnp
->gp_tasks
!= NULL
&&
1154 ULONG_CMP_LT(jiffies
, rnp
->boost_time
))
1155 rnp
->n_balk_notyet
++;
1160 #else /* #ifdef CONFIG_RCU_TRACE */
1162 static void rcu_initiate_boost_trace(struct rcu_node
*rnp
)
1166 #endif /* #else #ifdef CONFIG_RCU_TRACE */
1168 static struct lock_class_key rcu_boost_class
;
1171 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
1172 * or ->boost_tasks, advancing the pointer to the next task in the
1173 * ->blkd_tasks list.
1175 * Note that irqs must be enabled: boosting the task can block.
1176 * Returns 1 if there are more tasks needing to be boosted.
1178 static int rcu_boost(struct rcu_node
*rnp
)
1180 unsigned long flags
;
1181 struct rt_mutex mtx
;
1182 struct task_struct
*t
;
1183 struct list_head
*tb
;
1185 if (rnp
->exp_tasks
== NULL
&& rnp
->boost_tasks
== NULL
)
1186 return 0; /* Nothing left to boost. */
1188 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1191 * Recheck under the lock: all tasks in need of boosting
1192 * might exit their RCU read-side critical sections on their own.
1194 if (rnp
->exp_tasks
== NULL
&& rnp
->boost_tasks
== NULL
) {
1195 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1200 * Preferentially boost tasks blocking expedited grace periods.
1201 * This cannot starve the normal grace periods because a second
1202 * expedited grace period must boost all blocked tasks, including
1203 * those blocking the pre-existing normal grace period.
1205 if (rnp
->exp_tasks
!= NULL
) {
1206 tb
= rnp
->exp_tasks
;
1207 rnp
->n_exp_boosts
++;
1209 tb
= rnp
->boost_tasks
;
1210 rnp
->n_normal_boosts
++;
1212 rnp
->n_tasks_boosted
++;
1215 * We boost task t by manufacturing an rt_mutex that appears to
1216 * be held by task t. We leave a pointer to that rt_mutex where
1217 * task t can find it, and task t will release the mutex when it
1218 * exits its outermost RCU read-side critical section. Then
1219 * simply acquiring this artificial rt_mutex will boost task
1220 * t's priority. (Thanks to tglx for suggesting this approach!)
1222 * Note that task t must acquire rnp->lock to remove itself from
1223 * the ->blkd_tasks list, which it will do from exit() if from
1224 * nowhere else. We therefore are guaranteed that task t will
1225 * stay around at least until we drop rnp->lock. Note that
1226 * rnp->lock also resolves races between our priority boosting
1227 * and task t's exiting its outermost RCU read-side critical
1230 t
= container_of(tb
, struct task_struct
, rcu_node_entry
);
1231 rt_mutex_init_proxy_locked(&mtx
, t
);
1232 /* Avoid lockdep false positives. This rt_mutex is its own thing. */
1233 lockdep_set_class_and_name(&mtx
.wait_lock
, &rcu_boost_class
,
1235 t
->rcu_boost_mutex
= &mtx
;
1236 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1237 rt_mutex_lock(&mtx
); /* Side effect: boosts task t's priority. */
1238 rt_mutex_unlock(&mtx
); /* Keep lockdep happy. */
1240 return rnp
->exp_tasks
!= NULL
|| rnp
->boost_tasks
!= NULL
;
1244 * Timer handler to initiate waking up of boost kthreads that
1245 * have yielded the CPU due to excessive numbers of tasks to
1246 * boost. We wake up the per-rcu_node kthread, which in turn
1247 * will wake up the booster kthread.
1249 static void rcu_boost_kthread_timer(unsigned long arg
)
1251 invoke_rcu_node_kthread((struct rcu_node
*)arg
);
1255 * Priority-boosting kthread. One per leaf rcu_node and one for the
1258 static int rcu_boost_kthread(void *arg
)
1260 struct rcu_node
*rnp
= (struct rcu_node
*)arg
;
1264 trace_rcu_utilization("Start boost kthread@init");
1266 rnp
->boost_kthread_status
= RCU_KTHREAD_WAITING
;
1267 trace_rcu_utilization("End boost kthread@rcu_wait");
1268 rcu_wait(rnp
->boost_tasks
|| rnp
->exp_tasks
);
1269 trace_rcu_utilization("Start boost kthread@rcu_wait");
1270 rnp
->boost_kthread_status
= RCU_KTHREAD_RUNNING
;
1271 more2boost
= rcu_boost(rnp
);
1277 trace_rcu_utilization("End boost kthread@rcu_yield");
1278 rcu_yield(rcu_boost_kthread_timer
, (unsigned long)rnp
);
1279 trace_rcu_utilization("Start boost kthread@rcu_yield");
1284 trace_rcu_utilization("End boost kthread@notreached");
1289 * Check to see if it is time to start boosting RCU readers that are
1290 * blocking the current grace period, and, if so, tell the per-rcu_node
1291 * kthread to start boosting them. If there is an expedited grace
1292 * period in progress, it is always time to boost.
1294 * The caller must hold rnp->lock, which this function releases,
1295 * but irqs remain disabled. The ->boost_kthread_task is immortal,
1296 * so we don't need to worry about it going away.
1298 static void rcu_initiate_boost(struct rcu_node
*rnp
, unsigned long flags
)
1300 struct task_struct
*t
;
1302 if (!rcu_preempt_blocked_readers_cgp(rnp
) && rnp
->exp_tasks
== NULL
) {
1303 rnp
->n_balk_exp_gp_tasks
++;
1304 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1307 if (rnp
->exp_tasks
!= NULL
||
1308 (rnp
->gp_tasks
!= NULL
&&
1309 rnp
->boost_tasks
== NULL
&&
1311 ULONG_CMP_GE(jiffies
, rnp
->boost_time
))) {
1312 if (rnp
->exp_tasks
== NULL
)
1313 rnp
->boost_tasks
= rnp
->gp_tasks
;
1314 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1315 t
= rnp
->boost_kthread_task
;
1319 rcu_initiate_boost_trace(rnp
);
1320 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1325 * Wake up the per-CPU kthread to invoke RCU callbacks.
1327 static void invoke_rcu_callbacks_kthread(void)
1329 unsigned long flags
;
1331 local_irq_save(flags
);
1332 __this_cpu_write(rcu_cpu_has_work
, 1);
1333 if (__this_cpu_read(rcu_cpu_kthread_task
) != NULL
&&
1334 current
!= __this_cpu_read(rcu_cpu_kthread_task
))
1335 wake_up_process(__this_cpu_read(rcu_cpu_kthread_task
));
1336 local_irq_restore(flags
);
1340 * Set the affinity of the boost kthread. The CPU-hotplug locks are
1341 * held, so no one should be messing with the existence of the boost
1344 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
,
1347 struct task_struct
*t
;
1349 t
= rnp
->boost_kthread_task
;
1351 set_cpus_allowed_ptr(rnp
->boost_kthread_task
, cm
);
1354 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1357 * Do priority-boost accounting for the start of a new grace period.
1359 static void rcu_preempt_boost_start_gp(struct rcu_node
*rnp
)
1361 rnp
->boost_time
= jiffies
+ RCU_BOOST_DELAY_JIFFIES
;
1365 * Create an RCU-boost kthread for the specified node if one does not
1366 * already exist. We only create this kthread for preemptible RCU.
1367 * Returns zero if all is well, a negated errno otherwise.
1369 static int __cpuinit
rcu_spawn_one_boost_kthread(struct rcu_state
*rsp
,
1370 struct rcu_node
*rnp
,
1373 unsigned long flags
;
1374 struct sched_param sp
;
1375 struct task_struct
*t
;
1377 if (&rcu_preempt_state
!= rsp
)
1380 if (rnp
->boost_kthread_task
!= NULL
)
1382 t
= kthread_create(rcu_boost_kthread
, (void *)rnp
,
1383 "rcub/%d", rnp_index
);
1386 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1387 rnp
->boost_kthread_task
= t
;
1388 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1389 sp
.sched_priority
= RCU_BOOST_PRIO
;
1390 sched_setscheduler_nocheck(t
, SCHED_FIFO
, &sp
);
1391 wake_up_process(t
); /* get to TASK_INTERRUPTIBLE quickly. */
1395 #ifdef CONFIG_HOTPLUG_CPU
1398 * Stop the RCU's per-CPU kthread when its CPU goes offline,.
1400 static void rcu_stop_cpu_kthread(int cpu
)
1402 struct task_struct
*t
;
1404 /* Stop the CPU's kthread. */
1405 t
= per_cpu(rcu_cpu_kthread_task
, cpu
);
1407 per_cpu(rcu_cpu_kthread_task
, cpu
) = NULL
;
1412 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1414 static void rcu_kthread_do_work(void)
1416 rcu_do_batch(&rcu_sched_state
, &__get_cpu_var(rcu_sched_data
));
1417 rcu_do_batch(&rcu_bh_state
, &__get_cpu_var(rcu_bh_data
));
1418 rcu_preempt_do_callbacks();
1422 * Wake up the specified per-rcu_node-structure kthread.
1423 * Because the per-rcu_node kthreads are immortal, we don't need
1424 * to do anything to keep them alive.
1426 static void invoke_rcu_node_kthread(struct rcu_node
*rnp
)
1428 struct task_struct
*t
;
1430 t
= rnp
->node_kthread_task
;
1436 * Set the specified CPU's kthread to run RT or not, as specified by
1437 * the to_rt argument. The CPU-hotplug locks are held, so the task
1438 * is not going away.
1440 static void rcu_cpu_kthread_setrt(int cpu
, int to_rt
)
1443 struct sched_param sp
;
1444 struct task_struct
*t
;
1446 t
= per_cpu(rcu_cpu_kthread_task
, cpu
);
1450 policy
= SCHED_FIFO
;
1451 sp
.sched_priority
= RCU_KTHREAD_PRIO
;
1453 policy
= SCHED_NORMAL
;
1454 sp
.sched_priority
= 0;
1456 sched_setscheduler_nocheck(t
, policy
, &sp
);
1460 * Timer handler to initiate the waking up of per-CPU kthreads that
1461 * have yielded the CPU due to excess numbers of RCU callbacks.
1462 * We wake up the per-rcu_node kthread, which in turn will wake up
1463 * the booster kthread.
1465 static void rcu_cpu_kthread_timer(unsigned long arg
)
1467 struct rcu_data
*rdp
= per_cpu_ptr(rcu_state
->rda
, arg
);
1468 struct rcu_node
*rnp
= rdp
->mynode
;
1470 atomic_or(rdp
->grpmask
, &rnp
->wakemask
);
1471 invoke_rcu_node_kthread(rnp
);
1475 * Drop to non-real-time priority and yield, but only after posting a
1476 * timer that will cause us to regain our real-time priority if we
1477 * remain preempted. Either way, we restore our real-time priority
1480 static void rcu_yield(void (*f
)(unsigned long), unsigned long arg
)
1482 struct sched_param sp
;
1483 struct timer_list yield_timer
;
1484 int prio
= current
->rt_priority
;
1486 setup_timer_on_stack(&yield_timer
, f
, arg
);
1487 mod_timer(&yield_timer
, jiffies
+ 2);
1488 sp
.sched_priority
= 0;
1489 sched_setscheduler_nocheck(current
, SCHED_NORMAL
, &sp
);
1490 set_user_nice(current
, 19);
1492 set_user_nice(current
, 0);
1493 sp
.sched_priority
= prio
;
1494 sched_setscheduler_nocheck(current
, SCHED_FIFO
, &sp
);
1495 del_timer(&yield_timer
);
1499 * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU.
1500 * This can happen while the corresponding CPU is either coming online
1501 * or going offline. We cannot wait until the CPU is fully online
1502 * before starting the kthread, because the various notifier functions
1503 * can wait for RCU grace periods. So we park rcu_cpu_kthread() until
1504 * the corresponding CPU is online.
1506 * Return 1 if the kthread needs to stop, 0 otherwise.
1508 * Caller must disable bh. This function can momentarily enable it.
1510 static int rcu_cpu_kthread_should_stop(int cpu
)
1512 while (cpu_is_offline(cpu
) ||
1513 !cpumask_equal(¤t
->cpus_allowed
, cpumask_of(cpu
)) ||
1514 smp_processor_id() != cpu
) {
1515 if (kthread_should_stop())
1517 per_cpu(rcu_cpu_kthread_status
, cpu
) = RCU_KTHREAD_OFFCPU
;
1518 per_cpu(rcu_cpu_kthread_cpu
, cpu
) = raw_smp_processor_id();
1520 schedule_timeout_uninterruptible(1);
1521 if (!cpumask_equal(¤t
->cpus_allowed
, cpumask_of(cpu
)))
1522 set_cpus_allowed_ptr(current
, cpumask_of(cpu
));
1525 per_cpu(rcu_cpu_kthread_cpu
, cpu
) = cpu
;
1530 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
1531 * RCU softirq used in flavors and configurations of RCU that do not
1532 * support RCU priority boosting.
1534 static int rcu_cpu_kthread(void *arg
)
1536 int cpu
= (int)(long)arg
;
1537 unsigned long flags
;
1539 unsigned int *statusp
= &per_cpu(rcu_cpu_kthread_status
, cpu
);
1541 char *workp
= &per_cpu(rcu_cpu_has_work
, cpu
);
1543 trace_rcu_utilization("Start CPU kthread@init");
1545 *statusp
= RCU_KTHREAD_WAITING
;
1546 trace_rcu_utilization("End CPU kthread@rcu_wait");
1547 rcu_wait(*workp
!= 0 || kthread_should_stop());
1548 trace_rcu_utilization("Start CPU kthread@rcu_wait");
1550 if (rcu_cpu_kthread_should_stop(cpu
)) {
1554 *statusp
= RCU_KTHREAD_RUNNING
;
1555 per_cpu(rcu_cpu_kthread_loops
, cpu
)++;
1556 local_irq_save(flags
);
1559 local_irq_restore(flags
);
1561 rcu_kthread_do_work();
1568 *statusp
= RCU_KTHREAD_YIELDING
;
1569 trace_rcu_utilization("End CPU kthread@rcu_yield");
1570 rcu_yield(rcu_cpu_kthread_timer
, (unsigned long)cpu
);
1571 trace_rcu_utilization("Start CPU kthread@rcu_yield");
1575 *statusp
= RCU_KTHREAD_STOPPED
;
1576 trace_rcu_utilization("End CPU kthread@term");
1581 * Spawn a per-CPU kthread, setting up affinity and priority.
1582 * Because the CPU hotplug lock is held, no other CPU will be attempting
1583 * to manipulate rcu_cpu_kthread_task. There might be another CPU
1584 * attempting to access it during boot, but the locking in kthread_bind()
1585 * will enforce sufficient ordering.
1587 * Please note that we cannot simply refuse to wake up the per-CPU
1588 * kthread because kthreads are created in TASK_UNINTERRUPTIBLE state,
1589 * which can result in softlockup complaints if the task ends up being
1590 * idle for more than a couple of minutes.
1592 * However, please note also that we cannot bind the per-CPU kthread to its
1593 * CPU until that CPU is fully online. We also cannot wait until the
1594 * CPU is fully online before we create its per-CPU kthread, as this would
1595 * deadlock the system when CPU notifiers tried waiting for grace
1596 * periods. So we bind the per-CPU kthread to its CPU only if the CPU
1597 * is online. If its CPU is not yet fully online, then the code in
1598 * rcu_cpu_kthread() will wait until it is fully online, and then do
1601 static int __cpuinit
rcu_spawn_one_cpu_kthread(int cpu
)
1603 struct sched_param sp
;
1604 struct task_struct
*t
;
1606 if (!rcu_scheduler_fully_active
||
1607 per_cpu(rcu_cpu_kthread_task
, cpu
) != NULL
)
1609 t
= kthread_create_on_node(rcu_cpu_kthread
,
1615 if (cpu_online(cpu
))
1616 kthread_bind(t
, cpu
);
1617 per_cpu(rcu_cpu_kthread_cpu
, cpu
) = cpu
;
1618 WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task
, cpu
) != NULL
);
1619 sp
.sched_priority
= RCU_KTHREAD_PRIO
;
1620 sched_setscheduler_nocheck(t
, SCHED_FIFO
, &sp
);
1621 per_cpu(rcu_cpu_kthread_task
, cpu
) = t
;
1622 wake_up_process(t
); /* Get to TASK_INTERRUPTIBLE quickly. */
1627 * Per-rcu_node kthread, which is in charge of waking up the per-CPU
1628 * kthreads when needed. We ignore requests to wake up kthreads
1629 * for offline CPUs, which is OK because force_quiescent_state()
1630 * takes care of this case.
1632 static int rcu_node_kthread(void *arg
)
1635 unsigned long flags
;
1637 struct rcu_node
*rnp
= (struct rcu_node
*)arg
;
1638 struct sched_param sp
;
1639 struct task_struct
*t
;
1642 rnp
->node_kthread_status
= RCU_KTHREAD_WAITING
;
1643 rcu_wait(atomic_read(&rnp
->wakemask
) != 0);
1644 rnp
->node_kthread_status
= RCU_KTHREAD_RUNNING
;
1645 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1646 mask
= atomic_xchg(&rnp
->wakemask
, 0);
1647 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock. */
1648 for (cpu
= rnp
->grplo
; cpu
<= rnp
->grphi
; cpu
++, mask
>>= 1) {
1649 if ((mask
& 0x1) == 0)
1652 t
= per_cpu(rcu_cpu_kthread_task
, cpu
);
1653 if (!cpu_online(cpu
) || t
== NULL
) {
1657 per_cpu(rcu_cpu_has_work
, cpu
) = 1;
1658 sp
.sched_priority
= RCU_KTHREAD_PRIO
;
1659 sched_setscheduler_nocheck(t
, SCHED_FIFO
, &sp
);
1664 rnp
->node_kthread_status
= RCU_KTHREAD_STOPPED
;
1669 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1670 * served by the rcu_node in question. The CPU hotplug lock is still
1671 * held, so the value of rnp->qsmaskinit will be stable.
1673 * We don't include outgoingcpu in the affinity set, use -1 if there is
1674 * no outgoing CPU. If there are no CPUs left in the affinity set,
1675 * this function allows the kthread to execute on any CPU.
1677 static void rcu_node_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
)
1681 unsigned long mask
= rnp
->qsmaskinit
;
1683 if (rnp
->node_kthread_task
== NULL
)
1685 if (!alloc_cpumask_var(&cm
, GFP_KERNEL
))
1688 for (cpu
= rnp
->grplo
; cpu
<= rnp
->grphi
; cpu
++, mask
>>= 1)
1689 if ((mask
& 0x1) && cpu
!= outgoingcpu
)
1690 cpumask_set_cpu(cpu
, cm
);
1691 if (cpumask_weight(cm
) == 0) {
1693 for (cpu
= rnp
->grplo
; cpu
<= rnp
->grphi
; cpu
++)
1694 cpumask_clear_cpu(cpu
, cm
);
1695 WARN_ON_ONCE(cpumask_weight(cm
) == 0);
1697 set_cpus_allowed_ptr(rnp
->node_kthread_task
, cm
);
1698 rcu_boost_kthread_setaffinity(rnp
, cm
);
1699 free_cpumask_var(cm
);
1703 * Spawn a per-rcu_node kthread, setting priority and affinity.
1704 * Called during boot before online/offline can happen, or, if
1705 * during runtime, with the main CPU-hotplug locks held. So only
1706 * one of these can be executing at a time.
1708 static int __cpuinit
rcu_spawn_one_node_kthread(struct rcu_state
*rsp
,
1709 struct rcu_node
*rnp
)
1711 unsigned long flags
;
1712 int rnp_index
= rnp
- &rsp
->node
[0];
1713 struct sched_param sp
;
1714 struct task_struct
*t
;
1716 if (!rcu_scheduler_fully_active
||
1717 rnp
->qsmaskinit
== 0)
1719 if (rnp
->node_kthread_task
== NULL
) {
1720 t
= kthread_create(rcu_node_kthread
, (void *)rnp
,
1721 "rcun/%d", rnp_index
);
1724 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1725 rnp
->node_kthread_task
= t
;
1726 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1727 sp
.sched_priority
= 99;
1728 sched_setscheduler_nocheck(t
, SCHED_FIFO
, &sp
);
1729 wake_up_process(t
); /* get to TASK_INTERRUPTIBLE quickly. */
1731 return rcu_spawn_one_boost_kthread(rsp
, rnp
, rnp_index
);
1735 * Spawn all kthreads -- called as soon as the scheduler is running.
1737 static int __init
rcu_spawn_kthreads(void)
1740 struct rcu_node
*rnp
;
1742 rcu_scheduler_fully_active
= 1;
1743 for_each_possible_cpu(cpu
) {
1744 per_cpu(rcu_cpu_has_work
, cpu
) = 0;
1745 if (cpu_online(cpu
))
1746 (void)rcu_spawn_one_cpu_kthread(cpu
);
1748 rnp
= rcu_get_root(rcu_state
);
1749 (void)rcu_spawn_one_node_kthread(rcu_state
, rnp
);
1750 if (NUM_RCU_NODES
> 1) {
1751 rcu_for_each_leaf_node(rcu_state
, rnp
)
1752 (void)rcu_spawn_one_node_kthread(rcu_state
, rnp
);
1756 early_initcall(rcu_spawn_kthreads
);
1758 static void __cpuinit
rcu_prepare_kthreads(int cpu
)
1760 struct rcu_data
*rdp
= per_cpu_ptr(rcu_state
->rda
, cpu
);
1761 struct rcu_node
*rnp
= rdp
->mynode
;
1763 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1764 if (rcu_scheduler_fully_active
) {
1765 (void)rcu_spawn_one_cpu_kthread(cpu
);
1766 if (rnp
->node_kthread_task
== NULL
)
1767 (void)rcu_spawn_one_node_kthread(rcu_state
, rnp
);
1771 #else /* #ifdef CONFIG_RCU_BOOST */
1773 static void rcu_initiate_boost(struct rcu_node
*rnp
, unsigned long flags
)
1775 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1778 static void invoke_rcu_callbacks_kthread(void)
1783 static void rcu_preempt_boost_start_gp(struct rcu_node
*rnp
)
1787 #ifdef CONFIG_HOTPLUG_CPU
1789 static void rcu_stop_cpu_kthread(int cpu
)
1793 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1795 static void rcu_node_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
)
1799 static void rcu_cpu_kthread_setrt(int cpu
, int to_rt
)
1803 static int __init
rcu_scheduler_really_started(void)
1805 rcu_scheduler_fully_active
= 1;
1808 early_initcall(rcu_scheduler_really_started
);
1810 static void __cpuinit
rcu_prepare_kthreads(int cpu
)
1814 #endif /* #else #ifdef CONFIG_RCU_BOOST */
1818 void synchronize_sched_expedited(void)
1822 EXPORT_SYMBOL_GPL(synchronize_sched_expedited
);
1824 #else /* #ifndef CONFIG_SMP */
1826 static atomic_t sync_sched_expedited_started
= ATOMIC_INIT(0);
1827 static atomic_t sync_sched_expedited_done
= ATOMIC_INIT(0);
1829 static int synchronize_sched_expedited_cpu_stop(void *data
)
1832 * There must be a full memory barrier on each affected CPU
1833 * between the time that try_stop_cpus() is called and the
1834 * time that it returns.
1836 * In the current initial implementation of cpu_stop, the
1837 * above condition is already met when the control reaches
1838 * this point and the following smp_mb() is not strictly
1839 * necessary. Do smp_mb() anyway for documentation and
1840 * robustness against future implementation changes.
1842 smp_mb(); /* See above comment block. */
1847 * Wait for an rcu-sched grace period to elapse, but use "big hammer"
1848 * approach to force grace period to end quickly. This consumes
1849 * significant time on all CPUs, and is thus not recommended for
1850 * any sort of common-case code.
1852 * Note that it is illegal to call this function while holding any
1853 * lock that is acquired by a CPU-hotplug notifier. Failing to
1854 * observe this restriction will result in deadlock.
1856 * This implementation can be thought of as an application of ticket
1857 * locking to RCU, with sync_sched_expedited_started and
1858 * sync_sched_expedited_done taking on the roles of the halves
1859 * of the ticket-lock word. Each task atomically increments
1860 * sync_sched_expedited_started upon entry, snapshotting the old value,
1861 * then attempts to stop all the CPUs. If this succeeds, then each
1862 * CPU will have executed a context switch, resulting in an RCU-sched
1863 * grace period. We are then done, so we use atomic_cmpxchg() to
1864 * update sync_sched_expedited_done to match our snapshot -- but
1865 * only if someone else has not already advanced past our snapshot.
1867 * On the other hand, if try_stop_cpus() fails, we check the value
1868 * of sync_sched_expedited_done. If it has advanced past our
1869 * initial snapshot, then someone else must have forced a grace period
1870 * some time after we took our snapshot. In this case, our work is
1871 * done for us, and we can simply return. Otherwise, we try again,
1872 * but keep our initial snapshot for purposes of checking for someone
1873 * doing our work for us.
1875 * If we fail too many times in a row, we fall back to synchronize_sched().
1877 void synchronize_sched_expedited(void)
1879 int firstsnap
, s
, snap
, trycount
= 0;
1881 /* Note that atomic_inc_return() implies full memory barrier. */
1882 firstsnap
= snap
= atomic_inc_return(&sync_sched_expedited_started
);
1886 * Each pass through the following loop attempts to force a
1887 * context switch on each CPU.
1889 while (try_stop_cpus(cpu_online_mask
,
1890 synchronize_sched_expedited_cpu_stop
,
1894 /* No joy, try again later. Or just synchronize_sched(). */
1895 if (trycount
++ < 10)
1896 udelay(trycount
* num_online_cpus());
1898 synchronize_sched();
1902 /* Check to see if someone else did our work for us. */
1903 s
= atomic_read(&sync_sched_expedited_done
);
1904 if (UINT_CMP_GE((unsigned)s
, (unsigned)firstsnap
)) {
1905 smp_mb(); /* ensure test happens before caller kfree */
1910 * Refetching sync_sched_expedited_started allows later
1911 * callers to piggyback on our grace period. We subtract
1912 * 1 to get the same token that the last incrementer got.
1913 * We retry after they started, so our grace period works
1914 * for them, and they started after our first try, so their
1915 * grace period works for us.
1918 snap
= atomic_read(&sync_sched_expedited_started
);
1919 smp_mb(); /* ensure read is before try_stop_cpus(). */
1923 * Everyone up to our most recent fetch is covered by our grace
1924 * period. Update the counter, but only if our work is still
1925 * relevant -- which it won't be if someone who started later
1926 * than we did beat us to the punch.
1929 s
= atomic_read(&sync_sched_expedited_done
);
1930 if (UINT_CMP_GE((unsigned)s
, (unsigned)snap
)) {
1931 smp_mb(); /* ensure test happens before caller kfree */
1934 } while (atomic_cmpxchg(&sync_sched_expedited_done
, s
, snap
) != s
);
1938 EXPORT_SYMBOL_GPL(synchronize_sched_expedited
);
1940 #endif /* #else #ifndef CONFIG_SMP */
1942 #if !defined(CONFIG_RCU_FAST_NO_HZ)
1945 * Check to see if any future RCU-related work will need to be done
1946 * by the current CPU, even if none need be done immediately, returning
1947 * 1 if so. This function is part of the RCU implementation; it is -not-
1948 * an exported member of the RCU API.
1950 * Because we have preemptible RCU, just check whether this CPU needs
1951 * any flavor of RCU. Do not chew up lots of CPU cycles with preemption
1952 * disabled in a most-likely vain attempt to cause RCU not to need this CPU.
1954 int rcu_needs_cpu(int cpu
)
1956 return rcu_cpu_has_callbacks(cpu
);
1960 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=y,
1963 static void rcu_prepare_for_idle(int cpu
)
1968 * CPUs are never putting themselves to sleep with callbacks pending,
1969 * so there is no need to awaken them.
1971 static void rcu_wake_cpus_for_gp_end(void)
1976 * CPUs are never putting themselves to sleep with callbacks pending,
1977 * so there is no need to schedule the act of awakening them.
1979 static void rcu_schedule_wake_gp_end(void)
1983 #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1985 #define RCU_NEEDS_CPU_FLUSHES 5
1986 static DEFINE_PER_CPU(int, rcu_dyntick_drain
);
1987 static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff
);
1988 static DEFINE_PER_CPU(bool, rcu_awake_at_gp_end
);
1991 * Allow the CPU to enter dyntick-idle mode if either: (1) There are no
1992 * callbacks on this CPU, (2) this CPU has not yet attempted to enter
1993 * dyntick-idle mode, or (3) this CPU is in the process of attempting to
1994 * enter dyntick-idle mode. Otherwise, if we have recently tried and failed
1995 * to enter dyntick-idle mode, we refuse to try to enter it. After all,
1996 * it is better to incur scheduling-clock interrupts than to spin
1997 * continuously for the same time duration!
1999 int rcu_needs_cpu(int cpu
)
2001 /* If no callbacks, RCU doesn't need the CPU. */
2002 if (!rcu_cpu_has_callbacks(cpu
))
2004 /* Otherwise, RCU needs the CPU only if it recently tried and failed. */
2005 return per_cpu(rcu_dyntick_holdoff
, cpu
) == jiffies
;
2009 * Check to see if any RCU-related work can be done by the current CPU,
2010 * and if so, schedule a softirq to get it done. This function is part
2011 * of the RCU implementation; it is -not- an exported member of the RCU API.
2013 * The idea is for the current CPU to clear out all work required by the
2014 * RCU core for the current grace period, so that this CPU can be permitted
2015 * to enter dyntick-idle mode. In some cases, it will need to be awakened
2016 * at the end of the grace period by whatever CPU ends the grace period.
2017 * This allows CPUs to go dyntick-idle more quickly, and to reduce the
2018 * number of wakeups by a modest integer factor.
2020 * Because it is not legal to invoke rcu_process_callbacks() with irqs
2021 * disabled, we do one pass of force_quiescent_state(), then do a
2022 * invoke_rcu_core() to cause rcu_process_callbacks() to be invoked
2023 * later. The per-cpu rcu_dyntick_drain variable controls the sequencing.
2025 * The caller must have disabled interrupts.
2027 static void rcu_prepare_for_idle(int cpu
)
2031 /* If no callbacks or in the holdoff period, enter dyntick-idle. */
2032 if (!rcu_cpu_has_callbacks(cpu
)) {
2033 per_cpu(rcu_dyntick_holdoff
, cpu
) = jiffies
- 1;
2034 trace_rcu_prep_idle("No callbacks");
2037 if (per_cpu(rcu_dyntick_holdoff
, cpu
) == jiffies
) {
2038 trace_rcu_prep_idle("In holdoff");
2042 /* Check and update the rcu_dyntick_drain sequencing. */
2043 if (per_cpu(rcu_dyntick_drain
, cpu
) <= 0) {
2044 /* First time through, initialize the counter. */
2045 per_cpu(rcu_dyntick_drain
, cpu
) = RCU_NEEDS_CPU_FLUSHES
;
2046 } else if (--per_cpu(rcu_dyntick_drain
, cpu
) <= 0) {
2047 /* We have hit the limit, so time to give up. */
2048 per_cpu(rcu_dyntick_holdoff
, cpu
) = jiffies
;
2049 if (!rcu_pending(cpu
)) {
2050 trace_rcu_prep_idle("Dyntick with callbacks");
2051 per_cpu(rcu_awake_at_gp_end
, cpu
) = 1;
2052 return; /* Nothing to do immediately. */
2054 trace_rcu_prep_idle("Begin holdoff");
2055 invoke_rcu_core(); /* Force the CPU out of dyntick-idle. */
2060 * Do one step of pushing the remaining RCU callbacks through
2061 * the RCU core state machine.
2063 #ifdef CONFIG_TREE_PREEMPT_RCU
2064 if (per_cpu(rcu_preempt_data
, cpu
).nxtlist
) {
2065 rcu_preempt_qs(cpu
);
2066 force_quiescent_state(&rcu_preempt_state
, 0);
2067 c
= c
|| per_cpu(rcu_preempt_data
, cpu
).nxtlist
;
2069 #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
2070 if (per_cpu(rcu_sched_data
, cpu
).nxtlist
) {
2072 force_quiescent_state(&rcu_sched_state
, 0);
2073 c
= c
|| per_cpu(rcu_sched_data
, cpu
).nxtlist
;
2075 if (per_cpu(rcu_bh_data
, cpu
).nxtlist
) {
2077 force_quiescent_state(&rcu_bh_state
, 0);
2078 c
= c
|| per_cpu(rcu_bh_data
, cpu
).nxtlist
;
2082 * If RCU callbacks are still pending, RCU still needs this CPU.
2083 * So try forcing the callbacks through the grace period.
2086 trace_rcu_prep_idle("More callbacks");
2089 trace_rcu_prep_idle("Callbacks drained");
2093 * Wake up a CPU by invoking the RCU core. Intended for use by
2094 * rcu_wake_cpus_for_gp_end(), which passes this function to
2095 * smp_call_function_single().
2097 static void rcu_wake_cpu(void *unused
)
2099 trace_rcu_prep_idle("CPU awakened at GP end");
2104 * If an RCU grace period ended recently, scan the rcu_awake_at_gp_end
2105 * per-CPU variables, and wake up any CPUs that requested a wakeup.
2107 static void rcu_wake_cpus_for_gp_end(void)
2110 struct rcu_dynticks
*rdtp
= &__get_cpu_var(rcu_dynticks
);
2112 if (!rdtp
->wake_gp_end
)
2114 rdtp
->wake_gp_end
= 0;
2115 for_each_online_cpu(cpu
) {
2116 if (per_cpu(rcu_awake_at_gp_end
, cpu
)) {
2117 per_cpu(rcu_awake_at_gp_end
, cpu
) = 0;
2118 smp_call_function_single(cpu
, rcu_wake_cpu
, NULL
, 0);
2124 * A grace period has just ended, and so we will need to awaken CPUs
2125 * that now have work to do. But we cannot send IPIs with interrupts
2126 * disabled, so just set a flag so that this will happen upon exit
2127 * from RCU core processing.
2129 static void rcu_schedule_wake_gp_end(void)
2131 struct rcu_dynticks
*rdtp
= &__get_cpu_var(rcu_dynticks
);
2133 rdtp
->wake_gp_end
= 1;
2136 /* @@@ need tracing as well. */
2138 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */