2 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
3 * Internal non-public definitions that provide either classic
4 * or preemptible semantics.
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
20 * Copyright Red Hat, 2009
21 * Copyright IBM Corporation, 2009
23 * Author: Ingo Molnar <mingo@elte.hu>
24 * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
27 #include <linux/delay.h>
28 #include <linux/gfp.h>
29 #include <linux/oom.h>
30 #include <linux/smpboot.h>
31 #include "../time/tick-internal.h"
33 #define RCU_KTHREAD_PRIO 1
35 #ifdef CONFIG_RCU_BOOST
36 #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
38 #define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
41 #ifdef CONFIG_RCU_NOCB_CPU
42 static cpumask_var_t rcu_nocb_mask
; /* CPUs to have callbacks offloaded. */
43 static bool have_rcu_nocb_mask
; /* Was rcu_nocb_mask allocated? */
44 static bool __read_mostly rcu_nocb_poll
; /* Offload kthread are to poll. */
45 static char __initdata nocb_buf
[NR_CPUS
* 5];
46 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
49 * Check the RCU kernel configuration parameters and print informative
50 * messages about anything out of the ordinary. If you like #ifdef, you
51 * will love this function.
53 static void __init
rcu_bootup_announce_oddness(void)
55 #ifdef CONFIG_RCU_TRACE
56 pr_info("\tRCU debugfs-based tracing is enabled.\n");
58 #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
59 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
62 #ifdef CONFIG_RCU_FANOUT_EXACT
63 pr_info("\tHierarchical RCU autobalancing is disabled.\n");
65 #ifdef CONFIG_RCU_FAST_NO_HZ
66 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
68 #ifdef CONFIG_PROVE_RCU
69 pr_info("\tRCU lockdep checking is enabled.\n");
71 #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
72 pr_info("\tRCU torture testing starts during boot.\n");
74 #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
75 pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n");
77 #if defined(CONFIG_RCU_CPU_STALL_INFO)
78 pr_info("\tAdditional per-CPU info printed with stalls.\n");
80 #if NUM_RCU_LVL_4 != 0
81 pr_info("\tFour-level hierarchy is enabled.\n");
83 if (rcu_fanout_leaf
!= CONFIG_RCU_FANOUT_LEAF
)
84 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf
);
85 if (nr_cpu_ids
!= NR_CPUS
)
86 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS
, nr_cpu_ids
);
87 #ifdef CONFIG_RCU_NOCB_CPU
88 #ifndef CONFIG_RCU_NOCB_CPU_NONE
89 if (!have_rcu_nocb_mask
) {
90 zalloc_cpumask_var(&rcu_nocb_mask
, GFP_KERNEL
);
91 have_rcu_nocb_mask
= true;
93 #ifdef CONFIG_RCU_NOCB_CPU_ZERO
94 pr_info("\tOffload RCU callbacks from CPU 0\n");
95 cpumask_set_cpu(0, rcu_nocb_mask
);
96 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
97 #ifdef CONFIG_RCU_NOCB_CPU_ALL
98 pr_info("\tOffload RCU callbacks from all CPUs\n");
99 cpumask_copy(rcu_nocb_mask
, cpu_possible_mask
);
100 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
101 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
102 if (have_rcu_nocb_mask
) {
103 if (!cpumask_subset(rcu_nocb_mask
, cpu_possible_mask
)) {
104 pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
105 cpumask_and(rcu_nocb_mask
, cpu_possible_mask
,
108 cpulist_scnprintf(nocb_buf
, sizeof(nocb_buf
), rcu_nocb_mask
);
109 pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf
);
111 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
113 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
116 #ifdef CONFIG_TREE_PREEMPT_RCU
118 RCU_STATE_INITIALIZER(rcu_preempt
, 'p', call_rcu
);
119 static struct rcu_state
*rcu_state
= &rcu_preempt_state
;
121 static int rcu_preempted_readers_exp(struct rcu_node
*rnp
);
124 * Tell them what RCU they are running.
126 static void __init
rcu_bootup_announce(void)
128 pr_info("Preemptible hierarchical RCU implementation.\n");
129 rcu_bootup_announce_oddness();
133 * Return the number of RCU-preempt batches processed thus far
134 * for debug and statistics.
136 long rcu_batches_completed_preempt(void)
138 return rcu_preempt_state
.completed
;
140 EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt
);
143 * Return the number of RCU batches processed thus far for debug & stats.
145 long rcu_batches_completed(void)
147 return rcu_batches_completed_preempt();
149 EXPORT_SYMBOL_GPL(rcu_batches_completed
);
152 * Force a quiescent state for preemptible RCU.
154 void rcu_force_quiescent_state(void)
156 force_quiescent_state(&rcu_preempt_state
);
158 EXPORT_SYMBOL_GPL(rcu_force_quiescent_state
);
161 * Record a preemptible-RCU quiescent state for the specified CPU. Note
162 * that this just means that the task currently running on the CPU is
163 * not in a quiescent state. There might be any number of tasks blocked
164 * while in an RCU read-side critical section.
166 * Unlike the other rcu_*_qs() functions, callers to this function
167 * must disable irqs in order to protect the assignment to
168 * ->rcu_read_unlock_special.
170 static void rcu_preempt_qs(int cpu
)
172 struct rcu_data
*rdp
= &per_cpu(rcu_preempt_data
, cpu
);
174 if (rdp
->passed_quiesce
== 0)
175 trace_rcu_grace_period(TPS("rcu_preempt"), rdp
->gpnum
, TPS("cpuqs"));
176 rdp
->passed_quiesce
= 1;
177 current
->rcu_read_unlock_special
&= ~RCU_READ_UNLOCK_NEED_QS
;
181 * We have entered the scheduler, and the current task might soon be
182 * context-switched away from. If this task is in an RCU read-side
183 * critical section, we will no longer be able to rely on the CPU to
184 * record that fact, so we enqueue the task on the blkd_tasks list.
185 * The task will dequeue itself when it exits the outermost enclosing
186 * RCU read-side critical section. Therefore, the current grace period
187 * cannot be permitted to complete until the blkd_tasks list entries
188 * predating the current grace period drain, in other words, until
189 * rnp->gp_tasks becomes NULL.
191 * Caller must disable preemption.
193 static void rcu_preempt_note_context_switch(int cpu
)
195 struct task_struct
*t
= current
;
197 struct rcu_data
*rdp
;
198 struct rcu_node
*rnp
;
200 if (t
->rcu_read_lock_nesting
> 0 &&
201 (t
->rcu_read_unlock_special
& RCU_READ_UNLOCK_BLOCKED
) == 0) {
203 /* Possibly blocking in an RCU read-side critical section. */
204 rdp
= per_cpu_ptr(rcu_preempt_state
.rda
, cpu
);
206 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
207 smp_mb__after_unlock_lock();
208 t
->rcu_read_unlock_special
|= RCU_READ_UNLOCK_BLOCKED
;
209 t
->rcu_blocked_node
= rnp
;
212 * If this CPU has already checked in, then this task
213 * will hold up the next grace period rather than the
214 * current grace period. Queue the task accordingly.
215 * If the task is queued for the current grace period
216 * (i.e., this CPU has not yet passed through a quiescent
217 * state for the current grace period), then as long
218 * as that task remains queued, the current grace period
219 * cannot end. Note that there is some uncertainty as
220 * to exactly when the current grace period started.
221 * We take a conservative approach, which can result
222 * in unnecessarily waiting on tasks that started very
223 * slightly after the current grace period began. C'est
226 * But first, note that the current CPU must still be
229 WARN_ON_ONCE((rdp
->grpmask
& rnp
->qsmaskinit
) == 0);
230 WARN_ON_ONCE(!list_empty(&t
->rcu_node_entry
));
231 if ((rnp
->qsmask
& rdp
->grpmask
) && rnp
->gp_tasks
!= NULL
) {
232 list_add(&t
->rcu_node_entry
, rnp
->gp_tasks
->prev
);
233 rnp
->gp_tasks
= &t
->rcu_node_entry
;
234 #ifdef CONFIG_RCU_BOOST
235 if (rnp
->boost_tasks
!= NULL
)
236 rnp
->boost_tasks
= rnp
->gp_tasks
;
237 #endif /* #ifdef CONFIG_RCU_BOOST */
239 list_add(&t
->rcu_node_entry
, &rnp
->blkd_tasks
);
240 if (rnp
->qsmask
& rdp
->grpmask
)
241 rnp
->gp_tasks
= &t
->rcu_node_entry
;
243 trace_rcu_preempt_task(rdp
->rsp
->name
,
245 (rnp
->qsmask
& rdp
->grpmask
)
248 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
249 } else if (t
->rcu_read_lock_nesting
< 0 &&
250 t
->rcu_read_unlock_special
) {
253 * Complete exit from RCU read-side critical section on
254 * behalf of preempted instance of __rcu_read_unlock().
256 rcu_read_unlock_special(t
);
260 * Either we were not in an RCU read-side critical section to
261 * begin with, or we have now recorded that critical section
262 * globally. Either way, we can now note a quiescent state
263 * for this CPU. Again, if we were in an RCU read-side critical
264 * section, and if that critical section was blocking the current
265 * grace period, then the fact that the task has been enqueued
266 * means that we continue to block the current grace period.
268 local_irq_save(flags
);
270 local_irq_restore(flags
);
274 * Check for preempted RCU readers blocking the current grace period
275 * for the specified rcu_node structure. If the caller needs a reliable
276 * answer, it must hold the rcu_node's ->lock.
278 static int rcu_preempt_blocked_readers_cgp(struct rcu_node
*rnp
)
280 return rnp
->gp_tasks
!= NULL
;
284 * Record a quiescent state for all tasks that were previously queued
285 * on the specified rcu_node structure and that were blocking the current
286 * RCU grace period. The caller must hold the specified rnp->lock with
287 * irqs disabled, and this lock is released upon return, but irqs remain
290 static void rcu_report_unblock_qs_rnp(struct rcu_node
*rnp
, unsigned long flags
)
291 __releases(rnp
->lock
)
294 struct rcu_node
*rnp_p
;
296 if (rnp
->qsmask
!= 0 || rcu_preempt_blocked_readers_cgp(rnp
)) {
297 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
298 return; /* Still need more quiescent states! */
304 * Either there is only one rcu_node in the tree,
305 * or tasks were kicked up to root rcu_node due to
306 * CPUs going offline.
308 rcu_report_qs_rsp(&rcu_preempt_state
, flags
);
312 /* Report up the rest of the hierarchy. */
314 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
315 raw_spin_lock(&rnp_p
->lock
); /* irqs already disabled. */
316 smp_mb__after_unlock_lock();
317 rcu_report_qs_rnp(mask
, &rcu_preempt_state
, rnp_p
, flags
);
321 * Advance a ->blkd_tasks-list pointer to the next entry, instead
322 * returning NULL if at the end of the list.
324 static struct list_head
*rcu_next_node_entry(struct task_struct
*t
,
325 struct rcu_node
*rnp
)
327 struct list_head
*np
;
329 np
= t
->rcu_node_entry
.next
;
330 if (np
== &rnp
->blkd_tasks
)
336 * Handle special cases during rcu_read_unlock(), such as needing to
337 * notify RCU core processing or task having blocked during the RCU
338 * read-side critical section.
340 void rcu_read_unlock_special(struct task_struct
*t
)
346 struct list_head
*np
;
347 #ifdef CONFIG_RCU_BOOST
348 struct rt_mutex
*rbmp
= NULL
;
349 #endif /* #ifdef CONFIG_RCU_BOOST */
350 struct rcu_node
*rnp
;
353 /* NMI handlers cannot block and cannot safely manipulate state. */
357 local_irq_save(flags
);
360 * If RCU core is waiting for this CPU to exit critical section,
361 * let it know that we have done so.
363 special
= t
->rcu_read_unlock_special
;
364 if (special
& RCU_READ_UNLOCK_NEED_QS
) {
365 rcu_preempt_qs(smp_processor_id());
368 /* Hardware IRQ handlers cannot block. */
369 if (in_irq() || in_serving_softirq()) {
370 local_irq_restore(flags
);
374 /* Clean up if blocked during RCU read-side critical section. */
375 if (special
& RCU_READ_UNLOCK_BLOCKED
) {
376 t
->rcu_read_unlock_special
&= ~RCU_READ_UNLOCK_BLOCKED
;
379 * Remove this task from the list it blocked on. The
380 * task can migrate while we acquire the lock, but at
381 * most one time. So at most two passes through loop.
384 rnp
= t
->rcu_blocked_node
;
385 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
386 smp_mb__after_unlock_lock();
387 if (rnp
== t
->rcu_blocked_node
)
389 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
391 empty
= !rcu_preempt_blocked_readers_cgp(rnp
);
392 empty_exp
= !rcu_preempted_readers_exp(rnp
);
393 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
394 np
= rcu_next_node_entry(t
, rnp
);
395 list_del_init(&t
->rcu_node_entry
);
396 t
->rcu_blocked_node
= NULL
;
397 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
399 if (&t
->rcu_node_entry
== rnp
->gp_tasks
)
401 if (&t
->rcu_node_entry
== rnp
->exp_tasks
)
403 #ifdef CONFIG_RCU_BOOST
404 if (&t
->rcu_node_entry
== rnp
->boost_tasks
)
405 rnp
->boost_tasks
= np
;
406 /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
407 if (t
->rcu_boost_mutex
) {
408 rbmp
= t
->rcu_boost_mutex
;
409 t
->rcu_boost_mutex
= NULL
;
411 #endif /* #ifdef CONFIG_RCU_BOOST */
414 * If this was the last task on the current list, and if
415 * we aren't waiting on any CPUs, report the quiescent state.
416 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
417 * so we must take a snapshot of the expedited state.
419 empty_exp_now
= !rcu_preempted_readers_exp(rnp
);
420 if (!empty
&& !rcu_preempt_blocked_readers_cgp(rnp
)) {
421 trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
428 rcu_report_unblock_qs_rnp(rnp
, flags
);
430 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
433 #ifdef CONFIG_RCU_BOOST
434 /* Unboost if we were boosted. */
436 rt_mutex_unlock(rbmp
);
437 #endif /* #ifdef CONFIG_RCU_BOOST */
440 * If this was the last task on the expedited lists,
441 * then we need to report up the rcu_node hierarchy.
443 if (!empty_exp
&& empty_exp_now
)
444 rcu_report_exp_rnp(&rcu_preempt_state
, rnp
, true);
446 local_irq_restore(flags
);
450 #ifdef CONFIG_RCU_CPU_STALL_VERBOSE
453 * Dump detailed information for all tasks blocking the current RCU
454 * grace period on the specified rcu_node structure.
456 static void rcu_print_detail_task_stall_rnp(struct rcu_node
*rnp
)
459 struct task_struct
*t
;
461 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
462 if (!rcu_preempt_blocked_readers_cgp(rnp
)) {
463 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
466 t
= list_entry(rnp
->gp_tasks
,
467 struct task_struct
, rcu_node_entry
);
468 list_for_each_entry_continue(t
, &rnp
->blkd_tasks
, rcu_node_entry
)
470 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
474 * Dump detailed information for all tasks blocking the current RCU
477 static void rcu_print_detail_task_stall(struct rcu_state
*rsp
)
479 struct rcu_node
*rnp
= rcu_get_root(rsp
);
481 rcu_print_detail_task_stall_rnp(rnp
);
482 rcu_for_each_leaf_node(rsp
, rnp
)
483 rcu_print_detail_task_stall_rnp(rnp
);
486 #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
488 static void rcu_print_detail_task_stall(struct rcu_state
*rsp
)
492 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
494 #ifdef CONFIG_RCU_CPU_STALL_INFO
496 static void rcu_print_task_stall_begin(struct rcu_node
*rnp
)
498 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
499 rnp
->level
, rnp
->grplo
, rnp
->grphi
);
502 static void rcu_print_task_stall_end(void)
507 #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
509 static void rcu_print_task_stall_begin(struct rcu_node
*rnp
)
513 static void rcu_print_task_stall_end(void)
517 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
520 * Scan the current list of tasks blocked within RCU read-side critical
521 * sections, printing out the tid of each.
523 static int rcu_print_task_stall(struct rcu_node
*rnp
)
525 struct task_struct
*t
;
528 if (!rcu_preempt_blocked_readers_cgp(rnp
))
530 rcu_print_task_stall_begin(rnp
);
531 t
= list_entry(rnp
->gp_tasks
,
532 struct task_struct
, rcu_node_entry
);
533 list_for_each_entry_continue(t
, &rnp
->blkd_tasks
, rcu_node_entry
) {
534 pr_cont(" P%d", t
->pid
);
537 rcu_print_task_stall_end();
542 * Check that the list of blocked tasks for the newly completed grace
543 * period is in fact empty. It is a serious bug to complete a grace
544 * period that still has RCU readers blocked! This function must be
545 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
546 * must be held by the caller.
548 * Also, if there are blocked tasks on the list, they automatically
549 * block the newly created grace period, so set up ->gp_tasks accordingly.
551 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
553 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp
));
554 if (!list_empty(&rnp
->blkd_tasks
))
555 rnp
->gp_tasks
= rnp
->blkd_tasks
.next
;
556 WARN_ON_ONCE(rnp
->qsmask
);
559 #ifdef CONFIG_HOTPLUG_CPU
562 * Handle tasklist migration for case in which all CPUs covered by the
563 * specified rcu_node have gone offline. Move them up to the root
564 * rcu_node. The reason for not just moving them to the immediate
565 * parent is to remove the need for rcu_read_unlock_special() to
566 * make more than two attempts to acquire the target rcu_node's lock.
567 * Returns true if there were tasks blocking the current RCU grace
570 * Returns 1 if there was previously a task blocking the current grace
571 * period on the specified rcu_node structure.
573 * The caller must hold rnp->lock with irqs disabled.
575 static int rcu_preempt_offline_tasks(struct rcu_state
*rsp
,
576 struct rcu_node
*rnp
,
577 struct rcu_data
*rdp
)
579 struct list_head
*lp
;
580 struct list_head
*lp_root
;
582 struct rcu_node
*rnp_root
= rcu_get_root(rsp
);
583 struct task_struct
*t
;
585 if (rnp
== rnp_root
) {
586 WARN_ONCE(1, "Last CPU thought to be offlined?");
587 return 0; /* Shouldn't happen: at least one CPU online. */
590 /* If we are on an internal node, complain bitterly. */
591 WARN_ON_ONCE(rnp
!= rdp
->mynode
);
594 * Move tasks up to root rcu_node. Don't try to get fancy for
595 * this corner-case operation -- just put this node's tasks
596 * at the head of the root node's list, and update the root node's
597 * ->gp_tasks and ->exp_tasks pointers to those of this node's,
598 * if non-NULL. This might result in waiting for more tasks than
599 * absolutely necessary, but this is a good performance/complexity
602 if (rcu_preempt_blocked_readers_cgp(rnp
) && rnp
->qsmask
== 0)
603 retval
|= RCU_OFL_TASKS_NORM_GP
;
604 if (rcu_preempted_readers_exp(rnp
))
605 retval
|= RCU_OFL_TASKS_EXP_GP
;
606 lp
= &rnp
->blkd_tasks
;
607 lp_root
= &rnp_root
->blkd_tasks
;
608 while (!list_empty(lp
)) {
609 t
= list_entry(lp
->next
, typeof(*t
), rcu_node_entry
);
610 raw_spin_lock(&rnp_root
->lock
); /* irqs already disabled */
611 smp_mb__after_unlock_lock();
612 list_del(&t
->rcu_node_entry
);
613 t
->rcu_blocked_node
= rnp_root
;
614 list_add(&t
->rcu_node_entry
, lp_root
);
615 if (&t
->rcu_node_entry
== rnp
->gp_tasks
)
616 rnp_root
->gp_tasks
= rnp
->gp_tasks
;
617 if (&t
->rcu_node_entry
== rnp
->exp_tasks
)
618 rnp_root
->exp_tasks
= rnp
->exp_tasks
;
619 #ifdef CONFIG_RCU_BOOST
620 if (&t
->rcu_node_entry
== rnp
->boost_tasks
)
621 rnp_root
->boost_tasks
= rnp
->boost_tasks
;
622 #endif /* #ifdef CONFIG_RCU_BOOST */
623 raw_spin_unlock(&rnp_root
->lock
); /* irqs still disabled */
626 rnp
->gp_tasks
= NULL
;
627 rnp
->exp_tasks
= NULL
;
628 #ifdef CONFIG_RCU_BOOST
629 rnp
->boost_tasks
= NULL
;
631 * In case root is being boosted and leaf was not. Make sure
632 * that we boost the tasks blocking the current grace period
635 raw_spin_lock(&rnp_root
->lock
); /* irqs already disabled */
636 smp_mb__after_unlock_lock();
637 if (rnp_root
->boost_tasks
!= NULL
&&
638 rnp_root
->boost_tasks
!= rnp_root
->gp_tasks
&&
639 rnp_root
->boost_tasks
!= rnp_root
->exp_tasks
)
640 rnp_root
->boost_tasks
= rnp_root
->gp_tasks
;
641 raw_spin_unlock(&rnp_root
->lock
); /* irqs still disabled */
642 #endif /* #ifdef CONFIG_RCU_BOOST */
647 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
650 * Check for a quiescent state from the current CPU. When a task blocks,
651 * the task is recorded in the corresponding CPU's rcu_node structure,
652 * which is checked elsewhere.
654 * Caller must disable hard irqs.
656 static void rcu_preempt_check_callbacks(int cpu
)
658 struct task_struct
*t
= current
;
660 if (t
->rcu_read_lock_nesting
== 0) {
664 if (t
->rcu_read_lock_nesting
> 0 &&
665 per_cpu(rcu_preempt_data
, cpu
).qs_pending
)
666 t
->rcu_read_unlock_special
|= RCU_READ_UNLOCK_NEED_QS
;
669 #ifdef CONFIG_RCU_BOOST
671 static void rcu_preempt_do_callbacks(void)
673 rcu_do_batch(&rcu_preempt_state
, this_cpu_ptr(&rcu_preempt_data
));
676 #endif /* #ifdef CONFIG_RCU_BOOST */
679 * Queue a preemptible-RCU callback for invocation after a grace period.
681 void call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
683 __call_rcu(head
, func
, &rcu_preempt_state
, -1, 0);
685 EXPORT_SYMBOL_GPL(call_rcu
);
688 * Queue an RCU callback for lazy invocation after a grace period.
689 * This will likely be later named something like "call_rcu_lazy()",
690 * but this change will require some way of tagging the lazy RCU
691 * callbacks in the list of pending callbacks. Until then, this
692 * function may only be called from __kfree_rcu().
694 void kfree_call_rcu(struct rcu_head
*head
,
695 void (*func
)(struct rcu_head
*rcu
))
697 __call_rcu(head
, func
, &rcu_preempt_state
, -1, 1);
699 EXPORT_SYMBOL_GPL(kfree_call_rcu
);
702 * synchronize_rcu - wait until a grace period has elapsed.
704 * Control will return to the caller some time after a full grace
705 * period has elapsed, in other words after all currently executing RCU
706 * read-side critical sections have completed. Note, however, that
707 * upon return from synchronize_rcu(), the caller might well be executing
708 * concurrently with new RCU read-side critical sections that began while
709 * synchronize_rcu() was waiting. RCU read-side critical sections are
710 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
712 * See the description of synchronize_sched() for more detailed information
713 * on memory ordering guarantees.
715 void synchronize_rcu(void)
717 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
718 !lock_is_held(&rcu_lock_map
) &&
719 !lock_is_held(&rcu_sched_lock_map
),
720 "Illegal synchronize_rcu() in RCU read-side critical section");
721 if (!rcu_scheduler_active
)
724 synchronize_rcu_expedited();
726 wait_rcu_gp(call_rcu
);
728 EXPORT_SYMBOL_GPL(synchronize_rcu
);
730 static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq
);
731 static unsigned long sync_rcu_preempt_exp_count
;
732 static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex
);
735 * Return non-zero if there are any tasks in RCU read-side critical
736 * sections blocking the current preemptible-RCU expedited grace period.
737 * If there is no preemptible-RCU expedited grace period currently in
738 * progress, returns zero unconditionally.
740 static int rcu_preempted_readers_exp(struct rcu_node
*rnp
)
742 return rnp
->exp_tasks
!= NULL
;
746 * return non-zero if there is no RCU expedited grace period in progress
747 * for the specified rcu_node structure, in other words, if all CPUs and
748 * tasks covered by the specified rcu_node structure have done their bit
749 * for the current expedited grace period. Works only for preemptible
750 * RCU -- other RCU implementation use other means.
752 * Caller must hold sync_rcu_preempt_exp_mutex.
754 static int sync_rcu_preempt_exp_done(struct rcu_node
*rnp
)
756 return !rcu_preempted_readers_exp(rnp
) &&
757 ACCESS_ONCE(rnp
->expmask
) == 0;
761 * Report the exit from RCU read-side critical section for the last task
762 * that queued itself during or before the current expedited preemptible-RCU
763 * grace period. This event is reported either to the rcu_node structure on
764 * which the task was queued or to one of that rcu_node structure's ancestors,
765 * recursively up the tree. (Calm down, calm down, we do the recursion
768 * Most callers will set the "wake" flag, but the task initiating the
769 * expedited grace period need not wake itself.
771 * Caller must hold sync_rcu_preempt_exp_mutex.
773 static void rcu_report_exp_rnp(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
779 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
780 smp_mb__after_unlock_lock();
782 if (!sync_rcu_preempt_exp_done(rnp
)) {
783 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
786 if (rnp
->parent
== NULL
) {
787 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
789 wake_up(&sync_rcu_preempt_exp_wq
);
793 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
795 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
796 smp_mb__after_unlock_lock();
797 rnp
->expmask
&= ~mask
;
802 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
803 * grace period for the specified rcu_node structure. If there are no such
804 * tasks, report it up the rcu_node hierarchy.
806 * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
807 * CPU hotplug operations.
810 sync_rcu_preempt_exp_init(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
815 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
816 smp_mb__after_unlock_lock();
817 if (list_empty(&rnp
->blkd_tasks
)) {
818 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
820 rnp
->exp_tasks
= rnp
->blkd_tasks
.next
;
821 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock */
825 rcu_report_exp_rnp(rsp
, rnp
, false); /* Don't wake self. */
829 * synchronize_rcu_expedited - Brute-force RCU grace period
831 * Wait for an RCU-preempt grace period, but expedite it. The basic
832 * idea is to invoke synchronize_sched_expedited() to push all the tasks to
833 * the ->blkd_tasks lists and wait for this list to drain. This consumes
834 * significant time on all CPUs and is unfriendly to real-time workloads,
835 * so is thus not recommended for any sort of common-case code.
836 * In fact, if you are using synchronize_rcu_expedited() in a loop,
837 * please restructure your code to batch your updates, and then Use a
838 * single synchronize_rcu() instead.
840 * Note that it is illegal to call this function while holding any lock
841 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
842 * to call this function from a CPU-hotplug notifier. Failing to observe
843 * these restriction will result in deadlock.
845 void synchronize_rcu_expedited(void)
848 struct rcu_node
*rnp
;
849 struct rcu_state
*rsp
= &rcu_preempt_state
;
853 smp_mb(); /* Caller's modifications seen first by other CPUs. */
854 snap
= ACCESS_ONCE(sync_rcu_preempt_exp_count
) + 1;
855 smp_mb(); /* Above access cannot bleed into critical section. */
858 * Block CPU-hotplug operations. This means that any CPU-hotplug
859 * operation that finds an rcu_node structure with tasks in the
860 * process of being boosted will know that all tasks blocking
861 * this expedited grace period will already be in the process of
862 * being boosted. This simplifies the process of moving tasks
863 * from leaf to root rcu_node structures.
868 * Acquire lock, falling back to synchronize_rcu() if too many
869 * lock-acquisition failures. Of course, if someone does the
870 * expedited grace period for us, just leave.
872 while (!mutex_trylock(&sync_rcu_preempt_exp_mutex
)) {
873 if (ULONG_CMP_LT(snap
,
874 ACCESS_ONCE(sync_rcu_preempt_exp_count
))) {
876 goto mb_ret
; /* Others did our work for us. */
878 if (trycount
++ < 10) {
879 udelay(trycount
* num_online_cpus());
882 wait_rcu_gp(call_rcu
);
886 if (ULONG_CMP_LT(snap
, ACCESS_ONCE(sync_rcu_preempt_exp_count
))) {
888 goto unlock_mb_ret
; /* Others did our work for us. */
891 /* force all RCU readers onto ->blkd_tasks lists. */
892 synchronize_sched_expedited();
894 /* Initialize ->expmask for all non-leaf rcu_node structures. */
895 rcu_for_each_nonleaf_node_breadth_first(rsp
, rnp
) {
896 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
897 smp_mb__after_unlock_lock();
898 rnp
->expmask
= rnp
->qsmaskinit
;
899 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
902 /* Snapshot current state of ->blkd_tasks lists. */
903 rcu_for_each_leaf_node(rsp
, rnp
)
904 sync_rcu_preempt_exp_init(rsp
, rnp
);
905 if (NUM_RCU_NODES
> 1)
906 sync_rcu_preempt_exp_init(rsp
, rcu_get_root(rsp
));
910 /* Wait for snapshotted ->blkd_tasks lists to drain. */
911 rnp
= rcu_get_root(rsp
);
912 wait_event(sync_rcu_preempt_exp_wq
,
913 sync_rcu_preempt_exp_done(rnp
));
915 /* Clean up and exit. */
916 smp_mb(); /* ensure expedited GP seen before counter increment. */
917 ACCESS_ONCE(sync_rcu_preempt_exp_count
)++;
919 mutex_unlock(&sync_rcu_preempt_exp_mutex
);
921 smp_mb(); /* ensure subsequent action seen after grace period. */
923 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited
);
926 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
928 * Note that this primitive does not necessarily wait for an RCU grace period
929 * to complete. For example, if there are no RCU callbacks queued anywhere
930 * in the system, then rcu_barrier() is within its rights to return
931 * immediately, without waiting for anything, much less an RCU grace period.
933 void rcu_barrier(void)
935 _rcu_barrier(&rcu_preempt_state
);
937 EXPORT_SYMBOL_GPL(rcu_barrier
);
940 * Initialize preemptible RCU's state structures.
942 static void __init
__rcu_init_preempt(void)
944 rcu_init_one(&rcu_preempt_state
, &rcu_preempt_data
);
948 * Check for a task exiting while in a preemptible-RCU read-side
949 * critical section, clean up if so. No need to issue warnings,
950 * as debug_check_no_locks_held() already does this if lockdep
955 struct task_struct
*t
= current
;
957 if (likely(list_empty(¤t
->rcu_node_entry
)))
959 t
->rcu_read_lock_nesting
= 1;
961 t
->rcu_read_unlock_special
= RCU_READ_UNLOCK_BLOCKED
;
965 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
967 static struct rcu_state
*rcu_state
= &rcu_sched_state
;
970 * Tell them what RCU they are running.
972 static void __init
rcu_bootup_announce(void)
974 pr_info("Hierarchical RCU implementation.\n");
975 rcu_bootup_announce_oddness();
979 * Return the number of RCU batches processed thus far for debug & stats.
981 long rcu_batches_completed(void)
983 return rcu_batches_completed_sched();
985 EXPORT_SYMBOL_GPL(rcu_batches_completed
);
988 * Force a quiescent state for RCU, which, because there is no preemptible
989 * RCU, becomes the same as rcu-sched.
991 void rcu_force_quiescent_state(void)
993 rcu_sched_force_quiescent_state();
995 EXPORT_SYMBOL_GPL(rcu_force_quiescent_state
);
998 * Because preemptible RCU does not exist, we never have to check for
999 * CPUs being in quiescent states.
1001 static void rcu_preempt_note_context_switch(int cpu
)
1006 * Because preemptible RCU does not exist, there are never any preempted
1009 static int rcu_preempt_blocked_readers_cgp(struct rcu_node
*rnp
)
1014 #ifdef CONFIG_HOTPLUG_CPU
1016 /* Because preemptible RCU does not exist, no quieting of tasks. */
1017 static void rcu_report_unblock_qs_rnp(struct rcu_node
*rnp
, unsigned long flags
)
1019 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1022 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1025 * Because preemptible RCU does not exist, we never have to check for
1026 * tasks blocked within RCU read-side critical sections.
1028 static void rcu_print_detail_task_stall(struct rcu_state
*rsp
)
1033 * Because preemptible RCU does not exist, we never have to check for
1034 * tasks blocked within RCU read-side critical sections.
1036 static int rcu_print_task_stall(struct rcu_node
*rnp
)
1042 * Because there is no preemptible RCU, there can be no readers blocked,
1043 * so there is no need to check for blocked tasks. So check only for
1044 * bogus qsmask values.
1046 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
1048 WARN_ON_ONCE(rnp
->qsmask
);
1051 #ifdef CONFIG_HOTPLUG_CPU
1054 * Because preemptible RCU does not exist, it never needs to migrate
1055 * tasks that were blocked within RCU read-side critical sections, and
1056 * such non-existent tasks cannot possibly have been blocking the current
1059 static int rcu_preempt_offline_tasks(struct rcu_state
*rsp
,
1060 struct rcu_node
*rnp
,
1061 struct rcu_data
*rdp
)
1066 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1069 * Because preemptible RCU does not exist, it never has any callbacks
1072 static void rcu_preempt_check_callbacks(int cpu
)
1077 * Queue an RCU callback for lazy invocation after a grace period.
1078 * This will likely be later named something like "call_rcu_lazy()",
1079 * but this change will require some way of tagging the lazy RCU
1080 * callbacks in the list of pending callbacks. Until then, this
1081 * function may only be called from __kfree_rcu().
1083 * Because there is no preemptible RCU, we use RCU-sched instead.
1085 void kfree_call_rcu(struct rcu_head
*head
,
1086 void (*func
)(struct rcu_head
*rcu
))
1088 __call_rcu(head
, func
, &rcu_sched_state
, -1, 1);
1090 EXPORT_SYMBOL_GPL(kfree_call_rcu
);
1093 * Wait for an rcu-preempt grace period, but make it happen quickly.
1094 * But because preemptible RCU does not exist, map to rcu-sched.
1096 void synchronize_rcu_expedited(void)
1098 synchronize_sched_expedited();
1100 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited
);
1102 #ifdef CONFIG_HOTPLUG_CPU
1105 * Because preemptible RCU does not exist, there is never any need to
1106 * report on tasks preempted in RCU read-side critical sections during
1107 * expedited RCU grace periods.
1109 static void rcu_report_exp_rnp(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
1114 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1117 * Because preemptible RCU does not exist, rcu_barrier() is just
1118 * another name for rcu_barrier_sched().
1120 void rcu_barrier(void)
1122 rcu_barrier_sched();
1124 EXPORT_SYMBOL_GPL(rcu_barrier
);
1127 * Because preemptible RCU does not exist, it need not be initialized.
1129 static void __init
__rcu_init_preempt(void)
1134 * Because preemptible RCU does not exist, tasks cannot possibly exit
1135 * while in preemptible RCU read-side critical sections.
1141 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1143 #ifdef CONFIG_RCU_BOOST
1145 #include "../locking/rtmutex_common.h"
1147 #ifdef CONFIG_RCU_TRACE
1149 static void rcu_initiate_boost_trace(struct rcu_node
*rnp
)
1151 if (list_empty(&rnp
->blkd_tasks
))
1152 rnp
->n_balk_blkd_tasks
++;
1153 else if (rnp
->exp_tasks
== NULL
&& rnp
->gp_tasks
== NULL
)
1154 rnp
->n_balk_exp_gp_tasks
++;
1155 else if (rnp
->gp_tasks
!= NULL
&& rnp
->boost_tasks
!= NULL
)
1156 rnp
->n_balk_boost_tasks
++;
1157 else if (rnp
->gp_tasks
!= NULL
&& rnp
->qsmask
!= 0)
1158 rnp
->n_balk_notblocked
++;
1159 else if (rnp
->gp_tasks
!= NULL
&&
1160 ULONG_CMP_LT(jiffies
, rnp
->boost_time
))
1161 rnp
->n_balk_notyet
++;
1166 #else /* #ifdef CONFIG_RCU_TRACE */
1168 static void rcu_initiate_boost_trace(struct rcu_node
*rnp
)
1172 #endif /* #else #ifdef CONFIG_RCU_TRACE */
1174 static void rcu_wake_cond(struct task_struct
*t
, int status
)
1177 * If the thread is yielding, only wake it when this
1178 * is invoked from idle
1180 if (status
!= RCU_KTHREAD_YIELDING
|| is_idle_task(current
))
1185 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
1186 * or ->boost_tasks, advancing the pointer to the next task in the
1187 * ->blkd_tasks list.
1189 * Note that irqs must be enabled: boosting the task can block.
1190 * Returns 1 if there are more tasks needing to be boosted.
1192 static int rcu_boost(struct rcu_node
*rnp
)
1194 unsigned long flags
;
1195 struct rt_mutex mtx
;
1196 struct task_struct
*t
;
1197 struct list_head
*tb
;
1199 if (rnp
->exp_tasks
== NULL
&& rnp
->boost_tasks
== NULL
)
1200 return 0; /* Nothing left to boost. */
1202 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1203 smp_mb__after_unlock_lock();
1206 * Recheck under the lock: all tasks in need of boosting
1207 * might exit their RCU read-side critical sections on their own.
1209 if (rnp
->exp_tasks
== NULL
&& rnp
->boost_tasks
== NULL
) {
1210 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1215 * Preferentially boost tasks blocking expedited grace periods.
1216 * This cannot starve the normal grace periods because a second
1217 * expedited grace period must boost all blocked tasks, including
1218 * those blocking the pre-existing normal grace period.
1220 if (rnp
->exp_tasks
!= NULL
) {
1221 tb
= rnp
->exp_tasks
;
1222 rnp
->n_exp_boosts
++;
1224 tb
= rnp
->boost_tasks
;
1225 rnp
->n_normal_boosts
++;
1227 rnp
->n_tasks_boosted
++;
1230 * We boost task t by manufacturing an rt_mutex that appears to
1231 * be held by task t. We leave a pointer to that rt_mutex where
1232 * task t can find it, and task t will release the mutex when it
1233 * exits its outermost RCU read-side critical section. Then
1234 * simply acquiring this artificial rt_mutex will boost task
1235 * t's priority. (Thanks to tglx for suggesting this approach!)
1237 * Note that task t must acquire rnp->lock to remove itself from
1238 * the ->blkd_tasks list, which it will do from exit() if from
1239 * nowhere else. We therefore are guaranteed that task t will
1240 * stay around at least until we drop rnp->lock. Note that
1241 * rnp->lock also resolves races between our priority boosting
1242 * and task t's exiting its outermost RCU read-side critical
1245 t
= container_of(tb
, struct task_struct
, rcu_node_entry
);
1246 rt_mutex_init_proxy_locked(&mtx
, t
);
1247 t
->rcu_boost_mutex
= &mtx
;
1248 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1249 rt_mutex_lock(&mtx
); /* Side effect: boosts task t's priority. */
1250 rt_mutex_unlock(&mtx
); /* Keep lockdep happy. */
1252 return ACCESS_ONCE(rnp
->exp_tasks
) != NULL
||
1253 ACCESS_ONCE(rnp
->boost_tasks
) != NULL
;
1257 * Priority-boosting kthread. One per leaf rcu_node and one for the
1260 static int rcu_boost_kthread(void *arg
)
1262 struct rcu_node
*rnp
= (struct rcu_node
*)arg
;
1266 trace_rcu_utilization(TPS("Start boost kthread@init"));
1268 rnp
->boost_kthread_status
= RCU_KTHREAD_WAITING
;
1269 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1270 rcu_wait(rnp
->boost_tasks
|| rnp
->exp_tasks
);
1271 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1272 rnp
->boost_kthread_status
= RCU_KTHREAD_RUNNING
;
1273 more2boost
= rcu_boost(rnp
);
1279 rnp
->boost_kthread_status
= RCU_KTHREAD_YIELDING
;
1280 trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1281 schedule_timeout_interruptible(2);
1282 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1287 trace_rcu_utilization(TPS("End boost kthread@notreached"));
1292 * Check to see if it is time to start boosting RCU readers that are
1293 * blocking the current grace period, and, if so, tell the per-rcu_node
1294 * kthread to start boosting them. If there is an expedited grace
1295 * period in progress, it is always time to boost.
1297 * The caller must hold rnp->lock, which this function releases.
1298 * The ->boost_kthread_task is immortal, so we don't need to worry
1299 * about it going away.
1301 static void rcu_initiate_boost(struct rcu_node
*rnp
, unsigned long flags
)
1303 struct task_struct
*t
;
1305 if (!rcu_preempt_blocked_readers_cgp(rnp
) && rnp
->exp_tasks
== NULL
) {
1306 rnp
->n_balk_exp_gp_tasks
++;
1307 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1310 if (rnp
->exp_tasks
!= NULL
||
1311 (rnp
->gp_tasks
!= NULL
&&
1312 rnp
->boost_tasks
== NULL
&&
1314 ULONG_CMP_GE(jiffies
, rnp
->boost_time
))) {
1315 if (rnp
->exp_tasks
== NULL
)
1316 rnp
->boost_tasks
= rnp
->gp_tasks
;
1317 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1318 t
= rnp
->boost_kthread_task
;
1320 rcu_wake_cond(t
, rnp
->boost_kthread_status
);
1322 rcu_initiate_boost_trace(rnp
);
1323 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1328 * Wake up the per-CPU kthread to invoke RCU callbacks.
1330 static void invoke_rcu_callbacks_kthread(void)
1332 unsigned long flags
;
1334 local_irq_save(flags
);
1335 __this_cpu_write(rcu_cpu_has_work
, 1);
1336 if (__this_cpu_read(rcu_cpu_kthread_task
) != NULL
&&
1337 current
!= __this_cpu_read(rcu_cpu_kthread_task
)) {
1338 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task
),
1339 __this_cpu_read(rcu_cpu_kthread_status
));
1341 local_irq_restore(flags
);
1345 * Is the current CPU running the RCU-callbacks kthread?
1346 * Caller must have preemption disabled.
1348 static bool rcu_is_callbacks_kthread(void)
1350 return __this_cpu_read(rcu_cpu_kthread_task
) == current
;
1353 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1356 * Do priority-boost accounting for the start of a new grace period.
1358 static void rcu_preempt_boost_start_gp(struct rcu_node
*rnp
)
1360 rnp
->boost_time
= jiffies
+ RCU_BOOST_DELAY_JIFFIES
;
1364 * Create an RCU-boost kthread for the specified node if one does not
1365 * already exist. We only create this kthread for preemptible RCU.
1366 * Returns zero if all is well, a negated errno otherwise.
1368 static int rcu_spawn_one_boost_kthread(struct rcu_state
*rsp
,
1369 struct rcu_node
*rnp
)
1371 int rnp_index
= rnp
- &rsp
->node
[0];
1372 unsigned long flags
;
1373 struct sched_param sp
;
1374 struct task_struct
*t
;
1376 if (&rcu_preempt_state
!= rsp
)
1379 if (!rcu_scheduler_fully_active
|| rnp
->qsmaskinit
== 0)
1383 if (rnp
->boost_kthread_task
!= NULL
)
1385 t
= kthread_create(rcu_boost_kthread
, (void *)rnp
,
1386 "rcub/%d", rnp_index
);
1389 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1390 smp_mb__after_unlock_lock();
1391 rnp
->boost_kthread_task
= t
;
1392 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1393 sp
.sched_priority
= RCU_BOOST_PRIO
;
1394 sched_setscheduler_nocheck(t
, SCHED_FIFO
, &sp
);
1395 wake_up_process(t
); /* get to TASK_INTERRUPTIBLE quickly. */
1399 static void rcu_kthread_do_work(void)
1401 rcu_do_batch(&rcu_sched_state
, this_cpu_ptr(&rcu_sched_data
));
1402 rcu_do_batch(&rcu_bh_state
, this_cpu_ptr(&rcu_bh_data
));
1403 rcu_preempt_do_callbacks();
1406 static void rcu_cpu_kthread_setup(unsigned int cpu
)
1408 struct sched_param sp
;
1410 sp
.sched_priority
= RCU_KTHREAD_PRIO
;
1411 sched_setscheduler_nocheck(current
, SCHED_FIFO
, &sp
);
1414 static void rcu_cpu_kthread_park(unsigned int cpu
)
1416 per_cpu(rcu_cpu_kthread_status
, cpu
) = RCU_KTHREAD_OFFCPU
;
1419 static int rcu_cpu_kthread_should_run(unsigned int cpu
)
1421 return __this_cpu_read(rcu_cpu_has_work
);
1425 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
1426 * RCU softirq used in flavors and configurations of RCU that do not
1427 * support RCU priority boosting.
1429 static void rcu_cpu_kthread(unsigned int cpu
)
1431 unsigned int *statusp
= this_cpu_ptr(&rcu_cpu_kthread_status
);
1432 char work
, *workp
= this_cpu_ptr(&rcu_cpu_has_work
);
1435 for (spincnt
= 0; spincnt
< 10; spincnt
++) {
1436 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1438 *statusp
= RCU_KTHREAD_RUNNING
;
1439 this_cpu_inc(rcu_cpu_kthread_loops
);
1440 local_irq_disable();
1445 rcu_kthread_do_work();
1448 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1449 *statusp
= RCU_KTHREAD_WAITING
;
1453 *statusp
= RCU_KTHREAD_YIELDING
;
1454 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1455 schedule_timeout_interruptible(2);
1456 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1457 *statusp
= RCU_KTHREAD_WAITING
;
1461 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1462 * served by the rcu_node in question. The CPU hotplug lock is still
1463 * held, so the value of rnp->qsmaskinit will be stable.
1465 * We don't include outgoingcpu in the affinity set, use -1 if there is
1466 * no outgoing CPU. If there are no CPUs left in the affinity set,
1467 * this function allows the kthread to execute on any CPU.
1469 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
)
1471 struct task_struct
*t
= rnp
->boost_kthread_task
;
1472 unsigned long mask
= rnp
->qsmaskinit
;
1478 if (!zalloc_cpumask_var(&cm
, GFP_KERNEL
))
1480 for (cpu
= rnp
->grplo
; cpu
<= rnp
->grphi
; cpu
++, mask
>>= 1)
1481 if ((mask
& 0x1) && cpu
!= outgoingcpu
)
1482 cpumask_set_cpu(cpu
, cm
);
1483 if (cpumask_weight(cm
) == 0) {
1485 for (cpu
= rnp
->grplo
; cpu
<= rnp
->grphi
; cpu
++)
1486 cpumask_clear_cpu(cpu
, cm
);
1487 WARN_ON_ONCE(cpumask_weight(cm
) == 0);
1489 set_cpus_allowed_ptr(t
, cm
);
1490 free_cpumask_var(cm
);
1493 static struct smp_hotplug_thread rcu_cpu_thread_spec
= {
1494 .store
= &rcu_cpu_kthread_task
,
1495 .thread_should_run
= rcu_cpu_kthread_should_run
,
1496 .thread_fn
= rcu_cpu_kthread
,
1497 .thread_comm
= "rcuc/%u",
1498 .setup
= rcu_cpu_kthread_setup
,
1499 .park
= rcu_cpu_kthread_park
,
1503 * Spawn all kthreads -- called as soon as the scheduler is running.
1505 static int __init
rcu_spawn_kthreads(void)
1507 struct rcu_node
*rnp
;
1510 rcu_scheduler_fully_active
= 1;
1511 for_each_possible_cpu(cpu
)
1512 per_cpu(rcu_cpu_has_work
, cpu
) = 0;
1513 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec
));
1514 rnp
= rcu_get_root(rcu_state
);
1515 (void)rcu_spawn_one_boost_kthread(rcu_state
, rnp
);
1516 if (NUM_RCU_NODES
> 1) {
1517 rcu_for_each_leaf_node(rcu_state
, rnp
)
1518 (void)rcu_spawn_one_boost_kthread(rcu_state
, rnp
);
1522 early_initcall(rcu_spawn_kthreads
);
1524 static void rcu_prepare_kthreads(int cpu
)
1526 struct rcu_data
*rdp
= per_cpu_ptr(rcu_state
->rda
, cpu
);
1527 struct rcu_node
*rnp
= rdp
->mynode
;
1529 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1530 if (rcu_scheduler_fully_active
)
1531 (void)rcu_spawn_one_boost_kthread(rcu_state
, rnp
);
1534 #else /* #ifdef CONFIG_RCU_BOOST */
1536 static void rcu_initiate_boost(struct rcu_node
*rnp
, unsigned long flags
)
1538 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1541 static void invoke_rcu_callbacks_kthread(void)
1546 static bool rcu_is_callbacks_kthread(void)
1551 static void rcu_preempt_boost_start_gp(struct rcu_node
*rnp
)
1555 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
)
1559 static int __init
rcu_scheduler_really_started(void)
1561 rcu_scheduler_fully_active
= 1;
1564 early_initcall(rcu_scheduler_really_started
);
1566 static void rcu_prepare_kthreads(int cpu
)
1570 #endif /* #else #ifdef CONFIG_RCU_BOOST */
1572 #if !defined(CONFIG_RCU_FAST_NO_HZ)
1575 * Check to see if any future RCU-related work will need to be done
1576 * by the current CPU, even if none need be done immediately, returning
1577 * 1 if so. This function is part of the RCU implementation; it is -not-
1578 * an exported member of the RCU API.
1580 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1581 * any flavor of RCU.
1583 int rcu_needs_cpu(int cpu
, unsigned long *delta_jiffies
)
1585 *delta_jiffies
= ULONG_MAX
;
1586 return rcu_cpu_has_callbacks(cpu
, NULL
);
1590 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1593 static void rcu_cleanup_after_idle(int cpu
)
1598 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1601 static void rcu_prepare_for_idle(int cpu
)
1606 * Don't bother keeping a running count of the number of RCU callbacks
1607 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1609 static void rcu_idle_count_callbacks_posted(void)
1613 #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1616 * This code is invoked when a CPU goes idle, at which point we want
1617 * to have the CPU do everything required for RCU so that it can enter
1618 * the energy-efficient dyntick-idle mode. This is handled by a
1619 * state machine implemented by rcu_prepare_for_idle() below.
1621 * The following three proprocessor symbols control this state machine:
1623 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1624 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1625 * is sized to be roughly one RCU grace period. Those energy-efficiency
1626 * benchmarkers who might otherwise be tempted to set this to a large
1627 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1628 * system. And if you are -that- concerned about energy efficiency,
1629 * just power the system down and be done with it!
1630 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1631 * permitted to sleep in dyntick-idle mode with only lazy RCU
1632 * callbacks pending. Setting this too high can OOM your system.
1634 * The values below work well in practice. If future workloads require
1635 * adjustment, they can be converted into kernel config parameters, though
1636 * making the state machine smarter might be a better option.
1638 #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1639 #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1641 static int rcu_idle_gp_delay
= RCU_IDLE_GP_DELAY
;
1642 module_param(rcu_idle_gp_delay
, int, 0644);
1643 static int rcu_idle_lazy_gp_delay
= RCU_IDLE_LAZY_GP_DELAY
;
1644 module_param(rcu_idle_lazy_gp_delay
, int, 0644);
1646 extern int tick_nohz_enabled
;
1649 * Try to advance callbacks for all flavors of RCU on the current CPU, but
1650 * only if it has been awhile since the last time we did so. Afterwards,
1651 * if there are any callbacks ready for immediate invocation, return true.
1653 static bool rcu_try_advance_all_cbs(void)
1655 bool cbs_ready
= false;
1656 struct rcu_data
*rdp
;
1657 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
1658 struct rcu_node
*rnp
;
1659 struct rcu_state
*rsp
;
1661 /* Exit early if we advanced recently. */
1662 if (jiffies
== rdtp
->last_advance_all
)
1664 rdtp
->last_advance_all
= jiffies
;
1666 for_each_rcu_flavor(rsp
) {
1667 rdp
= this_cpu_ptr(rsp
->rda
);
1671 * Don't bother checking unless a grace period has
1672 * completed since we last checked and there are
1673 * callbacks not yet ready to invoke.
1675 if (rdp
->completed
!= rnp
->completed
&&
1676 rdp
->nxttail
[RCU_DONE_TAIL
] != rdp
->nxttail
[RCU_NEXT_TAIL
])
1677 note_gp_changes(rsp
, rdp
);
1679 if (cpu_has_callbacks_ready_to_invoke(rdp
))
1686 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1687 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1688 * caller to set the timeout based on whether or not there are non-lazy
1691 * The caller must have disabled interrupts.
1693 int rcu_needs_cpu(int cpu
, unsigned long *dj
)
1695 struct rcu_dynticks
*rdtp
= &per_cpu(rcu_dynticks
, cpu
);
1697 /* Snapshot to detect later posting of non-lazy callback. */
1698 rdtp
->nonlazy_posted_snap
= rdtp
->nonlazy_posted
;
1700 /* If no callbacks, RCU doesn't need the CPU. */
1701 if (!rcu_cpu_has_callbacks(cpu
, &rdtp
->all_lazy
)) {
1706 /* Attempt to advance callbacks. */
1707 if (rcu_try_advance_all_cbs()) {
1708 /* Some ready to invoke, so initiate later invocation. */
1712 rdtp
->last_accelerate
= jiffies
;
1714 /* Request timer delay depending on laziness, and round. */
1715 if (!rdtp
->all_lazy
) {
1716 *dj
= round_up(rcu_idle_gp_delay
+ jiffies
,
1717 rcu_idle_gp_delay
) - jiffies
;
1719 *dj
= round_jiffies(rcu_idle_lazy_gp_delay
+ jiffies
) - jiffies
;
1725 * Prepare a CPU for idle from an RCU perspective. The first major task
1726 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1727 * The second major task is to check to see if a non-lazy callback has
1728 * arrived at a CPU that previously had only lazy callbacks. The third
1729 * major task is to accelerate (that is, assign grace-period numbers to)
1730 * any recently arrived callbacks.
1732 * The caller must have disabled interrupts.
1734 static void rcu_prepare_for_idle(int cpu
)
1736 struct rcu_data
*rdp
;
1737 struct rcu_dynticks
*rdtp
= &per_cpu(rcu_dynticks
, cpu
);
1738 struct rcu_node
*rnp
;
1739 struct rcu_state
*rsp
;
1742 /* Handle nohz enablement switches conservatively. */
1743 tne
= ACCESS_ONCE(tick_nohz_enabled
);
1744 if (tne
!= rdtp
->tick_nohz_enabled_snap
) {
1745 if (rcu_cpu_has_callbacks(cpu
, NULL
))
1746 invoke_rcu_core(); /* force nohz to see update. */
1747 rdtp
->tick_nohz_enabled_snap
= tne
;
1753 /* If this is a no-CBs CPU, no callbacks, just return. */
1754 if (rcu_is_nocb_cpu(cpu
))
1758 * If a non-lazy callback arrived at a CPU having only lazy
1759 * callbacks, invoke RCU core for the side-effect of recalculating
1760 * idle duration on re-entry to idle.
1762 if (rdtp
->all_lazy
&&
1763 rdtp
->nonlazy_posted
!= rdtp
->nonlazy_posted_snap
) {
1764 rdtp
->all_lazy
= false;
1765 rdtp
->nonlazy_posted_snap
= rdtp
->nonlazy_posted
;
1771 * If we have not yet accelerated this jiffy, accelerate all
1772 * callbacks on this CPU.
1774 if (rdtp
->last_accelerate
== jiffies
)
1776 rdtp
->last_accelerate
= jiffies
;
1777 for_each_rcu_flavor(rsp
) {
1778 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1779 if (!*rdp
->nxttail
[RCU_DONE_TAIL
])
1782 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1783 smp_mb__after_unlock_lock();
1784 rcu_accelerate_cbs(rsp
, rnp
, rdp
);
1785 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1790 * Clean up for exit from idle. Attempt to advance callbacks based on
1791 * any grace periods that elapsed while the CPU was idle, and if any
1792 * callbacks are now ready to invoke, initiate invocation.
1794 static void rcu_cleanup_after_idle(int cpu
)
1797 if (rcu_is_nocb_cpu(cpu
))
1799 if (rcu_try_advance_all_cbs())
1804 * Keep a running count of the number of non-lazy callbacks posted
1805 * on this CPU. This running counter (which is never decremented) allows
1806 * rcu_prepare_for_idle() to detect when something out of the idle loop
1807 * posts a callback, even if an equal number of callbacks are invoked.
1808 * Of course, callbacks should only be posted from within a trace event
1809 * designed to be called from idle or from within RCU_NONIDLE().
1811 static void rcu_idle_count_callbacks_posted(void)
1813 __this_cpu_add(rcu_dynticks
.nonlazy_posted
, 1);
1817 * Data for flushing lazy RCU callbacks at OOM time.
1819 static atomic_t oom_callback_count
;
1820 static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq
);
1823 * RCU OOM callback -- decrement the outstanding count and deliver the
1824 * wake-up if we are the last one.
1826 static void rcu_oom_callback(struct rcu_head
*rhp
)
1828 if (atomic_dec_and_test(&oom_callback_count
))
1829 wake_up(&oom_callback_wq
);
1833 * Post an rcu_oom_notify callback on the current CPU if it has at
1834 * least one lazy callback. This will unnecessarily post callbacks
1835 * to CPUs that already have a non-lazy callback at the end of their
1836 * callback list, but this is an infrequent operation, so accept some
1837 * extra overhead to keep things simple.
1839 static void rcu_oom_notify_cpu(void *unused
)
1841 struct rcu_state
*rsp
;
1842 struct rcu_data
*rdp
;
1844 for_each_rcu_flavor(rsp
) {
1845 rdp
= __this_cpu_ptr(rsp
->rda
);
1846 if (rdp
->qlen_lazy
!= 0) {
1847 atomic_inc(&oom_callback_count
);
1848 rsp
->call(&rdp
->oom_head
, rcu_oom_callback
);
1854 * If low on memory, ensure that each CPU has a non-lazy callback.
1855 * This will wake up CPUs that have only lazy callbacks, in turn
1856 * ensuring that they free up the corresponding memory in a timely manner.
1857 * Because an uncertain amount of memory will be freed in some uncertain
1858 * timeframe, we do not claim to have freed anything.
1860 static int rcu_oom_notify(struct notifier_block
*self
,
1861 unsigned long notused
, void *nfreed
)
1865 /* Wait for callbacks from earlier instance to complete. */
1866 wait_event(oom_callback_wq
, atomic_read(&oom_callback_count
) == 0);
1869 * Prevent premature wakeup: ensure that all increments happen
1870 * before there is a chance of the counter reaching zero.
1872 atomic_set(&oom_callback_count
, 1);
1875 for_each_online_cpu(cpu
) {
1876 smp_call_function_single(cpu
, rcu_oom_notify_cpu
, NULL
, 1);
1881 /* Unconditionally decrement: no need to wake ourselves up. */
1882 atomic_dec(&oom_callback_count
);
1887 static struct notifier_block rcu_oom_nb
= {
1888 .notifier_call
= rcu_oom_notify
1891 static int __init
rcu_register_oom_notifier(void)
1893 register_oom_notifier(&rcu_oom_nb
);
1896 early_initcall(rcu_register_oom_notifier
);
1898 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1900 #ifdef CONFIG_RCU_CPU_STALL_INFO
1902 #ifdef CONFIG_RCU_FAST_NO_HZ
1904 static void print_cpu_stall_fast_no_hz(char *cp
, int cpu
)
1906 struct rcu_dynticks
*rdtp
= &per_cpu(rcu_dynticks
, cpu
);
1907 unsigned long nlpd
= rdtp
->nonlazy_posted
- rdtp
->nonlazy_posted_snap
;
1909 sprintf(cp
, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1910 rdtp
->last_accelerate
& 0xffff, jiffies
& 0xffff,
1912 rdtp
->all_lazy
? 'L' : '.',
1913 rdtp
->tick_nohz_enabled_snap
? '.' : 'D');
1916 #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1918 static void print_cpu_stall_fast_no_hz(char *cp
, int cpu
)
1923 #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1925 /* Initiate the stall-info list. */
1926 static void print_cpu_stall_info_begin(void)
1932 * Print out diagnostic information for the specified stalled CPU.
1934 * If the specified CPU is aware of the current RCU grace period
1935 * (flavor specified by rsp), then print the number of scheduling
1936 * clock interrupts the CPU has taken during the time that it has
1937 * been aware. Otherwise, print the number of RCU grace periods
1938 * that this CPU is ignorant of, for example, "1" if the CPU was
1939 * aware of the previous grace period.
1941 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1943 static void print_cpu_stall_info(struct rcu_state
*rsp
, int cpu
)
1945 char fast_no_hz
[72];
1946 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1947 struct rcu_dynticks
*rdtp
= rdp
->dynticks
;
1949 unsigned long ticks_value
;
1951 if (rsp
->gpnum
== rdp
->gpnum
) {
1952 ticks_title
= "ticks this GP";
1953 ticks_value
= rdp
->ticks_this_gp
;
1955 ticks_title
= "GPs behind";
1956 ticks_value
= rsp
->gpnum
- rdp
->gpnum
;
1958 print_cpu_stall_fast_no_hz(fast_no_hz
, cpu
);
1959 pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
1960 cpu
, ticks_value
, ticks_title
,
1961 atomic_read(&rdtp
->dynticks
) & 0xfff,
1962 rdtp
->dynticks_nesting
, rdtp
->dynticks_nmi_nesting
,
1963 rdp
->softirq_snap
, kstat_softirqs_cpu(RCU_SOFTIRQ
, cpu
),
1967 /* Terminate the stall-info list. */
1968 static void print_cpu_stall_info_end(void)
1973 /* Zero ->ticks_this_gp for all flavors of RCU. */
1974 static void zero_cpu_stall_ticks(struct rcu_data
*rdp
)
1976 rdp
->ticks_this_gp
= 0;
1977 rdp
->softirq_snap
= kstat_softirqs_cpu(RCU_SOFTIRQ
, smp_processor_id());
1980 /* Increment ->ticks_this_gp for all flavors of RCU. */
1981 static void increment_cpu_stall_ticks(void)
1983 struct rcu_state
*rsp
;
1985 for_each_rcu_flavor(rsp
)
1986 __this_cpu_ptr(rsp
->rda
)->ticks_this_gp
++;
1989 #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
1991 static void print_cpu_stall_info_begin(void)
1996 static void print_cpu_stall_info(struct rcu_state
*rsp
, int cpu
)
1998 pr_cont(" %d", cpu
);
2001 static void print_cpu_stall_info_end(void)
2006 static void zero_cpu_stall_ticks(struct rcu_data
*rdp
)
2010 static void increment_cpu_stall_ticks(void)
2014 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
2016 #ifdef CONFIG_RCU_NOCB_CPU
2019 * Offload callback processing from the boot-time-specified set of CPUs
2020 * specified by rcu_nocb_mask. For each CPU in the set, there is a
2021 * kthread created that pulls the callbacks from the corresponding CPU,
2022 * waits for a grace period to elapse, and invokes the callbacks.
2023 * The no-CBs CPUs do a wake_up() on their kthread when they insert
2024 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
2025 * has been specified, in which case each kthread actively polls its
2026 * CPU. (Which isn't so great for energy efficiency, but which does
2027 * reduce RCU's overhead on that CPU.)
2029 * This is intended to be used in conjunction with Frederic Weisbecker's
2030 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
2031 * running CPU-bound user-mode computations.
2033 * Offloading of callback processing could also in theory be used as
2034 * an energy-efficiency measure because CPUs with no RCU callbacks
2035 * queued are more aggressive about entering dyntick-idle mode.
2039 /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
2040 static int __init
rcu_nocb_setup(char *str
)
2042 alloc_bootmem_cpumask_var(&rcu_nocb_mask
);
2043 have_rcu_nocb_mask
= true;
2044 cpulist_parse(str
, rcu_nocb_mask
);
2047 __setup("rcu_nocbs=", rcu_nocb_setup
);
2049 static int __init
parse_rcu_nocb_poll(char *arg
)
2054 early_param("rcu_nocb_poll", parse_rcu_nocb_poll
);
2057 * Do any no-CBs CPUs need another grace period?
2059 * Interrupts must be disabled. If the caller does not hold the root
2060 * rnp_node structure's ->lock, the results are advisory only.
2062 static int rcu_nocb_needs_gp(struct rcu_state
*rsp
)
2064 struct rcu_node
*rnp
= rcu_get_root(rsp
);
2066 return rnp
->need_future_gp
[(ACCESS_ONCE(rnp
->completed
) + 1) & 0x1];
2070 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
2073 static void rcu_nocb_gp_cleanup(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
2075 wake_up_all(&rnp
->nocb_gp_wq
[rnp
->completed
& 0x1]);
2079 * Set the root rcu_node structure's ->need_future_gp field
2080 * based on the sum of those of all rcu_node structures. This does
2081 * double-count the root rcu_node structure's requests, but this
2082 * is necessary to handle the possibility of a rcu_nocb_kthread()
2083 * having awakened during the time that the rcu_node structures
2084 * were being updated for the end of the previous grace period.
2086 static void rcu_nocb_gp_set(struct rcu_node
*rnp
, int nrq
)
2088 rnp
->need_future_gp
[(rnp
->completed
+ 1) & 0x1] += nrq
;
2091 static void rcu_init_one_nocb(struct rcu_node
*rnp
)
2093 init_waitqueue_head(&rnp
->nocb_gp_wq
[0]);
2094 init_waitqueue_head(&rnp
->nocb_gp_wq
[1]);
2097 /* Is the specified CPU a no-CPUs CPU? */
2098 bool rcu_is_nocb_cpu(int cpu
)
2100 if (have_rcu_nocb_mask
)
2101 return cpumask_test_cpu(cpu
, rcu_nocb_mask
);
2106 * Enqueue the specified string of rcu_head structures onto the specified
2107 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
2108 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
2109 * counts are supplied by rhcount and rhcount_lazy.
2111 * If warranted, also wake up the kthread servicing this CPUs queues.
2113 static void __call_rcu_nocb_enqueue(struct rcu_data
*rdp
,
2114 struct rcu_head
*rhp
,
2115 struct rcu_head
**rhtp
,
2116 int rhcount
, int rhcount_lazy
)
2119 struct rcu_head
**old_rhpp
;
2120 struct task_struct
*t
;
2122 /* Enqueue the callback on the nocb list and update counts. */
2123 old_rhpp
= xchg(&rdp
->nocb_tail
, rhtp
);
2124 ACCESS_ONCE(*old_rhpp
) = rhp
;
2125 atomic_long_add(rhcount
, &rdp
->nocb_q_count
);
2126 atomic_long_add(rhcount_lazy
, &rdp
->nocb_q_count_lazy
);
2128 /* If we are not being polled and there is a kthread, awaken it ... */
2129 t
= ACCESS_ONCE(rdp
->nocb_kthread
);
2130 if (rcu_nocb_poll
|| !t
) {
2131 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2132 TPS("WakeNotPoll"));
2135 len
= atomic_long_read(&rdp
->nocb_q_count
);
2136 if (old_rhpp
== &rdp
->nocb_head
) {
2137 wake_up(&rdp
->nocb_wq
); /* ... only if queue was empty ... */
2138 rdp
->qlen_last_fqs_check
= 0;
2139 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, TPS("WakeEmpty"));
2140 } else if (len
> rdp
->qlen_last_fqs_check
+ qhimark
) {
2141 wake_up_process(t
); /* ... or if many callbacks queued. */
2142 rdp
->qlen_last_fqs_check
= LONG_MAX
/ 2;
2143 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, TPS("WakeOvf"));
2145 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, TPS("WakeNot"));
2151 * This is a helper for __call_rcu(), which invokes this when the normal
2152 * callback queue is inoperable. If this is not a no-CBs CPU, this
2153 * function returns failure back to __call_rcu(), which can complain
2156 * Otherwise, this function queues the callback where the corresponding
2157 * "rcuo" kthread can find it.
2159 static bool __call_rcu_nocb(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
2163 if (!rcu_is_nocb_cpu(rdp
->cpu
))
2165 __call_rcu_nocb_enqueue(rdp
, rhp
, &rhp
->next
, 1, lazy
);
2166 if (__is_kfree_rcu_offset((unsigned long)rhp
->func
))
2167 trace_rcu_kfree_callback(rdp
->rsp
->name
, rhp
,
2168 (unsigned long)rhp
->func
,
2169 -atomic_long_read(&rdp
->nocb_q_count_lazy
),
2170 -atomic_long_read(&rdp
->nocb_q_count
));
2172 trace_rcu_callback(rdp
->rsp
->name
, rhp
,
2173 -atomic_long_read(&rdp
->nocb_q_count_lazy
),
2174 -atomic_long_read(&rdp
->nocb_q_count
));
2179 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2182 static bool __maybe_unused
rcu_nocb_adopt_orphan_cbs(struct rcu_state
*rsp
,
2183 struct rcu_data
*rdp
)
2185 long ql
= rsp
->qlen
;
2186 long qll
= rsp
->qlen_lazy
;
2188 /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
2189 if (!rcu_is_nocb_cpu(smp_processor_id()))
2194 /* First, enqueue the donelist, if any. This preserves CB ordering. */
2195 if (rsp
->orphan_donelist
!= NULL
) {
2196 __call_rcu_nocb_enqueue(rdp
, rsp
->orphan_donelist
,
2197 rsp
->orphan_donetail
, ql
, qll
);
2199 rsp
->orphan_donelist
= NULL
;
2200 rsp
->orphan_donetail
= &rsp
->orphan_donelist
;
2202 if (rsp
->orphan_nxtlist
!= NULL
) {
2203 __call_rcu_nocb_enqueue(rdp
, rsp
->orphan_nxtlist
,
2204 rsp
->orphan_nxttail
, ql
, qll
);
2206 rsp
->orphan_nxtlist
= NULL
;
2207 rsp
->orphan_nxttail
= &rsp
->orphan_nxtlist
;
2213 * If necessary, kick off a new grace period, and either way wait
2214 * for a subsequent grace period to complete.
2216 static void rcu_nocb_wait_gp(struct rcu_data
*rdp
)
2220 unsigned long flags
;
2221 struct rcu_node
*rnp
= rdp
->mynode
;
2223 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2224 smp_mb__after_unlock_lock();
2225 c
= rcu_start_future_gp(rnp
, rdp
);
2226 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2229 * Wait for the grace period. Do so interruptibly to avoid messing
2230 * up the load average.
2232 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("StartWait"));
2234 wait_event_interruptible(
2235 rnp
->nocb_gp_wq
[c
& 0x1],
2236 (d
= ULONG_CMP_GE(ACCESS_ONCE(rnp
->completed
), c
)));
2239 flush_signals(current
);
2240 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("ResumeWait"));
2242 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("EndWait"));
2243 smp_mb(); /* Ensure that CB invocation happens after GP end. */
2247 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
2248 * callbacks queued by the corresponding no-CBs CPU.
2250 static int rcu_nocb_kthread(void *arg
)
2254 struct rcu_head
*list
;
2255 struct rcu_head
*next
;
2256 struct rcu_head
**tail
;
2257 struct rcu_data
*rdp
= arg
;
2259 /* Each pass through this loop invokes one batch of callbacks */
2261 /* If not polling, wait for next batch of callbacks. */
2262 if (!rcu_nocb_poll
) {
2263 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2265 wait_event_interruptible(rdp
->nocb_wq
, rdp
->nocb_head
);
2266 } else if (firsttime
) {
2268 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2271 list
= ACCESS_ONCE(rdp
->nocb_head
);
2274 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2276 schedule_timeout_interruptible(1);
2277 flush_signals(current
);
2281 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2282 TPS("WokeNonEmpty"));
2285 * Extract queued callbacks, update counts, and wait
2286 * for a grace period to elapse.
2288 ACCESS_ONCE(rdp
->nocb_head
) = NULL
;
2289 tail
= xchg(&rdp
->nocb_tail
, &rdp
->nocb_head
);
2290 c
= atomic_long_xchg(&rdp
->nocb_q_count
, 0);
2291 cl
= atomic_long_xchg(&rdp
->nocb_q_count_lazy
, 0);
2292 ACCESS_ONCE(rdp
->nocb_p_count
) += c
;
2293 ACCESS_ONCE(rdp
->nocb_p_count_lazy
) += cl
;
2294 rcu_nocb_wait_gp(rdp
);
2296 /* Each pass through the following loop invokes a callback. */
2297 trace_rcu_batch_start(rdp
->rsp
->name
, cl
, c
, -1);
2301 /* Wait for enqueuing to complete, if needed. */
2302 while (next
== NULL
&& &list
->next
!= tail
) {
2303 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2305 schedule_timeout_interruptible(1);
2306 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2310 debug_rcu_head_unqueue(list
);
2312 if (__rcu_reclaim(rdp
->rsp
->name
, list
))
2318 trace_rcu_batch_end(rdp
->rsp
->name
, c
, !!list
, 0, 0, 1);
2319 ACCESS_ONCE(rdp
->nocb_p_count
) -= c
;
2320 ACCESS_ONCE(rdp
->nocb_p_count_lazy
) -= cl
;
2321 rdp
->n_nocbs_invoked
+= c
;
2326 /* Initialize per-rcu_data variables for no-CBs CPUs. */
2327 static void __init
rcu_boot_init_nocb_percpu_data(struct rcu_data
*rdp
)
2329 rdp
->nocb_tail
= &rdp
->nocb_head
;
2330 init_waitqueue_head(&rdp
->nocb_wq
);
2333 /* Create a kthread for each RCU flavor for each no-CBs CPU. */
2334 static void __init
rcu_spawn_nocb_kthreads(struct rcu_state
*rsp
)
2337 struct rcu_data
*rdp
;
2338 struct task_struct
*t
;
2340 if (rcu_nocb_mask
== NULL
)
2342 for_each_cpu(cpu
, rcu_nocb_mask
) {
2343 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2344 t
= kthread_run(rcu_nocb_kthread
, rdp
,
2345 "rcuo%c/%d", rsp
->abbr
, cpu
);
2347 ACCESS_ONCE(rdp
->nocb_kthread
) = t
;
2351 /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2352 static bool init_nocb_callback_list(struct rcu_data
*rdp
)
2354 if (rcu_nocb_mask
== NULL
||
2355 !cpumask_test_cpu(rdp
->cpu
, rcu_nocb_mask
))
2357 rdp
->nxttail
[RCU_NEXT_TAIL
] = NULL
;
2361 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
2363 static int rcu_nocb_needs_gp(struct rcu_state
*rsp
)
2368 static void rcu_nocb_gp_cleanup(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
2372 static void rcu_nocb_gp_set(struct rcu_node
*rnp
, int nrq
)
2376 static void rcu_init_one_nocb(struct rcu_node
*rnp
)
2380 static bool __call_rcu_nocb(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
2386 static bool __maybe_unused
rcu_nocb_adopt_orphan_cbs(struct rcu_state
*rsp
,
2387 struct rcu_data
*rdp
)
2392 static void __init
rcu_boot_init_nocb_percpu_data(struct rcu_data
*rdp
)
2396 static void __init
rcu_spawn_nocb_kthreads(struct rcu_state
*rsp
)
2400 static bool init_nocb_callback_list(struct rcu_data
*rdp
)
2405 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2408 * An adaptive-ticks CPU can potentially execute in kernel mode for an
2409 * arbitrarily long period of time with the scheduling-clock tick turned
2410 * off. RCU will be paying attention to this CPU because it is in the
2411 * kernel, but the CPU cannot be guaranteed to be executing the RCU state
2412 * machine because the scheduling-clock tick has been disabled. Therefore,
2413 * if an adaptive-ticks CPU is failing to respond to the current grace
2414 * period and has not be idle from an RCU perspective, kick it.
2416 static void rcu_kick_nohz_cpu(int cpu
)
2418 #ifdef CONFIG_NO_HZ_FULL
2419 if (tick_nohz_full_cpu(cpu
))
2420 smp_send_reschedule(cpu
);
2421 #endif /* #ifdef CONFIG_NO_HZ_FULL */
2425 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
2428 * Define RCU flavor that holds sysidle state. This needs to be the
2429 * most active flavor of RCU.
2431 #ifdef CONFIG_PREEMPT_RCU
2432 static struct rcu_state
*rcu_sysidle_state
= &rcu_preempt_state
;
2433 #else /* #ifdef CONFIG_PREEMPT_RCU */
2434 static struct rcu_state
*rcu_sysidle_state
= &rcu_sched_state
;
2435 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
2437 static int full_sysidle_state
; /* Current system-idle state. */
2438 #define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */
2439 #define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */
2440 #define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */
2441 #define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */
2442 #define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */
2445 * Invoked to note exit from irq or task transition to idle. Note that
2446 * usermode execution does -not- count as idle here! After all, we want
2447 * to detect full-system idle states, not RCU quiescent states and grace
2448 * periods. The caller must have disabled interrupts.
2450 static void rcu_sysidle_enter(struct rcu_dynticks
*rdtp
, int irq
)
2454 /* Adjust nesting, check for fully idle. */
2456 rdtp
->dynticks_idle_nesting
--;
2457 WARN_ON_ONCE(rdtp
->dynticks_idle_nesting
< 0);
2458 if (rdtp
->dynticks_idle_nesting
!= 0)
2459 return; /* Still not fully idle. */
2461 if ((rdtp
->dynticks_idle_nesting
& DYNTICK_TASK_NEST_MASK
) ==
2462 DYNTICK_TASK_NEST_VALUE
) {
2463 rdtp
->dynticks_idle_nesting
= 0;
2465 rdtp
->dynticks_idle_nesting
-= DYNTICK_TASK_NEST_VALUE
;
2466 WARN_ON_ONCE(rdtp
->dynticks_idle_nesting
< 0);
2467 return; /* Still not fully idle. */
2471 /* Record start of fully idle period. */
2473 ACCESS_ONCE(rdtp
->dynticks_idle_jiffies
) = j
;
2474 smp_mb__before_atomic_inc();
2475 atomic_inc(&rdtp
->dynticks_idle
);
2476 smp_mb__after_atomic_inc();
2477 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks_idle
) & 0x1);
2481 * Unconditionally force exit from full system-idle state. This is
2482 * invoked when a normal CPU exits idle, but must be called separately
2483 * for the timekeeping CPU (tick_do_timer_cpu). The reason for this
2484 * is that the timekeeping CPU is permitted to take scheduling-clock
2485 * interrupts while the system is in system-idle state, and of course
2486 * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
2487 * interrupt from any other type of interrupt.
2489 void rcu_sysidle_force_exit(void)
2491 int oldstate
= ACCESS_ONCE(full_sysidle_state
);
2495 * Each pass through the following loop attempts to exit full
2496 * system-idle state. If contention proves to be a problem,
2497 * a trylock-based contention tree could be used here.
2499 while (oldstate
> RCU_SYSIDLE_SHORT
) {
2500 newoldstate
= cmpxchg(&full_sysidle_state
,
2501 oldstate
, RCU_SYSIDLE_NOT
);
2502 if (oldstate
== newoldstate
&&
2503 oldstate
== RCU_SYSIDLE_FULL_NOTED
) {
2504 rcu_kick_nohz_cpu(tick_do_timer_cpu
);
2505 return; /* We cleared it, done! */
2507 oldstate
= newoldstate
;
2509 smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
2513 * Invoked to note entry to irq or task transition from idle. Note that
2514 * usermode execution does -not- count as idle here! The caller must
2515 * have disabled interrupts.
2517 static void rcu_sysidle_exit(struct rcu_dynticks
*rdtp
, int irq
)
2519 /* Adjust nesting, check for already non-idle. */
2521 rdtp
->dynticks_idle_nesting
++;
2522 WARN_ON_ONCE(rdtp
->dynticks_idle_nesting
<= 0);
2523 if (rdtp
->dynticks_idle_nesting
!= 1)
2524 return; /* Already non-idle. */
2527 * Allow for irq misnesting. Yes, it really is possible
2528 * to enter an irq handler then never leave it, and maybe
2529 * also vice versa. Handle both possibilities.
2531 if (rdtp
->dynticks_idle_nesting
& DYNTICK_TASK_NEST_MASK
) {
2532 rdtp
->dynticks_idle_nesting
+= DYNTICK_TASK_NEST_VALUE
;
2533 WARN_ON_ONCE(rdtp
->dynticks_idle_nesting
<= 0);
2534 return; /* Already non-idle. */
2536 rdtp
->dynticks_idle_nesting
= DYNTICK_TASK_EXIT_IDLE
;
2540 /* Record end of idle period. */
2541 smp_mb__before_atomic_inc();
2542 atomic_inc(&rdtp
->dynticks_idle
);
2543 smp_mb__after_atomic_inc();
2544 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks_idle
) & 0x1));
2547 * If we are the timekeeping CPU, we are permitted to be non-idle
2548 * during a system-idle state. This must be the case, because
2549 * the timekeeping CPU has to take scheduling-clock interrupts
2550 * during the time that the system is transitioning to full
2551 * system-idle state. This means that the timekeeping CPU must
2552 * invoke rcu_sysidle_force_exit() directly if it does anything
2553 * more than take a scheduling-clock interrupt.
2555 if (smp_processor_id() == tick_do_timer_cpu
)
2558 /* Update system-idle state: We are clearly no longer fully idle! */
2559 rcu_sysidle_force_exit();
2563 * Check to see if the current CPU is idle. Note that usermode execution
2564 * does not count as idle. The caller must have disabled interrupts.
2566 static void rcu_sysidle_check_cpu(struct rcu_data
*rdp
, bool *isidle
,
2567 unsigned long *maxj
)
2571 struct rcu_dynticks
*rdtp
= rdp
->dynticks
;
2574 * If some other CPU has already reported non-idle, if this is
2575 * not the flavor of RCU that tracks sysidle state, or if this
2576 * is an offline or the timekeeping CPU, nothing to do.
2578 if (!*isidle
|| rdp
->rsp
!= rcu_sysidle_state
||
2579 cpu_is_offline(rdp
->cpu
) || rdp
->cpu
== tick_do_timer_cpu
)
2581 if (rcu_gp_in_progress(rdp
->rsp
))
2582 WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu
);
2584 /* Pick up current idle and NMI-nesting counter and check. */
2585 cur
= atomic_read(&rdtp
->dynticks_idle
);
2587 *isidle
= false; /* We are not idle! */
2590 smp_mb(); /* Read counters before timestamps. */
2592 /* Pick up timestamps. */
2593 j
= ACCESS_ONCE(rdtp
->dynticks_idle_jiffies
);
2594 /* If this CPU entered idle more recently, update maxj timestamp. */
2595 if (ULONG_CMP_LT(*maxj
, j
))
2600 * Is this the flavor of RCU that is handling full-system idle?
2602 static bool is_sysidle_rcu_state(struct rcu_state
*rsp
)
2604 return rsp
== rcu_sysidle_state
;
2608 * Bind the grace-period kthread for the sysidle flavor of RCU to the
2611 static void rcu_bind_gp_kthread(void)
2613 int cpu
= ACCESS_ONCE(tick_do_timer_cpu
);
2615 if (cpu
< 0 || cpu
>= nr_cpu_ids
)
2617 if (raw_smp_processor_id() != cpu
)
2618 set_cpus_allowed_ptr(current
, cpumask_of(cpu
));
2622 * Return a delay in jiffies based on the number of CPUs, rcu_node
2623 * leaf fanout, and jiffies tick rate. The idea is to allow larger
2624 * systems more time to transition to full-idle state in order to
2625 * avoid the cache thrashing that otherwise occur on the state variable.
2626 * Really small systems (less than a couple of tens of CPUs) should
2627 * instead use a single global atomically incremented counter, and later
2628 * versions of this will automatically reconfigure themselves accordingly.
2630 static unsigned long rcu_sysidle_delay(void)
2632 if (nr_cpu_ids
<= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
)
2634 return DIV_ROUND_UP(nr_cpu_ids
* HZ
, rcu_fanout_leaf
* 1000);
2638 * Advance the full-system-idle state. This is invoked when all of
2639 * the non-timekeeping CPUs are idle.
2641 static void rcu_sysidle(unsigned long j
)
2643 /* Check the current state. */
2644 switch (ACCESS_ONCE(full_sysidle_state
)) {
2645 case RCU_SYSIDLE_NOT
:
2647 /* First time all are idle, so note a short idle period. */
2648 ACCESS_ONCE(full_sysidle_state
) = RCU_SYSIDLE_SHORT
;
2651 case RCU_SYSIDLE_SHORT
:
2654 * Idle for a bit, time to advance to next state?
2655 * cmpxchg failure means race with non-idle, let them win.
2657 if (ULONG_CMP_GE(jiffies
, j
+ rcu_sysidle_delay()))
2658 (void)cmpxchg(&full_sysidle_state
,
2659 RCU_SYSIDLE_SHORT
, RCU_SYSIDLE_LONG
);
2662 case RCU_SYSIDLE_LONG
:
2665 * Do an additional check pass before advancing to full.
2666 * cmpxchg failure means race with non-idle, let them win.
2668 if (ULONG_CMP_GE(jiffies
, j
+ rcu_sysidle_delay()))
2669 (void)cmpxchg(&full_sysidle_state
,
2670 RCU_SYSIDLE_LONG
, RCU_SYSIDLE_FULL
);
2679 * Found a non-idle non-timekeeping CPU, so kick the system-idle state
2680 * back to the beginning.
2682 static void rcu_sysidle_cancel(void)
2685 ACCESS_ONCE(full_sysidle_state
) = RCU_SYSIDLE_NOT
;
2689 * Update the sysidle state based on the results of a force-quiescent-state
2690 * scan of the CPUs' dyntick-idle state.
2692 static void rcu_sysidle_report(struct rcu_state
*rsp
, int isidle
,
2693 unsigned long maxj
, bool gpkt
)
2695 if (rsp
!= rcu_sysidle_state
)
2696 return; /* Wrong flavor, ignore. */
2697 if (gpkt
&& nr_cpu_ids
<= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
)
2698 return; /* Running state machine from timekeeping CPU. */
2700 rcu_sysidle(maxj
); /* More idle! */
2702 rcu_sysidle_cancel(); /* Idle is over. */
2706 * Wrapper for rcu_sysidle_report() when called from the grace-period
2707 * kthread's context.
2709 static void rcu_sysidle_report_gp(struct rcu_state
*rsp
, int isidle
,
2712 rcu_sysidle_report(rsp
, isidle
, maxj
, true);
2715 /* Callback and function for forcing an RCU grace period. */
2716 struct rcu_sysidle_head
{
2721 static void rcu_sysidle_cb(struct rcu_head
*rhp
)
2723 struct rcu_sysidle_head
*rshp
;
2726 * The following memory barrier is needed to replace the
2727 * memory barriers that would normally be in the memory
2730 smp_mb(); /* grace period precedes setting inuse. */
2732 rshp
= container_of(rhp
, struct rcu_sysidle_head
, rh
);
2733 ACCESS_ONCE(rshp
->inuse
) = 0;
2737 * Check to see if the system is fully idle, other than the timekeeping CPU.
2738 * The caller must have disabled interrupts.
2740 bool rcu_sys_is_idle(void)
2742 static struct rcu_sysidle_head rsh
;
2743 int rss
= ACCESS_ONCE(full_sysidle_state
);
2745 if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu
))
2748 /* Handle small-system case by doing a full scan of CPUs. */
2749 if (nr_cpu_ids
<= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
) {
2750 int oldrss
= rss
- 1;
2753 * One pass to advance to each state up to _FULL.
2754 * Give up if any pass fails to advance the state.
2756 while (rss
< RCU_SYSIDLE_FULL
&& oldrss
< rss
) {
2759 unsigned long maxj
= jiffies
- ULONG_MAX
/ 4;
2760 struct rcu_data
*rdp
;
2762 /* Scan all the CPUs looking for nonidle CPUs. */
2763 for_each_possible_cpu(cpu
) {
2764 rdp
= per_cpu_ptr(rcu_sysidle_state
->rda
, cpu
);
2765 rcu_sysidle_check_cpu(rdp
, &isidle
, &maxj
);
2769 rcu_sysidle_report(rcu_sysidle_state
,
2770 isidle
, maxj
, false);
2772 rss
= ACCESS_ONCE(full_sysidle_state
);
2776 /* If this is the first observation of an idle period, record it. */
2777 if (rss
== RCU_SYSIDLE_FULL
) {
2778 rss
= cmpxchg(&full_sysidle_state
,
2779 RCU_SYSIDLE_FULL
, RCU_SYSIDLE_FULL_NOTED
);
2780 return rss
== RCU_SYSIDLE_FULL
;
2783 smp_mb(); /* ensure rss load happens before later caller actions. */
2785 /* If already fully idle, tell the caller (in case of races). */
2786 if (rss
== RCU_SYSIDLE_FULL_NOTED
)
2790 * If we aren't there yet, and a grace period is not in flight,
2791 * initiate a grace period. Either way, tell the caller that
2792 * we are not there yet. We use an xchg() rather than an assignment
2793 * to make up for the memory barriers that would otherwise be
2794 * provided by the memory allocator.
2796 if (nr_cpu_ids
> CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
&&
2797 !rcu_gp_in_progress(rcu_sysidle_state
) &&
2798 !rsh
.inuse
&& xchg(&rsh
.inuse
, 1) == 0)
2799 call_rcu(&rsh
.rh
, rcu_sysidle_cb
);
2804 * Initialize dynticks sysidle state for CPUs coming online.
2806 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks
*rdtp
)
2808 rdtp
->dynticks_idle_nesting
= DYNTICK_TASK_NEST_VALUE
;
2811 #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
2813 static void rcu_sysidle_enter(struct rcu_dynticks
*rdtp
, int irq
)
2817 static void rcu_sysidle_exit(struct rcu_dynticks
*rdtp
, int irq
)
2821 static void rcu_sysidle_check_cpu(struct rcu_data
*rdp
, bool *isidle
,
2822 unsigned long *maxj
)
2826 static bool is_sysidle_rcu_state(struct rcu_state
*rsp
)
2831 static void rcu_bind_gp_kthread(void)
2835 static void rcu_sysidle_report_gp(struct rcu_state
*rsp
, int isidle
,
2840 static void rcu_sysidle_init_percpu_data(struct rcu_dynticks
*rdtp
)
2844 #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */