1 /* SPDX-License-Identifier: GPL-2.0+ */
3 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
4 * Internal non-public definitions that provide either classic
5 * or preemptible semantics.
7 * Copyright Red Hat, 2009
8 * Copyright IBM Corporation, 2009
10 * Author: Ingo Molnar <mingo@elte.hu>
11 * Paul E. McKenney <paulmck@linux.ibm.com>
14 #include "../locking/rtmutex_common.h"
16 #ifdef CONFIG_RCU_NOCB_CPU
17 static cpumask_var_t rcu_nocb_mask
; /* CPUs to have callbacks offloaded. */
18 static bool __read_mostly rcu_nocb_poll
; /* Offload kthread are to poll. */
19 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
22 * Check the RCU kernel configuration parameters and print informative
23 * messages about anything out of the ordinary.
25 static void __init
rcu_bootup_announce_oddness(void)
27 if (IS_ENABLED(CONFIG_RCU_TRACE
))
28 pr_info("\tRCU event tracing is enabled.\n");
29 if ((IS_ENABLED(CONFIG_64BIT
) && RCU_FANOUT
!= 64) ||
30 (!IS_ENABLED(CONFIG_64BIT
) && RCU_FANOUT
!= 32))
31 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d.\n",
34 pr_info("\tHierarchical RCU autobalancing is disabled.\n");
35 if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ
))
36 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
37 if (IS_ENABLED(CONFIG_PROVE_RCU
))
38 pr_info("\tRCU lockdep checking is enabled.\n");
39 if (RCU_NUM_LVLS
>= 4)
40 pr_info("\tFour(or more)-level hierarchy is enabled.\n");
41 if (RCU_FANOUT_LEAF
!= 16)
42 pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
44 if (rcu_fanout_leaf
!= RCU_FANOUT_LEAF
)
45 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n",
47 if (nr_cpu_ids
!= NR_CPUS
)
48 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%u.\n", NR_CPUS
, nr_cpu_ids
);
49 #ifdef CONFIG_RCU_BOOST
50 pr_info("\tRCU priority boosting: priority %d delay %d ms.\n",
51 kthread_prio
, CONFIG_RCU_BOOST_DELAY
);
53 if (blimit
!= DEFAULT_RCU_BLIMIT
)
54 pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit
);
55 if (qhimark
!= DEFAULT_RCU_QHIMARK
)
56 pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark
);
57 if (qlowmark
!= DEFAULT_RCU_QLOMARK
)
58 pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark
);
59 if (jiffies_till_first_fqs
!= ULONG_MAX
)
60 pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs
);
61 if (jiffies_till_next_fqs
!= ULONG_MAX
)
62 pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs
);
63 if (jiffies_till_sched_qs
!= ULONG_MAX
)
64 pr_info("\tBoot-time adjustment of scheduler-enlistment delay to %ld jiffies.\n", jiffies_till_sched_qs
);
65 if (rcu_kick_kthreads
)
66 pr_info("\tKick kthreads if too-long grace period.\n");
67 if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD
))
68 pr_info("\tRCU callback double-/use-after-free debug enabled.\n");
70 pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay
);
72 pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay
);
74 pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay
);
76 pr_info("\tRCU_SOFTIRQ processing moved to rcuc kthreads.\n");
77 if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG
))
78 pr_info("\tRCU debug extended QS entry/exit.\n");
79 rcupdate_announce_bootup_oddness();
82 #ifdef CONFIG_PREEMPT_RCU
84 static void rcu_report_exp_rnp(struct rcu_node
*rnp
, bool wake
);
85 static void rcu_read_unlock_special(struct task_struct
*t
);
88 * Tell them what RCU they are running.
90 static void __init
rcu_bootup_announce(void)
92 pr_info("Preemptible hierarchical RCU implementation.\n");
93 rcu_bootup_announce_oddness();
96 /* Flags for rcu_preempt_ctxt_queue() decision table. */
97 #define RCU_GP_TASKS 0x8
98 #define RCU_EXP_TASKS 0x4
99 #define RCU_GP_BLKD 0x2
100 #define RCU_EXP_BLKD 0x1
103 * Queues a task preempted within an RCU-preempt read-side critical
104 * section into the appropriate location within the ->blkd_tasks list,
105 * depending on the states of any ongoing normal and expedited grace
106 * periods. The ->gp_tasks pointer indicates which element the normal
107 * grace period is waiting on (NULL if none), and the ->exp_tasks pointer
108 * indicates which element the expedited grace period is waiting on (again,
109 * NULL if none). If a grace period is waiting on a given element in the
110 * ->blkd_tasks list, it also waits on all subsequent elements. Thus,
111 * adding a task to the tail of the list blocks any grace period that is
112 * already waiting on one of the elements. In contrast, adding a task
113 * to the head of the list won't block any grace period that is already
114 * waiting on one of the elements.
116 * This queuing is imprecise, and can sometimes make an ongoing grace
117 * period wait for a task that is not strictly speaking blocking it.
118 * Given the choice, we needlessly block a normal grace period rather than
119 * blocking an expedited grace period.
121 * Note that an endless sequence of expedited grace periods still cannot
122 * indefinitely postpone a normal grace period. Eventually, all of the
123 * fixed number of preempted tasks blocking the normal grace period that are
124 * not also blocking the expedited grace period will resume and complete
125 * their RCU read-side critical sections. At that point, the ->gp_tasks
126 * pointer will equal the ->exp_tasks pointer, at which point the end of
127 * the corresponding expedited grace period will also be the end of the
128 * normal grace period.
130 static void rcu_preempt_ctxt_queue(struct rcu_node
*rnp
, struct rcu_data
*rdp
)
131 __releases(rnp
->lock
) /* But leaves rrupts disabled. */
133 int blkd_state
= (rnp
->gp_tasks
? RCU_GP_TASKS
: 0) +
134 (rnp
->exp_tasks
? RCU_EXP_TASKS
: 0) +
135 (rnp
->qsmask
& rdp
->grpmask
? RCU_GP_BLKD
: 0) +
136 (rnp
->expmask
& rdp
->grpmask
? RCU_EXP_BLKD
: 0);
137 struct task_struct
*t
= current
;
139 raw_lockdep_assert_held_rcu_node(rnp
);
140 WARN_ON_ONCE(rdp
->mynode
!= rnp
);
141 WARN_ON_ONCE(!rcu_is_leaf_node(rnp
));
142 /* RCU better not be waiting on newly onlined CPUs! */
143 WARN_ON_ONCE(rnp
->qsmaskinitnext
& ~rnp
->qsmaskinit
& rnp
->qsmask
&
147 * Decide where to queue the newly blocked task. In theory,
148 * this could be an if-statement. In practice, when I tried
149 * that, it was quite messy.
151 switch (blkd_state
) {
154 case RCU_EXP_TASKS
+ RCU_GP_BLKD
:
156 case RCU_GP_TASKS
+ RCU_EXP_TASKS
:
159 * Blocking neither GP, or first task blocking the normal
160 * GP but not blocking the already-waiting expedited GP.
161 * Queue at the head of the list to avoid unnecessarily
162 * blocking the already-waiting GPs.
164 list_add(&t
->rcu_node_entry
, &rnp
->blkd_tasks
);
169 case RCU_GP_BLKD
+ RCU_EXP_BLKD
:
170 case RCU_GP_TASKS
+ RCU_EXP_BLKD
:
171 case RCU_GP_TASKS
+ RCU_GP_BLKD
+ RCU_EXP_BLKD
:
172 case RCU_GP_TASKS
+ RCU_EXP_TASKS
+ RCU_GP_BLKD
+ RCU_EXP_BLKD
:
175 * First task arriving that blocks either GP, or first task
176 * arriving that blocks the expedited GP (with the normal
177 * GP already waiting), or a task arriving that blocks
178 * both GPs with both GPs already waiting. Queue at the
179 * tail of the list to avoid any GP waiting on any of the
180 * already queued tasks that are not blocking it.
182 list_add_tail(&t
->rcu_node_entry
, &rnp
->blkd_tasks
);
185 case RCU_EXP_TASKS
+ RCU_EXP_BLKD
:
186 case RCU_EXP_TASKS
+ RCU_GP_BLKD
+ RCU_EXP_BLKD
:
187 case RCU_GP_TASKS
+ RCU_EXP_TASKS
+ RCU_EXP_BLKD
:
190 * Second or subsequent task blocking the expedited GP.
191 * The task either does not block the normal GP, or is the
192 * first task blocking the normal GP. Queue just after
193 * the first task blocking the expedited GP.
195 list_add(&t
->rcu_node_entry
, rnp
->exp_tasks
);
198 case RCU_GP_TASKS
+ RCU_GP_BLKD
:
199 case RCU_GP_TASKS
+ RCU_EXP_TASKS
+ RCU_GP_BLKD
:
202 * Second or subsequent task blocking the normal GP.
203 * The task does not block the expedited GP. Queue just
204 * after the first task blocking the normal GP.
206 list_add(&t
->rcu_node_entry
, rnp
->gp_tasks
);
211 /* Yet another exercise in excessive paranoia. */
217 * We have now queued the task. If it was the first one to
218 * block either grace period, update the ->gp_tasks and/or
219 * ->exp_tasks pointers, respectively, to reference the newly
222 if (!rnp
->gp_tasks
&& (blkd_state
& RCU_GP_BLKD
)) {
223 rnp
->gp_tasks
= &t
->rcu_node_entry
;
224 WARN_ON_ONCE(rnp
->completedqs
== rnp
->gp_seq
);
226 if (!rnp
->exp_tasks
&& (blkd_state
& RCU_EXP_BLKD
))
227 rnp
->exp_tasks
= &t
->rcu_node_entry
;
228 WARN_ON_ONCE(!(blkd_state
& RCU_GP_BLKD
) !=
229 !(rnp
->qsmask
& rdp
->grpmask
));
230 WARN_ON_ONCE(!(blkd_state
& RCU_EXP_BLKD
) !=
231 !(rnp
->expmask
& rdp
->grpmask
));
232 raw_spin_unlock_rcu_node(rnp
); /* interrupts remain disabled. */
235 * Report the quiescent state for the expedited GP. This expedited
236 * GP should not be able to end until we report, so there should be
237 * no need to check for a subsequent expedited GP. (Though we are
238 * still in a quiescent state in any case.)
240 if (blkd_state
& RCU_EXP_BLKD
&& rdp
->exp_deferred_qs
)
241 rcu_report_exp_rdp(rdp
);
243 WARN_ON_ONCE(rdp
->exp_deferred_qs
);
247 * Record a preemptible-RCU quiescent state for the specified CPU.
248 * Note that this does not necessarily mean that the task currently running
249 * on the CPU is in a quiescent state: Instead, it means that the current
250 * grace period need not wait on any RCU read-side critical section that
251 * starts later on this CPU. It also means that if the current task is
252 * in an RCU read-side critical section, it has already added itself to
253 * some leaf rcu_node structure's ->blkd_tasks list. In addition to the
254 * current task, there might be any number of other tasks blocked while
255 * in an RCU read-side critical section.
257 * Callers to this function must disable preemption.
259 static void rcu_qs(void)
261 RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n");
262 if (__this_cpu_read(rcu_data
.cpu_no_qs
.s
)) {
263 trace_rcu_grace_period(TPS("rcu_preempt"),
264 __this_cpu_read(rcu_data
.gp_seq
),
266 __this_cpu_write(rcu_data
.cpu_no_qs
.b
.norm
, false);
267 barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */
268 WRITE_ONCE(current
->rcu_read_unlock_special
.b
.need_qs
, false);
273 * We have entered the scheduler, and the current task might soon be
274 * context-switched away from. If this task is in an RCU read-side
275 * critical section, we will no longer be able to rely on the CPU to
276 * record that fact, so we enqueue the task on the blkd_tasks list.
277 * The task will dequeue itself when it exits the outermost enclosing
278 * RCU read-side critical section. Therefore, the current grace period
279 * cannot be permitted to complete until the blkd_tasks list entries
280 * predating the current grace period drain, in other words, until
281 * rnp->gp_tasks becomes NULL.
283 * Caller must disable interrupts.
285 void rcu_note_context_switch(bool preempt
)
287 struct task_struct
*t
= current
;
288 struct rcu_data
*rdp
= this_cpu_ptr(&rcu_data
);
289 struct rcu_node
*rnp
;
291 trace_rcu_utilization(TPS("Start context switch"));
292 lockdep_assert_irqs_disabled();
293 WARN_ON_ONCE(!preempt
&& t
->rcu_read_lock_nesting
> 0);
294 if (t
->rcu_read_lock_nesting
> 0 &&
295 !t
->rcu_read_unlock_special
.b
.blocked
) {
297 /* Possibly blocking in an RCU read-side critical section. */
299 raw_spin_lock_rcu_node(rnp
);
300 t
->rcu_read_unlock_special
.b
.blocked
= true;
301 t
->rcu_blocked_node
= rnp
;
304 * Verify the CPU's sanity, trace the preemption, and
305 * then queue the task as required based on the states
306 * of any ongoing and expedited grace periods.
308 WARN_ON_ONCE((rdp
->grpmask
& rcu_rnp_online_cpus(rnp
)) == 0);
309 WARN_ON_ONCE(!list_empty(&t
->rcu_node_entry
));
310 trace_rcu_preempt_task(rcu_state
.name
,
312 (rnp
->qsmask
& rdp
->grpmask
)
314 : rcu_seq_snap(&rnp
->gp_seq
));
315 rcu_preempt_ctxt_queue(rnp
, rdp
);
317 rcu_preempt_deferred_qs(t
);
321 * Either we were not in an RCU read-side critical section to
322 * begin with, or we have now recorded that critical section
323 * globally. Either way, we can now note a quiescent state
324 * for this CPU. Again, if we were in an RCU read-side critical
325 * section, and if that critical section was blocking the current
326 * grace period, then the fact that the task has been enqueued
327 * means that we continue to block the current grace period.
330 if (rdp
->exp_deferred_qs
)
331 rcu_report_exp_rdp(rdp
);
332 trace_rcu_utilization(TPS("End context switch"));
334 EXPORT_SYMBOL_GPL(rcu_note_context_switch
);
337 * Check for preempted RCU readers blocking the current grace period
338 * for the specified rcu_node structure. If the caller needs a reliable
339 * answer, it must hold the rcu_node's ->lock.
341 static int rcu_preempt_blocked_readers_cgp(struct rcu_node
*rnp
)
343 return rnp
->gp_tasks
!= NULL
;
346 /* Bias and limit values for ->rcu_read_lock_nesting. */
347 #define RCU_NEST_BIAS INT_MAX
348 #define RCU_NEST_NMAX (-INT_MAX / 2)
349 #define RCU_NEST_PMAX (INT_MAX / 2)
352 * Preemptible RCU implementation for rcu_read_lock().
353 * Just increment ->rcu_read_lock_nesting, shared state will be updated
356 void __rcu_read_lock(void)
358 current
->rcu_read_lock_nesting
++;
359 if (IS_ENABLED(CONFIG_PROVE_LOCKING
))
360 WARN_ON_ONCE(current
->rcu_read_lock_nesting
> RCU_NEST_PMAX
);
361 barrier(); /* critical section after entry code. */
363 EXPORT_SYMBOL_GPL(__rcu_read_lock
);
366 * Preemptible RCU implementation for rcu_read_unlock().
367 * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
368 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
369 * invoke rcu_read_unlock_special() to clean up after a context switch
370 * in an RCU read-side critical section and other special cases.
372 void __rcu_read_unlock(void)
374 struct task_struct
*t
= current
;
376 if (t
->rcu_read_lock_nesting
!= 1) {
377 --t
->rcu_read_lock_nesting
;
379 barrier(); /* critical section before exit code. */
380 t
->rcu_read_lock_nesting
= -RCU_NEST_BIAS
;
381 barrier(); /* assign before ->rcu_read_unlock_special load */
382 if (unlikely(READ_ONCE(t
->rcu_read_unlock_special
.s
)))
383 rcu_read_unlock_special(t
);
384 barrier(); /* ->rcu_read_unlock_special load before assign */
385 t
->rcu_read_lock_nesting
= 0;
387 if (IS_ENABLED(CONFIG_PROVE_LOCKING
)) {
388 int rrln
= t
->rcu_read_lock_nesting
;
390 WARN_ON_ONCE(rrln
< 0 && rrln
> RCU_NEST_NMAX
);
393 EXPORT_SYMBOL_GPL(__rcu_read_unlock
);
396 * Advance a ->blkd_tasks-list pointer to the next entry, instead
397 * returning NULL if at the end of the list.
399 static struct list_head
*rcu_next_node_entry(struct task_struct
*t
,
400 struct rcu_node
*rnp
)
402 struct list_head
*np
;
404 np
= t
->rcu_node_entry
.next
;
405 if (np
== &rnp
->blkd_tasks
)
411 * Return true if the specified rcu_node structure has tasks that were
412 * preempted within an RCU read-side critical section.
414 static bool rcu_preempt_has_tasks(struct rcu_node
*rnp
)
416 return !list_empty(&rnp
->blkd_tasks
);
420 * Report deferred quiescent states. The deferral time can
421 * be quite short, for example, in the case of the call from
422 * rcu_read_unlock_special().
425 rcu_preempt_deferred_qs_irqrestore(struct task_struct
*t
, unsigned long flags
)
430 struct list_head
*np
;
431 bool drop_boost_mutex
= false;
432 struct rcu_data
*rdp
;
433 struct rcu_node
*rnp
;
434 union rcu_special special
;
437 * If RCU core is waiting for this CPU to exit its critical section,
438 * report the fact that it has exited. Because irqs are disabled,
439 * t->rcu_read_unlock_special cannot change.
441 special
= t
->rcu_read_unlock_special
;
442 rdp
= this_cpu_ptr(&rcu_data
);
443 if (!special
.s
&& !rdp
->exp_deferred_qs
) {
444 local_irq_restore(flags
);
447 t
->rcu_read_unlock_special
.b
.deferred_qs
= false;
448 if (special
.b
.need_qs
) {
450 t
->rcu_read_unlock_special
.b
.need_qs
= false;
451 if (!t
->rcu_read_unlock_special
.s
&& !rdp
->exp_deferred_qs
) {
452 local_irq_restore(flags
);
458 * Respond to a request by an expedited grace period for a
459 * quiescent state from this CPU. Note that requests from
460 * tasks are handled when removing the task from the
461 * blocked-tasks list below.
463 if (rdp
->exp_deferred_qs
) {
464 rcu_report_exp_rdp(rdp
);
465 if (!t
->rcu_read_unlock_special
.s
) {
466 local_irq_restore(flags
);
471 /* Clean up if blocked during RCU read-side critical section. */
472 if (special
.b
.blocked
) {
473 t
->rcu_read_unlock_special
.b
.blocked
= false;
476 * Remove this task from the list it blocked on. The task
477 * now remains queued on the rcu_node corresponding to the
478 * CPU it first blocked on, so there is no longer any need
479 * to loop. Retain a WARN_ON_ONCE() out of sheer paranoia.
481 rnp
= t
->rcu_blocked_node
;
482 raw_spin_lock_rcu_node(rnp
); /* irqs already disabled. */
483 WARN_ON_ONCE(rnp
!= t
->rcu_blocked_node
);
484 WARN_ON_ONCE(!rcu_is_leaf_node(rnp
));
485 empty_norm
= !rcu_preempt_blocked_readers_cgp(rnp
);
486 WARN_ON_ONCE(rnp
->completedqs
== rnp
->gp_seq
&&
487 (!empty_norm
|| rnp
->qsmask
));
488 empty_exp
= sync_rcu_preempt_exp_done(rnp
);
489 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
490 np
= rcu_next_node_entry(t
, rnp
);
491 list_del_init(&t
->rcu_node_entry
);
492 t
->rcu_blocked_node
= NULL
;
493 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
494 rnp
->gp_seq
, t
->pid
);
495 if (&t
->rcu_node_entry
== rnp
->gp_tasks
)
497 if (&t
->rcu_node_entry
== rnp
->exp_tasks
)
499 if (IS_ENABLED(CONFIG_RCU_BOOST
)) {
500 /* Snapshot ->boost_mtx ownership w/rnp->lock held. */
501 drop_boost_mutex
= rt_mutex_owner(&rnp
->boost_mtx
) == t
;
502 if (&t
->rcu_node_entry
== rnp
->boost_tasks
)
503 rnp
->boost_tasks
= np
;
507 * If this was the last task on the current list, and if
508 * we aren't waiting on any CPUs, report the quiescent state.
509 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
510 * so we must take a snapshot of the expedited state.
512 empty_exp_now
= sync_rcu_preempt_exp_done(rnp
);
513 if (!empty_norm
&& !rcu_preempt_blocked_readers_cgp(rnp
)) {
514 trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
521 rcu_report_unblock_qs_rnp(rnp
, flags
);
523 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
526 /* Unboost if we were boosted. */
527 if (IS_ENABLED(CONFIG_RCU_BOOST
) && drop_boost_mutex
)
528 rt_mutex_futex_unlock(&rnp
->boost_mtx
);
531 * If this was the last task on the expedited lists,
532 * then we need to report up the rcu_node hierarchy.
534 if (!empty_exp
&& empty_exp_now
)
535 rcu_report_exp_rnp(rnp
, true);
537 local_irq_restore(flags
);
542 * Is a deferred quiescent-state pending, and are we also not in
543 * an RCU read-side critical section? It is the caller's responsibility
544 * to ensure it is otherwise safe to report any deferred quiescent
545 * states. The reason for this is that it is safe to report a
546 * quiescent state during context switch even though preemption
547 * is disabled. This function cannot be expected to understand these
548 * nuances, so the caller must handle them.
550 static bool rcu_preempt_need_deferred_qs(struct task_struct
*t
)
552 return (__this_cpu_read(rcu_data
.exp_deferred_qs
) ||
553 READ_ONCE(t
->rcu_read_unlock_special
.s
)) &&
554 t
->rcu_read_lock_nesting
<= 0;
558 * Report a deferred quiescent state if needed and safe to do so.
559 * As with rcu_preempt_need_deferred_qs(), "safe" involves only
560 * not being in an RCU read-side critical section. The caller must
561 * evaluate safety in terms of interrupt, softirq, and preemption
564 static void rcu_preempt_deferred_qs(struct task_struct
*t
)
567 bool couldrecurse
= t
->rcu_read_lock_nesting
>= 0;
569 if (!rcu_preempt_need_deferred_qs(t
))
572 t
->rcu_read_lock_nesting
-= RCU_NEST_BIAS
;
573 local_irq_save(flags
);
574 rcu_preempt_deferred_qs_irqrestore(t
, flags
);
576 t
->rcu_read_lock_nesting
+= RCU_NEST_BIAS
;
580 * Minimal handler to give the scheduler a chance to re-evaluate.
582 static void rcu_preempt_deferred_qs_handler(struct irq_work
*iwp
)
584 struct rcu_data
*rdp
;
586 rdp
= container_of(iwp
, struct rcu_data
, defer_qs_iw
);
587 rdp
->defer_qs_iw_pending
= false;
591 * Handle special cases during rcu_read_unlock(), such as needing to
592 * notify RCU core processing or task having blocked during the RCU
593 * read-side critical section.
595 static void rcu_read_unlock_special(struct task_struct
*t
)
598 bool preempt_bh_were_disabled
=
599 !!(preempt_count() & (PREEMPT_MASK
| SOFTIRQ_MASK
));
600 bool irqs_were_disabled
;
602 /* NMI handlers cannot block and cannot safely manipulate state. */
606 local_irq_save(flags
);
607 irqs_were_disabled
= irqs_disabled_flags(flags
);
608 if (preempt_bh_were_disabled
|| irqs_were_disabled
) {
610 struct rcu_data
*rdp
= this_cpu_ptr(&rcu_data
);
611 struct rcu_node
*rnp
= rdp
->mynode
;
613 t
->rcu_read_unlock_special
.b
.exp_hint
= false;
614 exp
= (t
->rcu_blocked_node
&& t
->rcu_blocked_node
->exp_tasks
) ||
615 (rdp
->grpmask
& rnp
->expmask
) ||
616 tick_nohz_full_cpu(rdp
->cpu
);
617 // Need to defer quiescent state until everything is enabled.
618 if (irqs_were_disabled
&& use_softirq
&&
620 (exp
&& !t
->rcu_read_unlock_special
.b
.deferred_qs
))) {
621 // Using softirq, safe to awaken, and we get
622 // no help from enabling irqs, unlike bh/preempt.
623 raise_softirq_irqoff(RCU_SOFTIRQ
);
625 // Enabling BH or preempt does reschedule, so...
626 // Also if no expediting or NO_HZ_FULL, slow is OK.
627 set_tsk_need_resched(current
);
628 set_preempt_need_resched();
629 if (IS_ENABLED(CONFIG_IRQ_WORK
) && irqs_were_disabled
&&
630 !rdp
->defer_qs_iw_pending
&& exp
) {
631 // Get scheduler to re-evaluate and call hooks.
632 // If !IRQ_WORK, FQS scan will eventually IPI.
633 init_irq_work(&rdp
->defer_qs_iw
,
634 rcu_preempt_deferred_qs_handler
);
635 rdp
->defer_qs_iw_pending
= true;
636 irq_work_queue_on(&rdp
->defer_qs_iw
, rdp
->cpu
);
639 t
->rcu_read_unlock_special
.b
.deferred_qs
= true;
640 local_irq_restore(flags
);
643 WRITE_ONCE(t
->rcu_read_unlock_special
.b
.exp_hint
, false);
644 rcu_preempt_deferred_qs_irqrestore(t
, flags
);
648 * Check that the list of blocked tasks for the newly completed grace
649 * period is in fact empty. It is a serious bug to complete a grace
650 * period that still has RCU readers blocked! This function must be
651 * invoked -before- updating this rnp's ->gp_seq, and the rnp's ->lock
652 * must be held by the caller.
654 * Also, if there are blocked tasks on the list, they automatically
655 * block the newly created grace period, so set up ->gp_tasks accordingly.
657 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
659 struct task_struct
*t
;
661 RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
662 if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp
)))
663 dump_blkd_tasks(rnp
, 10);
664 if (rcu_preempt_has_tasks(rnp
) &&
665 (rnp
->qsmaskinit
|| rnp
->wait_blkd_tasks
)) {
666 rnp
->gp_tasks
= rnp
->blkd_tasks
.next
;
667 t
= container_of(rnp
->gp_tasks
, struct task_struct
,
669 trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
670 rnp
->gp_seq
, t
->pid
);
672 WARN_ON_ONCE(rnp
->qsmask
);
676 * Check for a quiescent state from the current CPU, including voluntary
677 * context switches for Tasks RCU. When a task blocks, the task is
678 * recorded in the corresponding CPU's rcu_node structure, which is checked
679 * elsewhere, hence this function need only check for quiescent states
680 * related to the current CPU, not to those related to tasks.
682 static void rcu_flavor_sched_clock_irq(int user
)
684 struct task_struct
*t
= current
;
686 if (user
|| rcu_is_cpu_rrupt_from_idle()) {
687 rcu_note_voluntary_context_switch(current
);
689 if (t
->rcu_read_lock_nesting
> 0 ||
690 (preempt_count() & (PREEMPT_MASK
| SOFTIRQ_MASK
))) {
691 /* No QS, force context switch if deferred. */
692 if (rcu_preempt_need_deferred_qs(t
)) {
693 set_tsk_need_resched(t
);
694 set_preempt_need_resched();
696 } else if (rcu_preempt_need_deferred_qs(t
)) {
697 rcu_preempt_deferred_qs(t
); /* Report deferred QS. */
699 } else if (!t
->rcu_read_lock_nesting
) {
700 rcu_qs(); /* Report immediate QS. */
704 /* If GP is oldish, ask for help from rcu_read_unlock_special(). */
705 if (t
->rcu_read_lock_nesting
> 0 &&
706 __this_cpu_read(rcu_data
.core_needs_qs
) &&
707 __this_cpu_read(rcu_data
.cpu_no_qs
.b
.norm
) &&
708 !t
->rcu_read_unlock_special
.b
.need_qs
&&
709 time_after(jiffies
, rcu_state
.gp_start
+ HZ
))
710 t
->rcu_read_unlock_special
.b
.need_qs
= true;
714 * Check for a task exiting while in a preemptible-RCU read-side
715 * critical section, clean up if so. No need to issue warnings, as
716 * debug_check_no_locks_held() already does this if lockdep is enabled.
717 * Besides, if this function does anything other than just immediately
718 * return, there was a bug of some sort. Spewing warnings from this
719 * function is like as not to simply obscure important prior warnings.
723 struct task_struct
*t
= current
;
725 if (unlikely(!list_empty(¤t
->rcu_node_entry
))) {
726 t
->rcu_read_lock_nesting
= 1;
728 WRITE_ONCE(t
->rcu_read_unlock_special
.b
.blocked
, true);
729 } else if (unlikely(t
->rcu_read_lock_nesting
)) {
730 t
->rcu_read_lock_nesting
= 1;
735 rcu_preempt_deferred_qs(current
);
739 * Dump the blocked-tasks state, but limit the list dump to the
740 * specified number of elements.
743 dump_blkd_tasks(struct rcu_node
*rnp
, int ncheck
)
747 struct list_head
*lhp
;
749 struct rcu_data
*rdp
;
750 struct rcu_node
*rnp1
;
752 raw_lockdep_assert_held_rcu_node(rnp
);
753 pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
754 __func__
, rnp
->grplo
, rnp
->grphi
, rnp
->level
,
755 (long)rnp
->gp_seq
, (long)rnp
->completedqs
);
756 for (rnp1
= rnp
; rnp1
; rnp1
= rnp1
->parent
)
757 pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n",
758 __func__
, rnp1
->grplo
, rnp1
->grphi
, rnp1
->qsmask
, rnp1
->qsmaskinit
, rnp1
->qsmaskinitnext
);
759 pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n",
760 __func__
, rnp
->gp_tasks
, rnp
->boost_tasks
, rnp
->exp_tasks
);
761 pr_info("%s: ->blkd_tasks", __func__
);
763 list_for_each(lhp
, &rnp
->blkd_tasks
) {
769 for (cpu
= rnp
->grplo
; cpu
<= rnp
->grphi
; cpu
++) {
770 rdp
= per_cpu_ptr(&rcu_data
, cpu
);
771 onl
= !!(rdp
->grpmask
& rcu_rnp_online_cpus(rnp
));
772 pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n",
774 (long)rdp
->rcu_onl_gp_seq
, rdp
->rcu_onl_gp_flags
,
775 (long)rdp
->rcu_ofl_gp_seq
, rdp
->rcu_ofl_gp_flags
);
779 #else /* #ifdef CONFIG_PREEMPT_RCU */
782 * Tell them what RCU they are running.
784 static void __init
rcu_bootup_announce(void)
786 pr_info("Hierarchical RCU implementation.\n");
787 rcu_bootup_announce_oddness();
791 * Note a quiescent state for PREEMPT=n. Because we do not need to know
792 * how many quiescent states passed, just if there was at least one since
793 * the start of the grace period, this just sets a flag. The caller must
794 * have disabled preemption.
796 static void rcu_qs(void)
798 RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!");
799 if (!__this_cpu_read(rcu_data
.cpu_no_qs
.s
))
801 trace_rcu_grace_period(TPS("rcu_sched"),
802 __this_cpu_read(rcu_data
.gp_seq
), TPS("cpuqs"));
803 __this_cpu_write(rcu_data
.cpu_no_qs
.b
.norm
, false);
804 if (!__this_cpu_read(rcu_data
.cpu_no_qs
.b
.exp
))
806 __this_cpu_write(rcu_data
.cpu_no_qs
.b
.exp
, false);
807 rcu_report_exp_rdp(this_cpu_ptr(&rcu_data
));
811 * Register an urgently needed quiescent state. If there is an
812 * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
813 * dyntick-idle quiescent state visible to other CPUs, which will in
814 * some cases serve for expedited as well as normal grace periods.
815 * Either way, register a lightweight quiescent state.
817 void rcu_all_qs(void)
821 if (!raw_cpu_read(rcu_data
.rcu_urgent_qs
))
824 /* Load rcu_urgent_qs before other flags. */
825 if (!smp_load_acquire(this_cpu_ptr(&rcu_data
.rcu_urgent_qs
))) {
829 this_cpu_write(rcu_data
.rcu_urgent_qs
, false);
830 if (unlikely(raw_cpu_read(rcu_data
.rcu_need_heavy_qs
))) {
831 local_irq_save(flags
);
832 rcu_momentary_dyntick_idle();
833 local_irq_restore(flags
);
838 EXPORT_SYMBOL_GPL(rcu_all_qs
);
841 * Note a PREEMPT=n context switch. The caller must have disabled interrupts.
843 void rcu_note_context_switch(bool preempt
)
845 trace_rcu_utilization(TPS("Start context switch"));
847 /* Load rcu_urgent_qs before other flags. */
848 if (!smp_load_acquire(this_cpu_ptr(&rcu_data
.rcu_urgent_qs
)))
850 this_cpu_write(rcu_data
.rcu_urgent_qs
, false);
851 if (unlikely(raw_cpu_read(rcu_data
.rcu_need_heavy_qs
)))
852 rcu_momentary_dyntick_idle();
854 rcu_tasks_qs(current
);
856 trace_rcu_utilization(TPS("End context switch"));
858 EXPORT_SYMBOL_GPL(rcu_note_context_switch
);
861 * Because preemptible RCU does not exist, there are never any preempted
864 static int rcu_preempt_blocked_readers_cgp(struct rcu_node
*rnp
)
870 * Because there is no preemptible RCU, there can be no readers blocked.
872 static bool rcu_preempt_has_tasks(struct rcu_node
*rnp
)
878 * Because there is no preemptible RCU, there can be no deferred quiescent
881 static bool rcu_preempt_need_deferred_qs(struct task_struct
*t
)
885 static void rcu_preempt_deferred_qs(struct task_struct
*t
) { }
888 * Because there is no preemptible RCU, there can be no readers blocked,
889 * so there is no need to check for blocked tasks. So check only for
890 * bogus qsmask values.
892 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
894 WARN_ON_ONCE(rnp
->qsmask
);
898 * Check to see if this CPU is in a non-context-switch quiescent state,
899 * namely user mode and idle loop.
901 static void rcu_flavor_sched_clock_irq(int user
)
903 if (user
|| rcu_is_cpu_rrupt_from_idle()) {
906 * Get here if this CPU took its interrupt from user
907 * mode or from the idle loop, and if this is not a
908 * nested interrupt. In this case, the CPU is in
909 * a quiescent state, so note it.
911 * No memory barrier is required here because rcu_qs()
912 * references only CPU-local variables that other CPUs
913 * neither access nor modify, at least not while the
914 * corresponding CPU is online.
922 * Because preemptible RCU does not exist, tasks cannot possibly exit
923 * while in preemptible RCU read-side critical sections.
930 * Dump the guaranteed-empty blocked-tasks state. Trust but verify.
933 dump_blkd_tasks(struct rcu_node
*rnp
, int ncheck
)
935 WARN_ON_ONCE(!list_empty(&rnp
->blkd_tasks
));
938 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
941 * If boosting, set rcuc kthreads to realtime priority.
943 static void rcu_cpu_kthread_setup(unsigned int cpu
)
945 #ifdef CONFIG_RCU_BOOST
946 struct sched_param sp
;
948 sp
.sched_priority
= kthread_prio
;
949 sched_setscheduler_nocheck(current
, SCHED_FIFO
, &sp
);
950 #endif /* #ifdef CONFIG_RCU_BOOST */
953 #ifdef CONFIG_RCU_BOOST
956 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
957 * or ->boost_tasks, advancing the pointer to the next task in the
960 * Note that irqs must be enabled: boosting the task can block.
961 * Returns 1 if there are more tasks needing to be boosted.
963 static int rcu_boost(struct rcu_node
*rnp
)
966 struct task_struct
*t
;
967 struct list_head
*tb
;
969 if (READ_ONCE(rnp
->exp_tasks
) == NULL
&&
970 READ_ONCE(rnp
->boost_tasks
) == NULL
)
971 return 0; /* Nothing left to boost. */
973 raw_spin_lock_irqsave_rcu_node(rnp
, flags
);
976 * Recheck under the lock: all tasks in need of boosting
977 * might exit their RCU read-side critical sections on their own.
979 if (rnp
->exp_tasks
== NULL
&& rnp
->boost_tasks
== NULL
) {
980 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
985 * Preferentially boost tasks blocking expedited grace periods.
986 * This cannot starve the normal grace periods because a second
987 * expedited grace period must boost all blocked tasks, including
988 * those blocking the pre-existing normal grace period.
990 if (rnp
->exp_tasks
!= NULL
)
993 tb
= rnp
->boost_tasks
;
996 * We boost task t by manufacturing an rt_mutex that appears to
997 * be held by task t. We leave a pointer to that rt_mutex where
998 * task t can find it, and task t will release the mutex when it
999 * exits its outermost RCU read-side critical section. Then
1000 * simply acquiring this artificial rt_mutex will boost task
1001 * t's priority. (Thanks to tglx for suggesting this approach!)
1003 * Note that task t must acquire rnp->lock to remove itself from
1004 * the ->blkd_tasks list, which it will do from exit() if from
1005 * nowhere else. We therefore are guaranteed that task t will
1006 * stay around at least until we drop rnp->lock. Note that
1007 * rnp->lock also resolves races between our priority boosting
1008 * and task t's exiting its outermost RCU read-side critical
1011 t
= container_of(tb
, struct task_struct
, rcu_node_entry
);
1012 rt_mutex_init_proxy_locked(&rnp
->boost_mtx
, t
);
1013 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
1014 /* Lock only for side effect: boosts task t's priority. */
1015 rt_mutex_lock(&rnp
->boost_mtx
);
1016 rt_mutex_unlock(&rnp
->boost_mtx
); /* Then keep lockdep happy. */
1018 return READ_ONCE(rnp
->exp_tasks
) != NULL
||
1019 READ_ONCE(rnp
->boost_tasks
) != NULL
;
1023 * Priority-boosting kthread, one per leaf rcu_node.
1025 static int rcu_boost_kthread(void *arg
)
1027 struct rcu_node
*rnp
= (struct rcu_node
*)arg
;
1031 trace_rcu_utilization(TPS("Start boost kthread@init"));
1033 rnp
->boost_kthread_status
= RCU_KTHREAD_WAITING
;
1034 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1035 rcu_wait(rnp
->boost_tasks
|| rnp
->exp_tasks
);
1036 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1037 rnp
->boost_kthread_status
= RCU_KTHREAD_RUNNING
;
1038 more2boost
= rcu_boost(rnp
);
1044 rnp
->boost_kthread_status
= RCU_KTHREAD_YIELDING
;
1045 trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1046 schedule_timeout_interruptible(2);
1047 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1052 trace_rcu_utilization(TPS("End boost kthread@notreached"));
1057 * Check to see if it is time to start boosting RCU readers that are
1058 * blocking the current grace period, and, if so, tell the per-rcu_node
1059 * kthread to start boosting them. If there is an expedited grace
1060 * period in progress, it is always time to boost.
1062 * The caller must hold rnp->lock, which this function releases.
1063 * The ->boost_kthread_task is immortal, so we don't need to worry
1064 * about it going away.
1066 static void rcu_initiate_boost(struct rcu_node
*rnp
, unsigned long flags
)
1067 __releases(rnp
->lock
)
1069 raw_lockdep_assert_held_rcu_node(rnp
);
1070 if (!rcu_preempt_blocked_readers_cgp(rnp
) && rnp
->exp_tasks
== NULL
) {
1071 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
1074 if (rnp
->exp_tasks
!= NULL
||
1075 (rnp
->gp_tasks
!= NULL
&&
1076 rnp
->boost_tasks
== NULL
&&
1078 ULONG_CMP_GE(jiffies
, rnp
->boost_time
))) {
1079 if (rnp
->exp_tasks
== NULL
)
1080 rnp
->boost_tasks
= rnp
->gp_tasks
;
1081 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
1082 rcu_wake_cond(rnp
->boost_kthread_task
,
1083 rnp
->boost_kthread_status
);
1085 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
1090 * Is the current CPU running the RCU-callbacks kthread?
1091 * Caller must have preemption disabled.
1093 static bool rcu_is_callbacks_kthread(void)
1095 return __this_cpu_read(rcu_data
.rcu_cpu_kthread_task
) == current
;
1098 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1101 * Do priority-boost accounting for the start of a new grace period.
1103 static void rcu_preempt_boost_start_gp(struct rcu_node
*rnp
)
1105 rnp
->boost_time
= jiffies
+ RCU_BOOST_DELAY_JIFFIES
;
1109 * Create an RCU-boost kthread for the specified node if one does not
1110 * already exist. We only create this kthread for preemptible RCU.
1111 * Returns zero if all is well, a negated errno otherwise.
1113 static void rcu_spawn_one_boost_kthread(struct rcu_node
*rnp
)
1115 int rnp_index
= rnp
- rcu_get_root();
1116 unsigned long flags
;
1117 struct sched_param sp
;
1118 struct task_struct
*t
;
1120 if (!IS_ENABLED(CONFIG_PREEMPT_RCU
))
1123 if (!rcu_scheduler_fully_active
|| rcu_rnp_online_cpus(rnp
) == 0)
1126 rcu_state
.boost
= 1;
1128 if (rnp
->boost_kthread_task
!= NULL
)
1131 t
= kthread_create(rcu_boost_kthread
, (void *)rnp
,
1132 "rcub/%d", rnp_index
);
1133 if (WARN_ON_ONCE(IS_ERR(t
)))
1136 raw_spin_lock_irqsave_rcu_node(rnp
, flags
);
1137 rnp
->boost_kthread_task
= t
;
1138 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
1139 sp
.sched_priority
= kthread_prio
;
1140 sched_setscheduler_nocheck(t
, SCHED_FIFO
, &sp
);
1141 wake_up_process(t
); /* get to TASK_INTERRUPTIBLE quickly. */
1145 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1146 * served by the rcu_node in question. The CPU hotplug lock is still
1147 * held, so the value of rnp->qsmaskinit will be stable.
1149 * We don't include outgoingcpu in the affinity set, use -1 if there is
1150 * no outgoing CPU. If there are no CPUs left in the affinity set,
1151 * this function allows the kthread to execute on any CPU.
1153 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
)
1155 struct task_struct
*t
= rnp
->boost_kthread_task
;
1156 unsigned long mask
= rcu_rnp_online_cpus(rnp
);
1162 if (!zalloc_cpumask_var(&cm
, GFP_KERNEL
))
1164 for_each_leaf_node_possible_cpu(rnp
, cpu
)
1165 if ((mask
& leaf_node_cpu_bit(rnp
, cpu
)) &&
1167 cpumask_set_cpu(cpu
, cm
);
1168 if (cpumask_weight(cm
) == 0)
1170 set_cpus_allowed_ptr(t
, cm
);
1171 free_cpumask_var(cm
);
1175 * Spawn boost kthreads -- called as soon as the scheduler is running.
1177 static void __init
rcu_spawn_boost_kthreads(void)
1179 struct rcu_node
*rnp
;
1181 rcu_for_each_leaf_node(rnp
)
1182 rcu_spawn_one_boost_kthread(rnp
);
1185 static void rcu_prepare_kthreads(int cpu
)
1187 struct rcu_data
*rdp
= per_cpu_ptr(&rcu_data
, cpu
);
1188 struct rcu_node
*rnp
= rdp
->mynode
;
1190 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1191 if (rcu_scheduler_fully_active
)
1192 rcu_spawn_one_boost_kthread(rnp
);
1195 #else /* #ifdef CONFIG_RCU_BOOST */
1197 static void rcu_initiate_boost(struct rcu_node
*rnp
, unsigned long flags
)
1198 __releases(rnp
->lock
)
1200 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
1203 static bool rcu_is_callbacks_kthread(void)
1208 static void rcu_preempt_boost_start_gp(struct rcu_node
*rnp
)
1212 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
)
1216 static void __init
rcu_spawn_boost_kthreads(void)
1220 static void rcu_prepare_kthreads(int cpu
)
1224 #endif /* #else #ifdef CONFIG_RCU_BOOST */
1226 #if !defined(CONFIG_RCU_FAST_NO_HZ)
1229 * Check to see if any future non-offloaded RCU-related work will need
1230 * to be done by the current CPU, even if none need be done immediately,
1231 * returning 1 if so. This function is part of the RCU implementation;
1232 * it is -not- an exported member of the RCU API.
1234 * Because we not have RCU_FAST_NO_HZ, just check whether or not this
1235 * CPU has RCU callbacks queued.
1237 int rcu_needs_cpu(u64 basemono
, u64
*nextevt
)
1239 *nextevt
= KTIME_MAX
;
1240 return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data
)->cblist
) &&
1241 !rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data
)->cblist
);
1245 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1248 static void rcu_cleanup_after_idle(void)
1253 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1256 static void rcu_prepare_for_idle(void)
1260 #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1263 * This code is invoked when a CPU goes idle, at which point we want
1264 * to have the CPU do everything required for RCU so that it can enter
1265 * the energy-efficient dyntick-idle mode. This is handled by a
1266 * state machine implemented by rcu_prepare_for_idle() below.
1268 * The following three proprocessor symbols control this state machine:
1270 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1271 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1272 * is sized to be roughly one RCU grace period. Those energy-efficiency
1273 * benchmarkers who might otherwise be tempted to set this to a large
1274 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1275 * system. And if you are -that- concerned about energy efficiency,
1276 * just power the system down and be done with it!
1277 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1278 * permitted to sleep in dyntick-idle mode with only lazy RCU
1279 * callbacks pending. Setting this too high can OOM your system.
1281 * The values below work well in practice. If future workloads require
1282 * adjustment, they can be converted into kernel config parameters, though
1283 * making the state machine smarter might be a better option.
1285 #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1286 #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1288 static int rcu_idle_gp_delay
= RCU_IDLE_GP_DELAY
;
1289 module_param(rcu_idle_gp_delay
, int, 0644);
1290 static int rcu_idle_lazy_gp_delay
= RCU_IDLE_LAZY_GP_DELAY
;
1291 module_param(rcu_idle_lazy_gp_delay
, int, 0644);
1294 * Try to advance callbacks on the current CPU, but only if it has been
1295 * awhile since the last time we did so. Afterwards, if there are any
1296 * callbacks ready for immediate invocation, return true.
1298 static bool __maybe_unused
rcu_try_advance_all_cbs(void)
1300 bool cbs_ready
= false;
1301 struct rcu_data
*rdp
= this_cpu_ptr(&rcu_data
);
1302 struct rcu_node
*rnp
;
1304 /* Exit early if we advanced recently. */
1305 if (jiffies
== rdp
->last_advance_all
)
1307 rdp
->last_advance_all
= jiffies
;
1312 * Don't bother checking unless a grace period has
1313 * completed since we last checked and there are
1314 * callbacks not yet ready to invoke.
1316 if ((rcu_seq_completed_gp(rdp
->gp_seq
,
1317 rcu_seq_current(&rnp
->gp_seq
)) ||
1318 unlikely(READ_ONCE(rdp
->gpwrap
))) &&
1319 rcu_segcblist_pend_cbs(&rdp
->cblist
))
1320 note_gp_changes(rdp
);
1322 if (rcu_segcblist_ready_cbs(&rdp
->cblist
))
1328 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1329 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1330 * caller to set the timeout based on whether or not there are non-lazy
1333 * The caller must have disabled interrupts.
1335 int rcu_needs_cpu(u64 basemono
, u64
*nextevt
)
1337 struct rcu_data
*rdp
= this_cpu_ptr(&rcu_data
);
1340 lockdep_assert_irqs_disabled();
1342 /* If no non-offloaded callbacks, RCU doesn't need the CPU. */
1343 if (rcu_segcblist_empty(&rdp
->cblist
) ||
1344 rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data
)->cblist
)) {
1345 *nextevt
= KTIME_MAX
;
1349 /* Attempt to advance callbacks. */
1350 if (rcu_try_advance_all_cbs()) {
1351 /* Some ready to invoke, so initiate later invocation. */
1355 rdp
->last_accelerate
= jiffies
;
1357 /* Request timer delay depending on laziness, and round. */
1358 rdp
->all_lazy
= !rcu_segcblist_n_nonlazy_cbs(&rdp
->cblist
);
1359 if (rdp
->all_lazy
) {
1360 dj
= round_jiffies(rcu_idle_lazy_gp_delay
+ jiffies
) - jiffies
;
1362 dj
= round_up(rcu_idle_gp_delay
+ jiffies
,
1363 rcu_idle_gp_delay
) - jiffies
;
1365 *nextevt
= basemono
+ dj
* TICK_NSEC
;
1370 * Prepare a CPU for idle from an RCU perspective. The first major task
1371 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1372 * The second major task is to check to see if a non-lazy callback has
1373 * arrived at a CPU that previously had only lazy callbacks. The third
1374 * major task is to accelerate (that is, assign grace-period numbers to)
1375 * any recently arrived callbacks.
1377 * The caller must have disabled interrupts.
1379 static void rcu_prepare_for_idle(void)
1382 struct rcu_data
*rdp
= this_cpu_ptr(&rcu_data
);
1383 struct rcu_node
*rnp
;
1386 lockdep_assert_irqs_disabled();
1387 if (rcu_segcblist_is_offloaded(&rdp
->cblist
))
1390 /* Handle nohz enablement switches conservatively. */
1391 tne
= READ_ONCE(tick_nohz_active
);
1392 if (tne
!= rdp
->tick_nohz_enabled_snap
) {
1393 if (!rcu_segcblist_empty(&rdp
->cblist
))
1394 invoke_rcu_core(); /* force nohz to see update. */
1395 rdp
->tick_nohz_enabled_snap
= tne
;
1402 * If a non-lazy callback arrived at a CPU having only lazy
1403 * callbacks, invoke RCU core for the side-effect of recalculating
1404 * idle duration on re-entry to idle.
1406 if (rdp
->all_lazy
&& rcu_segcblist_n_nonlazy_cbs(&rdp
->cblist
)) {
1407 rdp
->all_lazy
= false;
1413 * If we have not yet accelerated this jiffy, accelerate all
1414 * callbacks on this CPU.
1416 if (rdp
->last_accelerate
== jiffies
)
1418 rdp
->last_accelerate
= jiffies
;
1419 if (rcu_segcblist_pend_cbs(&rdp
->cblist
)) {
1421 raw_spin_lock_rcu_node(rnp
); /* irqs already disabled. */
1422 needwake
= rcu_accelerate_cbs(rnp
, rdp
);
1423 raw_spin_unlock_rcu_node(rnp
); /* irqs remain disabled. */
1425 rcu_gp_kthread_wake();
1430 * Clean up for exit from idle. Attempt to advance callbacks based on
1431 * any grace periods that elapsed while the CPU was idle, and if any
1432 * callbacks are now ready to invoke, initiate invocation.
1434 static void rcu_cleanup_after_idle(void)
1436 struct rcu_data
*rdp
= this_cpu_ptr(&rcu_data
);
1438 lockdep_assert_irqs_disabled();
1439 if (rcu_segcblist_is_offloaded(&rdp
->cblist
))
1441 if (rcu_try_advance_all_cbs())
1445 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1447 #ifdef CONFIG_RCU_NOCB_CPU
1450 * Offload callback processing from the boot-time-specified set of CPUs
1451 * specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads
1452 * created that pull the callbacks from the corresponding CPU, wait for
1453 * a grace period to elapse, and invoke the callbacks. These kthreads
1454 * are organized into GP kthreads, which manage incoming callbacks, wait for
1455 * grace periods, and awaken CB kthreads, and the CB kthreads, which only
1456 * invoke callbacks. Each GP kthread invokes its own CBs. The no-CBs CPUs
1457 * do a wake_up() on their GP kthread when they insert a callback into any
1458 * empty list, unless the rcu_nocb_poll boot parameter has been specified,
1459 * in which case each kthread actively polls its CPU. (Which isn't so great
1460 * for energy efficiency, but which does reduce RCU's overhead on that CPU.)
1462 * This is intended to be used in conjunction with Frederic Weisbecker's
1463 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
1464 * running CPU-bound user-mode computations.
1466 * Offloading of callbacks can also be used as an energy-efficiency
1467 * measure because CPUs with no RCU callbacks queued are more aggressive
1468 * about entering dyntick-idle mode.
1473 * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters.
1474 * The string after the "rcu_nocbs=" is either "all" for all CPUs, or a
1475 * comma-separated list of CPUs and/or CPU ranges. If an invalid list is
1476 * given, a warning is emitted and all CPUs are offloaded.
1478 static int __init
rcu_nocb_setup(char *str
)
1480 alloc_bootmem_cpumask_var(&rcu_nocb_mask
);
1481 if (!strcasecmp(str
, "all"))
1482 cpumask_setall(rcu_nocb_mask
);
1484 if (cpulist_parse(str
, rcu_nocb_mask
)) {
1485 pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
1486 cpumask_setall(rcu_nocb_mask
);
1490 __setup("rcu_nocbs=", rcu_nocb_setup
);
1492 static int __init
parse_rcu_nocb_poll(char *arg
)
1494 rcu_nocb_poll
= true;
1497 early_param("rcu_nocb_poll", parse_rcu_nocb_poll
);
1500 * Don't bother bypassing ->cblist if the call_rcu() rate is low.
1501 * After all, the main point of bypassing is to avoid lock contention
1502 * on ->nocb_lock, which only can happen at high call_rcu() rates.
1504 int nocb_nobypass_lim_per_jiffy
= 16 * 1000 / HZ
;
1505 module_param(nocb_nobypass_lim_per_jiffy
, int, 0);
1508 * Acquire the specified rcu_data structure's ->nocb_bypass_lock. If the
1509 * lock isn't immediately available, increment ->nocb_lock_contended to
1510 * flag the contention.
1512 static void rcu_nocb_bypass_lock(struct rcu_data
*rdp
)
1514 lockdep_assert_irqs_disabled();
1515 if (raw_spin_trylock(&rdp
->nocb_bypass_lock
))
1517 atomic_inc(&rdp
->nocb_lock_contended
);
1518 WARN_ON_ONCE(smp_processor_id() != rdp
->cpu
);
1519 smp_mb__after_atomic(); /* atomic_inc() before lock. */
1520 raw_spin_lock(&rdp
->nocb_bypass_lock
);
1521 smp_mb__before_atomic(); /* atomic_dec() after lock. */
1522 atomic_dec(&rdp
->nocb_lock_contended
);
1526 * Spinwait until the specified rcu_data structure's ->nocb_lock is
1527 * not contended. Please note that this is extremely special-purpose,
1528 * relying on the fact that at most two kthreads and one CPU contend for
1529 * this lock, and also that the two kthreads are guaranteed to have frequent
1530 * grace-period-duration time intervals between successive acquisitions
1531 * of the lock. This allows us to use an extremely simple throttling
1532 * mechanism, and further to apply it only to the CPU doing floods of
1533 * call_rcu() invocations. Don't try this at home!
1535 static void rcu_nocb_wait_contended(struct rcu_data
*rdp
)
1537 WARN_ON_ONCE(smp_processor_id() != rdp
->cpu
);
1538 while (WARN_ON_ONCE(atomic_read(&rdp
->nocb_lock_contended
)))
1543 * Conditionally acquire the specified rcu_data structure's
1544 * ->nocb_bypass_lock.
1546 static bool rcu_nocb_bypass_trylock(struct rcu_data
*rdp
)
1548 lockdep_assert_irqs_disabled();
1549 return raw_spin_trylock(&rdp
->nocb_bypass_lock
);
1553 * Release the specified rcu_data structure's ->nocb_bypass_lock.
1555 static void rcu_nocb_bypass_unlock(struct rcu_data
*rdp
)
1557 lockdep_assert_irqs_disabled();
1558 raw_spin_unlock(&rdp
->nocb_bypass_lock
);
1562 * Acquire the specified rcu_data structure's ->nocb_lock, but only
1563 * if it corresponds to a no-CBs CPU.
1565 static void rcu_nocb_lock(struct rcu_data
*rdp
)
1567 lockdep_assert_irqs_disabled();
1568 if (!rcu_segcblist_is_offloaded(&rdp
->cblist
))
1570 raw_spin_lock(&rdp
->nocb_lock
);
1574 * Release the specified rcu_data structure's ->nocb_lock, but only
1575 * if it corresponds to a no-CBs CPU.
1577 static void rcu_nocb_unlock(struct rcu_data
*rdp
)
1579 if (rcu_segcblist_is_offloaded(&rdp
->cblist
)) {
1580 lockdep_assert_irqs_disabled();
1581 raw_spin_unlock(&rdp
->nocb_lock
);
1586 * Release the specified rcu_data structure's ->nocb_lock and restore
1587 * interrupts, but only if it corresponds to a no-CBs CPU.
1589 static void rcu_nocb_unlock_irqrestore(struct rcu_data
*rdp
,
1590 unsigned long flags
)
1592 if (rcu_segcblist_is_offloaded(&rdp
->cblist
)) {
1593 lockdep_assert_irqs_disabled();
1594 raw_spin_unlock_irqrestore(&rdp
->nocb_lock
, flags
);
1596 local_irq_restore(flags
);
1600 /* Lockdep check that ->cblist may be safely accessed. */
1601 static void rcu_lockdep_assert_cblist_protected(struct rcu_data
*rdp
)
1603 lockdep_assert_irqs_disabled();
1604 if (rcu_segcblist_is_offloaded(&rdp
->cblist
) &&
1605 cpu_online(rdp
->cpu
))
1606 lockdep_assert_held(&rdp
->nocb_lock
);
1610 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
1613 static void rcu_nocb_gp_cleanup(struct swait_queue_head
*sq
)
1618 static struct swait_queue_head
*rcu_nocb_gp_get(struct rcu_node
*rnp
)
1620 return &rnp
->nocb_gp_wq
[rcu_seq_ctr(rnp
->gp_seq
) & 0x1];
1623 static void rcu_init_one_nocb(struct rcu_node
*rnp
)
1625 init_swait_queue_head(&rnp
->nocb_gp_wq
[0]);
1626 init_swait_queue_head(&rnp
->nocb_gp_wq
[1]);
1629 /* Is the specified CPU a no-CBs CPU? */
1630 bool rcu_is_nocb_cpu(int cpu
)
1632 if (cpumask_available(rcu_nocb_mask
))
1633 return cpumask_test_cpu(cpu
, rcu_nocb_mask
);
1638 * Kick the GP kthread for this NOCB group. Caller holds ->nocb_lock
1639 * and this function releases it.
1641 static void wake_nocb_gp(struct rcu_data
*rdp
, bool force
,
1642 unsigned long flags
)
1643 __releases(rdp
->nocb_lock
)
1645 bool needwake
= false;
1646 struct rcu_data
*rdp_gp
= rdp
->nocb_gp_rdp
;
1648 lockdep_assert_held(&rdp
->nocb_lock
);
1649 if (!READ_ONCE(rdp_gp
->nocb_gp_kthread
)) {
1650 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
,
1651 TPS("AlreadyAwake"));
1652 rcu_nocb_unlock_irqrestore(rdp
, flags
);
1655 del_timer(&rdp
->nocb_timer
);
1656 rcu_nocb_unlock_irqrestore(rdp
, flags
);
1657 raw_spin_lock_irqsave(&rdp_gp
->nocb_gp_lock
, flags
);
1658 if (force
|| READ_ONCE(rdp_gp
->nocb_gp_sleep
)) {
1659 WRITE_ONCE(rdp_gp
->nocb_gp_sleep
, false);
1661 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
, TPS("DoWake"));
1663 raw_spin_unlock_irqrestore(&rdp_gp
->nocb_gp_lock
, flags
);
1665 wake_up_process(rdp_gp
->nocb_gp_kthread
);
1669 * Arrange to wake the GP kthread for this NOCB group at some future
1670 * time when it is safe to do so.
1672 static void wake_nocb_gp_defer(struct rcu_data
*rdp
, int waketype
,
1675 if (rdp
->nocb_defer_wakeup
== RCU_NOCB_WAKE_NOT
)
1676 mod_timer(&rdp
->nocb_timer
, jiffies
+ 1);
1677 if (rdp
->nocb_defer_wakeup
< waketype
)
1678 WRITE_ONCE(rdp
->nocb_defer_wakeup
, waketype
);
1679 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
, reason
);
1683 * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
1684 * However, if there is a callback to be enqueued and if ->nocb_bypass
1685 * proves to be initially empty, just return false because the no-CB GP
1686 * kthread may need to be awakened in this case.
1688 * Note that this function always returns true if rhp is NULL.
1690 static bool rcu_nocb_do_flush_bypass(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
1693 struct rcu_cblist rcl
;
1695 WARN_ON_ONCE(!rcu_segcblist_is_offloaded(&rdp
->cblist
));
1696 rcu_lockdep_assert_cblist_protected(rdp
);
1697 lockdep_assert_held(&rdp
->nocb_bypass_lock
);
1698 if (rhp
&& !rcu_cblist_n_cbs(&rdp
->nocb_bypass
)) {
1699 raw_spin_unlock(&rdp
->nocb_bypass_lock
);
1702 /* Note: ->cblist.len already accounts for ->nocb_bypass contents. */
1704 rcu_segcblist_inc_len(&rdp
->cblist
); /* Must precede enqueue. */
1705 rcu_cblist_flush_enqueue(&rcl
, &rdp
->nocb_bypass
, rhp
);
1706 rcu_segcblist_insert_pend_cbs(&rdp
->cblist
, &rcl
);
1707 WRITE_ONCE(rdp
->nocb_bypass_first
, j
);
1708 rcu_nocb_bypass_unlock(rdp
);
1713 * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
1714 * However, if there is a callback to be enqueued and if ->nocb_bypass
1715 * proves to be initially empty, just return false because the no-CB GP
1716 * kthread may need to be awakened in this case.
1718 * Note that this function always returns true if rhp is NULL.
1720 static bool rcu_nocb_flush_bypass(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
1723 if (!rcu_segcblist_is_offloaded(&rdp
->cblist
))
1725 rcu_lockdep_assert_cblist_protected(rdp
);
1726 rcu_nocb_bypass_lock(rdp
);
1727 return rcu_nocb_do_flush_bypass(rdp
, rhp
, j
);
1731 * If the ->nocb_bypass_lock is immediately available, flush the
1732 * ->nocb_bypass queue into ->cblist.
1734 static void rcu_nocb_try_flush_bypass(struct rcu_data
*rdp
, unsigned long j
)
1736 rcu_lockdep_assert_cblist_protected(rdp
);
1737 if (!rcu_segcblist_is_offloaded(&rdp
->cblist
) ||
1738 !rcu_nocb_bypass_trylock(rdp
))
1740 WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp
, NULL
, j
));
1744 * See whether it is appropriate to use the ->nocb_bypass list in order
1745 * to control contention on ->nocb_lock. A limited number of direct
1746 * enqueues are permitted into ->cblist per jiffy. If ->nocb_bypass
1747 * is non-empty, further callbacks must be placed into ->nocb_bypass,
1748 * otherwise rcu_barrier() breaks. Use rcu_nocb_flush_bypass() to switch
1749 * back to direct use of ->cblist. However, ->nocb_bypass should not be
1750 * used if ->cblist is empty, because otherwise callbacks can be stranded
1751 * on ->nocb_bypass because we cannot count on the current CPU ever again
1752 * invoking call_rcu(). The general rule is that if ->nocb_bypass is
1753 * non-empty, the corresponding no-CBs grace-period kthread must not be
1754 * in an indefinite sleep state.
1756 * Finally, it is not permitted to use the bypass during early boot,
1757 * as doing so would confuse the auto-initialization code. Besides
1758 * which, there is no point in worrying about lock contention while
1759 * there is only one CPU in operation.
1761 static bool rcu_nocb_try_bypass(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
1762 bool *was_alldone
, unsigned long flags
)
1765 unsigned long cur_gp_seq
;
1766 unsigned long j
= jiffies
;
1767 long ncbs
= rcu_cblist_n_cbs(&rdp
->nocb_bypass
);
1769 if (!rcu_segcblist_is_offloaded(&rdp
->cblist
)) {
1770 *was_alldone
= !rcu_segcblist_pend_cbs(&rdp
->cblist
);
1771 return false; /* Not offloaded, no bypassing. */
1773 lockdep_assert_irqs_disabled();
1775 // Don't use ->nocb_bypass during early boot.
1776 if (rcu_scheduler_active
!= RCU_SCHEDULER_RUNNING
) {
1778 WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp
->nocb_bypass
));
1779 *was_alldone
= !rcu_segcblist_pend_cbs(&rdp
->cblist
);
1783 // If we have advanced to a new jiffy, reset counts to allow
1784 // moving back from ->nocb_bypass to ->cblist.
1785 if (j
== rdp
->nocb_nobypass_last
) {
1786 c
= rdp
->nocb_nobypass_count
+ 1;
1788 WRITE_ONCE(rdp
->nocb_nobypass_last
, j
);
1789 c
= rdp
->nocb_nobypass_count
- nocb_nobypass_lim_per_jiffy
;
1790 if (ULONG_CMP_LT(rdp
->nocb_nobypass_count
,
1791 nocb_nobypass_lim_per_jiffy
))
1793 else if (c
> nocb_nobypass_lim_per_jiffy
)
1794 c
= nocb_nobypass_lim_per_jiffy
;
1796 WRITE_ONCE(rdp
->nocb_nobypass_count
, c
);
1798 // If there hasn't yet been all that many ->cblist enqueues
1799 // this jiffy, tell the caller to enqueue onto ->cblist. But flush
1800 // ->nocb_bypass first.
1801 if (rdp
->nocb_nobypass_count
< nocb_nobypass_lim_per_jiffy
) {
1803 *was_alldone
= !rcu_segcblist_pend_cbs(&rdp
->cblist
);
1805 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
,
1807 WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp
, NULL
, j
));
1808 WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp
->nocb_bypass
));
1809 return false; // Caller must enqueue the callback.
1812 // If ->nocb_bypass has been used too long or is too full,
1813 // flush ->nocb_bypass to ->cblist.
1814 if ((ncbs
&& j
!= READ_ONCE(rdp
->nocb_bypass_first
)) ||
1817 if (!rcu_nocb_flush_bypass(rdp
, rhp
, j
)) {
1818 *was_alldone
= !rcu_segcblist_pend_cbs(&rdp
->cblist
);
1820 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
,
1822 WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp
->nocb_bypass
));
1823 return false; // Caller must enqueue the callback.
1825 if (j
!= rdp
->nocb_gp_adv_time
&&
1826 rcu_segcblist_nextgp(&rdp
->cblist
, &cur_gp_seq
) &&
1827 rcu_seq_done(&rdp
->mynode
->gp_seq
, cur_gp_seq
)) {
1828 rcu_advance_cbs_nowake(rdp
->mynode
, rdp
);
1829 rdp
->nocb_gp_adv_time
= j
;
1831 rcu_nocb_unlock_irqrestore(rdp
, flags
);
1832 return true; // Callback already enqueued.
1835 // We need to use the bypass.
1836 rcu_nocb_wait_contended(rdp
);
1837 rcu_nocb_bypass_lock(rdp
);
1838 ncbs
= rcu_cblist_n_cbs(&rdp
->nocb_bypass
);
1839 rcu_segcblist_inc_len(&rdp
->cblist
); /* Must precede enqueue. */
1840 rcu_cblist_enqueue(&rdp
->nocb_bypass
, rhp
);
1842 WRITE_ONCE(rdp
->nocb_bypass_first
, j
);
1843 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
, TPS("FirstBQ"));
1845 rcu_nocb_bypass_unlock(rdp
);
1846 smp_mb(); /* Order enqueue before wake. */
1848 local_irq_restore(flags
);
1850 // No-CBs GP kthread might be indefinitely asleep, if so, wake.
1851 rcu_nocb_lock(rdp
); // Rare during call_rcu() flood.
1852 if (!rcu_segcblist_pend_cbs(&rdp
->cblist
)) {
1853 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
,
1854 TPS("FirstBQwake"));
1855 __call_rcu_nocb_wake(rdp
, true, flags
);
1857 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
,
1858 TPS("FirstBQnoWake"));
1859 rcu_nocb_unlock_irqrestore(rdp
, flags
);
1862 return true; // Callback already enqueued.
1866 * Awaken the no-CBs grace-period kthead if needed, either due to it
1867 * legitimately being asleep or due to overload conditions.
1869 * If warranted, also wake up the kthread servicing this CPUs queues.
1871 static void __call_rcu_nocb_wake(struct rcu_data
*rdp
, bool was_alldone
,
1872 unsigned long flags
)
1873 __releases(rdp
->nocb_lock
)
1875 unsigned long cur_gp_seq
;
1878 struct task_struct
*t
;
1880 // If we are being polled or there is no kthread, just leave.
1881 t
= READ_ONCE(rdp
->nocb_gp_kthread
);
1882 if (rcu_nocb_poll
|| !t
) {
1883 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
,
1884 TPS("WakeNotPoll"));
1885 rcu_nocb_unlock_irqrestore(rdp
, flags
);
1888 // Need to actually to a wakeup.
1889 len
= rcu_segcblist_n_cbs(&rdp
->cblist
);
1891 rdp
->qlen_last_fqs_check
= len
;
1892 if (!irqs_disabled_flags(flags
)) {
1893 /* ... if queue was empty ... */
1894 wake_nocb_gp(rdp
, false, flags
);
1895 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
,
1898 wake_nocb_gp_defer(rdp
, RCU_NOCB_WAKE
,
1899 TPS("WakeEmptyIsDeferred"));
1900 rcu_nocb_unlock_irqrestore(rdp
, flags
);
1902 } else if (len
> rdp
->qlen_last_fqs_check
+ qhimark
) {
1903 /* ... or if many callbacks queued. */
1904 rdp
->qlen_last_fqs_check
= len
;
1906 if (j
!= rdp
->nocb_gp_adv_time
&&
1907 rcu_segcblist_nextgp(&rdp
->cblist
, &cur_gp_seq
) &&
1908 rcu_seq_done(&rdp
->mynode
->gp_seq
, cur_gp_seq
)) {
1909 rcu_advance_cbs_nowake(rdp
->mynode
, rdp
);
1910 rdp
->nocb_gp_adv_time
= j
;
1912 smp_mb(); /* Enqueue before timer_pending(). */
1913 if ((rdp
->nocb_cb_sleep
||
1914 !rcu_segcblist_ready_cbs(&rdp
->cblist
)) &&
1915 !timer_pending(&rdp
->nocb_bypass_timer
))
1916 wake_nocb_gp_defer(rdp
, RCU_NOCB_WAKE_FORCE
,
1917 TPS("WakeOvfIsDeferred"));
1918 rcu_nocb_unlock_irqrestore(rdp
, flags
);
1920 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
, TPS("WakeNot"));
1921 rcu_nocb_unlock_irqrestore(rdp
, flags
);
1926 /* Wake up the no-CBs GP kthread to flush ->nocb_bypass. */
1927 static void do_nocb_bypass_wakeup_timer(struct timer_list
*t
)
1929 unsigned long flags
;
1930 struct rcu_data
*rdp
= from_timer(rdp
, t
, nocb_bypass_timer
);
1932 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
, TPS("Timer"));
1933 rcu_nocb_lock_irqsave(rdp
, flags
);
1934 smp_mb__after_spinlock(); /* Timer expire before wakeup. */
1935 __call_rcu_nocb_wake(rdp
, true, flags
);
1939 * No-CBs GP kthreads come here to wait for additional callbacks to show up
1940 * or for grace periods to end.
1942 static void nocb_gp_wait(struct rcu_data
*my_rdp
)
1944 bool bypass
= false;
1946 int __maybe_unused cpu
= my_rdp
->cpu
;
1947 unsigned long cur_gp_seq
;
1948 unsigned long flags
;
1949 bool gotcbs
= false;
1950 unsigned long j
= jiffies
;
1951 bool needwait_gp
= false; // This prevents actual uninitialized use.
1954 struct rcu_data
*rdp
;
1955 struct rcu_node
*rnp
;
1956 unsigned long wait_gp_seq
= 0; // Suppress "use uninitialized" warning.
1959 * Each pass through the following loop checks for CBs and for the
1960 * nearest grace period (if any) to wait for next. The CB kthreads
1961 * and the global grace-period kthread are awakened if needed.
1963 for (rdp
= my_rdp
; rdp
; rdp
= rdp
->nocb_next_cb_rdp
) {
1964 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
, TPS("Check"));
1965 rcu_nocb_lock_irqsave(rdp
, flags
);
1966 bypass_ncbs
= rcu_cblist_n_cbs(&rdp
->nocb_bypass
);
1968 (time_after(j
, READ_ONCE(rdp
->nocb_bypass_first
) + 1) ||
1969 bypass_ncbs
> 2 * qhimark
)) {
1970 // Bypass full or old, so flush it.
1971 (void)rcu_nocb_try_flush_bypass(rdp
, j
);
1972 bypass_ncbs
= rcu_cblist_n_cbs(&rdp
->nocb_bypass
);
1973 } else if (!bypass_ncbs
&& rcu_segcblist_empty(&rdp
->cblist
)) {
1974 rcu_nocb_unlock_irqrestore(rdp
, flags
);
1975 continue; /* No callbacks here, try next. */
1978 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
,
1983 if (bypass
) { // Avoid race with first bypass CB.
1984 WRITE_ONCE(my_rdp
->nocb_defer_wakeup
,
1986 del_timer(&my_rdp
->nocb_timer
);
1988 // Advance callbacks if helpful and low contention.
1989 needwake_gp
= false;
1990 if (!rcu_segcblist_restempty(&rdp
->cblist
,
1991 RCU_NEXT_READY_TAIL
) ||
1992 (rcu_segcblist_nextgp(&rdp
->cblist
, &cur_gp_seq
) &&
1993 rcu_seq_done(&rnp
->gp_seq
, cur_gp_seq
))) {
1994 raw_spin_lock_rcu_node(rnp
); /* irqs disabled. */
1995 needwake_gp
= rcu_advance_cbs(rnp
, rdp
);
1996 raw_spin_unlock_rcu_node(rnp
); /* irqs disabled. */
1998 // Need to wait on some grace period?
1999 WARN_ON_ONCE(!rcu_segcblist_restempty(&rdp
->cblist
,
2000 RCU_NEXT_READY_TAIL
));
2001 if (rcu_segcblist_nextgp(&rdp
->cblist
, &cur_gp_seq
)) {
2003 ULONG_CMP_LT(cur_gp_seq
, wait_gp_seq
))
2004 wait_gp_seq
= cur_gp_seq
;
2006 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
,
2009 if (rcu_segcblist_ready_cbs(&rdp
->cblist
)) {
2010 needwake
= rdp
->nocb_cb_sleep
;
2011 WRITE_ONCE(rdp
->nocb_cb_sleep
, false);
2012 smp_mb(); /* CB invocation -after- GP end. */
2016 rcu_nocb_unlock_irqrestore(rdp
, flags
);
2018 swake_up_one(&rdp
->nocb_cb_wq
);
2022 rcu_gp_kthread_wake();
2025 my_rdp
->nocb_gp_bypass
= bypass
;
2026 my_rdp
->nocb_gp_gp
= needwait_gp
;
2027 my_rdp
->nocb_gp_seq
= needwait_gp
? wait_gp_seq
: 0;
2028 if (bypass
&& !rcu_nocb_poll
) {
2029 // At least one child with non-empty ->nocb_bypass, so set
2030 // timer in order to avoid stranding its callbacks.
2031 raw_spin_lock_irqsave(&my_rdp
->nocb_gp_lock
, flags
);
2032 mod_timer(&my_rdp
->nocb_bypass_timer
, j
+ 2);
2033 raw_spin_unlock_irqrestore(&my_rdp
->nocb_gp_lock
, flags
);
2035 if (rcu_nocb_poll
) {
2036 /* Polling, so trace if first poll in the series. */
2038 trace_rcu_nocb_wake(rcu_state
.name
, cpu
, TPS("Poll"));
2039 schedule_timeout_interruptible(1);
2040 } else if (!needwait_gp
) {
2041 /* Wait for callbacks to appear. */
2042 trace_rcu_nocb_wake(rcu_state
.name
, cpu
, TPS("Sleep"));
2043 swait_event_interruptible_exclusive(my_rdp
->nocb_gp_wq
,
2044 !READ_ONCE(my_rdp
->nocb_gp_sleep
));
2045 trace_rcu_nocb_wake(rcu_state
.name
, cpu
, TPS("EndSleep"));
2047 rnp
= my_rdp
->mynode
;
2048 trace_rcu_this_gp(rnp
, my_rdp
, wait_gp_seq
, TPS("StartWait"));
2049 swait_event_interruptible_exclusive(
2050 rnp
->nocb_gp_wq
[rcu_seq_ctr(wait_gp_seq
) & 0x1],
2051 rcu_seq_done(&rnp
->gp_seq
, wait_gp_seq
) ||
2052 !READ_ONCE(my_rdp
->nocb_gp_sleep
));
2053 trace_rcu_this_gp(rnp
, my_rdp
, wait_gp_seq
, TPS("EndWait"));
2055 if (!rcu_nocb_poll
) {
2056 raw_spin_lock_irqsave(&my_rdp
->nocb_gp_lock
, flags
);
2058 del_timer(&my_rdp
->nocb_bypass_timer
);
2059 WRITE_ONCE(my_rdp
->nocb_gp_sleep
, true);
2060 raw_spin_unlock_irqrestore(&my_rdp
->nocb_gp_lock
, flags
);
2062 my_rdp
->nocb_gp_seq
= -1;
2063 WARN_ON(signal_pending(current
));
2067 * No-CBs grace-period-wait kthread. There is one of these per group
2068 * of CPUs, but only once at least one CPU in that group has come online
2069 * at least once since boot. This kthread checks for newly posted
2070 * callbacks from any of the CPUs it is responsible for, waits for a
2071 * grace period, then awakens all of the rcu_nocb_cb_kthread() instances
2072 * that then have callback-invocation work to do.
2074 static int rcu_nocb_gp_kthread(void *arg
)
2076 struct rcu_data
*rdp
= arg
;
2079 WRITE_ONCE(rdp
->nocb_gp_loops
, rdp
->nocb_gp_loops
+ 1);
2081 cond_resched_tasks_rcu_qs();
2087 * Invoke any ready callbacks from the corresponding no-CBs CPU,
2088 * then, if there are no more, wait for more to appear.
2090 static void nocb_cb_wait(struct rcu_data
*rdp
)
2092 unsigned long cur_gp_seq
;
2093 unsigned long flags
;
2094 bool needwake_gp
= false;
2095 struct rcu_node
*rnp
= rdp
->mynode
;
2097 local_irq_save(flags
);
2098 rcu_momentary_dyntick_idle();
2099 local_irq_restore(flags
);
2103 lockdep_assert_irqs_enabled();
2104 rcu_nocb_lock_irqsave(rdp
, flags
);
2105 if (rcu_segcblist_nextgp(&rdp
->cblist
, &cur_gp_seq
) &&
2106 rcu_seq_done(&rnp
->gp_seq
, cur_gp_seq
) &&
2107 raw_spin_trylock_rcu_node(rnp
)) { /* irqs already disabled. */
2108 needwake_gp
= rcu_advance_cbs(rdp
->mynode
, rdp
);
2109 raw_spin_unlock_rcu_node(rnp
); /* irqs remain disabled. */
2111 if (rcu_segcblist_ready_cbs(&rdp
->cblist
)) {
2112 rcu_nocb_unlock_irqrestore(rdp
, flags
);
2114 rcu_gp_kthread_wake();
2118 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
, TPS("CBSleep"));
2119 WRITE_ONCE(rdp
->nocb_cb_sleep
, true);
2120 rcu_nocb_unlock_irqrestore(rdp
, flags
);
2122 rcu_gp_kthread_wake();
2123 swait_event_interruptible_exclusive(rdp
->nocb_cb_wq
,
2124 !READ_ONCE(rdp
->nocb_cb_sleep
));
2125 if (!smp_load_acquire(&rdp
->nocb_cb_sleep
)) { /* VVV */
2126 /* ^^^ Ensure CB invocation follows _sleep test. */
2129 WARN_ON(signal_pending(current
));
2130 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
, TPS("WokeEmpty"));
2134 * Per-rcu_data kthread, but only for no-CBs CPUs. Repeatedly invoke
2135 * nocb_cb_wait() to do the dirty work.
2137 static int rcu_nocb_cb_kthread(void *arg
)
2139 struct rcu_data
*rdp
= arg
;
2141 // Each pass through this loop does one callback batch, and,
2142 // if there are no more ready callbacks, waits for them.
2145 cond_resched_tasks_rcu_qs();
2150 /* Is a deferred wakeup of rcu_nocb_kthread() required? */
2151 static int rcu_nocb_need_deferred_wakeup(struct rcu_data
*rdp
)
2153 return READ_ONCE(rdp
->nocb_defer_wakeup
);
2156 /* Do a deferred wakeup of rcu_nocb_kthread(). */
2157 static void do_nocb_deferred_wakeup_common(struct rcu_data
*rdp
)
2159 unsigned long flags
;
2162 rcu_nocb_lock_irqsave(rdp
, flags
);
2163 if (!rcu_nocb_need_deferred_wakeup(rdp
)) {
2164 rcu_nocb_unlock_irqrestore(rdp
, flags
);
2167 ndw
= READ_ONCE(rdp
->nocb_defer_wakeup
);
2168 WRITE_ONCE(rdp
->nocb_defer_wakeup
, RCU_NOCB_WAKE_NOT
);
2169 wake_nocb_gp(rdp
, ndw
== RCU_NOCB_WAKE_FORCE
, flags
);
2170 trace_rcu_nocb_wake(rcu_state
.name
, rdp
->cpu
, TPS("DeferredWake"));
2173 /* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
2174 static void do_nocb_deferred_wakeup_timer(struct timer_list
*t
)
2176 struct rcu_data
*rdp
= from_timer(rdp
, t
, nocb_timer
);
2178 do_nocb_deferred_wakeup_common(rdp
);
2182 * Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
2183 * This means we do an inexact common-case check. Note that if
2184 * we miss, ->nocb_timer will eventually clean things up.
2186 static void do_nocb_deferred_wakeup(struct rcu_data
*rdp
)
2188 if (rcu_nocb_need_deferred_wakeup(rdp
))
2189 do_nocb_deferred_wakeup_common(rdp
);
2192 void __init
rcu_init_nohz(void)
2195 bool need_rcu_nocb_mask
= false;
2196 struct rcu_data
*rdp
;
2198 #if defined(CONFIG_NO_HZ_FULL)
2199 if (tick_nohz_full_running
&& cpumask_weight(tick_nohz_full_mask
))
2200 need_rcu_nocb_mask
= true;
2201 #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2203 if (!cpumask_available(rcu_nocb_mask
) && need_rcu_nocb_mask
) {
2204 if (!zalloc_cpumask_var(&rcu_nocb_mask
, GFP_KERNEL
)) {
2205 pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
2209 if (!cpumask_available(rcu_nocb_mask
))
2212 #if defined(CONFIG_NO_HZ_FULL)
2213 if (tick_nohz_full_running
)
2214 cpumask_or(rcu_nocb_mask
, rcu_nocb_mask
, tick_nohz_full_mask
);
2215 #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2217 if (!cpumask_subset(rcu_nocb_mask
, cpu_possible_mask
)) {
2218 pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
2219 cpumask_and(rcu_nocb_mask
, cpu_possible_mask
,
2222 if (cpumask_empty(rcu_nocb_mask
))
2223 pr_info("\tOffload RCU callbacks from CPUs: (none).\n");
2225 pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
2226 cpumask_pr_args(rcu_nocb_mask
));
2228 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
2230 for_each_cpu(cpu
, rcu_nocb_mask
) {
2231 rdp
= per_cpu_ptr(&rcu_data
, cpu
);
2232 if (rcu_segcblist_empty(&rdp
->cblist
))
2233 rcu_segcblist_init(&rdp
->cblist
);
2234 rcu_segcblist_offload(&rdp
->cblist
);
2236 rcu_organize_nocb_kthreads();
2239 /* Initialize per-rcu_data variables for no-CBs CPUs. */
2240 static void __init
rcu_boot_init_nocb_percpu_data(struct rcu_data
*rdp
)
2242 init_swait_queue_head(&rdp
->nocb_cb_wq
);
2243 init_swait_queue_head(&rdp
->nocb_gp_wq
);
2244 raw_spin_lock_init(&rdp
->nocb_lock
);
2245 raw_spin_lock_init(&rdp
->nocb_bypass_lock
);
2246 raw_spin_lock_init(&rdp
->nocb_gp_lock
);
2247 timer_setup(&rdp
->nocb_timer
, do_nocb_deferred_wakeup_timer
, 0);
2248 timer_setup(&rdp
->nocb_bypass_timer
, do_nocb_bypass_wakeup_timer
, 0);
2249 rcu_cblist_init(&rdp
->nocb_bypass
);
2253 * If the specified CPU is a no-CBs CPU that does not already have its
2254 * rcuo CB kthread, spawn it. Additionally, if the rcuo GP kthread
2255 * for this CPU's group has not yet been created, spawn it as well.
2257 static void rcu_spawn_one_nocb_kthread(int cpu
)
2259 struct rcu_data
*rdp
= per_cpu_ptr(&rcu_data
, cpu
);
2260 struct rcu_data
*rdp_gp
;
2261 struct task_struct
*t
;
2264 * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
2265 * then nothing to do.
2267 if (!rcu_is_nocb_cpu(cpu
) || rdp
->nocb_cb_kthread
)
2270 /* If we didn't spawn the GP kthread first, reorganize! */
2271 rdp_gp
= rdp
->nocb_gp_rdp
;
2272 if (!rdp_gp
->nocb_gp_kthread
) {
2273 t
= kthread_run(rcu_nocb_gp_kthread
, rdp_gp
,
2274 "rcuog/%d", rdp_gp
->cpu
);
2275 if (WARN_ONCE(IS_ERR(t
), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__
))
2277 WRITE_ONCE(rdp_gp
->nocb_gp_kthread
, t
);
2280 /* Spawn the kthread for this CPU. */
2281 t
= kthread_run(rcu_nocb_cb_kthread
, rdp
,
2282 "rcuo%c/%d", rcu_state
.abbr
, cpu
);
2283 if (WARN_ONCE(IS_ERR(t
), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__
))
2285 WRITE_ONCE(rdp
->nocb_cb_kthread
, t
);
2286 WRITE_ONCE(rdp
->nocb_gp_kthread
, rdp_gp
->nocb_gp_kthread
);
2290 * If the specified CPU is a no-CBs CPU that does not already have its
2291 * rcuo kthread, spawn it.
2293 static void rcu_spawn_cpu_nocb_kthread(int cpu
)
2295 if (rcu_scheduler_fully_active
)
2296 rcu_spawn_one_nocb_kthread(cpu
);
2300 * Once the scheduler is running, spawn rcuo kthreads for all online
2301 * no-CBs CPUs. This assumes that the early_initcall()s happen before
2302 * non-boot CPUs come online -- if this changes, we will need to add
2303 * some mutual exclusion.
2305 static void __init
rcu_spawn_nocb_kthreads(void)
2309 for_each_online_cpu(cpu
)
2310 rcu_spawn_cpu_nocb_kthread(cpu
);
2313 /* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */
2314 static int rcu_nocb_gp_stride
= -1;
2315 module_param(rcu_nocb_gp_stride
, int, 0444);
2318 * Initialize GP-CB relationships for all no-CBs CPU.
2320 static void __init
rcu_organize_nocb_kthreads(void)
2323 bool firsttime
= true;
2324 int ls
= rcu_nocb_gp_stride
;
2325 int nl
= 0; /* Next GP kthread. */
2326 struct rcu_data
*rdp
;
2327 struct rcu_data
*rdp_gp
= NULL
; /* Suppress misguided gcc warn. */
2328 struct rcu_data
*rdp_prev
= NULL
;
2330 if (!cpumask_available(rcu_nocb_mask
))
2333 ls
= nr_cpu_ids
/ int_sqrt(nr_cpu_ids
);
2334 rcu_nocb_gp_stride
= ls
;
2338 * Each pass through this loop sets up one rcu_data structure.
2339 * Should the corresponding CPU come online in the future, then
2340 * we will spawn the needed set of rcu_nocb_kthread() kthreads.
2342 for_each_cpu(cpu
, rcu_nocb_mask
) {
2343 rdp
= per_cpu_ptr(&rcu_data
, cpu
);
2344 if (rdp
->cpu
>= nl
) {
2345 /* New GP kthread, set up for CBs & next GP. */
2346 nl
= DIV_ROUND_UP(rdp
->cpu
+ 1, ls
) * ls
;
2347 rdp
->nocb_gp_rdp
= rdp
;
2349 if (!firsttime
&& dump_tree
)
2352 pr_alert("%s: No-CB GP kthread CPU %d:", __func__
, cpu
);
2354 /* Another CB kthread, link to previous GP kthread. */
2355 rdp
->nocb_gp_rdp
= rdp_gp
;
2356 rdp_prev
->nocb_next_cb_rdp
= rdp
;
2357 pr_alert(" %d", cpu
);
2364 * Bind the current task to the offloaded CPUs. If there are no offloaded
2365 * CPUs, leave the task unbound. Splat if the bind attempt fails.
2367 void rcu_bind_current_to_nocb(void)
2369 if (cpumask_available(rcu_nocb_mask
) && cpumask_weight(rcu_nocb_mask
))
2370 WARN_ON(sched_setaffinity(current
->pid
, rcu_nocb_mask
));
2372 EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb
);
2375 * Dump out nocb grace-period kthread state for the specified rcu_data
2378 static void show_rcu_nocb_gp_state(struct rcu_data
*rdp
)
2380 struct rcu_node
*rnp
= rdp
->mynode
;
2382 pr_info("nocb GP %d %c%c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu\n",
2384 "kK"[!!rdp
->nocb_gp_kthread
],
2385 "lL"[raw_spin_is_locked(&rdp
->nocb_gp_lock
)],
2386 "dD"[!!rdp
->nocb_defer_wakeup
],
2387 "tT"[timer_pending(&rdp
->nocb_timer
)],
2388 "bB"[timer_pending(&rdp
->nocb_bypass_timer
)],
2389 "sS"[!!rdp
->nocb_gp_sleep
],
2390 ".W"[swait_active(&rdp
->nocb_gp_wq
)],
2391 ".W"[swait_active(&rnp
->nocb_gp_wq
[0])],
2392 ".W"[swait_active(&rnp
->nocb_gp_wq
[1])],
2393 ".B"[!!rdp
->nocb_gp_bypass
],
2394 ".G"[!!rdp
->nocb_gp_gp
],
2395 (long)rdp
->nocb_gp_seq
,
2396 rnp
->grplo
, rnp
->grphi
, READ_ONCE(rdp
->nocb_gp_loops
));
2399 /* Dump out nocb kthread state for the specified rcu_data structure. */
2400 static void show_rcu_nocb_state(struct rcu_data
*rdp
)
2402 struct rcu_segcblist
*rsclp
= &rdp
->cblist
;
2407 if (rdp
->nocb_gp_rdp
== rdp
)
2408 show_rcu_nocb_gp_state(rdp
);
2410 pr_info(" CB %d->%d %c%c%c%c%c%c F%ld L%ld C%d %c%c%c%c%c q%ld\n",
2411 rdp
->cpu
, rdp
->nocb_gp_rdp
->cpu
,
2412 "kK"[!!rdp
->nocb_cb_kthread
],
2413 "bB"[raw_spin_is_locked(&rdp
->nocb_bypass_lock
)],
2414 "cC"[!!atomic_read(&rdp
->nocb_lock_contended
)],
2415 "lL"[raw_spin_is_locked(&rdp
->nocb_lock
)],
2416 "sS"[!!rdp
->nocb_cb_sleep
],
2417 ".W"[swait_active(&rdp
->nocb_cb_wq
)],
2418 jiffies
- rdp
->nocb_bypass_first
,
2419 jiffies
- rdp
->nocb_nobypass_last
,
2420 rdp
->nocb_nobypass_count
,
2421 ".D"[rcu_segcblist_ready_cbs(rsclp
)],
2422 ".W"[!rcu_segcblist_restempty(rsclp
, RCU_DONE_TAIL
)],
2423 ".R"[!rcu_segcblist_restempty(rsclp
, RCU_WAIT_TAIL
)],
2424 ".N"[!rcu_segcblist_restempty(rsclp
, RCU_NEXT_READY_TAIL
)],
2425 ".B"[!!rcu_cblist_n_cbs(&rdp
->nocb_bypass
)],
2426 rcu_segcblist_n_cbs(&rdp
->cblist
));
2428 /* It is OK for GP kthreads to have GP state. */
2429 if (rdp
->nocb_gp_rdp
== rdp
)
2432 waslocked
= raw_spin_is_locked(&rdp
->nocb_gp_lock
);
2433 wastimer
= timer_pending(&rdp
->nocb_timer
);
2434 wassleep
= swait_active(&rdp
->nocb_gp_wq
);
2435 if (!rdp
->nocb_defer_wakeup
&& !rdp
->nocb_gp_sleep
&&
2436 !waslocked
&& !wastimer
&& !wassleep
)
2437 return; /* Nothing untowards. */
2439 pr_info(" !!! %c%c%c%c %c\n",
2441 "dD"[!!rdp
->nocb_defer_wakeup
],
2443 "sS"[!!rdp
->nocb_gp_sleep
],
2447 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
2449 /* No ->nocb_lock to acquire. */
2450 static void rcu_nocb_lock(struct rcu_data
*rdp
)
2454 /* No ->nocb_lock to release. */
2455 static void rcu_nocb_unlock(struct rcu_data
*rdp
)
2459 /* No ->nocb_lock to release. */
2460 static void rcu_nocb_unlock_irqrestore(struct rcu_data
*rdp
,
2461 unsigned long flags
)
2463 local_irq_restore(flags
);
2466 /* Lockdep check that ->cblist may be safely accessed. */
2467 static void rcu_lockdep_assert_cblist_protected(struct rcu_data
*rdp
)
2469 lockdep_assert_irqs_disabled();
2472 static void rcu_nocb_gp_cleanup(struct swait_queue_head
*sq
)
2476 static struct swait_queue_head
*rcu_nocb_gp_get(struct rcu_node
*rnp
)
2481 static void rcu_init_one_nocb(struct rcu_node
*rnp
)
2485 static bool rcu_nocb_flush_bypass(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
2491 static bool rcu_nocb_try_bypass(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
2492 bool *was_alldone
, unsigned long flags
)
2497 static void __call_rcu_nocb_wake(struct rcu_data
*rdp
, bool was_empty
,
2498 unsigned long flags
)
2500 WARN_ON_ONCE(1); /* Should be dead code! */
2503 static void __init
rcu_boot_init_nocb_percpu_data(struct rcu_data
*rdp
)
2507 static int rcu_nocb_need_deferred_wakeup(struct rcu_data
*rdp
)
2512 static void do_nocb_deferred_wakeup(struct rcu_data
*rdp
)
2516 static void rcu_spawn_cpu_nocb_kthread(int cpu
)
2520 static void __init
rcu_spawn_nocb_kthreads(void)
2524 static void show_rcu_nocb_state(struct rcu_data
*rdp
)
2528 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2531 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
2532 * grace-period kthread will do force_quiescent_state() processing?
2533 * The idea is to avoid waking up RCU core processing on such a
2534 * CPU unless the grace period has extended for too long.
2536 * This code relies on the fact that all NO_HZ_FULL CPUs are also
2537 * CONFIG_RCU_NOCB_CPU CPUs.
2539 static bool rcu_nohz_full_cpu(void)
2541 #ifdef CONFIG_NO_HZ_FULL
2542 if (tick_nohz_full_cpu(smp_processor_id()) &&
2543 (!rcu_gp_in_progress() ||
2544 ULONG_CMP_LT(jiffies
, READ_ONCE(rcu_state
.gp_start
) + HZ
)))
2546 #endif /* #ifdef CONFIG_NO_HZ_FULL */
2551 * Bind the RCU grace-period kthreads to the housekeeping CPU.
2553 static void rcu_bind_gp_kthread(void)
2555 if (!tick_nohz_full_enabled())
2557 housekeeping_affine(current
, HK_FLAG_RCU
);
2560 /* Record the current task on dyntick-idle entry. */
2561 static void rcu_dynticks_task_enter(void)
2563 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2564 WRITE_ONCE(current
->rcu_tasks_idle_cpu
, smp_processor_id());
2565 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
2568 /* Record no current task on dyntick-idle exit. */
2569 static void rcu_dynticks_task_exit(void)
2571 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2572 WRITE_ONCE(current
->rcu_tasks_idle_cpu
, -1);
2573 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */