2 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
3 * Internal non-public definitions that provide either classic
4 * or preemptible semantics.
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, you can access it online at
18 * http://www.gnu.org/licenses/gpl-2.0.html.
20 * Copyright Red Hat, 2009
21 * Copyright IBM Corporation, 2009
23 * Author: Ingo Molnar <mingo@elte.hu>
24 * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
27 #include <linux/delay.h>
28 #include <linux/gfp.h>
29 #include <linux/oom.h>
30 #include <linux/sched/debug.h>
31 #include <linux/smpboot.h>
32 #include <linux/sched/isolation.h>
33 #include <uapi/linux/sched/types.h>
34 #include "../time/tick-internal.h"
36 #ifdef CONFIG_RCU_BOOST
38 #include "../locking/rtmutex_common.h"
41 * Control variables for per-CPU and per-rcu_node kthreads. These
42 * handle all flavors of RCU.
44 static DEFINE_PER_CPU(struct task_struct
*, rcu_cpu_kthread_task
);
45 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status
);
46 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops
);
47 DEFINE_PER_CPU(char, rcu_cpu_has_work
);
49 #else /* #ifdef CONFIG_RCU_BOOST */
52 * Some architectures do not define rt_mutexes, but if !CONFIG_RCU_BOOST,
53 * all uses are in dead code. Provide a definition to keep the compiler
54 * happy, but add WARN_ON_ONCE() to complain if used in the wrong place.
55 * This probably needs to be excluded from -rt builds.
57 #define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; })
58 #define rt_mutex_futex_unlock(x) WARN_ON_ONCE(1)
60 #endif /* #else #ifdef CONFIG_RCU_BOOST */
62 #ifdef CONFIG_RCU_NOCB_CPU
63 static cpumask_var_t rcu_nocb_mask
; /* CPUs to have callbacks offloaded. */
64 static bool have_rcu_nocb_mask
; /* Was rcu_nocb_mask allocated? */
65 static bool __read_mostly rcu_nocb_poll
; /* Offload kthread are to poll. */
66 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
69 * Check the RCU kernel configuration parameters and print informative
70 * messages about anything out of the ordinary.
72 static void __init
rcu_bootup_announce_oddness(void)
74 if (IS_ENABLED(CONFIG_RCU_TRACE
))
75 pr_info("\tRCU event tracing is enabled.\n");
76 if ((IS_ENABLED(CONFIG_64BIT
) && RCU_FANOUT
!= 64) ||
77 (!IS_ENABLED(CONFIG_64BIT
) && RCU_FANOUT
!= 32))
78 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
81 pr_info("\tHierarchical RCU autobalancing is disabled.\n");
82 if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ
))
83 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
84 if (IS_ENABLED(CONFIG_PROVE_RCU
))
85 pr_info("\tRCU lockdep checking is enabled.\n");
86 if (RCU_NUM_LVLS
>= 4)
87 pr_info("\tFour(or more)-level hierarchy is enabled.\n");
88 if (RCU_FANOUT_LEAF
!= 16)
89 pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
91 if (rcu_fanout_leaf
!= RCU_FANOUT_LEAF
)
92 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf
);
93 if (nr_cpu_ids
!= NR_CPUS
)
94 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%u.\n", NR_CPUS
, nr_cpu_ids
);
95 #ifdef CONFIG_RCU_BOOST
96 pr_info("\tRCU priority boosting: priority %d delay %d ms.\n", kthread_prio
, CONFIG_RCU_BOOST_DELAY
);
98 if (blimit
!= DEFAULT_RCU_BLIMIT
)
99 pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit
);
100 if (qhimark
!= DEFAULT_RCU_QHIMARK
)
101 pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark
);
102 if (qlowmark
!= DEFAULT_RCU_QLOMARK
)
103 pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark
);
104 if (jiffies_till_first_fqs
!= ULONG_MAX
)
105 pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs
);
106 if (jiffies_till_next_fqs
!= ULONG_MAX
)
107 pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs
);
108 if (rcu_kick_kthreads
)
109 pr_info("\tKick kthreads if too-long grace period.\n");
110 if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD
))
111 pr_info("\tRCU callback double-/use-after-free debug enabled.\n");
112 if (gp_preinit_delay
)
113 pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay
);
115 pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay
);
116 if (gp_cleanup_delay
)
117 pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay
);
118 if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG
))
119 pr_info("\tRCU debug extended QS entry/exit.\n");
120 rcupdate_announce_bootup_oddness();
123 #ifdef CONFIG_PREEMPT_RCU
125 RCU_STATE_INITIALIZER(rcu_preempt
, 'p', call_rcu
);
126 static struct rcu_state
*const rcu_state_p
= &rcu_preempt_state
;
127 static struct rcu_data __percpu
*const rcu_data_p
= &rcu_preempt_data
;
129 static void rcu_report_exp_rnp(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
133 * Tell them what RCU they are running.
135 static void __init
rcu_bootup_announce(void)
137 pr_info("Preemptible hierarchical RCU implementation.\n");
138 rcu_bootup_announce_oddness();
141 /* Flags for rcu_preempt_ctxt_queue() decision table. */
142 #define RCU_GP_TASKS 0x8
143 #define RCU_EXP_TASKS 0x4
144 #define RCU_GP_BLKD 0x2
145 #define RCU_EXP_BLKD 0x1
148 * Queues a task preempted within an RCU-preempt read-side critical
149 * section into the appropriate location within the ->blkd_tasks list,
150 * depending on the states of any ongoing normal and expedited grace
151 * periods. The ->gp_tasks pointer indicates which element the normal
152 * grace period is waiting on (NULL if none), and the ->exp_tasks pointer
153 * indicates which element the expedited grace period is waiting on (again,
154 * NULL if none). If a grace period is waiting on a given element in the
155 * ->blkd_tasks list, it also waits on all subsequent elements. Thus,
156 * adding a task to the tail of the list blocks any grace period that is
157 * already waiting on one of the elements. In contrast, adding a task
158 * to the head of the list won't block any grace period that is already
159 * waiting on one of the elements.
161 * This queuing is imprecise, and can sometimes make an ongoing grace
162 * period wait for a task that is not strictly speaking blocking it.
163 * Given the choice, we needlessly block a normal grace period rather than
164 * blocking an expedited grace period.
166 * Note that an endless sequence of expedited grace periods still cannot
167 * indefinitely postpone a normal grace period. Eventually, all of the
168 * fixed number of preempted tasks blocking the normal grace period that are
169 * not also blocking the expedited grace period will resume and complete
170 * their RCU read-side critical sections. At that point, the ->gp_tasks
171 * pointer will equal the ->exp_tasks pointer, at which point the end of
172 * the corresponding expedited grace period will also be the end of the
173 * normal grace period.
175 static void rcu_preempt_ctxt_queue(struct rcu_node
*rnp
, struct rcu_data
*rdp
)
176 __releases(rnp
->lock
) /* But leaves rrupts disabled. */
178 int blkd_state
= (rnp
->gp_tasks
? RCU_GP_TASKS
: 0) +
179 (rnp
->exp_tasks
? RCU_EXP_TASKS
: 0) +
180 (rnp
->qsmask
& rdp
->grpmask
? RCU_GP_BLKD
: 0) +
181 (rnp
->expmask
& rdp
->grpmask
? RCU_EXP_BLKD
: 0);
182 struct task_struct
*t
= current
;
184 lockdep_assert_held(&rnp
->lock
);
185 WARN_ON_ONCE(rdp
->mynode
!= rnp
);
186 WARN_ON_ONCE(rnp
->level
!= rcu_num_lvls
- 1);
189 * Decide where to queue the newly blocked task. In theory,
190 * this could be an if-statement. In practice, when I tried
191 * that, it was quite messy.
193 switch (blkd_state
) {
196 case RCU_EXP_TASKS
+ RCU_GP_BLKD
:
198 case RCU_GP_TASKS
+ RCU_EXP_TASKS
:
201 * Blocking neither GP, or first task blocking the normal
202 * GP but not blocking the already-waiting expedited GP.
203 * Queue at the head of the list to avoid unnecessarily
204 * blocking the already-waiting GPs.
206 list_add(&t
->rcu_node_entry
, &rnp
->blkd_tasks
);
211 case RCU_GP_BLKD
+ RCU_EXP_BLKD
:
212 case RCU_GP_TASKS
+ RCU_EXP_BLKD
:
213 case RCU_GP_TASKS
+ RCU_GP_BLKD
+ RCU_EXP_BLKD
:
214 case RCU_GP_TASKS
+ RCU_EXP_TASKS
+ RCU_GP_BLKD
+ RCU_EXP_BLKD
:
217 * First task arriving that blocks either GP, or first task
218 * arriving that blocks the expedited GP (with the normal
219 * GP already waiting), or a task arriving that blocks
220 * both GPs with both GPs already waiting. Queue at the
221 * tail of the list to avoid any GP waiting on any of the
222 * already queued tasks that are not blocking it.
224 list_add_tail(&t
->rcu_node_entry
, &rnp
->blkd_tasks
);
227 case RCU_EXP_TASKS
+ RCU_EXP_BLKD
:
228 case RCU_EXP_TASKS
+ RCU_GP_BLKD
+ RCU_EXP_BLKD
:
229 case RCU_GP_TASKS
+ RCU_EXP_TASKS
+ RCU_EXP_BLKD
:
232 * Second or subsequent task blocking the expedited GP.
233 * The task either does not block the normal GP, or is the
234 * first task blocking the normal GP. Queue just after
235 * the first task blocking the expedited GP.
237 list_add(&t
->rcu_node_entry
, rnp
->exp_tasks
);
240 case RCU_GP_TASKS
+ RCU_GP_BLKD
:
241 case RCU_GP_TASKS
+ RCU_EXP_TASKS
+ RCU_GP_BLKD
:
244 * Second or subsequent task blocking the normal GP.
245 * The task does not block the expedited GP. Queue just
246 * after the first task blocking the normal GP.
248 list_add(&t
->rcu_node_entry
, rnp
->gp_tasks
);
253 /* Yet another exercise in excessive paranoia. */
259 * We have now queued the task. If it was the first one to
260 * block either grace period, update the ->gp_tasks and/or
261 * ->exp_tasks pointers, respectively, to reference the newly
264 if (!rnp
->gp_tasks
&& (blkd_state
& RCU_GP_BLKD
))
265 rnp
->gp_tasks
= &t
->rcu_node_entry
;
266 if (!rnp
->exp_tasks
&& (blkd_state
& RCU_EXP_BLKD
))
267 rnp
->exp_tasks
= &t
->rcu_node_entry
;
268 WARN_ON_ONCE(!(blkd_state
& RCU_GP_BLKD
) !=
269 !(rnp
->qsmask
& rdp
->grpmask
));
270 WARN_ON_ONCE(!(blkd_state
& RCU_EXP_BLKD
) !=
271 !(rnp
->expmask
& rdp
->grpmask
));
272 raw_spin_unlock_rcu_node(rnp
); /* interrupts remain disabled. */
275 * Report the quiescent state for the expedited GP. This expedited
276 * GP should not be able to end until we report, so there should be
277 * no need to check for a subsequent expedited GP. (Though we are
278 * still in a quiescent state in any case.)
280 if (blkd_state
& RCU_EXP_BLKD
&&
281 t
->rcu_read_unlock_special
.b
.exp_need_qs
) {
282 t
->rcu_read_unlock_special
.b
.exp_need_qs
= false;
283 rcu_report_exp_rdp(rdp
->rsp
, rdp
, true);
285 WARN_ON_ONCE(t
->rcu_read_unlock_special
.b
.exp_need_qs
);
290 * Record a preemptible-RCU quiescent state for the specified CPU. Note
291 * that this just means that the task currently running on the CPU is
292 * not in a quiescent state. There might be any number of tasks blocked
293 * while in an RCU read-side critical section.
295 * As with the other rcu_*_qs() functions, callers to this function
296 * must disable preemption.
298 static void rcu_preempt_qs(void)
300 RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_qs() invoked with preemption enabled!!!\n");
301 if (__this_cpu_read(rcu_data_p
->cpu_no_qs
.s
)) {
302 trace_rcu_grace_period(TPS("rcu_preempt"),
303 __this_cpu_read(rcu_data_p
->gpnum
),
305 __this_cpu_write(rcu_data_p
->cpu_no_qs
.b
.norm
, false);
306 barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
307 current
->rcu_read_unlock_special
.b
.need_qs
= false;
312 * We have entered the scheduler, and the current task might soon be
313 * context-switched away from. If this task is in an RCU read-side
314 * critical section, we will no longer be able to rely on the CPU to
315 * record that fact, so we enqueue the task on the blkd_tasks list.
316 * The task will dequeue itself when it exits the outermost enclosing
317 * RCU read-side critical section. Therefore, the current grace period
318 * cannot be permitted to complete until the blkd_tasks list entries
319 * predating the current grace period drain, in other words, until
320 * rnp->gp_tasks becomes NULL.
322 * Caller must disable interrupts.
324 static void rcu_preempt_note_context_switch(bool preempt
)
326 struct task_struct
*t
= current
;
327 struct rcu_data
*rdp
;
328 struct rcu_node
*rnp
;
330 lockdep_assert_irqs_disabled();
331 WARN_ON_ONCE(!preempt
&& t
->rcu_read_lock_nesting
> 0);
332 if (t
->rcu_read_lock_nesting
> 0 &&
333 !t
->rcu_read_unlock_special
.b
.blocked
) {
335 /* Possibly blocking in an RCU read-side critical section. */
336 rdp
= this_cpu_ptr(rcu_state_p
->rda
);
338 raw_spin_lock_rcu_node(rnp
);
339 t
->rcu_read_unlock_special
.b
.blocked
= true;
340 t
->rcu_blocked_node
= rnp
;
343 * Verify the CPU's sanity, trace the preemption, and
344 * then queue the task as required based on the states
345 * of any ongoing and expedited grace periods.
347 WARN_ON_ONCE((rdp
->grpmask
& rcu_rnp_online_cpus(rnp
)) == 0);
348 WARN_ON_ONCE(!list_empty(&t
->rcu_node_entry
));
349 trace_rcu_preempt_task(rdp
->rsp
->name
,
351 (rnp
->qsmask
& rdp
->grpmask
)
354 rcu_preempt_ctxt_queue(rnp
, rdp
);
355 } else if (t
->rcu_read_lock_nesting
< 0 &&
356 t
->rcu_read_unlock_special
.s
) {
359 * Complete exit from RCU read-side critical section on
360 * behalf of preempted instance of __rcu_read_unlock().
362 rcu_read_unlock_special(t
);
366 * Either we were not in an RCU read-side critical section to
367 * begin with, or we have now recorded that critical section
368 * globally. Either way, we can now note a quiescent state
369 * for this CPU. Again, if we were in an RCU read-side critical
370 * section, and if that critical section was blocking the current
371 * grace period, then the fact that the task has been enqueued
372 * means that we continue to block the current grace period.
378 * Check for preempted RCU readers blocking the current grace period
379 * for the specified rcu_node structure. If the caller needs a reliable
380 * answer, it must hold the rcu_node's ->lock.
382 static int rcu_preempt_blocked_readers_cgp(struct rcu_node
*rnp
)
384 return rnp
->gp_tasks
!= NULL
;
388 * Advance a ->blkd_tasks-list pointer to the next entry, instead
389 * returning NULL if at the end of the list.
391 static struct list_head
*rcu_next_node_entry(struct task_struct
*t
,
392 struct rcu_node
*rnp
)
394 struct list_head
*np
;
396 np
= t
->rcu_node_entry
.next
;
397 if (np
== &rnp
->blkd_tasks
)
403 * Return true if the specified rcu_node structure has tasks that were
404 * preempted within an RCU read-side critical section.
406 static bool rcu_preempt_has_tasks(struct rcu_node
*rnp
)
408 return !list_empty(&rnp
->blkd_tasks
);
412 * Handle special cases during rcu_read_unlock(), such as needing to
413 * notify RCU core processing or task having blocked during the RCU
414 * read-side critical section.
416 void rcu_read_unlock_special(struct task_struct
*t
)
422 struct list_head
*np
;
423 bool drop_boost_mutex
= false;
424 struct rcu_data
*rdp
;
425 struct rcu_node
*rnp
;
426 union rcu_special special
;
428 /* NMI handlers cannot block and cannot safely manipulate state. */
432 local_irq_save(flags
);
435 * If RCU core is waiting for this CPU to exit its critical section,
436 * report the fact that it has exited. Because irqs are disabled,
437 * t->rcu_read_unlock_special cannot change.
439 special
= t
->rcu_read_unlock_special
;
440 if (special
.b
.need_qs
) {
442 t
->rcu_read_unlock_special
.b
.need_qs
= false;
443 if (!t
->rcu_read_unlock_special
.s
) {
444 local_irq_restore(flags
);
450 * Respond to a request for an expedited grace period, but only if
451 * we were not preempted, meaning that we were running on the same
452 * CPU throughout. If we were preempted, the exp_need_qs flag
453 * would have been cleared at the time of the first preemption,
454 * and the quiescent state would be reported when we were dequeued.
456 if (special
.b
.exp_need_qs
) {
457 WARN_ON_ONCE(special
.b
.blocked
);
458 t
->rcu_read_unlock_special
.b
.exp_need_qs
= false;
459 rdp
= this_cpu_ptr(rcu_state_p
->rda
);
460 rcu_report_exp_rdp(rcu_state_p
, rdp
, true);
461 if (!t
->rcu_read_unlock_special
.s
) {
462 local_irq_restore(flags
);
467 /* Hardware IRQ handlers cannot block, complain if they get here. */
468 if (in_irq() || in_serving_softirq()) {
469 lockdep_rcu_suspicious(__FILE__
, __LINE__
,
470 "rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n");
471 pr_alert("->rcu_read_unlock_special: %#x (b: %d, enq: %d nq: %d)\n",
472 t
->rcu_read_unlock_special
.s
,
473 t
->rcu_read_unlock_special
.b
.blocked
,
474 t
->rcu_read_unlock_special
.b
.exp_need_qs
,
475 t
->rcu_read_unlock_special
.b
.need_qs
);
476 local_irq_restore(flags
);
480 /* Clean up if blocked during RCU read-side critical section. */
481 if (special
.b
.blocked
) {
482 t
->rcu_read_unlock_special
.b
.blocked
= false;
485 * Remove this task from the list it blocked on. The task
486 * now remains queued on the rcu_node corresponding to the
487 * CPU it first blocked on, so there is no longer any need
488 * to loop. Retain a WARN_ON_ONCE() out of sheer paranoia.
490 rnp
= t
->rcu_blocked_node
;
491 raw_spin_lock_rcu_node(rnp
); /* irqs already disabled. */
492 WARN_ON_ONCE(rnp
!= t
->rcu_blocked_node
);
493 WARN_ON_ONCE(rnp
->level
!= rcu_num_lvls
- 1);
494 empty_norm
= !rcu_preempt_blocked_readers_cgp(rnp
);
495 empty_exp
= sync_rcu_preempt_exp_done(rnp
);
496 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
497 np
= rcu_next_node_entry(t
, rnp
);
498 list_del_init(&t
->rcu_node_entry
);
499 t
->rcu_blocked_node
= NULL
;
500 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
502 if (&t
->rcu_node_entry
== rnp
->gp_tasks
)
504 if (&t
->rcu_node_entry
== rnp
->exp_tasks
)
506 if (IS_ENABLED(CONFIG_RCU_BOOST
)) {
507 /* Snapshot ->boost_mtx ownership w/rnp->lock held. */
508 drop_boost_mutex
= rt_mutex_owner(&rnp
->boost_mtx
) == t
;
509 if (&t
->rcu_node_entry
== rnp
->boost_tasks
)
510 rnp
->boost_tasks
= np
;
514 * If this was the last task on the current list, and if
515 * we aren't waiting on any CPUs, report the quiescent state.
516 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
517 * so we must take a snapshot of the expedited state.
519 empty_exp_now
= sync_rcu_preempt_exp_done(rnp
);
520 if (!empty_norm
&& !rcu_preempt_blocked_readers_cgp(rnp
)) {
521 trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
528 rcu_report_unblock_qs_rnp(rcu_state_p
, rnp
, flags
);
530 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
533 /* Unboost if we were boosted. */
534 if (IS_ENABLED(CONFIG_RCU_BOOST
) && drop_boost_mutex
)
535 rt_mutex_futex_unlock(&rnp
->boost_mtx
);
538 * If this was the last task on the expedited lists,
539 * then we need to report up the rcu_node hierarchy.
541 if (!empty_exp
&& empty_exp_now
)
542 rcu_report_exp_rnp(rcu_state_p
, rnp
, true);
544 local_irq_restore(flags
);
549 * Dump detailed information for all tasks blocking the current RCU
550 * grace period on the specified rcu_node structure.
552 static void rcu_print_detail_task_stall_rnp(struct rcu_node
*rnp
)
555 struct task_struct
*t
;
557 raw_spin_lock_irqsave_rcu_node(rnp
, flags
);
558 if (!rcu_preempt_blocked_readers_cgp(rnp
)) {
559 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
562 t
= list_entry(rnp
->gp_tasks
->prev
,
563 struct task_struct
, rcu_node_entry
);
564 list_for_each_entry_continue(t
, &rnp
->blkd_tasks
, rcu_node_entry
)
566 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
570 * Dump detailed information for all tasks blocking the current RCU
573 static void rcu_print_detail_task_stall(struct rcu_state
*rsp
)
575 struct rcu_node
*rnp
= rcu_get_root(rsp
);
577 rcu_print_detail_task_stall_rnp(rnp
);
578 rcu_for_each_leaf_node(rsp
, rnp
)
579 rcu_print_detail_task_stall_rnp(rnp
);
582 static void rcu_print_task_stall_begin(struct rcu_node
*rnp
)
584 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
585 rnp
->level
, rnp
->grplo
, rnp
->grphi
);
588 static void rcu_print_task_stall_end(void)
594 * Scan the current list of tasks blocked within RCU read-side critical
595 * sections, printing out the tid of each.
597 static int rcu_print_task_stall(struct rcu_node
*rnp
)
599 struct task_struct
*t
;
602 if (!rcu_preempt_blocked_readers_cgp(rnp
))
604 rcu_print_task_stall_begin(rnp
);
605 t
= list_entry(rnp
->gp_tasks
->prev
,
606 struct task_struct
, rcu_node_entry
);
607 list_for_each_entry_continue(t
, &rnp
->blkd_tasks
, rcu_node_entry
) {
608 pr_cont(" P%d", t
->pid
);
611 rcu_print_task_stall_end();
616 * Scan the current list of tasks blocked within RCU read-side critical
617 * sections, printing out the tid of each that is blocking the current
618 * expedited grace period.
620 static int rcu_print_task_exp_stall(struct rcu_node
*rnp
)
622 struct task_struct
*t
;
627 t
= list_entry(rnp
->exp_tasks
->prev
,
628 struct task_struct
, rcu_node_entry
);
629 list_for_each_entry_continue(t
, &rnp
->blkd_tasks
, rcu_node_entry
) {
630 pr_cont(" P%d", t
->pid
);
637 * Check that the list of blocked tasks for the newly completed grace
638 * period is in fact empty. It is a serious bug to complete a grace
639 * period that still has RCU readers blocked! This function must be
640 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
641 * must be held by the caller.
643 * Also, if there are blocked tasks on the list, they automatically
644 * block the newly created grace period, so set up ->gp_tasks accordingly.
646 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
648 struct task_struct
*t
;
650 RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
651 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp
));
652 if (rcu_preempt_has_tasks(rnp
)) {
653 rnp
->gp_tasks
= rnp
->blkd_tasks
.next
;
654 t
= container_of(rnp
->gp_tasks
, struct task_struct
,
656 trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
659 WARN_ON_ONCE(rnp
->qsmask
);
663 * Check for a quiescent state from the current CPU. When a task blocks,
664 * the task is recorded in the corresponding CPU's rcu_node structure,
665 * which is checked elsewhere.
667 * Caller must disable hard irqs.
669 static void rcu_preempt_check_callbacks(void)
671 struct task_struct
*t
= current
;
673 if (t
->rcu_read_lock_nesting
== 0) {
677 if (t
->rcu_read_lock_nesting
> 0 &&
678 __this_cpu_read(rcu_data_p
->core_needs_qs
) &&
679 __this_cpu_read(rcu_data_p
->cpu_no_qs
.b
.norm
))
680 t
->rcu_read_unlock_special
.b
.need_qs
= true;
683 #ifdef CONFIG_RCU_BOOST
685 static void rcu_preempt_do_callbacks(void)
687 rcu_do_batch(rcu_state_p
, this_cpu_ptr(rcu_data_p
));
690 #endif /* #ifdef CONFIG_RCU_BOOST */
693 * call_rcu() - Queue an RCU callback for invocation after a grace period.
694 * @head: structure to be used for queueing the RCU updates.
695 * @func: actual callback function to be invoked after the grace period
697 * The callback function will be invoked some time after a full grace
698 * period elapses, in other words after all pre-existing RCU read-side
699 * critical sections have completed. However, the callback function
700 * might well execute concurrently with RCU read-side critical sections
701 * that started after call_rcu() was invoked. RCU read-side critical
702 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
705 * Note that all CPUs must agree that the grace period extended beyond
706 * all pre-existing RCU read-side critical section. On systems with more
707 * than one CPU, this means that when "func()" is invoked, each CPU is
708 * guaranteed to have executed a full memory barrier since the end of its
709 * last RCU read-side critical section whose beginning preceded the call
710 * to call_rcu(). It also means that each CPU executing an RCU read-side
711 * critical section that continues beyond the start of "func()" must have
712 * executed a memory barrier after the call_rcu() but before the beginning
713 * of that RCU read-side critical section. Note that these guarantees
714 * include CPUs that are offline, idle, or executing in user mode, as
715 * well as CPUs that are executing in the kernel.
717 * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
718 * resulting RCU callback function "func()", then both CPU A and CPU B are
719 * guaranteed to execute a full memory barrier during the time interval
720 * between the call to call_rcu() and the invocation of "func()" -- even
721 * if CPU A and CPU B are the same CPU (but again only if the system has
722 * more than one CPU).
724 void call_rcu(struct rcu_head
*head
, rcu_callback_t func
)
726 __call_rcu(head
, func
, rcu_state_p
, -1, 0);
728 EXPORT_SYMBOL_GPL(call_rcu
);
731 * synchronize_rcu - wait until a grace period has elapsed.
733 * Control will return to the caller some time after a full grace
734 * period has elapsed, in other words after all currently executing RCU
735 * read-side critical sections have completed. Note, however, that
736 * upon return from synchronize_rcu(), the caller might well be executing
737 * concurrently with new RCU read-side critical sections that began while
738 * synchronize_rcu() was waiting. RCU read-side critical sections are
739 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
741 * See the description of synchronize_sched() for more detailed
742 * information on memory-ordering guarantees. However, please note
743 * that -only- the memory-ordering guarantees apply. For example,
744 * synchronize_rcu() is -not- guaranteed to wait on things like code
745 * protected by preempt_disable(), instead, synchronize_rcu() is -only-
746 * guaranteed to wait on RCU read-side critical sections, that is, sections
747 * of code protected by rcu_read_lock().
749 void synchronize_rcu(void)
751 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map
) ||
752 lock_is_held(&rcu_lock_map
) ||
753 lock_is_held(&rcu_sched_lock_map
),
754 "Illegal synchronize_rcu() in RCU read-side critical section");
755 if (rcu_scheduler_active
== RCU_SCHEDULER_INACTIVE
)
757 if (rcu_gp_is_expedited())
758 synchronize_rcu_expedited();
760 wait_rcu_gp(call_rcu
);
762 EXPORT_SYMBOL_GPL(synchronize_rcu
);
765 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
767 * Note that this primitive does not necessarily wait for an RCU grace period
768 * to complete. For example, if there are no RCU callbacks queued anywhere
769 * in the system, then rcu_barrier() is within its rights to return
770 * immediately, without waiting for anything, much less an RCU grace period.
772 void rcu_barrier(void)
774 _rcu_barrier(rcu_state_p
);
776 EXPORT_SYMBOL_GPL(rcu_barrier
);
779 * Initialize preemptible RCU's state structures.
781 static void __init
__rcu_init_preempt(void)
783 rcu_init_one(rcu_state_p
);
787 * Check for a task exiting while in a preemptible-RCU read-side
788 * critical section, clean up if so. No need to issue warnings,
789 * as debug_check_no_locks_held() already does this if lockdep
794 struct task_struct
*t
= current
;
796 if (likely(list_empty(¤t
->rcu_node_entry
)))
798 t
->rcu_read_lock_nesting
= 1;
800 t
->rcu_read_unlock_special
.b
.blocked
= true;
804 #else /* #ifdef CONFIG_PREEMPT_RCU */
806 static struct rcu_state
*const rcu_state_p
= &rcu_sched_state
;
809 * Tell them what RCU they are running.
811 static void __init
rcu_bootup_announce(void)
813 pr_info("Hierarchical RCU implementation.\n");
814 rcu_bootup_announce_oddness();
818 * Because preemptible RCU does not exist, we never have to check for
819 * CPUs being in quiescent states.
821 static void rcu_preempt_note_context_switch(bool preempt
)
826 * Because preemptible RCU does not exist, there are never any preempted
829 static int rcu_preempt_blocked_readers_cgp(struct rcu_node
*rnp
)
835 * Because there is no preemptible RCU, there can be no readers blocked.
837 static bool rcu_preempt_has_tasks(struct rcu_node
*rnp
)
843 * Because preemptible RCU does not exist, we never have to check for
844 * tasks blocked within RCU read-side critical sections.
846 static void rcu_print_detail_task_stall(struct rcu_state
*rsp
)
851 * Because preemptible RCU does not exist, we never have to check for
852 * tasks blocked within RCU read-side critical sections.
854 static int rcu_print_task_stall(struct rcu_node
*rnp
)
860 * Because preemptible RCU does not exist, we never have to check for
861 * tasks blocked within RCU read-side critical sections that are
862 * blocking the current expedited grace period.
864 static int rcu_print_task_exp_stall(struct rcu_node
*rnp
)
870 * Because there is no preemptible RCU, there can be no readers blocked,
871 * so there is no need to check for blocked tasks. So check only for
872 * bogus qsmask values.
874 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
876 WARN_ON_ONCE(rnp
->qsmask
);
880 * Because preemptible RCU does not exist, it never has any callbacks
883 static void rcu_preempt_check_callbacks(void)
888 * Because preemptible RCU does not exist, rcu_barrier() is just
889 * another name for rcu_barrier_sched().
891 void rcu_barrier(void)
895 EXPORT_SYMBOL_GPL(rcu_barrier
);
898 * Because preemptible RCU does not exist, it need not be initialized.
900 static void __init
__rcu_init_preempt(void)
905 * Because preemptible RCU does not exist, tasks cannot possibly exit
906 * while in preemptible RCU read-side critical sections.
912 #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
914 #ifdef CONFIG_RCU_BOOST
916 static void rcu_wake_cond(struct task_struct
*t
, int status
)
919 * If the thread is yielding, only wake it when this
920 * is invoked from idle
922 if (status
!= RCU_KTHREAD_YIELDING
|| is_idle_task(current
))
927 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
928 * or ->boost_tasks, advancing the pointer to the next task in the
931 * Note that irqs must be enabled: boosting the task can block.
932 * Returns 1 if there are more tasks needing to be boosted.
934 static int rcu_boost(struct rcu_node
*rnp
)
937 struct task_struct
*t
;
938 struct list_head
*tb
;
940 if (READ_ONCE(rnp
->exp_tasks
) == NULL
&&
941 READ_ONCE(rnp
->boost_tasks
) == NULL
)
942 return 0; /* Nothing left to boost. */
944 raw_spin_lock_irqsave_rcu_node(rnp
, flags
);
947 * Recheck under the lock: all tasks in need of boosting
948 * might exit their RCU read-side critical sections on their own.
950 if (rnp
->exp_tasks
== NULL
&& rnp
->boost_tasks
== NULL
) {
951 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
956 * Preferentially boost tasks blocking expedited grace periods.
957 * This cannot starve the normal grace periods because a second
958 * expedited grace period must boost all blocked tasks, including
959 * those blocking the pre-existing normal grace period.
961 if (rnp
->exp_tasks
!= NULL
) {
965 tb
= rnp
->boost_tasks
;
966 rnp
->n_normal_boosts
++;
968 rnp
->n_tasks_boosted
++;
971 * We boost task t by manufacturing an rt_mutex that appears to
972 * be held by task t. We leave a pointer to that rt_mutex where
973 * task t can find it, and task t will release the mutex when it
974 * exits its outermost RCU read-side critical section. Then
975 * simply acquiring this artificial rt_mutex will boost task
976 * t's priority. (Thanks to tglx for suggesting this approach!)
978 * Note that task t must acquire rnp->lock to remove itself from
979 * the ->blkd_tasks list, which it will do from exit() if from
980 * nowhere else. We therefore are guaranteed that task t will
981 * stay around at least until we drop rnp->lock. Note that
982 * rnp->lock also resolves races between our priority boosting
983 * and task t's exiting its outermost RCU read-side critical
986 t
= container_of(tb
, struct task_struct
, rcu_node_entry
);
987 rt_mutex_init_proxy_locked(&rnp
->boost_mtx
, t
);
988 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
989 /* Lock only for side effect: boosts task t's priority. */
990 rt_mutex_lock(&rnp
->boost_mtx
);
991 rt_mutex_unlock(&rnp
->boost_mtx
); /* Then keep lockdep happy. */
993 return READ_ONCE(rnp
->exp_tasks
) != NULL
||
994 READ_ONCE(rnp
->boost_tasks
) != NULL
;
998 * Priority-boosting kthread, one per leaf rcu_node.
1000 static int rcu_boost_kthread(void *arg
)
1002 struct rcu_node
*rnp
= (struct rcu_node
*)arg
;
1006 trace_rcu_utilization(TPS("Start boost kthread@init"));
1008 rnp
->boost_kthread_status
= RCU_KTHREAD_WAITING
;
1009 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1010 rcu_wait(rnp
->boost_tasks
|| rnp
->exp_tasks
);
1011 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1012 rnp
->boost_kthread_status
= RCU_KTHREAD_RUNNING
;
1013 more2boost
= rcu_boost(rnp
);
1019 rnp
->boost_kthread_status
= RCU_KTHREAD_YIELDING
;
1020 trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1021 schedule_timeout_interruptible(2);
1022 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1027 trace_rcu_utilization(TPS("End boost kthread@notreached"));
1032 * Check to see if it is time to start boosting RCU readers that are
1033 * blocking the current grace period, and, if so, tell the per-rcu_node
1034 * kthread to start boosting them. If there is an expedited grace
1035 * period in progress, it is always time to boost.
1037 * The caller must hold rnp->lock, which this function releases.
1038 * The ->boost_kthread_task is immortal, so we don't need to worry
1039 * about it going away.
1041 static void rcu_initiate_boost(struct rcu_node
*rnp
, unsigned long flags
)
1042 __releases(rnp
->lock
)
1044 struct task_struct
*t
;
1046 lockdep_assert_held(&rnp
->lock
);
1047 if (!rcu_preempt_blocked_readers_cgp(rnp
) && rnp
->exp_tasks
== NULL
) {
1048 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
1051 if (rnp
->exp_tasks
!= NULL
||
1052 (rnp
->gp_tasks
!= NULL
&&
1053 rnp
->boost_tasks
== NULL
&&
1055 ULONG_CMP_GE(jiffies
, rnp
->boost_time
))) {
1056 if (rnp
->exp_tasks
== NULL
)
1057 rnp
->boost_tasks
= rnp
->gp_tasks
;
1058 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
1059 t
= rnp
->boost_kthread_task
;
1061 rcu_wake_cond(t
, rnp
->boost_kthread_status
);
1063 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
1068 * Wake up the per-CPU kthread to invoke RCU callbacks.
1070 static void invoke_rcu_callbacks_kthread(void)
1072 unsigned long flags
;
1074 local_irq_save(flags
);
1075 __this_cpu_write(rcu_cpu_has_work
, 1);
1076 if (__this_cpu_read(rcu_cpu_kthread_task
) != NULL
&&
1077 current
!= __this_cpu_read(rcu_cpu_kthread_task
)) {
1078 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task
),
1079 __this_cpu_read(rcu_cpu_kthread_status
));
1081 local_irq_restore(flags
);
1085 * Is the current CPU running the RCU-callbacks kthread?
1086 * Caller must have preemption disabled.
1088 static bool rcu_is_callbacks_kthread(void)
1090 return __this_cpu_read(rcu_cpu_kthread_task
) == current
;
1093 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1096 * Do priority-boost accounting for the start of a new grace period.
1098 static void rcu_preempt_boost_start_gp(struct rcu_node
*rnp
)
1100 rnp
->boost_time
= jiffies
+ RCU_BOOST_DELAY_JIFFIES
;
1104 * Create an RCU-boost kthread for the specified node if one does not
1105 * already exist. We only create this kthread for preemptible RCU.
1106 * Returns zero if all is well, a negated errno otherwise.
1108 static int rcu_spawn_one_boost_kthread(struct rcu_state
*rsp
,
1109 struct rcu_node
*rnp
)
1111 int rnp_index
= rnp
- &rsp
->node
[0];
1112 unsigned long flags
;
1113 struct sched_param sp
;
1114 struct task_struct
*t
;
1116 if (rcu_state_p
!= rsp
)
1119 if (!rcu_scheduler_fully_active
|| rcu_rnp_online_cpus(rnp
) == 0)
1123 if (rnp
->boost_kthread_task
!= NULL
)
1125 t
= kthread_create(rcu_boost_kthread
, (void *)rnp
,
1126 "rcub/%d", rnp_index
);
1129 raw_spin_lock_irqsave_rcu_node(rnp
, flags
);
1130 rnp
->boost_kthread_task
= t
;
1131 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
1132 sp
.sched_priority
= kthread_prio
;
1133 sched_setscheduler_nocheck(t
, SCHED_FIFO
, &sp
);
1134 wake_up_process(t
); /* get to TASK_INTERRUPTIBLE quickly. */
1138 static void rcu_kthread_do_work(void)
1140 rcu_do_batch(&rcu_sched_state
, this_cpu_ptr(&rcu_sched_data
));
1141 rcu_do_batch(&rcu_bh_state
, this_cpu_ptr(&rcu_bh_data
));
1142 rcu_preempt_do_callbacks();
1145 static void rcu_cpu_kthread_setup(unsigned int cpu
)
1147 struct sched_param sp
;
1149 sp
.sched_priority
= kthread_prio
;
1150 sched_setscheduler_nocheck(current
, SCHED_FIFO
, &sp
);
1153 static void rcu_cpu_kthread_park(unsigned int cpu
)
1155 per_cpu(rcu_cpu_kthread_status
, cpu
) = RCU_KTHREAD_OFFCPU
;
1158 static int rcu_cpu_kthread_should_run(unsigned int cpu
)
1160 return __this_cpu_read(rcu_cpu_has_work
);
1164 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
1165 * RCU softirq used in flavors and configurations of RCU that do not
1166 * support RCU priority boosting.
1168 static void rcu_cpu_kthread(unsigned int cpu
)
1170 unsigned int *statusp
= this_cpu_ptr(&rcu_cpu_kthread_status
);
1171 char work
, *workp
= this_cpu_ptr(&rcu_cpu_has_work
);
1174 for (spincnt
= 0; spincnt
< 10; spincnt
++) {
1175 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1177 *statusp
= RCU_KTHREAD_RUNNING
;
1178 this_cpu_inc(rcu_cpu_kthread_loops
);
1179 local_irq_disable();
1184 rcu_kthread_do_work();
1187 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1188 *statusp
= RCU_KTHREAD_WAITING
;
1192 *statusp
= RCU_KTHREAD_YIELDING
;
1193 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1194 schedule_timeout_interruptible(2);
1195 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1196 *statusp
= RCU_KTHREAD_WAITING
;
1200 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1201 * served by the rcu_node in question. The CPU hotplug lock is still
1202 * held, so the value of rnp->qsmaskinit will be stable.
1204 * We don't include outgoingcpu in the affinity set, use -1 if there is
1205 * no outgoing CPU. If there are no CPUs left in the affinity set,
1206 * this function allows the kthread to execute on any CPU.
1208 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
)
1210 struct task_struct
*t
= rnp
->boost_kthread_task
;
1211 unsigned long mask
= rcu_rnp_online_cpus(rnp
);
1217 if (!zalloc_cpumask_var(&cm
, GFP_KERNEL
))
1219 for_each_leaf_node_possible_cpu(rnp
, cpu
)
1220 if ((mask
& leaf_node_cpu_bit(rnp
, cpu
)) &&
1222 cpumask_set_cpu(cpu
, cm
);
1223 if (cpumask_weight(cm
) == 0)
1225 set_cpus_allowed_ptr(t
, cm
);
1226 free_cpumask_var(cm
);
1229 static struct smp_hotplug_thread rcu_cpu_thread_spec
= {
1230 .store
= &rcu_cpu_kthread_task
,
1231 .thread_should_run
= rcu_cpu_kthread_should_run
,
1232 .thread_fn
= rcu_cpu_kthread
,
1233 .thread_comm
= "rcuc/%u",
1234 .setup
= rcu_cpu_kthread_setup
,
1235 .park
= rcu_cpu_kthread_park
,
1239 * Spawn boost kthreads -- called as soon as the scheduler is running.
1241 static void __init
rcu_spawn_boost_kthreads(void)
1243 struct rcu_node
*rnp
;
1246 for_each_possible_cpu(cpu
)
1247 per_cpu(rcu_cpu_has_work
, cpu
) = 0;
1248 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec
));
1249 rcu_for_each_leaf_node(rcu_state_p
, rnp
)
1250 (void)rcu_spawn_one_boost_kthread(rcu_state_p
, rnp
);
1253 static void rcu_prepare_kthreads(int cpu
)
1255 struct rcu_data
*rdp
= per_cpu_ptr(rcu_state_p
->rda
, cpu
);
1256 struct rcu_node
*rnp
= rdp
->mynode
;
1258 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1259 if (rcu_scheduler_fully_active
)
1260 (void)rcu_spawn_one_boost_kthread(rcu_state_p
, rnp
);
1263 #else /* #ifdef CONFIG_RCU_BOOST */
1265 static void rcu_initiate_boost(struct rcu_node
*rnp
, unsigned long flags
)
1266 __releases(rnp
->lock
)
1268 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
1271 static void invoke_rcu_callbacks_kthread(void)
1276 static bool rcu_is_callbacks_kthread(void)
1281 static void rcu_preempt_boost_start_gp(struct rcu_node
*rnp
)
1285 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
)
1289 static void __init
rcu_spawn_boost_kthreads(void)
1293 static void rcu_prepare_kthreads(int cpu
)
1297 #endif /* #else #ifdef CONFIG_RCU_BOOST */
1299 #if !defined(CONFIG_RCU_FAST_NO_HZ)
1302 * Check to see if any future RCU-related work will need to be done
1303 * by the current CPU, even if none need be done immediately, returning
1304 * 1 if so. This function is part of the RCU implementation; it is -not-
1305 * an exported member of the RCU API.
1307 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1308 * any flavor of RCU.
1310 int rcu_needs_cpu(u64 basemono
, u64
*nextevt
)
1312 *nextevt
= KTIME_MAX
;
1313 return rcu_cpu_has_callbacks(NULL
);
1317 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1320 static void rcu_cleanup_after_idle(void)
1325 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1328 static void rcu_prepare_for_idle(void)
1333 * Don't bother keeping a running count of the number of RCU callbacks
1334 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1336 static void rcu_idle_count_callbacks_posted(void)
1340 #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1343 * This code is invoked when a CPU goes idle, at which point we want
1344 * to have the CPU do everything required for RCU so that it can enter
1345 * the energy-efficient dyntick-idle mode. This is handled by a
1346 * state machine implemented by rcu_prepare_for_idle() below.
1348 * The following three proprocessor symbols control this state machine:
1350 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1351 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1352 * is sized to be roughly one RCU grace period. Those energy-efficiency
1353 * benchmarkers who might otherwise be tempted to set this to a large
1354 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1355 * system. And if you are -that- concerned about energy efficiency,
1356 * just power the system down and be done with it!
1357 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1358 * permitted to sleep in dyntick-idle mode with only lazy RCU
1359 * callbacks pending. Setting this too high can OOM your system.
1361 * The values below work well in practice. If future workloads require
1362 * adjustment, they can be converted into kernel config parameters, though
1363 * making the state machine smarter might be a better option.
1365 #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1366 #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1368 static int rcu_idle_gp_delay
= RCU_IDLE_GP_DELAY
;
1369 module_param(rcu_idle_gp_delay
, int, 0644);
1370 static int rcu_idle_lazy_gp_delay
= RCU_IDLE_LAZY_GP_DELAY
;
1371 module_param(rcu_idle_lazy_gp_delay
, int, 0644);
1374 * Try to advance callbacks for all flavors of RCU on the current CPU, but
1375 * only if it has been awhile since the last time we did so. Afterwards,
1376 * if there are any callbacks ready for immediate invocation, return true.
1378 static bool __maybe_unused
rcu_try_advance_all_cbs(void)
1380 bool cbs_ready
= false;
1381 struct rcu_data
*rdp
;
1382 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
1383 struct rcu_node
*rnp
;
1384 struct rcu_state
*rsp
;
1386 /* Exit early if we advanced recently. */
1387 if (jiffies
== rdtp
->last_advance_all
)
1389 rdtp
->last_advance_all
= jiffies
;
1391 for_each_rcu_flavor(rsp
) {
1392 rdp
= this_cpu_ptr(rsp
->rda
);
1396 * Don't bother checking unless a grace period has
1397 * completed since we last checked and there are
1398 * callbacks not yet ready to invoke.
1400 if ((rdp
->completed
!= rnp
->completed
||
1401 unlikely(READ_ONCE(rdp
->gpwrap
))) &&
1402 rcu_segcblist_pend_cbs(&rdp
->cblist
))
1403 note_gp_changes(rsp
, rdp
);
1405 if (rcu_segcblist_ready_cbs(&rdp
->cblist
))
1412 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1413 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1414 * caller to set the timeout based on whether or not there are non-lazy
1417 * The caller must have disabled interrupts.
1419 int rcu_needs_cpu(u64 basemono
, u64
*nextevt
)
1421 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
1424 lockdep_assert_irqs_disabled();
1426 /* Snapshot to detect later posting of non-lazy callback. */
1427 rdtp
->nonlazy_posted_snap
= rdtp
->nonlazy_posted
;
1429 /* If no callbacks, RCU doesn't need the CPU. */
1430 if (!rcu_cpu_has_callbacks(&rdtp
->all_lazy
)) {
1431 *nextevt
= KTIME_MAX
;
1435 /* Attempt to advance callbacks. */
1436 if (rcu_try_advance_all_cbs()) {
1437 /* Some ready to invoke, so initiate later invocation. */
1441 rdtp
->last_accelerate
= jiffies
;
1443 /* Request timer delay depending on laziness, and round. */
1444 if (!rdtp
->all_lazy
) {
1445 dj
= round_up(rcu_idle_gp_delay
+ jiffies
,
1446 rcu_idle_gp_delay
) - jiffies
;
1448 dj
= round_jiffies(rcu_idle_lazy_gp_delay
+ jiffies
) - jiffies
;
1450 *nextevt
= basemono
+ dj
* TICK_NSEC
;
1455 * Prepare a CPU for idle from an RCU perspective. The first major task
1456 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1457 * The second major task is to check to see if a non-lazy callback has
1458 * arrived at a CPU that previously had only lazy callbacks. The third
1459 * major task is to accelerate (that is, assign grace-period numbers to)
1460 * any recently arrived callbacks.
1462 * The caller must have disabled interrupts.
1464 static void rcu_prepare_for_idle(void)
1467 struct rcu_data
*rdp
;
1468 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
1469 struct rcu_node
*rnp
;
1470 struct rcu_state
*rsp
;
1473 lockdep_assert_irqs_disabled();
1474 if (rcu_is_nocb_cpu(smp_processor_id()))
1477 /* Handle nohz enablement switches conservatively. */
1478 tne
= READ_ONCE(tick_nohz_active
);
1479 if (tne
!= rdtp
->tick_nohz_enabled_snap
) {
1480 if (rcu_cpu_has_callbacks(NULL
))
1481 invoke_rcu_core(); /* force nohz to see update. */
1482 rdtp
->tick_nohz_enabled_snap
= tne
;
1489 * If a non-lazy callback arrived at a CPU having only lazy
1490 * callbacks, invoke RCU core for the side-effect of recalculating
1491 * idle duration on re-entry to idle.
1493 if (rdtp
->all_lazy
&&
1494 rdtp
->nonlazy_posted
!= rdtp
->nonlazy_posted_snap
) {
1495 rdtp
->all_lazy
= false;
1496 rdtp
->nonlazy_posted_snap
= rdtp
->nonlazy_posted
;
1502 * If we have not yet accelerated this jiffy, accelerate all
1503 * callbacks on this CPU.
1505 if (rdtp
->last_accelerate
== jiffies
)
1507 rdtp
->last_accelerate
= jiffies
;
1508 for_each_rcu_flavor(rsp
) {
1509 rdp
= this_cpu_ptr(rsp
->rda
);
1510 if (!rcu_segcblist_pend_cbs(&rdp
->cblist
))
1513 raw_spin_lock_rcu_node(rnp
); /* irqs already disabled. */
1514 needwake
= rcu_accelerate_cbs(rsp
, rnp
, rdp
);
1515 raw_spin_unlock_rcu_node(rnp
); /* irqs remain disabled. */
1517 rcu_gp_kthread_wake(rsp
);
1522 * Clean up for exit from idle. Attempt to advance callbacks based on
1523 * any grace periods that elapsed while the CPU was idle, and if any
1524 * callbacks are now ready to invoke, initiate invocation.
1526 static void rcu_cleanup_after_idle(void)
1528 lockdep_assert_irqs_disabled();
1529 if (rcu_is_nocb_cpu(smp_processor_id()))
1531 if (rcu_try_advance_all_cbs())
1536 * Keep a running count of the number of non-lazy callbacks posted
1537 * on this CPU. This running counter (which is never decremented) allows
1538 * rcu_prepare_for_idle() to detect when something out of the idle loop
1539 * posts a callback, even if an equal number of callbacks are invoked.
1540 * Of course, callbacks should only be posted from within a trace event
1541 * designed to be called from idle or from within RCU_NONIDLE().
1543 static void rcu_idle_count_callbacks_posted(void)
1545 __this_cpu_add(rcu_dynticks
.nonlazy_posted
, 1);
1549 * Data for flushing lazy RCU callbacks at OOM time.
1551 static atomic_t oom_callback_count
;
1552 static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq
);
1555 * RCU OOM callback -- decrement the outstanding count and deliver the
1556 * wake-up if we are the last one.
1558 static void rcu_oom_callback(struct rcu_head
*rhp
)
1560 if (atomic_dec_and_test(&oom_callback_count
))
1561 wake_up(&oom_callback_wq
);
1565 * Post an rcu_oom_notify callback on the current CPU if it has at
1566 * least one lazy callback. This will unnecessarily post callbacks
1567 * to CPUs that already have a non-lazy callback at the end of their
1568 * callback list, but this is an infrequent operation, so accept some
1569 * extra overhead to keep things simple.
1571 static void rcu_oom_notify_cpu(void *unused
)
1573 struct rcu_state
*rsp
;
1574 struct rcu_data
*rdp
;
1576 for_each_rcu_flavor(rsp
) {
1577 rdp
= raw_cpu_ptr(rsp
->rda
);
1578 if (rcu_segcblist_n_lazy_cbs(&rdp
->cblist
)) {
1579 atomic_inc(&oom_callback_count
);
1580 rsp
->call(&rdp
->oom_head
, rcu_oom_callback
);
1586 * If low on memory, ensure that each CPU has a non-lazy callback.
1587 * This will wake up CPUs that have only lazy callbacks, in turn
1588 * ensuring that they free up the corresponding memory in a timely manner.
1589 * Because an uncertain amount of memory will be freed in some uncertain
1590 * timeframe, we do not claim to have freed anything.
1592 static int rcu_oom_notify(struct notifier_block
*self
,
1593 unsigned long notused
, void *nfreed
)
1597 /* Wait for callbacks from earlier instance to complete. */
1598 wait_event(oom_callback_wq
, atomic_read(&oom_callback_count
) == 0);
1599 smp_mb(); /* Ensure callback reuse happens after callback invocation. */
1602 * Prevent premature wakeup: ensure that all increments happen
1603 * before there is a chance of the counter reaching zero.
1605 atomic_set(&oom_callback_count
, 1);
1607 for_each_online_cpu(cpu
) {
1608 smp_call_function_single(cpu
, rcu_oom_notify_cpu
, NULL
, 1);
1609 cond_resched_rcu_qs();
1612 /* Unconditionally decrement: no need to wake ourselves up. */
1613 atomic_dec(&oom_callback_count
);
1618 static struct notifier_block rcu_oom_nb
= {
1619 .notifier_call
= rcu_oom_notify
1622 static int __init
rcu_register_oom_notifier(void)
1624 register_oom_notifier(&rcu_oom_nb
);
1627 early_initcall(rcu_register_oom_notifier
);
1629 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1631 #ifdef CONFIG_RCU_FAST_NO_HZ
1633 static void print_cpu_stall_fast_no_hz(char *cp
, int cpu
)
1635 struct rcu_dynticks
*rdtp
= &per_cpu(rcu_dynticks
, cpu
);
1636 unsigned long nlpd
= rdtp
->nonlazy_posted
- rdtp
->nonlazy_posted_snap
;
1638 sprintf(cp
, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1639 rdtp
->last_accelerate
& 0xffff, jiffies
& 0xffff,
1641 rdtp
->all_lazy
? 'L' : '.',
1642 rdtp
->tick_nohz_enabled_snap
? '.' : 'D');
1645 #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1647 static void print_cpu_stall_fast_no_hz(char *cp
, int cpu
)
1652 #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1654 /* Initiate the stall-info list. */
1655 static void print_cpu_stall_info_begin(void)
1661 * Print out diagnostic information for the specified stalled CPU.
1663 * If the specified CPU is aware of the current RCU grace period
1664 * (flavor specified by rsp), then print the number of scheduling
1665 * clock interrupts the CPU has taken during the time that it has
1666 * been aware. Otherwise, print the number of RCU grace periods
1667 * that this CPU is ignorant of, for example, "1" if the CPU was
1668 * aware of the previous grace period.
1670 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1672 static void print_cpu_stall_info(struct rcu_state
*rsp
, int cpu
)
1674 unsigned long delta
;
1675 char fast_no_hz
[72];
1676 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1677 struct rcu_dynticks
*rdtp
= rdp
->dynticks
;
1679 unsigned long ticks_value
;
1681 if (rsp
->gpnum
== rdp
->gpnum
) {
1682 ticks_title
= "ticks this GP";
1683 ticks_value
= rdp
->ticks_this_gp
;
1685 ticks_title
= "GPs behind";
1686 ticks_value
= rsp
->gpnum
- rdp
->gpnum
;
1688 print_cpu_stall_fast_no_hz(fast_no_hz
, cpu
);
1689 delta
= rdp
->mynode
->gpnum
- rdp
->rcu_iw_gpnum
;
1690 pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s\n",
1692 "O."[!!cpu_online(cpu
)],
1693 "o."[!!(rdp
->grpmask
& rdp
->mynode
->qsmaskinit
)],
1694 "N."[!!(rdp
->grpmask
& rdp
->mynode
->qsmaskinitnext
)],
1695 !IS_ENABLED(CONFIG_IRQ_WORK
) ? '?' :
1696 rdp
->rcu_iw_pending
? (int)min(delta
, 9UL) + '0' :
1698 ticks_value
, ticks_title
,
1699 rcu_dynticks_snap(rdtp
) & 0xfff,
1700 rdtp
->dynticks_nesting
, rdtp
->dynticks_nmi_nesting
,
1701 rdp
->softirq_snap
, kstat_softirqs_cpu(RCU_SOFTIRQ
, cpu
),
1702 READ_ONCE(rsp
->n_force_qs
) - rsp
->n_force_qs_gpstart
,
1706 /* Terminate the stall-info list. */
1707 static void print_cpu_stall_info_end(void)
1712 /* Zero ->ticks_this_gp for all flavors of RCU. */
1713 static void zero_cpu_stall_ticks(struct rcu_data
*rdp
)
1715 rdp
->ticks_this_gp
= 0;
1716 rdp
->softirq_snap
= kstat_softirqs_cpu(RCU_SOFTIRQ
, smp_processor_id());
1719 /* Increment ->ticks_this_gp for all flavors of RCU. */
1720 static void increment_cpu_stall_ticks(void)
1722 struct rcu_state
*rsp
;
1724 for_each_rcu_flavor(rsp
)
1725 raw_cpu_inc(rsp
->rda
->ticks_this_gp
);
1728 #ifdef CONFIG_RCU_NOCB_CPU
1731 * Offload callback processing from the boot-time-specified set of CPUs
1732 * specified by rcu_nocb_mask. For each CPU in the set, there is a
1733 * kthread created that pulls the callbacks from the corresponding CPU,
1734 * waits for a grace period to elapse, and invokes the callbacks.
1735 * The no-CBs CPUs do a wake_up() on their kthread when they insert
1736 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
1737 * has been specified, in which case each kthread actively polls its
1738 * CPU. (Which isn't so great for energy efficiency, but which does
1739 * reduce RCU's overhead on that CPU.)
1741 * This is intended to be used in conjunction with Frederic Weisbecker's
1742 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
1743 * running CPU-bound user-mode computations.
1745 * Offloading of callback processing could also in theory be used as
1746 * an energy-efficiency measure because CPUs with no RCU callbacks
1747 * queued are more aggressive about entering dyntick-idle mode.
1751 /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
1752 static int __init
rcu_nocb_setup(char *str
)
1754 alloc_bootmem_cpumask_var(&rcu_nocb_mask
);
1755 have_rcu_nocb_mask
= true;
1756 cpulist_parse(str
, rcu_nocb_mask
);
1759 __setup("rcu_nocbs=", rcu_nocb_setup
);
1761 static int __init
parse_rcu_nocb_poll(char *arg
)
1763 rcu_nocb_poll
= true;
1766 early_param("rcu_nocb_poll", parse_rcu_nocb_poll
);
1769 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
1772 static void rcu_nocb_gp_cleanup(struct swait_queue_head
*sq
)
1778 * Set the root rcu_node structure's ->need_future_gp field
1779 * based on the sum of those of all rcu_node structures. This does
1780 * double-count the root rcu_node structure's requests, but this
1781 * is necessary to handle the possibility of a rcu_nocb_kthread()
1782 * having awakened during the time that the rcu_node structures
1783 * were being updated for the end of the previous grace period.
1785 static void rcu_nocb_gp_set(struct rcu_node
*rnp
, int nrq
)
1787 rnp
->need_future_gp
[(rnp
->completed
+ 1) & 0x1] += nrq
;
1790 static struct swait_queue_head
*rcu_nocb_gp_get(struct rcu_node
*rnp
)
1792 return &rnp
->nocb_gp_wq
[rnp
->completed
& 0x1];
1795 static void rcu_init_one_nocb(struct rcu_node
*rnp
)
1797 init_swait_queue_head(&rnp
->nocb_gp_wq
[0]);
1798 init_swait_queue_head(&rnp
->nocb_gp_wq
[1]);
1801 /* Is the specified CPU a no-CBs CPU? */
1802 bool rcu_is_nocb_cpu(int cpu
)
1804 if (have_rcu_nocb_mask
)
1805 return cpumask_test_cpu(cpu
, rcu_nocb_mask
);
1810 * Kick the leader kthread for this NOCB group. Caller holds ->nocb_lock
1811 * and this function releases it.
1813 static void __wake_nocb_leader(struct rcu_data
*rdp
, bool force
,
1814 unsigned long flags
)
1815 __releases(rdp
->nocb_lock
)
1817 struct rcu_data
*rdp_leader
= rdp
->nocb_leader
;
1819 lockdep_assert_held(&rdp
->nocb_lock
);
1820 if (!READ_ONCE(rdp_leader
->nocb_kthread
)) {
1821 raw_spin_unlock_irqrestore(&rdp
->nocb_lock
, flags
);
1824 if (rdp_leader
->nocb_leader_sleep
|| force
) {
1825 /* Prior smp_mb__after_atomic() orders against prior enqueue. */
1826 WRITE_ONCE(rdp_leader
->nocb_leader_sleep
, false);
1827 del_timer(&rdp
->nocb_timer
);
1828 raw_spin_unlock_irqrestore(&rdp
->nocb_lock
, flags
);
1829 smp_mb(); /* ->nocb_leader_sleep before swake_up(). */
1830 swake_up(&rdp_leader
->nocb_wq
);
1832 raw_spin_unlock_irqrestore(&rdp
->nocb_lock
, flags
);
1837 * Kick the leader kthread for this NOCB group, but caller has not
1840 static void wake_nocb_leader(struct rcu_data
*rdp
, bool force
)
1842 unsigned long flags
;
1844 raw_spin_lock_irqsave(&rdp
->nocb_lock
, flags
);
1845 __wake_nocb_leader(rdp
, force
, flags
);
1849 * Arrange to wake the leader kthread for this NOCB group at some
1850 * future time when it is safe to do so.
1852 static void wake_nocb_leader_defer(struct rcu_data
*rdp
, int waketype
,
1855 unsigned long flags
;
1857 raw_spin_lock_irqsave(&rdp
->nocb_lock
, flags
);
1858 if (rdp
->nocb_defer_wakeup
== RCU_NOCB_WAKE_NOT
)
1859 mod_timer(&rdp
->nocb_timer
, jiffies
+ 1);
1860 WRITE_ONCE(rdp
->nocb_defer_wakeup
, waketype
);
1861 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, reason
);
1862 raw_spin_unlock_irqrestore(&rdp
->nocb_lock
, flags
);
1866 * Does the specified CPU need an RCU callback for the specified flavor
1869 static bool rcu_nocb_cpu_needs_barrier(struct rcu_state
*rsp
, int cpu
)
1871 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1873 #ifdef CONFIG_PROVE_RCU
1874 struct rcu_head
*rhp
;
1875 #endif /* #ifdef CONFIG_PROVE_RCU */
1878 * Check count of all no-CBs callbacks awaiting invocation.
1879 * There needs to be a barrier before this function is called,
1880 * but associated with a prior determination that no more
1881 * callbacks would be posted. In the worst case, the first
1882 * barrier in _rcu_barrier() suffices (but the caller cannot
1883 * necessarily rely on this, not a substitute for the caller
1884 * getting the concurrency design right!). There must also be
1885 * a barrier between the following load an posting of a callback
1886 * (if a callback is in fact needed). This is associated with an
1887 * atomic_inc() in the caller.
1889 ret
= atomic_long_read(&rdp
->nocb_q_count
);
1891 #ifdef CONFIG_PROVE_RCU
1892 rhp
= READ_ONCE(rdp
->nocb_head
);
1894 rhp
= READ_ONCE(rdp
->nocb_gp_head
);
1896 rhp
= READ_ONCE(rdp
->nocb_follower_head
);
1898 /* Having no rcuo kthread but CBs after scheduler starts is bad! */
1899 if (!READ_ONCE(rdp
->nocb_kthread
) && rhp
&&
1900 rcu_scheduler_fully_active
) {
1901 /* RCU callback enqueued before CPU first came online??? */
1902 pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
1906 #endif /* #ifdef CONFIG_PROVE_RCU */
1912 * Enqueue the specified string of rcu_head structures onto the specified
1913 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
1914 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
1915 * counts are supplied by rhcount and rhcount_lazy.
1917 * If warranted, also wake up the kthread servicing this CPUs queues.
1919 static void __call_rcu_nocb_enqueue(struct rcu_data
*rdp
,
1920 struct rcu_head
*rhp
,
1921 struct rcu_head
**rhtp
,
1922 int rhcount
, int rhcount_lazy
,
1923 unsigned long flags
)
1926 struct rcu_head
**old_rhpp
;
1927 struct task_struct
*t
;
1929 /* Enqueue the callback on the nocb list and update counts. */
1930 atomic_long_add(rhcount
, &rdp
->nocb_q_count
);
1931 /* rcu_barrier() relies on ->nocb_q_count add before xchg. */
1932 old_rhpp
= xchg(&rdp
->nocb_tail
, rhtp
);
1933 WRITE_ONCE(*old_rhpp
, rhp
);
1934 atomic_long_add(rhcount_lazy
, &rdp
->nocb_q_count_lazy
);
1935 smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
1937 /* If we are not being polled and there is a kthread, awaken it ... */
1938 t
= READ_ONCE(rdp
->nocb_kthread
);
1939 if (rcu_nocb_poll
|| !t
) {
1940 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
1941 TPS("WakeNotPoll"));
1944 len
= atomic_long_read(&rdp
->nocb_q_count
);
1945 if (old_rhpp
== &rdp
->nocb_head
) {
1946 if (!irqs_disabled_flags(flags
)) {
1947 /* ... if queue was empty ... */
1948 wake_nocb_leader(rdp
, false);
1949 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
1952 wake_nocb_leader_defer(rdp
, RCU_NOCB_WAKE
,
1953 TPS("WakeEmptyIsDeferred"));
1955 rdp
->qlen_last_fqs_check
= 0;
1956 } else if (len
> rdp
->qlen_last_fqs_check
+ qhimark
) {
1957 /* ... or if many callbacks queued. */
1958 if (!irqs_disabled_flags(flags
)) {
1959 wake_nocb_leader(rdp
, true);
1960 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
1963 wake_nocb_leader_defer(rdp
, RCU_NOCB_WAKE
,
1964 TPS("WakeOvfIsDeferred"));
1966 rdp
->qlen_last_fqs_check
= LONG_MAX
/ 2;
1968 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, TPS("WakeNot"));
1974 * This is a helper for __call_rcu(), which invokes this when the normal
1975 * callback queue is inoperable. If this is not a no-CBs CPU, this
1976 * function returns failure back to __call_rcu(), which can complain
1979 * Otherwise, this function queues the callback where the corresponding
1980 * "rcuo" kthread can find it.
1982 static bool __call_rcu_nocb(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
1983 bool lazy
, unsigned long flags
)
1986 if (!rcu_is_nocb_cpu(rdp
->cpu
))
1988 __call_rcu_nocb_enqueue(rdp
, rhp
, &rhp
->next
, 1, lazy
, flags
);
1989 if (__is_kfree_rcu_offset((unsigned long)rhp
->func
))
1990 trace_rcu_kfree_callback(rdp
->rsp
->name
, rhp
,
1991 (unsigned long)rhp
->func
,
1992 -atomic_long_read(&rdp
->nocb_q_count_lazy
),
1993 -atomic_long_read(&rdp
->nocb_q_count
));
1995 trace_rcu_callback(rdp
->rsp
->name
, rhp
,
1996 -atomic_long_read(&rdp
->nocb_q_count_lazy
),
1997 -atomic_long_read(&rdp
->nocb_q_count
));
2000 * If called from an extended quiescent state with interrupts
2001 * disabled, invoke the RCU core in order to allow the idle-entry
2002 * deferred-wakeup check to function.
2004 if (irqs_disabled_flags(flags
) &&
2005 !rcu_is_watching() &&
2006 cpu_online(smp_processor_id()))
2013 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2016 static bool __maybe_unused
rcu_nocb_adopt_orphan_cbs(struct rcu_data
*my_rdp
,
2017 struct rcu_data
*rdp
,
2018 unsigned long flags
)
2020 lockdep_assert_irqs_disabled();
2021 if (!rcu_is_nocb_cpu(smp_processor_id()))
2022 return false; /* Not NOCBs CPU, caller must migrate CBs. */
2023 __call_rcu_nocb_enqueue(my_rdp
, rcu_segcblist_head(&rdp
->cblist
),
2024 rcu_segcblist_tail(&rdp
->cblist
),
2025 rcu_segcblist_n_cbs(&rdp
->cblist
),
2026 rcu_segcblist_n_lazy_cbs(&rdp
->cblist
), flags
);
2027 rcu_segcblist_init(&rdp
->cblist
);
2028 rcu_segcblist_disable(&rdp
->cblist
);
2033 * If necessary, kick off a new grace period, and either way wait
2034 * for a subsequent grace period to complete.
2036 static void rcu_nocb_wait_gp(struct rcu_data
*rdp
)
2040 unsigned long flags
;
2042 struct rcu_node
*rnp
= rdp
->mynode
;
2044 raw_spin_lock_irqsave_rcu_node(rnp
, flags
);
2045 needwake
= rcu_start_future_gp(rnp
, rdp
, &c
);
2046 raw_spin_unlock_irqrestore_rcu_node(rnp
, flags
);
2048 rcu_gp_kthread_wake(rdp
->rsp
);
2051 * Wait for the grace period. Do so interruptibly to avoid messing
2052 * up the load average.
2054 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("StartWait"));
2056 swait_event_interruptible(
2057 rnp
->nocb_gp_wq
[c
& 0x1],
2058 (d
= ULONG_CMP_GE(READ_ONCE(rnp
->completed
), c
)));
2061 WARN_ON(signal_pending(current
));
2062 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("ResumeWait"));
2064 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("EndWait"));
2065 smp_mb(); /* Ensure that CB invocation happens after GP end. */
2069 * Leaders come here to wait for additional callbacks to show up.
2070 * This function does not return until callbacks appear.
2072 static void nocb_leader_wait(struct rcu_data
*my_rdp
)
2074 bool firsttime
= true;
2075 unsigned long flags
;
2077 struct rcu_data
*rdp
;
2078 struct rcu_head
**tail
;
2082 /* Wait for callbacks to appear. */
2083 if (!rcu_nocb_poll
) {
2084 trace_rcu_nocb_wake(my_rdp
->rsp
->name
, my_rdp
->cpu
, TPS("Sleep"));
2085 swait_event_interruptible(my_rdp
->nocb_wq
,
2086 !READ_ONCE(my_rdp
->nocb_leader_sleep
));
2087 raw_spin_lock_irqsave(&my_rdp
->nocb_lock
, flags
);
2088 my_rdp
->nocb_leader_sleep
= true;
2089 WRITE_ONCE(my_rdp
->nocb_defer_wakeup
, RCU_NOCB_WAKE_NOT
);
2090 del_timer(&my_rdp
->nocb_timer
);
2091 raw_spin_unlock_irqrestore(&my_rdp
->nocb_lock
, flags
);
2092 } else if (firsttime
) {
2093 firsttime
= false; /* Don't drown trace log with "Poll"! */
2094 trace_rcu_nocb_wake(my_rdp
->rsp
->name
, my_rdp
->cpu
, TPS("Poll"));
2098 * Each pass through the following loop checks a follower for CBs.
2099 * We are our own first follower. Any CBs found are moved to
2100 * nocb_gp_head, where they await a grace period.
2103 smp_mb(); /* wakeup and _sleep before ->nocb_head reads. */
2104 for (rdp
= my_rdp
; rdp
; rdp
= rdp
->nocb_next_follower
) {
2105 rdp
->nocb_gp_head
= READ_ONCE(rdp
->nocb_head
);
2106 if (!rdp
->nocb_gp_head
)
2107 continue; /* No CBs here, try next follower. */
2109 /* Move callbacks to wait-for-GP list, which is empty. */
2110 WRITE_ONCE(rdp
->nocb_head
, NULL
);
2111 rdp
->nocb_gp_tail
= xchg(&rdp
->nocb_tail
, &rdp
->nocb_head
);
2115 /* No callbacks? Sleep a bit if polling, and go retry. */
2116 if (unlikely(!gotcbs
)) {
2117 WARN_ON(signal_pending(current
));
2118 if (rcu_nocb_poll
) {
2119 schedule_timeout_interruptible(1);
2121 trace_rcu_nocb_wake(my_rdp
->rsp
->name
, my_rdp
->cpu
,
2127 /* Wait for one grace period. */
2128 rcu_nocb_wait_gp(my_rdp
);
2130 /* Each pass through the following loop wakes a follower, if needed. */
2131 for (rdp
= my_rdp
; rdp
; rdp
= rdp
->nocb_next_follower
) {
2132 if (!rcu_nocb_poll
&&
2133 READ_ONCE(rdp
->nocb_head
) &&
2134 READ_ONCE(my_rdp
->nocb_leader_sleep
)) {
2135 raw_spin_lock_irqsave(&my_rdp
->nocb_lock
, flags
);
2136 my_rdp
->nocb_leader_sleep
= false;/* No need to sleep.*/
2137 raw_spin_unlock_irqrestore(&my_rdp
->nocb_lock
, flags
);
2139 if (!rdp
->nocb_gp_head
)
2140 continue; /* No CBs, so no need to wake follower. */
2142 /* Append callbacks to follower's "done" list. */
2143 raw_spin_lock_irqsave(&rdp
->nocb_lock
, flags
);
2144 tail
= rdp
->nocb_follower_tail
;
2145 rdp
->nocb_follower_tail
= rdp
->nocb_gp_tail
;
2146 *tail
= rdp
->nocb_gp_head
;
2147 raw_spin_unlock_irqrestore(&rdp
->nocb_lock
, flags
);
2148 if (rdp
!= my_rdp
&& tail
== &rdp
->nocb_follower_head
) {
2149 /* List was empty, so wake up the follower. */
2150 swake_up(&rdp
->nocb_wq
);
2154 /* If we (the leader) don't have CBs, go wait some more. */
2155 if (!my_rdp
->nocb_follower_head
)
2160 * Followers come here to wait for additional callbacks to show up.
2161 * This function does not return until callbacks appear.
2163 static void nocb_follower_wait(struct rcu_data
*rdp
)
2166 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, TPS("FollowerSleep"));
2167 swait_event_interruptible(rdp
->nocb_wq
,
2168 READ_ONCE(rdp
->nocb_follower_head
));
2169 if (smp_load_acquire(&rdp
->nocb_follower_head
)) {
2170 /* ^^^ Ensure CB invocation follows _head test. */
2173 WARN_ON(signal_pending(current
));
2174 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, TPS("WokeEmpty"));
2179 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
2180 * callbacks queued by the corresponding no-CBs CPU, however, there is
2181 * an optional leader-follower relationship so that the grace-period
2182 * kthreads don't have to do quite so many wakeups.
2184 static int rcu_nocb_kthread(void *arg
)
2187 unsigned long flags
;
2188 struct rcu_head
*list
;
2189 struct rcu_head
*next
;
2190 struct rcu_head
**tail
;
2191 struct rcu_data
*rdp
= arg
;
2193 /* Each pass through this loop invokes one batch of callbacks */
2195 /* Wait for callbacks. */
2196 if (rdp
->nocb_leader
== rdp
)
2197 nocb_leader_wait(rdp
);
2199 nocb_follower_wait(rdp
);
2201 /* Pull the ready-to-invoke callbacks onto local list. */
2202 raw_spin_lock_irqsave(&rdp
->nocb_lock
, flags
);
2203 list
= rdp
->nocb_follower_head
;
2204 rdp
->nocb_follower_head
= NULL
;
2205 tail
= rdp
->nocb_follower_tail
;
2206 rdp
->nocb_follower_tail
= &rdp
->nocb_follower_head
;
2207 raw_spin_unlock_irqrestore(&rdp
->nocb_lock
, flags
);
2209 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, TPS("WokeNonEmpty"));
2211 /* Each pass through the following loop invokes a callback. */
2212 trace_rcu_batch_start(rdp
->rsp
->name
,
2213 atomic_long_read(&rdp
->nocb_q_count_lazy
),
2214 atomic_long_read(&rdp
->nocb_q_count
), -1);
2218 /* Wait for enqueuing to complete, if needed. */
2219 while (next
== NULL
&& &list
->next
!= tail
) {
2220 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2222 schedule_timeout_interruptible(1);
2223 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
,
2227 debug_rcu_head_unqueue(list
);
2229 if (__rcu_reclaim(rdp
->rsp
->name
, list
))
2233 cond_resched_rcu_qs();
2236 trace_rcu_batch_end(rdp
->rsp
->name
, c
, !!list
, 0, 0, 1);
2237 smp_mb__before_atomic(); /* _add after CB invocation. */
2238 atomic_long_add(-c
, &rdp
->nocb_q_count
);
2239 atomic_long_add(-cl
, &rdp
->nocb_q_count_lazy
);
2240 rdp
->n_nocbs_invoked
+= c
;
2245 /* Is a deferred wakeup of rcu_nocb_kthread() required? */
2246 static int rcu_nocb_need_deferred_wakeup(struct rcu_data
*rdp
)
2248 return READ_ONCE(rdp
->nocb_defer_wakeup
);
2251 /* Do a deferred wakeup of rcu_nocb_kthread(). */
2252 static void do_nocb_deferred_wakeup_common(struct rcu_data
*rdp
)
2254 unsigned long flags
;
2257 raw_spin_lock_irqsave(&rdp
->nocb_lock
, flags
);
2258 if (!rcu_nocb_need_deferred_wakeup(rdp
)) {
2259 raw_spin_unlock_irqrestore(&rdp
->nocb_lock
, flags
);
2262 ndw
= READ_ONCE(rdp
->nocb_defer_wakeup
);
2263 WRITE_ONCE(rdp
->nocb_defer_wakeup
, RCU_NOCB_WAKE_NOT
);
2264 __wake_nocb_leader(rdp
, ndw
== RCU_NOCB_WAKE_FORCE
, flags
);
2265 trace_rcu_nocb_wake(rdp
->rsp
->name
, rdp
->cpu
, TPS("DeferredWake"));
2268 /* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
2269 static void do_nocb_deferred_wakeup_timer(struct timer_list
*t
)
2271 struct rcu_data
*rdp
= from_timer(rdp
, t
, nocb_timer
);
2273 do_nocb_deferred_wakeup_common(rdp
);
2277 * Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
2278 * This means we do an inexact common-case check. Note that if
2279 * we miss, ->nocb_timer will eventually clean things up.
2281 static void do_nocb_deferred_wakeup(struct rcu_data
*rdp
)
2283 if (rcu_nocb_need_deferred_wakeup(rdp
))
2284 do_nocb_deferred_wakeup_common(rdp
);
2287 void __init
rcu_init_nohz(void)
2290 bool need_rcu_nocb_mask
= true;
2291 struct rcu_state
*rsp
;
2293 #if defined(CONFIG_NO_HZ_FULL)
2294 if (tick_nohz_full_running
&& cpumask_weight(tick_nohz_full_mask
))
2295 need_rcu_nocb_mask
= true;
2296 #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2298 if (!have_rcu_nocb_mask
&& need_rcu_nocb_mask
) {
2299 if (!zalloc_cpumask_var(&rcu_nocb_mask
, GFP_KERNEL
)) {
2300 pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
2303 have_rcu_nocb_mask
= true;
2305 if (!have_rcu_nocb_mask
)
2308 #if defined(CONFIG_NO_HZ_FULL)
2309 if (tick_nohz_full_running
)
2310 cpumask_or(rcu_nocb_mask
, rcu_nocb_mask
, tick_nohz_full_mask
);
2311 #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2313 if (!cpumask_subset(rcu_nocb_mask
, cpu_possible_mask
)) {
2314 pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
2315 cpumask_and(rcu_nocb_mask
, cpu_possible_mask
,
2318 pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
2319 cpumask_pr_args(rcu_nocb_mask
));
2321 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
2323 for_each_rcu_flavor(rsp
) {
2324 for_each_cpu(cpu
, rcu_nocb_mask
)
2325 init_nocb_callback_list(per_cpu_ptr(rsp
->rda
, cpu
));
2326 rcu_organize_nocb_kthreads(rsp
);
2330 /* Initialize per-rcu_data variables for no-CBs CPUs. */
2331 static void __init
rcu_boot_init_nocb_percpu_data(struct rcu_data
*rdp
)
2333 rdp
->nocb_tail
= &rdp
->nocb_head
;
2334 init_swait_queue_head(&rdp
->nocb_wq
);
2335 rdp
->nocb_follower_tail
= &rdp
->nocb_follower_head
;
2336 raw_spin_lock_init(&rdp
->nocb_lock
);
2337 timer_setup(&rdp
->nocb_timer
, do_nocb_deferred_wakeup_timer
, 0);
2341 * If the specified CPU is a no-CBs CPU that does not already have its
2342 * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are
2343 * brought online out of order, this can require re-organizing the
2344 * leader-follower relationships.
2346 static void rcu_spawn_one_nocb_kthread(struct rcu_state
*rsp
, int cpu
)
2348 struct rcu_data
*rdp
;
2349 struct rcu_data
*rdp_last
;
2350 struct rcu_data
*rdp_old_leader
;
2351 struct rcu_data
*rdp_spawn
= per_cpu_ptr(rsp
->rda
, cpu
);
2352 struct task_struct
*t
;
2355 * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
2356 * then nothing to do.
2358 if (!rcu_is_nocb_cpu(cpu
) || rdp_spawn
->nocb_kthread
)
2361 /* If we didn't spawn the leader first, reorganize! */
2362 rdp_old_leader
= rdp_spawn
->nocb_leader
;
2363 if (rdp_old_leader
!= rdp_spawn
&& !rdp_old_leader
->nocb_kthread
) {
2365 rdp
= rdp_old_leader
;
2367 rdp
->nocb_leader
= rdp_spawn
;
2368 if (rdp_last
&& rdp
!= rdp_spawn
)
2369 rdp_last
->nocb_next_follower
= rdp
;
2370 if (rdp
== rdp_spawn
) {
2371 rdp
= rdp
->nocb_next_follower
;
2374 rdp
= rdp
->nocb_next_follower
;
2375 rdp_last
->nocb_next_follower
= NULL
;
2378 rdp_spawn
->nocb_next_follower
= rdp_old_leader
;
2381 /* Spawn the kthread for this CPU and RCU flavor. */
2382 t
= kthread_run(rcu_nocb_kthread
, rdp_spawn
,
2383 "rcuo%c/%d", rsp
->abbr
, cpu
);
2385 WRITE_ONCE(rdp_spawn
->nocb_kthread
, t
);
2389 * If the specified CPU is a no-CBs CPU that does not already have its
2390 * rcuo kthreads, spawn them.
2392 static void rcu_spawn_all_nocb_kthreads(int cpu
)
2394 struct rcu_state
*rsp
;
2396 if (rcu_scheduler_fully_active
)
2397 for_each_rcu_flavor(rsp
)
2398 rcu_spawn_one_nocb_kthread(rsp
, cpu
);
2402 * Once the scheduler is running, spawn rcuo kthreads for all online
2403 * no-CBs CPUs. This assumes that the early_initcall()s happen before
2404 * non-boot CPUs come online -- if this changes, we will need to add
2405 * some mutual exclusion.
2407 static void __init
rcu_spawn_nocb_kthreads(void)
2411 for_each_online_cpu(cpu
)
2412 rcu_spawn_all_nocb_kthreads(cpu
);
2415 /* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */
2416 static int rcu_nocb_leader_stride
= -1;
2417 module_param(rcu_nocb_leader_stride
, int, 0444);
2420 * Initialize leader-follower relationships for all no-CBs CPU.
2422 static void __init
rcu_organize_nocb_kthreads(struct rcu_state
*rsp
)
2425 int ls
= rcu_nocb_leader_stride
;
2426 int nl
= 0; /* Next leader. */
2427 struct rcu_data
*rdp
;
2428 struct rcu_data
*rdp_leader
= NULL
; /* Suppress misguided gcc warn. */
2429 struct rcu_data
*rdp_prev
= NULL
;
2431 if (!have_rcu_nocb_mask
)
2434 ls
= int_sqrt(nr_cpu_ids
);
2435 rcu_nocb_leader_stride
= ls
;
2439 * Each pass through this loop sets up one rcu_data structure.
2440 * Should the corresponding CPU come online in the future, then
2441 * we will spawn the needed set of rcu_nocb_kthread() kthreads.
2443 for_each_cpu(cpu
, rcu_nocb_mask
) {
2444 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2445 if (rdp
->cpu
>= nl
) {
2446 /* New leader, set up for followers & next leader. */
2447 nl
= DIV_ROUND_UP(rdp
->cpu
+ 1, ls
) * ls
;
2448 rdp
->nocb_leader
= rdp
;
2451 /* Another follower, link to previous leader. */
2452 rdp
->nocb_leader
= rdp_leader
;
2453 rdp_prev
->nocb_next_follower
= rdp
;
2459 /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2460 static bool init_nocb_callback_list(struct rcu_data
*rdp
)
2462 if (!rcu_is_nocb_cpu(rdp
->cpu
))
2465 /* If there are early-boot callbacks, move them to nocb lists. */
2466 if (!rcu_segcblist_empty(&rdp
->cblist
)) {
2467 rdp
->nocb_head
= rcu_segcblist_head(&rdp
->cblist
);
2468 rdp
->nocb_tail
= rcu_segcblist_tail(&rdp
->cblist
);
2469 atomic_long_set(&rdp
->nocb_q_count
,
2470 rcu_segcblist_n_cbs(&rdp
->cblist
));
2471 atomic_long_set(&rdp
->nocb_q_count_lazy
,
2472 rcu_segcblist_n_lazy_cbs(&rdp
->cblist
));
2473 rcu_segcblist_init(&rdp
->cblist
);
2475 rcu_segcblist_disable(&rdp
->cblist
);
2479 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
2481 static bool rcu_nocb_cpu_needs_barrier(struct rcu_state
*rsp
, int cpu
)
2483 WARN_ON_ONCE(1); /* Should be dead code. */
2487 static void rcu_nocb_gp_cleanup(struct swait_queue_head
*sq
)
2491 static void rcu_nocb_gp_set(struct rcu_node
*rnp
, int nrq
)
2495 static struct swait_queue_head
*rcu_nocb_gp_get(struct rcu_node
*rnp
)
2500 static void rcu_init_one_nocb(struct rcu_node
*rnp
)
2504 static bool __call_rcu_nocb(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
2505 bool lazy
, unsigned long flags
)
2510 static bool __maybe_unused
rcu_nocb_adopt_orphan_cbs(struct rcu_data
*my_rdp
,
2511 struct rcu_data
*rdp
,
2512 unsigned long flags
)
2517 static void __init
rcu_boot_init_nocb_percpu_data(struct rcu_data
*rdp
)
2521 static int rcu_nocb_need_deferred_wakeup(struct rcu_data
*rdp
)
2526 static void do_nocb_deferred_wakeup(struct rcu_data
*rdp
)
2530 static void rcu_spawn_all_nocb_kthreads(int cpu
)
2534 static void __init
rcu_spawn_nocb_kthreads(void)
2538 static bool init_nocb_callback_list(struct rcu_data
*rdp
)
2543 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2546 * An adaptive-ticks CPU can potentially execute in kernel mode for an
2547 * arbitrarily long period of time with the scheduling-clock tick turned
2548 * off. RCU will be paying attention to this CPU because it is in the
2549 * kernel, but the CPU cannot be guaranteed to be executing the RCU state
2550 * machine because the scheduling-clock tick has been disabled. Therefore,
2551 * if an adaptive-ticks CPU is failing to respond to the current grace
2552 * period and has not be idle from an RCU perspective, kick it.
2554 static void __maybe_unused
rcu_kick_nohz_cpu(int cpu
)
2556 #ifdef CONFIG_NO_HZ_FULL
2557 if (tick_nohz_full_cpu(cpu
))
2558 smp_send_reschedule(cpu
);
2559 #endif /* #ifdef CONFIG_NO_HZ_FULL */
2563 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
2564 * grace-period kthread will do force_quiescent_state() processing?
2565 * The idea is to avoid waking up RCU core processing on such a
2566 * CPU unless the grace period has extended for too long.
2568 * This code relies on the fact that all NO_HZ_FULL CPUs are also
2569 * CONFIG_RCU_NOCB_CPU CPUs.
2571 static bool rcu_nohz_full_cpu(struct rcu_state
*rsp
)
2573 #ifdef CONFIG_NO_HZ_FULL
2574 if (tick_nohz_full_cpu(smp_processor_id()) &&
2575 (!rcu_gp_in_progress(rsp
) ||
2576 ULONG_CMP_LT(jiffies
, READ_ONCE(rsp
->gp_start
) + HZ
)))
2578 #endif /* #ifdef CONFIG_NO_HZ_FULL */
2583 * Bind the grace-period kthread for the sysidle flavor of RCU to the
2586 static void rcu_bind_gp_kthread(void)
2588 int __maybe_unused cpu
;
2590 if (!tick_nohz_full_enabled())
2592 housekeeping_affine(current
, HK_FLAG_RCU
);
2595 /* Record the current task on dyntick-idle entry. */
2596 static void rcu_dynticks_task_enter(void)
2598 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2599 WRITE_ONCE(current
->rcu_tasks_idle_cpu
, smp_processor_id());
2600 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
2603 /* Record no current task on dyntick-idle exit. */
2604 static void rcu_dynticks_task_exit(void)
2606 #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2607 WRITE_ONCE(current
->rcu_tasks_idle_cpu
, -1);
2608 #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */