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[linux/fpc-iii.git] / kernel / rcu / tree_plugin.h
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1 /*
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",
79 RCU_FANOUT);
80 if (rcu_fanout_exact)
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",
90 RCU_FANOUT_LEAF);
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);
97 #endif
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);
114 if (gp_init_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,
130 bool wake);
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) {
194 case 0:
195 case RCU_EXP_TASKS:
196 case RCU_EXP_TASKS + RCU_GP_BLKD:
197 case RCU_GP_TASKS:
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);
207 break;
209 case RCU_EXP_BLKD:
210 case RCU_GP_BLKD:
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);
225 break;
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);
238 break;
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);
249 break;
251 default:
253 /* Yet another exercise in excessive paranoia. */
254 WARN_ON_ONCE(1);
255 break;
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
262 * blocked tasks.
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);
284 } else {
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),
304 TPS("cpuqs"));
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);
337 rnp = rdp->mynode;
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,
350 t->pid,
351 (rnp->qsmask & rdp->grpmask)
352 ? rnp->gpnum
353 : rnp->gpnum + 1);
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.
374 rcu_preempt_qs();
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)
398 np = NULL;
399 return np;
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)
418 bool empty_exp;
419 bool empty_norm;
420 bool empty_exp_now;
421 unsigned long flags;
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. */
429 if (in_nmi())
430 return;
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) {
441 rcu_preempt_qs();
442 t->rcu_read_unlock_special.b.need_qs = false;
443 if (!t->rcu_read_unlock_special.s) {
444 local_irq_restore(flags);
445 return;
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);
463 return;
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);
477 return;
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"),
501 rnp->gpnum, t->pid);
502 if (&t->rcu_node_entry == rnp->gp_tasks)
503 rnp->gp_tasks = np;
504 if (&t->rcu_node_entry == rnp->exp_tasks)
505 rnp->exp_tasks = np;
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"),
522 rnp->gpnum,
523 0, rnp->qsmask,
524 rnp->level,
525 rnp->grplo,
526 rnp->grphi,
527 !!rnp->gp_tasks);
528 rcu_report_unblock_qs_rnp(rcu_state_p, rnp, flags);
529 } else {
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);
543 } else {
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)
554 unsigned long flags;
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);
560 return;
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)
565 sched_show_task(t);
566 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
570 * Dump detailed information for all tasks blocking the current RCU
571 * grace period.
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)
590 pr_cont("\n");
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;
600 int ndetected = 0;
602 if (!rcu_preempt_blocked_readers_cgp(rnp))
603 return 0;
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);
609 ndetected++;
611 rcu_print_task_stall_end();
612 return ndetected;
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;
623 int ndetected = 0;
625 if (!rnp->exp_tasks)
626 return 0;
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);
631 ndetected++;
633 return ndetected;
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,
655 rcu_node_entry);
656 trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
657 rnp->gpnum, t->pid);
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) {
674 rcu_preempt_qs();
675 return;
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(),
703 * and may be nested.
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)
756 return;
757 if (rcu_gp_is_expedited())
758 synchronize_rcu_expedited();
759 else
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
790 * is enabled.
792 void exit_rcu(void)
794 struct task_struct *t = current;
796 if (likely(list_empty(&current->rcu_node_entry)))
797 return;
798 t->rcu_read_lock_nesting = 1;
799 barrier();
800 t->rcu_read_unlock_special.b.blocked = true;
801 __rcu_read_unlock();
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
827 * RCU readers.
829 static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
831 return 0;
835 * Because there is no preemptible RCU, there can be no readers blocked.
837 static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
839 return false;
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)
856 return 0;
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)
866 return 0;
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
881 * to check.
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)
893 rcu_barrier_sched();
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.
908 void exit_rcu(void)
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))
923 wake_up_process(t);
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
929 * ->blkd_tasks list.
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)
936 unsigned long flags;
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);
952 return 0;
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) {
962 tb = rnp->exp_tasks;
963 rnp->n_exp_boosts++;
964 } else {
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
984 * section.
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;
1003 int spincnt = 0;
1004 int more2boost;
1006 trace_rcu_utilization(TPS("Start boost kthread@init"));
1007 for (;;) {
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);
1014 if (more2boost)
1015 spincnt++;
1016 else
1017 spincnt = 0;
1018 if (spincnt > 10) {
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"));
1023 spincnt = 0;
1026 /* NOTREACHED */
1027 trace_rcu_utilization(TPS("End boost kthread@notreached"));
1028 return 0;
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);
1049 return;
1051 if (rnp->exp_tasks != NULL ||
1052 (rnp->gp_tasks != NULL &&
1053 rnp->boost_tasks == NULL &&
1054 rnp->qsmask == 0 &&
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;
1060 if (t)
1061 rcu_wake_cond(t, rnp->boost_kthread_status);
1062 } else {
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)
1117 return 0;
1119 if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
1120 return 0;
1122 rsp->boost = 1;
1123 if (rnp->boost_kthread_task != NULL)
1124 return 0;
1125 t = kthread_create(rcu_boost_kthread, (void *)rnp,
1126 "rcub/%d", rnp_index);
1127 if (IS_ERR(t))
1128 return PTR_ERR(t);
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. */
1135 return 0;
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);
1172 int spincnt;
1174 for (spincnt = 0; spincnt < 10; spincnt++) {
1175 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1176 local_bh_disable();
1177 *statusp = RCU_KTHREAD_RUNNING;
1178 this_cpu_inc(rcu_cpu_kthread_loops);
1179 local_irq_disable();
1180 work = *workp;
1181 *workp = 0;
1182 local_irq_enable();
1183 if (work)
1184 rcu_kthread_do_work();
1185 local_bh_enable();
1186 if (*workp == 0) {
1187 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1188 *statusp = RCU_KTHREAD_WAITING;
1189 return;
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);
1212 cpumask_var_t cm;
1213 int cpu;
1215 if (!t)
1216 return;
1217 if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1218 return;
1219 for_each_leaf_node_possible_cpu(rnp, cpu)
1220 if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
1221 cpu != outgoingcpu)
1222 cpumask_set_cpu(cpu, cm);
1223 if (cpumask_weight(cm) == 0)
1224 cpumask_setall(cm);
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;
1244 int cpu;
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)
1273 WARN_ON_ONCE(1);
1276 static bool rcu_is_callbacks_kthread(void)
1278 return false;
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
1318 * after it.
1320 static void rcu_cleanup_after_idle(void)
1325 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1326 * is nothing.
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)
1388 return false;
1389 rdtp->last_advance_all = jiffies;
1391 for_each_rcu_flavor(rsp) {
1392 rdp = this_cpu_ptr(rsp->rda);
1393 rnp = rdp->mynode;
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))
1406 cbs_ready = true;
1408 return cbs_ready;
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
1415 * callbacks.
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);
1422 unsigned long dj;
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;
1432 return 0;
1435 /* Attempt to advance callbacks. */
1436 if (rcu_try_advance_all_cbs()) {
1437 /* Some ready to invoke, so initiate later invocation. */
1438 invoke_rcu_core();
1439 return 1;
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;
1447 } else {
1448 dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1450 *nextevt = basemono + dj * TICK_NSEC;
1451 return 0;
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)
1466 bool needwake;
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;
1471 int tne;
1473 lockdep_assert_irqs_disabled();
1474 if (rcu_is_nocb_cpu(smp_processor_id()))
1475 return;
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;
1483 return;
1485 if (!tne)
1486 return;
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;
1497 invoke_rcu_core();
1498 return;
1502 * If we have not yet accelerated this jiffy, accelerate all
1503 * callbacks on this CPU.
1505 if (rdtp->last_accelerate == jiffies)
1506 return;
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))
1511 continue;
1512 rnp = rdp->mynode;
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. */
1516 if (needwake)
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()))
1530 return;
1531 if (rcu_try_advance_all_cbs())
1532 invoke_rcu_core();
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)
1595 int cpu;
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);
1615 return NOTIFY_OK;
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);
1625 return 0;
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,
1640 ulong2long(nlpd),
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)
1649 *cp = '\0';
1652 #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1654 /* Initiate the stall-info list. */
1655 static void print_cpu_stall_info_begin(void)
1657 pr_cont("\n");
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;
1678 char *ticks_title;
1679 unsigned long ticks_value;
1681 if (rsp->gpnum == rdp->gpnum) {
1682 ticks_title = "ticks this GP";
1683 ticks_value = rdp->ticks_this_gp;
1684 } else {
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",
1691 cpu,
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' :
1697 "!."[!delta],
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,
1703 fast_no_hz);
1706 /* Terminate the stall-info list. */
1707 static void print_cpu_stall_info_end(void)
1709 pr_err("\t");
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);
1757 return 1;
1759 __setup("rcu_nocbs=", rcu_nocb_setup);
1761 static int __init parse_rcu_nocb_poll(char *arg)
1763 rcu_nocb_poll = true;
1764 return 0;
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
1770 * grace period.
1772 static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
1774 swake_up_all(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);
1806 return false;
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);
1822 return;
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);
1831 } else {
1832 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1837 * Kick the leader kthread for this NOCB group, but caller has not
1838 * acquired locks.
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,
1853 const char *reason)
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
1867 * of rcu_barrier()?
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);
1872 unsigned long ret;
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);
1893 if (!rhp)
1894 rhp = READ_ONCE(rdp->nocb_gp_head);
1895 if (!rhp)
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",
1903 cpu, rhp->func);
1904 WARN_ON_ONCE(1);
1906 #endif /* #ifdef CONFIG_PROVE_RCU */
1908 return !!ret;
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)
1925 int len;
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"));
1942 return;
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,
1950 TPS("WakeEmpty"));
1951 } else {
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,
1961 TPS("WakeOvf"));
1962 } else {
1963 wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE,
1964 TPS("WakeOvfIsDeferred"));
1966 rdp->qlen_last_fqs_check = LONG_MAX / 2;
1967 } else {
1968 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
1970 return;
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
1977 * appropriately.
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))
1987 return false;
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));
1994 else
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()))
2007 invoke_rcu_core();
2009 return true;
2013 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2014 * not a no-CBs CPU.
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);
2029 return true;
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)
2038 unsigned long c;
2039 bool d;
2040 unsigned long flags;
2041 bool needwake;
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);
2047 if (needwake)
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"));
2055 for (;;) {
2056 swait_event_interruptible(
2057 rnp->nocb_gp_wq[c & 0x1],
2058 (d = ULONG_CMP_GE(READ_ONCE(rnp->completed), c)));
2059 if (likely(d))
2060 break;
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;
2076 bool gotcbs;
2077 struct rcu_data *rdp;
2078 struct rcu_head **tail;
2080 wait_again:
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.
2102 gotcbs = false;
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);
2112 gotcbs = true;
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);
2120 } else {
2121 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
2122 TPS("WokeEmpty"));
2124 goto wait_again;
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)
2156 goto wait_again;
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)
2165 for (;;) {
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. */
2171 return;
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)
2186 int c, cl;
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 */
2194 for (;;) {
2195 /* Wait for callbacks. */
2196 if (rdp->nocb_leader == rdp)
2197 nocb_leader_wait(rdp);
2198 else
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);
2208 BUG_ON(!list);
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);
2215 c = cl = 0;
2216 while (list) {
2217 next = list->next;
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,
2221 TPS("WaitQueue"));
2222 schedule_timeout_interruptible(1);
2223 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2224 TPS("WokeQueue"));
2225 next = list->next;
2227 debug_rcu_head_unqueue(list);
2228 local_bh_disable();
2229 if (__rcu_reclaim(rdp->rsp->name, list))
2230 cl++;
2231 c++;
2232 local_bh_enable();
2233 cond_resched_rcu_qs();
2234 list = next;
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;
2242 return 0;
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;
2255 int ndw;
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);
2260 return;
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)
2289 int cpu;
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");
2301 return;
2303 have_rcu_nocb_mask = true;
2305 if (!have_rcu_nocb_mask)
2306 return;
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,
2316 rcu_nocb_mask);
2318 pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
2319 cpumask_pr_args(rcu_nocb_mask));
2320 if (rcu_nocb_poll)
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)
2359 return;
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) {
2364 rdp_last = NULL;
2365 rdp = rdp_old_leader;
2366 do {
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;
2372 } else {
2373 rdp_last = rdp;
2374 rdp = rdp->nocb_next_follower;
2375 rdp_last->nocb_next_follower = NULL;
2377 } while (rdp);
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);
2384 BUG_ON(IS_ERR(t));
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)
2409 int cpu;
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)
2424 int cpu;
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)
2432 return;
2433 if (ls == -1) {
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;
2449 rdp_leader = rdp;
2450 } else {
2451 /* Another follower, link to previous leader. */
2452 rdp->nocb_leader = rdp_leader;
2453 rdp_prev->nocb_next_follower = rdp;
2455 rdp_prev = 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))
2463 return false;
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);
2476 return true;
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. */
2484 return false;
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)
2497 return NULL;
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)
2507 return false;
2510 static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
2511 struct rcu_data *rdp,
2512 unsigned long flags)
2514 return false;
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)
2523 return false;
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)
2540 return false;
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)))
2577 return true;
2578 #endif /* #ifdef CONFIG_NO_HZ_FULL */
2579 return false;
2583 * Bind the grace-period kthread for the sysidle flavor of RCU to the
2584 * timekeeping CPU.
2586 static void rcu_bind_gp_kthread(void)
2588 int __maybe_unused cpu;
2590 if (!tick_nohz_full_enabled())
2591 return;
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) */