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1/* SPDX-License-Identifier: GPL-2.0+ */
2/*
3 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
4 * Internal non-public definitions that provide either classic
5 * or preemptible semantics.
6 *
7 * Copyright Red Hat, 2009
8 * Copyright IBM Corporation, 2009
9 *
10 * Author: Ingo Molnar <mingo@elte.hu>
11 * Paul E. McKenney <paulmck@linux.ibm.com>
12 */
13
14#include "../locking/rtmutex_common.h"
15
16#ifdef CONFIG_RCU_NOCB_CPU
17static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
18static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
19#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
20
21/*
22 * Check the RCU kernel configuration parameters and print informative
23 * messages about anything out of the ordinary.
24 */
25static void __init rcu_bootup_announce_oddness(void)
26{
27 if (IS_ENABLED(CONFIG_RCU_TRACE))
28 pr_info("\tRCU event tracing is enabled.\n");
29 if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||
30 (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))
31 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d.\n",
32 RCU_FANOUT);
33 if (rcu_fanout_exact)
34 pr_info("\tHierarchical RCU autobalancing is disabled.\n");
35 if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ))
36 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
37 if (IS_ENABLED(CONFIG_PROVE_RCU))
38 pr_info("\tRCU lockdep checking is enabled.\n");
39 if (RCU_NUM_LVLS >= 4)
40 pr_info("\tFour(or more)-level hierarchy is enabled.\n");
41 if (RCU_FANOUT_LEAF != 16)
42 pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
43 RCU_FANOUT_LEAF);
44 if (rcu_fanout_leaf != RCU_FANOUT_LEAF)
45 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n",
46 rcu_fanout_leaf);
47 if (nr_cpu_ids != NR_CPUS)
48 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%u.\n", NR_CPUS, nr_cpu_ids);
49#ifdef CONFIG_RCU_BOOST
50 pr_info("\tRCU priority boosting: priority %d delay %d ms.\n",
51 kthread_prio, CONFIG_RCU_BOOST_DELAY);
52#endif
53 if (blimit != DEFAULT_RCU_BLIMIT)
54 pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit);
55 if (qhimark != DEFAULT_RCU_QHIMARK)
56 pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark);
57 if (qlowmark != DEFAULT_RCU_QLOMARK)
58 pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark);
59 if (jiffies_till_first_fqs != ULONG_MAX)
60 pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs);
61 if (jiffies_till_next_fqs != ULONG_MAX)
62 pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs);
63 if (jiffies_till_sched_qs != ULONG_MAX)
64 pr_info("\tBoot-time adjustment of scheduler-enlistment delay to %ld jiffies.\n", jiffies_till_sched_qs);
65 if (rcu_kick_kthreads)
66 pr_info("\tKick kthreads if too-long grace period.\n");
67 if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD))
68 pr_info("\tRCU callback double-/use-after-free debug enabled.\n");
69 if (gp_preinit_delay)
70 pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay);
71 if (gp_init_delay)
72 pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay);
73 if (gp_cleanup_delay)
74 pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay);
75 if (!use_softirq)
76 pr_info("\tRCU_SOFTIRQ processing moved to rcuc kthreads.\n");
77 if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))
78 pr_info("\tRCU debug extended QS entry/exit.\n");
79 rcupdate_announce_bootup_oddness();
80}
81
82#ifdef CONFIG_PREEMPT_RCU
83
84static void rcu_report_exp_rnp(struct rcu_node *rnp, bool wake);
85static void rcu_read_unlock_special(struct task_struct *t);
86
87/*
88 * Tell them what RCU they are running.
89 */
90static void __init rcu_bootup_announce(void)
91{
92 pr_info("Preemptible hierarchical RCU implementation.\n");
93 rcu_bootup_announce_oddness();
94}
95
96/* Flags for rcu_preempt_ctxt_queue() decision table. */
97#define RCU_GP_TASKS 0x8
98#define RCU_EXP_TASKS 0x4
99#define RCU_GP_BLKD 0x2
100#define RCU_EXP_BLKD 0x1
101
102/*
103 * Queues a task preempted within an RCU-preempt read-side critical
104 * section into the appropriate location within the ->blkd_tasks list,
105 * depending on the states of any ongoing normal and expedited grace
106 * periods. The ->gp_tasks pointer indicates which element the normal
107 * grace period is waiting on (NULL if none), and the ->exp_tasks pointer
108 * indicates which element the expedited grace period is waiting on (again,
109 * NULL if none). If a grace period is waiting on a given element in the
110 * ->blkd_tasks list, it also waits on all subsequent elements. Thus,
111 * adding a task to the tail of the list blocks any grace period that is
112 * already waiting on one of the elements. In contrast, adding a task
113 * to the head of the list won't block any grace period that is already
114 * waiting on one of the elements.
115 *
116 * This queuing is imprecise, and can sometimes make an ongoing grace
117 * period wait for a task that is not strictly speaking blocking it.
118 * Given the choice, we needlessly block a normal grace period rather than
119 * blocking an expedited grace period.
120 *
121 * Note that an endless sequence of expedited grace periods still cannot
122 * indefinitely postpone a normal grace period. Eventually, all of the
123 * fixed number of preempted tasks blocking the normal grace period that are
124 * not also blocking the expedited grace period will resume and complete
125 * their RCU read-side critical sections. At that point, the ->gp_tasks
126 * pointer will equal the ->exp_tasks pointer, at which point the end of
127 * the corresponding expedited grace period will also be the end of the
128 * normal grace period.
129 */
130static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
131 __releases(rnp->lock) /* But leaves rrupts disabled. */
132{
133 int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) +
134 (rnp->exp_tasks ? RCU_EXP_TASKS : 0) +
135 (rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) +
136 (rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0);
137 struct task_struct *t = current;
138
139 raw_lockdep_assert_held_rcu_node(rnp);
140 WARN_ON_ONCE(rdp->mynode != rnp);
141 WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
142 /* RCU better not be waiting on newly onlined CPUs! */
143 WARN_ON_ONCE(rnp->qsmaskinitnext & ~rnp->qsmaskinit & rnp->qsmask &
144 rdp->grpmask);
145
146 /*
147 * Decide where to queue the newly blocked task. In theory,
148 * this could be an if-statement. In practice, when I tried
149 * that, it was quite messy.
150 */
151 switch (blkd_state) {
152 case 0:
153 case RCU_EXP_TASKS:
154 case RCU_EXP_TASKS + RCU_GP_BLKD:
155 case RCU_GP_TASKS:
156 case RCU_GP_TASKS + RCU_EXP_TASKS:
157
158 /*
159 * Blocking neither GP, or first task blocking the normal
160 * GP but not blocking the already-waiting expedited GP.
161 * Queue at the head of the list to avoid unnecessarily
162 * blocking the already-waiting GPs.
163 */
164 list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
165 break;
166
167 case RCU_EXP_BLKD:
168 case RCU_GP_BLKD:
169 case RCU_GP_BLKD + RCU_EXP_BLKD:
170 case RCU_GP_TASKS + RCU_EXP_BLKD:
171 case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
172 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
173
174 /*
175 * First task arriving that blocks either GP, or first task
176 * arriving that blocks the expedited GP (with the normal
177 * GP already waiting), or a task arriving that blocks
178 * both GPs with both GPs already waiting. Queue at the
179 * tail of the list to avoid any GP waiting on any of the
180 * already queued tasks that are not blocking it.
181 */
182 list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);
183 break;
184
185 case RCU_EXP_TASKS + RCU_EXP_BLKD:
186 case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
187 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD:
188
189 /*
190 * Second or subsequent task blocking the expedited GP.
191 * The task either does not block the normal GP, or is the
192 * first task blocking the normal GP. Queue just after
193 * the first task blocking the expedited GP.
194 */
195 list_add(&t->rcu_node_entry, rnp->exp_tasks);
196 break;
197
198 case RCU_GP_TASKS + RCU_GP_BLKD:
199 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD:
200
201 /*
202 * Second or subsequent task blocking the normal GP.
203 * The task does not block the expedited GP. Queue just
204 * after the first task blocking the normal GP.
205 */
206 list_add(&t->rcu_node_entry, rnp->gp_tasks);
207 break;
208
209 default:
210
211 /* Yet another exercise in excessive paranoia. */
212 WARN_ON_ONCE(1);
213 break;
214 }
215
216 /*
217 * We have now queued the task. If it was the first one to
218 * block either grace period, update the ->gp_tasks and/or
219 * ->exp_tasks pointers, respectively, to reference the newly
220 * blocked tasks.
221 */
222 if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) {
223 rnp->gp_tasks = &t->rcu_node_entry;
224 WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq);
225 }
226 if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
227 rnp->exp_tasks = &t->rcu_node_entry;
228 WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=
229 !(rnp->qsmask & rdp->grpmask));
230 WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) !=
231 !(rnp->expmask & rdp->grpmask));
232 raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */
233
234 /*
235 * Report the quiescent state for the expedited GP. This expedited
236 * GP should not be able to end until we report, so there should be
237 * no need to check for a subsequent expedited GP. (Though we are
238 * still in a quiescent state in any case.)
239 */
240 if (blkd_state & RCU_EXP_BLKD && rdp->exp_deferred_qs)
241 rcu_report_exp_rdp(rdp);
242 else
243 WARN_ON_ONCE(rdp->exp_deferred_qs);
244}
245
246/*
247 * Record a preemptible-RCU quiescent state for the specified CPU.
248 * Note that this does not necessarily mean that the task currently running
249 * on the CPU is in a quiescent state: Instead, it means that the current
250 * grace period need not wait on any RCU read-side critical section that
251 * starts later on this CPU. It also means that if the current task is
252 * in an RCU read-side critical section, it has already added itself to
253 * some leaf rcu_node structure's ->blkd_tasks list. In addition to the
254 * current task, there might be any number of other tasks blocked while
255 * in an RCU read-side critical section.
256 *
257 * Callers to this function must disable preemption.
258 */
259static void rcu_qs(void)
260{
261 RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n");
262 if (__this_cpu_read(rcu_data.cpu_no_qs.s)) {
263 trace_rcu_grace_period(TPS("rcu_preempt"),
264 __this_cpu_read(rcu_data.gp_seq),
265 TPS("cpuqs"));
266 __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
267 barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */
268 WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, false);
269 }
270}
271
272/*
273 * We have entered the scheduler, and the current task might soon be
274 * context-switched away from. If this task is in an RCU read-side
275 * critical section, we will no longer be able to rely on the CPU to
276 * record that fact, so we enqueue the task on the blkd_tasks list.
277 * The task will dequeue itself when it exits the outermost enclosing
278 * RCU read-side critical section. Therefore, the current grace period
279 * cannot be permitted to complete until the blkd_tasks list entries
280 * predating the current grace period drain, in other words, until
281 * rnp->gp_tasks becomes NULL.
282 *
283 * Caller must disable interrupts.
284 */
285void rcu_note_context_switch(bool preempt)
286{
287 struct task_struct *t = current;
288 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
289 struct rcu_node *rnp;
290
291 trace_rcu_utilization(TPS("Start context switch"));
292 lockdep_assert_irqs_disabled();
293 WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0);
294 if (t->rcu_read_lock_nesting > 0 &&
295 !t->rcu_read_unlock_special.b.blocked) {
296
297 /* Possibly blocking in an RCU read-side critical section. */
298 rnp = rdp->mynode;
299 raw_spin_lock_rcu_node(rnp);
300 t->rcu_read_unlock_special.b.blocked = true;
301 t->rcu_blocked_node = rnp;
302
303 /*
304 * Verify the CPU's sanity, trace the preemption, and
305 * then queue the task as required based on the states
306 * of any ongoing and expedited grace periods.
307 */
308 WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);
309 WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
310 trace_rcu_preempt_task(rcu_state.name,
311 t->pid,
312 (rnp->qsmask & rdp->grpmask)
313 ? rnp->gp_seq
314 : rcu_seq_snap(&rnp->gp_seq));
315 rcu_preempt_ctxt_queue(rnp, rdp);
316 } else {
317 rcu_preempt_deferred_qs(t);
318 }
319
320 /*
321 * Either we were not in an RCU read-side critical section to
322 * begin with, or we have now recorded that critical section
323 * globally. Either way, we can now note a quiescent state
324 * for this CPU. Again, if we were in an RCU read-side critical
325 * section, and if that critical section was blocking the current
326 * grace period, then the fact that the task has been enqueued
327 * means that we continue to block the current grace period.
328 */
329 rcu_qs();
330 if (rdp->exp_deferred_qs)
331 rcu_report_exp_rdp(rdp);
332 trace_rcu_utilization(TPS("End context switch"));
333}
334EXPORT_SYMBOL_GPL(rcu_note_context_switch);
335
336/*
337 * Check for preempted RCU readers blocking the current grace period
338 * for the specified rcu_node structure. If the caller needs a reliable
339 * answer, it must hold the rcu_node's ->lock.
340 */
341static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
342{
343 return rnp->gp_tasks != NULL;
344}
345
346/* Bias and limit values for ->rcu_read_lock_nesting. */
347#define RCU_NEST_BIAS INT_MAX
348#define RCU_NEST_NMAX (-INT_MAX / 2)
349#define RCU_NEST_PMAX (INT_MAX / 2)
350
351/*
352 * Preemptible RCU implementation for rcu_read_lock().
353 * Just increment ->rcu_read_lock_nesting, shared state will be updated
354 * if we block.
355 */
356void __rcu_read_lock(void)
357{
358 current->rcu_read_lock_nesting++;
359 if (IS_ENABLED(CONFIG_PROVE_LOCKING))
360 WARN_ON_ONCE(current->rcu_read_lock_nesting > RCU_NEST_PMAX);
361 barrier(); /* critical section after entry code. */
362}
363EXPORT_SYMBOL_GPL(__rcu_read_lock);
364
365/*
366 * Preemptible RCU implementation for rcu_read_unlock().
367 * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
368 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
369 * invoke rcu_read_unlock_special() to clean up after a context switch
370 * in an RCU read-side critical section and other special cases.
371 */
372void __rcu_read_unlock(void)
373{
374 struct task_struct *t = current;
375
376 if (t->rcu_read_lock_nesting != 1) {
377 --t->rcu_read_lock_nesting;
378 } else {
379 barrier(); /* critical section before exit code. */
380 t->rcu_read_lock_nesting = -RCU_NEST_BIAS;
381 barrier(); /* assign before ->rcu_read_unlock_special load */
382 if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
383 rcu_read_unlock_special(t);
384 barrier(); /* ->rcu_read_unlock_special load before assign */
385 t->rcu_read_lock_nesting = 0;
386 }
387 if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
388 int rrln = t->rcu_read_lock_nesting;
389
390 WARN_ON_ONCE(rrln < 0 && rrln > RCU_NEST_NMAX);
391 }
392}
393EXPORT_SYMBOL_GPL(__rcu_read_unlock);
394
395/*
396 * Advance a ->blkd_tasks-list pointer to the next entry, instead
397 * returning NULL if at the end of the list.
398 */
399static struct list_head *rcu_next_node_entry(struct task_struct *t,
400 struct rcu_node *rnp)
401{
402 struct list_head *np;
403
404 np = t->rcu_node_entry.next;
405 if (np == &rnp->blkd_tasks)
406 np = NULL;
407 return np;
408}
409
410/*
411 * Return true if the specified rcu_node structure has tasks that were
412 * preempted within an RCU read-side critical section.
413 */
414static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
415{
416 return !list_empty(&rnp->blkd_tasks);
417}
418
419/*
420 * Report deferred quiescent states. The deferral time can
421 * be quite short, for example, in the case of the call from
422 * rcu_read_unlock_special().
423 */
424static void
425rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
426{
427 bool empty_exp;
428 bool empty_norm;
429 bool empty_exp_now;
430 struct list_head *np;
431 bool drop_boost_mutex = false;
432 struct rcu_data *rdp;
433 struct rcu_node *rnp;
434 union rcu_special special;
435
436 /*
437 * If RCU core is waiting for this CPU to exit its critical section,
438 * report the fact that it has exited. Because irqs are disabled,
439 * t->rcu_read_unlock_special cannot change.
440 */
441 special = t->rcu_read_unlock_special;
442 rdp = this_cpu_ptr(&rcu_data);
443 if (!special.s && !rdp->exp_deferred_qs) {
444 local_irq_restore(flags);
445 return;
446 }
447 t->rcu_read_unlock_special.b.deferred_qs = false;
448 if (special.b.need_qs) {
449 rcu_qs();
450 t->rcu_read_unlock_special.b.need_qs = false;
451 if (!t->rcu_read_unlock_special.s && !rdp->exp_deferred_qs) {
452 local_irq_restore(flags);
453 return;
454 }
455 }
456
457 /*
458 * Respond to a request by an expedited grace period for a
459 * quiescent state from this CPU. Note that requests from
460 * tasks are handled when removing the task from the
461 * blocked-tasks list below.
462 */
463 if (rdp->exp_deferred_qs) {
464 rcu_report_exp_rdp(rdp);
465 if (!t->rcu_read_unlock_special.s) {
466 local_irq_restore(flags);
467 return;
468 }
469 }
470
471 /* Clean up if blocked during RCU read-side critical section. */
472 if (special.b.blocked) {
473 t->rcu_read_unlock_special.b.blocked = false;
474
475 /*
476 * Remove this task from the list it blocked on. The task
477 * now remains queued on the rcu_node corresponding to the
478 * CPU it first blocked on, so there is no longer any need
479 * to loop. Retain a WARN_ON_ONCE() out of sheer paranoia.
480 */
481 rnp = t->rcu_blocked_node;
482 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
483 WARN_ON_ONCE(rnp != t->rcu_blocked_node);
484 WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
485 empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
486 WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq &&
487 (!empty_norm || rnp->qsmask));
488 empty_exp = sync_rcu_preempt_exp_done(rnp);
489 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
490 np = rcu_next_node_entry(t, rnp);
491 list_del_init(&t->rcu_node_entry);
492 t->rcu_blocked_node = NULL;
493 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
494 rnp->gp_seq, t->pid);
495 if (&t->rcu_node_entry == rnp->gp_tasks)
496 rnp->gp_tasks = np;
497 if (&t->rcu_node_entry == rnp->exp_tasks)
498 rnp->exp_tasks = np;
499 if (IS_ENABLED(CONFIG_RCU_BOOST)) {
500 /* Snapshot ->boost_mtx ownership w/rnp->lock held. */
501 drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
502 if (&t->rcu_node_entry == rnp->boost_tasks)
503 rnp->boost_tasks = np;
504 }
505
506 /*
507 * If this was the last task on the current list, and if
508 * we aren't waiting on any CPUs, report the quiescent state.
509 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
510 * so we must take a snapshot of the expedited state.
511 */
512 empty_exp_now = sync_rcu_preempt_exp_done(rnp);
513 if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
514 trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
515 rnp->gp_seq,
516 0, rnp->qsmask,
517 rnp->level,
518 rnp->grplo,
519 rnp->grphi,
520 !!rnp->gp_tasks);
521 rcu_report_unblock_qs_rnp(rnp, flags);
522 } else {
523 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
524 }
525
526 /* Unboost if we were boosted. */
527 if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
528 rt_mutex_futex_unlock(&rnp->boost_mtx);
529
530 /*
531 * If this was the last task on the expedited lists,
532 * then we need to report up the rcu_node hierarchy.
533 */
534 if (!empty_exp && empty_exp_now)
535 rcu_report_exp_rnp(rnp, true);
536 } else {
537 local_irq_restore(flags);
538 }
539}
540
541/*
542 * Is a deferred quiescent-state pending, and are we also not in
543 * an RCU read-side critical section? It is the caller's responsibility
544 * to ensure it is otherwise safe to report any deferred quiescent
545 * states. The reason for this is that it is safe to report a
546 * quiescent state during context switch even though preemption
547 * is disabled. This function cannot be expected to understand these
548 * nuances, so the caller must handle them.
549 */
550static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
551{
552 return (__this_cpu_read(rcu_data.exp_deferred_qs) ||
553 READ_ONCE(t->rcu_read_unlock_special.s)) &&
554 t->rcu_read_lock_nesting <= 0;
555}
556
557/*
558 * Report a deferred quiescent state if needed and safe to do so.
559 * As with rcu_preempt_need_deferred_qs(), "safe" involves only
560 * not being in an RCU read-side critical section. The caller must
561 * evaluate safety in terms of interrupt, softirq, and preemption
562 * disabling.
563 */
564static void rcu_preempt_deferred_qs(struct task_struct *t)
565{
566 unsigned long flags;
567 bool couldrecurse = t->rcu_read_lock_nesting >= 0;
568
569 if (!rcu_preempt_need_deferred_qs(t))
570 return;
571 if (couldrecurse)
572 t->rcu_read_lock_nesting -= RCU_NEST_BIAS;
573 local_irq_save(flags);
574 rcu_preempt_deferred_qs_irqrestore(t, flags);
575 if (couldrecurse)
576 t->rcu_read_lock_nesting += RCU_NEST_BIAS;
577}
578
579/*
580 * Minimal handler to give the scheduler a chance to re-evaluate.
581 */
582static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp)
583{
584 struct rcu_data *rdp;
585
586 rdp = container_of(iwp, struct rcu_data, defer_qs_iw);
587 rdp->defer_qs_iw_pending = false;
588}
589
590/*
591 * Handle special cases during rcu_read_unlock(), such as needing to
592 * notify RCU core processing or task having blocked during the RCU
593 * read-side critical section.
594 */
595static void rcu_read_unlock_special(struct task_struct *t)
596{
597 unsigned long flags;
598 bool preempt_bh_were_disabled =
599 !!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK));
600 bool irqs_were_disabled;
601
602 /* NMI handlers cannot block and cannot safely manipulate state. */
603 if (in_nmi())
604 return;
605
606 local_irq_save(flags);
607 irqs_were_disabled = irqs_disabled_flags(flags);
608 if (preempt_bh_were_disabled || irqs_were_disabled) {
609 bool exp;
610 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
611 struct rcu_node *rnp = rdp->mynode;
612
613 t->rcu_read_unlock_special.b.exp_hint = false;
614 exp = (t->rcu_blocked_node && t->rcu_blocked_node->exp_tasks) ||
615 (rdp->grpmask & rnp->expmask) ||
616 tick_nohz_full_cpu(rdp->cpu);
617 // Need to defer quiescent state until everything is enabled.
618 if (irqs_were_disabled && use_softirq &&
619 (in_interrupt() ||
620 (exp && !t->rcu_read_unlock_special.b.deferred_qs))) {
621 // Using softirq, safe to awaken, and we get
622 // no help from enabling irqs, unlike bh/preempt.
623 raise_softirq_irqoff(RCU_SOFTIRQ);
624 } else {
625 // Enabling BH or preempt does reschedule, so...
626 // Also if no expediting or NO_HZ_FULL, slow is OK.
627 set_tsk_need_resched(current);
628 set_preempt_need_resched();
629 if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled &&
630 !rdp->defer_qs_iw_pending && exp) {
631 // Get scheduler to re-evaluate and call hooks.
632 // If !IRQ_WORK, FQS scan will eventually IPI.
633 init_irq_work(&rdp->defer_qs_iw,
634 rcu_preempt_deferred_qs_handler);
635 rdp->defer_qs_iw_pending = true;
636 irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
637 }
638 }
639 t->rcu_read_unlock_special.b.deferred_qs = true;
640 local_irq_restore(flags);
641 return;
642 }
643 WRITE_ONCE(t->rcu_read_unlock_special.b.exp_hint, false);
644 rcu_preempt_deferred_qs_irqrestore(t, flags);
645}
646
647/*
648 * Check that the list of blocked tasks for the newly completed grace
649 * period is in fact empty. It is a serious bug to complete a grace
650 * period that still has RCU readers blocked! This function must be
651 * invoked -before- updating this rnp's ->gp_seq, and the rnp's ->lock
652 * must be held by the caller.
653 *
654 * Also, if there are blocked tasks on the list, they automatically
655 * block the newly created grace period, so set up ->gp_tasks accordingly.
656 */
657static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
658{
659 struct task_struct *t;
660
661 RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
662 if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
663 dump_blkd_tasks(rnp, 10);
664 if (rcu_preempt_has_tasks(rnp) &&
665 (rnp->qsmaskinit || rnp->wait_blkd_tasks)) {
666 rnp->gp_tasks = rnp->blkd_tasks.next;
667 t = container_of(rnp->gp_tasks, struct task_struct,
668 rcu_node_entry);
669 trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
670 rnp->gp_seq, t->pid);
671 }
672 WARN_ON_ONCE(rnp->qsmask);
673}
674
675/*
676 * Check for a quiescent state from the current CPU, including voluntary
677 * context switches for Tasks RCU. When a task blocks, the task is
678 * recorded in the corresponding CPU's rcu_node structure, which is checked
679 * elsewhere, hence this function need only check for quiescent states
680 * related to the current CPU, not to those related to tasks.
681 */
682static void rcu_flavor_sched_clock_irq(int user)
683{
684 struct task_struct *t = current;
685
686 if (user || rcu_is_cpu_rrupt_from_idle()) {
687 rcu_note_voluntary_context_switch(current);
688 }
689 if (t->rcu_read_lock_nesting > 0 ||
690 (preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) {
691 /* No QS, force context switch if deferred. */
692 if (rcu_preempt_need_deferred_qs(t)) {
693 set_tsk_need_resched(t);
694 set_preempt_need_resched();
695 }
696 } else if (rcu_preempt_need_deferred_qs(t)) {
697 rcu_preempt_deferred_qs(t); /* Report deferred QS. */
698 return;
699 } else if (!t->rcu_read_lock_nesting) {
700 rcu_qs(); /* Report immediate QS. */
701 return;
702 }
703
704 /* If GP is oldish, ask for help from rcu_read_unlock_special(). */
705 if (t->rcu_read_lock_nesting > 0 &&
706 __this_cpu_read(rcu_data.core_needs_qs) &&
707 __this_cpu_read(rcu_data.cpu_no_qs.b.norm) &&
708 !t->rcu_read_unlock_special.b.need_qs &&
709 time_after(jiffies, rcu_state.gp_start + HZ))
710 t->rcu_read_unlock_special.b.need_qs = true;
711}
712
713/*
714 * Check for a task exiting while in a preemptible-RCU read-side
715 * critical section, clean up if so. No need to issue warnings, as
716 * debug_check_no_locks_held() already does this if lockdep is enabled.
717 * Besides, if this function does anything other than just immediately
718 * return, there was a bug of some sort. Spewing warnings from this
719 * function is like as not to simply obscure important prior warnings.
720 */
721void exit_rcu(void)
722{
723 struct task_struct *t = current;
724
725 if (unlikely(!list_empty(¤t->rcu_node_entry))) {
726 t->rcu_read_lock_nesting = 1;
727 barrier();
728 WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true);
729 } else if (unlikely(t->rcu_read_lock_nesting)) {
730 t->rcu_read_lock_nesting = 1;
731 } else {
732 return;
733 }
734 __rcu_read_unlock();
735 rcu_preempt_deferred_qs(current);
736}
737
738/*
739 * Dump the blocked-tasks state, but limit the list dump to the
740 * specified number of elements.
741 */
742static void
743dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
744{
745 int cpu;
746 int i;
747 struct list_head *lhp;
748 bool onl;
749 struct rcu_data *rdp;
750 struct rcu_node *rnp1;
751
752 raw_lockdep_assert_held_rcu_node(rnp);
753 pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
754 __func__, rnp->grplo, rnp->grphi, rnp->level,
755 (long)rnp->gp_seq, (long)rnp->completedqs);
756 for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
757 pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n",
758 __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext);
759 pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n",
760 __func__, rnp->gp_tasks, rnp->boost_tasks, rnp->exp_tasks);
761 pr_info("%s: ->blkd_tasks", __func__);
762 i = 0;
763 list_for_each(lhp, &rnp->blkd_tasks) {
764 pr_cont(" %p", lhp);
765 if (++i >= ncheck)
766 break;
767 }
768 pr_cont("\n");
769 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
770 rdp = per_cpu_ptr(&rcu_data, cpu);
771 onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
772 pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n",
773 cpu, ".o"[onl],
774 (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
775 (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
776 }
777}
778
779#else /* #ifdef CONFIG_PREEMPT_RCU */
780
781/*
782 * Tell them what RCU they are running.
783 */
784static void __init rcu_bootup_announce(void)
785{
786 pr_info("Hierarchical RCU implementation.\n");
787 rcu_bootup_announce_oddness();
788}
789
790/*
791 * Note a quiescent state for PREEMPT=n. Because we do not need to know
792 * how many quiescent states passed, just if there was at least one since
793 * the start of the grace period, this just sets a flag. The caller must
794 * have disabled preemption.
795 */
796static void rcu_qs(void)
797{
798 RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!");
799 if (!__this_cpu_read(rcu_data.cpu_no_qs.s))
800 return;
801 trace_rcu_grace_period(TPS("rcu_sched"),
802 __this_cpu_read(rcu_data.gp_seq), TPS("cpuqs"));
803 __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
804 if (!__this_cpu_read(rcu_data.cpu_no_qs.b.exp))
805 return;
806 __this_cpu_write(rcu_data.cpu_no_qs.b.exp, false);
807 rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
808}
809
810/*
811 * Register an urgently needed quiescent state. If there is an
812 * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
813 * dyntick-idle quiescent state visible to other CPUs, which will in
814 * some cases serve for expedited as well as normal grace periods.
815 * Either way, register a lightweight quiescent state.
816 */
817void rcu_all_qs(void)
818{
819 unsigned long flags;
820
821 if (!raw_cpu_read(rcu_data.rcu_urgent_qs))
822 return;
823 preempt_disable();
824 /* Load rcu_urgent_qs before other flags. */
825 if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
826 preempt_enable();
827 return;
828 }
829 this_cpu_write(rcu_data.rcu_urgent_qs, false);
830 if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) {
831 local_irq_save(flags);
832 rcu_momentary_dyntick_idle();
833 local_irq_restore(flags);
834 }
835 rcu_qs();
836 preempt_enable();
837}
838EXPORT_SYMBOL_GPL(rcu_all_qs);
839
840/*
841 * Note a PREEMPT=n context switch. The caller must have disabled interrupts.
842 */
843void rcu_note_context_switch(bool preempt)
844{
845 trace_rcu_utilization(TPS("Start context switch"));
846 rcu_qs();
847 /* Load rcu_urgent_qs before other flags. */
848 if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs)))
849 goto out;
850 this_cpu_write(rcu_data.rcu_urgent_qs, false);
851 if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs)))
852 rcu_momentary_dyntick_idle();
853 if (!preempt)
854 rcu_tasks_qs(current);
855out:
856 trace_rcu_utilization(TPS("End context switch"));
857}
858EXPORT_SYMBOL_GPL(rcu_note_context_switch);
859
860/*
861 * Because preemptible RCU does not exist, there are never any preempted
862 * RCU readers.
863 */
864static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
865{
866 return 0;
867}
868
869/*
870 * Because there is no preemptible RCU, there can be no readers blocked.
871 */
872static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
873{
874 return false;
875}
876
877/*
878 * Because there is no preemptible RCU, there can be no deferred quiescent
879 * states.
880 */
881static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
882{
883 return false;
884}
885static void rcu_preempt_deferred_qs(struct task_struct *t) { }
886
887/*
888 * Because there is no preemptible RCU, there can be no readers blocked,
889 * so there is no need to check for blocked tasks. So check only for
890 * bogus qsmask values.
891 */
892static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
893{
894 WARN_ON_ONCE(rnp->qsmask);
895}
896
897/*
898 * Check to see if this CPU is in a non-context-switch quiescent state,
899 * namely user mode and idle loop.
900 */
901static void rcu_flavor_sched_clock_irq(int user)
902{
903 if (user || rcu_is_cpu_rrupt_from_idle()) {
904
905 /*
906 * Get here if this CPU took its interrupt from user
907 * mode or from the idle loop, and if this is not a
908 * nested interrupt. In this case, the CPU is in
909 * a quiescent state, so note it.
910 *
911 * No memory barrier is required here because rcu_qs()
912 * references only CPU-local variables that other CPUs
913 * neither access nor modify, at least not while the
914 * corresponding CPU is online.
915 */
916
917 rcu_qs();
918 }
919}
920
921/*
922 * Because preemptible RCU does not exist, tasks cannot possibly exit
923 * while in preemptible RCU read-side critical sections.
924 */
925void exit_rcu(void)
926{
927}
928
929/*
930 * Dump the guaranteed-empty blocked-tasks state. Trust but verify.
931 */
932static void
933dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
934{
935 WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));
936}
937
938#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
939
940/*
941 * If boosting, set rcuc kthreads to realtime priority.
942 */
943static void rcu_cpu_kthread_setup(unsigned int cpu)
944{
945#ifdef CONFIG_RCU_BOOST
946 struct sched_param sp;
947
948 sp.sched_priority = kthread_prio;
949 sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
950#endif /* #ifdef CONFIG_RCU_BOOST */
951}
952
953#ifdef CONFIG_RCU_BOOST
954
955/*
956 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
957 * or ->boost_tasks, advancing the pointer to the next task in the
958 * ->blkd_tasks list.
959 *
960 * Note that irqs must be enabled: boosting the task can block.
961 * Returns 1 if there are more tasks needing to be boosted.
962 */
963static int rcu_boost(struct rcu_node *rnp)
964{
965 unsigned long flags;
966 struct task_struct *t;
967 struct list_head *tb;
968
969 if (READ_ONCE(rnp->exp_tasks) == NULL &&
970 READ_ONCE(rnp->boost_tasks) == NULL)
971 return 0; /* Nothing left to boost. */
972
973 raw_spin_lock_irqsave_rcu_node(rnp, flags);
974
975 /*
976 * Recheck under the lock: all tasks in need of boosting
977 * might exit their RCU read-side critical sections on their own.
978 */
979 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
980 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
981 return 0;
982 }
983
984 /*
985 * Preferentially boost tasks blocking expedited grace periods.
986 * This cannot starve the normal grace periods because a second
987 * expedited grace period must boost all blocked tasks, including
988 * those blocking the pre-existing normal grace period.
989 */
990 if (rnp->exp_tasks != NULL)
991 tb = rnp->exp_tasks;
992 else
993 tb = rnp->boost_tasks;
994
995 /*
996 * We boost task t by manufacturing an rt_mutex that appears to
997 * be held by task t. We leave a pointer to that rt_mutex where
998 * task t can find it, and task t will release the mutex when it
999 * exits its outermost RCU read-side critical section. Then
1000 * simply acquiring this artificial rt_mutex will boost task
1001 * t's priority. (Thanks to tglx for suggesting this approach!)
1002 *
1003 * Note that task t must acquire rnp->lock to remove itself from
1004 * the ->blkd_tasks list, which it will do from exit() if from
1005 * nowhere else. We therefore are guaranteed that task t will
1006 * stay around at least until we drop rnp->lock. Note that
1007 * rnp->lock also resolves races between our priority boosting
1008 * and task t's exiting its outermost RCU read-side critical
1009 * section.
1010 */
1011 t = container_of(tb, struct task_struct, rcu_node_entry);
1012 rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
1013 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1014 /* Lock only for side effect: boosts task t's priority. */
1015 rt_mutex_lock(&rnp->boost_mtx);
1016 rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
1017
1018 return READ_ONCE(rnp->exp_tasks) != NULL ||
1019 READ_ONCE(rnp->boost_tasks) != NULL;
1020}
1021
1022/*
1023 * Priority-boosting kthread, one per leaf rcu_node.
1024 */
1025static int rcu_boost_kthread(void *arg)
1026{
1027 struct rcu_node *rnp = (struct rcu_node *)arg;
1028 int spincnt = 0;
1029 int more2boost;
1030
1031 trace_rcu_utilization(TPS("Start boost kthread@init"));
1032 for (;;) {
1033 rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1034 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1035 rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1036 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1037 rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1038 more2boost = rcu_boost(rnp);
1039 if (more2boost)
1040 spincnt++;
1041 else
1042 spincnt = 0;
1043 if (spincnt > 10) {
1044 rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1045 trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1046 schedule_timeout_interruptible(2);
1047 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1048 spincnt = 0;
1049 }
1050 }
1051 /* NOTREACHED */
1052 trace_rcu_utilization(TPS("End boost kthread@notreached"));
1053 return 0;
1054}
1055
1056/*
1057 * Check to see if it is time to start boosting RCU readers that are
1058 * blocking the current grace period, and, if so, tell the per-rcu_node
1059 * kthread to start boosting them. If there is an expedited grace
1060 * period in progress, it is always time to boost.
1061 *
1062 * The caller must hold rnp->lock, which this function releases.
1063 * The ->boost_kthread_task is immortal, so we don't need to worry
1064 * about it going away.
1065 */
1066static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1067 __releases(rnp->lock)
1068{
1069 raw_lockdep_assert_held_rcu_node(rnp);
1070 if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1071 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1072 return;
1073 }
1074 if (rnp->exp_tasks != NULL ||
1075 (rnp->gp_tasks != NULL &&
1076 rnp->boost_tasks == NULL &&
1077 rnp->qsmask == 0 &&
1078 ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1079 if (rnp->exp_tasks == NULL)
1080 rnp->boost_tasks = rnp->gp_tasks;
1081 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1082 rcu_wake_cond(rnp->boost_kthread_task,
1083 rnp->boost_kthread_status);
1084 } else {
1085 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1086 }
1087}
1088
1089/*
1090 * Is the current CPU running the RCU-callbacks kthread?
1091 * Caller must have preemption disabled.
1092 */
1093static bool rcu_is_callbacks_kthread(void)
1094{
1095 return __this_cpu_read(rcu_data.rcu_cpu_kthread_task) == current;
1096}
1097
1098#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1099
1100/*
1101 * Do priority-boost accounting for the start of a new grace period.
1102 */
1103static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1104{
1105 rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1106}
1107
1108/*
1109 * Create an RCU-boost kthread for the specified node if one does not
1110 * already exist. We only create this kthread for preemptible RCU.
1111 * Returns zero if all is well, a negated errno otherwise.
1112 */
1113static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
1114{
1115 int rnp_index = rnp - rcu_get_root();
1116 unsigned long flags;
1117 struct sched_param sp;
1118 struct task_struct *t;
1119
1120 if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
1121 return;
1122
1123 if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
1124 return;
1125
1126 rcu_state.boost = 1;
1127
1128 if (rnp->boost_kthread_task != NULL)
1129 return;
1130
1131 t = kthread_create(rcu_boost_kthread, (void *)rnp,
1132 "rcub/%d", rnp_index);
1133 if (WARN_ON_ONCE(IS_ERR(t)))
1134 return;
1135
1136 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1137 rnp->boost_kthread_task = t;
1138 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1139 sp.sched_priority = kthread_prio;
1140 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1141 wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1142}
1143
1144/*
1145 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1146 * served by the rcu_node in question. The CPU hotplug lock is still
1147 * held, so the value of rnp->qsmaskinit will be stable.
1148 *
1149 * We don't include outgoingcpu in the affinity set, use -1 if there is
1150 * no outgoing CPU. If there are no CPUs left in the affinity set,
1151 * this function allows the kthread to execute on any CPU.
1152 */
1153static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1154{
1155 struct task_struct *t = rnp->boost_kthread_task;
1156 unsigned long mask = rcu_rnp_online_cpus(rnp);
1157 cpumask_var_t cm;
1158 int cpu;
1159
1160 if (!t)
1161 return;
1162 if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1163 return;
1164 for_each_leaf_node_possible_cpu(rnp, cpu)
1165 if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
1166 cpu != outgoingcpu)
1167 cpumask_set_cpu(cpu, cm);
1168 if (cpumask_weight(cm) == 0)
1169 cpumask_setall(cm);
1170 set_cpus_allowed_ptr(t, cm);
1171 free_cpumask_var(cm);
1172}
1173
1174/*
1175 * Spawn boost kthreads -- called as soon as the scheduler is running.
1176 */
1177static void __init rcu_spawn_boost_kthreads(void)
1178{
1179 struct rcu_node *rnp;
1180
1181 rcu_for_each_leaf_node(rnp)
1182 rcu_spawn_one_boost_kthread(rnp);
1183}
1184
1185static void rcu_prepare_kthreads(int cpu)
1186{
1187 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
1188 struct rcu_node *rnp = rdp->mynode;
1189
1190 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1191 if (rcu_scheduler_fully_active)
1192 rcu_spawn_one_boost_kthread(rnp);
1193}
1194
1195#else /* #ifdef CONFIG_RCU_BOOST */
1196
1197static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1198 __releases(rnp->lock)
1199{
1200 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1201}
1202
1203static bool rcu_is_callbacks_kthread(void)
1204{
1205 return false;
1206}
1207
1208static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1209{
1210}
1211
1212static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1213{
1214}
1215
1216static void __init rcu_spawn_boost_kthreads(void)
1217{
1218}
1219
1220static void rcu_prepare_kthreads(int cpu)
1221{
1222}
1223
1224#endif /* #else #ifdef CONFIG_RCU_BOOST */
1225
1226#if !defined(CONFIG_RCU_FAST_NO_HZ)
1227
1228/*
1229 * Check to see if any future non-offloaded RCU-related work will need
1230 * to be done by the current CPU, even if none need be done immediately,
1231 * returning 1 if so. This function is part of the RCU implementation;
1232 * it is -not- an exported member of the RCU API.
1233 *
1234 * Because we not have RCU_FAST_NO_HZ, just check whether or not this
1235 * CPU has RCU callbacks queued.
1236 */
1237int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1238{
1239 *nextevt = KTIME_MAX;
1240 return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) &&
1241 !rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist);
1242}
1243
1244/*
1245 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1246 * after it.
1247 */
1248static void rcu_cleanup_after_idle(void)
1249{
1250}
1251
1252/*
1253 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1254 * is nothing.
1255 */
1256static void rcu_prepare_for_idle(void)
1257{
1258}
1259
1260#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1261
1262/*
1263 * This code is invoked when a CPU goes idle, at which point we want
1264 * to have the CPU do everything required for RCU so that it can enter
1265 * the energy-efficient dyntick-idle mode. This is handled by a
1266 * state machine implemented by rcu_prepare_for_idle() below.
1267 *
1268 * The following three proprocessor symbols control this state machine:
1269 *
1270 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1271 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1272 * is sized to be roughly one RCU grace period. Those energy-efficiency
1273 * benchmarkers who might otherwise be tempted to set this to a large
1274 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1275 * system. And if you are -that- concerned about energy efficiency,
1276 * just power the system down and be done with it!
1277 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1278 * permitted to sleep in dyntick-idle mode with only lazy RCU
1279 * callbacks pending. Setting this too high can OOM your system.
1280 *
1281 * The values below work well in practice. If future workloads require
1282 * adjustment, they can be converted into kernel config parameters, though
1283 * making the state machine smarter might be a better option.
1284 */
1285#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1286#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1287
1288static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
1289module_param(rcu_idle_gp_delay, int, 0644);
1290static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
1291module_param(rcu_idle_lazy_gp_delay, int, 0644);
1292
1293/*
1294 * Try to advance callbacks on the current CPU, but only if it has been
1295 * awhile since the last time we did so. Afterwards, if there are any
1296 * callbacks ready for immediate invocation, return true.
1297 */
1298static bool __maybe_unused rcu_try_advance_all_cbs(void)
1299{
1300 bool cbs_ready = false;
1301 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1302 struct rcu_node *rnp;
1303
1304 /* Exit early if we advanced recently. */
1305 if (jiffies == rdp->last_advance_all)
1306 return false;
1307 rdp->last_advance_all = jiffies;
1308
1309 rnp = rdp->mynode;
1310
1311 /*
1312 * Don't bother checking unless a grace period has
1313 * completed since we last checked and there are
1314 * callbacks not yet ready to invoke.
1315 */
1316 if ((rcu_seq_completed_gp(rdp->gp_seq,
1317 rcu_seq_current(&rnp->gp_seq)) ||
1318 unlikely(READ_ONCE(rdp->gpwrap))) &&
1319 rcu_segcblist_pend_cbs(&rdp->cblist))
1320 note_gp_changes(rdp);
1321
1322 if (rcu_segcblist_ready_cbs(&rdp->cblist))
1323 cbs_ready = true;
1324 return cbs_ready;
1325}
1326
1327/*
1328 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1329 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1330 * caller to set the timeout based on whether or not there are non-lazy
1331 * callbacks.
1332 *
1333 * The caller must have disabled interrupts.
1334 */
1335int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1336{
1337 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1338 unsigned long dj;
1339
1340 lockdep_assert_irqs_disabled();
1341
1342 /* If no non-offloaded callbacks, RCU doesn't need the CPU. */
1343 if (rcu_segcblist_empty(&rdp->cblist) ||
1344 rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist)) {
1345 *nextevt = KTIME_MAX;
1346 return 0;
1347 }
1348
1349 /* Attempt to advance callbacks. */
1350 if (rcu_try_advance_all_cbs()) {
1351 /* Some ready to invoke, so initiate later invocation. */
1352 invoke_rcu_core();
1353 return 1;
1354 }
1355 rdp->last_accelerate = jiffies;
1356
1357 /* Request timer delay depending on laziness, and round. */
1358 rdp->all_lazy = !rcu_segcblist_n_nonlazy_cbs(&rdp->cblist);
1359 if (rdp->all_lazy) {
1360 dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1361 } else {
1362 dj = round_up(rcu_idle_gp_delay + jiffies,
1363 rcu_idle_gp_delay) - jiffies;
1364 }
1365 *nextevt = basemono + dj * TICK_NSEC;
1366 return 0;
1367}
1368
1369/*
1370 * Prepare a CPU for idle from an RCU perspective. The first major task
1371 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1372 * The second major task is to check to see if a non-lazy callback has
1373 * arrived at a CPU that previously had only lazy callbacks. The third
1374 * major task is to accelerate (that is, assign grace-period numbers to)
1375 * any recently arrived callbacks.
1376 *
1377 * The caller must have disabled interrupts.
1378 */
1379static void rcu_prepare_for_idle(void)
1380{
1381 bool needwake;
1382 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1383 struct rcu_node *rnp;
1384 int tne;
1385
1386 lockdep_assert_irqs_disabled();
1387 if (rcu_segcblist_is_offloaded(&rdp->cblist))
1388 return;
1389
1390 /* Handle nohz enablement switches conservatively. */
1391 tne = READ_ONCE(tick_nohz_active);
1392 if (tne != rdp->tick_nohz_enabled_snap) {
1393 if (!rcu_segcblist_empty(&rdp->cblist))
1394 invoke_rcu_core(); /* force nohz to see update. */
1395 rdp->tick_nohz_enabled_snap = tne;
1396 return;
1397 }
1398 if (!tne)
1399 return;
1400
1401 /*
1402 * If a non-lazy callback arrived at a CPU having only lazy
1403 * callbacks, invoke RCU core for the side-effect of recalculating
1404 * idle duration on re-entry to idle.
1405 */
1406 if (rdp->all_lazy && rcu_segcblist_n_nonlazy_cbs(&rdp->cblist)) {
1407 rdp->all_lazy = false;
1408 invoke_rcu_core();
1409 return;
1410 }
1411
1412 /*
1413 * If we have not yet accelerated this jiffy, accelerate all
1414 * callbacks on this CPU.
1415 */
1416 if (rdp->last_accelerate == jiffies)
1417 return;
1418 rdp->last_accelerate = jiffies;
1419 if (rcu_segcblist_pend_cbs(&rdp->cblist)) {
1420 rnp = rdp->mynode;
1421 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
1422 needwake = rcu_accelerate_cbs(rnp, rdp);
1423 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
1424 if (needwake)
1425 rcu_gp_kthread_wake();
1426 }
1427}
1428
1429/*
1430 * Clean up for exit from idle. Attempt to advance callbacks based on
1431 * any grace periods that elapsed while the CPU was idle, and if any
1432 * callbacks are now ready to invoke, initiate invocation.
1433 */
1434static void rcu_cleanup_after_idle(void)
1435{
1436 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1437
1438 lockdep_assert_irqs_disabled();
1439 if (rcu_segcblist_is_offloaded(&rdp->cblist))
1440 return;
1441 if (rcu_try_advance_all_cbs())
1442 invoke_rcu_core();
1443}
1444
1445#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1446
1447#ifdef CONFIG_RCU_NOCB_CPU
1448
1449/*
1450 * Offload callback processing from the boot-time-specified set of CPUs
1451 * specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads
1452 * created that pull the callbacks from the corresponding CPU, wait for
1453 * a grace period to elapse, and invoke the callbacks. These kthreads
1454 * are organized into GP kthreads, which manage incoming callbacks, wait for
1455 * grace periods, and awaken CB kthreads, and the CB kthreads, which only
1456 * invoke callbacks. Each GP kthread invokes its own CBs. The no-CBs CPUs
1457 * do a wake_up() on their GP kthread when they insert a callback into any
1458 * empty list, unless the rcu_nocb_poll boot parameter has been specified,
1459 * in which case each kthread actively polls its CPU. (Which isn't so great
1460 * for energy efficiency, but which does reduce RCU's overhead on that CPU.)
1461 *
1462 * This is intended to be used in conjunction with Frederic Weisbecker's
1463 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
1464 * running CPU-bound user-mode computations.
1465 *
1466 * Offloading of callbacks can also be used as an energy-efficiency
1467 * measure because CPUs with no RCU callbacks queued are more aggressive
1468 * about entering dyntick-idle mode.
1469 */
1470
1471
1472/*
1473 * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters.
1474 * The string after the "rcu_nocbs=" is either "all" for all CPUs, or a
1475 * comma-separated list of CPUs and/or CPU ranges. If an invalid list is
1476 * given, a warning is emitted and all CPUs are offloaded.
1477 */
1478static int __init rcu_nocb_setup(char *str)
1479{
1480 alloc_bootmem_cpumask_var(&rcu_nocb_mask);
1481 if (!strcasecmp(str, "all"))
1482 cpumask_setall(rcu_nocb_mask);
1483 else
1484 if (cpulist_parse(str, rcu_nocb_mask)) {
1485 pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
1486 cpumask_setall(rcu_nocb_mask);
1487 }
1488 return 1;
1489}
1490__setup("rcu_nocbs=", rcu_nocb_setup);
1491
1492static int __init parse_rcu_nocb_poll(char *arg)
1493{
1494 rcu_nocb_poll = true;
1495 return 0;
1496}
1497early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
1498
1499/*
1500 * Don't bother bypassing ->cblist if the call_rcu() rate is low.
1501 * After all, the main point of bypassing is to avoid lock contention
1502 * on ->nocb_lock, which only can happen at high call_rcu() rates.
1503 */
1504int nocb_nobypass_lim_per_jiffy = 16 * 1000 / HZ;
1505module_param(nocb_nobypass_lim_per_jiffy, int, 0);
1506
1507/*
1508 * Acquire the specified rcu_data structure's ->nocb_bypass_lock. If the
1509 * lock isn't immediately available, increment ->nocb_lock_contended to
1510 * flag the contention.
1511 */
1512static void rcu_nocb_bypass_lock(struct rcu_data *rdp)
1513{
1514 lockdep_assert_irqs_disabled();
1515 if (raw_spin_trylock(&rdp->nocb_bypass_lock))
1516 return;
1517 atomic_inc(&rdp->nocb_lock_contended);
1518 WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
1519 smp_mb__after_atomic(); /* atomic_inc() before lock. */
1520 raw_spin_lock(&rdp->nocb_bypass_lock);
1521 smp_mb__before_atomic(); /* atomic_dec() after lock. */
1522 atomic_dec(&rdp->nocb_lock_contended);
1523}
1524
1525/*
1526 * Spinwait until the specified rcu_data structure's ->nocb_lock is
1527 * not contended. Please note that this is extremely special-purpose,
1528 * relying on the fact that at most two kthreads and one CPU contend for
1529 * this lock, and also that the two kthreads are guaranteed to have frequent
1530 * grace-period-duration time intervals between successive acquisitions
1531 * of the lock. This allows us to use an extremely simple throttling
1532 * mechanism, and further to apply it only to the CPU doing floods of
1533 * call_rcu() invocations. Don't try this at home!
1534 */
1535static void rcu_nocb_wait_contended(struct rcu_data *rdp)
1536{
1537 WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
1538 while (WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended)))
1539 cpu_relax();
1540}
1541
1542/*
1543 * Conditionally acquire the specified rcu_data structure's
1544 * ->nocb_bypass_lock.
1545 */
1546static bool rcu_nocb_bypass_trylock(struct rcu_data *rdp)
1547{
1548 lockdep_assert_irqs_disabled();
1549 return raw_spin_trylock(&rdp->nocb_bypass_lock);
1550}
1551
1552/*
1553 * Release the specified rcu_data structure's ->nocb_bypass_lock.
1554 */
1555static void rcu_nocb_bypass_unlock(struct rcu_data *rdp)
1556{
1557 lockdep_assert_irqs_disabled();
1558 raw_spin_unlock(&rdp->nocb_bypass_lock);
1559}
1560
1561/*
1562 * Acquire the specified rcu_data structure's ->nocb_lock, but only
1563 * if it corresponds to a no-CBs CPU.
1564 */
1565static void rcu_nocb_lock(struct rcu_data *rdp)
1566{
1567 lockdep_assert_irqs_disabled();
1568 if (!rcu_segcblist_is_offloaded(&rdp->cblist))
1569 return;
1570 raw_spin_lock(&rdp->nocb_lock);
1571}
1572
1573/*
1574 * Release the specified rcu_data structure's ->nocb_lock, but only
1575 * if it corresponds to a no-CBs CPU.
1576 */
1577static void rcu_nocb_unlock(struct rcu_data *rdp)
1578{
1579 if (rcu_segcblist_is_offloaded(&rdp->cblist)) {
1580 lockdep_assert_irqs_disabled();
1581 raw_spin_unlock(&rdp->nocb_lock);
1582 }
1583}
1584
1585/*
1586 * Release the specified rcu_data structure's ->nocb_lock and restore
1587 * interrupts, but only if it corresponds to a no-CBs CPU.
1588 */
1589static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
1590 unsigned long flags)
1591{
1592 if (rcu_segcblist_is_offloaded(&rdp->cblist)) {
1593 lockdep_assert_irqs_disabled();
1594 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1595 } else {
1596 local_irq_restore(flags);
1597 }
1598}
1599
1600/* Lockdep check that ->cblist may be safely accessed. */
1601static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
1602{
1603 lockdep_assert_irqs_disabled();
1604 if (rcu_segcblist_is_offloaded(&rdp->cblist) &&
1605 cpu_online(rdp->cpu))
1606 lockdep_assert_held(&rdp->nocb_lock);
1607}
1608
1609/*
1610 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
1611 * grace period.
1612 */
1613static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
1614{
1615 swake_up_all(sq);
1616}
1617
1618static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
1619{
1620 return &rnp->nocb_gp_wq[rcu_seq_ctr(rnp->gp_seq) & 0x1];
1621}
1622
1623static void rcu_init_one_nocb(struct rcu_node *rnp)
1624{
1625 init_swait_queue_head(&rnp->nocb_gp_wq[0]);
1626 init_swait_queue_head(&rnp->nocb_gp_wq[1]);
1627}
1628
1629/* Is the specified CPU a no-CBs CPU? */
1630bool rcu_is_nocb_cpu(int cpu)
1631{
1632 if (cpumask_available(rcu_nocb_mask))
1633 return cpumask_test_cpu(cpu, rcu_nocb_mask);
1634 return false;
1635}
1636
1637/*
1638 * Kick the GP kthread for this NOCB group. Caller holds ->nocb_lock
1639 * and this function releases it.
1640 */
1641static void wake_nocb_gp(struct rcu_data *rdp, bool force,
1642 unsigned long flags)
1643 __releases(rdp->nocb_lock)
1644{
1645 bool needwake = false;
1646 struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
1647
1648 lockdep_assert_held(&rdp->nocb_lock);
1649 if (!READ_ONCE(rdp_gp->nocb_gp_kthread)) {
1650 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1651 TPS("AlreadyAwake"));
1652 rcu_nocb_unlock_irqrestore(rdp, flags);
1653 return;
1654 }
1655 del_timer(&rdp->nocb_timer);
1656 rcu_nocb_unlock_irqrestore(rdp, flags);
1657 raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
1658 if (force || READ_ONCE(rdp_gp->nocb_gp_sleep)) {
1659 WRITE_ONCE(rdp_gp->nocb_gp_sleep, false);
1660 needwake = true;
1661 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DoWake"));
1662 }
1663 raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
1664 if (needwake)
1665 wake_up_process(rdp_gp->nocb_gp_kthread);
1666}
1667
1668/*
1669 * Arrange to wake the GP kthread for this NOCB group at some future
1670 * time when it is safe to do so.
1671 */
1672static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
1673 const char *reason)
1674{
1675 if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
1676 mod_timer(&rdp->nocb_timer, jiffies + 1);
1677 if (rdp->nocb_defer_wakeup < waketype)
1678 WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
1679 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason);
1680}
1681
1682/*
1683 * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
1684 * However, if there is a callback to be enqueued and if ->nocb_bypass
1685 * proves to be initially empty, just return false because the no-CB GP
1686 * kthread may need to be awakened in this case.
1687 *
1688 * Note that this function always returns true if rhp is NULL.
1689 */
1690static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
1691 unsigned long j)
1692{
1693 struct rcu_cblist rcl;
1694
1695 WARN_ON_ONCE(!rcu_segcblist_is_offloaded(&rdp->cblist));
1696 rcu_lockdep_assert_cblist_protected(rdp);
1697 lockdep_assert_held(&rdp->nocb_bypass_lock);
1698 if (rhp && !rcu_cblist_n_cbs(&rdp->nocb_bypass)) {
1699 raw_spin_unlock(&rdp->nocb_bypass_lock);
1700 return false;
1701 }
1702 /* Note: ->cblist.len already accounts for ->nocb_bypass contents. */
1703 if (rhp)
1704 rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
1705 rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp);
1706 rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl);
1707 WRITE_ONCE(rdp->nocb_bypass_first, j);
1708 rcu_nocb_bypass_unlock(rdp);
1709 return true;
1710}
1711
1712/*
1713 * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
1714 * However, if there is a callback to be enqueued and if ->nocb_bypass
1715 * proves to be initially empty, just return false because the no-CB GP
1716 * kthread may need to be awakened in this case.
1717 *
1718 * Note that this function always returns true if rhp is NULL.
1719 */
1720static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
1721 unsigned long j)
1722{
1723 if (!rcu_segcblist_is_offloaded(&rdp->cblist))
1724 return true;
1725 rcu_lockdep_assert_cblist_protected(rdp);
1726 rcu_nocb_bypass_lock(rdp);
1727 return rcu_nocb_do_flush_bypass(rdp, rhp, j);
1728}
1729
1730/*
1731 * If the ->nocb_bypass_lock is immediately available, flush the
1732 * ->nocb_bypass queue into ->cblist.
1733 */
1734static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j)
1735{
1736 rcu_lockdep_assert_cblist_protected(rdp);
1737 if (!rcu_segcblist_is_offloaded(&rdp->cblist) ||
1738 !rcu_nocb_bypass_trylock(rdp))
1739 return;
1740 WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j));
1741}
1742
1743/*
1744 * See whether it is appropriate to use the ->nocb_bypass list in order
1745 * to control contention on ->nocb_lock. A limited number of direct
1746 * enqueues are permitted into ->cblist per jiffy. If ->nocb_bypass
1747 * is non-empty, further callbacks must be placed into ->nocb_bypass,
1748 * otherwise rcu_barrier() breaks. Use rcu_nocb_flush_bypass() to switch
1749 * back to direct use of ->cblist. However, ->nocb_bypass should not be
1750 * used if ->cblist is empty, because otherwise callbacks can be stranded
1751 * on ->nocb_bypass because we cannot count on the current CPU ever again
1752 * invoking call_rcu(). The general rule is that if ->nocb_bypass is
1753 * non-empty, the corresponding no-CBs grace-period kthread must not be
1754 * in an indefinite sleep state.
1755 *
1756 * Finally, it is not permitted to use the bypass during early boot,
1757 * as doing so would confuse the auto-initialization code. Besides
1758 * which, there is no point in worrying about lock contention while
1759 * there is only one CPU in operation.
1760 */
1761static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
1762 bool *was_alldone, unsigned long flags)
1763{
1764 unsigned long c;
1765 unsigned long cur_gp_seq;
1766 unsigned long j = jiffies;
1767 long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
1768
1769 if (!rcu_segcblist_is_offloaded(&rdp->cblist)) {
1770 *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
1771 return false; /* Not offloaded, no bypassing. */
1772 }
1773 lockdep_assert_irqs_disabled();
1774
1775 // Don't use ->nocb_bypass during early boot.
1776 if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING) {
1777 rcu_nocb_lock(rdp);
1778 WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
1779 *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
1780 return false;
1781 }
1782
1783 // If we have advanced to a new jiffy, reset counts to allow
1784 // moving back from ->nocb_bypass to ->cblist.
1785 if (j == rdp->nocb_nobypass_last) {
1786 c = rdp->nocb_nobypass_count + 1;
1787 } else {
1788 WRITE_ONCE(rdp->nocb_nobypass_last, j);
1789 c = rdp->nocb_nobypass_count - nocb_nobypass_lim_per_jiffy;
1790 if (ULONG_CMP_LT(rdp->nocb_nobypass_count,
1791 nocb_nobypass_lim_per_jiffy))
1792 c = 0;
1793 else if (c > nocb_nobypass_lim_per_jiffy)
1794 c = nocb_nobypass_lim_per_jiffy;
1795 }
1796 WRITE_ONCE(rdp->nocb_nobypass_count, c);
1797
1798 // If there hasn't yet been all that many ->cblist enqueues
1799 // this jiffy, tell the caller to enqueue onto ->cblist. But flush
1800 // ->nocb_bypass first.
1801 if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy) {
1802 rcu_nocb_lock(rdp);
1803 *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
1804 if (*was_alldone)
1805 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1806 TPS("FirstQ"));
1807 WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j));
1808 WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
1809 return false; // Caller must enqueue the callback.
1810 }
1811
1812 // If ->nocb_bypass has been used too long or is too full,
1813 // flush ->nocb_bypass to ->cblist.
1814 if ((ncbs && j != READ_ONCE(rdp->nocb_bypass_first)) ||
1815 ncbs >= qhimark) {
1816 rcu_nocb_lock(rdp);
1817 if (!rcu_nocb_flush_bypass(rdp, rhp, j)) {
1818 *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
1819 if (*was_alldone)
1820 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1821 TPS("FirstQ"));
1822 WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
1823 return false; // Caller must enqueue the callback.
1824 }
1825 if (j != rdp->nocb_gp_adv_time &&
1826 rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
1827 rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
1828 rcu_advance_cbs_nowake(rdp->mynode, rdp);
1829 rdp->nocb_gp_adv_time = j;
1830 }
1831 rcu_nocb_unlock_irqrestore(rdp, flags);
1832 return true; // Callback already enqueued.
1833 }
1834
1835 // We need to use the bypass.
1836 rcu_nocb_wait_contended(rdp);
1837 rcu_nocb_bypass_lock(rdp);
1838 ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
1839 rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
1840 rcu_cblist_enqueue(&rdp->nocb_bypass, rhp);
1841 if (!ncbs) {
1842 WRITE_ONCE(rdp->nocb_bypass_first, j);
1843 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstBQ"));
1844 }
1845 rcu_nocb_bypass_unlock(rdp);
1846 smp_mb(); /* Order enqueue before wake. */
1847 if (ncbs) {
1848 local_irq_restore(flags);
1849 } else {
1850 // No-CBs GP kthread might be indefinitely asleep, if so, wake.
1851 rcu_nocb_lock(rdp); // Rare during call_rcu() flood.
1852 if (!rcu_segcblist_pend_cbs(&rdp->cblist)) {
1853 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1854 TPS("FirstBQwake"));
1855 __call_rcu_nocb_wake(rdp, true, flags);
1856 } else {
1857 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1858 TPS("FirstBQnoWake"));
1859 rcu_nocb_unlock_irqrestore(rdp, flags);
1860 }
1861 }
1862 return true; // Callback already enqueued.
1863}
1864
1865/*
1866 * Awaken the no-CBs grace-period kthead if needed, either due to it
1867 * legitimately being asleep or due to overload conditions.
1868 *
1869 * If warranted, also wake up the kthread servicing this CPUs queues.
1870 */
1871static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
1872 unsigned long flags)
1873 __releases(rdp->nocb_lock)
1874{
1875 unsigned long cur_gp_seq;
1876 unsigned long j;
1877 long len;
1878 struct task_struct *t;
1879
1880 // If we are being polled or there is no kthread, just leave.
1881 t = READ_ONCE(rdp->nocb_gp_kthread);
1882 if (rcu_nocb_poll || !t) {
1883 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1884 TPS("WakeNotPoll"));
1885 rcu_nocb_unlock_irqrestore(rdp, flags);
1886 return;
1887 }
1888 // Need to actually to a wakeup.
1889 len = rcu_segcblist_n_cbs(&rdp->cblist);
1890 if (was_alldone) {
1891 rdp->qlen_last_fqs_check = len;
1892 if (!irqs_disabled_flags(flags)) {
1893 /* ... if queue was empty ... */
1894 wake_nocb_gp(rdp, false, flags);
1895 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1896 TPS("WakeEmpty"));
1897 } else {
1898 wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE,
1899 TPS("WakeEmptyIsDeferred"));
1900 rcu_nocb_unlock_irqrestore(rdp, flags);
1901 }
1902 } else if (len > rdp->qlen_last_fqs_check + qhimark) {
1903 /* ... or if many callbacks queued. */
1904 rdp->qlen_last_fqs_check = len;
1905 j = jiffies;
1906 if (j != rdp->nocb_gp_adv_time &&
1907 rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
1908 rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
1909 rcu_advance_cbs_nowake(rdp->mynode, rdp);
1910 rdp->nocb_gp_adv_time = j;
1911 }
1912 smp_mb(); /* Enqueue before timer_pending(). */
1913 if ((rdp->nocb_cb_sleep ||
1914 !rcu_segcblist_ready_cbs(&rdp->cblist)) &&
1915 !timer_pending(&rdp->nocb_bypass_timer))
1916 wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
1917 TPS("WakeOvfIsDeferred"));
1918 rcu_nocb_unlock_irqrestore(rdp, flags);
1919 } else {
1920 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
1921 rcu_nocb_unlock_irqrestore(rdp, flags);
1922 }
1923 return;
1924}
1925
1926/* Wake up the no-CBs GP kthread to flush ->nocb_bypass. */
1927static void do_nocb_bypass_wakeup_timer(struct timer_list *t)
1928{
1929 unsigned long flags;
1930 struct rcu_data *rdp = from_timer(rdp, t, nocb_bypass_timer);
1931
1932 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Timer"));
1933 rcu_nocb_lock_irqsave(rdp, flags);
1934 smp_mb__after_spinlock(); /* Timer expire before wakeup. */
1935 __call_rcu_nocb_wake(rdp, true, flags);
1936}
1937
1938/*
1939 * No-CBs GP kthreads come here to wait for additional callbacks to show up
1940 * or for grace periods to end.
1941 */
1942static void nocb_gp_wait(struct rcu_data *my_rdp)
1943{
1944 bool bypass = false;
1945 long bypass_ncbs;
1946 int __maybe_unused cpu = my_rdp->cpu;
1947 unsigned long cur_gp_seq;
1948 unsigned long flags;
1949 bool gotcbs;
1950 unsigned long j = jiffies;
1951 bool needwait_gp = false; // This prevents actual uninitialized use.
1952 bool needwake;
1953 bool needwake_gp;
1954 struct rcu_data *rdp;
1955 struct rcu_node *rnp;
1956 unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning.
1957
1958 /*
1959 * Each pass through the following loop checks for CBs and for the
1960 * nearest grace period (if any) to wait for next. The CB kthreads
1961 * and the global grace-period kthread are awakened if needed.
1962 */
1963 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_cb_rdp) {
1964 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check"));
1965 rcu_nocb_lock_irqsave(rdp, flags);
1966 bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
1967 if (bypass_ncbs &&
1968 (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) ||
1969 bypass_ncbs > 2 * qhimark)) {
1970 // Bypass full or old, so flush it.
1971 (void)rcu_nocb_try_flush_bypass(rdp, j);
1972 bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
1973 } else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) {
1974 rcu_nocb_unlock_irqrestore(rdp, flags);
1975 continue; /* No callbacks here, try next. */
1976 }
1977 if (bypass_ncbs) {
1978 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1979 TPS("Bypass"));
1980 bypass = true;
1981 }
1982 rnp = rdp->mynode;
1983 if (bypass) { // Avoid race with first bypass CB.
1984 WRITE_ONCE(my_rdp->nocb_defer_wakeup,
1985 RCU_NOCB_WAKE_NOT);
1986 del_timer(&my_rdp->nocb_timer);
1987 }
1988 // Advance callbacks if helpful and low contention.
1989 needwake_gp = false;
1990 if (!rcu_segcblist_restempty(&rdp->cblist,
1991 RCU_NEXT_READY_TAIL) ||
1992 (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
1993 rcu_seq_done(&rnp->gp_seq, cur_gp_seq))) {
1994 raw_spin_lock_rcu_node(rnp); /* irqs disabled. */
1995 needwake_gp = rcu_advance_cbs(rnp, rdp);
1996 raw_spin_unlock_rcu_node(rnp); /* irqs disabled. */
1997 }
1998 // Need to wait on some grace period?
1999 WARN_ON_ONCE(!rcu_segcblist_restempty(&rdp->cblist,
2000 RCU_NEXT_READY_TAIL));
2001 if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq)) {
2002 if (!needwait_gp ||
2003 ULONG_CMP_LT(cur_gp_seq, wait_gp_seq))
2004 wait_gp_seq = cur_gp_seq;
2005 needwait_gp = true;
2006 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
2007 TPS("NeedWaitGP"));
2008 }
2009 if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
2010 needwake = rdp->nocb_cb_sleep;
2011 WRITE_ONCE(rdp->nocb_cb_sleep, false);
2012 smp_mb(); /* CB invocation -after- GP end. */
2013 } else {
2014 needwake = false;
2015 }
2016 rcu_nocb_unlock_irqrestore(rdp, flags);
2017 if (needwake) {
2018 swake_up_one(&rdp->nocb_cb_wq);
2019 gotcbs = true;
2020 }
2021 if (needwake_gp)
2022 rcu_gp_kthread_wake();
2023 }
2024
2025 my_rdp->nocb_gp_bypass = bypass;
2026 my_rdp->nocb_gp_gp = needwait_gp;
2027 my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;
2028 if (bypass && !rcu_nocb_poll) {
2029 // At least one child with non-empty ->nocb_bypass, so set
2030 // timer in order to avoid stranding its callbacks.
2031 raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
2032 mod_timer(&my_rdp->nocb_bypass_timer, j + 2);
2033 raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
2034 }
2035 if (rcu_nocb_poll) {
2036 /* Polling, so trace if first poll in the series. */
2037 if (gotcbs)
2038 trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
2039 schedule_timeout_interruptible(1);
2040 } else if (!needwait_gp) {
2041 /* Wait for callbacks to appear. */
2042 trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
2043 swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq,
2044 !READ_ONCE(my_rdp->nocb_gp_sleep));
2045 trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep"));
2046 } else {
2047 rnp = my_rdp->mynode;
2048 trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("StartWait"));
2049 swait_event_interruptible_exclusive(
2050 rnp->nocb_gp_wq[rcu_seq_ctr(wait_gp_seq) & 0x1],
2051 rcu_seq_done(&rnp->gp_seq, wait_gp_seq) ||
2052 !READ_ONCE(my_rdp->nocb_gp_sleep));
2053 trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("EndWait"));
2054 }
2055 if (!rcu_nocb_poll) {
2056 raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
2057 if (bypass)
2058 del_timer(&my_rdp->nocb_bypass_timer);
2059 WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
2060 raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
2061 }
2062 my_rdp->nocb_gp_seq = -1;
2063 WARN_ON(signal_pending(current));
2064}
2065
2066/*
2067 * No-CBs grace-period-wait kthread. There is one of these per group
2068 * of CPUs, but only once at least one CPU in that group has come online
2069 * at least once since boot. This kthread checks for newly posted
2070 * callbacks from any of the CPUs it is responsible for, waits for a
2071 * grace period, then awakens all of the rcu_nocb_cb_kthread() instances
2072 * that then have callback-invocation work to do.
2073 */
2074static int rcu_nocb_gp_kthread(void *arg)
2075{
2076 struct rcu_data *rdp = arg;
2077
2078 for (;;) {
2079 WRITE_ONCE(rdp->nocb_gp_loops, rdp->nocb_gp_loops + 1);
2080 nocb_gp_wait(rdp);
2081 cond_resched_tasks_rcu_qs();
2082 }
2083 return 0;
2084}
2085
2086/*
2087 * Invoke any ready callbacks from the corresponding no-CBs CPU,
2088 * then, if there are no more, wait for more to appear.
2089 */
2090static void nocb_cb_wait(struct rcu_data *rdp)
2091{
2092 unsigned long cur_gp_seq;
2093 unsigned long flags;
2094 bool needwake_gp = false;
2095 struct rcu_node *rnp = rdp->mynode;
2096
2097 local_irq_save(flags);
2098 rcu_momentary_dyntick_idle();
2099 local_irq_restore(flags);
2100 local_bh_disable();
2101 rcu_do_batch(rdp);
2102 local_bh_enable();
2103 lockdep_assert_irqs_enabled();
2104 rcu_nocb_lock_irqsave(rdp, flags);
2105 if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
2106 rcu_seq_done(&rnp->gp_seq, cur_gp_seq) &&
2107 raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */
2108 needwake_gp = rcu_advance_cbs(rdp->mynode, rdp);
2109 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2110 }
2111 if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
2112 rcu_nocb_unlock_irqrestore(rdp, flags);
2113 if (needwake_gp)
2114 rcu_gp_kthread_wake();
2115 return;
2116 }
2117
2118 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("CBSleep"));
2119 WRITE_ONCE(rdp->nocb_cb_sleep, true);
2120 rcu_nocb_unlock_irqrestore(rdp, flags);
2121 if (needwake_gp)
2122 rcu_gp_kthread_wake();
2123 swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
2124 !READ_ONCE(rdp->nocb_cb_sleep));
2125 if (!smp_load_acquire(&rdp->nocb_cb_sleep)) { /* VVV */
2126 /* ^^^ Ensure CB invocation follows _sleep test. */
2127 return;
2128 }
2129 WARN_ON(signal_pending(current));
2130 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty"));
2131}
2132
2133/*
2134 * Per-rcu_data kthread, but only for no-CBs CPUs. Repeatedly invoke
2135 * nocb_cb_wait() to do the dirty work.
2136 */
2137static int rcu_nocb_cb_kthread(void *arg)
2138{
2139 struct rcu_data *rdp = arg;
2140
2141 // Each pass through this loop does one callback batch, and,
2142 // if there are no more ready callbacks, waits for them.
2143 for (;;) {
2144 nocb_cb_wait(rdp);
2145 cond_resched_tasks_rcu_qs();
2146 }
2147 return 0;
2148}
2149
2150/* Is a deferred wakeup of rcu_nocb_kthread() required? */
2151static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2152{
2153 return READ_ONCE(rdp->nocb_defer_wakeup);
2154}
2155
2156/* Do a deferred wakeup of rcu_nocb_kthread(). */
2157static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
2158{
2159 unsigned long flags;
2160 int ndw;
2161
2162 rcu_nocb_lock_irqsave(rdp, flags);
2163 if (!rcu_nocb_need_deferred_wakeup(rdp)) {
2164 rcu_nocb_unlock_irqrestore(rdp, flags);
2165 return;
2166 }
2167 ndw = READ_ONCE(rdp->nocb_defer_wakeup);
2168 WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
2169 wake_nocb_gp(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
2170 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DeferredWake"));
2171}
2172
2173/* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
2174static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
2175{
2176 struct rcu_data *rdp = from_timer(rdp, t, nocb_timer);
2177
2178 do_nocb_deferred_wakeup_common(rdp);
2179}
2180
2181/*
2182 * Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
2183 * This means we do an inexact common-case check. Note that if
2184 * we miss, ->nocb_timer will eventually clean things up.
2185 */
2186static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2187{
2188 if (rcu_nocb_need_deferred_wakeup(rdp))
2189 do_nocb_deferred_wakeup_common(rdp);
2190}
2191
2192void __init rcu_init_nohz(void)
2193{
2194 int cpu;
2195 bool need_rcu_nocb_mask = false;
2196 struct rcu_data *rdp;
2197
2198#if defined(CONFIG_NO_HZ_FULL)
2199 if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
2200 need_rcu_nocb_mask = true;
2201#endif /* #if defined(CONFIG_NO_HZ_FULL) */
2202
2203 if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) {
2204 if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
2205 pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
2206 return;
2207 }
2208 }
2209 if (!cpumask_available(rcu_nocb_mask))
2210 return;
2211
2212#if defined(CONFIG_NO_HZ_FULL)
2213 if (tick_nohz_full_running)
2214 cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
2215#endif /* #if defined(CONFIG_NO_HZ_FULL) */
2216
2217 if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
2218 pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
2219 cpumask_and(rcu_nocb_mask, cpu_possible_mask,
2220 rcu_nocb_mask);
2221 }
2222 if (cpumask_empty(rcu_nocb_mask))
2223 pr_info("\tOffload RCU callbacks from CPUs: (none).\n");
2224 else
2225 pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
2226 cpumask_pr_args(rcu_nocb_mask));
2227 if (rcu_nocb_poll)
2228 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
2229
2230 for_each_cpu(cpu, rcu_nocb_mask) {
2231 rdp = per_cpu_ptr(&rcu_data, cpu);
2232 if (rcu_segcblist_empty(&rdp->cblist))
2233 rcu_segcblist_init(&rdp->cblist);
2234 rcu_segcblist_offload(&rdp->cblist);
2235 }
2236 rcu_organize_nocb_kthreads();
2237}
2238
2239/* Initialize per-rcu_data variables for no-CBs CPUs. */
2240static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2241{
2242 init_swait_queue_head(&rdp->nocb_cb_wq);
2243 init_swait_queue_head(&rdp->nocb_gp_wq);
2244 raw_spin_lock_init(&rdp->nocb_lock);
2245 raw_spin_lock_init(&rdp->nocb_bypass_lock);
2246 raw_spin_lock_init(&rdp->nocb_gp_lock);
2247 timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
2248 timer_setup(&rdp->nocb_bypass_timer, do_nocb_bypass_wakeup_timer, 0);
2249 rcu_cblist_init(&rdp->nocb_bypass);
2250}
2251
2252/*
2253 * If the specified CPU is a no-CBs CPU that does not already have its
2254 * rcuo CB kthread, spawn it. Additionally, if the rcuo GP kthread
2255 * for this CPU's group has not yet been created, spawn it as well.
2256 */
2257static void rcu_spawn_one_nocb_kthread(int cpu)
2258{
2259 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
2260 struct rcu_data *rdp_gp;
2261 struct task_struct *t;
2262
2263 /*
2264 * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
2265 * then nothing to do.
2266 */
2267 if (!rcu_is_nocb_cpu(cpu) || rdp->nocb_cb_kthread)
2268 return;
2269
2270 /* If we didn't spawn the GP kthread first, reorganize! */
2271 rdp_gp = rdp->nocb_gp_rdp;
2272 if (!rdp_gp->nocb_gp_kthread) {
2273 t = kthread_run(rcu_nocb_gp_kthread, rdp_gp,
2274 "rcuog/%d", rdp_gp->cpu);
2275 if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__))
2276 return;
2277 WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);
2278 }
2279
2280 /* Spawn the kthread for this CPU. */
2281 t = kthread_run(rcu_nocb_cb_kthread, rdp,
2282 "rcuo%c/%d", rcu_state.abbr, cpu);
2283 if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__))
2284 return;
2285 WRITE_ONCE(rdp->nocb_cb_kthread, t);
2286 WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread);
2287}
2288
2289/*
2290 * If the specified CPU is a no-CBs CPU that does not already have its
2291 * rcuo kthread, spawn it.
2292 */
2293static void rcu_spawn_cpu_nocb_kthread(int cpu)
2294{
2295 if (rcu_scheduler_fully_active)
2296 rcu_spawn_one_nocb_kthread(cpu);
2297}
2298
2299/*
2300 * Once the scheduler is running, spawn rcuo kthreads for all online
2301 * no-CBs CPUs. This assumes that the early_initcall()s happen before
2302 * non-boot CPUs come online -- if this changes, we will need to add
2303 * some mutual exclusion.
2304 */
2305static void __init rcu_spawn_nocb_kthreads(void)
2306{
2307 int cpu;
2308
2309 for_each_online_cpu(cpu)
2310 rcu_spawn_cpu_nocb_kthread(cpu);
2311}
2312
2313/* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */
2314static int rcu_nocb_gp_stride = -1;
2315module_param(rcu_nocb_gp_stride, int, 0444);
2316
2317/*
2318 * Initialize GP-CB relationships for all no-CBs CPU.
2319 */
2320static void __init rcu_organize_nocb_kthreads(void)
2321{
2322 int cpu;
2323 bool firsttime = true;
2324 int ls = rcu_nocb_gp_stride;
2325 int nl = 0; /* Next GP kthread. */
2326 struct rcu_data *rdp;
2327 struct rcu_data *rdp_gp = NULL; /* Suppress misguided gcc warn. */
2328 struct rcu_data *rdp_prev = NULL;
2329
2330 if (!cpumask_available(rcu_nocb_mask))
2331 return;
2332 if (ls == -1) {
2333 ls = nr_cpu_ids / int_sqrt(nr_cpu_ids);
2334 rcu_nocb_gp_stride = ls;
2335 }
2336
2337 /*
2338 * Each pass through this loop sets up one rcu_data structure.
2339 * Should the corresponding CPU come online in the future, then
2340 * we will spawn the needed set of rcu_nocb_kthread() kthreads.
2341 */
2342 for_each_cpu(cpu, rcu_nocb_mask) {
2343 rdp = per_cpu_ptr(&rcu_data, cpu);
2344 if (rdp->cpu >= nl) {
2345 /* New GP kthread, set up for CBs & next GP. */
2346 nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
2347 rdp->nocb_gp_rdp = rdp;
2348 rdp_gp = rdp;
2349 if (!firsttime && dump_tree)
2350 pr_cont("\n");
2351 firsttime = false;
2352 pr_alert("%s: No-CB GP kthread CPU %d:", __func__, cpu);
2353 } else {
2354 /* Another CB kthread, link to previous GP kthread. */
2355 rdp->nocb_gp_rdp = rdp_gp;
2356 rdp_prev->nocb_next_cb_rdp = rdp;
2357 pr_alert(" %d", cpu);
2358 }
2359 rdp_prev = rdp;
2360 }
2361}
2362
2363/*
2364 * Bind the current task to the offloaded CPUs. If there are no offloaded
2365 * CPUs, leave the task unbound. Splat if the bind attempt fails.
2366 */
2367void rcu_bind_current_to_nocb(void)
2368{
2369 if (cpumask_available(rcu_nocb_mask) && cpumask_weight(rcu_nocb_mask))
2370 WARN_ON(sched_setaffinity(current->pid, rcu_nocb_mask));
2371}
2372EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb);
2373
2374/*
2375 * Dump out nocb grace-period kthread state for the specified rcu_data
2376 * structure.
2377 */
2378static void show_rcu_nocb_gp_state(struct rcu_data *rdp)
2379{
2380 struct rcu_node *rnp = rdp->mynode;
2381
2382 pr_info("nocb GP %d %c%c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu\n",
2383 rdp->cpu,
2384 "kK"[!!rdp->nocb_gp_kthread],
2385 "lL"[raw_spin_is_locked(&rdp->nocb_gp_lock)],
2386 "dD"[!!rdp->nocb_defer_wakeup],
2387 "tT"[timer_pending(&rdp->nocb_timer)],
2388 "bB"[timer_pending(&rdp->nocb_bypass_timer)],
2389 "sS"[!!rdp->nocb_gp_sleep],
2390 ".W"[swait_active(&rdp->nocb_gp_wq)],
2391 ".W"[swait_active(&rnp->nocb_gp_wq[0])],
2392 ".W"[swait_active(&rnp->nocb_gp_wq[1])],
2393 ".B"[!!rdp->nocb_gp_bypass],
2394 ".G"[!!rdp->nocb_gp_gp],
2395 (long)rdp->nocb_gp_seq,
2396 rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops));
2397}
2398
2399/* Dump out nocb kthread state for the specified rcu_data structure. */
2400static void show_rcu_nocb_state(struct rcu_data *rdp)
2401{
2402 struct rcu_segcblist *rsclp = &rdp->cblist;
2403 bool waslocked;
2404 bool wastimer;
2405 bool wassleep;
2406
2407 if (rdp->nocb_gp_rdp == rdp)
2408 show_rcu_nocb_gp_state(rdp);
2409
2410 pr_info(" CB %d->%d %c%c%c%c%c%c F%ld L%ld C%d %c%c%c%c%c q%ld\n",
2411 rdp->cpu, rdp->nocb_gp_rdp->cpu,
2412 "kK"[!!rdp->nocb_cb_kthread],
2413 "bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)],
2414 "cC"[!!atomic_read(&rdp->nocb_lock_contended)],
2415 "lL"[raw_spin_is_locked(&rdp->nocb_lock)],
2416 "sS"[!!rdp->nocb_cb_sleep],
2417 ".W"[swait_active(&rdp->nocb_cb_wq)],
2418 jiffies - rdp->nocb_bypass_first,
2419 jiffies - rdp->nocb_nobypass_last,
2420 rdp->nocb_nobypass_count,
2421 ".D"[rcu_segcblist_ready_cbs(rsclp)],
2422 ".W"[!rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL)],
2423 ".R"[!rcu_segcblist_restempty(rsclp, RCU_WAIT_TAIL)],
2424 ".N"[!rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL)],
2425 ".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)],
2426 rcu_segcblist_n_cbs(&rdp->cblist));
2427
2428 /* It is OK for GP kthreads to have GP state. */
2429 if (rdp->nocb_gp_rdp == rdp)
2430 return;
2431
2432 waslocked = raw_spin_is_locked(&rdp->nocb_gp_lock);
2433 wastimer = timer_pending(&rdp->nocb_timer);
2434 wassleep = swait_active(&rdp->nocb_gp_wq);
2435 if (!rdp->nocb_defer_wakeup && !rdp->nocb_gp_sleep &&
2436 !waslocked && !wastimer && !wassleep)
2437 return; /* Nothing untowards. */
2438
2439 pr_info(" !!! %c%c%c%c %c\n",
2440 "lL"[waslocked],
2441 "dD"[!!rdp->nocb_defer_wakeup],
2442 "tT"[wastimer],
2443 "sS"[!!rdp->nocb_gp_sleep],
2444 ".W"[wassleep]);
2445}
2446
2447#else /* #ifdef CONFIG_RCU_NOCB_CPU */
2448
2449/* No ->nocb_lock to acquire. */
2450static void rcu_nocb_lock(struct rcu_data *rdp)
2451{
2452}
2453
2454/* No ->nocb_lock to release. */
2455static void rcu_nocb_unlock(struct rcu_data *rdp)
2456{
2457}
2458
2459/* No ->nocb_lock to release. */
2460static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
2461 unsigned long flags)
2462{
2463 local_irq_restore(flags);
2464}
2465
2466/* Lockdep check that ->cblist may be safely accessed. */
2467static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
2468{
2469 lockdep_assert_irqs_disabled();
2470}
2471
2472static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
2473{
2474}
2475
2476static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
2477{
2478 return NULL;
2479}
2480
2481static void rcu_init_one_nocb(struct rcu_node *rnp)
2482{
2483}
2484
2485static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
2486 unsigned long j)
2487{
2488 return true;
2489}
2490
2491static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
2492 bool *was_alldone, unsigned long flags)
2493{
2494 return false;
2495}
2496
2497static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
2498 unsigned long flags)
2499{
2500 WARN_ON_ONCE(1); /* Should be dead code! */
2501}
2502
2503static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2504{
2505}
2506
2507static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2508{
2509 return false;
2510}
2511
2512static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2513{
2514}
2515
2516static void rcu_spawn_cpu_nocb_kthread(int cpu)
2517{
2518}
2519
2520static void __init rcu_spawn_nocb_kthreads(void)
2521{
2522}
2523
2524static void show_rcu_nocb_state(struct rcu_data *rdp)
2525{
2526}
2527
2528#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2529
2530/*
2531 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
2532 * grace-period kthread will do force_quiescent_state() processing?
2533 * The idea is to avoid waking up RCU core processing on such a
2534 * CPU unless the grace period has extended for too long.
2535 *
2536 * This code relies on the fact that all NO_HZ_FULL CPUs are also
2537 * CONFIG_RCU_NOCB_CPU CPUs.
2538 */
2539static bool rcu_nohz_full_cpu(void)
2540{
2541#ifdef CONFIG_NO_HZ_FULL
2542 if (tick_nohz_full_cpu(smp_processor_id()) &&
2543 (!rcu_gp_in_progress() ||
2544 ULONG_CMP_LT(jiffies, READ_ONCE(rcu_state.gp_start) + HZ)))
2545 return true;
2546#endif /* #ifdef CONFIG_NO_HZ_FULL */
2547 return false;
2548}
2549
2550/*
2551 * Bind the RCU grace-period kthreads to the housekeeping CPU.
2552 */
2553static void rcu_bind_gp_kthread(void)
2554{
2555 if (!tick_nohz_full_enabled())
2556 return;
2557 housekeeping_affine(current, HK_FLAG_RCU);
2558}
2559
2560/* Record the current task on dyntick-idle entry. */
2561static void rcu_dynticks_task_enter(void)
2562{
2563#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2564 WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
2565#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
2566}
2567
2568/* Record no current task on dyntick-idle exit. */
2569static void rcu_dynticks_task_exit(void)
2570{
2571#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2572 WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
2573#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
2574}
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.
5 *
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.
10 *
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.
15 *
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.
19 *
20 * Copyright Red Hat, 2009
21 * Copyright IBM Corporation, 2009
22 *
23 * Author: Ingo Molnar <mingo@elte.hu>
24 * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
25 */
26
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"
35
36#ifdef CONFIG_RCU_BOOST
37
38#include "../locking/rtmutex_common.h"
39
40/*
41 * Control variables for per-CPU and per-rcu_node kthreads. These
42 * handle all flavors of RCU.
43 */
44static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
45DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
46DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
47DEFINE_PER_CPU(char, rcu_cpu_has_work);
48
49#else /* #ifdef CONFIG_RCU_BOOST */
50
51/*
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.
56 */
57#define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; })
58#define rt_mutex_futex_unlock(x) WARN_ON_ONCE(1)
59
60#endif /* #else #ifdef CONFIG_RCU_BOOST */
61
62#ifdef CONFIG_RCU_NOCB_CPU
63static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
64static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
65#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
66
67/*
68 * Check the RCU kernel configuration parameters and print informative
69 * messages about anything out of the ordinary.
70 */
71static void __init rcu_bootup_announce_oddness(void)
72{
73 if (IS_ENABLED(CONFIG_RCU_TRACE))
74 pr_info("\tRCU event tracing is enabled.\n");
75 if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||
76 (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))
77 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
78 RCU_FANOUT);
79 if (rcu_fanout_exact)
80 pr_info("\tHierarchical RCU autobalancing is disabled.\n");
81 if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ))
82 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
83 if (IS_ENABLED(CONFIG_PROVE_RCU))
84 pr_info("\tRCU lockdep checking is enabled.\n");
85 if (RCU_NUM_LVLS >= 4)
86 pr_info("\tFour(or more)-level hierarchy is enabled.\n");
87 if (RCU_FANOUT_LEAF != 16)
88 pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
89 RCU_FANOUT_LEAF);
90 if (rcu_fanout_leaf != RCU_FANOUT_LEAF)
91 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
92 if (nr_cpu_ids != NR_CPUS)
93 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%u.\n", NR_CPUS, nr_cpu_ids);
94#ifdef CONFIG_RCU_BOOST
95 pr_info("\tRCU priority boosting: priority %d delay %d ms.\n", kthread_prio, CONFIG_RCU_BOOST_DELAY);
96#endif
97 if (blimit != DEFAULT_RCU_BLIMIT)
98 pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit);
99 if (qhimark != DEFAULT_RCU_QHIMARK)
100 pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark);
101 if (qlowmark != DEFAULT_RCU_QLOMARK)
102 pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark);
103 if (jiffies_till_first_fqs != ULONG_MAX)
104 pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs);
105 if (jiffies_till_next_fqs != ULONG_MAX)
106 pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs);
107 if (rcu_kick_kthreads)
108 pr_info("\tKick kthreads if too-long grace period.\n");
109 if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD))
110 pr_info("\tRCU callback double-/use-after-free debug enabled.\n");
111 if (gp_preinit_delay)
112 pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay);
113 if (gp_init_delay)
114 pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay);
115 if (gp_cleanup_delay)
116 pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay);
117 if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))
118 pr_info("\tRCU debug extended QS entry/exit.\n");
119 rcupdate_announce_bootup_oddness();
120}
121
122#ifdef CONFIG_PREEMPT_RCU
123
124RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
125static struct rcu_state *const rcu_state_p = &rcu_preempt_state;
126static struct rcu_data __percpu *const rcu_data_p = &rcu_preempt_data;
127
128static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
129 bool wake);
130
131/*
132 * Tell them what RCU they are running.
133 */
134static void __init rcu_bootup_announce(void)
135{
136 pr_info("Preemptible hierarchical RCU implementation.\n");
137 rcu_bootup_announce_oddness();
138}
139
140/* Flags for rcu_preempt_ctxt_queue() decision table. */
141#define RCU_GP_TASKS 0x8
142#define RCU_EXP_TASKS 0x4
143#define RCU_GP_BLKD 0x2
144#define RCU_EXP_BLKD 0x1
145
146/*
147 * Queues a task preempted within an RCU-preempt read-side critical
148 * section into the appropriate location within the ->blkd_tasks list,
149 * depending on the states of any ongoing normal and expedited grace
150 * periods. The ->gp_tasks pointer indicates which element the normal
151 * grace period is waiting on (NULL if none), and the ->exp_tasks pointer
152 * indicates which element the expedited grace period is waiting on (again,
153 * NULL if none). If a grace period is waiting on a given element in the
154 * ->blkd_tasks list, it also waits on all subsequent elements. Thus,
155 * adding a task to the tail of the list blocks any grace period that is
156 * already waiting on one of the elements. In contrast, adding a task
157 * to the head of the list won't block any grace period that is already
158 * waiting on one of the elements.
159 *
160 * This queuing is imprecise, and can sometimes make an ongoing grace
161 * period wait for a task that is not strictly speaking blocking it.
162 * Given the choice, we needlessly block a normal grace period rather than
163 * blocking an expedited grace period.
164 *
165 * Note that an endless sequence of expedited grace periods still cannot
166 * indefinitely postpone a normal grace period. Eventually, all of the
167 * fixed number of preempted tasks blocking the normal grace period that are
168 * not also blocking the expedited grace period will resume and complete
169 * their RCU read-side critical sections. At that point, the ->gp_tasks
170 * pointer will equal the ->exp_tasks pointer, at which point the end of
171 * the corresponding expedited grace period will also be the end of the
172 * normal grace period.
173 */
174static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
175 __releases(rnp->lock) /* But leaves rrupts disabled. */
176{
177 int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) +
178 (rnp->exp_tasks ? RCU_EXP_TASKS : 0) +
179 (rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) +
180 (rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0);
181 struct task_struct *t = current;
182
183 raw_lockdep_assert_held_rcu_node(rnp);
184 WARN_ON_ONCE(rdp->mynode != rnp);
185 WARN_ON_ONCE(rnp->level != rcu_num_lvls - 1);
186
187 /*
188 * Decide where to queue the newly blocked task. In theory,
189 * this could be an if-statement. In practice, when I tried
190 * that, it was quite messy.
191 */
192 switch (blkd_state) {
193 case 0:
194 case RCU_EXP_TASKS:
195 case RCU_EXP_TASKS + RCU_GP_BLKD:
196 case RCU_GP_TASKS:
197 case RCU_GP_TASKS + RCU_EXP_TASKS:
198
199 /*
200 * Blocking neither GP, or first task blocking the normal
201 * GP but not blocking the already-waiting expedited GP.
202 * Queue at the head of the list to avoid unnecessarily
203 * blocking the already-waiting GPs.
204 */
205 list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
206 break;
207
208 case RCU_EXP_BLKD:
209 case RCU_GP_BLKD:
210 case RCU_GP_BLKD + RCU_EXP_BLKD:
211 case RCU_GP_TASKS + RCU_EXP_BLKD:
212 case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
213 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
214
215 /*
216 * First task arriving that blocks either GP, or first task
217 * arriving that blocks the expedited GP (with the normal
218 * GP already waiting), or a task arriving that blocks
219 * both GPs with both GPs already waiting. Queue at the
220 * tail of the list to avoid any GP waiting on any of the
221 * already queued tasks that are not blocking it.
222 */
223 list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);
224 break;
225
226 case RCU_EXP_TASKS + RCU_EXP_BLKD:
227 case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
228 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD:
229
230 /*
231 * Second or subsequent task blocking the expedited GP.
232 * The task either does not block the normal GP, or is the
233 * first task blocking the normal GP. Queue just after
234 * the first task blocking the expedited GP.
235 */
236 list_add(&t->rcu_node_entry, rnp->exp_tasks);
237 break;
238
239 case RCU_GP_TASKS + RCU_GP_BLKD:
240 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD:
241
242 /*
243 * Second or subsequent task blocking the normal GP.
244 * The task does not block the expedited GP. Queue just
245 * after the first task blocking the normal GP.
246 */
247 list_add(&t->rcu_node_entry, rnp->gp_tasks);
248 break;
249
250 default:
251
252 /* Yet another exercise in excessive paranoia. */
253 WARN_ON_ONCE(1);
254 break;
255 }
256
257 /*
258 * We have now queued the task. If it was the first one to
259 * block either grace period, update the ->gp_tasks and/or
260 * ->exp_tasks pointers, respectively, to reference the newly
261 * blocked tasks.
262 */
263 if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD))
264 rnp->gp_tasks = &t->rcu_node_entry;
265 if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
266 rnp->exp_tasks = &t->rcu_node_entry;
267 WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=
268 !(rnp->qsmask & rdp->grpmask));
269 WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) !=
270 !(rnp->expmask & rdp->grpmask));
271 raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */
272
273 /*
274 * Report the quiescent state for the expedited GP. This expedited
275 * GP should not be able to end until we report, so there should be
276 * no need to check for a subsequent expedited GP. (Though we are
277 * still in a quiescent state in any case.)
278 */
279 if (blkd_state & RCU_EXP_BLKD &&
280 t->rcu_read_unlock_special.b.exp_need_qs) {
281 t->rcu_read_unlock_special.b.exp_need_qs = false;
282 rcu_report_exp_rdp(rdp->rsp, rdp, true);
283 } else {
284 WARN_ON_ONCE(t->rcu_read_unlock_special.b.exp_need_qs);
285 }
286}
287
288/*
289 * Record a preemptible-RCU quiescent state for the specified CPU. Note
290 * that this just means that the task currently running on the CPU is
291 * not in a quiescent state. There might be any number of tasks blocked
292 * while in an RCU read-side critical section.
293 *
294 * As with the other rcu_*_qs() functions, callers to this function
295 * must disable preemption.
296 */
297static void rcu_preempt_qs(void)
298{
299 RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_qs() invoked with preemption enabled!!!\n");
300 if (__this_cpu_read(rcu_data_p->cpu_no_qs.s)) {
301 trace_rcu_grace_period(TPS("rcu_preempt"),
302 __this_cpu_read(rcu_data_p->gpnum),
303 TPS("cpuqs"));
304 __this_cpu_write(rcu_data_p->cpu_no_qs.b.norm, false);
305 barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
306 current->rcu_read_unlock_special.b.need_qs = false;
307 }
308}
309
310/*
311 * We have entered the scheduler, and the current task might soon be
312 * context-switched away from. If this task is in an RCU read-side
313 * critical section, we will no longer be able to rely on the CPU to
314 * record that fact, so we enqueue the task on the blkd_tasks list.
315 * The task will dequeue itself when it exits the outermost enclosing
316 * RCU read-side critical section. Therefore, the current grace period
317 * cannot be permitted to complete until the blkd_tasks list entries
318 * predating the current grace period drain, in other words, until
319 * rnp->gp_tasks becomes NULL.
320 *
321 * Caller must disable interrupts.
322 */
323static void rcu_preempt_note_context_switch(bool preempt)
324{
325 struct task_struct *t = current;
326 struct rcu_data *rdp;
327 struct rcu_node *rnp;
328
329 lockdep_assert_irqs_disabled();
330 WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0);
331 if (t->rcu_read_lock_nesting > 0 &&
332 !t->rcu_read_unlock_special.b.blocked) {
333
334 /* Possibly blocking in an RCU read-side critical section. */
335 rdp = this_cpu_ptr(rcu_state_p->rda);
336 rnp = rdp->mynode;
337 raw_spin_lock_rcu_node(rnp);
338 t->rcu_read_unlock_special.b.blocked = true;
339 t->rcu_blocked_node = rnp;
340
341 /*
342 * Verify the CPU's sanity, trace the preemption, and
343 * then queue the task as required based on the states
344 * of any ongoing and expedited grace periods.
345 */
346 WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);
347 WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
348 trace_rcu_preempt_task(rdp->rsp->name,
349 t->pid,
350 (rnp->qsmask & rdp->grpmask)
351 ? rnp->gpnum
352 : rnp->gpnum + 1);
353 rcu_preempt_ctxt_queue(rnp, rdp);
354 } else if (t->rcu_read_lock_nesting < 0 &&
355 t->rcu_read_unlock_special.s) {
356
357 /*
358 * Complete exit from RCU read-side critical section on
359 * behalf of preempted instance of __rcu_read_unlock().
360 */
361 rcu_read_unlock_special(t);
362 }
363
364 /*
365 * Either we were not in an RCU read-side critical section to
366 * begin with, or we have now recorded that critical section
367 * globally. Either way, we can now note a quiescent state
368 * for this CPU. Again, if we were in an RCU read-side critical
369 * section, and if that critical section was blocking the current
370 * grace period, then the fact that the task has been enqueued
371 * means that we continue to block the current grace period.
372 */
373 rcu_preempt_qs();
374}
375
376/*
377 * Check for preempted RCU readers blocking the current grace period
378 * for the specified rcu_node structure. If the caller needs a reliable
379 * answer, it must hold the rcu_node's ->lock.
380 */
381static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
382{
383 return rnp->gp_tasks != NULL;
384}
385
386/*
387 * Advance a ->blkd_tasks-list pointer to the next entry, instead
388 * returning NULL if at the end of the list.
389 */
390static struct list_head *rcu_next_node_entry(struct task_struct *t,
391 struct rcu_node *rnp)
392{
393 struct list_head *np;
394
395 np = t->rcu_node_entry.next;
396 if (np == &rnp->blkd_tasks)
397 np = NULL;
398 return np;
399}
400
401/*
402 * Return true if the specified rcu_node structure has tasks that were
403 * preempted within an RCU read-side critical section.
404 */
405static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
406{
407 return !list_empty(&rnp->blkd_tasks);
408}
409
410/*
411 * Handle special cases during rcu_read_unlock(), such as needing to
412 * notify RCU core processing or task having blocked during the RCU
413 * read-side critical section.
414 */
415void rcu_read_unlock_special(struct task_struct *t)
416{
417 bool empty_exp;
418 bool empty_norm;
419 bool empty_exp_now;
420 unsigned long flags;
421 struct list_head *np;
422 bool drop_boost_mutex = false;
423 struct rcu_data *rdp;
424 struct rcu_node *rnp;
425 union rcu_special special;
426
427 /* NMI handlers cannot block and cannot safely manipulate state. */
428 if (in_nmi())
429 return;
430
431 local_irq_save(flags);
432
433 /*
434 * If RCU core is waiting for this CPU to exit its critical section,
435 * report the fact that it has exited. Because irqs are disabled,
436 * t->rcu_read_unlock_special cannot change.
437 */
438 special = t->rcu_read_unlock_special;
439 if (special.b.need_qs) {
440 rcu_preempt_qs();
441 t->rcu_read_unlock_special.b.need_qs = false;
442 if (!t->rcu_read_unlock_special.s) {
443 local_irq_restore(flags);
444 return;
445 }
446 }
447
448 /*
449 * Respond to a request for an expedited grace period, but only if
450 * we were not preempted, meaning that we were running on the same
451 * CPU throughout. If we were preempted, the exp_need_qs flag
452 * would have been cleared at the time of the first preemption,
453 * and the quiescent state would be reported when we were dequeued.
454 */
455 if (special.b.exp_need_qs) {
456 WARN_ON_ONCE(special.b.blocked);
457 t->rcu_read_unlock_special.b.exp_need_qs = false;
458 rdp = this_cpu_ptr(rcu_state_p->rda);
459 rcu_report_exp_rdp(rcu_state_p, rdp, true);
460 if (!t->rcu_read_unlock_special.s) {
461 local_irq_restore(flags);
462 return;
463 }
464 }
465
466 /* Hardware IRQ handlers cannot block, complain if they get here. */
467 if (in_irq() || in_serving_softirq()) {
468 lockdep_rcu_suspicious(__FILE__, __LINE__,
469 "rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n");
470 pr_alert("->rcu_read_unlock_special: %#x (b: %d, enq: %d nq: %d)\n",
471 t->rcu_read_unlock_special.s,
472 t->rcu_read_unlock_special.b.blocked,
473 t->rcu_read_unlock_special.b.exp_need_qs,
474 t->rcu_read_unlock_special.b.need_qs);
475 local_irq_restore(flags);
476 return;
477 }
478
479 /* Clean up if blocked during RCU read-side critical section. */
480 if (special.b.blocked) {
481 t->rcu_read_unlock_special.b.blocked = false;
482
483 /*
484 * Remove this task from the list it blocked on. The task
485 * now remains queued on the rcu_node corresponding to the
486 * CPU it first blocked on, so there is no longer any need
487 * to loop. Retain a WARN_ON_ONCE() out of sheer paranoia.
488 */
489 rnp = t->rcu_blocked_node;
490 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
491 WARN_ON_ONCE(rnp != t->rcu_blocked_node);
492 WARN_ON_ONCE(rnp->level != rcu_num_lvls - 1);
493 empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
494 empty_exp = sync_rcu_preempt_exp_done(rnp);
495 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
496 np = rcu_next_node_entry(t, rnp);
497 list_del_init(&t->rcu_node_entry);
498 t->rcu_blocked_node = NULL;
499 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
500 rnp->gpnum, t->pid);
501 if (&t->rcu_node_entry == rnp->gp_tasks)
502 rnp->gp_tasks = np;
503 if (&t->rcu_node_entry == rnp->exp_tasks)
504 rnp->exp_tasks = np;
505 if (IS_ENABLED(CONFIG_RCU_BOOST)) {
506 /* Snapshot ->boost_mtx ownership w/rnp->lock held. */
507 drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
508 if (&t->rcu_node_entry == rnp->boost_tasks)
509 rnp->boost_tasks = np;
510 }
511
512 /*
513 * If this was the last task on the current list, and if
514 * we aren't waiting on any CPUs, report the quiescent state.
515 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
516 * so we must take a snapshot of the expedited state.
517 */
518 empty_exp_now = sync_rcu_preempt_exp_done(rnp);
519 if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
520 trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
521 rnp->gpnum,
522 0, rnp->qsmask,
523 rnp->level,
524 rnp->grplo,
525 rnp->grphi,
526 !!rnp->gp_tasks);
527 rcu_report_unblock_qs_rnp(rcu_state_p, rnp, flags);
528 } else {
529 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
530 }
531
532 /* Unboost if we were boosted. */
533 if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
534 rt_mutex_futex_unlock(&rnp->boost_mtx);
535
536 /*
537 * If this was the last task on the expedited lists,
538 * then we need to report up the rcu_node hierarchy.
539 */
540 if (!empty_exp && empty_exp_now)
541 rcu_report_exp_rnp(rcu_state_p, rnp, true);
542 } else {
543 local_irq_restore(flags);
544 }
545}
546
547/*
548 * Dump detailed information for all tasks blocking the current RCU
549 * grace period on the specified rcu_node structure.
550 */
551static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
552{
553 unsigned long flags;
554 struct task_struct *t;
555
556 raw_spin_lock_irqsave_rcu_node(rnp, flags);
557 if (!rcu_preempt_blocked_readers_cgp(rnp)) {
558 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
559 return;
560 }
561 t = list_entry(rnp->gp_tasks->prev,
562 struct task_struct, rcu_node_entry);
563 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
564 /*
565 * We could be printing a lot while holding a spinlock.
566 * Avoid triggering hard lockup.
567 */
568 touch_nmi_watchdog();
569 sched_show_task(t);
570 }
571 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
572}
573
574/*
575 * Dump detailed information for all tasks blocking the current RCU
576 * grace period.
577 */
578static void rcu_print_detail_task_stall(struct rcu_state *rsp)
579{
580 struct rcu_node *rnp = rcu_get_root(rsp);
581
582 rcu_print_detail_task_stall_rnp(rnp);
583 rcu_for_each_leaf_node(rsp, rnp)
584 rcu_print_detail_task_stall_rnp(rnp);
585}
586
587static void rcu_print_task_stall_begin(struct rcu_node *rnp)
588{
589 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
590 rnp->level, rnp->grplo, rnp->grphi);
591}
592
593static void rcu_print_task_stall_end(void)
594{
595 pr_cont("\n");
596}
597
598/*
599 * Scan the current list of tasks blocked within RCU read-side critical
600 * sections, printing out the tid of each.
601 */
602static int rcu_print_task_stall(struct rcu_node *rnp)
603{
604 struct task_struct *t;
605 int ndetected = 0;
606
607 if (!rcu_preempt_blocked_readers_cgp(rnp))
608 return 0;
609 rcu_print_task_stall_begin(rnp);
610 t = list_entry(rnp->gp_tasks->prev,
611 struct task_struct, rcu_node_entry);
612 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
613 pr_cont(" P%d", t->pid);
614 ndetected++;
615 }
616 rcu_print_task_stall_end();
617 return ndetected;
618}
619
620/*
621 * Scan the current list of tasks blocked within RCU read-side critical
622 * sections, printing out the tid of each that is blocking the current
623 * expedited grace period.
624 */
625static int rcu_print_task_exp_stall(struct rcu_node *rnp)
626{
627 struct task_struct *t;
628 int ndetected = 0;
629
630 if (!rnp->exp_tasks)
631 return 0;
632 t = list_entry(rnp->exp_tasks->prev,
633 struct task_struct, rcu_node_entry);
634 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
635 pr_cont(" P%d", t->pid);
636 ndetected++;
637 }
638 return ndetected;
639}
640
641/*
642 * Check that the list of blocked tasks for the newly completed grace
643 * period is in fact empty. It is a serious bug to complete a grace
644 * period that still has RCU readers blocked! This function must be
645 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
646 * must be held by the caller.
647 *
648 * Also, if there are blocked tasks on the list, they automatically
649 * block the newly created grace period, so set up ->gp_tasks accordingly.
650 */
651static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
652{
653 struct task_struct *t;
654
655 RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
656 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
657 if (rcu_preempt_has_tasks(rnp)) {
658 rnp->gp_tasks = rnp->blkd_tasks.next;
659 t = container_of(rnp->gp_tasks, struct task_struct,
660 rcu_node_entry);
661 trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
662 rnp->gpnum, t->pid);
663 }
664 WARN_ON_ONCE(rnp->qsmask);
665}
666
667/*
668 * Check for a quiescent state from the current CPU. When a task blocks,
669 * the task is recorded in the corresponding CPU's rcu_node structure,
670 * which is checked elsewhere.
671 *
672 * Caller must disable hard irqs.
673 */
674static void rcu_preempt_check_callbacks(void)
675{
676 struct task_struct *t = current;
677
678 if (t->rcu_read_lock_nesting == 0) {
679 rcu_preempt_qs();
680 return;
681 }
682 if (t->rcu_read_lock_nesting > 0 &&
683 __this_cpu_read(rcu_data_p->core_needs_qs) &&
684 __this_cpu_read(rcu_data_p->cpu_no_qs.b.norm))
685 t->rcu_read_unlock_special.b.need_qs = true;
686}
687
688#ifdef CONFIG_RCU_BOOST
689
690static void rcu_preempt_do_callbacks(void)
691{
692 rcu_do_batch(rcu_state_p, this_cpu_ptr(rcu_data_p));
693}
694
695#endif /* #ifdef CONFIG_RCU_BOOST */
696
697/**
698 * call_rcu() - Queue an RCU callback for invocation after a grace period.
699 * @head: structure to be used for queueing the RCU updates.
700 * @func: actual callback function to be invoked after the grace period
701 *
702 * The callback function will be invoked some time after a full grace
703 * period elapses, in other words after all pre-existing RCU read-side
704 * critical sections have completed. However, the callback function
705 * might well execute concurrently with RCU read-side critical sections
706 * that started after call_rcu() was invoked. RCU read-side critical
707 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
708 * and may be nested.
709 *
710 * Note that all CPUs must agree that the grace period extended beyond
711 * all pre-existing RCU read-side critical section. On systems with more
712 * than one CPU, this means that when "func()" is invoked, each CPU is
713 * guaranteed to have executed a full memory barrier since the end of its
714 * last RCU read-side critical section whose beginning preceded the call
715 * to call_rcu(). It also means that each CPU executing an RCU read-side
716 * critical section that continues beyond the start of "func()" must have
717 * executed a memory barrier after the call_rcu() but before the beginning
718 * of that RCU read-side critical section. Note that these guarantees
719 * include CPUs that are offline, idle, or executing in user mode, as
720 * well as CPUs that are executing in the kernel.
721 *
722 * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
723 * resulting RCU callback function "func()", then both CPU A and CPU B are
724 * guaranteed to execute a full memory barrier during the time interval
725 * between the call to call_rcu() and the invocation of "func()" -- even
726 * if CPU A and CPU B are the same CPU (but again only if the system has
727 * more than one CPU).
728 */
729void call_rcu(struct rcu_head *head, rcu_callback_t func)
730{
731 __call_rcu(head, func, rcu_state_p, -1, 0);
732}
733EXPORT_SYMBOL_GPL(call_rcu);
734
735/**
736 * synchronize_rcu - wait until a grace period has elapsed.
737 *
738 * Control will return to the caller some time after a full grace
739 * period has elapsed, in other words after all currently executing RCU
740 * read-side critical sections have completed. Note, however, that
741 * upon return from synchronize_rcu(), the caller might well be executing
742 * concurrently with new RCU read-side critical sections that began while
743 * synchronize_rcu() was waiting. RCU read-side critical sections are
744 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
745 *
746 * See the description of synchronize_sched() for more detailed
747 * information on memory-ordering guarantees. However, please note
748 * that -only- the memory-ordering guarantees apply. For example,
749 * synchronize_rcu() is -not- guaranteed to wait on things like code
750 * protected by preempt_disable(), instead, synchronize_rcu() is -only-
751 * guaranteed to wait on RCU read-side critical sections, that is, sections
752 * of code protected by rcu_read_lock().
753 */
754void synchronize_rcu(void)
755{
756 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
757 lock_is_held(&rcu_lock_map) ||
758 lock_is_held(&rcu_sched_lock_map),
759 "Illegal synchronize_rcu() in RCU read-side critical section");
760 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
761 return;
762 if (rcu_gp_is_expedited())
763 synchronize_rcu_expedited();
764 else
765 wait_rcu_gp(call_rcu);
766}
767EXPORT_SYMBOL_GPL(synchronize_rcu);
768
769/**
770 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
771 *
772 * Note that this primitive does not necessarily wait for an RCU grace period
773 * to complete. For example, if there are no RCU callbacks queued anywhere
774 * in the system, then rcu_barrier() is within its rights to return
775 * immediately, without waiting for anything, much less an RCU grace period.
776 */
777void rcu_barrier(void)
778{
779 _rcu_barrier(rcu_state_p);
780}
781EXPORT_SYMBOL_GPL(rcu_barrier);
782
783/*
784 * Initialize preemptible RCU's state structures.
785 */
786static void __init __rcu_init_preempt(void)
787{
788 rcu_init_one(rcu_state_p);
789}
790
791/*
792 * Check for a task exiting while in a preemptible-RCU read-side
793 * critical section, clean up if so. No need to issue warnings,
794 * as debug_check_no_locks_held() already does this if lockdep
795 * is enabled.
796 */
797void exit_rcu(void)
798{
799 struct task_struct *t = current;
800
801 if (likely(list_empty(¤t->rcu_node_entry)))
802 return;
803 t->rcu_read_lock_nesting = 1;
804 barrier();
805 t->rcu_read_unlock_special.b.blocked = true;
806 __rcu_read_unlock();
807}
808
809#else /* #ifdef CONFIG_PREEMPT_RCU */
810
811static struct rcu_state *const rcu_state_p = &rcu_sched_state;
812
813/*
814 * Tell them what RCU they are running.
815 */
816static void __init rcu_bootup_announce(void)
817{
818 pr_info("Hierarchical RCU implementation.\n");
819 rcu_bootup_announce_oddness();
820}
821
822/*
823 * Because preemptible RCU does not exist, we never have to check for
824 * CPUs being in quiescent states.
825 */
826static void rcu_preempt_note_context_switch(bool preempt)
827{
828}
829
830/*
831 * Because preemptible RCU does not exist, there are never any preempted
832 * RCU readers.
833 */
834static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
835{
836 return 0;
837}
838
839/*
840 * Because there is no preemptible RCU, there can be no readers blocked.
841 */
842static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
843{
844 return false;
845}
846
847/*
848 * Because preemptible RCU does not exist, we never have to check for
849 * tasks blocked within RCU read-side critical sections.
850 */
851static void rcu_print_detail_task_stall(struct rcu_state *rsp)
852{
853}
854
855/*
856 * Because preemptible RCU does not exist, we never have to check for
857 * tasks blocked within RCU read-side critical sections.
858 */
859static int rcu_print_task_stall(struct rcu_node *rnp)
860{
861 return 0;
862}
863
864/*
865 * Because preemptible RCU does not exist, we never have to check for
866 * tasks blocked within RCU read-side critical sections that are
867 * blocking the current expedited grace period.
868 */
869static int rcu_print_task_exp_stall(struct rcu_node *rnp)
870{
871 return 0;
872}
873
874/*
875 * Because there is no preemptible RCU, there can be no readers blocked,
876 * so there is no need to check for blocked tasks. So check only for
877 * bogus qsmask values.
878 */
879static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
880{
881 WARN_ON_ONCE(rnp->qsmask);
882}
883
884/*
885 * Because preemptible RCU does not exist, it never has any callbacks
886 * to check.
887 */
888static void rcu_preempt_check_callbacks(void)
889{
890}
891
892/*
893 * Because preemptible RCU does not exist, rcu_barrier() is just
894 * another name for rcu_barrier_sched().
895 */
896void rcu_barrier(void)
897{
898 rcu_barrier_sched();
899}
900EXPORT_SYMBOL_GPL(rcu_barrier);
901
902/*
903 * Because preemptible RCU does not exist, it need not be initialized.
904 */
905static void __init __rcu_init_preempt(void)
906{
907}
908
909/*
910 * Because preemptible RCU does not exist, tasks cannot possibly exit
911 * while in preemptible RCU read-side critical sections.
912 */
913void exit_rcu(void)
914{
915}
916
917#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
918
919#ifdef CONFIG_RCU_BOOST
920
921static void rcu_wake_cond(struct task_struct *t, int status)
922{
923 /*
924 * If the thread is yielding, only wake it when this
925 * is invoked from idle
926 */
927 if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
928 wake_up_process(t);
929}
930
931/*
932 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
933 * or ->boost_tasks, advancing the pointer to the next task in the
934 * ->blkd_tasks list.
935 *
936 * Note that irqs must be enabled: boosting the task can block.
937 * Returns 1 if there are more tasks needing to be boosted.
938 */
939static int rcu_boost(struct rcu_node *rnp)
940{
941 unsigned long flags;
942 struct task_struct *t;
943 struct list_head *tb;
944
945 if (READ_ONCE(rnp->exp_tasks) == NULL &&
946 READ_ONCE(rnp->boost_tasks) == NULL)
947 return 0; /* Nothing left to boost. */
948
949 raw_spin_lock_irqsave_rcu_node(rnp, flags);
950
951 /*
952 * Recheck under the lock: all tasks in need of boosting
953 * might exit their RCU read-side critical sections on their own.
954 */
955 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
956 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
957 return 0;
958 }
959
960 /*
961 * Preferentially boost tasks blocking expedited grace periods.
962 * This cannot starve the normal grace periods because a second
963 * expedited grace period must boost all blocked tasks, including
964 * those blocking the pre-existing normal grace period.
965 */
966 if (rnp->exp_tasks != NULL)
967 tb = rnp->exp_tasks;
968 else
969 tb = rnp->boost_tasks;
970
971 /*
972 * We boost task t by manufacturing an rt_mutex that appears to
973 * be held by task t. We leave a pointer to that rt_mutex where
974 * task t can find it, and task t will release the mutex when it
975 * exits its outermost RCU read-side critical section. Then
976 * simply acquiring this artificial rt_mutex will boost task
977 * t's priority. (Thanks to tglx for suggesting this approach!)
978 *
979 * Note that task t must acquire rnp->lock to remove itself from
980 * the ->blkd_tasks list, which it will do from exit() if from
981 * nowhere else. We therefore are guaranteed that task t will
982 * stay around at least until we drop rnp->lock. Note that
983 * rnp->lock also resolves races between our priority boosting
984 * and task t's exiting its outermost RCU read-side critical
985 * section.
986 */
987 t = container_of(tb, struct task_struct, rcu_node_entry);
988 rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
989 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
990 /* Lock only for side effect: boosts task t's priority. */
991 rt_mutex_lock(&rnp->boost_mtx);
992 rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
993
994 return READ_ONCE(rnp->exp_tasks) != NULL ||
995 READ_ONCE(rnp->boost_tasks) != NULL;
996}
997
998/*
999 * Priority-boosting kthread, one per leaf rcu_node.
1000 */
1001static int rcu_boost_kthread(void *arg)
1002{
1003 struct rcu_node *rnp = (struct rcu_node *)arg;
1004 int spincnt = 0;
1005 int more2boost;
1006
1007 trace_rcu_utilization(TPS("Start boost kthread@init"));
1008 for (;;) {
1009 rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1010 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1011 rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1012 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1013 rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1014 more2boost = rcu_boost(rnp);
1015 if (more2boost)
1016 spincnt++;
1017 else
1018 spincnt = 0;
1019 if (spincnt > 10) {
1020 rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1021 trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1022 schedule_timeout_interruptible(2);
1023 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1024 spincnt = 0;
1025 }
1026 }
1027 /* NOTREACHED */
1028 trace_rcu_utilization(TPS("End boost kthread@notreached"));
1029 return 0;
1030}
1031
1032/*
1033 * Check to see if it is time to start boosting RCU readers that are
1034 * blocking the current grace period, and, if so, tell the per-rcu_node
1035 * kthread to start boosting them. If there is an expedited grace
1036 * period in progress, it is always time to boost.
1037 *
1038 * The caller must hold rnp->lock, which this function releases.
1039 * The ->boost_kthread_task is immortal, so we don't need to worry
1040 * about it going away.
1041 */
1042static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1043 __releases(rnp->lock)
1044{
1045 struct task_struct *t;
1046
1047 raw_lockdep_assert_held_rcu_node(rnp);
1048 if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1049 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1050 return;
1051 }
1052 if (rnp->exp_tasks != NULL ||
1053 (rnp->gp_tasks != NULL &&
1054 rnp->boost_tasks == NULL &&
1055 rnp->qsmask == 0 &&
1056 ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1057 if (rnp->exp_tasks == NULL)
1058 rnp->boost_tasks = rnp->gp_tasks;
1059 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1060 t = rnp->boost_kthread_task;
1061 if (t)
1062 rcu_wake_cond(t, rnp->boost_kthread_status);
1063 } else {
1064 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1065 }
1066}
1067
1068/*
1069 * Wake up the per-CPU kthread to invoke RCU callbacks.
1070 */
1071static void invoke_rcu_callbacks_kthread(void)
1072{
1073 unsigned long flags;
1074
1075 local_irq_save(flags);
1076 __this_cpu_write(rcu_cpu_has_work, 1);
1077 if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
1078 current != __this_cpu_read(rcu_cpu_kthread_task)) {
1079 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
1080 __this_cpu_read(rcu_cpu_kthread_status));
1081 }
1082 local_irq_restore(flags);
1083}
1084
1085/*
1086 * Is the current CPU running the RCU-callbacks kthread?
1087 * Caller must have preemption disabled.
1088 */
1089static bool rcu_is_callbacks_kthread(void)
1090{
1091 return __this_cpu_read(rcu_cpu_kthread_task) == current;
1092}
1093
1094#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1095
1096/*
1097 * Do priority-boost accounting for the start of a new grace period.
1098 */
1099static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1100{
1101 rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1102}
1103
1104/*
1105 * Create an RCU-boost kthread for the specified node if one does not
1106 * already exist. We only create this kthread for preemptible RCU.
1107 * Returns zero if all is well, a negated errno otherwise.
1108 */
1109static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
1110 struct rcu_node *rnp)
1111{
1112 int rnp_index = rnp - &rsp->node[0];
1113 unsigned long flags;
1114 struct sched_param sp;
1115 struct task_struct *t;
1116
1117 if (rcu_state_p != rsp)
1118 return 0;
1119
1120 if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
1121 return 0;
1122
1123 rsp->boost = 1;
1124 if (rnp->boost_kthread_task != NULL)
1125 return 0;
1126 t = kthread_create(rcu_boost_kthread, (void *)rnp,
1127 "rcub/%d", rnp_index);
1128 if (IS_ERR(t))
1129 return PTR_ERR(t);
1130 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1131 rnp->boost_kthread_task = t;
1132 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1133 sp.sched_priority = kthread_prio;
1134 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1135 wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1136 return 0;
1137}
1138
1139static void rcu_kthread_do_work(void)
1140{
1141 rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
1142 rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
1143 rcu_preempt_do_callbacks();
1144}
1145
1146static void rcu_cpu_kthread_setup(unsigned int cpu)
1147{
1148 struct sched_param sp;
1149
1150 sp.sched_priority = kthread_prio;
1151 sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
1152}
1153
1154static void rcu_cpu_kthread_park(unsigned int cpu)
1155{
1156 per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1157}
1158
1159static int rcu_cpu_kthread_should_run(unsigned int cpu)
1160{
1161 return __this_cpu_read(rcu_cpu_has_work);
1162}
1163
1164/*
1165 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
1166 * RCU softirq used in flavors and configurations of RCU that do not
1167 * support RCU priority boosting.
1168 */
1169static void rcu_cpu_kthread(unsigned int cpu)
1170{
1171 unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
1172 char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
1173 int spincnt;
1174
1175 for (spincnt = 0; spincnt < 10; spincnt++) {
1176 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1177 local_bh_disable();
1178 *statusp = RCU_KTHREAD_RUNNING;
1179 this_cpu_inc(rcu_cpu_kthread_loops);
1180 local_irq_disable();
1181 work = *workp;
1182 *workp = 0;
1183 local_irq_enable();
1184 if (work)
1185 rcu_kthread_do_work();
1186 local_bh_enable();
1187 if (*workp == 0) {
1188 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1189 *statusp = RCU_KTHREAD_WAITING;
1190 return;
1191 }
1192 }
1193 *statusp = RCU_KTHREAD_YIELDING;
1194 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1195 schedule_timeout_interruptible(2);
1196 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1197 *statusp = RCU_KTHREAD_WAITING;
1198}
1199
1200/*
1201 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1202 * served by the rcu_node in question. The CPU hotplug lock is still
1203 * held, so the value of rnp->qsmaskinit will be stable.
1204 *
1205 * We don't include outgoingcpu in the affinity set, use -1 if there is
1206 * no outgoing CPU. If there are no CPUs left in the affinity set,
1207 * this function allows the kthread to execute on any CPU.
1208 */
1209static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1210{
1211 struct task_struct *t = rnp->boost_kthread_task;
1212 unsigned long mask = rcu_rnp_online_cpus(rnp);
1213 cpumask_var_t cm;
1214 int cpu;
1215
1216 if (!t)
1217 return;
1218 if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1219 return;
1220 for_each_leaf_node_possible_cpu(rnp, cpu)
1221 if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
1222 cpu != outgoingcpu)
1223 cpumask_set_cpu(cpu, cm);
1224 if (cpumask_weight(cm) == 0)
1225 cpumask_setall(cm);
1226 set_cpus_allowed_ptr(t, cm);
1227 free_cpumask_var(cm);
1228}
1229
1230static struct smp_hotplug_thread rcu_cpu_thread_spec = {
1231 .store = &rcu_cpu_kthread_task,
1232 .thread_should_run = rcu_cpu_kthread_should_run,
1233 .thread_fn = rcu_cpu_kthread,
1234 .thread_comm = "rcuc/%u",
1235 .setup = rcu_cpu_kthread_setup,
1236 .park = rcu_cpu_kthread_park,
1237};
1238
1239/*
1240 * Spawn boost kthreads -- called as soon as the scheduler is running.
1241 */
1242static void __init rcu_spawn_boost_kthreads(void)
1243{
1244 struct rcu_node *rnp;
1245 int cpu;
1246
1247 for_each_possible_cpu(cpu)
1248 per_cpu(rcu_cpu_has_work, cpu) = 0;
1249 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
1250 rcu_for_each_leaf_node(rcu_state_p, rnp)
1251 (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1252}
1253
1254static void rcu_prepare_kthreads(int cpu)
1255{
1256 struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
1257 struct rcu_node *rnp = rdp->mynode;
1258
1259 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1260 if (rcu_scheduler_fully_active)
1261 (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1262}
1263
1264#else /* #ifdef CONFIG_RCU_BOOST */
1265
1266static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1267 __releases(rnp->lock)
1268{
1269 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1270}
1271
1272static void invoke_rcu_callbacks_kthread(void)
1273{
1274 WARN_ON_ONCE(1);
1275}
1276
1277static bool rcu_is_callbacks_kthread(void)
1278{
1279 return false;
1280}
1281
1282static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1283{
1284}
1285
1286static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1287{
1288}
1289
1290static void __init rcu_spawn_boost_kthreads(void)
1291{
1292}
1293
1294static void rcu_prepare_kthreads(int cpu)
1295{
1296}
1297
1298#endif /* #else #ifdef CONFIG_RCU_BOOST */
1299
1300#if !defined(CONFIG_RCU_FAST_NO_HZ)
1301
1302/*
1303 * Check to see if any future RCU-related work will need to be done
1304 * by the current CPU, even if none need be done immediately, returning
1305 * 1 if so. This function is part of the RCU implementation; it is -not-
1306 * an exported member of the RCU API.
1307 *
1308 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1309 * any flavor of RCU.
1310 */
1311int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1312{
1313 *nextevt = KTIME_MAX;
1314 return rcu_cpu_has_callbacks(NULL);
1315}
1316
1317/*
1318 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1319 * after it.
1320 */
1321static void rcu_cleanup_after_idle(void)
1322{
1323}
1324
1325/*
1326 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1327 * is nothing.
1328 */
1329static void rcu_prepare_for_idle(void)
1330{
1331}
1332
1333/*
1334 * Don't bother keeping a running count of the number of RCU callbacks
1335 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1336 */
1337static void rcu_idle_count_callbacks_posted(void)
1338{
1339}
1340
1341#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1342
1343/*
1344 * This code is invoked when a CPU goes idle, at which point we want
1345 * to have the CPU do everything required for RCU so that it can enter
1346 * the energy-efficient dyntick-idle mode. This is handled by a
1347 * state machine implemented by rcu_prepare_for_idle() below.
1348 *
1349 * The following three proprocessor symbols control this state machine:
1350 *
1351 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1352 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1353 * is sized to be roughly one RCU grace period. Those energy-efficiency
1354 * benchmarkers who might otherwise be tempted to set this to a large
1355 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1356 * system. And if you are -that- concerned about energy efficiency,
1357 * just power the system down and be done with it!
1358 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1359 * permitted to sleep in dyntick-idle mode with only lazy RCU
1360 * callbacks pending. Setting this too high can OOM your system.
1361 *
1362 * The values below work well in practice. If future workloads require
1363 * adjustment, they can be converted into kernel config parameters, though
1364 * making the state machine smarter might be a better option.
1365 */
1366#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1367#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1368
1369static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
1370module_param(rcu_idle_gp_delay, int, 0644);
1371static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
1372module_param(rcu_idle_lazy_gp_delay, int, 0644);
1373
1374/*
1375 * Try to advance callbacks for all flavors of RCU on the current CPU, but
1376 * only if it has been awhile since the last time we did so. Afterwards,
1377 * if there are any callbacks ready for immediate invocation, return true.
1378 */
1379static bool __maybe_unused rcu_try_advance_all_cbs(void)
1380{
1381 bool cbs_ready = false;
1382 struct rcu_data *rdp;
1383 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1384 struct rcu_node *rnp;
1385 struct rcu_state *rsp;
1386
1387 /* Exit early if we advanced recently. */
1388 if (jiffies == rdtp->last_advance_all)
1389 return false;
1390 rdtp->last_advance_all = jiffies;
1391
1392 for_each_rcu_flavor(rsp) {
1393 rdp = this_cpu_ptr(rsp->rda);
1394 rnp = rdp->mynode;
1395
1396 /*
1397 * Don't bother checking unless a grace period has
1398 * completed since we last checked and there are
1399 * callbacks not yet ready to invoke.
1400 */
1401 if ((rdp->completed != rnp->completed ||
1402 unlikely(READ_ONCE(rdp->gpwrap))) &&
1403 rcu_segcblist_pend_cbs(&rdp->cblist))
1404 note_gp_changes(rsp, rdp);
1405
1406 if (rcu_segcblist_ready_cbs(&rdp->cblist))
1407 cbs_ready = true;
1408 }
1409 return cbs_ready;
1410}
1411
1412/*
1413 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1414 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1415 * caller to set the timeout based on whether or not there are non-lazy
1416 * callbacks.
1417 *
1418 * The caller must have disabled interrupts.
1419 */
1420int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1421{
1422 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1423 unsigned long dj;
1424
1425 lockdep_assert_irqs_disabled();
1426
1427 /* Snapshot to detect later posting of non-lazy callback. */
1428 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1429
1430 /* If no callbacks, RCU doesn't need the CPU. */
1431 if (!rcu_cpu_has_callbacks(&rdtp->all_lazy)) {
1432 *nextevt = KTIME_MAX;
1433 return 0;
1434 }
1435
1436 /* Attempt to advance callbacks. */
1437 if (rcu_try_advance_all_cbs()) {
1438 /* Some ready to invoke, so initiate later invocation. */
1439 invoke_rcu_core();
1440 return 1;
1441 }
1442 rdtp->last_accelerate = jiffies;
1443
1444 /* Request timer delay depending on laziness, and round. */
1445 if (!rdtp->all_lazy) {
1446 dj = round_up(rcu_idle_gp_delay + jiffies,
1447 rcu_idle_gp_delay) - jiffies;
1448 } else {
1449 dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1450 }
1451 *nextevt = basemono + dj * TICK_NSEC;
1452 return 0;
1453}
1454
1455/*
1456 * Prepare a CPU for idle from an RCU perspective. The first major task
1457 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1458 * The second major task is to check to see if a non-lazy callback has
1459 * arrived at a CPU that previously had only lazy callbacks. The third
1460 * major task is to accelerate (that is, assign grace-period numbers to)
1461 * any recently arrived callbacks.
1462 *
1463 * The caller must have disabled interrupts.
1464 */
1465static void rcu_prepare_for_idle(void)
1466{
1467 bool needwake;
1468 struct rcu_data *rdp;
1469 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1470 struct rcu_node *rnp;
1471 struct rcu_state *rsp;
1472 int tne;
1473
1474 lockdep_assert_irqs_disabled();
1475 if (rcu_is_nocb_cpu(smp_processor_id()))
1476 return;
1477
1478 /* Handle nohz enablement switches conservatively. */
1479 tne = READ_ONCE(tick_nohz_active);
1480 if (tne != rdtp->tick_nohz_enabled_snap) {
1481 if (rcu_cpu_has_callbacks(NULL))
1482 invoke_rcu_core(); /* force nohz to see update. */
1483 rdtp->tick_nohz_enabled_snap = tne;
1484 return;
1485 }
1486 if (!tne)
1487 return;
1488
1489 /*
1490 * If a non-lazy callback arrived at a CPU having only lazy
1491 * callbacks, invoke RCU core for the side-effect of recalculating
1492 * idle duration on re-entry to idle.
1493 */
1494 if (rdtp->all_lazy &&
1495 rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
1496 rdtp->all_lazy = false;
1497 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1498 invoke_rcu_core();
1499 return;
1500 }
1501
1502 /*
1503 * If we have not yet accelerated this jiffy, accelerate all
1504 * callbacks on this CPU.
1505 */
1506 if (rdtp->last_accelerate == jiffies)
1507 return;
1508 rdtp->last_accelerate = jiffies;
1509 for_each_rcu_flavor(rsp) {
1510 rdp = this_cpu_ptr(rsp->rda);
1511 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1512 continue;
1513 rnp = rdp->mynode;
1514 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
1515 needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
1516 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
1517 if (needwake)
1518 rcu_gp_kthread_wake(rsp);
1519 }
1520}
1521
1522/*
1523 * Clean up for exit from idle. Attempt to advance callbacks based on
1524 * any grace periods that elapsed while the CPU was idle, and if any
1525 * callbacks are now ready to invoke, initiate invocation.
1526 */
1527static void rcu_cleanup_after_idle(void)
1528{
1529 lockdep_assert_irqs_disabled();
1530 if (rcu_is_nocb_cpu(smp_processor_id()))
1531 return;
1532 if (rcu_try_advance_all_cbs())
1533 invoke_rcu_core();
1534}
1535
1536/*
1537 * Keep a running count of the number of non-lazy callbacks posted
1538 * on this CPU. This running counter (which is never decremented) allows
1539 * rcu_prepare_for_idle() to detect when something out of the idle loop
1540 * posts a callback, even if an equal number of callbacks are invoked.
1541 * Of course, callbacks should only be posted from within a trace event
1542 * designed to be called from idle or from within RCU_NONIDLE().
1543 */
1544static void rcu_idle_count_callbacks_posted(void)
1545{
1546 __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
1547}
1548
1549/*
1550 * Data for flushing lazy RCU callbacks at OOM time.
1551 */
1552static atomic_t oom_callback_count;
1553static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
1554
1555/*
1556 * RCU OOM callback -- decrement the outstanding count and deliver the
1557 * wake-up if we are the last one.
1558 */
1559static void rcu_oom_callback(struct rcu_head *rhp)
1560{
1561 if (atomic_dec_and_test(&oom_callback_count))
1562 wake_up(&oom_callback_wq);
1563}
1564
1565/*
1566 * Post an rcu_oom_notify callback on the current CPU if it has at
1567 * least one lazy callback. This will unnecessarily post callbacks
1568 * to CPUs that already have a non-lazy callback at the end of their
1569 * callback list, but this is an infrequent operation, so accept some
1570 * extra overhead to keep things simple.
1571 */
1572static void rcu_oom_notify_cpu(void *unused)
1573{
1574 struct rcu_state *rsp;
1575 struct rcu_data *rdp;
1576
1577 for_each_rcu_flavor(rsp) {
1578 rdp = raw_cpu_ptr(rsp->rda);
1579 if (rcu_segcblist_n_lazy_cbs(&rdp->cblist)) {
1580 atomic_inc(&oom_callback_count);
1581 rsp->call(&rdp->oom_head, rcu_oom_callback);
1582 }
1583 }
1584}
1585
1586/*
1587 * If low on memory, ensure that each CPU has a non-lazy callback.
1588 * This will wake up CPUs that have only lazy callbacks, in turn
1589 * ensuring that they free up the corresponding memory in a timely manner.
1590 * Because an uncertain amount of memory will be freed in some uncertain
1591 * timeframe, we do not claim to have freed anything.
1592 */
1593static int rcu_oom_notify(struct notifier_block *self,
1594 unsigned long notused, void *nfreed)
1595{
1596 int cpu;
1597
1598 /* Wait for callbacks from earlier instance to complete. */
1599 wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
1600 smp_mb(); /* Ensure callback reuse happens after callback invocation. */
1601
1602 /*
1603 * Prevent premature wakeup: ensure that all increments happen
1604 * before there is a chance of the counter reaching zero.
1605 */
1606 atomic_set(&oom_callback_count, 1);
1607
1608 for_each_online_cpu(cpu) {
1609 smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
1610 cond_resched_rcu_qs();
1611 }
1612
1613 /* Unconditionally decrement: no need to wake ourselves up. */
1614 atomic_dec(&oom_callback_count);
1615
1616 return NOTIFY_OK;
1617}
1618
1619static struct notifier_block rcu_oom_nb = {
1620 .notifier_call = rcu_oom_notify
1621};
1622
1623static int __init rcu_register_oom_notifier(void)
1624{
1625 register_oom_notifier(&rcu_oom_nb);
1626 return 0;
1627}
1628early_initcall(rcu_register_oom_notifier);
1629
1630#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1631
1632#ifdef CONFIG_RCU_FAST_NO_HZ
1633
1634static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1635{
1636 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1637 unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
1638
1639 sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1640 rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
1641 ulong2long(nlpd),
1642 rdtp->all_lazy ? 'L' : '.',
1643 rdtp->tick_nohz_enabled_snap ? '.' : 'D');
1644}
1645
1646#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1647
1648static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1649{
1650 *cp = '\0';
1651}
1652
1653#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1654
1655/* Initiate the stall-info list. */
1656static void print_cpu_stall_info_begin(void)
1657{
1658 pr_cont("\n");
1659}
1660
1661/*
1662 * Print out diagnostic information for the specified stalled CPU.
1663 *
1664 * If the specified CPU is aware of the current RCU grace period
1665 * (flavor specified by rsp), then print the number of scheduling
1666 * clock interrupts the CPU has taken during the time that it has
1667 * been aware. Otherwise, print the number of RCU grace periods
1668 * that this CPU is ignorant of, for example, "1" if the CPU was
1669 * aware of the previous grace period.
1670 *
1671 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1672 */
1673static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1674{
1675 unsigned long delta;
1676 char fast_no_hz[72];
1677 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1678 struct rcu_dynticks *rdtp = rdp->dynticks;
1679 char *ticks_title;
1680 unsigned long ticks_value;
1681
1682 /*
1683 * We could be printing a lot while holding a spinlock. Avoid
1684 * triggering hard lockup.
1685 */
1686 touch_nmi_watchdog();
1687
1688 if (rsp->gpnum == rdp->gpnum) {
1689 ticks_title = "ticks this GP";
1690 ticks_value = rdp->ticks_this_gp;
1691 } else {
1692 ticks_title = "GPs behind";
1693 ticks_value = rsp->gpnum - rdp->gpnum;
1694 }
1695 print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
1696 delta = rdp->mynode->gpnum - rdp->rcu_iw_gpnum;
1697 pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%ld softirq=%u/%u fqs=%ld %s\n",
1698 cpu,
1699 "O."[!!cpu_online(cpu)],
1700 "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
1701 "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
1702 !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
1703 rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
1704 "!."[!delta],
1705 ticks_value, ticks_title,
1706 rcu_dynticks_snap(rdtp) & 0xfff,
1707 rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
1708 rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
1709 READ_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart,
1710 fast_no_hz);
1711}
1712
1713/* Terminate the stall-info list. */
1714static void print_cpu_stall_info_end(void)
1715{
1716 pr_err("\t");
1717}
1718
1719/* Zero ->ticks_this_gp for all flavors of RCU. */
1720static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1721{
1722 rdp->ticks_this_gp = 0;
1723 rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
1724}
1725
1726/* Increment ->ticks_this_gp for all flavors of RCU. */
1727static void increment_cpu_stall_ticks(void)
1728{
1729 struct rcu_state *rsp;
1730
1731 for_each_rcu_flavor(rsp)
1732 raw_cpu_inc(rsp->rda->ticks_this_gp);
1733}
1734
1735#ifdef CONFIG_RCU_NOCB_CPU
1736
1737/*
1738 * Offload callback processing from the boot-time-specified set of CPUs
1739 * specified by rcu_nocb_mask. For each CPU in the set, there is a
1740 * kthread created that pulls the callbacks from the corresponding CPU,
1741 * waits for a grace period to elapse, and invokes the callbacks.
1742 * The no-CBs CPUs do a wake_up() on their kthread when they insert
1743 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
1744 * has been specified, in which case each kthread actively polls its
1745 * CPU. (Which isn't so great for energy efficiency, but which does
1746 * reduce RCU's overhead on that CPU.)
1747 *
1748 * This is intended to be used in conjunction with Frederic Weisbecker's
1749 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
1750 * running CPU-bound user-mode computations.
1751 *
1752 * Offloading of callback processing could also in theory be used as
1753 * an energy-efficiency measure because CPUs with no RCU callbacks
1754 * queued are more aggressive about entering dyntick-idle mode.
1755 */
1756
1757
1758/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
1759static int __init rcu_nocb_setup(char *str)
1760{
1761 alloc_bootmem_cpumask_var(&rcu_nocb_mask);
1762 cpulist_parse(str, rcu_nocb_mask);
1763 return 1;
1764}
1765__setup("rcu_nocbs=", rcu_nocb_setup);
1766
1767static int __init parse_rcu_nocb_poll(char *arg)
1768{
1769 rcu_nocb_poll = true;
1770 return 0;
1771}
1772early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
1773
1774/*
1775 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
1776 * grace period.
1777 */
1778static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
1779{
1780 swake_up_all(sq);
1781}
1782
1783/*
1784 * Set the root rcu_node structure's ->need_future_gp field
1785 * based on the sum of those of all rcu_node structures. This does
1786 * double-count the root rcu_node structure's requests, but this
1787 * is necessary to handle the possibility of a rcu_nocb_kthread()
1788 * having awakened during the time that the rcu_node structures
1789 * were being updated for the end of the previous grace period.
1790 */
1791static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
1792{
1793 rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
1794}
1795
1796static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
1797{
1798 return &rnp->nocb_gp_wq[rnp->completed & 0x1];
1799}
1800
1801static void rcu_init_one_nocb(struct rcu_node *rnp)
1802{
1803 init_swait_queue_head(&rnp->nocb_gp_wq[0]);
1804 init_swait_queue_head(&rnp->nocb_gp_wq[1]);
1805}
1806
1807/* Is the specified CPU a no-CBs CPU? */
1808bool rcu_is_nocb_cpu(int cpu)
1809{
1810 if (cpumask_available(rcu_nocb_mask))
1811 return cpumask_test_cpu(cpu, rcu_nocb_mask);
1812 return false;
1813}
1814
1815/*
1816 * Kick the leader kthread for this NOCB group. Caller holds ->nocb_lock
1817 * and this function releases it.
1818 */
1819static void __wake_nocb_leader(struct rcu_data *rdp, bool force,
1820 unsigned long flags)
1821 __releases(rdp->nocb_lock)
1822{
1823 struct rcu_data *rdp_leader = rdp->nocb_leader;
1824
1825 lockdep_assert_held(&rdp->nocb_lock);
1826 if (!READ_ONCE(rdp_leader->nocb_kthread)) {
1827 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1828 return;
1829 }
1830 if (rdp_leader->nocb_leader_sleep || force) {
1831 /* Prior smp_mb__after_atomic() orders against prior enqueue. */
1832 WRITE_ONCE(rdp_leader->nocb_leader_sleep, false);
1833 del_timer(&rdp->nocb_timer);
1834 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1835 smp_mb(); /* ->nocb_leader_sleep before swake_up(). */
1836 swake_up(&rdp_leader->nocb_wq);
1837 } else {
1838 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1839 }
1840}
1841
1842/*
1843 * Kick the leader kthread for this NOCB group, but caller has not
1844 * acquired locks.
1845 */
1846static void wake_nocb_leader(struct rcu_data *rdp, bool force)
1847{
1848 unsigned long flags;
1849
1850 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
1851 __wake_nocb_leader(rdp, force, flags);
1852}
1853
1854/*
1855 * Arrange to wake the leader kthread for this NOCB group at some
1856 * future time when it is safe to do so.
1857 */
1858static void wake_nocb_leader_defer(struct rcu_data *rdp, int waketype,
1859 const char *reason)
1860{
1861 unsigned long flags;
1862
1863 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
1864 if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
1865 mod_timer(&rdp->nocb_timer, jiffies + 1);
1866 WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
1867 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, reason);
1868 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1869}
1870
1871/*
1872 * Does the specified CPU need an RCU callback for the specified flavor
1873 * of rcu_barrier()?
1874 */
1875static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
1876{
1877 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1878 unsigned long ret;
1879#ifdef CONFIG_PROVE_RCU
1880 struct rcu_head *rhp;
1881#endif /* #ifdef CONFIG_PROVE_RCU */
1882
1883 /*
1884 * Check count of all no-CBs callbacks awaiting invocation.
1885 * There needs to be a barrier before this function is called,
1886 * but associated with a prior determination that no more
1887 * callbacks would be posted. In the worst case, the first
1888 * barrier in _rcu_barrier() suffices (but the caller cannot
1889 * necessarily rely on this, not a substitute for the caller
1890 * getting the concurrency design right!). There must also be
1891 * a barrier between the following load an posting of a callback
1892 * (if a callback is in fact needed). This is associated with an
1893 * atomic_inc() in the caller.
1894 */
1895 ret = atomic_long_read(&rdp->nocb_q_count);
1896
1897#ifdef CONFIG_PROVE_RCU
1898 rhp = READ_ONCE(rdp->nocb_head);
1899 if (!rhp)
1900 rhp = READ_ONCE(rdp->nocb_gp_head);
1901 if (!rhp)
1902 rhp = READ_ONCE(rdp->nocb_follower_head);
1903
1904 /* Having no rcuo kthread but CBs after scheduler starts is bad! */
1905 if (!READ_ONCE(rdp->nocb_kthread) && rhp &&
1906 rcu_scheduler_fully_active) {
1907 /* RCU callback enqueued before CPU first came online??? */
1908 pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
1909 cpu, rhp->func);
1910 WARN_ON_ONCE(1);
1911 }
1912#endif /* #ifdef CONFIG_PROVE_RCU */
1913
1914 return !!ret;
1915}
1916
1917/*
1918 * Enqueue the specified string of rcu_head structures onto the specified
1919 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
1920 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
1921 * counts are supplied by rhcount and rhcount_lazy.
1922 *
1923 * If warranted, also wake up the kthread servicing this CPUs queues.
1924 */
1925static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
1926 struct rcu_head *rhp,
1927 struct rcu_head **rhtp,
1928 int rhcount, int rhcount_lazy,
1929 unsigned long flags)
1930{
1931 int len;
1932 struct rcu_head **old_rhpp;
1933 struct task_struct *t;
1934
1935 /* Enqueue the callback on the nocb list and update counts. */
1936 atomic_long_add(rhcount, &rdp->nocb_q_count);
1937 /* rcu_barrier() relies on ->nocb_q_count add before xchg. */
1938 old_rhpp = xchg(&rdp->nocb_tail, rhtp);
1939 WRITE_ONCE(*old_rhpp, rhp);
1940 atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
1941 smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
1942
1943 /* If we are not being polled and there is a kthread, awaken it ... */
1944 t = READ_ONCE(rdp->nocb_kthread);
1945 if (rcu_nocb_poll || !t) {
1946 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
1947 TPS("WakeNotPoll"));
1948 return;
1949 }
1950 len = atomic_long_read(&rdp->nocb_q_count);
1951 if (old_rhpp == &rdp->nocb_head) {
1952 if (!irqs_disabled_flags(flags)) {
1953 /* ... if queue was empty ... */
1954 wake_nocb_leader(rdp, false);
1955 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
1956 TPS("WakeEmpty"));
1957 } else {
1958 wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE,
1959 TPS("WakeEmptyIsDeferred"));
1960 }
1961 rdp->qlen_last_fqs_check = 0;
1962 } else if (len > rdp->qlen_last_fqs_check + qhimark) {
1963 /* ... or if many callbacks queued. */
1964 if (!irqs_disabled_flags(flags)) {
1965 wake_nocb_leader(rdp, true);
1966 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
1967 TPS("WakeOvf"));
1968 } else {
1969 wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE,
1970 TPS("WakeOvfIsDeferred"));
1971 }
1972 rdp->qlen_last_fqs_check = LONG_MAX / 2;
1973 } else {
1974 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
1975 }
1976 return;
1977}
1978
1979/*
1980 * This is a helper for __call_rcu(), which invokes this when the normal
1981 * callback queue is inoperable. If this is not a no-CBs CPU, this
1982 * function returns failure back to __call_rcu(), which can complain
1983 * appropriately.
1984 *
1985 * Otherwise, this function queues the callback where the corresponding
1986 * "rcuo" kthread can find it.
1987 */
1988static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
1989 bool lazy, unsigned long flags)
1990{
1991
1992 if (!rcu_is_nocb_cpu(rdp->cpu))
1993 return false;
1994 __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
1995 if (__is_kfree_rcu_offset((unsigned long)rhp->func))
1996 trace_rcu_kfree_callback(rdp->rsp->name, rhp,
1997 (unsigned long)rhp->func,
1998 -atomic_long_read(&rdp->nocb_q_count_lazy),
1999 -atomic_long_read(&rdp->nocb_q_count));
2000 else
2001 trace_rcu_callback(rdp->rsp->name, rhp,
2002 -atomic_long_read(&rdp->nocb_q_count_lazy),
2003 -atomic_long_read(&rdp->nocb_q_count));
2004
2005 /*
2006 * If called from an extended quiescent state with interrupts
2007 * disabled, invoke the RCU core in order to allow the idle-entry
2008 * deferred-wakeup check to function.
2009 */
2010 if (irqs_disabled_flags(flags) &&
2011 !rcu_is_watching() &&
2012 cpu_online(smp_processor_id()))
2013 invoke_rcu_core();
2014
2015 return true;
2016}
2017
2018/*
2019 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2020 * not a no-CBs CPU.
2021 */
2022static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
2023 struct rcu_data *rdp,
2024 unsigned long flags)
2025{
2026 lockdep_assert_irqs_disabled();
2027 if (!rcu_is_nocb_cpu(smp_processor_id()))
2028 return false; /* Not NOCBs CPU, caller must migrate CBs. */
2029 __call_rcu_nocb_enqueue(my_rdp, rcu_segcblist_head(&rdp->cblist),
2030 rcu_segcblist_tail(&rdp->cblist),
2031 rcu_segcblist_n_cbs(&rdp->cblist),
2032 rcu_segcblist_n_lazy_cbs(&rdp->cblist), flags);
2033 rcu_segcblist_init(&rdp->cblist);
2034 rcu_segcblist_disable(&rdp->cblist);
2035 return true;
2036}
2037
2038/*
2039 * If necessary, kick off a new grace period, and either way wait
2040 * for a subsequent grace period to complete.
2041 */
2042static void rcu_nocb_wait_gp(struct rcu_data *rdp)
2043{
2044 unsigned long c;
2045 bool d;
2046 unsigned long flags;
2047 bool needwake;
2048 struct rcu_node *rnp = rdp->mynode;
2049
2050 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2051 needwake = rcu_start_future_gp(rnp, rdp, &c);
2052 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2053 if (needwake)
2054 rcu_gp_kthread_wake(rdp->rsp);
2055
2056 /*
2057 * Wait for the grace period. Do so interruptibly to avoid messing
2058 * up the load average.
2059 */
2060 trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
2061 for (;;) {
2062 swait_event_interruptible(
2063 rnp->nocb_gp_wq[c & 0x1],
2064 (d = ULONG_CMP_GE(READ_ONCE(rnp->completed), c)));
2065 if (likely(d))
2066 break;
2067 WARN_ON(signal_pending(current));
2068 trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
2069 }
2070 trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
2071 smp_mb(); /* Ensure that CB invocation happens after GP end. */
2072}
2073
2074/*
2075 * Leaders come here to wait for additional callbacks to show up.
2076 * This function does not return until callbacks appear.
2077 */
2078static void nocb_leader_wait(struct rcu_data *my_rdp)
2079{
2080 bool firsttime = true;
2081 unsigned long flags;
2082 bool gotcbs;
2083 struct rcu_data *rdp;
2084 struct rcu_head **tail;
2085
2086wait_again:
2087
2088 /* Wait for callbacks to appear. */
2089 if (!rcu_nocb_poll) {
2090 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, TPS("Sleep"));
2091 swait_event_interruptible(my_rdp->nocb_wq,
2092 !READ_ONCE(my_rdp->nocb_leader_sleep));
2093 raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags);
2094 my_rdp->nocb_leader_sleep = true;
2095 WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
2096 del_timer(&my_rdp->nocb_timer);
2097 raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags);
2098 } else if (firsttime) {
2099 firsttime = false; /* Don't drown trace log with "Poll"! */
2100 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, TPS("Poll"));
2101 }
2102
2103 /*
2104 * Each pass through the following loop checks a follower for CBs.
2105 * We are our own first follower. Any CBs found are moved to
2106 * nocb_gp_head, where they await a grace period.
2107 */
2108 gotcbs = false;
2109 smp_mb(); /* wakeup and _sleep before ->nocb_head reads. */
2110 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
2111 rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head);
2112 if (!rdp->nocb_gp_head)
2113 continue; /* No CBs here, try next follower. */
2114
2115 /* Move callbacks to wait-for-GP list, which is empty. */
2116 WRITE_ONCE(rdp->nocb_head, NULL);
2117 rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
2118 gotcbs = true;
2119 }
2120
2121 /* No callbacks? Sleep a bit if polling, and go retry. */
2122 if (unlikely(!gotcbs)) {
2123 WARN_ON(signal_pending(current));
2124 if (rcu_nocb_poll) {
2125 schedule_timeout_interruptible(1);
2126 } else {
2127 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
2128 TPS("WokeEmpty"));
2129 }
2130 goto wait_again;
2131 }
2132
2133 /* Wait for one grace period. */
2134 rcu_nocb_wait_gp(my_rdp);
2135
2136 /* Each pass through the following loop wakes a follower, if needed. */
2137 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
2138 if (!rcu_nocb_poll &&
2139 READ_ONCE(rdp->nocb_head) &&
2140 READ_ONCE(my_rdp->nocb_leader_sleep)) {
2141 raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags);
2142 my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/
2143 raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags);
2144 }
2145 if (!rdp->nocb_gp_head)
2146 continue; /* No CBs, so no need to wake follower. */
2147
2148 /* Append callbacks to follower's "done" list. */
2149 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
2150 tail = rdp->nocb_follower_tail;
2151 rdp->nocb_follower_tail = rdp->nocb_gp_tail;
2152 *tail = rdp->nocb_gp_head;
2153 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
2154 if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
2155 /* List was empty, so wake up the follower. */
2156 swake_up(&rdp->nocb_wq);
2157 }
2158 }
2159
2160 /* If we (the leader) don't have CBs, go wait some more. */
2161 if (!my_rdp->nocb_follower_head)
2162 goto wait_again;
2163}
2164
2165/*
2166 * Followers come here to wait for additional callbacks to show up.
2167 * This function does not return until callbacks appear.
2168 */
2169static void nocb_follower_wait(struct rcu_data *rdp)
2170{
2171 for (;;) {
2172 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("FollowerSleep"));
2173 swait_event_interruptible(rdp->nocb_wq,
2174 READ_ONCE(rdp->nocb_follower_head));
2175 if (smp_load_acquire(&rdp->nocb_follower_head)) {
2176 /* ^^^ Ensure CB invocation follows _head test. */
2177 return;
2178 }
2179 WARN_ON(signal_pending(current));
2180 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeEmpty"));
2181 }
2182}
2183
2184/*
2185 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
2186 * callbacks queued by the corresponding no-CBs CPU, however, there is
2187 * an optional leader-follower relationship so that the grace-period
2188 * kthreads don't have to do quite so many wakeups.
2189 */
2190static int rcu_nocb_kthread(void *arg)
2191{
2192 int c, cl;
2193 unsigned long flags;
2194 struct rcu_head *list;
2195 struct rcu_head *next;
2196 struct rcu_head **tail;
2197 struct rcu_data *rdp = arg;
2198
2199 /* Each pass through this loop invokes one batch of callbacks */
2200 for (;;) {
2201 /* Wait for callbacks. */
2202 if (rdp->nocb_leader == rdp)
2203 nocb_leader_wait(rdp);
2204 else
2205 nocb_follower_wait(rdp);
2206
2207 /* Pull the ready-to-invoke callbacks onto local list. */
2208 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
2209 list = rdp->nocb_follower_head;
2210 rdp->nocb_follower_head = NULL;
2211 tail = rdp->nocb_follower_tail;
2212 rdp->nocb_follower_tail = &rdp->nocb_follower_head;
2213 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
2214 BUG_ON(!list);
2215 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeNonEmpty"));
2216
2217 /* Each pass through the following loop invokes a callback. */
2218 trace_rcu_batch_start(rdp->rsp->name,
2219 atomic_long_read(&rdp->nocb_q_count_lazy),
2220 atomic_long_read(&rdp->nocb_q_count), -1);
2221 c = cl = 0;
2222 while (list) {
2223 next = list->next;
2224 /* Wait for enqueuing to complete, if needed. */
2225 while (next == NULL && &list->next != tail) {
2226 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2227 TPS("WaitQueue"));
2228 schedule_timeout_interruptible(1);
2229 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2230 TPS("WokeQueue"));
2231 next = list->next;
2232 }
2233 debug_rcu_head_unqueue(list);
2234 local_bh_disable();
2235 if (__rcu_reclaim(rdp->rsp->name, list))
2236 cl++;
2237 c++;
2238 local_bh_enable();
2239 cond_resched_rcu_qs();
2240 list = next;
2241 }
2242 trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
2243 smp_mb__before_atomic(); /* _add after CB invocation. */
2244 atomic_long_add(-c, &rdp->nocb_q_count);
2245 atomic_long_add(-cl, &rdp->nocb_q_count_lazy);
2246 }
2247 return 0;
2248}
2249
2250/* Is a deferred wakeup of rcu_nocb_kthread() required? */
2251static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2252{
2253 return READ_ONCE(rdp->nocb_defer_wakeup);
2254}
2255
2256/* Do a deferred wakeup of rcu_nocb_kthread(). */
2257static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
2258{
2259 unsigned long flags;
2260 int ndw;
2261
2262 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
2263 if (!rcu_nocb_need_deferred_wakeup(rdp)) {
2264 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
2265 return;
2266 }
2267 ndw = READ_ONCE(rdp->nocb_defer_wakeup);
2268 WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
2269 __wake_nocb_leader(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
2270 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake"));
2271}
2272
2273/* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
2274static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
2275{
2276 struct rcu_data *rdp = from_timer(rdp, t, nocb_timer);
2277
2278 do_nocb_deferred_wakeup_common(rdp);
2279}
2280
2281/*
2282 * Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
2283 * This means we do an inexact common-case check. Note that if
2284 * we miss, ->nocb_timer will eventually clean things up.
2285 */
2286static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2287{
2288 if (rcu_nocb_need_deferred_wakeup(rdp))
2289 do_nocb_deferred_wakeup_common(rdp);
2290}
2291
2292void __init rcu_init_nohz(void)
2293{
2294 int cpu;
2295 bool need_rcu_nocb_mask = true;
2296 struct rcu_state *rsp;
2297
2298#if defined(CONFIG_NO_HZ_FULL)
2299 if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
2300 need_rcu_nocb_mask = true;
2301#endif /* #if defined(CONFIG_NO_HZ_FULL) */
2302
2303 if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) {
2304 if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
2305 pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
2306 return;
2307 }
2308 }
2309 if (!cpumask_available(rcu_nocb_mask))
2310 return;
2311
2312#if defined(CONFIG_NO_HZ_FULL)
2313 if (tick_nohz_full_running)
2314 cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
2315#endif /* #if defined(CONFIG_NO_HZ_FULL) */
2316
2317 if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
2318 pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
2319 cpumask_and(rcu_nocb_mask, cpu_possible_mask,
2320 rcu_nocb_mask);
2321 }
2322 if (cpumask_empty(rcu_nocb_mask))
2323 pr_info("\tOffload RCU callbacks from CPUs: (none).\n");
2324 else
2325 pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
2326 cpumask_pr_args(rcu_nocb_mask));
2327 if (rcu_nocb_poll)
2328 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
2329
2330 for_each_rcu_flavor(rsp) {
2331 for_each_cpu(cpu, rcu_nocb_mask)
2332 init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu));
2333 rcu_organize_nocb_kthreads(rsp);
2334 }
2335}
2336
2337/* Initialize per-rcu_data variables for no-CBs CPUs. */
2338static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2339{
2340 rdp->nocb_tail = &rdp->nocb_head;
2341 init_swait_queue_head(&rdp->nocb_wq);
2342 rdp->nocb_follower_tail = &rdp->nocb_follower_head;
2343 raw_spin_lock_init(&rdp->nocb_lock);
2344 timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
2345}
2346
2347/*
2348 * If the specified CPU is a no-CBs CPU that does not already have its
2349 * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are
2350 * brought online out of order, this can require re-organizing the
2351 * leader-follower relationships.
2352 */
2353static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu)
2354{
2355 struct rcu_data *rdp;
2356 struct rcu_data *rdp_last;
2357 struct rcu_data *rdp_old_leader;
2358 struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu);
2359 struct task_struct *t;
2360
2361 /*
2362 * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
2363 * then nothing to do.
2364 */
2365 if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread)
2366 return;
2367
2368 /* If we didn't spawn the leader first, reorganize! */
2369 rdp_old_leader = rdp_spawn->nocb_leader;
2370 if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) {
2371 rdp_last = NULL;
2372 rdp = rdp_old_leader;
2373 do {
2374 rdp->nocb_leader = rdp_spawn;
2375 if (rdp_last && rdp != rdp_spawn)
2376 rdp_last->nocb_next_follower = rdp;
2377 if (rdp == rdp_spawn) {
2378 rdp = rdp->nocb_next_follower;
2379 } else {
2380 rdp_last = rdp;
2381 rdp = rdp->nocb_next_follower;
2382 rdp_last->nocb_next_follower = NULL;
2383 }
2384 } while (rdp);
2385 rdp_spawn->nocb_next_follower = rdp_old_leader;
2386 }
2387
2388 /* Spawn the kthread for this CPU and RCU flavor. */
2389 t = kthread_run(rcu_nocb_kthread, rdp_spawn,
2390 "rcuo%c/%d", rsp->abbr, cpu);
2391 BUG_ON(IS_ERR(t));
2392 WRITE_ONCE(rdp_spawn->nocb_kthread, t);
2393}
2394
2395/*
2396 * If the specified CPU is a no-CBs CPU that does not already have its
2397 * rcuo kthreads, spawn them.
2398 */
2399static void rcu_spawn_all_nocb_kthreads(int cpu)
2400{
2401 struct rcu_state *rsp;
2402
2403 if (rcu_scheduler_fully_active)
2404 for_each_rcu_flavor(rsp)
2405 rcu_spawn_one_nocb_kthread(rsp, cpu);
2406}
2407
2408/*
2409 * Once the scheduler is running, spawn rcuo kthreads for all online
2410 * no-CBs CPUs. This assumes that the early_initcall()s happen before
2411 * non-boot CPUs come online -- if this changes, we will need to add
2412 * some mutual exclusion.
2413 */
2414static void __init rcu_spawn_nocb_kthreads(void)
2415{
2416 int cpu;
2417
2418 for_each_online_cpu(cpu)
2419 rcu_spawn_all_nocb_kthreads(cpu);
2420}
2421
2422/* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */
2423static int rcu_nocb_leader_stride = -1;
2424module_param(rcu_nocb_leader_stride, int, 0444);
2425
2426/*
2427 * Initialize leader-follower relationships for all no-CBs CPU.
2428 */
2429static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp)
2430{
2431 int cpu;
2432 int ls = rcu_nocb_leader_stride;
2433 int nl = 0; /* Next leader. */
2434 struct rcu_data *rdp;
2435 struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */
2436 struct rcu_data *rdp_prev = NULL;
2437
2438 if (!cpumask_available(rcu_nocb_mask))
2439 return;
2440 if (ls == -1) {
2441 ls = int_sqrt(nr_cpu_ids);
2442 rcu_nocb_leader_stride = ls;
2443 }
2444
2445 /*
2446 * Each pass through this loop sets up one rcu_data structure.
2447 * Should the corresponding CPU come online in the future, then
2448 * we will spawn the needed set of rcu_nocb_kthread() kthreads.
2449 */
2450 for_each_cpu(cpu, rcu_nocb_mask) {
2451 rdp = per_cpu_ptr(rsp->rda, cpu);
2452 if (rdp->cpu >= nl) {
2453 /* New leader, set up for followers & next leader. */
2454 nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
2455 rdp->nocb_leader = rdp;
2456 rdp_leader = rdp;
2457 } else {
2458 /* Another follower, link to previous leader. */
2459 rdp->nocb_leader = rdp_leader;
2460 rdp_prev->nocb_next_follower = rdp;
2461 }
2462 rdp_prev = rdp;
2463 }
2464}
2465
2466/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2467static bool init_nocb_callback_list(struct rcu_data *rdp)
2468{
2469 if (!rcu_is_nocb_cpu(rdp->cpu))
2470 return false;
2471
2472 /* If there are early-boot callbacks, move them to nocb lists. */
2473 if (!rcu_segcblist_empty(&rdp->cblist)) {
2474 rdp->nocb_head = rcu_segcblist_head(&rdp->cblist);
2475 rdp->nocb_tail = rcu_segcblist_tail(&rdp->cblist);
2476 atomic_long_set(&rdp->nocb_q_count,
2477 rcu_segcblist_n_cbs(&rdp->cblist));
2478 atomic_long_set(&rdp->nocb_q_count_lazy,
2479 rcu_segcblist_n_lazy_cbs(&rdp->cblist));
2480 rcu_segcblist_init(&rdp->cblist);
2481 }
2482 rcu_segcblist_disable(&rdp->cblist);
2483 return true;
2484}
2485
2486#else /* #ifdef CONFIG_RCU_NOCB_CPU */
2487
2488static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
2489{
2490 WARN_ON_ONCE(1); /* Should be dead code. */
2491 return false;
2492}
2493
2494static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
2495{
2496}
2497
2498static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2499{
2500}
2501
2502static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
2503{
2504 return NULL;
2505}
2506
2507static void rcu_init_one_nocb(struct rcu_node *rnp)
2508{
2509}
2510
2511static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2512 bool lazy, unsigned long flags)
2513{
2514 return false;
2515}
2516
2517static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
2518 struct rcu_data *rdp,
2519 unsigned long flags)
2520{
2521 return false;
2522}
2523
2524static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2525{
2526}
2527
2528static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2529{
2530 return false;
2531}
2532
2533static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2534{
2535}
2536
2537static void rcu_spawn_all_nocb_kthreads(int cpu)
2538{
2539}
2540
2541static void __init rcu_spawn_nocb_kthreads(void)
2542{
2543}
2544
2545static bool init_nocb_callback_list(struct rcu_data *rdp)
2546{
2547 return false;
2548}
2549
2550#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2551
2552/*
2553 * An adaptive-ticks CPU can potentially execute in kernel mode for an
2554 * arbitrarily long period of time with the scheduling-clock tick turned
2555 * off. RCU will be paying attention to this CPU because it is in the
2556 * kernel, but the CPU cannot be guaranteed to be executing the RCU state
2557 * machine because the scheduling-clock tick has been disabled. Therefore,
2558 * if an adaptive-ticks CPU is failing to respond to the current grace
2559 * period and has not be idle from an RCU perspective, kick it.
2560 */
2561static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
2562{
2563#ifdef CONFIG_NO_HZ_FULL
2564 if (tick_nohz_full_cpu(cpu))
2565 smp_send_reschedule(cpu);
2566#endif /* #ifdef CONFIG_NO_HZ_FULL */
2567}
2568
2569/*
2570 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
2571 * grace-period kthread will do force_quiescent_state() processing?
2572 * The idea is to avoid waking up RCU core processing on such a
2573 * CPU unless the grace period has extended for too long.
2574 *
2575 * This code relies on the fact that all NO_HZ_FULL CPUs are also
2576 * CONFIG_RCU_NOCB_CPU CPUs.
2577 */
2578static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
2579{
2580#ifdef CONFIG_NO_HZ_FULL
2581 if (tick_nohz_full_cpu(smp_processor_id()) &&
2582 (!rcu_gp_in_progress(rsp) ||
2583 ULONG_CMP_LT(jiffies, READ_ONCE(rsp->gp_start) + HZ)))
2584 return true;
2585#endif /* #ifdef CONFIG_NO_HZ_FULL */
2586 return false;
2587}
2588
2589/*
2590 * Bind the grace-period kthread for the sysidle flavor of RCU to the
2591 * timekeeping CPU.
2592 */
2593static void rcu_bind_gp_kthread(void)
2594{
2595 int __maybe_unused cpu;
2596
2597 if (!tick_nohz_full_enabled())
2598 return;
2599 housekeeping_affine(current, HK_FLAG_RCU);
2600}
2601
2602/* Record the current task on dyntick-idle entry. */
2603static void rcu_dynticks_task_enter(void)
2604{
2605#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2606 WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
2607#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
2608}
2609
2610/* Record no current task on dyntick-idle exit. */
2611static void rcu_dynticks_task_exit(void)
2612{
2613#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2614 WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
2615#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
2616}