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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/smpboot.h>
31#include "../time/tick-internal.h"
32
33#define RCU_KTHREAD_PRIO 1
34
35#ifdef CONFIG_RCU_BOOST
36#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
37#else
38#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
39#endif
40
41#ifdef CONFIG_RCU_NOCB_CPU
42static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
43static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */
44static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
45static char __initdata nocb_buf[NR_CPUS * 5];
46#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
47
48/*
49 * Check the RCU kernel configuration parameters and print informative
50 * messages about anything out of the ordinary. If you like #ifdef, you
51 * will love this function.
52 */
53static void __init rcu_bootup_announce_oddness(void)
54{
55#ifdef CONFIG_RCU_TRACE
56 pr_info("\tRCU debugfs-based tracing is enabled.\n");
57#endif
58#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
59 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
60 CONFIG_RCU_FANOUT);
61#endif
62#ifdef CONFIG_RCU_FANOUT_EXACT
63 pr_info("\tHierarchical RCU autobalancing is disabled.\n");
64#endif
65#ifdef CONFIG_RCU_FAST_NO_HZ
66 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
67#endif
68#ifdef CONFIG_PROVE_RCU
69 pr_info("\tRCU lockdep checking is enabled.\n");
70#endif
71#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
72 pr_info("\tRCU torture testing starts during boot.\n");
73#endif
74#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
75 pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n");
76#endif
77#if defined(CONFIG_RCU_CPU_STALL_INFO)
78 pr_info("\tAdditional per-CPU info printed with stalls.\n");
79#endif
80#if NUM_RCU_LVL_4 != 0
81 pr_info("\tFour-level hierarchy is enabled.\n");
82#endif
83 if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
84 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
85 if (nr_cpu_ids != NR_CPUS)
86 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
87#ifdef CONFIG_RCU_NOCB_CPU
88#ifndef CONFIG_RCU_NOCB_CPU_NONE
89 if (!have_rcu_nocb_mask) {
90 zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
91 have_rcu_nocb_mask = true;
92 }
93#ifdef CONFIG_RCU_NOCB_CPU_ZERO
94 pr_info("\tOffload RCU callbacks from CPU 0\n");
95 cpumask_set_cpu(0, rcu_nocb_mask);
96#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
97#ifdef CONFIG_RCU_NOCB_CPU_ALL
98 pr_info("\tOffload RCU callbacks from all CPUs\n");
99 cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
100#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
101#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
102 if (have_rcu_nocb_mask) {
103 if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
104 pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
105 cpumask_and(rcu_nocb_mask, cpu_possible_mask,
106 rcu_nocb_mask);
107 }
108 cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
109 pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
110 if (rcu_nocb_poll)
111 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
112 }
113#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
114}
115
116#ifdef CONFIG_TREE_PREEMPT_RCU
117
118RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
119static struct rcu_state *rcu_state = &rcu_preempt_state;
120
121static int rcu_preempted_readers_exp(struct rcu_node *rnp);
122
123/*
124 * Tell them what RCU they are running.
125 */
126static void __init rcu_bootup_announce(void)
127{
128 pr_info("Preemptible hierarchical RCU implementation.\n");
129 rcu_bootup_announce_oddness();
130}
131
132/*
133 * Return the number of RCU-preempt batches processed thus far
134 * for debug and statistics.
135 */
136long rcu_batches_completed_preempt(void)
137{
138 return rcu_preempt_state.completed;
139}
140EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
141
142/*
143 * Return the number of RCU batches processed thus far for debug & stats.
144 */
145long rcu_batches_completed(void)
146{
147 return rcu_batches_completed_preempt();
148}
149EXPORT_SYMBOL_GPL(rcu_batches_completed);
150
151/*
152 * Force a quiescent state for preemptible RCU.
153 */
154void rcu_force_quiescent_state(void)
155{
156 force_quiescent_state(&rcu_preempt_state);
157}
158EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
159
160/*
161 * Record a preemptible-RCU quiescent state for the specified CPU. Note
162 * that this just means that the task currently running on the CPU is
163 * not in a quiescent state. There might be any number of tasks blocked
164 * while in an RCU read-side critical section.
165 *
166 * Unlike the other rcu_*_qs() functions, callers to this function
167 * must disable irqs in order to protect the assignment to
168 * ->rcu_read_unlock_special.
169 */
170static void rcu_preempt_qs(int cpu)
171{
172 struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
173
174 if (rdp->passed_quiesce == 0)
175 trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs"));
176 rdp->passed_quiesce = 1;
177 current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
178}
179
180/*
181 * We have entered the scheduler, and the current task might soon be
182 * context-switched away from. If this task is in an RCU read-side
183 * critical section, we will no longer be able to rely on the CPU to
184 * record that fact, so we enqueue the task on the blkd_tasks list.
185 * The task will dequeue itself when it exits the outermost enclosing
186 * RCU read-side critical section. Therefore, the current grace period
187 * cannot be permitted to complete until the blkd_tasks list entries
188 * predating the current grace period drain, in other words, until
189 * rnp->gp_tasks becomes NULL.
190 *
191 * Caller must disable preemption.
192 */
193static void rcu_preempt_note_context_switch(int cpu)
194{
195 struct task_struct *t = current;
196 unsigned long flags;
197 struct rcu_data *rdp;
198 struct rcu_node *rnp;
199
200 if (t->rcu_read_lock_nesting > 0 &&
201 (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
202
203 /* Possibly blocking in an RCU read-side critical section. */
204 rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
205 rnp = rdp->mynode;
206 raw_spin_lock_irqsave(&rnp->lock, flags);
207 smp_mb__after_unlock_lock();
208 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
209 t->rcu_blocked_node = rnp;
210
211 /*
212 * If this CPU has already checked in, then this task
213 * will hold up the next grace period rather than the
214 * current grace period. Queue the task accordingly.
215 * If the task is queued for the current grace period
216 * (i.e., this CPU has not yet passed through a quiescent
217 * state for the current grace period), then as long
218 * as that task remains queued, the current grace period
219 * cannot end. Note that there is some uncertainty as
220 * to exactly when the current grace period started.
221 * We take a conservative approach, which can result
222 * in unnecessarily waiting on tasks that started very
223 * slightly after the current grace period began. C'est
224 * la vie!!!
225 *
226 * But first, note that the current CPU must still be
227 * on line!
228 */
229 WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
230 WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
231 if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
232 list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
233 rnp->gp_tasks = &t->rcu_node_entry;
234#ifdef CONFIG_RCU_BOOST
235 if (rnp->boost_tasks != NULL)
236 rnp->boost_tasks = rnp->gp_tasks;
237#endif /* #ifdef CONFIG_RCU_BOOST */
238 } else {
239 list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
240 if (rnp->qsmask & rdp->grpmask)
241 rnp->gp_tasks = &t->rcu_node_entry;
242 }
243 trace_rcu_preempt_task(rdp->rsp->name,
244 t->pid,
245 (rnp->qsmask & rdp->grpmask)
246 ? rnp->gpnum
247 : rnp->gpnum + 1);
248 raw_spin_unlock_irqrestore(&rnp->lock, flags);
249 } else if (t->rcu_read_lock_nesting < 0 &&
250 t->rcu_read_unlock_special) {
251
252 /*
253 * Complete exit from RCU read-side critical section on
254 * behalf of preempted instance of __rcu_read_unlock().
255 */
256 rcu_read_unlock_special(t);
257 }
258
259 /*
260 * Either we were not in an RCU read-side critical section to
261 * begin with, or we have now recorded that critical section
262 * globally. Either way, we can now note a quiescent state
263 * for this CPU. Again, if we were in an RCU read-side critical
264 * section, and if that critical section was blocking the current
265 * grace period, then the fact that the task has been enqueued
266 * means that we continue to block the current grace period.
267 */
268 local_irq_save(flags);
269 rcu_preempt_qs(cpu);
270 local_irq_restore(flags);
271}
272
273/*
274 * Check for preempted RCU readers blocking the current grace period
275 * for the specified rcu_node structure. If the caller needs a reliable
276 * answer, it must hold the rcu_node's ->lock.
277 */
278static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
279{
280 return rnp->gp_tasks != NULL;
281}
282
283/*
284 * Record a quiescent state for all tasks that were previously queued
285 * on the specified rcu_node structure and that were blocking the current
286 * RCU grace period. The caller must hold the specified rnp->lock with
287 * irqs disabled, and this lock is released upon return, but irqs remain
288 * disabled.
289 */
290static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
291 __releases(rnp->lock)
292{
293 unsigned long mask;
294 struct rcu_node *rnp_p;
295
296 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
297 raw_spin_unlock_irqrestore(&rnp->lock, flags);
298 return; /* Still need more quiescent states! */
299 }
300
301 rnp_p = rnp->parent;
302 if (rnp_p == NULL) {
303 /*
304 * Either there is only one rcu_node in the tree,
305 * or tasks were kicked up to root rcu_node due to
306 * CPUs going offline.
307 */
308 rcu_report_qs_rsp(&rcu_preempt_state, flags);
309 return;
310 }
311
312 /* Report up the rest of the hierarchy. */
313 mask = rnp->grpmask;
314 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
315 raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */
316 smp_mb__after_unlock_lock();
317 rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
318}
319
320/*
321 * Advance a ->blkd_tasks-list pointer to the next entry, instead
322 * returning NULL if at the end of the list.
323 */
324static struct list_head *rcu_next_node_entry(struct task_struct *t,
325 struct rcu_node *rnp)
326{
327 struct list_head *np;
328
329 np = t->rcu_node_entry.next;
330 if (np == &rnp->blkd_tasks)
331 np = NULL;
332 return np;
333}
334
335/*
336 * Handle special cases during rcu_read_unlock(), such as needing to
337 * notify RCU core processing or task having blocked during the RCU
338 * read-side critical section.
339 */
340void rcu_read_unlock_special(struct task_struct *t)
341{
342 int empty;
343 int empty_exp;
344 int empty_exp_now;
345 unsigned long flags;
346 struct list_head *np;
347#ifdef CONFIG_RCU_BOOST
348 struct rt_mutex *rbmp = NULL;
349#endif /* #ifdef CONFIG_RCU_BOOST */
350 struct rcu_node *rnp;
351 int special;
352
353 /* NMI handlers cannot block and cannot safely manipulate state. */
354 if (in_nmi())
355 return;
356
357 local_irq_save(flags);
358
359 /*
360 * If RCU core is waiting for this CPU to exit critical section,
361 * let it know that we have done so.
362 */
363 special = t->rcu_read_unlock_special;
364 if (special & RCU_READ_UNLOCK_NEED_QS) {
365 rcu_preempt_qs(smp_processor_id());
366 if (!t->rcu_read_unlock_special) {
367 local_irq_restore(flags);
368 return;
369 }
370 }
371
372 /* Hardware IRQ handlers cannot block, complain if they get here. */
373 if (WARN_ON_ONCE(in_irq() || in_serving_softirq())) {
374 local_irq_restore(flags);
375 return;
376 }
377
378 /* Clean up if blocked during RCU read-side critical section. */
379 if (special & RCU_READ_UNLOCK_BLOCKED) {
380 t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
381
382 /*
383 * Remove this task from the list it blocked on. The
384 * task can migrate while we acquire the lock, but at
385 * most one time. So at most two passes through loop.
386 */
387 for (;;) {
388 rnp = t->rcu_blocked_node;
389 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
390 smp_mb__after_unlock_lock();
391 if (rnp == t->rcu_blocked_node)
392 break;
393 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
394 }
395 empty = !rcu_preempt_blocked_readers_cgp(rnp);
396 empty_exp = !rcu_preempted_readers_exp(rnp);
397 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
398 np = rcu_next_node_entry(t, rnp);
399 list_del_init(&t->rcu_node_entry);
400 t->rcu_blocked_node = NULL;
401 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
402 rnp->gpnum, t->pid);
403 if (&t->rcu_node_entry == rnp->gp_tasks)
404 rnp->gp_tasks = np;
405 if (&t->rcu_node_entry == rnp->exp_tasks)
406 rnp->exp_tasks = np;
407#ifdef CONFIG_RCU_BOOST
408 if (&t->rcu_node_entry == rnp->boost_tasks)
409 rnp->boost_tasks = np;
410 /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
411 if (t->rcu_boost_mutex) {
412 rbmp = t->rcu_boost_mutex;
413 t->rcu_boost_mutex = NULL;
414 }
415#endif /* #ifdef CONFIG_RCU_BOOST */
416
417 /*
418 * If this was the last task on the current list, and if
419 * we aren't waiting on any CPUs, report the quiescent state.
420 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
421 * so we must take a snapshot of the expedited state.
422 */
423 empty_exp_now = !rcu_preempted_readers_exp(rnp);
424 if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
425 trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
426 rnp->gpnum,
427 0, rnp->qsmask,
428 rnp->level,
429 rnp->grplo,
430 rnp->grphi,
431 !!rnp->gp_tasks);
432 rcu_report_unblock_qs_rnp(rnp, flags);
433 } else {
434 raw_spin_unlock_irqrestore(&rnp->lock, flags);
435 }
436
437#ifdef CONFIG_RCU_BOOST
438 /* Unboost if we were boosted. */
439 if (rbmp)
440 rt_mutex_unlock(rbmp);
441#endif /* #ifdef CONFIG_RCU_BOOST */
442
443 /*
444 * If this was the last task on the expedited lists,
445 * then we need to report up the rcu_node hierarchy.
446 */
447 if (!empty_exp && empty_exp_now)
448 rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
449 } else {
450 local_irq_restore(flags);
451 }
452}
453
454#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
455
456/*
457 * Dump detailed information for all tasks blocking the current RCU
458 * grace period on the specified rcu_node structure.
459 */
460static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
461{
462 unsigned long flags;
463 struct task_struct *t;
464
465 raw_spin_lock_irqsave(&rnp->lock, flags);
466 if (!rcu_preempt_blocked_readers_cgp(rnp)) {
467 raw_spin_unlock_irqrestore(&rnp->lock, flags);
468 return;
469 }
470 t = list_entry(rnp->gp_tasks,
471 struct task_struct, rcu_node_entry);
472 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
473 sched_show_task(t);
474 raw_spin_unlock_irqrestore(&rnp->lock, flags);
475}
476
477/*
478 * Dump detailed information for all tasks blocking the current RCU
479 * grace period.
480 */
481static void rcu_print_detail_task_stall(struct rcu_state *rsp)
482{
483 struct rcu_node *rnp = rcu_get_root(rsp);
484
485 rcu_print_detail_task_stall_rnp(rnp);
486 rcu_for_each_leaf_node(rsp, rnp)
487 rcu_print_detail_task_stall_rnp(rnp);
488}
489
490#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
491
492static void rcu_print_detail_task_stall(struct rcu_state *rsp)
493{
494}
495
496#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
497
498#ifdef CONFIG_RCU_CPU_STALL_INFO
499
500static void rcu_print_task_stall_begin(struct rcu_node *rnp)
501{
502 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
503 rnp->level, rnp->grplo, rnp->grphi);
504}
505
506static void rcu_print_task_stall_end(void)
507{
508 pr_cont("\n");
509}
510
511#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
512
513static void rcu_print_task_stall_begin(struct rcu_node *rnp)
514{
515}
516
517static void rcu_print_task_stall_end(void)
518{
519}
520
521#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
522
523/*
524 * Scan the current list of tasks blocked within RCU read-side critical
525 * sections, printing out the tid of each.
526 */
527static int rcu_print_task_stall(struct rcu_node *rnp)
528{
529 struct task_struct *t;
530 int ndetected = 0;
531
532 if (!rcu_preempt_blocked_readers_cgp(rnp))
533 return 0;
534 rcu_print_task_stall_begin(rnp);
535 t = list_entry(rnp->gp_tasks,
536 struct task_struct, rcu_node_entry);
537 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
538 pr_cont(" P%d", t->pid);
539 ndetected++;
540 }
541 rcu_print_task_stall_end();
542 return ndetected;
543}
544
545/*
546 * Check that the list of blocked tasks for the newly completed grace
547 * period is in fact empty. It is a serious bug to complete a grace
548 * period that still has RCU readers blocked! This function must be
549 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
550 * must be held by the caller.
551 *
552 * Also, if there are blocked tasks on the list, they automatically
553 * block the newly created grace period, so set up ->gp_tasks accordingly.
554 */
555static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
556{
557 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
558 if (!list_empty(&rnp->blkd_tasks))
559 rnp->gp_tasks = rnp->blkd_tasks.next;
560 WARN_ON_ONCE(rnp->qsmask);
561}
562
563#ifdef CONFIG_HOTPLUG_CPU
564
565/*
566 * Handle tasklist migration for case in which all CPUs covered by the
567 * specified rcu_node have gone offline. Move them up to the root
568 * rcu_node. The reason for not just moving them to the immediate
569 * parent is to remove the need for rcu_read_unlock_special() to
570 * make more than two attempts to acquire the target rcu_node's lock.
571 * Returns true if there were tasks blocking the current RCU grace
572 * period.
573 *
574 * Returns 1 if there was previously a task blocking the current grace
575 * period on the specified rcu_node structure.
576 *
577 * The caller must hold rnp->lock with irqs disabled.
578 */
579static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
580 struct rcu_node *rnp,
581 struct rcu_data *rdp)
582{
583 struct list_head *lp;
584 struct list_head *lp_root;
585 int retval = 0;
586 struct rcu_node *rnp_root = rcu_get_root(rsp);
587 struct task_struct *t;
588
589 if (rnp == rnp_root) {
590 WARN_ONCE(1, "Last CPU thought to be offlined?");
591 return 0; /* Shouldn't happen: at least one CPU online. */
592 }
593
594 /* If we are on an internal node, complain bitterly. */
595 WARN_ON_ONCE(rnp != rdp->mynode);
596
597 /*
598 * Move tasks up to root rcu_node. Don't try to get fancy for
599 * this corner-case operation -- just put this node's tasks
600 * at the head of the root node's list, and update the root node's
601 * ->gp_tasks and ->exp_tasks pointers to those of this node's,
602 * if non-NULL. This might result in waiting for more tasks than
603 * absolutely necessary, but this is a good performance/complexity
604 * tradeoff.
605 */
606 if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
607 retval |= RCU_OFL_TASKS_NORM_GP;
608 if (rcu_preempted_readers_exp(rnp))
609 retval |= RCU_OFL_TASKS_EXP_GP;
610 lp = &rnp->blkd_tasks;
611 lp_root = &rnp_root->blkd_tasks;
612 while (!list_empty(lp)) {
613 t = list_entry(lp->next, typeof(*t), rcu_node_entry);
614 raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
615 smp_mb__after_unlock_lock();
616 list_del(&t->rcu_node_entry);
617 t->rcu_blocked_node = rnp_root;
618 list_add(&t->rcu_node_entry, lp_root);
619 if (&t->rcu_node_entry == rnp->gp_tasks)
620 rnp_root->gp_tasks = rnp->gp_tasks;
621 if (&t->rcu_node_entry == rnp->exp_tasks)
622 rnp_root->exp_tasks = rnp->exp_tasks;
623#ifdef CONFIG_RCU_BOOST
624 if (&t->rcu_node_entry == rnp->boost_tasks)
625 rnp_root->boost_tasks = rnp->boost_tasks;
626#endif /* #ifdef CONFIG_RCU_BOOST */
627 raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
628 }
629
630 rnp->gp_tasks = NULL;
631 rnp->exp_tasks = NULL;
632#ifdef CONFIG_RCU_BOOST
633 rnp->boost_tasks = NULL;
634 /*
635 * In case root is being boosted and leaf was not. Make sure
636 * that we boost the tasks blocking the current grace period
637 * in this case.
638 */
639 raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
640 smp_mb__after_unlock_lock();
641 if (rnp_root->boost_tasks != NULL &&
642 rnp_root->boost_tasks != rnp_root->gp_tasks &&
643 rnp_root->boost_tasks != rnp_root->exp_tasks)
644 rnp_root->boost_tasks = rnp_root->gp_tasks;
645 raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
646#endif /* #ifdef CONFIG_RCU_BOOST */
647
648 return retval;
649}
650
651#endif /* #ifdef CONFIG_HOTPLUG_CPU */
652
653/*
654 * Check for a quiescent state from the current CPU. When a task blocks,
655 * the task is recorded in the corresponding CPU's rcu_node structure,
656 * which is checked elsewhere.
657 *
658 * Caller must disable hard irqs.
659 */
660static void rcu_preempt_check_callbacks(int cpu)
661{
662 struct task_struct *t = current;
663
664 if (t->rcu_read_lock_nesting == 0) {
665 rcu_preempt_qs(cpu);
666 return;
667 }
668 if (t->rcu_read_lock_nesting > 0 &&
669 per_cpu(rcu_preempt_data, cpu).qs_pending)
670 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
671}
672
673#ifdef CONFIG_RCU_BOOST
674
675static void rcu_preempt_do_callbacks(void)
676{
677 rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
678}
679
680#endif /* #ifdef CONFIG_RCU_BOOST */
681
682/*
683 * Queue a preemptible-RCU callback for invocation after a grace period.
684 */
685void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
686{
687 __call_rcu(head, func, &rcu_preempt_state, -1, 0);
688}
689EXPORT_SYMBOL_GPL(call_rcu);
690
691/*
692 * Queue an RCU callback for lazy invocation after a grace period.
693 * This will likely be later named something like "call_rcu_lazy()",
694 * but this change will require some way of tagging the lazy RCU
695 * callbacks in the list of pending callbacks. Until then, this
696 * function may only be called from __kfree_rcu().
697 */
698void kfree_call_rcu(struct rcu_head *head,
699 void (*func)(struct rcu_head *rcu))
700{
701 __call_rcu(head, func, &rcu_preempt_state, -1, 1);
702}
703EXPORT_SYMBOL_GPL(kfree_call_rcu);
704
705/**
706 * synchronize_rcu - wait until a grace period has elapsed.
707 *
708 * Control will return to the caller some time after a full grace
709 * period has elapsed, in other words after all currently executing RCU
710 * read-side critical sections have completed. Note, however, that
711 * upon return from synchronize_rcu(), the caller might well be executing
712 * concurrently with new RCU read-side critical sections that began while
713 * synchronize_rcu() was waiting. RCU read-side critical sections are
714 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
715 *
716 * See the description of synchronize_sched() for more detailed information
717 * on memory ordering guarantees.
718 */
719void synchronize_rcu(void)
720{
721 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
722 !lock_is_held(&rcu_lock_map) &&
723 !lock_is_held(&rcu_sched_lock_map),
724 "Illegal synchronize_rcu() in RCU read-side critical section");
725 if (!rcu_scheduler_active)
726 return;
727 if (rcu_expedited)
728 synchronize_rcu_expedited();
729 else
730 wait_rcu_gp(call_rcu);
731}
732EXPORT_SYMBOL_GPL(synchronize_rcu);
733
734static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
735static unsigned long sync_rcu_preempt_exp_count;
736static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
737
738/*
739 * Return non-zero if there are any tasks in RCU read-side critical
740 * sections blocking the current preemptible-RCU expedited grace period.
741 * If there is no preemptible-RCU expedited grace period currently in
742 * progress, returns zero unconditionally.
743 */
744static int rcu_preempted_readers_exp(struct rcu_node *rnp)
745{
746 return rnp->exp_tasks != NULL;
747}
748
749/*
750 * return non-zero if there is no RCU expedited grace period in progress
751 * for the specified rcu_node structure, in other words, if all CPUs and
752 * tasks covered by the specified rcu_node structure have done their bit
753 * for the current expedited grace period. Works only for preemptible
754 * RCU -- other RCU implementation use other means.
755 *
756 * Caller must hold sync_rcu_preempt_exp_mutex.
757 */
758static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
759{
760 return !rcu_preempted_readers_exp(rnp) &&
761 ACCESS_ONCE(rnp->expmask) == 0;
762}
763
764/*
765 * Report the exit from RCU read-side critical section for the last task
766 * that queued itself during or before the current expedited preemptible-RCU
767 * grace period. This event is reported either to the rcu_node structure on
768 * which the task was queued or to one of that rcu_node structure's ancestors,
769 * recursively up the tree. (Calm down, calm down, we do the recursion
770 * iteratively!)
771 *
772 * Most callers will set the "wake" flag, but the task initiating the
773 * expedited grace period need not wake itself.
774 *
775 * Caller must hold sync_rcu_preempt_exp_mutex.
776 */
777static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
778 bool wake)
779{
780 unsigned long flags;
781 unsigned long mask;
782
783 raw_spin_lock_irqsave(&rnp->lock, flags);
784 smp_mb__after_unlock_lock();
785 for (;;) {
786 if (!sync_rcu_preempt_exp_done(rnp)) {
787 raw_spin_unlock_irqrestore(&rnp->lock, flags);
788 break;
789 }
790 if (rnp->parent == NULL) {
791 raw_spin_unlock_irqrestore(&rnp->lock, flags);
792 if (wake) {
793 smp_mb(); /* EGP done before wake_up(). */
794 wake_up(&sync_rcu_preempt_exp_wq);
795 }
796 break;
797 }
798 mask = rnp->grpmask;
799 raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
800 rnp = rnp->parent;
801 raw_spin_lock(&rnp->lock); /* irqs already disabled */
802 smp_mb__after_unlock_lock();
803 rnp->expmask &= ~mask;
804 }
805}
806
807/*
808 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
809 * grace period for the specified rcu_node structure. If there are no such
810 * tasks, report it up the rcu_node hierarchy.
811 *
812 * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
813 * CPU hotplug operations.
814 */
815static void
816sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
817{
818 unsigned long flags;
819 int must_wait = 0;
820
821 raw_spin_lock_irqsave(&rnp->lock, flags);
822 smp_mb__after_unlock_lock();
823 if (list_empty(&rnp->blkd_tasks)) {
824 raw_spin_unlock_irqrestore(&rnp->lock, flags);
825 } else {
826 rnp->exp_tasks = rnp->blkd_tasks.next;
827 rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
828 must_wait = 1;
829 }
830 if (!must_wait)
831 rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
832}
833
834/**
835 * synchronize_rcu_expedited - Brute-force RCU grace period
836 *
837 * Wait for an RCU-preempt grace period, but expedite it. The basic
838 * idea is to invoke synchronize_sched_expedited() to push all the tasks to
839 * the ->blkd_tasks lists and wait for this list to drain. This consumes
840 * significant time on all CPUs and is unfriendly to real-time workloads,
841 * so is thus not recommended for any sort of common-case code.
842 * In fact, if you are using synchronize_rcu_expedited() in a loop,
843 * please restructure your code to batch your updates, and then Use a
844 * single synchronize_rcu() instead.
845 *
846 * Note that it is illegal to call this function while holding any lock
847 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
848 * to call this function from a CPU-hotplug notifier. Failing to observe
849 * these restriction will result in deadlock.
850 */
851void synchronize_rcu_expedited(void)
852{
853 unsigned long flags;
854 struct rcu_node *rnp;
855 struct rcu_state *rsp = &rcu_preempt_state;
856 unsigned long snap;
857 int trycount = 0;
858
859 smp_mb(); /* Caller's modifications seen first by other CPUs. */
860 snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
861 smp_mb(); /* Above access cannot bleed into critical section. */
862
863 /*
864 * Block CPU-hotplug operations. This means that any CPU-hotplug
865 * operation that finds an rcu_node structure with tasks in the
866 * process of being boosted will know that all tasks blocking
867 * this expedited grace period will already be in the process of
868 * being boosted. This simplifies the process of moving tasks
869 * from leaf to root rcu_node structures.
870 */
871 get_online_cpus();
872
873 /*
874 * Acquire lock, falling back to synchronize_rcu() if too many
875 * lock-acquisition failures. Of course, if someone does the
876 * expedited grace period for us, just leave.
877 */
878 while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
879 if (ULONG_CMP_LT(snap,
880 ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
881 put_online_cpus();
882 goto mb_ret; /* Others did our work for us. */
883 }
884 if (trycount++ < 10) {
885 udelay(trycount * num_online_cpus());
886 } else {
887 put_online_cpus();
888 wait_rcu_gp(call_rcu);
889 return;
890 }
891 }
892 if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
893 put_online_cpus();
894 goto unlock_mb_ret; /* Others did our work for us. */
895 }
896
897 /* force all RCU readers onto ->blkd_tasks lists. */
898 synchronize_sched_expedited();
899
900 /* Initialize ->expmask for all non-leaf rcu_node structures. */
901 rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
902 raw_spin_lock_irqsave(&rnp->lock, flags);
903 smp_mb__after_unlock_lock();
904 rnp->expmask = rnp->qsmaskinit;
905 raw_spin_unlock_irqrestore(&rnp->lock, flags);
906 }
907
908 /* Snapshot current state of ->blkd_tasks lists. */
909 rcu_for_each_leaf_node(rsp, rnp)
910 sync_rcu_preempt_exp_init(rsp, rnp);
911 if (NUM_RCU_NODES > 1)
912 sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
913
914 put_online_cpus();
915
916 /* Wait for snapshotted ->blkd_tasks lists to drain. */
917 rnp = rcu_get_root(rsp);
918 wait_event(sync_rcu_preempt_exp_wq,
919 sync_rcu_preempt_exp_done(rnp));
920
921 /* Clean up and exit. */
922 smp_mb(); /* ensure expedited GP seen before counter increment. */
923 ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
924unlock_mb_ret:
925 mutex_unlock(&sync_rcu_preempt_exp_mutex);
926mb_ret:
927 smp_mb(); /* ensure subsequent action seen after grace period. */
928}
929EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
930
931/**
932 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
933 *
934 * Note that this primitive does not necessarily wait for an RCU grace period
935 * to complete. For example, if there are no RCU callbacks queued anywhere
936 * in the system, then rcu_barrier() is within its rights to return
937 * immediately, without waiting for anything, much less an RCU grace period.
938 */
939void rcu_barrier(void)
940{
941 _rcu_barrier(&rcu_preempt_state);
942}
943EXPORT_SYMBOL_GPL(rcu_barrier);
944
945/*
946 * Initialize preemptible RCU's state structures.
947 */
948static void __init __rcu_init_preempt(void)
949{
950 rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
951}
952
953/*
954 * Check for a task exiting while in a preemptible-RCU read-side
955 * critical section, clean up if so. No need to issue warnings,
956 * as debug_check_no_locks_held() already does this if lockdep
957 * is enabled.
958 */
959void exit_rcu(void)
960{
961 struct task_struct *t = current;
962
963 if (likely(list_empty(¤t->rcu_node_entry)))
964 return;
965 t->rcu_read_lock_nesting = 1;
966 barrier();
967 t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
968 __rcu_read_unlock();
969}
970
971#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
972
973static struct rcu_state *rcu_state = &rcu_sched_state;
974
975/*
976 * Tell them what RCU they are running.
977 */
978static void __init rcu_bootup_announce(void)
979{
980 pr_info("Hierarchical RCU implementation.\n");
981 rcu_bootup_announce_oddness();
982}
983
984/*
985 * Return the number of RCU batches processed thus far for debug & stats.
986 */
987long rcu_batches_completed(void)
988{
989 return rcu_batches_completed_sched();
990}
991EXPORT_SYMBOL_GPL(rcu_batches_completed);
992
993/*
994 * Force a quiescent state for RCU, which, because there is no preemptible
995 * RCU, becomes the same as rcu-sched.
996 */
997void rcu_force_quiescent_state(void)
998{
999 rcu_sched_force_quiescent_state();
1000}
1001EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
1002
1003/*
1004 * Because preemptible RCU does not exist, we never have to check for
1005 * CPUs being in quiescent states.
1006 */
1007static void rcu_preempt_note_context_switch(int cpu)
1008{
1009}
1010
1011/*
1012 * Because preemptible RCU does not exist, there are never any preempted
1013 * RCU readers.
1014 */
1015static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
1016{
1017 return 0;
1018}
1019
1020#ifdef CONFIG_HOTPLUG_CPU
1021
1022/* Because preemptible RCU does not exist, no quieting of tasks. */
1023static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
1024{
1025 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1026}
1027
1028#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1029
1030/*
1031 * Because preemptible RCU does not exist, we never have to check for
1032 * tasks blocked within RCU read-side critical sections.
1033 */
1034static void rcu_print_detail_task_stall(struct rcu_state *rsp)
1035{
1036}
1037
1038/*
1039 * Because preemptible RCU does not exist, we never have to check for
1040 * tasks blocked within RCU read-side critical sections.
1041 */
1042static int rcu_print_task_stall(struct rcu_node *rnp)
1043{
1044 return 0;
1045}
1046
1047/*
1048 * Because there is no preemptible RCU, there can be no readers blocked,
1049 * so there is no need to check for blocked tasks. So check only for
1050 * bogus qsmask values.
1051 */
1052static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
1053{
1054 WARN_ON_ONCE(rnp->qsmask);
1055}
1056
1057#ifdef CONFIG_HOTPLUG_CPU
1058
1059/*
1060 * Because preemptible RCU does not exist, it never needs to migrate
1061 * tasks that were blocked within RCU read-side critical sections, and
1062 * such non-existent tasks cannot possibly have been blocking the current
1063 * grace period.
1064 */
1065static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
1066 struct rcu_node *rnp,
1067 struct rcu_data *rdp)
1068{
1069 return 0;
1070}
1071
1072#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1073
1074/*
1075 * Because preemptible RCU does not exist, it never has any callbacks
1076 * to check.
1077 */
1078static void rcu_preempt_check_callbacks(int cpu)
1079{
1080}
1081
1082/*
1083 * Queue an RCU callback for lazy invocation after a grace period.
1084 * This will likely be later named something like "call_rcu_lazy()",
1085 * but this change will require some way of tagging the lazy RCU
1086 * callbacks in the list of pending callbacks. Until then, this
1087 * function may only be called from __kfree_rcu().
1088 *
1089 * Because there is no preemptible RCU, we use RCU-sched instead.
1090 */
1091void kfree_call_rcu(struct rcu_head *head,
1092 void (*func)(struct rcu_head *rcu))
1093{
1094 __call_rcu(head, func, &rcu_sched_state, -1, 1);
1095}
1096EXPORT_SYMBOL_GPL(kfree_call_rcu);
1097
1098/*
1099 * Wait for an rcu-preempt grace period, but make it happen quickly.
1100 * But because preemptible RCU does not exist, map to rcu-sched.
1101 */
1102void synchronize_rcu_expedited(void)
1103{
1104 synchronize_sched_expedited();
1105}
1106EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
1107
1108#ifdef CONFIG_HOTPLUG_CPU
1109
1110/*
1111 * Because preemptible RCU does not exist, there is never any need to
1112 * report on tasks preempted in RCU read-side critical sections during
1113 * expedited RCU grace periods.
1114 */
1115static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
1116 bool wake)
1117{
1118}
1119
1120#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1121
1122/*
1123 * Because preemptible RCU does not exist, rcu_barrier() is just
1124 * another name for rcu_barrier_sched().
1125 */
1126void rcu_barrier(void)
1127{
1128 rcu_barrier_sched();
1129}
1130EXPORT_SYMBOL_GPL(rcu_barrier);
1131
1132/*
1133 * Because preemptible RCU does not exist, it need not be initialized.
1134 */
1135static void __init __rcu_init_preempt(void)
1136{
1137}
1138
1139/*
1140 * Because preemptible RCU does not exist, tasks cannot possibly exit
1141 * while in preemptible RCU read-side critical sections.
1142 */
1143void exit_rcu(void)
1144{
1145}
1146
1147#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1148
1149#ifdef CONFIG_RCU_BOOST
1150
1151#include "../locking/rtmutex_common.h"
1152
1153#ifdef CONFIG_RCU_TRACE
1154
1155static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1156{
1157 if (list_empty(&rnp->blkd_tasks))
1158 rnp->n_balk_blkd_tasks++;
1159 else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
1160 rnp->n_balk_exp_gp_tasks++;
1161 else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
1162 rnp->n_balk_boost_tasks++;
1163 else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
1164 rnp->n_balk_notblocked++;
1165 else if (rnp->gp_tasks != NULL &&
1166 ULONG_CMP_LT(jiffies, rnp->boost_time))
1167 rnp->n_balk_notyet++;
1168 else
1169 rnp->n_balk_nos++;
1170}
1171
1172#else /* #ifdef CONFIG_RCU_TRACE */
1173
1174static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1175{
1176}
1177
1178#endif /* #else #ifdef CONFIG_RCU_TRACE */
1179
1180static void rcu_wake_cond(struct task_struct *t, int status)
1181{
1182 /*
1183 * If the thread is yielding, only wake it when this
1184 * is invoked from idle
1185 */
1186 if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
1187 wake_up_process(t);
1188}
1189
1190/*
1191 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
1192 * or ->boost_tasks, advancing the pointer to the next task in the
1193 * ->blkd_tasks list.
1194 *
1195 * Note that irqs must be enabled: boosting the task can block.
1196 * Returns 1 if there are more tasks needing to be boosted.
1197 */
1198static int rcu_boost(struct rcu_node *rnp)
1199{
1200 unsigned long flags;
1201 struct rt_mutex mtx;
1202 struct task_struct *t;
1203 struct list_head *tb;
1204
1205 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
1206 return 0; /* Nothing left to boost. */
1207
1208 raw_spin_lock_irqsave(&rnp->lock, flags);
1209 smp_mb__after_unlock_lock();
1210
1211 /*
1212 * Recheck under the lock: all tasks in need of boosting
1213 * might exit their RCU read-side critical sections on their own.
1214 */
1215 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
1216 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1217 return 0;
1218 }
1219
1220 /*
1221 * Preferentially boost tasks blocking expedited grace periods.
1222 * This cannot starve the normal grace periods because a second
1223 * expedited grace period must boost all blocked tasks, including
1224 * those blocking the pre-existing normal grace period.
1225 */
1226 if (rnp->exp_tasks != NULL) {
1227 tb = rnp->exp_tasks;
1228 rnp->n_exp_boosts++;
1229 } else {
1230 tb = rnp->boost_tasks;
1231 rnp->n_normal_boosts++;
1232 }
1233 rnp->n_tasks_boosted++;
1234
1235 /*
1236 * We boost task t by manufacturing an rt_mutex that appears to
1237 * be held by task t. We leave a pointer to that rt_mutex where
1238 * task t can find it, and task t will release the mutex when it
1239 * exits its outermost RCU read-side critical section. Then
1240 * simply acquiring this artificial rt_mutex will boost task
1241 * t's priority. (Thanks to tglx for suggesting this approach!)
1242 *
1243 * Note that task t must acquire rnp->lock to remove itself from
1244 * the ->blkd_tasks list, which it will do from exit() if from
1245 * nowhere else. We therefore are guaranteed that task t will
1246 * stay around at least until we drop rnp->lock. Note that
1247 * rnp->lock also resolves races between our priority boosting
1248 * and task t's exiting its outermost RCU read-side critical
1249 * section.
1250 */
1251 t = container_of(tb, struct task_struct, rcu_node_entry);
1252 rt_mutex_init_proxy_locked(&mtx, t);
1253 t->rcu_boost_mutex = &mtx;
1254 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1255 rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */
1256 rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
1257
1258 return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
1259 ACCESS_ONCE(rnp->boost_tasks) != NULL;
1260}
1261
1262/*
1263 * Priority-boosting kthread. One per leaf rcu_node and one for the
1264 * root rcu_node.
1265 */
1266static int rcu_boost_kthread(void *arg)
1267{
1268 struct rcu_node *rnp = (struct rcu_node *)arg;
1269 int spincnt = 0;
1270 int more2boost;
1271
1272 trace_rcu_utilization(TPS("Start boost kthread@init"));
1273 for (;;) {
1274 rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1275 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1276 rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1277 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1278 rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1279 more2boost = rcu_boost(rnp);
1280 if (more2boost)
1281 spincnt++;
1282 else
1283 spincnt = 0;
1284 if (spincnt > 10) {
1285 rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1286 trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1287 schedule_timeout_interruptible(2);
1288 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1289 spincnt = 0;
1290 }
1291 }
1292 /* NOTREACHED */
1293 trace_rcu_utilization(TPS("End boost kthread@notreached"));
1294 return 0;
1295}
1296
1297/*
1298 * Check to see if it is time to start boosting RCU readers that are
1299 * blocking the current grace period, and, if so, tell the per-rcu_node
1300 * kthread to start boosting them. If there is an expedited grace
1301 * period in progress, it is always time to boost.
1302 *
1303 * The caller must hold rnp->lock, which this function releases.
1304 * The ->boost_kthread_task is immortal, so we don't need to worry
1305 * about it going away.
1306 */
1307static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1308{
1309 struct task_struct *t;
1310
1311 if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1312 rnp->n_balk_exp_gp_tasks++;
1313 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1314 return;
1315 }
1316 if (rnp->exp_tasks != NULL ||
1317 (rnp->gp_tasks != NULL &&
1318 rnp->boost_tasks == NULL &&
1319 rnp->qsmask == 0 &&
1320 ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1321 if (rnp->exp_tasks == NULL)
1322 rnp->boost_tasks = rnp->gp_tasks;
1323 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1324 t = rnp->boost_kthread_task;
1325 if (t)
1326 rcu_wake_cond(t, rnp->boost_kthread_status);
1327 } else {
1328 rcu_initiate_boost_trace(rnp);
1329 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1330 }
1331}
1332
1333/*
1334 * Wake up the per-CPU kthread to invoke RCU callbacks.
1335 */
1336static void invoke_rcu_callbacks_kthread(void)
1337{
1338 unsigned long flags;
1339
1340 local_irq_save(flags);
1341 __this_cpu_write(rcu_cpu_has_work, 1);
1342 if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
1343 current != __this_cpu_read(rcu_cpu_kthread_task)) {
1344 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
1345 __this_cpu_read(rcu_cpu_kthread_status));
1346 }
1347 local_irq_restore(flags);
1348}
1349
1350/*
1351 * Is the current CPU running the RCU-callbacks kthread?
1352 * Caller must have preemption disabled.
1353 */
1354static bool rcu_is_callbacks_kthread(void)
1355{
1356 return __this_cpu_read(rcu_cpu_kthread_task) == current;
1357}
1358
1359#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1360
1361/*
1362 * Do priority-boost accounting for the start of a new grace period.
1363 */
1364static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1365{
1366 rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1367}
1368
1369/*
1370 * Create an RCU-boost kthread for the specified node if one does not
1371 * already exist. We only create this kthread for preemptible RCU.
1372 * Returns zero if all is well, a negated errno otherwise.
1373 */
1374static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
1375 struct rcu_node *rnp)
1376{
1377 int rnp_index = rnp - &rsp->node[0];
1378 unsigned long flags;
1379 struct sched_param sp;
1380 struct task_struct *t;
1381
1382 if (&rcu_preempt_state != rsp)
1383 return 0;
1384
1385 if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
1386 return 0;
1387
1388 rsp->boost = 1;
1389 if (rnp->boost_kthread_task != NULL)
1390 return 0;
1391 t = kthread_create(rcu_boost_kthread, (void *)rnp,
1392 "rcub/%d", rnp_index);
1393 if (IS_ERR(t))
1394 return PTR_ERR(t);
1395 raw_spin_lock_irqsave(&rnp->lock, flags);
1396 smp_mb__after_unlock_lock();
1397 rnp->boost_kthread_task = t;
1398 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1399 sp.sched_priority = RCU_BOOST_PRIO;
1400 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1401 wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1402 return 0;
1403}
1404
1405static void rcu_kthread_do_work(void)
1406{
1407 rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
1408 rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
1409 rcu_preempt_do_callbacks();
1410}
1411
1412static void rcu_cpu_kthread_setup(unsigned int cpu)
1413{
1414 struct sched_param sp;
1415
1416 sp.sched_priority = RCU_KTHREAD_PRIO;
1417 sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
1418}
1419
1420static void rcu_cpu_kthread_park(unsigned int cpu)
1421{
1422 per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1423}
1424
1425static int rcu_cpu_kthread_should_run(unsigned int cpu)
1426{
1427 return __this_cpu_read(rcu_cpu_has_work);
1428}
1429
1430/*
1431 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
1432 * RCU softirq used in flavors and configurations of RCU that do not
1433 * support RCU priority boosting.
1434 */
1435static void rcu_cpu_kthread(unsigned int cpu)
1436{
1437 unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
1438 char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
1439 int spincnt;
1440
1441 for (spincnt = 0; spincnt < 10; spincnt++) {
1442 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1443 local_bh_disable();
1444 *statusp = RCU_KTHREAD_RUNNING;
1445 this_cpu_inc(rcu_cpu_kthread_loops);
1446 local_irq_disable();
1447 work = *workp;
1448 *workp = 0;
1449 local_irq_enable();
1450 if (work)
1451 rcu_kthread_do_work();
1452 local_bh_enable();
1453 if (*workp == 0) {
1454 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1455 *statusp = RCU_KTHREAD_WAITING;
1456 return;
1457 }
1458 }
1459 *statusp = RCU_KTHREAD_YIELDING;
1460 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1461 schedule_timeout_interruptible(2);
1462 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1463 *statusp = RCU_KTHREAD_WAITING;
1464}
1465
1466/*
1467 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1468 * served by the rcu_node in question. The CPU hotplug lock is still
1469 * held, so the value of rnp->qsmaskinit will be stable.
1470 *
1471 * We don't include outgoingcpu in the affinity set, use -1 if there is
1472 * no outgoing CPU. If there are no CPUs left in the affinity set,
1473 * this function allows the kthread to execute on any CPU.
1474 */
1475static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1476{
1477 struct task_struct *t = rnp->boost_kthread_task;
1478 unsigned long mask = rnp->qsmaskinit;
1479 cpumask_var_t cm;
1480 int cpu;
1481
1482 if (!t)
1483 return;
1484 if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1485 return;
1486 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
1487 if ((mask & 0x1) && cpu != outgoingcpu)
1488 cpumask_set_cpu(cpu, cm);
1489 if (cpumask_weight(cm) == 0) {
1490 cpumask_setall(cm);
1491 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
1492 cpumask_clear_cpu(cpu, cm);
1493 WARN_ON_ONCE(cpumask_weight(cm) == 0);
1494 }
1495 set_cpus_allowed_ptr(t, cm);
1496 free_cpumask_var(cm);
1497}
1498
1499static struct smp_hotplug_thread rcu_cpu_thread_spec = {
1500 .store = &rcu_cpu_kthread_task,
1501 .thread_should_run = rcu_cpu_kthread_should_run,
1502 .thread_fn = rcu_cpu_kthread,
1503 .thread_comm = "rcuc/%u",
1504 .setup = rcu_cpu_kthread_setup,
1505 .park = rcu_cpu_kthread_park,
1506};
1507
1508/*
1509 * Spawn all kthreads -- called as soon as the scheduler is running.
1510 */
1511static int __init rcu_spawn_kthreads(void)
1512{
1513 struct rcu_node *rnp;
1514 int cpu;
1515
1516 rcu_scheduler_fully_active = 1;
1517 for_each_possible_cpu(cpu)
1518 per_cpu(rcu_cpu_has_work, cpu) = 0;
1519 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
1520 rnp = rcu_get_root(rcu_state);
1521 (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1522 if (NUM_RCU_NODES > 1) {
1523 rcu_for_each_leaf_node(rcu_state, rnp)
1524 (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1525 }
1526 return 0;
1527}
1528early_initcall(rcu_spawn_kthreads);
1529
1530static void rcu_prepare_kthreads(int cpu)
1531{
1532 struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
1533 struct rcu_node *rnp = rdp->mynode;
1534
1535 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1536 if (rcu_scheduler_fully_active)
1537 (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1538}
1539
1540#else /* #ifdef CONFIG_RCU_BOOST */
1541
1542static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1543{
1544 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1545}
1546
1547static void invoke_rcu_callbacks_kthread(void)
1548{
1549 WARN_ON_ONCE(1);
1550}
1551
1552static bool rcu_is_callbacks_kthread(void)
1553{
1554 return false;
1555}
1556
1557static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1558{
1559}
1560
1561static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1562{
1563}
1564
1565static int __init rcu_scheduler_really_started(void)
1566{
1567 rcu_scheduler_fully_active = 1;
1568 return 0;
1569}
1570early_initcall(rcu_scheduler_really_started);
1571
1572static void rcu_prepare_kthreads(int cpu)
1573{
1574}
1575
1576#endif /* #else #ifdef CONFIG_RCU_BOOST */
1577
1578#if !defined(CONFIG_RCU_FAST_NO_HZ)
1579
1580/*
1581 * Check to see if any future RCU-related work will need to be done
1582 * by the current CPU, even if none need be done immediately, returning
1583 * 1 if so. This function is part of the RCU implementation; it is -not-
1584 * an exported member of the RCU API.
1585 *
1586 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1587 * any flavor of RCU.
1588 */
1589#ifndef CONFIG_RCU_NOCB_CPU_ALL
1590int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
1591{
1592 *delta_jiffies = ULONG_MAX;
1593 return rcu_cpu_has_callbacks(cpu, NULL);
1594}
1595#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1596
1597/*
1598 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1599 * after it.
1600 */
1601static void rcu_cleanup_after_idle(int cpu)
1602{
1603}
1604
1605/*
1606 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1607 * is nothing.
1608 */
1609static void rcu_prepare_for_idle(int cpu)
1610{
1611}
1612
1613/*
1614 * Don't bother keeping a running count of the number of RCU callbacks
1615 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1616 */
1617static void rcu_idle_count_callbacks_posted(void)
1618{
1619}
1620
1621#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1622
1623/*
1624 * This code is invoked when a CPU goes idle, at which point we want
1625 * to have the CPU do everything required for RCU so that it can enter
1626 * the energy-efficient dyntick-idle mode. This is handled by a
1627 * state machine implemented by rcu_prepare_for_idle() below.
1628 *
1629 * The following three proprocessor symbols control this state machine:
1630 *
1631 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1632 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1633 * is sized to be roughly one RCU grace period. Those energy-efficiency
1634 * benchmarkers who might otherwise be tempted to set this to a large
1635 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1636 * system. And if you are -that- concerned about energy efficiency,
1637 * just power the system down and be done with it!
1638 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1639 * permitted to sleep in dyntick-idle mode with only lazy RCU
1640 * callbacks pending. Setting this too high can OOM your system.
1641 *
1642 * The values below work well in practice. If future workloads require
1643 * adjustment, they can be converted into kernel config parameters, though
1644 * making the state machine smarter might be a better option.
1645 */
1646#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1647#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1648
1649static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
1650module_param(rcu_idle_gp_delay, int, 0644);
1651static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
1652module_param(rcu_idle_lazy_gp_delay, int, 0644);
1653
1654extern int tick_nohz_active;
1655
1656/*
1657 * Try to advance callbacks for all flavors of RCU on the current CPU, but
1658 * only if it has been awhile since the last time we did so. Afterwards,
1659 * if there are any callbacks ready for immediate invocation, return true.
1660 */
1661static bool __maybe_unused rcu_try_advance_all_cbs(void)
1662{
1663 bool cbs_ready = false;
1664 struct rcu_data *rdp;
1665 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1666 struct rcu_node *rnp;
1667 struct rcu_state *rsp;
1668
1669 /* Exit early if we advanced recently. */
1670 if (jiffies == rdtp->last_advance_all)
1671 return 0;
1672 rdtp->last_advance_all = jiffies;
1673
1674 for_each_rcu_flavor(rsp) {
1675 rdp = this_cpu_ptr(rsp->rda);
1676 rnp = rdp->mynode;
1677
1678 /*
1679 * Don't bother checking unless a grace period has
1680 * completed since we last checked and there are
1681 * callbacks not yet ready to invoke.
1682 */
1683 if (rdp->completed != rnp->completed &&
1684 rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
1685 note_gp_changes(rsp, rdp);
1686
1687 if (cpu_has_callbacks_ready_to_invoke(rdp))
1688 cbs_ready = true;
1689 }
1690 return cbs_ready;
1691}
1692
1693/*
1694 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1695 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1696 * caller to set the timeout based on whether or not there are non-lazy
1697 * callbacks.
1698 *
1699 * The caller must have disabled interrupts.
1700 */
1701#ifndef CONFIG_RCU_NOCB_CPU_ALL
1702int rcu_needs_cpu(int cpu, unsigned long *dj)
1703{
1704 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1705
1706 /* Snapshot to detect later posting of non-lazy callback. */
1707 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1708
1709 /* If no callbacks, RCU doesn't need the CPU. */
1710 if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) {
1711 *dj = ULONG_MAX;
1712 return 0;
1713 }
1714
1715 /* Attempt to advance callbacks. */
1716 if (rcu_try_advance_all_cbs()) {
1717 /* Some ready to invoke, so initiate later invocation. */
1718 invoke_rcu_core();
1719 return 1;
1720 }
1721 rdtp->last_accelerate = jiffies;
1722
1723 /* Request timer delay depending on laziness, and round. */
1724 if (!rdtp->all_lazy) {
1725 *dj = round_up(rcu_idle_gp_delay + jiffies,
1726 rcu_idle_gp_delay) - jiffies;
1727 } else {
1728 *dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1729 }
1730 return 0;
1731}
1732#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1733
1734/*
1735 * Prepare a CPU for idle from an RCU perspective. The first major task
1736 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1737 * The second major task is to check to see if a non-lazy callback has
1738 * arrived at a CPU that previously had only lazy callbacks. The third
1739 * major task is to accelerate (that is, assign grace-period numbers to)
1740 * any recently arrived callbacks.
1741 *
1742 * The caller must have disabled interrupts.
1743 */
1744static void rcu_prepare_for_idle(int cpu)
1745{
1746#ifndef CONFIG_RCU_NOCB_CPU_ALL
1747 struct rcu_data *rdp;
1748 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1749 struct rcu_node *rnp;
1750 struct rcu_state *rsp;
1751 int tne;
1752
1753 /* Handle nohz enablement switches conservatively. */
1754 tne = ACCESS_ONCE(tick_nohz_active);
1755 if (tne != rdtp->tick_nohz_enabled_snap) {
1756 if (rcu_cpu_has_callbacks(cpu, NULL))
1757 invoke_rcu_core(); /* force nohz to see update. */
1758 rdtp->tick_nohz_enabled_snap = tne;
1759 return;
1760 }
1761 if (!tne)
1762 return;
1763
1764 /* If this is a no-CBs CPU, no callbacks, just return. */
1765 if (rcu_is_nocb_cpu(cpu))
1766 return;
1767
1768 /*
1769 * If a non-lazy callback arrived at a CPU having only lazy
1770 * callbacks, invoke RCU core for the side-effect of recalculating
1771 * idle duration on re-entry to idle.
1772 */
1773 if (rdtp->all_lazy &&
1774 rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
1775 rdtp->all_lazy = false;
1776 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1777 invoke_rcu_core();
1778 return;
1779 }
1780
1781 /*
1782 * If we have not yet accelerated this jiffy, accelerate all
1783 * callbacks on this CPU.
1784 */
1785 if (rdtp->last_accelerate == jiffies)
1786 return;
1787 rdtp->last_accelerate = jiffies;
1788 for_each_rcu_flavor(rsp) {
1789 rdp = per_cpu_ptr(rsp->rda, cpu);
1790 if (!*rdp->nxttail[RCU_DONE_TAIL])
1791 continue;
1792 rnp = rdp->mynode;
1793 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
1794 smp_mb__after_unlock_lock();
1795 rcu_accelerate_cbs(rsp, rnp, rdp);
1796 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1797 }
1798#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1799}
1800
1801/*
1802 * Clean up for exit from idle. Attempt to advance callbacks based on
1803 * any grace periods that elapsed while the CPU was idle, and if any
1804 * callbacks are now ready to invoke, initiate invocation.
1805 */
1806static void rcu_cleanup_after_idle(int cpu)
1807{
1808#ifndef CONFIG_RCU_NOCB_CPU_ALL
1809 if (rcu_is_nocb_cpu(cpu))
1810 return;
1811 if (rcu_try_advance_all_cbs())
1812 invoke_rcu_core();
1813#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1814}
1815
1816/*
1817 * Keep a running count of the number of non-lazy callbacks posted
1818 * on this CPU. This running counter (which is never decremented) allows
1819 * rcu_prepare_for_idle() to detect when something out of the idle loop
1820 * posts a callback, even if an equal number of callbacks are invoked.
1821 * Of course, callbacks should only be posted from within a trace event
1822 * designed to be called from idle or from within RCU_NONIDLE().
1823 */
1824static void rcu_idle_count_callbacks_posted(void)
1825{
1826 __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
1827}
1828
1829/*
1830 * Data for flushing lazy RCU callbacks at OOM time.
1831 */
1832static atomic_t oom_callback_count;
1833static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
1834
1835/*
1836 * RCU OOM callback -- decrement the outstanding count and deliver the
1837 * wake-up if we are the last one.
1838 */
1839static void rcu_oom_callback(struct rcu_head *rhp)
1840{
1841 if (atomic_dec_and_test(&oom_callback_count))
1842 wake_up(&oom_callback_wq);
1843}
1844
1845/*
1846 * Post an rcu_oom_notify callback on the current CPU if it has at
1847 * least one lazy callback. This will unnecessarily post callbacks
1848 * to CPUs that already have a non-lazy callback at the end of their
1849 * callback list, but this is an infrequent operation, so accept some
1850 * extra overhead to keep things simple.
1851 */
1852static void rcu_oom_notify_cpu(void *unused)
1853{
1854 struct rcu_state *rsp;
1855 struct rcu_data *rdp;
1856
1857 for_each_rcu_flavor(rsp) {
1858 rdp = __this_cpu_ptr(rsp->rda);
1859 if (rdp->qlen_lazy != 0) {
1860 atomic_inc(&oom_callback_count);
1861 rsp->call(&rdp->oom_head, rcu_oom_callback);
1862 }
1863 }
1864}
1865
1866/*
1867 * If low on memory, ensure that each CPU has a non-lazy callback.
1868 * This will wake up CPUs that have only lazy callbacks, in turn
1869 * ensuring that they free up the corresponding memory in a timely manner.
1870 * Because an uncertain amount of memory will be freed in some uncertain
1871 * timeframe, we do not claim to have freed anything.
1872 */
1873static int rcu_oom_notify(struct notifier_block *self,
1874 unsigned long notused, void *nfreed)
1875{
1876 int cpu;
1877
1878 /* Wait for callbacks from earlier instance to complete. */
1879 wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
1880 smp_mb(); /* Ensure callback reuse happens after callback invocation. */
1881
1882 /*
1883 * Prevent premature wakeup: ensure that all increments happen
1884 * before there is a chance of the counter reaching zero.
1885 */
1886 atomic_set(&oom_callback_count, 1);
1887
1888 get_online_cpus();
1889 for_each_online_cpu(cpu) {
1890 smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
1891 cond_resched();
1892 }
1893 put_online_cpus();
1894
1895 /* Unconditionally decrement: no need to wake ourselves up. */
1896 atomic_dec(&oom_callback_count);
1897
1898 return NOTIFY_OK;
1899}
1900
1901static struct notifier_block rcu_oom_nb = {
1902 .notifier_call = rcu_oom_notify
1903};
1904
1905static int __init rcu_register_oom_notifier(void)
1906{
1907 register_oom_notifier(&rcu_oom_nb);
1908 return 0;
1909}
1910early_initcall(rcu_register_oom_notifier);
1911
1912#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1913
1914#ifdef CONFIG_RCU_CPU_STALL_INFO
1915
1916#ifdef CONFIG_RCU_FAST_NO_HZ
1917
1918static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1919{
1920 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1921 unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
1922
1923 sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1924 rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
1925 ulong2long(nlpd),
1926 rdtp->all_lazy ? 'L' : '.',
1927 rdtp->tick_nohz_enabled_snap ? '.' : 'D');
1928}
1929
1930#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1931
1932static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1933{
1934 *cp = '\0';
1935}
1936
1937#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1938
1939/* Initiate the stall-info list. */
1940static void print_cpu_stall_info_begin(void)
1941{
1942 pr_cont("\n");
1943}
1944
1945/*
1946 * Print out diagnostic information for the specified stalled CPU.
1947 *
1948 * If the specified CPU is aware of the current RCU grace period
1949 * (flavor specified by rsp), then print the number of scheduling
1950 * clock interrupts the CPU has taken during the time that it has
1951 * been aware. Otherwise, print the number of RCU grace periods
1952 * that this CPU is ignorant of, for example, "1" if the CPU was
1953 * aware of the previous grace period.
1954 *
1955 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1956 */
1957static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1958{
1959 char fast_no_hz[72];
1960 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1961 struct rcu_dynticks *rdtp = rdp->dynticks;
1962 char *ticks_title;
1963 unsigned long ticks_value;
1964
1965 if (rsp->gpnum == rdp->gpnum) {
1966 ticks_title = "ticks this GP";
1967 ticks_value = rdp->ticks_this_gp;
1968 } else {
1969 ticks_title = "GPs behind";
1970 ticks_value = rsp->gpnum - rdp->gpnum;
1971 }
1972 print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
1973 pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
1974 cpu, ticks_value, ticks_title,
1975 atomic_read(&rdtp->dynticks) & 0xfff,
1976 rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
1977 rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
1978 fast_no_hz);
1979}
1980
1981/* Terminate the stall-info list. */
1982static void print_cpu_stall_info_end(void)
1983{
1984 pr_err("\t");
1985}
1986
1987/* Zero ->ticks_this_gp for all flavors of RCU. */
1988static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1989{
1990 rdp->ticks_this_gp = 0;
1991 rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
1992}
1993
1994/* Increment ->ticks_this_gp for all flavors of RCU. */
1995static void increment_cpu_stall_ticks(void)
1996{
1997 struct rcu_state *rsp;
1998
1999 for_each_rcu_flavor(rsp)
2000 __this_cpu_ptr(rsp->rda)->ticks_this_gp++;
2001}
2002
2003#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
2004
2005static void print_cpu_stall_info_begin(void)
2006{
2007 pr_cont(" {");
2008}
2009
2010static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
2011{
2012 pr_cont(" %d", cpu);
2013}
2014
2015static void print_cpu_stall_info_end(void)
2016{
2017 pr_cont("} ");
2018}
2019
2020static void zero_cpu_stall_ticks(struct rcu_data *rdp)
2021{
2022}
2023
2024static void increment_cpu_stall_ticks(void)
2025{
2026}
2027
2028#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
2029
2030#ifdef CONFIG_RCU_NOCB_CPU
2031
2032/*
2033 * Offload callback processing from the boot-time-specified set of CPUs
2034 * specified by rcu_nocb_mask. For each CPU in the set, there is a
2035 * kthread created that pulls the callbacks from the corresponding CPU,
2036 * waits for a grace period to elapse, and invokes the callbacks.
2037 * The no-CBs CPUs do a wake_up() on their kthread when they insert
2038 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
2039 * has been specified, in which case each kthread actively polls its
2040 * CPU. (Which isn't so great for energy efficiency, but which does
2041 * reduce RCU's overhead on that CPU.)
2042 *
2043 * This is intended to be used in conjunction with Frederic Weisbecker's
2044 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
2045 * running CPU-bound user-mode computations.
2046 *
2047 * Offloading of callback processing could also in theory be used as
2048 * an energy-efficiency measure because CPUs with no RCU callbacks
2049 * queued are more aggressive about entering dyntick-idle mode.
2050 */
2051
2052
2053/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
2054static int __init rcu_nocb_setup(char *str)
2055{
2056 alloc_bootmem_cpumask_var(&rcu_nocb_mask);
2057 have_rcu_nocb_mask = true;
2058 cpulist_parse(str, rcu_nocb_mask);
2059 return 1;
2060}
2061__setup("rcu_nocbs=", rcu_nocb_setup);
2062
2063static int __init parse_rcu_nocb_poll(char *arg)
2064{
2065 rcu_nocb_poll = 1;
2066 return 0;
2067}
2068early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
2069
2070/*
2071 * Do any no-CBs CPUs need another grace period?
2072 *
2073 * Interrupts must be disabled. If the caller does not hold the root
2074 * rnp_node structure's ->lock, the results are advisory only.
2075 */
2076static int rcu_nocb_needs_gp(struct rcu_state *rsp)
2077{
2078 struct rcu_node *rnp = rcu_get_root(rsp);
2079
2080 return rnp->need_future_gp[(ACCESS_ONCE(rnp->completed) + 1) & 0x1];
2081}
2082
2083/*
2084 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
2085 * grace period.
2086 */
2087static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2088{
2089 wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
2090}
2091
2092/*
2093 * Set the root rcu_node structure's ->need_future_gp field
2094 * based on the sum of those of all rcu_node structures. This does
2095 * double-count the root rcu_node structure's requests, but this
2096 * is necessary to handle the possibility of a rcu_nocb_kthread()
2097 * having awakened during the time that the rcu_node structures
2098 * were being updated for the end of the previous grace period.
2099 */
2100static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2101{
2102 rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
2103}
2104
2105static void rcu_init_one_nocb(struct rcu_node *rnp)
2106{
2107 init_waitqueue_head(&rnp->nocb_gp_wq[0]);
2108 init_waitqueue_head(&rnp->nocb_gp_wq[1]);
2109}
2110
2111#ifndef CONFIG_RCU_NOCB_CPU_ALL
2112/* Is the specified CPU a no-CPUs CPU? */
2113bool rcu_is_nocb_cpu(int cpu)
2114{
2115 if (have_rcu_nocb_mask)
2116 return cpumask_test_cpu(cpu, rcu_nocb_mask);
2117 return false;
2118}
2119#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
2120
2121/*
2122 * Enqueue the specified string of rcu_head structures onto the specified
2123 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
2124 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
2125 * counts are supplied by rhcount and rhcount_lazy.
2126 *
2127 * If warranted, also wake up the kthread servicing this CPUs queues.
2128 */
2129static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
2130 struct rcu_head *rhp,
2131 struct rcu_head **rhtp,
2132 int rhcount, int rhcount_lazy,
2133 unsigned long flags)
2134{
2135 int len;
2136 struct rcu_head **old_rhpp;
2137 struct task_struct *t;
2138
2139 /* Enqueue the callback on the nocb list and update counts. */
2140 old_rhpp = xchg(&rdp->nocb_tail, rhtp);
2141 ACCESS_ONCE(*old_rhpp) = rhp;
2142 atomic_long_add(rhcount, &rdp->nocb_q_count);
2143 atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
2144
2145 /* If we are not being polled and there is a kthread, awaken it ... */
2146 t = ACCESS_ONCE(rdp->nocb_kthread);
2147 if (rcu_nocb_poll || !t) {
2148 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2149 TPS("WakeNotPoll"));
2150 return;
2151 }
2152 len = atomic_long_read(&rdp->nocb_q_count);
2153 if (old_rhpp == &rdp->nocb_head) {
2154 if (!irqs_disabled_flags(flags)) {
2155 wake_up(&rdp->nocb_wq); /* ... if queue was empty ... */
2156 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2157 TPS("WakeEmpty"));
2158 } else {
2159 rdp->nocb_defer_wakeup = true;
2160 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2161 TPS("WakeEmptyIsDeferred"));
2162 }
2163 rdp->qlen_last_fqs_check = 0;
2164 } else if (len > rdp->qlen_last_fqs_check + qhimark) {
2165 wake_up_process(t); /* ... or if many callbacks queued. */
2166 rdp->qlen_last_fqs_check = LONG_MAX / 2;
2167 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf"));
2168 } else {
2169 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
2170 }
2171 return;
2172}
2173
2174/*
2175 * This is a helper for __call_rcu(), which invokes this when the normal
2176 * callback queue is inoperable. If this is not a no-CBs CPU, this
2177 * function returns failure back to __call_rcu(), which can complain
2178 * appropriately.
2179 *
2180 * Otherwise, this function queues the callback where the corresponding
2181 * "rcuo" kthread can find it.
2182 */
2183static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2184 bool lazy, unsigned long flags)
2185{
2186
2187 if (!rcu_is_nocb_cpu(rdp->cpu))
2188 return 0;
2189 __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
2190 if (__is_kfree_rcu_offset((unsigned long)rhp->func))
2191 trace_rcu_kfree_callback(rdp->rsp->name, rhp,
2192 (unsigned long)rhp->func,
2193 -atomic_long_read(&rdp->nocb_q_count_lazy),
2194 -atomic_long_read(&rdp->nocb_q_count));
2195 else
2196 trace_rcu_callback(rdp->rsp->name, rhp,
2197 -atomic_long_read(&rdp->nocb_q_count_lazy),
2198 -atomic_long_read(&rdp->nocb_q_count));
2199 return 1;
2200}
2201
2202/*
2203 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2204 * not a no-CBs CPU.
2205 */
2206static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2207 struct rcu_data *rdp,
2208 unsigned long flags)
2209{
2210 long ql = rsp->qlen;
2211 long qll = rsp->qlen_lazy;
2212
2213 /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
2214 if (!rcu_is_nocb_cpu(smp_processor_id()))
2215 return 0;
2216 rsp->qlen = 0;
2217 rsp->qlen_lazy = 0;
2218
2219 /* First, enqueue the donelist, if any. This preserves CB ordering. */
2220 if (rsp->orphan_donelist != NULL) {
2221 __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
2222 rsp->orphan_donetail, ql, qll, flags);
2223 ql = qll = 0;
2224 rsp->orphan_donelist = NULL;
2225 rsp->orphan_donetail = &rsp->orphan_donelist;
2226 }
2227 if (rsp->orphan_nxtlist != NULL) {
2228 __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
2229 rsp->orphan_nxttail, ql, qll, flags);
2230 ql = qll = 0;
2231 rsp->orphan_nxtlist = NULL;
2232 rsp->orphan_nxttail = &rsp->orphan_nxtlist;
2233 }
2234 return 1;
2235}
2236
2237/*
2238 * If necessary, kick off a new grace period, and either way wait
2239 * for a subsequent grace period to complete.
2240 */
2241static void rcu_nocb_wait_gp(struct rcu_data *rdp)
2242{
2243 unsigned long c;
2244 bool d;
2245 unsigned long flags;
2246 struct rcu_node *rnp = rdp->mynode;
2247
2248 raw_spin_lock_irqsave(&rnp->lock, flags);
2249 smp_mb__after_unlock_lock();
2250 c = rcu_start_future_gp(rnp, rdp);
2251 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2252
2253 /*
2254 * Wait for the grace period. Do so interruptibly to avoid messing
2255 * up the load average.
2256 */
2257 trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
2258 for (;;) {
2259 wait_event_interruptible(
2260 rnp->nocb_gp_wq[c & 0x1],
2261 (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
2262 if (likely(d))
2263 break;
2264 flush_signals(current);
2265 trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
2266 }
2267 trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
2268 smp_mb(); /* Ensure that CB invocation happens after GP end. */
2269}
2270
2271/*
2272 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
2273 * callbacks queued by the corresponding no-CBs CPU.
2274 */
2275static int rcu_nocb_kthread(void *arg)
2276{
2277 int c, cl;
2278 bool firsttime = 1;
2279 struct rcu_head *list;
2280 struct rcu_head *next;
2281 struct rcu_head **tail;
2282 struct rcu_data *rdp = arg;
2283
2284 /* Each pass through this loop invokes one batch of callbacks */
2285 for (;;) {
2286 /* If not polling, wait for next batch of callbacks. */
2287 if (!rcu_nocb_poll) {
2288 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2289 TPS("Sleep"));
2290 wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
2291 /* Memory barrier provide by xchg() below. */
2292 } else if (firsttime) {
2293 firsttime = 0;
2294 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2295 TPS("Poll"));
2296 }
2297 list = ACCESS_ONCE(rdp->nocb_head);
2298 if (!list) {
2299 if (!rcu_nocb_poll)
2300 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2301 TPS("WokeEmpty"));
2302 schedule_timeout_interruptible(1);
2303 flush_signals(current);
2304 continue;
2305 }
2306 firsttime = 1;
2307 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2308 TPS("WokeNonEmpty"));
2309
2310 /*
2311 * Extract queued callbacks, update counts, and wait
2312 * for a grace period to elapse.
2313 */
2314 ACCESS_ONCE(rdp->nocb_head) = NULL;
2315 tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
2316 c = atomic_long_xchg(&rdp->nocb_q_count, 0);
2317 cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0);
2318 ACCESS_ONCE(rdp->nocb_p_count) += c;
2319 ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl;
2320 rcu_nocb_wait_gp(rdp);
2321
2322 /* Each pass through the following loop invokes a callback. */
2323 trace_rcu_batch_start(rdp->rsp->name, cl, c, -1);
2324 c = cl = 0;
2325 while (list) {
2326 next = list->next;
2327 /* Wait for enqueuing to complete, if needed. */
2328 while (next == NULL && &list->next != tail) {
2329 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2330 TPS("WaitQueue"));
2331 schedule_timeout_interruptible(1);
2332 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2333 TPS("WokeQueue"));
2334 next = list->next;
2335 }
2336 debug_rcu_head_unqueue(list);
2337 local_bh_disable();
2338 if (__rcu_reclaim(rdp->rsp->name, list))
2339 cl++;
2340 c++;
2341 local_bh_enable();
2342 list = next;
2343 }
2344 trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
2345 ACCESS_ONCE(rdp->nocb_p_count) -= c;
2346 ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl;
2347 rdp->n_nocbs_invoked += c;
2348 }
2349 return 0;
2350}
2351
2352/* Is a deferred wakeup of rcu_nocb_kthread() required? */
2353static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2354{
2355 return ACCESS_ONCE(rdp->nocb_defer_wakeup);
2356}
2357
2358/* Do a deferred wakeup of rcu_nocb_kthread(). */
2359static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2360{
2361 if (!rcu_nocb_need_deferred_wakeup(rdp))
2362 return;
2363 ACCESS_ONCE(rdp->nocb_defer_wakeup) = false;
2364 wake_up(&rdp->nocb_wq);
2365 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWakeEmpty"));
2366}
2367
2368/* Initialize per-rcu_data variables for no-CBs CPUs. */
2369static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2370{
2371 rdp->nocb_tail = &rdp->nocb_head;
2372 init_waitqueue_head(&rdp->nocb_wq);
2373}
2374
2375/* Create a kthread for each RCU flavor for each no-CBs CPU. */
2376static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
2377{
2378 int cpu;
2379 struct rcu_data *rdp;
2380 struct task_struct *t;
2381
2382 if (rcu_nocb_mask == NULL)
2383 return;
2384 for_each_cpu(cpu, rcu_nocb_mask) {
2385 rdp = per_cpu_ptr(rsp->rda, cpu);
2386 t = kthread_run(rcu_nocb_kthread, rdp,
2387 "rcuo%c/%d", rsp->abbr, cpu);
2388 BUG_ON(IS_ERR(t));
2389 ACCESS_ONCE(rdp->nocb_kthread) = t;
2390 }
2391}
2392
2393/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2394static bool init_nocb_callback_list(struct rcu_data *rdp)
2395{
2396 if (rcu_nocb_mask == NULL ||
2397 !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
2398 return false;
2399 rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2400 return true;
2401}
2402
2403#else /* #ifdef CONFIG_RCU_NOCB_CPU */
2404
2405static int rcu_nocb_needs_gp(struct rcu_state *rsp)
2406{
2407 return 0;
2408}
2409
2410static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2411{
2412}
2413
2414static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2415{
2416}
2417
2418static void rcu_init_one_nocb(struct rcu_node *rnp)
2419{
2420}
2421
2422static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2423 bool lazy, unsigned long flags)
2424{
2425 return 0;
2426}
2427
2428static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2429 struct rcu_data *rdp,
2430 unsigned long flags)
2431{
2432 return 0;
2433}
2434
2435static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2436{
2437}
2438
2439static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2440{
2441 return false;
2442}
2443
2444static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2445{
2446}
2447
2448static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
2449{
2450}
2451
2452static bool init_nocb_callback_list(struct rcu_data *rdp)
2453{
2454 return false;
2455}
2456
2457#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2458
2459/*
2460 * An adaptive-ticks CPU can potentially execute in kernel mode for an
2461 * arbitrarily long period of time with the scheduling-clock tick turned
2462 * off. RCU will be paying attention to this CPU because it is in the
2463 * kernel, but the CPU cannot be guaranteed to be executing the RCU state
2464 * machine because the scheduling-clock tick has been disabled. Therefore,
2465 * if an adaptive-ticks CPU is failing to respond to the current grace
2466 * period and has not be idle from an RCU perspective, kick it.
2467 */
2468static void rcu_kick_nohz_cpu(int cpu)
2469{
2470#ifdef CONFIG_NO_HZ_FULL
2471 if (tick_nohz_full_cpu(cpu))
2472 smp_send_reschedule(cpu);
2473#endif /* #ifdef CONFIG_NO_HZ_FULL */
2474}
2475
2476
2477#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
2478
2479/*
2480 * Define RCU flavor that holds sysidle state. This needs to be the
2481 * most active flavor of RCU.
2482 */
2483#ifdef CONFIG_PREEMPT_RCU
2484static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state;
2485#else /* #ifdef CONFIG_PREEMPT_RCU */
2486static struct rcu_state *rcu_sysidle_state = &rcu_sched_state;
2487#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
2488
2489static int full_sysidle_state; /* Current system-idle state. */
2490#define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */
2491#define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */
2492#define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */
2493#define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */
2494#define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */
2495
2496/*
2497 * Invoked to note exit from irq or task transition to idle. Note that
2498 * usermode execution does -not- count as idle here! After all, we want
2499 * to detect full-system idle states, not RCU quiescent states and grace
2500 * periods. The caller must have disabled interrupts.
2501 */
2502static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
2503{
2504 unsigned long j;
2505
2506 /* Adjust nesting, check for fully idle. */
2507 if (irq) {
2508 rdtp->dynticks_idle_nesting--;
2509 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
2510 if (rdtp->dynticks_idle_nesting != 0)
2511 return; /* Still not fully idle. */
2512 } else {
2513 if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) ==
2514 DYNTICK_TASK_NEST_VALUE) {
2515 rdtp->dynticks_idle_nesting = 0;
2516 } else {
2517 rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE;
2518 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
2519 return; /* Still not fully idle. */
2520 }
2521 }
2522
2523 /* Record start of fully idle period. */
2524 j = jiffies;
2525 ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j;
2526 smp_mb__before_atomic_inc();
2527 atomic_inc(&rdtp->dynticks_idle);
2528 smp_mb__after_atomic_inc();
2529 WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
2530}
2531
2532/*
2533 * Unconditionally force exit from full system-idle state. This is
2534 * invoked when a normal CPU exits idle, but must be called separately
2535 * for the timekeeping CPU (tick_do_timer_cpu). The reason for this
2536 * is that the timekeeping CPU is permitted to take scheduling-clock
2537 * interrupts while the system is in system-idle state, and of course
2538 * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
2539 * interrupt from any other type of interrupt.
2540 */
2541void rcu_sysidle_force_exit(void)
2542{
2543 int oldstate = ACCESS_ONCE(full_sysidle_state);
2544 int newoldstate;
2545
2546 /*
2547 * Each pass through the following loop attempts to exit full
2548 * system-idle state. If contention proves to be a problem,
2549 * a trylock-based contention tree could be used here.
2550 */
2551 while (oldstate > RCU_SYSIDLE_SHORT) {
2552 newoldstate = cmpxchg(&full_sysidle_state,
2553 oldstate, RCU_SYSIDLE_NOT);
2554 if (oldstate == newoldstate &&
2555 oldstate == RCU_SYSIDLE_FULL_NOTED) {
2556 rcu_kick_nohz_cpu(tick_do_timer_cpu);
2557 return; /* We cleared it, done! */
2558 }
2559 oldstate = newoldstate;
2560 }
2561 smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
2562}
2563
2564/*
2565 * Invoked to note entry to irq or task transition from idle. Note that
2566 * usermode execution does -not- count as idle here! The caller must
2567 * have disabled interrupts.
2568 */
2569static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
2570{
2571 /* Adjust nesting, check for already non-idle. */
2572 if (irq) {
2573 rdtp->dynticks_idle_nesting++;
2574 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
2575 if (rdtp->dynticks_idle_nesting != 1)
2576 return; /* Already non-idle. */
2577 } else {
2578 /*
2579 * Allow for irq misnesting. Yes, it really is possible
2580 * to enter an irq handler then never leave it, and maybe
2581 * also vice versa. Handle both possibilities.
2582 */
2583 if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) {
2584 rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE;
2585 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
2586 return; /* Already non-idle. */
2587 } else {
2588 rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE;
2589 }
2590 }
2591
2592 /* Record end of idle period. */
2593 smp_mb__before_atomic_inc();
2594 atomic_inc(&rdtp->dynticks_idle);
2595 smp_mb__after_atomic_inc();
2596 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
2597
2598 /*
2599 * If we are the timekeeping CPU, we are permitted to be non-idle
2600 * during a system-idle state. This must be the case, because
2601 * the timekeeping CPU has to take scheduling-clock interrupts
2602 * during the time that the system is transitioning to full
2603 * system-idle state. This means that the timekeeping CPU must
2604 * invoke rcu_sysidle_force_exit() directly if it does anything
2605 * more than take a scheduling-clock interrupt.
2606 */
2607 if (smp_processor_id() == tick_do_timer_cpu)
2608 return;
2609
2610 /* Update system-idle state: We are clearly no longer fully idle! */
2611 rcu_sysidle_force_exit();
2612}
2613
2614/*
2615 * Check to see if the current CPU is idle. Note that usermode execution
2616 * does not count as idle. The caller must have disabled interrupts.
2617 */
2618static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
2619 unsigned long *maxj)
2620{
2621 int cur;
2622 unsigned long j;
2623 struct rcu_dynticks *rdtp = rdp->dynticks;
2624
2625 /*
2626 * If some other CPU has already reported non-idle, if this is
2627 * not the flavor of RCU that tracks sysidle state, or if this
2628 * is an offline or the timekeeping CPU, nothing to do.
2629 */
2630 if (!*isidle || rdp->rsp != rcu_sysidle_state ||
2631 cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
2632 return;
2633 if (rcu_gp_in_progress(rdp->rsp))
2634 WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
2635
2636 /* Pick up current idle and NMI-nesting counter and check. */
2637 cur = atomic_read(&rdtp->dynticks_idle);
2638 if (cur & 0x1) {
2639 *isidle = false; /* We are not idle! */
2640 return;
2641 }
2642 smp_mb(); /* Read counters before timestamps. */
2643
2644 /* Pick up timestamps. */
2645 j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies);
2646 /* If this CPU entered idle more recently, update maxj timestamp. */
2647 if (ULONG_CMP_LT(*maxj, j))
2648 *maxj = j;
2649}
2650
2651/*
2652 * Is this the flavor of RCU that is handling full-system idle?
2653 */
2654static bool is_sysidle_rcu_state(struct rcu_state *rsp)
2655{
2656 return rsp == rcu_sysidle_state;
2657}
2658
2659/*
2660 * Bind the grace-period kthread for the sysidle flavor of RCU to the
2661 * timekeeping CPU.
2662 */
2663static void rcu_bind_gp_kthread(void)
2664{
2665 int cpu = ACCESS_ONCE(tick_do_timer_cpu);
2666
2667 if (cpu < 0 || cpu >= nr_cpu_ids)
2668 return;
2669 if (raw_smp_processor_id() != cpu)
2670 set_cpus_allowed_ptr(current, cpumask_of(cpu));
2671}
2672
2673/*
2674 * Return a delay in jiffies based on the number of CPUs, rcu_node
2675 * leaf fanout, and jiffies tick rate. The idea is to allow larger
2676 * systems more time to transition to full-idle state in order to
2677 * avoid the cache thrashing that otherwise occur on the state variable.
2678 * Really small systems (less than a couple of tens of CPUs) should
2679 * instead use a single global atomically incremented counter, and later
2680 * versions of this will automatically reconfigure themselves accordingly.
2681 */
2682static unsigned long rcu_sysidle_delay(void)
2683{
2684 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
2685 return 0;
2686 return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000);
2687}
2688
2689/*
2690 * Advance the full-system-idle state. This is invoked when all of
2691 * the non-timekeeping CPUs are idle.
2692 */
2693static void rcu_sysidle(unsigned long j)
2694{
2695 /* Check the current state. */
2696 switch (ACCESS_ONCE(full_sysidle_state)) {
2697 case RCU_SYSIDLE_NOT:
2698
2699 /* First time all are idle, so note a short idle period. */
2700 ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT;
2701 break;
2702
2703 case RCU_SYSIDLE_SHORT:
2704
2705 /*
2706 * Idle for a bit, time to advance to next state?
2707 * cmpxchg failure means race with non-idle, let them win.
2708 */
2709 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
2710 (void)cmpxchg(&full_sysidle_state,
2711 RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG);
2712 break;
2713
2714 case RCU_SYSIDLE_LONG:
2715
2716 /*
2717 * Do an additional check pass before advancing to full.
2718 * cmpxchg failure means race with non-idle, let them win.
2719 */
2720 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
2721 (void)cmpxchg(&full_sysidle_state,
2722 RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL);
2723 break;
2724
2725 default:
2726 break;
2727 }
2728}
2729
2730/*
2731 * Found a non-idle non-timekeeping CPU, so kick the system-idle state
2732 * back to the beginning.
2733 */
2734static void rcu_sysidle_cancel(void)
2735{
2736 smp_mb();
2737 ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT;
2738}
2739
2740/*
2741 * Update the sysidle state based on the results of a force-quiescent-state
2742 * scan of the CPUs' dyntick-idle state.
2743 */
2744static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
2745 unsigned long maxj, bool gpkt)
2746{
2747 if (rsp != rcu_sysidle_state)
2748 return; /* Wrong flavor, ignore. */
2749 if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
2750 return; /* Running state machine from timekeeping CPU. */
2751 if (isidle)
2752 rcu_sysidle(maxj); /* More idle! */
2753 else
2754 rcu_sysidle_cancel(); /* Idle is over. */
2755}
2756
2757/*
2758 * Wrapper for rcu_sysidle_report() when called from the grace-period
2759 * kthread's context.
2760 */
2761static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
2762 unsigned long maxj)
2763{
2764 rcu_sysidle_report(rsp, isidle, maxj, true);
2765}
2766
2767/* Callback and function for forcing an RCU grace period. */
2768struct rcu_sysidle_head {
2769 struct rcu_head rh;
2770 int inuse;
2771};
2772
2773static void rcu_sysidle_cb(struct rcu_head *rhp)
2774{
2775 struct rcu_sysidle_head *rshp;
2776
2777 /*
2778 * The following memory barrier is needed to replace the
2779 * memory barriers that would normally be in the memory
2780 * allocator.
2781 */
2782 smp_mb(); /* grace period precedes setting inuse. */
2783
2784 rshp = container_of(rhp, struct rcu_sysidle_head, rh);
2785 ACCESS_ONCE(rshp->inuse) = 0;
2786}
2787
2788/*
2789 * Check to see if the system is fully idle, other than the timekeeping CPU.
2790 * The caller must have disabled interrupts.
2791 */
2792bool rcu_sys_is_idle(void)
2793{
2794 static struct rcu_sysidle_head rsh;
2795 int rss = ACCESS_ONCE(full_sysidle_state);
2796
2797 if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu))
2798 return false;
2799
2800 /* Handle small-system case by doing a full scan of CPUs. */
2801 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) {
2802 int oldrss = rss - 1;
2803
2804 /*
2805 * One pass to advance to each state up to _FULL.
2806 * Give up if any pass fails to advance the state.
2807 */
2808 while (rss < RCU_SYSIDLE_FULL && oldrss < rss) {
2809 int cpu;
2810 bool isidle = true;
2811 unsigned long maxj = jiffies - ULONG_MAX / 4;
2812 struct rcu_data *rdp;
2813
2814 /* Scan all the CPUs looking for nonidle CPUs. */
2815 for_each_possible_cpu(cpu) {
2816 rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu);
2817 rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
2818 if (!isidle)
2819 break;
2820 }
2821 rcu_sysidle_report(rcu_sysidle_state,
2822 isidle, maxj, false);
2823 oldrss = rss;
2824 rss = ACCESS_ONCE(full_sysidle_state);
2825 }
2826 }
2827
2828 /* If this is the first observation of an idle period, record it. */
2829 if (rss == RCU_SYSIDLE_FULL) {
2830 rss = cmpxchg(&full_sysidle_state,
2831 RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED);
2832 return rss == RCU_SYSIDLE_FULL;
2833 }
2834
2835 smp_mb(); /* ensure rss load happens before later caller actions. */
2836
2837 /* If already fully idle, tell the caller (in case of races). */
2838 if (rss == RCU_SYSIDLE_FULL_NOTED)
2839 return true;
2840
2841 /*
2842 * If we aren't there yet, and a grace period is not in flight,
2843 * initiate a grace period. Either way, tell the caller that
2844 * we are not there yet. We use an xchg() rather than an assignment
2845 * to make up for the memory barriers that would otherwise be
2846 * provided by the memory allocator.
2847 */
2848 if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
2849 !rcu_gp_in_progress(rcu_sysidle_state) &&
2850 !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
2851 call_rcu(&rsh.rh, rcu_sysidle_cb);
2852 return false;
2853}
2854
2855/*
2856 * Initialize dynticks sysidle state for CPUs coming online.
2857 */
2858static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
2859{
2860 rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE;
2861}
2862
2863#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
2864
2865static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
2866{
2867}
2868
2869static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
2870{
2871}
2872
2873static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
2874 unsigned long *maxj)
2875{
2876}
2877
2878static bool is_sysidle_rcu_state(struct rcu_state *rsp)
2879{
2880 return false;
2881}
2882
2883static void rcu_bind_gp_kthread(void)
2884{
2885}
2886
2887static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
2888 unsigned long maxj)
2889{
2890}
2891
2892static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
2893{
2894}
2895
2896#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
2897
2898/*
2899 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
2900 * grace-period kthread will do force_quiescent_state() processing?
2901 * The idea is to avoid waking up RCU core processing on such a
2902 * CPU unless the grace period has extended for too long.
2903 *
2904 * This code relies on the fact that all NO_HZ_FULL CPUs are also
2905 * CONFIG_RCU_NOCB_CPU CPUs.
2906 */
2907static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
2908{
2909#ifdef CONFIG_NO_HZ_FULL
2910 if (tick_nohz_full_cpu(smp_processor_id()) &&
2911 (!rcu_gp_in_progress(rsp) ||
2912 ULONG_CMP_LT(jiffies, ACCESS_ONCE(rsp->gp_start) + HZ)))
2913 return 1;
2914#endif /* #ifdef CONFIG_NO_HZ_FULL */
2915 return 0;
2916}