Loading...
Note: File does not exist in v4.6.
1/* SPDX-License-Identifier: GPL-2.0+ */
2/*
3 * RCU expedited grace periods
4 *
5 * Copyright IBM Corporation, 2016
6 *
7 * Authors: Paul E. McKenney <paulmck@linux.ibm.com>
8 */
9
10#include <linux/lockdep.h>
11
12static void rcu_exp_handler(void *unused);
13static int rcu_print_task_exp_stall(struct rcu_node *rnp);
14
15/*
16 * Record the start of an expedited grace period.
17 */
18static void rcu_exp_gp_seq_start(void)
19{
20 rcu_seq_start(&rcu_state.expedited_sequence);
21 rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap);
22}
23
24/*
25 * Return the value that the expedited-grace-period counter will have
26 * at the end of the current grace period.
27 */
28static __maybe_unused unsigned long rcu_exp_gp_seq_endval(void)
29{
30 return rcu_seq_endval(&rcu_state.expedited_sequence);
31}
32
33/*
34 * Record the end of an expedited grace period.
35 */
36static void rcu_exp_gp_seq_end(void)
37{
38 rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap);
39 rcu_seq_end(&rcu_state.expedited_sequence);
40 smp_mb(); /* Ensure that consecutive grace periods serialize. */
41}
42
43/*
44 * Take a snapshot of the expedited-grace-period counter, which is the
45 * earliest value that will indicate that a full grace period has
46 * elapsed since the current time.
47 */
48static unsigned long rcu_exp_gp_seq_snap(void)
49{
50 unsigned long s;
51
52 smp_mb(); /* Caller's modifications seen first by other CPUs. */
53 s = rcu_seq_snap(&rcu_state.expedited_sequence);
54 trace_rcu_exp_grace_period(rcu_state.name, s, TPS("snap"));
55 return s;
56}
57
58/*
59 * Given a counter snapshot from rcu_exp_gp_seq_snap(), return true
60 * if a full expedited grace period has elapsed since that snapshot
61 * was taken.
62 */
63static bool rcu_exp_gp_seq_done(unsigned long s)
64{
65 return rcu_seq_done(&rcu_state.expedited_sequence, s);
66}
67
68/*
69 * Reset the ->expmaskinit values in the rcu_node tree to reflect any
70 * recent CPU-online activity. Note that these masks are not cleared
71 * when CPUs go offline, so they reflect the union of all CPUs that have
72 * ever been online. This means that this function normally takes its
73 * no-work-to-do fastpath.
74 */
75static void sync_exp_reset_tree_hotplug(void)
76{
77 bool done;
78 unsigned long flags;
79 unsigned long mask;
80 unsigned long oldmask;
81 int ncpus = smp_load_acquire(&rcu_state.ncpus); /* Order vs. locking. */
82 struct rcu_node *rnp;
83 struct rcu_node *rnp_up;
84
85 /* If no new CPUs onlined since last time, nothing to do. */
86 if (likely(ncpus == rcu_state.ncpus_snap))
87 return;
88 rcu_state.ncpus_snap = ncpus;
89
90 /*
91 * Each pass through the following loop propagates newly onlined
92 * CPUs for the current rcu_node structure up the rcu_node tree.
93 */
94 rcu_for_each_leaf_node(rnp) {
95 raw_spin_lock_irqsave_rcu_node(rnp, flags);
96 if (rnp->expmaskinit == rnp->expmaskinitnext) {
97 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
98 continue; /* No new CPUs, nothing to do. */
99 }
100
101 /* Update this node's mask, track old value for propagation. */
102 oldmask = rnp->expmaskinit;
103 rnp->expmaskinit = rnp->expmaskinitnext;
104 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
105
106 /* If was already nonzero, nothing to propagate. */
107 if (oldmask)
108 continue;
109
110 /* Propagate the new CPU up the tree. */
111 mask = rnp->grpmask;
112 rnp_up = rnp->parent;
113 done = false;
114 while (rnp_up) {
115 raw_spin_lock_irqsave_rcu_node(rnp_up, flags);
116 if (rnp_up->expmaskinit)
117 done = true;
118 rnp_up->expmaskinit |= mask;
119 raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);
120 if (done)
121 break;
122 mask = rnp_up->grpmask;
123 rnp_up = rnp_up->parent;
124 }
125 }
126}
127
128/*
129 * Reset the ->expmask values in the rcu_node tree in preparation for
130 * a new expedited grace period.
131 */
132static void __maybe_unused sync_exp_reset_tree(void)
133{
134 unsigned long flags;
135 struct rcu_node *rnp;
136
137 sync_exp_reset_tree_hotplug();
138 rcu_for_each_node_breadth_first(rnp) {
139 raw_spin_lock_irqsave_rcu_node(rnp, flags);
140 WARN_ON_ONCE(rnp->expmask);
141 WRITE_ONCE(rnp->expmask, rnp->expmaskinit);
142 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
143 }
144}
145
146/*
147 * Return non-zero if there is no RCU expedited grace period in progress
148 * for the specified rcu_node structure, in other words, if all CPUs and
149 * tasks covered by the specified rcu_node structure have done their bit
150 * for the current expedited grace period.
151 */
152static bool sync_rcu_exp_done(struct rcu_node *rnp)
153{
154 raw_lockdep_assert_held_rcu_node(rnp);
155 return READ_ONCE(rnp->exp_tasks) == NULL &&
156 READ_ONCE(rnp->expmask) == 0;
157}
158
159/*
160 * Like sync_rcu_exp_done(), but where the caller does not hold the
161 * rcu_node's ->lock.
162 */
163static bool sync_rcu_exp_done_unlocked(struct rcu_node *rnp)
164{
165 unsigned long flags;
166 bool ret;
167
168 raw_spin_lock_irqsave_rcu_node(rnp, flags);
169 ret = sync_rcu_exp_done(rnp);
170 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
171
172 return ret;
173}
174
175
176/*
177 * Report the exit from RCU read-side critical section for the last task
178 * that queued itself during or before the current expedited preemptible-RCU
179 * grace period. This event is reported either to the rcu_node structure on
180 * which the task was queued or to one of that rcu_node structure's ancestors,
181 * recursively up the tree. (Calm down, calm down, we do the recursion
182 * iteratively!)
183 */
184static void __rcu_report_exp_rnp(struct rcu_node *rnp,
185 bool wake, unsigned long flags)
186 __releases(rnp->lock)
187{
188 unsigned long mask;
189
190 raw_lockdep_assert_held_rcu_node(rnp);
191 for (;;) {
192 if (!sync_rcu_exp_done(rnp)) {
193 if (!rnp->expmask)
194 rcu_initiate_boost(rnp, flags);
195 else
196 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
197 break;
198 }
199 if (rnp->parent == NULL) {
200 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
201 if (wake) {
202 smp_mb(); /* EGP done before wake_up(). */
203 swake_up_one(&rcu_state.expedited_wq);
204 }
205 break;
206 }
207 mask = rnp->grpmask;
208 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */
209 rnp = rnp->parent;
210 raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
211 WARN_ON_ONCE(!(rnp->expmask & mask));
212 WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
213 }
214}
215
216/*
217 * Report expedited quiescent state for specified node. This is a
218 * lock-acquisition wrapper function for __rcu_report_exp_rnp().
219 */
220static void __maybe_unused rcu_report_exp_rnp(struct rcu_node *rnp, bool wake)
221{
222 unsigned long flags;
223
224 raw_spin_lock_irqsave_rcu_node(rnp, flags);
225 __rcu_report_exp_rnp(rnp, wake, flags);
226}
227
228/*
229 * Report expedited quiescent state for multiple CPUs, all covered by the
230 * specified leaf rcu_node structure.
231 */
232static void rcu_report_exp_cpu_mult(struct rcu_node *rnp,
233 unsigned long mask, bool wake)
234{
235 int cpu;
236 unsigned long flags;
237 struct rcu_data *rdp;
238
239 raw_spin_lock_irqsave_rcu_node(rnp, flags);
240 if (!(rnp->expmask & mask)) {
241 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
242 return;
243 }
244 WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
245 for_each_leaf_node_cpu_mask(rnp, cpu, mask) {
246 rdp = per_cpu_ptr(&rcu_data, cpu);
247 if (!IS_ENABLED(CONFIG_NO_HZ_FULL) || !rdp->rcu_forced_tick_exp)
248 continue;
249 rdp->rcu_forced_tick_exp = false;
250 tick_dep_clear_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
251 }
252 __rcu_report_exp_rnp(rnp, wake, flags); /* Releases rnp->lock. */
253}
254
255/*
256 * Report expedited quiescent state for specified rcu_data (CPU).
257 */
258static void rcu_report_exp_rdp(struct rcu_data *rdp)
259{
260 WRITE_ONCE(rdp->cpu_no_qs.b.exp, false);
261 rcu_report_exp_cpu_mult(rdp->mynode, rdp->grpmask, true);
262}
263
264/* Common code for work-done checking. */
265static bool sync_exp_work_done(unsigned long s)
266{
267 if (rcu_exp_gp_seq_done(s)) {
268 trace_rcu_exp_grace_period(rcu_state.name, s, TPS("done"));
269 smp_mb(); /* Ensure test happens before caller kfree(). */
270 return true;
271 }
272 return false;
273}
274
275/*
276 * Funnel-lock acquisition for expedited grace periods. Returns true
277 * if some other task completed an expedited grace period that this task
278 * can piggy-back on, and with no mutex held. Otherwise, returns false
279 * with the mutex held, indicating that the caller must actually do the
280 * expedited grace period.
281 */
282static bool exp_funnel_lock(unsigned long s)
283{
284 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
285 struct rcu_node *rnp = rdp->mynode;
286 struct rcu_node *rnp_root = rcu_get_root();
287
288 /* Low-contention fastpath. */
289 if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) &&
290 (rnp == rnp_root ||
291 ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) &&
292 mutex_trylock(&rcu_state.exp_mutex))
293 goto fastpath;
294
295 /*
296 * Each pass through the following loop works its way up
297 * the rcu_node tree, returning if others have done the work or
298 * otherwise falls through to acquire ->exp_mutex. The mapping
299 * from CPU to rcu_node structure can be inexact, as it is just
300 * promoting locality and is not strictly needed for correctness.
301 */
302 for (; rnp != NULL; rnp = rnp->parent) {
303 if (sync_exp_work_done(s))
304 return true;
305
306 /* Work not done, either wait here or go up. */
307 spin_lock(&rnp->exp_lock);
308 if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) {
309
310 /* Someone else doing GP, so wait for them. */
311 spin_unlock(&rnp->exp_lock);
312 trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
313 rnp->grplo, rnp->grphi,
314 TPS("wait"));
315 wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
316 sync_exp_work_done(s));
317 return true;
318 }
319 WRITE_ONCE(rnp->exp_seq_rq, s); /* Followers can wait on us. */
320 spin_unlock(&rnp->exp_lock);
321 trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
322 rnp->grplo, rnp->grphi, TPS("nxtlvl"));
323 }
324 mutex_lock(&rcu_state.exp_mutex);
325fastpath:
326 if (sync_exp_work_done(s)) {
327 mutex_unlock(&rcu_state.exp_mutex);
328 return true;
329 }
330 rcu_exp_gp_seq_start();
331 trace_rcu_exp_grace_period(rcu_state.name, s, TPS("start"));
332 return false;
333}
334
335/*
336 * Select the CPUs within the specified rcu_node that the upcoming
337 * expedited grace period needs to wait for.
338 */
339static void __sync_rcu_exp_select_node_cpus(struct rcu_exp_work *rewp)
340{
341 int cpu;
342 unsigned long flags;
343 unsigned long mask_ofl_test;
344 unsigned long mask_ofl_ipi;
345 int ret;
346 struct rcu_node *rnp = container_of(rewp, struct rcu_node, rew);
347
348 raw_spin_lock_irqsave_rcu_node(rnp, flags);
349
350 /* Each pass checks a CPU for identity, offline, and idle. */
351 mask_ofl_test = 0;
352 for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) {
353 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
354 unsigned long mask = rdp->grpmask;
355 int snap;
356
357 if (raw_smp_processor_id() == cpu ||
358 !(rnp->qsmaskinitnext & mask)) {
359 mask_ofl_test |= mask;
360 } else {
361 snap = rcu_dynticks_snap(cpu);
362 if (rcu_dynticks_in_eqs(snap))
363 mask_ofl_test |= mask;
364 else
365 rdp->exp_dynticks_snap = snap;
366 }
367 }
368 mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
369
370 /*
371 * Need to wait for any blocked tasks as well. Note that
372 * additional blocking tasks will also block the expedited GP
373 * until such time as the ->expmask bits are cleared.
374 */
375 if (rcu_preempt_has_tasks(rnp))
376 WRITE_ONCE(rnp->exp_tasks, rnp->blkd_tasks.next);
377 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
378
379 /* IPI the remaining CPUs for expedited quiescent state. */
380 for_each_leaf_node_cpu_mask(rnp, cpu, mask_ofl_ipi) {
381 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
382 unsigned long mask = rdp->grpmask;
383
384retry_ipi:
385 if (rcu_dynticks_in_eqs_since(rdp, rdp->exp_dynticks_snap)) {
386 mask_ofl_test |= mask;
387 continue;
388 }
389 if (get_cpu() == cpu) {
390 mask_ofl_test |= mask;
391 put_cpu();
392 continue;
393 }
394 ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
395 put_cpu();
396 /* The CPU will report the QS in response to the IPI. */
397 if (!ret)
398 continue;
399
400 /* Failed, raced with CPU hotplug operation. */
401 raw_spin_lock_irqsave_rcu_node(rnp, flags);
402 if ((rnp->qsmaskinitnext & mask) &&
403 (rnp->expmask & mask)) {
404 /* Online, so delay for a bit and try again. */
405 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
406 trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("selectofl"));
407 schedule_timeout_idle(1);
408 goto retry_ipi;
409 }
410 /* CPU really is offline, so we must report its QS. */
411 if (rnp->expmask & mask)
412 mask_ofl_test |= mask;
413 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
414 }
415 /* Report quiescent states for those that went offline. */
416 if (mask_ofl_test)
417 rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false);
418}
419
420static void rcu_exp_sel_wait_wake(unsigned long s);
421
422#ifdef CONFIG_RCU_EXP_KTHREAD
423static void sync_rcu_exp_select_node_cpus(struct kthread_work *wp)
424{
425 struct rcu_exp_work *rewp =
426 container_of(wp, struct rcu_exp_work, rew_work);
427
428 __sync_rcu_exp_select_node_cpus(rewp);
429}
430
431static inline bool rcu_gp_par_worker_started(void)
432{
433 return !!READ_ONCE(rcu_exp_par_gp_kworker);
434}
435
436static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
437{
438 kthread_init_work(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
439 /*
440 * Use rcu_exp_par_gp_kworker, because flushing a work item from
441 * another work item on the same kthread worker can result in
442 * deadlock.
443 */
444 kthread_queue_work(rcu_exp_par_gp_kworker, &rnp->rew.rew_work);
445}
446
447static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
448{
449 kthread_flush_work(&rnp->rew.rew_work);
450}
451
452/*
453 * Work-queue handler to drive an expedited grace period forward.
454 */
455static void wait_rcu_exp_gp(struct kthread_work *wp)
456{
457 struct rcu_exp_work *rewp;
458
459 rewp = container_of(wp, struct rcu_exp_work, rew_work);
460 rcu_exp_sel_wait_wake(rewp->rew_s);
461}
462
463static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew)
464{
465 kthread_init_work(&rew->rew_work, wait_rcu_exp_gp);
466 kthread_queue_work(rcu_exp_gp_kworker, &rew->rew_work);
467}
468
469static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew)
470{
471}
472#else /* !CONFIG_RCU_EXP_KTHREAD */
473static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
474{
475 struct rcu_exp_work *rewp =
476 container_of(wp, struct rcu_exp_work, rew_work);
477
478 __sync_rcu_exp_select_node_cpus(rewp);
479}
480
481static inline bool rcu_gp_par_worker_started(void)
482{
483 return !!READ_ONCE(rcu_par_gp_wq);
484}
485
486static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp)
487{
488 int cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1);
489
490 INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
491 /* If all offline, queue the work on an unbound CPU. */
492 if (unlikely(cpu > rnp->grphi - rnp->grplo))
493 cpu = WORK_CPU_UNBOUND;
494 else
495 cpu += rnp->grplo;
496 queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
497}
498
499static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp)
500{
501 flush_work(&rnp->rew.rew_work);
502}
503
504/*
505 * Work-queue handler to drive an expedited grace period forward.
506 */
507static void wait_rcu_exp_gp(struct work_struct *wp)
508{
509 struct rcu_exp_work *rewp;
510
511 rewp = container_of(wp, struct rcu_exp_work, rew_work);
512 rcu_exp_sel_wait_wake(rewp->rew_s);
513}
514
515static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew)
516{
517 INIT_WORK_ONSTACK(&rew->rew_work, wait_rcu_exp_gp);
518 queue_work(rcu_gp_wq, &rew->rew_work);
519}
520
521static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew)
522{
523 destroy_work_on_stack(&rew->rew_work);
524}
525#endif /* CONFIG_RCU_EXP_KTHREAD */
526
527/*
528 * Select the nodes that the upcoming expedited grace period needs
529 * to wait for.
530 */
531static void sync_rcu_exp_select_cpus(void)
532{
533 struct rcu_node *rnp;
534
535 trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("reset"));
536 sync_exp_reset_tree();
537 trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("select"));
538
539 /* Schedule work for each leaf rcu_node structure. */
540 rcu_for_each_leaf_node(rnp) {
541 rnp->exp_need_flush = false;
542 if (!READ_ONCE(rnp->expmask))
543 continue; /* Avoid early boot non-existent wq. */
544 if (!rcu_gp_par_worker_started() ||
545 rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
546 rcu_is_last_leaf_node(rnp)) {
547 /* No worker started yet or last leaf, do direct call. */
548 sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work);
549 continue;
550 }
551 sync_rcu_exp_select_cpus_queue_work(rnp);
552 rnp->exp_need_flush = true;
553 }
554
555 /* Wait for jobs (if any) to complete. */
556 rcu_for_each_leaf_node(rnp)
557 if (rnp->exp_need_flush)
558 sync_rcu_exp_select_cpus_flush_work(rnp);
559}
560
561/*
562 * Wait for the expedited grace period to elapse, within time limit.
563 * If the time limit is exceeded without the grace period elapsing,
564 * return false, otherwise return true.
565 */
566static bool synchronize_rcu_expedited_wait_once(long tlimit)
567{
568 int t;
569 struct rcu_node *rnp_root = rcu_get_root();
570
571 t = swait_event_timeout_exclusive(rcu_state.expedited_wq,
572 sync_rcu_exp_done_unlocked(rnp_root),
573 tlimit);
574 // Workqueues should not be signaled.
575 if (t > 0 || sync_rcu_exp_done_unlocked(rnp_root))
576 return true;
577 WARN_ON(t < 0); /* workqueues should not be signaled. */
578 return false;
579}
580
581/*
582 * Wait for the expedited grace period to elapse, issuing any needed
583 * RCU CPU stall warnings along the way.
584 */
585static void synchronize_rcu_expedited_wait(void)
586{
587 int cpu;
588 unsigned long j;
589 unsigned long jiffies_stall;
590 unsigned long jiffies_start;
591 unsigned long mask;
592 int ndetected;
593 struct rcu_data *rdp;
594 struct rcu_node *rnp;
595 struct rcu_node *rnp_root = rcu_get_root();
596
597 trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait"));
598 jiffies_stall = rcu_exp_jiffies_till_stall_check();
599 jiffies_start = jiffies;
600 if (tick_nohz_full_enabled() && rcu_inkernel_boot_has_ended()) {
601 if (synchronize_rcu_expedited_wait_once(1))
602 return;
603 rcu_for_each_leaf_node(rnp) {
604 mask = READ_ONCE(rnp->expmask);
605 for_each_leaf_node_cpu_mask(rnp, cpu, mask) {
606 rdp = per_cpu_ptr(&rcu_data, cpu);
607 if (rdp->rcu_forced_tick_exp)
608 continue;
609 rdp->rcu_forced_tick_exp = true;
610 preempt_disable();
611 if (cpu_online(cpu))
612 tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
613 preempt_enable();
614 }
615 }
616 j = READ_ONCE(jiffies_till_first_fqs);
617 if (synchronize_rcu_expedited_wait_once(j + HZ))
618 return;
619 }
620
621 for (;;) {
622 if (synchronize_rcu_expedited_wait_once(jiffies_stall))
623 return;
624 if (rcu_stall_is_suppressed())
625 continue;
626 trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall"));
627 pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
628 rcu_state.name);
629 ndetected = 0;
630 rcu_for_each_leaf_node(rnp) {
631 ndetected += rcu_print_task_exp_stall(rnp);
632 for_each_leaf_node_possible_cpu(rnp, cpu) {
633 struct rcu_data *rdp;
634
635 mask = leaf_node_cpu_bit(rnp, cpu);
636 if (!(READ_ONCE(rnp->expmask) & mask))
637 continue;
638 ndetected++;
639 rdp = per_cpu_ptr(&rcu_data, cpu);
640 pr_cont(" %d-%c%c%c%c", cpu,
641 "O."[!!cpu_online(cpu)],
642 "o."[!!(rdp->grpmask & rnp->expmaskinit)],
643 "N."[!!(rdp->grpmask & rnp->expmaskinitnext)],
644 "D."[!!(rdp->cpu_no_qs.b.exp)]);
645 }
646 }
647 pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
648 jiffies - jiffies_start, rcu_state.expedited_sequence,
649 data_race(rnp_root->expmask),
650 ".T"[!!data_race(rnp_root->exp_tasks)]);
651 if (ndetected) {
652 pr_err("blocking rcu_node structures (internal RCU debug):");
653 rcu_for_each_node_breadth_first(rnp) {
654 if (rnp == rnp_root)
655 continue; /* printed unconditionally */
656 if (sync_rcu_exp_done_unlocked(rnp))
657 continue;
658 pr_cont(" l=%u:%d-%d:%#lx/%c",
659 rnp->level, rnp->grplo, rnp->grphi,
660 data_race(rnp->expmask),
661 ".T"[!!data_race(rnp->exp_tasks)]);
662 }
663 pr_cont("\n");
664 }
665 rcu_for_each_leaf_node(rnp) {
666 for_each_leaf_node_possible_cpu(rnp, cpu) {
667 mask = leaf_node_cpu_bit(rnp, cpu);
668 if (!(READ_ONCE(rnp->expmask) & mask))
669 continue;
670 dump_cpu_task(cpu);
671 }
672 }
673 jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
674 panic_on_rcu_stall();
675 }
676}
677
678/*
679 * Wait for the current expedited grace period to complete, and then
680 * wake up everyone who piggybacked on the just-completed expedited
681 * grace period. Also update all the ->exp_seq_rq counters as needed
682 * in order to avoid counter-wrap problems.
683 */
684static void rcu_exp_wait_wake(unsigned long s)
685{
686 struct rcu_node *rnp;
687
688 synchronize_rcu_expedited_wait();
689
690 // Switch over to wakeup mode, allowing the next GP to proceed.
691 // End the previous grace period only after acquiring the mutex
692 // to ensure that only one GP runs concurrently with wakeups.
693 mutex_lock(&rcu_state.exp_wake_mutex);
694 rcu_exp_gp_seq_end();
695 trace_rcu_exp_grace_period(rcu_state.name, s, TPS("end"));
696
697 rcu_for_each_node_breadth_first(rnp) {
698 if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) {
699 spin_lock(&rnp->exp_lock);
700 /* Recheck, avoid hang in case someone just arrived. */
701 if (ULONG_CMP_LT(rnp->exp_seq_rq, s))
702 WRITE_ONCE(rnp->exp_seq_rq, s);
703 spin_unlock(&rnp->exp_lock);
704 }
705 smp_mb(); /* All above changes before wakeup. */
706 wake_up_all(&rnp->exp_wq[rcu_seq_ctr(s) & 0x3]);
707 }
708 trace_rcu_exp_grace_period(rcu_state.name, s, TPS("endwake"));
709 mutex_unlock(&rcu_state.exp_wake_mutex);
710}
711
712/*
713 * Common code to drive an expedited grace period forward, used by
714 * workqueues and mid-boot-time tasks.
715 */
716static void rcu_exp_sel_wait_wake(unsigned long s)
717{
718 /* Initialize the rcu_node tree in preparation for the wait. */
719 sync_rcu_exp_select_cpus();
720
721 /* Wait and clean up, including waking everyone. */
722 rcu_exp_wait_wake(s);
723}
724
725#ifdef CONFIG_PREEMPT_RCU
726
727/*
728 * Remote handler for smp_call_function_single(). If there is an
729 * RCU read-side critical section in effect, request that the
730 * next rcu_read_unlock() record the quiescent state up the
731 * ->expmask fields in the rcu_node tree. Otherwise, immediately
732 * report the quiescent state.
733 */
734static void rcu_exp_handler(void *unused)
735{
736 int depth = rcu_preempt_depth();
737 unsigned long flags;
738 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
739 struct rcu_node *rnp = rdp->mynode;
740 struct task_struct *t = current;
741
742 /*
743 * First, the common case of not being in an RCU read-side
744 * critical section. If also enabled or idle, immediately
745 * report the quiescent state, otherwise defer.
746 */
747 if (!depth) {
748 if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) ||
749 rcu_is_cpu_rrupt_from_idle()) {
750 rcu_report_exp_rdp(rdp);
751 } else {
752 WRITE_ONCE(rdp->cpu_no_qs.b.exp, true);
753 set_tsk_need_resched(t);
754 set_preempt_need_resched();
755 }
756 return;
757 }
758
759 /*
760 * Second, the less-common case of being in an RCU read-side
761 * critical section. In this case we can count on a future
762 * rcu_read_unlock(). However, this rcu_read_unlock() might
763 * execute on some other CPU, but in that case there will be
764 * a future context switch. Either way, if the expedited
765 * grace period is still waiting on this CPU, set ->deferred_qs
766 * so that the eventual quiescent state will be reported.
767 * Note that there is a large group of race conditions that
768 * can have caused this quiescent state to already have been
769 * reported, so we really do need to check ->expmask.
770 */
771 if (depth > 0) {
772 raw_spin_lock_irqsave_rcu_node(rnp, flags);
773 if (rnp->expmask & rdp->grpmask) {
774 WRITE_ONCE(rdp->cpu_no_qs.b.exp, true);
775 t->rcu_read_unlock_special.b.exp_hint = true;
776 }
777 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
778 return;
779 }
780
781 // Finally, negative nesting depth should not happen.
782 WARN_ON_ONCE(1);
783}
784
785/* PREEMPTION=y, so no PREEMPTION=n expedited grace period to clean up after. */
786static void sync_sched_exp_online_cleanup(int cpu)
787{
788}
789
790/*
791 * Scan the current list of tasks blocked within RCU read-side critical
792 * sections, printing out the tid of each that is blocking the current
793 * expedited grace period.
794 */
795static int rcu_print_task_exp_stall(struct rcu_node *rnp)
796{
797 unsigned long flags;
798 int ndetected = 0;
799 struct task_struct *t;
800
801 if (!READ_ONCE(rnp->exp_tasks))
802 return 0;
803 raw_spin_lock_irqsave_rcu_node(rnp, flags);
804 t = list_entry(rnp->exp_tasks->prev,
805 struct task_struct, rcu_node_entry);
806 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
807 pr_cont(" P%d", t->pid);
808 ndetected++;
809 }
810 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
811 return ndetected;
812}
813
814#else /* #ifdef CONFIG_PREEMPT_RCU */
815
816/* Request an expedited quiescent state. */
817static void rcu_exp_need_qs(void)
818{
819 __this_cpu_write(rcu_data.cpu_no_qs.b.exp, true);
820 /* Store .exp before .rcu_urgent_qs. */
821 smp_store_release(this_cpu_ptr(&rcu_data.rcu_urgent_qs), true);
822 set_tsk_need_resched(current);
823 set_preempt_need_resched();
824}
825
826/* Invoked on each online non-idle CPU for expedited quiescent state. */
827static void rcu_exp_handler(void *unused)
828{
829 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
830 struct rcu_node *rnp = rdp->mynode;
831 bool preempt_bh_enabled = !(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK));
832
833 if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
834 __this_cpu_read(rcu_data.cpu_no_qs.b.exp))
835 return;
836 if (rcu_is_cpu_rrupt_from_idle() ||
837 (IS_ENABLED(CONFIG_PREEMPT_COUNT) && preempt_bh_enabled)) {
838 rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
839 return;
840 }
841 rcu_exp_need_qs();
842}
843
844/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
845static void sync_sched_exp_online_cleanup(int cpu)
846{
847 unsigned long flags;
848 int my_cpu;
849 struct rcu_data *rdp;
850 int ret;
851 struct rcu_node *rnp;
852
853 rdp = per_cpu_ptr(&rcu_data, cpu);
854 rnp = rdp->mynode;
855 my_cpu = get_cpu();
856 /* Quiescent state either not needed or already requested, leave. */
857 if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
858 READ_ONCE(rdp->cpu_no_qs.b.exp)) {
859 put_cpu();
860 return;
861 }
862 /* Quiescent state needed on current CPU, so set it up locally. */
863 if (my_cpu == cpu) {
864 local_irq_save(flags);
865 rcu_exp_need_qs();
866 local_irq_restore(flags);
867 put_cpu();
868 return;
869 }
870 /* Quiescent state needed on some other CPU, send IPI. */
871 ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
872 put_cpu();
873 WARN_ON_ONCE(ret);
874}
875
876/*
877 * Because preemptible RCU does not exist, we never have to check for
878 * tasks blocked within RCU read-side critical sections that are
879 * blocking the current expedited grace period.
880 */
881static int rcu_print_task_exp_stall(struct rcu_node *rnp)
882{
883 return 0;
884}
885
886#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
887
888/**
889 * synchronize_rcu_expedited - Brute-force RCU grace period
890 *
891 * Wait for an RCU grace period, but expedite it. The basic idea is to
892 * IPI all non-idle non-nohz online CPUs. The IPI handler checks whether
893 * the CPU is in an RCU critical section, and if so, it sets a flag that
894 * causes the outermost rcu_read_unlock() to report the quiescent state
895 * for RCU-preempt or asks the scheduler for help for RCU-sched. On the
896 * other hand, if the CPU is not in an RCU read-side critical section,
897 * the IPI handler reports the quiescent state immediately.
898 *
899 * Although this is a great improvement over previous expedited
900 * implementations, it is still unfriendly to real-time workloads, so is
901 * thus not recommended for any sort of common-case code. In fact, if
902 * you are using synchronize_rcu_expedited() in a loop, please restructure
903 * your code to batch your updates, and then use a single synchronize_rcu()
904 * instead.
905 *
906 * This has the same semantics as (but is more brutal than) synchronize_rcu().
907 */
908void synchronize_rcu_expedited(void)
909{
910 bool boottime = (rcu_scheduler_active == RCU_SCHEDULER_INIT);
911 unsigned long flags;
912 struct rcu_exp_work rew;
913 struct rcu_node *rnp;
914 unsigned long s;
915
916 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
917 lock_is_held(&rcu_lock_map) ||
918 lock_is_held(&rcu_sched_lock_map),
919 "Illegal synchronize_rcu_expedited() in RCU read-side critical section");
920
921 /* Is the state is such that the call is a grace period? */
922 if (rcu_blocking_is_gp()) {
923 // Note well that this code runs with !PREEMPT && !SMP.
924 // In addition, all code that advances grace periods runs
925 // at process level. Therefore, this expedited GP overlaps
926 // with other expedited GPs only by being fully nested within
927 // them, which allows reuse of ->gp_seq_polled_exp_snap.
928 rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap);
929 rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap);
930
931 local_irq_save(flags);
932 WARN_ON_ONCE(num_online_cpus() > 1);
933 rcu_state.expedited_sequence += (1 << RCU_SEQ_CTR_SHIFT);
934 local_irq_restore(flags);
935 return; // Context allows vacuous grace periods.
936 }
937
938 /* If expedited grace periods are prohibited, fall back to normal. */
939 if (rcu_gp_is_normal()) {
940 wait_rcu_gp(call_rcu_hurry);
941 return;
942 }
943
944 /* Take a snapshot of the sequence number. */
945 s = rcu_exp_gp_seq_snap();
946 if (exp_funnel_lock(s))
947 return; /* Someone else did our work for us. */
948
949 /* Ensure that load happens before action based on it. */
950 if (unlikely(boottime)) {
951 /* Direct call during scheduler init and early_initcalls(). */
952 rcu_exp_sel_wait_wake(s);
953 } else {
954 /* Marshall arguments & schedule the expedited grace period. */
955 rew.rew_s = s;
956 synchronize_rcu_expedited_queue_work(&rew);
957 }
958
959 /* Wait for expedited grace period to complete. */
960 rnp = rcu_get_root();
961 wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
962 sync_exp_work_done(s));
963 smp_mb(); /* Work actions happen before return. */
964
965 /* Let the next expedited grace period start. */
966 mutex_unlock(&rcu_state.exp_mutex);
967
968 if (likely(!boottime))
969 synchronize_rcu_expedited_destroy_work(&rew);
970}
971EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
972
973/*
974 * Ensure that start_poll_synchronize_rcu_expedited() has the expedited
975 * RCU grace periods that it needs.
976 */
977static void sync_rcu_do_polled_gp(struct work_struct *wp)
978{
979 unsigned long flags;
980 int i = 0;
981 struct rcu_node *rnp = container_of(wp, struct rcu_node, exp_poll_wq);
982 unsigned long s;
983
984 raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
985 s = rnp->exp_seq_poll_rq;
986 rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
987 raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
988 if (s == RCU_GET_STATE_COMPLETED)
989 return;
990 while (!poll_state_synchronize_rcu(s)) {
991 synchronize_rcu_expedited();
992 if (i == 10 || i == 20)
993 pr_info("%s: i = %d s = %lx gp_seq_polled = %lx\n", __func__, i, s, READ_ONCE(rcu_state.gp_seq_polled));
994 i++;
995 }
996 raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
997 s = rnp->exp_seq_poll_rq;
998 if (poll_state_synchronize_rcu(s))
999 rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED;
1000 raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
1001}
1002
1003/**
1004 * start_poll_synchronize_rcu_expedited - Snapshot current RCU state and start expedited grace period
1005 *
1006 * Returns a cookie to pass to a call to cond_synchronize_rcu(),
1007 * cond_synchronize_rcu_expedited(), or poll_state_synchronize_rcu(),
1008 * allowing them to determine whether or not any sort of grace period has
1009 * elapsed in the meantime. If the needed expedited grace period is not
1010 * already slated to start, initiates that grace period.
1011 */
1012unsigned long start_poll_synchronize_rcu_expedited(void)
1013{
1014 unsigned long flags;
1015 struct rcu_data *rdp;
1016 struct rcu_node *rnp;
1017 unsigned long s;
1018
1019 s = get_state_synchronize_rcu();
1020 rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
1021 rnp = rdp->mynode;
1022 if (rcu_init_invoked())
1023 raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
1024 if (!poll_state_synchronize_rcu(s)) {
1025 rnp->exp_seq_poll_rq = s;
1026 if (rcu_init_invoked())
1027 queue_work(rcu_gp_wq, &rnp->exp_poll_wq);
1028 }
1029 if (rcu_init_invoked())
1030 raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
1031
1032 return s;
1033}
1034EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited);
1035
1036/**
1037 * start_poll_synchronize_rcu_expedited_full - Take a full snapshot and start expedited grace period
1038 * @rgosp: Place to put snapshot of grace-period state
1039 *
1040 * Places the normal and expedited grace-period states in rgosp. This
1041 * state value can be passed to a later call to cond_synchronize_rcu_full()
1042 * or poll_state_synchronize_rcu_full() to determine whether or not a
1043 * grace period (whether normal or expedited) has elapsed in the meantime.
1044 * If the needed expedited grace period is not already slated to start,
1045 * initiates that grace period.
1046 */
1047void start_poll_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
1048{
1049 get_state_synchronize_rcu_full(rgosp);
1050 (void)start_poll_synchronize_rcu_expedited();
1051}
1052EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited_full);
1053
1054/**
1055 * cond_synchronize_rcu_expedited - Conditionally wait for an expedited RCU grace period
1056 *
1057 * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited()
1058 *
1059 * If any type of full RCU grace period has elapsed since the earlier
1060 * call to get_state_synchronize_rcu(), start_poll_synchronize_rcu(),
1061 * or start_poll_synchronize_rcu_expedited(), just return. Otherwise,
1062 * invoke synchronize_rcu_expedited() to wait for a full grace period.
1063 *
1064 * Yes, this function does not take counter wrap into account.
1065 * But counter wrap is harmless. If the counter wraps, we have waited for
1066 * more than 2 billion grace periods (and way more on a 64-bit system!),
1067 * so waiting for a couple of additional grace periods should be just fine.
1068 *
1069 * This function provides the same memory-ordering guarantees that
1070 * would be provided by a synchronize_rcu() that was invoked at the call
1071 * to the function that provided @oldstate and that returned at the end
1072 * of this function.
1073 */
1074void cond_synchronize_rcu_expedited(unsigned long oldstate)
1075{
1076 if (!poll_state_synchronize_rcu(oldstate))
1077 synchronize_rcu_expedited();
1078}
1079EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited);
1080
1081/**
1082 * cond_synchronize_rcu_expedited_full - Conditionally wait for an expedited RCU grace period
1083 * @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full()
1084 *
1085 * If a full RCU grace period has elapsed since the call to
1086 * get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(),
1087 * or start_poll_synchronize_rcu_expedited_full() from which @rgosp was
1088 * obtained, just return. Otherwise, invoke synchronize_rcu_expedited()
1089 * to wait for a full grace period.
1090 *
1091 * Yes, this function does not take counter wrap into account.
1092 * But counter wrap is harmless. If the counter wraps, we have waited for
1093 * more than 2 billion grace periods (and way more on a 64-bit system!),
1094 * so waiting for a couple of additional grace periods should be just fine.
1095 *
1096 * This function provides the same memory-ordering guarantees that
1097 * would be provided by a synchronize_rcu() that was invoked at the call
1098 * to the function that provided @rgosp and that returned at the end of
1099 * this function.
1100 */
1101void cond_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp)
1102{
1103 if (!poll_state_synchronize_rcu_full(rgosp))
1104 synchronize_rcu_expedited();
1105}
1106EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited_full);