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1/*
2 * RCU expedited grace periods
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, you can access it online at
16 * http://www.gnu.org/licenses/gpl-2.0.html.
17 *
18 * Copyright IBM Corporation, 2016
19 *
20 * Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
21 */
22
23/*
24 * Record the start of an expedited grace period.
25 */
26static void rcu_exp_gp_seq_start(struct rcu_state *rsp)
27{
28 rcu_seq_start(&rsp->expedited_sequence);
29}
30
31/*
32 * Return then value that expedited-grace-period counter will have
33 * at the end of the current grace period.
34 */
35static __maybe_unused unsigned long rcu_exp_gp_seq_endval(struct rcu_state *rsp)
36{
37 return rcu_seq_endval(&rsp->expedited_sequence);
38}
39
40/*
41 * Record the end of an expedited grace period.
42 */
43static void rcu_exp_gp_seq_end(struct rcu_state *rsp)
44{
45 rcu_seq_end(&rsp->expedited_sequence);
46 smp_mb(); /* Ensure that consecutive grace periods serialize. */
47}
48
49/*
50 * Take a snapshot of the expedited-grace-period counter.
51 */
52static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp)
53{
54 unsigned long s;
55
56 smp_mb(); /* Caller's modifications seen first by other CPUs. */
57 s = rcu_seq_snap(&rsp->expedited_sequence);
58 trace_rcu_exp_grace_period(rsp->name, s, TPS("snap"));
59 return s;
60}
61
62/*
63 * Given a counter snapshot from rcu_exp_gp_seq_snap(), return true
64 * if a full expedited grace period has elapsed since that snapshot
65 * was taken.
66 */
67static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s)
68{
69 return rcu_seq_done(&rsp->expedited_sequence, s);
70}
71
72/*
73 * Reset the ->expmaskinit values in the rcu_node tree to reflect any
74 * recent CPU-online activity. Note that these masks are not cleared
75 * when CPUs go offline, so they reflect the union of all CPUs that have
76 * ever been online. This means that this function normally takes its
77 * no-work-to-do fastpath.
78 */
79static void sync_exp_reset_tree_hotplug(struct rcu_state *rsp)
80{
81 bool done;
82 unsigned long flags;
83 unsigned long mask;
84 unsigned long oldmask;
85 int ncpus = smp_load_acquire(&rsp->ncpus); /* Order against locking. */
86 struct rcu_node *rnp;
87 struct rcu_node *rnp_up;
88
89 /* If no new CPUs onlined since last time, nothing to do. */
90 if (likely(ncpus == rsp->ncpus_snap))
91 return;
92 rsp->ncpus_snap = ncpus;
93
94 /*
95 * Each pass through the following loop propagates newly onlined
96 * CPUs for the current rcu_node structure up the rcu_node tree.
97 */
98 rcu_for_each_leaf_node(rsp, rnp) {
99 raw_spin_lock_irqsave_rcu_node(rnp, flags);
100 if (rnp->expmaskinit == rnp->expmaskinitnext) {
101 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
102 continue; /* No new CPUs, nothing to do. */
103 }
104
105 /* Update this node's mask, track old value for propagation. */
106 oldmask = rnp->expmaskinit;
107 rnp->expmaskinit = rnp->expmaskinitnext;
108 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
109
110 /* If was already nonzero, nothing to propagate. */
111 if (oldmask)
112 continue;
113
114 /* Propagate the new CPU up the tree. */
115 mask = rnp->grpmask;
116 rnp_up = rnp->parent;
117 done = false;
118 while (rnp_up) {
119 raw_spin_lock_irqsave_rcu_node(rnp_up, flags);
120 if (rnp_up->expmaskinit)
121 done = true;
122 rnp_up->expmaskinit |= mask;
123 raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);
124 if (done)
125 break;
126 mask = rnp_up->grpmask;
127 rnp_up = rnp_up->parent;
128 }
129 }
130}
131
132/*
133 * Reset the ->expmask values in the rcu_node tree in preparation for
134 * a new expedited grace period.
135 */
136static void __maybe_unused sync_exp_reset_tree(struct rcu_state *rsp)
137{
138 unsigned long flags;
139 struct rcu_node *rnp;
140
141 sync_exp_reset_tree_hotplug(rsp);
142 rcu_for_each_node_breadth_first(rsp, rnp) {
143 raw_spin_lock_irqsave_rcu_node(rnp, flags);
144 WARN_ON_ONCE(rnp->expmask);
145 rnp->expmask = rnp->expmaskinit;
146 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
147 }
148}
149
150/*
151 * Return non-zero if there is no RCU expedited grace period in progress
152 * for the specified rcu_node structure, in other words, if all CPUs and
153 * tasks covered by the specified rcu_node structure have done their bit
154 * for the current expedited grace period. Works only for preemptible
155 * RCU -- other RCU implementation use other means.
156 *
157 * Caller must hold the rcu_state's exp_mutex.
158 */
159static bool sync_rcu_preempt_exp_done(struct rcu_node *rnp)
160{
161 return rnp->exp_tasks == NULL &&
162 READ_ONCE(rnp->expmask) == 0;
163}
164
165/*
166 * Report the exit from RCU read-side critical section for the last task
167 * that queued itself during or before the current expedited preemptible-RCU
168 * grace period. This event is reported either to the rcu_node structure on
169 * which the task was queued or to one of that rcu_node structure's ancestors,
170 * recursively up the tree. (Calm down, calm down, we do the recursion
171 * iteratively!)
172 *
173 * Caller must hold the rcu_state's exp_mutex and the specified rcu_node
174 * structure's ->lock.
175 */
176static void __rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
177 bool wake, unsigned long flags)
178 __releases(rnp->lock)
179{
180 unsigned long mask;
181
182 for (;;) {
183 if (!sync_rcu_preempt_exp_done(rnp)) {
184 if (!rnp->expmask)
185 rcu_initiate_boost(rnp, flags);
186 else
187 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
188 break;
189 }
190 if (rnp->parent == NULL) {
191 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
192 if (wake) {
193 smp_mb(); /* EGP done before wake_up(). */
194 swake_up(&rsp->expedited_wq);
195 }
196 break;
197 }
198 mask = rnp->grpmask;
199 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */
200 rnp = rnp->parent;
201 raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
202 WARN_ON_ONCE(!(rnp->expmask & mask));
203 rnp->expmask &= ~mask;
204 }
205}
206
207/*
208 * Report expedited quiescent state for specified node. This is a
209 * lock-acquisition wrapper function for __rcu_report_exp_rnp().
210 *
211 * Caller must hold the rcu_state's exp_mutex.
212 */
213static void __maybe_unused rcu_report_exp_rnp(struct rcu_state *rsp,
214 struct rcu_node *rnp, bool wake)
215{
216 unsigned long flags;
217
218 raw_spin_lock_irqsave_rcu_node(rnp, flags);
219 __rcu_report_exp_rnp(rsp, rnp, wake, flags);
220}
221
222/*
223 * Report expedited quiescent state for multiple CPUs, all covered by the
224 * specified leaf rcu_node structure. Caller must hold the rcu_state's
225 * exp_mutex.
226 */
227static void rcu_report_exp_cpu_mult(struct rcu_state *rsp, struct rcu_node *rnp,
228 unsigned long mask, bool wake)
229{
230 unsigned long flags;
231
232 raw_spin_lock_irqsave_rcu_node(rnp, flags);
233 if (!(rnp->expmask & mask)) {
234 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
235 return;
236 }
237 rnp->expmask &= ~mask;
238 __rcu_report_exp_rnp(rsp, rnp, wake, flags); /* Releases rnp->lock. */
239}
240
241/*
242 * Report expedited quiescent state for specified rcu_data (CPU).
243 */
244static void rcu_report_exp_rdp(struct rcu_state *rsp, struct rcu_data *rdp,
245 bool wake)
246{
247 rcu_report_exp_cpu_mult(rsp, rdp->mynode, rdp->grpmask, wake);
248}
249
250/* Common code for synchronize_{rcu,sched}_expedited() work-done checking. */
251static bool sync_exp_work_done(struct rcu_state *rsp, atomic_long_t *stat,
252 unsigned long s)
253{
254 if (rcu_exp_gp_seq_done(rsp, s)) {
255 trace_rcu_exp_grace_period(rsp->name, s, TPS("done"));
256 /* Ensure test happens before caller kfree(). */
257 smp_mb__before_atomic(); /* ^^^ */
258 atomic_long_inc(stat);
259 return true;
260 }
261 return false;
262}
263
264/*
265 * Funnel-lock acquisition for expedited grace periods. Returns true
266 * if some other task completed an expedited grace period that this task
267 * can piggy-back on, and with no mutex held. Otherwise, returns false
268 * with the mutex held, indicating that the caller must actually do the
269 * expedited grace period.
270 */
271static bool exp_funnel_lock(struct rcu_state *rsp, unsigned long s)
272{
273 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id());
274 struct rcu_node *rnp = rdp->mynode;
275 struct rcu_node *rnp_root = rcu_get_root(rsp);
276
277 /* Low-contention fastpath. */
278 if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) &&
279 (rnp == rnp_root ||
280 ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) &&
281 mutex_trylock(&rsp->exp_mutex))
282 goto fastpath;
283
284 /*
285 * Each pass through the following loop works its way up
286 * the rcu_node tree, returning if others have done the work or
287 * otherwise falls through to acquire rsp->exp_mutex. The mapping
288 * from CPU to rcu_node structure can be inexact, as it is just
289 * promoting locality and is not strictly needed for correctness.
290 */
291 for (; rnp != NULL; rnp = rnp->parent) {
292 if (sync_exp_work_done(rsp, &rdp->exp_workdone1, s))
293 return true;
294
295 /* Work not done, either wait here or go up. */
296 spin_lock(&rnp->exp_lock);
297 if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) {
298
299 /* Someone else doing GP, so wait for them. */
300 spin_unlock(&rnp->exp_lock);
301 trace_rcu_exp_funnel_lock(rsp->name, rnp->level,
302 rnp->grplo, rnp->grphi,
303 TPS("wait"));
304 wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
305 sync_exp_work_done(rsp,
306 &rdp->exp_workdone2, s));
307 return true;
308 }
309 rnp->exp_seq_rq = s; /* Followers can wait on us. */
310 spin_unlock(&rnp->exp_lock);
311 trace_rcu_exp_funnel_lock(rsp->name, rnp->level, rnp->grplo,
312 rnp->grphi, TPS("nxtlvl"));
313 }
314 mutex_lock(&rsp->exp_mutex);
315fastpath:
316 if (sync_exp_work_done(rsp, &rdp->exp_workdone3, s)) {
317 mutex_unlock(&rsp->exp_mutex);
318 return true;
319 }
320 rcu_exp_gp_seq_start(rsp);
321 trace_rcu_exp_grace_period(rsp->name, s, TPS("start"));
322 return false;
323}
324
325/* Invoked on each online non-idle CPU for expedited quiescent state. */
326static void sync_sched_exp_handler(void *data)
327{
328 struct rcu_data *rdp;
329 struct rcu_node *rnp;
330 struct rcu_state *rsp = data;
331
332 rdp = this_cpu_ptr(rsp->rda);
333 rnp = rdp->mynode;
334 if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
335 __this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
336 return;
337 if (rcu_is_cpu_rrupt_from_idle()) {
338 rcu_report_exp_rdp(&rcu_sched_state,
339 this_cpu_ptr(&rcu_sched_data), true);
340 return;
341 }
342 __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, true);
343 /* Store .exp before .rcu_urgent_qs. */
344 smp_store_release(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs), true);
345 resched_cpu(smp_processor_id());
346}
347
348/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
349static void sync_sched_exp_online_cleanup(int cpu)
350{
351 struct rcu_data *rdp;
352 int ret;
353 struct rcu_node *rnp;
354 struct rcu_state *rsp = &rcu_sched_state;
355
356 rdp = per_cpu_ptr(rsp->rda, cpu);
357 rnp = rdp->mynode;
358 if (!(READ_ONCE(rnp->expmask) & rdp->grpmask))
359 return;
360 ret = smp_call_function_single(cpu, sync_sched_exp_handler, rsp, 0);
361 WARN_ON_ONCE(ret);
362}
363
364/*
365 * Select the nodes that the upcoming expedited grace period needs
366 * to wait for.
367 */
368static void sync_rcu_exp_select_cpus(struct rcu_state *rsp,
369 smp_call_func_t func)
370{
371 int cpu;
372 unsigned long flags;
373 unsigned long mask_ofl_test;
374 unsigned long mask_ofl_ipi;
375 int ret;
376 struct rcu_node *rnp;
377
378 trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("reset"));
379 sync_exp_reset_tree(rsp);
380 trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("select"));
381 rcu_for_each_leaf_node(rsp, rnp) {
382 raw_spin_lock_irqsave_rcu_node(rnp, flags);
383
384 /* Each pass checks a CPU for identity, offline, and idle. */
385 mask_ofl_test = 0;
386 for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) {
387 unsigned long mask = leaf_node_cpu_bit(rnp, cpu);
388 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
389 struct rcu_dynticks *rdtp = per_cpu_ptr(&rcu_dynticks, cpu);
390 int snap;
391
392 if (raw_smp_processor_id() == cpu ||
393 !(rnp->qsmaskinitnext & mask)) {
394 mask_ofl_test |= mask;
395 } else {
396 snap = rcu_dynticks_snap(rdtp);
397 if (rcu_dynticks_in_eqs(snap))
398 mask_ofl_test |= mask;
399 else
400 rdp->exp_dynticks_snap = snap;
401 }
402 }
403 mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
404
405 /*
406 * Need to wait for any blocked tasks as well. Note that
407 * additional blocking tasks will also block the expedited
408 * GP until such time as the ->expmask bits are cleared.
409 */
410 if (rcu_preempt_has_tasks(rnp))
411 rnp->exp_tasks = rnp->blkd_tasks.next;
412 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
413
414 /* IPI the remaining CPUs for expedited quiescent state. */
415 for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) {
416 unsigned long mask = leaf_node_cpu_bit(rnp, cpu);
417 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
418
419 if (!(mask_ofl_ipi & mask))
420 continue;
421retry_ipi:
422 if (rcu_dynticks_in_eqs_since(rdp->dynticks,
423 rdp->exp_dynticks_snap)) {
424 mask_ofl_test |= mask;
425 continue;
426 }
427 ret = smp_call_function_single(cpu, func, rsp, 0);
428 if (!ret) {
429 mask_ofl_ipi &= ~mask;
430 continue;
431 }
432 /* Failed, raced with CPU hotplug operation. */
433 raw_spin_lock_irqsave_rcu_node(rnp, flags);
434 if ((rnp->qsmaskinitnext & mask) &&
435 (rnp->expmask & mask)) {
436 /* Online, so delay for a bit and try again. */
437 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
438 trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("selectofl"));
439 schedule_timeout_uninterruptible(1);
440 goto retry_ipi;
441 }
442 /* CPU really is offline, so we can ignore it. */
443 if (!(rnp->expmask & mask))
444 mask_ofl_ipi &= ~mask;
445 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
446 }
447 /* Report quiescent states for those that went offline. */
448 mask_ofl_test |= mask_ofl_ipi;
449 if (mask_ofl_test)
450 rcu_report_exp_cpu_mult(rsp, rnp, mask_ofl_test, false);
451 }
452}
453
454static void synchronize_sched_expedited_wait(struct rcu_state *rsp)
455{
456 int cpu;
457 unsigned long jiffies_stall;
458 unsigned long jiffies_start;
459 unsigned long mask;
460 int ndetected;
461 struct rcu_node *rnp;
462 struct rcu_node *rnp_root = rcu_get_root(rsp);
463 int ret;
464
465 trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("startwait"));
466 jiffies_stall = rcu_jiffies_till_stall_check();
467 jiffies_start = jiffies;
468
469 for (;;) {
470 ret = swait_event_timeout(
471 rsp->expedited_wq,
472 sync_rcu_preempt_exp_done(rnp_root),
473 jiffies_stall);
474 if (ret > 0 || sync_rcu_preempt_exp_done(rnp_root))
475 return;
476 WARN_ON(ret < 0); /* workqueues should not be signaled. */
477 if (rcu_cpu_stall_suppress)
478 continue;
479 panic_on_rcu_stall();
480 pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
481 rsp->name);
482 ndetected = 0;
483 rcu_for_each_leaf_node(rsp, rnp) {
484 ndetected += rcu_print_task_exp_stall(rnp);
485 for_each_leaf_node_possible_cpu(rnp, cpu) {
486 struct rcu_data *rdp;
487
488 mask = leaf_node_cpu_bit(rnp, cpu);
489 if (!(rnp->expmask & mask))
490 continue;
491 ndetected++;
492 rdp = per_cpu_ptr(rsp->rda, cpu);
493 pr_cont(" %d-%c%c%c", cpu,
494 "O."[!!cpu_online(cpu)],
495 "o."[!!(rdp->grpmask & rnp->expmaskinit)],
496 "N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);
497 }
498 }
499 pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
500 jiffies - jiffies_start, rsp->expedited_sequence,
501 rnp_root->expmask, ".T"[!!rnp_root->exp_tasks]);
502 if (ndetected) {
503 pr_err("blocking rcu_node structures:");
504 rcu_for_each_node_breadth_first(rsp, rnp) {
505 if (rnp == rnp_root)
506 continue; /* printed unconditionally */
507 if (sync_rcu_preempt_exp_done(rnp))
508 continue;
509 pr_cont(" l=%u:%d-%d:%#lx/%c",
510 rnp->level, rnp->grplo, rnp->grphi,
511 rnp->expmask,
512 ".T"[!!rnp->exp_tasks]);
513 }
514 pr_cont("\n");
515 }
516 rcu_for_each_leaf_node(rsp, rnp) {
517 for_each_leaf_node_possible_cpu(rnp, cpu) {
518 mask = leaf_node_cpu_bit(rnp, cpu);
519 if (!(rnp->expmask & mask))
520 continue;
521 dump_cpu_task(cpu);
522 }
523 }
524 jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;
525 }
526}
527
528/*
529 * Wait for the current expedited grace period to complete, and then
530 * wake up everyone who piggybacked on the just-completed expedited
531 * grace period. Also update all the ->exp_seq_rq counters as needed
532 * in order to avoid counter-wrap problems.
533 */
534static void rcu_exp_wait_wake(struct rcu_state *rsp, unsigned long s)
535{
536 struct rcu_node *rnp;
537
538 synchronize_sched_expedited_wait(rsp);
539 rcu_exp_gp_seq_end(rsp);
540 trace_rcu_exp_grace_period(rsp->name, s, TPS("end"));
541
542 /*
543 * Switch over to wakeup mode, allowing the next GP, but -only- the
544 * next GP, to proceed.
545 */
546 mutex_lock(&rsp->exp_wake_mutex);
547
548 rcu_for_each_node_breadth_first(rsp, rnp) {
549 if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) {
550 spin_lock(&rnp->exp_lock);
551 /* Recheck, avoid hang in case someone just arrived. */
552 if (ULONG_CMP_LT(rnp->exp_seq_rq, s))
553 rnp->exp_seq_rq = s;
554 spin_unlock(&rnp->exp_lock);
555 }
556 smp_mb(); /* All above changes before wakeup. */
557 wake_up_all(&rnp->exp_wq[rcu_seq_ctr(rsp->expedited_sequence) & 0x3]);
558 }
559 trace_rcu_exp_grace_period(rsp->name, s, TPS("endwake"));
560 mutex_unlock(&rsp->exp_wake_mutex);
561}
562
563/* Let the workqueue handler know what it is supposed to do. */
564struct rcu_exp_work {
565 smp_call_func_t rew_func;
566 struct rcu_state *rew_rsp;
567 unsigned long rew_s;
568 struct work_struct rew_work;
569};
570
571/*
572 * Common code to drive an expedited grace period forward, used by
573 * workqueues and mid-boot-time tasks.
574 */
575static void rcu_exp_sel_wait_wake(struct rcu_state *rsp,
576 smp_call_func_t func, unsigned long s)
577{
578 /* Initialize the rcu_node tree in preparation for the wait. */
579 sync_rcu_exp_select_cpus(rsp, func);
580
581 /* Wait and clean up, including waking everyone. */
582 rcu_exp_wait_wake(rsp, s);
583}
584
585/*
586 * Work-queue handler to drive an expedited grace period forward.
587 */
588static void wait_rcu_exp_gp(struct work_struct *wp)
589{
590 struct rcu_exp_work *rewp;
591
592 rewp = container_of(wp, struct rcu_exp_work, rew_work);
593 rcu_exp_sel_wait_wake(rewp->rew_rsp, rewp->rew_func, rewp->rew_s);
594}
595
596/*
597 * Given an rcu_state pointer and a smp_call_function() handler, kick
598 * off the specified flavor of expedited grace period.
599 */
600static void _synchronize_rcu_expedited(struct rcu_state *rsp,
601 smp_call_func_t func)
602{
603 struct rcu_data *rdp;
604 struct rcu_exp_work rew;
605 struct rcu_node *rnp;
606 unsigned long s;
607
608 /* If expedited grace periods are prohibited, fall back to normal. */
609 if (rcu_gp_is_normal()) {
610 wait_rcu_gp(rsp->call);
611 return;
612 }
613
614 /* Take a snapshot of the sequence number. */
615 s = rcu_exp_gp_seq_snap(rsp);
616 if (exp_funnel_lock(rsp, s))
617 return; /* Someone else did our work for us. */
618
619 /* Ensure that load happens before action based on it. */
620 if (unlikely(rcu_scheduler_active == RCU_SCHEDULER_INIT)) {
621 /* Direct call during scheduler init and early_initcalls(). */
622 rcu_exp_sel_wait_wake(rsp, func, s);
623 } else {
624 /* Marshall arguments & schedule the expedited grace period. */
625 rew.rew_func = func;
626 rew.rew_rsp = rsp;
627 rew.rew_s = s;
628 INIT_WORK_ONSTACK(&rew.rew_work, wait_rcu_exp_gp);
629 queue_work(rcu_gp_wq, &rew.rew_work);
630 }
631
632 /* Wait for expedited grace period to complete. */
633 rdp = per_cpu_ptr(rsp->rda, raw_smp_processor_id());
634 rnp = rcu_get_root(rsp);
635 wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
636 sync_exp_work_done(rsp, &rdp->exp_workdone0, s));
637 smp_mb(); /* Workqueue actions happen before return. */
638
639 /* Let the next expedited grace period start. */
640 mutex_unlock(&rsp->exp_mutex);
641}
642
643/**
644 * synchronize_sched_expedited - Brute-force RCU-sched grace period
645 *
646 * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
647 * approach to force the grace period to end quickly. This consumes
648 * significant time on all CPUs and is unfriendly to real-time workloads,
649 * so is thus not recommended for any sort of common-case code. In fact,
650 * if you are using synchronize_sched_expedited() in a loop, please
651 * restructure your code to batch your updates, and then use a single
652 * synchronize_sched() instead.
653 *
654 * This implementation can be thought of as an application of sequence
655 * locking to expedited grace periods, but using the sequence counter to
656 * determine when someone else has already done the work instead of for
657 * retrying readers.
658 */
659void synchronize_sched_expedited(void)
660{
661 struct rcu_state *rsp = &rcu_sched_state;
662
663 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
664 lock_is_held(&rcu_lock_map) ||
665 lock_is_held(&rcu_sched_lock_map),
666 "Illegal synchronize_sched_expedited() in RCU read-side critical section");
667
668 /* If only one CPU, this is automatically a grace period. */
669 if (rcu_blocking_is_gp())
670 return;
671
672 _synchronize_rcu_expedited(rsp, sync_sched_exp_handler);
673}
674EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
675
676#ifdef CONFIG_PREEMPT_RCU
677
678/*
679 * Remote handler for smp_call_function_single(). If there is an
680 * RCU read-side critical section in effect, request that the
681 * next rcu_read_unlock() record the quiescent state up the
682 * ->expmask fields in the rcu_node tree. Otherwise, immediately
683 * report the quiescent state.
684 */
685static void sync_rcu_exp_handler(void *info)
686{
687 struct rcu_data *rdp;
688 struct rcu_state *rsp = info;
689 struct task_struct *t = current;
690
691 /*
692 * Within an RCU read-side critical section, request that the next
693 * rcu_read_unlock() report. Unless this RCU read-side critical
694 * section has already blocked, in which case it is already set
695 * up for the expedited grace period to wait on it.
696 */
697 if (t->rcu_read_lock_nesting > 0 &&
698 !t->rcu_read_unlock_special.b.blocked) {
699 t->rcu_read_unlock_special.b.exp_need_qs = true;
700 return;
701 }
702
703 /*
704 * We are either exiting an RCU read-side critical section (negative
705 * values of t->rcu_read_lock_nesting) or are not in one at all
706 * (zero value of t->rcu_read_lock_nesting). Or we are in an RCU
707 * read-side critical section that blocked before this expedited
708 * grace period started. Either way, we can immediately report
709 * the quiescent state.
710 */
711 rdp = this_cpu_ptr(rsp->rda);
712 rcu_report_exp_rdp(rsp, rdp, true);
713}
714
715/**
716 * synchronize_rcu_expedited - Brute-force RCU grace period
717 *
718 * Wait for an RCU-preempt grace period, but expedite it. The basic
719 * idea is to IPI all non-idle non-nohz online CPUs. The IPI handler
720 * checks whether the CPU is in an RCU-preempt critical section, and
721 * if so, it sets a flag that causes the outermost rcu_read_unlock()
722 * to report the quiescent state. On the other hand, if the CPU is
723 * not in an RCU read-side critical section, the IPI handler reports
724 * the quiescent state immediately.
725 *
726 * Although this is a greate improvement over previous expedited
727 * implementations, it is still unfriendly to real-time workloads, so is
728 * thus not recommended for any sort of common-case code. In fact, if
729 * you are using synchronize_rcu_expedited() in a loop, please restructure
730 * your code to batch your updates, and then Use a single synchronize_rcu()
731 * instead.
732 */
733void synchronize_rcu_expedited(void)
734{
735 struct rcu_state *rsp = rcu_state_p;
736
737 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
738 lock_is_held(&rcu_lock_map) ||
739 lock_is_held(&rcu_sched_lock_map),
740 "Illegal synchronize_rcu_expedited() in RCU read-side critical section");
741
742 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
743 return;
744 _synchronize_rcu_expedited(rsp, sync_rcu_exp_handler);
745}
746EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
747
748#else /* #ifdef CONFIG_PREEMPT_RCU */
749
750/*
751 * Wait for an rcu-preempt grace period, but make it happen quickly.
752 * But because preemptible RCU does not exist, map to rcu-sched.
753 */
754void synchronize_rcu_expedited(void)
755{
756 synchronize_sched_expedited();
757}
758EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
759
760#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
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}
22
23/*
24 * Return the value that the expedited-grace-period counter will have
25 * at the end of the current grace period.
26 */
27static __maybe_unused unsigned long rcu_exp_gp_seq_endval(void)
28{
29 return rcu_seq_endval(&rcu_state.expedited_sequence);
30}
31
32/*
33 * Record the end of an expedited grace period.
34 */
35static void rcu_exp_gp_seq_end(void)
36{
37 rcu_seq_end(&rcu_state.expedited_sequence);
38 smp_mb(); /* Ensure that consecutive grace periods serialize. */
39}
40
41/*
42 * Take a snapshot of the expedited-grace-period counter, which is the
43 * earliest value that will indicate that a full grace period has
44 * elapsed since the current time.
45 */
46static unsigned long rcu_exp_gp_seq_snap(void)
47{
48 unsigned long s;
49
50 smp_mb(); /* Caller's modifications seen first by other CPUs. */
51 s = rcu_seq_snap(&rcu_state.expedited_sequence);
52 trace_rcu_exp_grace_period(rcu_state.name, s, TPS("snap"));
53 return s;
54}
55
56/*
57 * Given a counter snapshot from rcu_exp_gp_seq_snap(), return true
58 * if a full expedited grace period has elapsed since that snapshot
59 * was taken.
60 */
61static bool rcu_exp_gp_seq_done(unsigned long s)
62{
63 return rcu_seq_done(&rcu_state.expedited_sequence, s);
64}
65
66/*
67 * Reset the ->expmaskinit values in the rcu_node tree to reflect any
68 * recent CPU-online activity. Note that these masks are not cleared
69 * when CPUs go offline, so they reflect the union of all CPUs that have
70 * ever been online. This means that this function normally takes its
71 * no-work-to-do fastpath.
72 */
73static void sync_exp_reset_tree_hotplug(void)
74{
75 bool done;
76 unsigned long flags;
77 unsigned long mask;
78 unsigned long oldmask;
79 int ncpus = smp_load_acquire(&rcu_state.ncpus); /* Order vs. locking. */
80 struct rcu_node *rnp;
81 struct rcu_node *rnp_up;
82
83 /* If no new CPUs onlined since last time, nothing to do. */
84 if (likely(ncpus == rcu_state.ncpus_snap))
85 return;
86 rcu_state.ncpus_snap = ncpus;
87
88 /*
89 * Each pass through the following loop propagates newly onlined
90 * CPUs for the current rcu_node structure up the rcu_node tree.
91 */
92 rcu_for_each_leaf_node(rnp) {
93 raw_spin_lock_irqsave_rcu_node(rnp, flags);
94 if (rnp->expmaskinit == rnp->expmaskinitnext) {
95 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
96 continue; /* No new CPUs, nothing to do. */
97 }
98
99 /* Update this node's mask, track old value for propagation. */
100 oldmask = rnp->expmaskinit;
101 rnp->expmaskinit = rnp->expmaskinitnext;
102 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
103
104 /* If was already nonzero, nothing to propagate. */
105 if (oldmask)
106 continue;
107
108 /* Propagate the new CPU up the tree. */
109 mask = rnp->grpmask;
110 rnp_up = rnp->parent;
111 done = false;
112 while (rnp_up) {
113 raw_spin_lock_irqsave_rcu_node(rnp_up, flags);
114 if (rnp_up->expmaskinit)
115 done = true;
116 rnp_up->expmaskinit |= mask;
117 raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags);
118 if (done)
119 break;
120 mask = rnp_up->grpmask;
121 rnp_up = rnp_up->parent;
122 }
123 }
124}
125
126/*
127 * Reset the ->expmask values in the rcu_node tree in preparation for
128 * a new expedited grace period.
129 */
130static void __maybe_unused sync_exp_reset_tree(void)
131{
132 unsigned long flags;
133 struct rcu_node *rnp;
134
135 sync_exp_reset_tree_hotplug();
136 rcu_for_each_node_breadth_first(rnp) {
137 raw_spin_lock_irqsave_rcu_node(rnp, flags);
138 WARN_ON_ONCE(rnp->expmask);
139 WRITE_ONCE(rnp->expmask, rnp->expmaskinit);
140 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
141 }
142}
143
144/*
145 * Return non-zero if there is no RCU expedited grace period in progress
146 * for the specified rcu_node structure, in other words, if all CPUs and
147 * tasks covered by the specified rcu_node structure have done their bit
148 * for the current expedited grace period.
149 */
150static bool sync_rcu_exp_done(struct rcu_node *rnp)
151{
152 raw_lockdep_assert_held_rcu_node(rnp);
153 return READ_ONCE(rnp->exp_tasks) == NULL &&
154 READ_ONCE(rnp->expmask) == 0;
155}
156
157/*
158 * Like sync_rcu_exp_done(), but where the caller does not hold the
159 * rcu_node's ->lock.
160 */
161static bool sync_rcu_exp_done_unlocked(struct rcu_node *rnp)
162{
163 unsigned long flags;
164 bool ret;
165
166 raw_spin_lock_irqsave_rcu_node(rnp, flags);
167 ret = sync_rcu_exp_done(rnp);
168 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
169
170 return ret;
171}
172
173
174/*
175 * Report the exit from RCU read-side critical section for the last task
176 * that queued itself during or before the current expedited preemptible-RCU
177 * grace period. This event is reported either to the rcu_node structure on
178 * which the task was queued or to one of that rcu_node structure's ancestors,
179 * recursively up the tree. (Calm down, calm down, we do the recursion
180 * iteratively!)
181 */
182static void __rcu_report_exp_rnp(struct rcu_node *rnp,
183 bool wake, unsigned long flags)
184 __releases(rnp->lock)
185{
186 unsigned long mask;
187
188 raw_lockdep_assert_held_rcu_node(rnp);
189 for (;;) {
190 if (!sync_rcu_exp_done(rnp)) {
191 if (!rnp->expmask)
192 rcu_initiate_boost(rnp, flags);
193 else
194 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
195 break;
196 }
197 if (rnp->parent == NULL) {
198 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
199 if (wake) {
200 smp_mb(); /* EGP done before wake_up(). */
201 swake_up_one(&rcu_state.expedited_wq);
202 }
203 break;
204 }
205 mask = rnp->grpmask;
206 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */
207 rnp = rnp->parent;
208 raw_spin_lock_rcu_node(rnp); /* irqs already disabled */
209 WARN_ON_ONCE(!(rnp->expmask & mask));
210 WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
211 }
212}
213
214/*
215 * Report expedited quiescent state for specified node. This is a
216 * lock-acquisition wrapper function for __rcu_report_exp_rnp().
217 */
218static void __maybe_unused rcu_report_exp_rnp(struct rcu_node *rnp, bool wake)
219{
220 unsigned long flags;
221
222 raw_spin_lock_irqsave_rcu_node(rnp, flags);
223 __rcu_report_exp_rnp(rnp, wake, flags);
224}
225
226/*
227 * Report expedited quiescent state for multiple CPUs, all covered by the
228 * specified leaf rcu_node structure.
229 */
230static void rcu_report_exp_cpu_mult(struct rcu_node *rnp,
231 unsigned long mask, bool wake)
232{
233 int cpu;
234 unsigned long flags;
235 struct rcu_data *rdp;
236
237 raw_spin_lock_irqsave_rcu_node(rnp, flags);
238 if (!(rnp->expmask & mask)) {
239 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
240 return;
241 }
242 WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask);
243 for_each_leaf_node_cpu_mask(rnp, cpu, mask) {
244 rdp = per_cpu_ptr(&rcu_data, cpu);
245 if (!IS_ENABLED(CONFIG_NO_HZ_FULL) || !rdp->rcu_forced_tick_exp)
246 continue;
247 rdp->rcu_forced_tick_exp = false;
248 tick_dep_clear_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
249 }
250 __rcu_report_exp_rnp(rnp, wake, flags); /* Releases rnp->lock. */
251}
252
253/*
254 * Report expedited quiescent state for specified rcu_data (CPU).
255 */
256static void rcu_report_exp_rdp(struct rcu_data *rdp)
257{
258 WRITE_ONCE(rdp->exp_deferred_qs, false);
259 rcu_report_exp_cpu_mult(rdp->mynode, rdp->grpmask, true);
260}
261
262/* Common code for work-done checking. */
263static bool sync_exp_work_done(unsigned long s)
264{
265 if (rcu_exp_gp_seq_done(s)) {
266 trace_rcu_exp_grace_period(rcu_state.name, s, TPS("done"));
267 smp_mb(); /* Ensure test happens before caller kfree(). */
268 return true;
269 }
270 return false;
271}
272
273/*
274 * Funnel-lock acquisition for expedited grace periods. Returns true
275 * if some other task completed an expedited grace period that this task
276 * can piggy-back on, and with no mutex held. Otherwise, returns false
277 * with the mutex held, indicating that the caller must actually do the
278 * expedited grace period.
279 */
280static bool exp_funnel_lock(unsigned long s)
281{
282 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id());
283 struct rcu_node *rnp = rdp->mynode;
284 struct rcu_node *rnp_root = rcu_get_root();
285
286 /* Low-contention fastpath. */
287 if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) &&
288 (rnp == rnp_root ||
289 ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) &&
290 mutex_trylock(&rcu_state.exp_mutex))
291 goto fastpath;
292
293 /*
294 * Each pass through the following loop works its way up
295 * the rcu_node tree, returning if others have done the work or
296 * otherwise falls through to acquire ->exp_mutex. The mapping
297 * from CPU to rcu_node structure can be inexact, as it is just
298 * promoting locality and is not strictly needed for correctness.
299 */
300 for (; rnp != NULL; rnp = rnp->parent) {
301 if (sync_exp_work_done(s))
302 return true;
303
304 /* Work not done, either wait here or go up. */
305 spin_lock(&rnp->exp_lock);
306 if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) {
307
308 /* Someone else doing GP, so wait for them. */
309 spin_unlock(&rnp->exp_lock);
310 trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
311 rnp->grplo, rnp->grphi,
312 TPS("wait"));
313 wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
314 sync_exp_work_done(s));
315 return true;
316 }
317 WRITE_ONCE(rnp->exp_seq_rq, s); /* Followers can wait on us. */
318 spin_unlock(&rnp->exp_lock);
319 trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level,
320 rnp->grplo, rnp->grphi, TPS("nxtlvl"));
321 }
322 mutex_lock(&rcu_state.exp_mutex);
323fastpath:
324 if (sync_exp_work_done(s)) {
325 mutex_unlock(&rcu_state.exp_mutex);
326 return true;
327 }
328 rcu_exp_gp_seq_start();
329 trace_rcu_exp_grace_period(rcu_state.name, s, TPS("start"));
330 return false;
331}
332
333/*
334 * Select the CPUs within the specified rcu_node that the upcoming
335 * expedited grace period needs to wait for.
336 */
337static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
338{
339 int cpu;
340 unsigned long flags;
341 unsigned long mask_ofl_test;
342 unsigned long mask_ofl_ipi;
343 int ret;
344 struct rcu_exp_work *rewp =
345 container_of(wp, struct rcu_exp_work, rew_work);
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(rdp);
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 put_cpu();
391 continue;
392 }
393 ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
394 put_cpu();
395 /* The CPU will report the QS in response to the IPI. */
396 if (!ret)
397 continue;
398
399 /* Failed, raced with CPU hotplug operation. */
400 raw_spin_lock_irqsave_rcu_node(rnp, flags);
401 if ((rnp->qsmaskinitnext & mask) &&
402 (rnp->expmask & mask)) {
403 /* Online, so delay for a bit and try again. */
404 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
405 trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("selectofl"));
406 schedule_timeout_idle(1);
407 goto retry_ipi;
408 }
409 /* CPU really is offline, so we must report its QS. */
410 if (rnp->expmask & mask)
411 mask_ofl_test |= mask;
412 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
413 }
414 /* Report quiescent states for those that went offline. */
415 if (mask_ofl_test)
416 rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false);
417}
418
419/*
420 * Select the nodes that the upcoming expedited grace period needs
421 * to wait for.
422 */
423static void sync_rcu_exp_select_cpus(void)
424{
425 int cpu;
426 struct rcu_node *rnp;
427
428 trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("reset"));
429 sync_exp_reset_tree();
430 trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("select"));
431
432 /* Schedule work for each leaf rcu_node structure. */
433 rcu_for_each_leaf_node(rnp) {
434 rnp->exp_need_flush = false;
435 if (!READ_ONCE(rnp->expmask))
436 continue; /* Avoid early boot non-existent wq. */
437 if (!READ_ONCE(rcu_par_gp_wq) ||
438 rcu_scheduler_active != RCU_SCHEDULER_RUNNING ||
439 rcu_is_last_leaf_node(rnp)) {
440 /* No workqueues yet or last leaf, do direct call. */
441 sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work);
442 continue;
443 }
444 INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus);
445 cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1);
446 /* If all offline, queue the work on an unbound CPU. */
447 if (unlikely(cpu > rnp->grphi - rnp->grplo))
448 cpu = WORK_CPU_UNBOUND;
449 else
450 cpu += rnp->grplo;
451 queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work);
452 rnp->exp_need_flush = true;
453 }
454
455 /* Wait for workqueue jobs (if any) to complete. */
456 rcu_for_each_leaf_node(rnp)
457 if (rnp->exp_need_flush)
458 flush_work(&rnp->rew.rew_work);
459}
460
461/*
462 * Wait for the expedited grace period to elapse, within time limit.
463 * If the time limit is exceeded without the grace period elapsing,
464 * return false, otherwise return true.
465 */
466static bool synchronize_rcu_expedited_wait_once(long tlimit)
467{
468 int t;
469 struct rcu_node *rnp_root = rcu_get_root();
470
471 t = swait_event_timeout_exclusive(rcu_state.expedited_wq,
472 sync_rcu_exp_done_unlocked(rnp_root),
473 tlimit);
474 // Workqueues should not be signaled.
475 if (t > 0 || sync_rcu_exp_done_unlocked(rnp_root))
476 return true;
477 WARN_ON(t < 0); /* workqueues should not be signaled. */
478 return false;
479}
480
481/*
482 * Wait for the expedited grace period to elapse, issuing any needed
483 * RCU CPU stall warnings along the way.
484 */
485static void synchronize_rcu_expedited_wait(void)
486{
487 int cpu;
488 unsigned long j;
489 unsigned long jiffies_stall;
490 unsigned long jiffies_start;
491 unsigned long mask;
492 int ndetected;
493 struct rcu_data *rdp;
494 struct rcu_node *rnp;
495 struct rcu_node *rnp_root = rcu_get_root();
496
497 trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait"));
498 jiffies_stall = rcu_jiffies_till_stall_check();
499 jiffies_start = jiffies;
500 if (tick_nohz_full_enabled() && rcu_inkernel_boot_has_ended()) {
501 if (synchronize_rcu_expedited_wait_once(1))
502 return;
503 rcu_for_each_leaf_node(rnp) {
504 for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) {
505 rdp = per_cpu_ptr(&rcu_data, cpu);
506 if (rdp->rcu_forced_tick_exp)
507 continue;
508 rdp->rcu_forced_tick_exp = true;
509 tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP);
510 }
511 }
512 j = READ_ONCE(jiffies_till_first_fqs);
513 if (synchronize_rcu_expedited_wait_once(j + HZ))
514 return;
515 WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_RT));
516 }
517
518 for (;;) {
519 if (synchronize_rcu_expedited_wait_once(jiffies_stall))
520 return;
521 if (rcu_stall_is_suppressed())
522 continue;
523 panic_on_rcu_stall();
524 trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall"));
525 pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
526 rcu_state.name);
527 ndetected = 0;
528 rcu_for_each_leaf_node(rnp) {
529 ndetected += rcu_print_task_exp_stall(rnp);
530 for_each_leaf_node_possible_cpu(rnp, cpu) {
531 struct rcu_data *rdp;
532
533 mask = leaf_node_cpu_bit(rnp, cpu);
534 if (!(READ_ONCE(rnp->expmask) & mask))
535 continue;
536 ndetected++;
537 rdp = per_cpu_ptr(&rcu_data, cpu);
538 pr_cont(" %d-%c%c%c", cpu,
539 "O."[!!cpu_online(cpu)],
540 "o."[!!(rdp->grpmask & rnp->expmaskinit)],
541 "N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);
542 }
543 }
544 pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
545 jiffies - jiffies_start, rcu_state.expedited_sequence,
546 data_race(rnp_root->expmask),
547 ".T"[!!data_race(rnp_root->exp_tasks)]);
548 if (ndetected) {
549 pr_err("blocking rcu_node structures (internal RCU debug):");
550 rcu_for_each_node_breadth_first(rnp) {
551 if (rnp == rnp_root)
552 continue; /* printed unconditionally */
553 if (sync_rcu_exp_done_unlocked(rnp))
554 continue;
555 pr_cont(" l=%u:%d-%d:%#lx/%c",
556 rnp->level, rnp->grplo, rnp->grphi,
557 data_race(rnp->expmask),
558 ".T"[!!data_race(rnp->exp_tasks)]);
559 }
560 pr_cont("\n");
561 }
562 rcu_for_each_leaf_node(rnp) {
563 for_each_leaf_node_possible_cpu(rnp, cpu) {
564 mask = leaf_node_cpu_bit(rnp, cpu);
565 if (!(READ_ONCE(rnp->expmask) & mask))
566 continue;
567 dump_cpu_task(cpu);
568 }
569 }
570 jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3;
571 }
572}
573
574/*
575 * Wait for the current expedited grace period to complete, and then
576 * wake up everyone who piggybacked on the just-completed expedited
577 * grace period. Also update all the ->exp_seq_rq counters as needed
578 * in order to avoid counter-wrap problems.
579 */
580static void rcu_exp_wait_wake(unsigned long s)
581{
582 struct rcu_node *rnp;
583
584 synchronize_rcu_expedited_wait();
585
586 // Switch over to wakeup mode, allowing the next GP to proceed.
587 // End the previous grace period only after acquiring the mutex
588 // to ensure that only one GP runs concurrently with wakeups.
589 mutex_lock(&rcu_state.exp_wake_mutex);
590 rcu_exp_gp_seq_end();
591 trace_rcu_exp_grace_period(rcu_state.name, s, TPS("end"));
592
593 rcu_for_each_node_breadth_first(rnp) {
594 if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) {
595 spin_lock(&rnp->exp_lock);
596 /* Recheck, avoid hang in case someone just arrived. */
597 if (ULONG_CMP_LT(rnp->exp_seq_rq, s))
598 WRITE_ONCE(rnp->exp_seq_rq, s);
599 spin_unlock(&rnp->exp_lock);
600 }
601 smp_mb(); /* All above changes before wakeup. */
602 wake_up_all(&rnp->exp_wq[rcu_seq_ctr(s) & 0x3]);
603 }
604 trace_rcu_exp_grace_period(rcu_state.name, s, TPS("endwake"));
605 mutex_unlock(&rcu_state.exp_wake_mutex);
606}
607
608/*
609 * Common code to drive an expedited grace period forward, used by
610 * workqueues and mid-boot-time tasks.
611 */
612static void rcu_exp_sel_wait_wake(unsigned long s)
613{
614 /* Initialize the rcu_node tree in preparation for the wait. */
615 sync_rcu_exp_select_cpus();
616
617 /* Wait and clean up, including waking everyone. */
618 rcu_exp_wait_wake(s);
619}
620
621/*
622 * Work-queue handler to drive an expedited grace period forward.
623 */
624static void wait_rcu_exp_gp(struct work_struct *wp)
625{
626 struct rcu_exp_work *rewp;
627
628 rewp = container_of(wp, struct rcu_exp_work, rew_work);
629 rcu_exp_sel_wait_wake(rewp->rew_s);
630}
631
632#ifdef CONFIG_PREEMPT_RCU
633
634/*
635 * Remote handler for smp_call_function_single(). If there is an
636 * RCU read-side critical section in effect, request that the
637 * next rcu_read_unlock() record the quiescent state up the
638 * ->expmask fields in the rcu_node tree. Otherwise, immediately
639 * report the quiescent state.
640 */
641static void rcu_exp_handler(void *unused)
642{
643 int depth = rcu_preempt_depth();
644 unsigned long flags;
645 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
646 struct rcu_node *rnp = rdp->mynode;
647 struct task_struct *t = current;
648
649 /*
650 * First, the common case of not being in an RCU read-side
651 * critical section. If also enabled or idle, immediately
652 * report the quiescent state, otherwise defer.
653 */
654 if (!depth) {
655 if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) ||
656 rcu_dynticks_curr_cpu_in_eqs()) {
657 rcu_report_exp_rdp(rdp);
658 } else {
659 rdp->exp_deferred_qs = true;
660 set_tsk_need_resched(t);
661 set_preempt_need_resched();
662 }
663 return;
664 }
665
666 /*
667 * Second, the less-common case of being in an RCU read-side
668 * critical section. In this case we can count on a future
669 * rcu_read_unlock(). However, this rcu_read_unlock() might
670 * execute on some other CPU, but in that case there will be
671 * a future context switch. Either way, if the expedited
672 * grace period is still waiting on this CPU, set ->deferred_qs
673 * so that the eventual quiescent state will be reported.
674 * Note that there is a large group of race conditions that
675 * can have caused this quiescent state to already have been
676 * reported, so we really do need to check ->expmask.
677 */
678 if (depth > 0) {
679 raw_spin_lock_irqsave_rcu_node(rnp, flags);
680 if (rnp->expmask & rdp->grpmask) {
681 rdp->exp_deferred_qs = true;
682 t->rcu_read_unlock_special.b.exp_hint = true;
683 }
684 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
685 return;
686 }
687
688 // Finally, negative nesting depth should not happen.
689 WARN_ON_ONCE(1);
690}
691
692/* PREEMPTION=y, so no PREEMPTION=n expedited grace period to clean up after. */
693static void sync_sched_exp_online_cleanup(int cpu)
694{
695}
696
697/*
698 * Scan the current list of tasks blocked within RCU read-side critical
699 * sections, printing out the tid of each that is blocking the current
700 * expedited grace period.
701 */
702static int rcu_print_task_exp_stall(struct rcu_node *rnp)
703{
704 unsigned long flags;
705 int ndetected = 0;
706 struct task_struct *t;
707
708 if (!READ_ONCE(rnp->exp_tasks))
709 return 0;
710 raw_spin_lock_irqsave_rcu_node(rnp, flags);
711 t = list_entry(rnp->exp_tasks->prev,
712 struct task_struct, rcu_node_entry);
713 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
714 pr_cont(" P%d", t->pid);
715 ndetected++;
716 }
717 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
718 return ndetected;
719}
720
721#else /* #ifdef CONFIG_PREEMPT_RCU */
722
723/* Request an expedited quiescent state. */
724static void rcu_exp_need_qs(void)
725{
726 __this_cpu_write(rcu_data.cpu_no_qs.b.exp, true);
727 /* Store .exp before .rcu_urgent_qs. */
728 smp_store_release(this_cpu_ptr(&rcu_data.rcu_urgent_qs), true);
729 set_tsk_need_resched(current);
730 set_preempt_need_resched();
731}
732
733/* Invoked on each online non-idle CPU for expedited quiescent state. */
734static void rcu_exp_handler(void *unused)
735{
736 struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
737 struct rcu_node *rnp = rdp->mynode;
738
739 if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
740 __this_cpu_read(rcu_data.cpu_no_qs.b.exp))
741 return;
742 if (rcu_is_cpu_rrupt_from_idle()) {
743 rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
744 return;
745 }
746 rcu_exp_need_qs();
747}
748
749/* Send IPI for expedited cleanup if needed at end of CPU-hotplug operation. */
750static void sync_sched_exp_online_cleanup(int cpu)
751{
752 unsigned long flags;
753 int my_cpu;
754 struct rcu_data *rdp;
755 int ret;
756 struct rcu_node *rnp;
757
758 rdp = per_cpu_ptr(&rcu_data, cpu);
759 rnp = rdp->mynode;
760 my_cpu = get_cpu();
761 /* Quiescent state either not needed or already requested, leave. */
762 if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) ||
763 __this_cpu_read(rcu_data.cpu_no_qs.b.exp)) {
764 put_cpu();
765 return;
766 }
767 /* Quiescent state needed on current CPU, so set it up locally. */
768 if (my_cpu == cpu) {
769 local_irq_save(flags);
770 rcu_exp_need_qs();
771 local_irq_restore(flags);
772 put_cpu();
773 return;
774 }
775 /* Quiescent state needed on some other CPU, send IPI. */
776 ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0);
777 put_cpu();
778 WARN_ON_ONCE(ret);
779}
780
781/*
782 * Because preemptible RCU does not exist, we never have to check for
783 * tasks blocked within RCU read-side critical sections that are
784 * blocking the current expedited grace period.
785 */
786static int rcu_print_task_exp_stall(struct rcu_node *rnp)
787{
788 return 0;
789}
790
791#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
792
793/**
794 * synchronize_rcu_expedited - Brute-force RCU grace period
795 *
796 * Wait for an RCU grace period, but expedite it. The basic idea is to
797 * IPI all non-idle non-nohz online CPUs. The IPI handler checks whether
798 * the CPU is in an RCU critical section, and if so, it sets a flag that
799 * causes the outermost rcu_read_unlock() to report the quiescent state
800 * for RCU-preempt or asks the scheduler for help for RCU-sched. On the
801 * other hand, if the CPU is not in an RCU read-side critical section,
802 * the IPI handler reports the quiescent state immediately.
803 *
804 * Although this is a great improvement over previous expedited
805 * implementations, it is still unfriendly to real-time workloads, so is
806 * thus not recommended for any sort of common-case code. In fact, if
807 * you are using synchronize_rcu_expedited() in a loop, please restructure
808 * your code to batch your updates, and then use a single synchronize_rcu()
809 * instead.
810 *
811 * This has the same semantics as (but is more brutal than) synchronize_rcu().
812 */
813void synchronize_rcu_expedited(void)
814{
815 bool boottime = (rcu_scheduler_active == RCU_SCHEDULER_INIT);
816 struct rcu_exp_work rew;
817 struct rcu_node *rnp;
818 unsigned long s;
819
820 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
821 lock_is_held(&rcu_lock_map) ||
822 lock_is_held(&rcu_sched_lock_map),
823 "Illegal synchronize_rcu_expedited() in RCU read-side critical section");
824
825 /* Is the state is such that the call is a grace period? */
826 if (rcu_blocking_is_gp())
827 return;
828
829 /* If expedited grace periods are prohibited, fall back to normal. */
830 if (rcu_gp_is_normal()) {
831 wait_rcu_gp(call_rcu);
832 return;
833 }
834
835 /* Take a snapshot of the sequence number. */
836 s = rcu_exp_gp_seq_snap();
837 if (exp_funnel_lock(s))
838 return; /* Someone else did our work for us. */
839
840 /* Ensure that load happens before action based on it. */
841 if (unlikely(boottime)) {
842 /* Direct call during scheduler init and early_initcalls(). */
843 rcu_exp_sel_wait_wake(s);
844 } else {
845 /* Marshall arguments & schedule the expedited grace period. */
846 rew.rew_s = s;
847 INIT_WORK_ONSTACK(&rew.rew_work, wait_rcu_exp_gp);
848 queue_work(rcu_gp_wq, &rew.rew_work);
849 }
850
851 /* Wait for expedited grace period to complete. */
852 rnp = rcu_get_root();
853 wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3],
854 sync_exp_work_done(s));
855 smp_mb(); /* Workqueue actions happen before return. */
856
857 /* Let the next expedited grace period start. */
858 mutex_unlock(&rcu_state.exp_mutex);
859
860 if (likely(!boottime))
861 destroy_work_on_stack(&rew.rew_work);
862}
863EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);