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