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1/* SPDX-License-Identifier: GPL-2.0+ */
2/*
3 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
4 * Internal non-public definitions that provide either classic
5 * or preemptible semantics.
6 *
7 * Copyright Red Hat, 2009
8 * Copyright IBM Corporation, 2009
9 * Copyright SUSE, 2021
10 *
11 * Author: Ingo Molnar <mingo@elte.hu>
12 * Paul E. McKenney <paulmck@linux.ibm.com>
13 * Frederic Weisbecker <frederic@kernel.org>
14 */
15
16#ifdef CONFIG_RCU_NOCB_CPU
17static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
18static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
19
20static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp)
21{
22 /* Race on early boot between thread creation and assignment */
23 if (!rdp->nocb_cb_kthread || !rdp->nocb_gp_kthread)
24 return true;
25
26 if (current == rdp->nocb_cb_kthread || current == rdp->nocb_gp_kthread)
27 if (in_task())
28 return true;
29 return false;
30}
31
32/*
33 * Offload callback processing from the boot-time-specified set of CPUs
34 * specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads
35 * created that pull the callbacks from the corresponding CPU, wait for
36 * a grace period to elapse, and invoke the callbacks. These kthreads
37 * are organized into GP kthreads, which manage incoming callbacks, wait for
38 * grace periods, and awaken CB kthreads, and the CB kthreads, which only
39 * invoke callbacks. Each GP kthread invokes its own CBs. The no-CBs CPUs
40 * do a wake_up() on their GP kthread when they insert a callback into any
41 * empty list, unless the rcu_nocb_poll boot parameter has been specified,
42 * in which case each kthread actively polls its CPU. (Which isn't so great
43 * for energy efficiency, but which does reduce RCU's overhead on that CPU.)
44 *
45 * This is intended to be used in conjunction with Frederic Weisbecker's
46 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
47 * running CPU-bound user-mode computations.
48 *
49 * Offloading of callbacks can also be used as an energy-efficiency
50 * measure because CPUs with no RCU callbacks queued are more aggressive
51 * about entering dyntick-idle mode.
52 */
53
54
55/*
56 * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters.
57 * If the list is invalid, a warning is emitted and all CPUs are offloaded.
58 */
59static int __init rcu_nocb_setup(char *str)
60{
61 alloc_bootmem_cpumask_var(&rcu_nocb_mask);
62 if (*str == '=') {
63 if (cpulist_parse(++str, rcu_nocb_mask)) {
64 pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
65 cpumask_setall(rcu_nocb_mask);
66 }
67 }
68 rcu_state.nocb_is_setup = true;
69 return 1;
70}
71__setup("rcu_nocbs", rcu_nocb_setup);
72
73static int __init parse_rcu_nocb_poll(char *arg)
74{
75 rcu_nocb_poll = true;
76 return 1;
77}
78__setup("rcu_nocb_poll", parse_rcu_nocb_poll);
79
80/*
81 * Don't bother bypassing ->cblist if the call_rcu() rate is low.
82 * After all, the main point of bypassing is to avoid lock contention
83 * on ->nocb_lock, which only can happen at high call_rcu() rates.
84 */
85static int nocb_nobypass_lim_per_jiffy = 16 * 1000 / HZ;
86module_param(nocb_nobypass_lim_per_jiffy, int, 0);
87
88/*
89 * Acquire the specified rcu_data structure's ->nocb_bypass_lock. If the
90 * lock isn't immediately available, perform minimal sanity check.
91 */
92static void rcu_nocb_bypass_lock(struct rcu_data *rdp)
93 __acquires(&rdp->nocb_bypass_lock)
94{
95 lockdep_assert_irqs_disabled();
96 if (raw_spin_trylock(&rdp->nocb_bypass_lock))
97 return;
98 /*
99 * Contention expected only when local enqueue collide with
100 * remote flush from kthreads.
101 */
102 WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
103 raw_spin_lock(&rdp->nocb_bypass_lock);
104}
105
106/*
107 * Conditionally acquire the specified rcu_data structure's
108 * ->nocb_bypass_lock.
109 */
110static bool rcu_nocb_bypass_trylock(struct rcu_data *rdp)
111{
112 lockdep_assert_irqs_disabled();
113 return raw_spin_trylock(&rdp->nocb_bypass_lock);
114}
115
116/*
117 * Release the specified rcu_data structure's ->nocb_bypass_lock.
118 */
119static void rcu_nocb_bypass_unlock(struct rcu_data *rdp)
120 __releases(&rdp->nocb_bypass_lock)
121{
122 lockdep_assert_irqs_disabled();
123 raw_spin_unlock(&rdp->nocb_bypass_lock);
124}
125
126/*
127 * Acquire the specified rcu_data structure's ->nocb_lock, but only
128 * if it corresponds to a no-CBs CPU.
129 */
130static void rcu_nocb_lock(struct rcu_data *rdp)
131{
132 lockdep_assert_irqs_disabled();
133 if (!rcu_rdp_is_offloaded(rdp))
134 return;
135 raw_spin_lock(&rdp->nocb_lock);
136}
137
138/*
139 * Release the specified rcu_data structure's ->nocb_lock, but only
140 * if it corresponds to a no-CBs CPU.
141 */
142static void rcu_nocb_unlock(struct rcu_data *rdp)
143{
144 if (rcu_rdp_is_offloaded(rdp)) {
145 lockdep_assert_irqs_disabled();
146 raw_spin_unlock(&rdp->nocb_lock);
147 }
148}
149
150/*
151 * Release the specified rcu_data structure's ->nocb_lock and restore
152 * interrupts, but only if it corresponds to a no-CBs CPU.
153 */
154static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
155 unsigned long flags)
156{
157 if (rcu_rdp_is_offloaded(rdp)) {
158 lockdep_assert_irqs_disabled();
159 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
160 } else {
161 local_irq_restore(flags);
162 }
163}
164
165/* Lockdep check that ->cblist may be safely accessed. */
166static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
167{
168 lockdep_assert_irqs_disabled();
169 if (rcu_rdp_is_offloaded(rdp))
170 lockdep_assert_held(&rdp->nocb_lock);
171}
172
173/*
174 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
175 * grace period.
176 */
177static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
178{
179 swake_up_all(sq);
180}
181
182static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
183{
184 return &rnp->nocb_gp_wq[rcu_seq_ctr(rnp->gp_seq) & 0x1];
185}
186
187static void rcu_init_one_nocb(struct rcu_node *rnp)
188{
189 init_swait_queue_head(&rnp->nocb_gp_wq[0]);
190 init_swait_queue_head(&rnp->nocb_gp_wq[1]);
191}
192
193static bool __wake_nocb_gp(struct rcu_data *rdp_gp,
194 struct rcu_data *rdp,
195 bool force, unsigned long flags)
196 __releases(rdp_gp->nocb_gp_lock)
197{
198 bool needwake = false;
199
200 if (!READ_ONCE(rdp_gp->nocb_gp_kthread)) {
201 raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
202 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
203 TPS("AlreadyAwake"));
204 return false;
205 }
206
207 if (rdp_gp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) {
208 WRITE_ONCE(rdp_gp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
209 del_timer(&rdp_gp->nocb_timer);
210 }
211
212 if (force || READ_ONCE(rdp_gp->nocb_gp_sleep)) {
213 WRITE_ONCE(rdp_gp->nocb_gp_sleep, false);
214 needwake = true;
215 }
216 raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
217 if (needwake) {
218 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DoWake"));
219 swake_up_one_online(&rdp_gp->nocb_gp_wq);
220 }
221
222 return needwake;
223}
224
225/*
226 * Kick the GP kthread for this NOCB group.
227 */
228static bool wake_nocb_gp(struct rcu_data *rdp, bool force)
229{
230 unsigned long flags;
231 struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
232
233 raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
234 return __wake_nocb_gp(rdp_gp, rdp, force, flags);
235}
236
237#ifdef CONFIG_RCU_LAZY
238/*
239 * LAZY_FLUSH_JIFFIES decides the maximum amount of time that
240 * can elapse before lazy callbacks are flushed. Lazy callbacks
241 * could be flushed much earlier for a number of other reasons
242 * however, LAZY_FLUSH_JIFFIES will ensure no lazy callbacks are
243 * left unsubmitted to RCU after those many jiffies.
244 */
245#define LAZY_FLUSH_JIFFIES (10 * HZ)
246static unsigned long jiffies_lazy_flush = LAZY_FLUSH_JIFFIES;
247
248// To be called only from test code.
249void rcu_set_jiffies_lazy_flush(unsigned long jif)
250{
251 jiffies_lazy_flush = jif;
252}
253EXPORT_SYMBOL(rcu_set_jiffies_lazy_flush);
254
255unsigned long rcu_get_jiffies_lazy_flush(void)
256{
257 return jiffies_lazy_flush;
258}
259EXPORT_SYMBOL(rcu_get_jiffies_lazy_flush);
260#endif
261
262/*
263 * Arrange to wake the GP kthread for this NOCB group at some future
264 * time when it is safe to do so.
265 */
266static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
267 const char *reason)
268{
269 unsigned long flags;
270 struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
271
272 raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
273
274 /*
275 * Bypass wakeup overrides previous deferments. In case of
276 * callback storms, no need to wake up too early.
277 */
278 if (waketype == RCU_NOCB_WAKE_LAZY &&
279 rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) {
280 mod_timer(&rdp_gp->nocb_timer, jiffies + rcu_get_jiffies_lazy_flush());
281 WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
282 } else if (waketype == RCU_NOCB_WAKE_BYPASS) {
283 mod_timer(&rdp_gp->nocb_timer, jiffies + 2);
284 WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
285 } else {
286 if (rdp_gp->nocb_defer_wakeup < RCU_NOCB_WAKE)
287 mod_timer(&rdp_gp->nocb_timer, jiffies + 1);
288 if (rdp_gp->nocb_defer_wakeup < waketype)
289 WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype);
290 }
291
292 raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
293
294 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason);
295}
296
297/*
298 * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
299 * However, if there is a callback to be enqueued and if ->nocb_bypass
300 * proves to be initially empty, just return false because the no-CB GP
301 * kthread may need to be awakened in this case.
302 *
303 * Return true if there was something to be flushed and it succeeded, otherwise
304 * false.
305 *
306 * Note that this function always returns true if rhp is NULL.
307 */
308static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp_in,
309 unsigned long j, bool lazy)
310{
311 struct rcu_cblist rcl;
312 struct rcu_head *rhp = rhp_in;
313
314 WARN_ON_ONCE(!rcu_rdp_is_offloaded(rdp));
315 rcu_lockdep_assert_cblist_protected(rdp);
316 lockdep_assert_held(&rdp->nocb_bypass_lock);
317 if (rhp && !rcu_cblist_n_cbs(&rdp->nocb_bypass)) {
318 raw_spin_unlock(&rdp->nocb_bypass_lock);
319 return false;
320 }
321 /* Note: ->cblist.len already accounts for ->nocb_bypass contents. */
322 if (rhp)
323 rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
324
325 /*
326 * If the new CB requested was a lazy one, queue it onto the main
327 * ->cblist so that we can take advantage of the grace-period that will
328 * happen regardless. But queue it onto the bypass list first so that
329 * the lazy CB is ordered with the existing CBs in the bypass list.
330 */
331 if (lazy && rhp) {
332 rcu_cblist_enqueue(&rdp->nocb_bypass, rhp);
333 rhp = NULL;
334 }
335 rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp);
336 WRITE_ONCE(rdp->lazy_len, 0);
337
338 rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl);
339 WRITE_ONCE(rdp->nocb_bypass_first, j);
340 rcu_nocb_bypass_unlock(rdp);
341 return true;
342}
343
344/*
345 * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
346 * However, if there is a callback to be enqueued and if ->nocb_bypass
347 * proves to be initially empty, just return false because the no-CB GP
348 * kthread may need to be awakened in this case.
349 *
350 * Note that this function always returns true if rhp is NULL.
351 */
352static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
353 unsigned long j, bool lazy)
354{
355 if (!rcu_rdp_is_offloaded(rdp))
356 return true;
357 rcu_lockdep_assert_cblist_protected(rdp);
358 rcu_nocb_bypass_lock(rdp);
359 return rcu_nocb_do_flush_bypass(rdp, rhp, j, lazy);
360}
361
362/*
363 * If the ->nocb_bypass_lock is immediately available, flush the
364 * ->nocb_bypass queue into ->cblist.
365 */
366static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j)
367{
368 rcu_lockdep_assert_cblist_protected(rdp);
369 if (!rcu_rdp_is_offloaded(rdp) ||
370 !rcu_nocb_bypass_trylock(rdp))
371 return;
372 WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j, false));
373}
374
375/*
376 * See whether it is appropriate to use the ->nocb_bypass list in order
377 * to control contention on ->nocb_lock. A limited number of direct
378 * enqueues are permitted into ->cblist per jiffy. If ->nocb_bypass
379 * is non-empty, further callbacks must be placed into ->nocb_bypass,
380 * otherwise rcu_barrier() breaks. Use rcu_nocb_flush_bypass() to switch
381 * back to direct use of ->cblist. However, ->nocb_bypass should not be
382 * used if ->cblist is empty, because otherwise callbacks can be stranded
383 * on ->nocb_bypass because we cannot count on the current CPU ever again
384 * invoking call_rcu(). The general rule is that if ->nocb_bypass is
385 * non-empty, the corresponding no-CBs grace-period kthread must not be
386 * in an indefinite sleep state.
387 *
388 * Finally, it is not permitted to use the bypass during early boot,
389 * as doing so would confuse the auto-initialization code. Besides
390 * which, there is no point in worrying about lock contention while
391 * there is only one CPU in operation.
392 */
393static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
394 bool *was_alldone, unsigned long flags,
395 bool lazy)
396{
397 unsigned long c;
398 unsigned long cur_gp_seq;
399 unsigned long j = jiffies;
400 long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
401 bool bypass_is_lazy = (ncbs == READ_ONCE(rdp->lazy_len));
402
403 lockdep_assert_irqs_disabled();
404
405 // Pure softirq/rcuc based processing: no bypassing, no
406 // locking.
407 if (!rcu_rdp_is_offloaded(rdp)) {
408 *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
409 return false;
410 }
411
412 // Don't use ->nocb_bypass during early boot.
413 if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING) {
414 rcu_nocb_lock(rdp);
415 WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
416 *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
417 return false;
418 }
419
420 // If we have advanced to a new jiffy, reset counts to allow
421 // moving back from ->nocb_bypass to ->cblist.
422 if (j == rdp->nocb_nobypass_last) {
423 c = rdp->nocb_nobypass_count + 1;
424 } else {
425 WRITE_ONCE(rdp->nocb_nobypass_last, j);
426 c = rdp->nocb_nobypass_count - nocb_nobypass_lim_per_jiffy;
427 if (ULONG_CMP_LT(rdp->nocb_nobypass_count,
428 nocb_nobypass_lim_per_jiffy))
429 c = 0;
430 else if (c > nocb_nobypass_lim_per_jiffy)
431 c = nocb_nobypass_lim_per_jiffy;
432 }
433 WRITE_ONCE(rdp->nocb_nobypass_count, c);
434
435 // If there hasn't yet been all that many ->cblist enqueues
436 // this jiffy, tell the caller to enqueue onto ->cblist. But flush
437 // ->nocb_bypass first.
438 // Lazy CBs throttle this back and do immediate bypass queuing.
439 if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy && !lazy) {
440 rcu_nocb_lock(rdp);
441 *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
442 if (*was_alldone)
443 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
444 TPS("FirstQ"));
445
446 WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j, false));
447 WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
448 return false; // Caller must enqueue the callback.
449 }
450
451 // If ->nocb_bypass has been used too long or is too full,
452 // flush ->nocb_bypass to ->cblist.
453 if ((ncbs && !bypass_is_lazy && j != READ_ONCE(rdp->nocb_bypass_first)) ||
454 (ncbs && bypass_is_lazy &&
455 (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + rcu_get_jiffies_lazy_flush()))) ||
456 ncbs >= qhimark) {
457 rcu_nocb_lock(rdp);
458 *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
459
460 if (!rcu_nocb_flush_bypass(rdp, rhp, j, lazy)) {
461 if (*was_alldone)
462 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
463 TPS("FirstQ"));
464 WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
465 return false; // Caller must enqueue the callback.
466 }
467 if (j != rdp->nocb_gp_adv_time &&
468 rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
469 rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
470 rcu_advance_cbs_nowake(rdp->mynode, rdp);
471 rdp->nocb_gp_adv_time = j;
472 }
473
474 // The flush succeeded and we moved CBs into the regular list.
475 // Don't wait for the wake up timer as it may be too far ahead.
476 // Wake up the GP thread now instead, if the cblist was empty.
477 __call_rcu_nocb_wake(rdp, *was_alldone, flags);
478
479 return true; // Callback already enqueued.
480 }
481
482 // We need to use the bypass.
483 rcu_nocb_bypass_lock(rdp);
484 ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
485 rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
486 rcu_cblist_enqueue(&rdp->nocb_bypass, rhp);
487
488 if (lazy)
489 WRITE_ONCE(rdp->lazy_len, rdp->lazy_len + 1);
490
491 if (!ncbs) {
492 WRITE_ONCE(rdp->nocb_bypass_first, j);
493 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstBQ"));
494 }
495 rcu_nocb_bypass_unlock(rdp);
496
497 // A wake up of the grace period kthread or timer adjustment
498 // needs to be done only if:
499 // 1. Bypass list was fully empty before (this is the first
500 // bypass list entry), or:
501 // 2. Both of these conditions are met:
502 // a. The bypass list previously had only lazy CBs, and:
503 // b. The new CB is non-lazy.
504 if (!ncbs || (bypass_is_lazy && !lazy)) {
505 // No-CBs GP kthread might be indefinitely asleep, if so, wake.
506 rcu_nocb_lock(rdp); // Rare during call_rcu() flood.
507 if (!rcu_segcblist_pend_cbs(&rdp->cblist)) {
508 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
509 TPS("FirstBQwake"));
510 __call_rcu_nocb_wake(rdp, true, flags);
511 } else {
512 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
513 TPS("FirstBQnoWake"));
514 rcu_nocb_unlock(rdp);
515 }
516 }
517 return true; // Callback already enqueued.
518}
519
520/*
521 * Awaken the no-CBs grace-period kthread if needed, either due to it
522 * legitimately being asleep or due to overload conditions.
523 *
524 * If warranted, also wake up the kthread servicing this CPUs queues.
525 */
526static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
527 unsigned long flags)
528 __releases(rdp->nocb_lock)
529{
530 long bypass_len;
531 unsigned long cur_gp_seq;
532 unsigned long j;
533 long lazy_len;
534 long len;
535 struct task_struct *t;
536 struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
537
538 // If we are being polled or there is no kthread, just leave.
539 t = READ_ONCE(rdp->nocb_gp_kthread);
540 if (rcu_nocb_poll || !t) {
541 rcu_nocb_unlock(rdp);
542 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
543 TPS("WakeNotPoll"));
544 return;
545 }
546 // Need to actually to a wakeup.
547 len = rcu_segcblist_n_cbs(&rdp->cblist);
548 bypass_len = rcu_cblist_n_cbs(&rdp->nocb_bypass);
549 lazy_len = READ_ONCE(rdp->lazy_len);
550 if (was_alldone) {
551 rdp->qlen_last_fqs_check = len;
552 // Only lazy CBs in bypass list
553 if (lazy_len && bypass_len == lazy_len) {
554 rcu_nocb_unlock(rdp);
555 wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_LAZY,
556 TPS("WakeLazy"));
557 } else if (!irqs_disabled_flags(flags) && cpu_online(rdp->cpu)) {
558 /* ... if queue was empty ... */
559 rcu_nocb_unlock(rdp);
560 wake_nocb_gp(rdp, false);
561 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
562 TPS("WakeEmpty"));
563 } else {
564 /*
565 * Don't do the wake-up upfront on fragile paths.
566 * Also offline CPUs can't call swake_up_one_online() from
567 * (soft-)IRQs. Rely on the final deferred wake-up from
568 * rcutree_report_cpu_dead()
569 */
570 rcu_nocb_unlock(rdp);
571 wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE,
572 TPS("WakeEmptyIsDeferred"));
573 }
574 } else if (len > rdp->qlen_last_fqs_check + qhimark) {
575 /* ... or if many callbacks queued. */
576 rdp->qlen_last_fqs_check = len;
577 j = jiffies;
578 if (j != rdp->nocb_gp_adv_time &&
579 rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
580 rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
581 rcu_advance_cbs_nowake(rdp->mynode, rdp);
582 rdp->nocb_gp_adv_time = j;
583 }
584 smp_mb(); /* Enqueue before timer_pending(). */
585 if ((rdp->nocb_cb_sleep ||
586 !rcu_segcblist_ready_cbs(&rdp->cblist)) &&
587 !timer_pending(&rdp_gp->nocb_timer)) {
588 rcu_nocb_unlock(rdp);
589 wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
590 TPS("WakeOvfIsDeferred"));
591 } else {
592 rcu_nocb_unlock(rdp);
593 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
594 }
595 } else {
596 rcu_nocb_unlock(rdp);
597 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
598 }
599}
600
601static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head,
602 rcu_callback_t func, unsigned long flags, bool lazy)
603{
604 bool was_alldone;
605
606 if (!rcu_nocb_try_bypass(rdp, head, &was_alldone, flags, lazy)) {
607 /* Not enqueued on bypass but locked, do regular enqueue */
608 rcutree_enqueue(rdp, head, func);
609 __call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
610 }
611}
612
613static void nocb_gp_toggle_rdp(struct rcu_data *rdp_gp, struct rcu_data *rdp)
614{
615 struct rcu_segcblist *cblist = &rdp->cblist;
616 unsigned long flags;
617
618 /*
619 * Locking orders future de-offloaded callbacks enqueue against previous
620 * handling of this rdp. Ie: Make sure rcuog is done with this rdp before
621 * deoffloaded callbacks can be enqueued.
622 */
623 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
624 if (!rcu_segcblist_test_flags(cblist, SEGCBLIST_OFFLOADED)) {
625 /*
626 * Offloading. Set our flag and notify the offload worker.
627 * We will handle this rdp until it ever gets de-offloaded.
628 */
629 list_add_tail(&rdp->nocb_entry_rdp, &rdp_gp->nocb_head_rdp);
630 rcu_segcblist_set_flags(cblist, SEGCBLIST_OFFLOADED);
631 } else {
632 /*
633 * De-offloading. Clear our flag and notify the de-offload worker.
634 * We will ignore this rdp until it ever gets re-offloaded.
635 */
636 list_del(&rdp->nocb_entry_rdp);
637 rcu_segcblist_clear_flags(cblist, SEGCBLIST_OFFLOADED);
638 }
639 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
640}
641
642static void nocb_gp_sleep(struct rcu_data *my_rdp, int cpu)
643{
644 trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
645 swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq,
646 !READ_ONCE(my_rdp->nocb_gp_sleep));
647 trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep"));
648}
649
650/*
651 * No-CBs GP kthreads come here to wait for additional callbacks to show up
652 * or for grace periods to end.
653 */
654static void nocb_gp_wait(struct rcu_data *my_rdp)
655{
656 bool bypass = false;
657 int __maybe_unused cpu = my_rdp->cpu;
658 unsigned long cur_gp_seq;
659 unsigned long flags;
660 bool gotcbs = false;
661 unsigned long j = jiffies;
662 bool lazy = false;
663 bool needwait_gp = false; // This prevents actual uninitialized use.
664 bool needwake;
665 bool needwake_gp;
666 struct rcu_data *rdp, *rdp_toggling = NULL;
667 struct rcu_node *rnp;
668 unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning.
669 bool wasempty = false;
670
671 /*
672 * Each pass through the following loop checks for CBs and for the
673 * nearest grace period (if any) to wait for next. The CB kthreads
674 * and the global grace-period kthread are awakened if needed.
675 */
676 WARN_ON_ONCE(my_rdp->nocb_gp_rdp != my_rdp);
677 /*
678 * An rcu_data structure is removed from the list after its
679 * CPU is de-offloaded and added to the list before that CPU is
680 * (re-)offloaded. If the following loop happens to be referencing
681 * that rcu_data structure during the time that the corresponding
682 * CPU is de-offloaded and then immediately re-offloaded, this
683 * loop's rdp pointer will be carried to the end of the list by
684 * the resulting pair of list operations. This can cause the loop
685 * to skip over some of the rcu_data structures that were supposed
686 * to have been scanned. Fortunately a new iteration through the
687 * entire loop is forced after a given CPU's rcu_data structure
688 * is added to the list, so the skipped-over rcu_data structures
689 * won't be ignored for long.
690 */
691 list_for_each_entry(rdp, &my_rdp->nocb_head_rdp, nocb_entry_rdp) {
692 long bypass_ncbs;
693 bool flush_bypass = false;
694 long lazy_ncbs;
695
696 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check"));
697 rcu_nocb_lock_irqsave(rdp, flags);
698 lockdep_assert_held(&rdp->nocb_lock);
699 bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
700 lazy_ncbs = READ_ONCE(rdp->lazy_len);
701
702 if (bypass_ncbs && (lazy_ncbs == bypass_ncbs) &&
703 (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + rcu_get_jiffies_lazy_flush()) ||
704 bypass_ncbs > 2 * qhimark)) {
705 flush_bypass = true;
706 } else if (bypass_ncbs && (lazy_ncbs != bypass_ncbs) &&
707 (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) ||
708 bypass_ncbs > 2 * qhimark)) {
709 flush_bypass = true;
710 } else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) {
711 rcu_nocb_unlock_irqrestore(rdp, flags);
712 continue; /* No callbacks here, try next. */
713 }
714
715 if (flush_bypass) {
716 // Bypass full or old, so flush it.
717 (void)rcu_nocb_try_flush_bypass(rdp, j);
718 bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
719 lazy_ncbs = READ_ONCE(rdp->lazy_len);
720 }
721
722 if (bypass_ncbs) {
723 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
724 bypass_ncbs == lazy_ncbs ? TPS("Lazy") : TPS("Bypass"));
725 if (bypass_ncbs == lazy_ncbs)
726 lazy = true;
727 else
728 bypass = true;
729 }
730 rnp = rdp->mynode;
731
732 // Advance callbacks if helpful and low contention.
733 needwake_gp = false;
734 if (!rcu_segcblist_restempty(&rdp->cblist,
735 RCU_NEXT_READY_TAIL) ||
736 (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
737 rcu_seq_done(&rnp->gp_seq, cur_gp_seq))) {
738 raw_spin_lock_rcu_node(rnp); /* irqs disabled. */
739 needwake_gp = rcu_advance_cbs(rnp, rdp);
740 wasempty = rcu_segcblist_restempty(&rdp->cblist,
741 RCU_NEXT_READY_TAIL);
742 raw_spin_unlock_rcu_node(rnp); /* irqs disabled. */
743 }
744 // Need to wait on some grace period?
745 WARN_ON_ONCE(wasempty &&
746 !rcu_segcblist_restempty(&rdp->cblist,
747 RCU_NEXT_READY_TAIL));
748 if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq)) {
749 if (!needwait_gp ||
750 ULONG_CMP_LT(cur_gp_seq, wait_gp_seq))
751 wait_gp_seq = cur_gp_seq;
752 needwait_gp = true;
753 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
754 TPS("NeedWaitGP"));
755 }
756 if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
757 needwake = rdp->nocb_cb_sleep;
758 WRITE_ONCE(rdp->nocb_cb_sleep, false);
759 } else {
760 needwake = false;
761 }
762 rcu_nocb_unlock_irqrestore(rdp, flags);
763 if (needwake) {
764 swake_up_one(&rdp->nocb_cb_wq);
765 gotcbs = true;
766 }
767 if (needwake_gp)
768 rcu_gp_kthread_wake();
769 }
770
771 my_rdp->nocb_gp_bypass = bypass;
772 my_rdp->nocb_gp_gp = needwait_gp;
773 my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;
774
775 // At least one child with non-empty ->nocb_bypass, so set
776 // timer in order to avoid stranding its callbacks.
777 if (!rcu_nocb_poll) {
778 // If bypass list only has lazy CBs. Add a deferred lazy wake up.
779 if (lazy && !bypass) {
780 wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_LAZY,
781 TPS("WakeLazyIsDeferred"));
782 // Otherwise add a deferred bypass wake up.
783 } else if (bypass) {
784 wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_BYPASS,
785 TPS("WakeBypassIsDeferred"));
786 }
787 }
788
789 if (rcu_nocb_poll) {
790 /* Polling, so trace if first poll in the series. */
791 if (gotcbs)
792 trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
793 if (list_empty(&my_rdp->nocb_head_rdp)) {
794 raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
795 if (!my_rdp->nocb_toggling_rdp)
796 WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
797 raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
798 /* Wait for any offloading rdp */
799 nocb_gp_sleep(my_rdp, cpu);
800 } else {
801 schedule_timeout_idle(1);
802 }
803 } else if (!needwait_gp) {
804 /* Wait for callbacks to appear. */
805 nocb_gp_sleep(my_rdp, cpu);
806 } else {
807 rnp = my_rdp->mynode;
808 trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("StartWait"));
809 swait_event_interruptible_exclusive(
810 rnp->nocb_gp_wq[rcu_seq_ctr(wait_gp_seq) & 0x1],
811 rcu_seq_done(&rnp->gp_seq, wait_gp_seq) ||
812 !READ_ONCE(my_rdp->nocb_gp_sleep));
813 trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("EndWait"));
814 }
815
816 if (!rcu_nocb_poll) {
817 raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
818 // (De-)queue an rdp to/from the group if its nocb state is changing
819 rdp_toggling = my_rdp->nocb_toggling_rdp;
820 if (rdp_toggling)
821 my_rdp->nocb_toggling_rdp = NULL;
822
823 if (my_rdp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) {
824 WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
825 del_timer(&my_rdp->nocb_timer);
826 }
827 WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
828 raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
829 } else {
830 rdp_toggling = READ_ONCE(my_rdp->nocb_toggling_rdp);
831 if (rdp_toggling) {
832 /*
833 * Paranoid locking to make sure nocb_toggling_rdp is well
834 * reset *before* we (re)set SEGCBLIST_KTHREAD_GP or we could
835 * race with another round of nocb toggling for this rdp.
836 * Nocb locking should prevent from that already but we stick
837 * to paranoia, especially in rare path.
838 */
839 raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
840 my_rdp->nocb_toggling_rdp = NULL;
841 raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
842 }
843 }
844
845 if (rdp_toggling) {
846 nocb_gp_toggle_rdp(my_rdp, rdp_toggling);
847 swake_up_one(&rdp_toggling->nocb_state_wq);
848 }
849
850 my_rdp->nocb_gp_seq = -1;
851 WARN_ON(signal_pending(current));
852}
853
854/*
855 * No-CBs grace-period-wait kthread. There is one of these per group
856 * of CPUs, but only once at least one CPU in that group has come online
857 * at least once since boot. This kthread checks for newly posted
858 * callbacks from any of the CPUs it is responsible for, waits for a
859 * grace period, then awakens all of the rcu_nocb_cb_kthread() instances
860 * that then have callback-invocation work to do.
861 */
862static int rcu_nocb_gp_kthread(void *arg)
863{
864 struct rcu_data *rdp = arg;
865
866 for (;;) {
867 WRITE_ONCE(rdp->nocb_gp_loops, rdp->nocb_gp_loops + 1);
868 nocb_gp_wait(rdp);
869 cond_resched_tasks_rcu_qs();
870 }
871 return 0;
872}
873
874static inline bool nocb_cb_wait_cond(struct rcu_data *rdp)
875{
876 return !READ_ONCE(rdp->nocb_cb_sleep) || kthread_should_park();
877}
878
879/*
880 * Invoke any ready callbacks from the corresponding no-CBs CPU,
881 * then, if there are no more, wait for more to appear.
882 */
883static void nocb_cb_wait(struct rcu_data *rdp)
884{
885 struct rcu_segcblist *cblist = &rdp->cblist;
886 unsigned long cur_gp_seq;
887 unsigned long flags;
888 bool needwake_gp = false;
889 struct rcu_node *rnp = rdp->mynode;
890
891 swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
892 nocb_cb_wait_cond(rdp));
893 if (kthread_should_park()) {
894 /*
895 * kthread_park() must be preceded by an rcu_barrier().
896 * But yet another rcu_barrier() might have sneaked in between
897 * the barrier callback execution and the callbacks counter
898 * decrement.
899 */
900 if (rdp->nocb_cb_sleep) {
901 rcu_nocb_lock_irqsave(rdp, flags);
902 WARN_ON_ONCE(rcu_segcblist_n_cbs(&rdp->cblist));
903 rcu_nocb_unlock_irqrestore(rdp, flags);
904 kthread_parkme();
905 }
906 } else if (READ_ONCE(rdp->nocb_cb_sleep)) {
907 WARN_ON(signal_pending(current));
908 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty"));
909 }
910
911 WARN_ON_ONCE(!rcu_rdp_is_offloaded(rdp));
912
913 local_irq_save(flags);
914 rcu_momentary_eqs();
915 local_irq_restore(flags);
916 /*
917 * Disable BH to provide the expected environment. Also, when
918 * transitioning to/from NOCB mode, a self-requeuing callback might
919 * be invoked from softirq. A short grace period could cause both
920 * instances of this callback would execute concurrently.
921 */
922 local_bh_disable();
923 rcu_do_batch(rdp);
924 local_bh_enable();
925 lockdep_assert_irqs_enabled();
926 rcu_nocb_lock_irqsave(rdp, flags);
927 if (rcu_segcblist_nextgp(cblist, &cur_gp_seq) &&
928 rcu_seq_done(&rnp->gp_seq, cur_gp_seq) &&
929 raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */
930 needwake_gp = rcu_advance_cbs(rdp->mynode, rdp);
931 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
932 }
933
934 if (!rcu_segcblist_ready_cbs(cblist)) {
935 WRITE_ONCE(rdp->nocb_cb_sleep, true);
936 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("CBSleep"));
937 } else {
938 WRITE_ONCE(rdp->nocb_cb_sleep, false);
939 }
940
941 rcu_nocb_unlock_irqrestore(rdp, flags);
942 if (needwake_gp)
943 rcu_gp_kthread_wake();
944}
945
946/*
947 * Per-rcu_data kthread, but only for no-CBs CPUs. Repeatedly invoke
948 * nocb_cb_wait() to do the dirty work.
949 */
950static int rcu_nocb_cb_kthread(void *arg)
951{
952 struct rcu_data *rdp = arg;
953
954 // Each pass through this loop does one callback batch, and,
955 // if there are no more ready callbacks, waits for them.
956 for (;;) {
957 nocb_cb_wait(rdp);
958 cond_resched_tasks_rcu_qs();
959 }
960 return 0;
961}
962
963/* Is a deferred wakeup of rcu_nocb_kthread() required? */
964static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level)
965{
966 return READ_ONCE(rdp->nocb_defer_wakeup) >= level;
967}
968
969/* Do a deferred wakeup of rcu_nocb_kthread(). */
970static bool do_nocb_deferred_wakeup_common(struct rcu_data *rdp_gp,
971 struct rcu_data *rdp, int level,
972 unsigned long flags)
973 __releases(rdp_gp->nocb_gp_lock)
974{
975 int ndw;
976 int ret;
977
978 if (!rcu_nocb_need_deferred_wakeup(rdp_gp, level)) {
979 raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
980 return false;
981 }
982
983 ndw = rdp_gp->nocb_defer_wakeup;
984 ret = __wake_nocb_gp(rdp_gp, rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
985 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DeferredWake"));
986
987 return ret;
988}
989
990/* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
991static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
992{
993 unsigned long flags;
994 struct rcu_data *rdp = from_timer(rdp, t, nocb_timer);
995
996 WARN_ON_ONCE(rdp->nocb_gp_rdp != rdp);
997 trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Timer"));
998
999 raw_spin_lock_irqsave(&rdp->nocb_gp_lock, flags);
1000 smp_mb__after_spinlock(); /* Timer expire before wakeup. */
1001 do_nocb_deferred_wakeup_common(rdp, rdp, RCU_NOCB_WAKE_BYPASS, flags);
1002}
1003
1004/*
1005 * Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
1006 * This means we do an inexact common-case check. Note that if
1007 * we miss, ->nocb_timer will eventually clean things up.
1008 */
1009static bool do_nocb_deferred_wakeup(struct rcu_data *rdp)
1010{
1011 unsigned long flags;
1012 struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
1013
1014 if (!rdp_gp || !rcu_nocb_need_deferred_wakeup(rdp_gp, RCU_NOCB_WAKE))
1015 return false;
1016
1017 raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
1018 return do_nocb_deferred_wakeup_common(rdp_gp, rdp, RCU_NOCB_WAKE, flags);
1019}
1020
1021void rcu_nocb_flush_deferred_wakeup(void)
1022{
1023 do_nocb_deferred_wakeup(this_cpu_ptr(&rcu_data));
1024}
1025EXPORT_SYMBOL_GPL(rcu_nocb_flush_deferred_wakeup);
1026
1027static int rcu_nocb_queue_toggle_rdp(struct rcu_data *rdp)
1028{
1029 struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
1030 bool wake_gp = false;
1031 unsigned long flags;
1032
1033 raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
1034 // Queue this rdp for add/del to/from the list to iterate on rcuog
1035 WRITE_ONCE(rdp_gp->nocb_toggling_rdp, rdp);
1036 if (rdp_gp->nocb_gp_sleep) {
1037 rdp_gp->nocb_gp_sleep = false;
1038 wake_gp = true;
1039 }
1040 raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
1041
1042 return wake_gp;
1043}
1044
1045static bool rcu_nocb_rdp_deoffload_wait_cond(struct rcu_data *rdp)
1046{
1047 unsigned long flags;
1048 bool ret;
1049
1050 /*
1051 * Locking makes sure rcuog is done handling this rdp before deoffloaded
1052 * enqueue can happen. Also it keeps the SEGCBLIST_OFFLOADED flag stable
1053 * while the ->nocb_lock is held.
1054 */
1055 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
1056 ret = !rcu_segcblist_test_flags(&rdp->cblist, SEGCBLIST_OFFLOADED);
1057 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1058
1059 return ret;
1060}
1061
1062static int rcu_nocb_rdp_deoffload(struct rcu_data *rdp)
1063{
1064 unsigned long flags;
1065 int wake_gp;
1066 struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
1067
1068 /* CPU must be offline, unless it's early boot */
1069 WARN_ON_ONCE(cpu_online(rdp->cpu) && rdp->cpu != raw_smp_processor_id());
1070
1071 pr_info("De-offloading %d\n", rdp->cpu);
1072
1073 /* Flush all callbacks from segcblist and bypass */
1074 rcu_barrier();
1075
1076 /*
1077 * Make sure the rcuoc kthread isn't in the middle of a nocb locked
1078 * sequence while offloading is deactivated, along with nocb locking.
1079 */
1080 if (rdp->nocb_cb_kthread)
1081 kthread_park(rdp->nocb_cb_kthread);
1082
1083 rcu_nocb_lock_irqsave(rdp, flags);
1084 WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
1085 WARN_ON_ONCE(rcu_segcblist_n_cbs(&rdp->cblist));
1086 rcu_nocb_unlock_irqrestore(rdp, flags);
1087
1088 wake_gp = rcu_nocb_queue_toggle_rdp(rdp);
1089
1090 mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
1091
1092 if (rdp_gp->nocb_gp_kthread) {
1093 if (wake_gp)
1094 wake_up_process(rdp_gp->nocb_gp_kthread);
1095
1096 swait_event_exclusive(rdp->nocb_state_wq,
1097 rcu_nocb_rdp_deoffload_wait_cond(rdp));
1098 } else {
1099 /*
1100 * No kthread to clear the flags for us or remove the rdp from the nocb list
1101 * to iterate. Do it here instead. Locking doesn't look stricly necessary
1102 * but we stick to paranoia in this rare path.
1103 */
1104 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
1105 rcu_segcblist_clear_flags(&rdp->cblist, SEGCBLIST_OFFLOADED);
1106 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1107
1108 list_del(&rdp->nocb_entry_rdp);
1109 }
1110
1111 mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex);
1112
1113 return 0;
1114}
1115
1116int rcu_nocb_cpu_deoffload(int cpu)
1117{
1118 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
1119 int ret = 0;
1120
1121 cpus_read_lock();
1122 mutex_lock(&rcu_state.nocb_mutex);
1123 if (rcu_rdp_is_offloaded(rdp)) {
1124 if (!cpu_online(cpu)) {
1125 ret = rcu_nocb_rdp_deoffload(rdp);
1126 if (!ret)
1127 cpumask_clear_cpu(cpu, rcu_nocb_mask);
1128 } else {
1129 pr_info("NOCB: Cannot CB-deoffload online CPU %d\n", rdp->cpu);
1130 ret = -EINVAL;
1131 }
1132 }
1133 mutex_unlock(&rcu_state.nocb_mutex);
1134 cpus_read_unlock();
1135
1136 return ret;
1137}
1138EXPORT_SYMBOL_GPL(rcu_nocb_cpu_deoffload);
1139
1140static bool rcu_nocb_rdp_offload_wait_cond(struct rcu_data *rdp)
1141{
1142 unsigned long flags;
1143 bool ret;
1144
1145 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
1146 ret = rcu_segcblist_test_flags(&rdp->cblist, SEGCBLIST_OFFLOADED);
1147 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1148
1149 return ret;
1150}
1151
1152static int rcu_nocb_rdp_offload(struct rcu_data *rdp)
1153{
1154 int wake_gp;
1155 struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
1156
1157 WARN_ON_ONCE(cpu_online(rdp->cpu));
1158 /*
1159 * For now we only support re-offload, ie: the rdp must have been
1160 * offloaded on boot first.
1161 */
1162 if (!rdp->nocb_gp_rdp)
1163 return -EINVAL;
1164
1165 if (WARN_ON_ONCE(!rdp_gp->nocb_gp_kthread))
1166 return -EINVAL;
1167
1168 pr_info("Offloading %d\n", rdp->cpu);
1169
1170 WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
1171 WARN_ON_ONCE(rcu_segcblist_n_cbs(&rdp->cblist));
1172
1173 wake_gp = rcu_nocb_queue_toggle_rdp(rdp);
1174 if (wake_gp)
1175 wake_up_process(rdp_gp->nocb_gp_kthread);
1176
1177 swait_event_exclusive(rdp->nocb_state_wq,
1178 rcu_nocb_rdp_offload_wait_cond(rdp));
1179
1180 kthread_unpark(rdp->nocb_cb_kthread);
1181
1182 return 0;
1183}
1184
1185int rcu_nocb_cpu_offload(int cpu)
1186{
1187 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
1188 int ret = 0;
1189
1190 cpus_read_lock();
1191 mutex_lock(&rcu_state.nocb_mutex);
1192 if (!rcu_rdp_is_offloaded(rdp)) {
1193 if (!cpu_online(cpu)) {
1194 ret = rcu_nocb_rdp_offload(rdp);
1195 if (!ret)
1196 cpumask_set_cpu(cpu, rcu_nocb_mask);
1197 } else {
1198 pr_info("NOCB: Cannot CB-offload online CPU %d\n", rdp->cpu);
1199 ret = -EINVAL;
1200 }
1201 }
1202 mutex_unlock(&rcu_state.nocb_mutex);
1203 cpus_read_unlock();
1204
1205 return ret;
1206}
1207EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
1208
1209#ifdef CONFIG_RCU_LAZY
1210static unsigned long
1211lazy_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
1212{
1213 int cpu;
1214 unsigned long count = 0;
1215
1216 if (WARN_ON_ONCE(!cpumask_available(rcu_nocb_mask)))
1217 return 0;
1218
1219 /* Protect rcu_nocb_mask against concurrent (de-)offloading. */
1220 if (!mutex_trylock(&rcu_state.nocb_mutex))
1221 return 0;
1222
1223 /* Snapshot count of all CPUs */
1224 for_each_cpu(cpu, rcu_nocb_mask) {
1225 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
1226
1227 count += READ_ONCE(rdp->lazy_len);
1228 }
1229
1230 mutex_unlock(&rcu_state.nocb_mutex);
1231
1232 return count ? count : SHRINK_EMPTY;
1233}
1234
1235static unsigned long
1236lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
1237{
1238 int cpu;
1239 unsigned long flags;
1240 unsigned long count = 0;
1241
1242 if (WARN_ON_ONCE(!cpumask_available(rcu_nocb_mask)))
1243 return 0;
1244 /*
1245 * Protect against concurrent (de-)offloading. Otherwise nocb locking
1246 * may be ignored or imbalanced.
1247 */
1248 if (!mutex_trylock(&rcu_state.nocb_mutex)) {
1249 /*
1250 * But really don't insist if nocb_mutex is contended since we
1251 * can't guarantee that it will never engage in a dependency
1252 * chain involving memory allocation. The lock is seldom contended
1253 * anyway.
1254 */
1255 return 0;
1256 }
1257
1258 /* Snapshot count of all CPUs */
1259 for_each_cpu(cpu, rcu_nocb_mask) {
1260 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
1261 int _count;
1262
1263 if (WARN_ON_ONCE(!rcu_rdp_is_offloaded(rdp)))
1264 continue;
1265
1266 if (!READ_ONCE(rdp->lazy_len))
1267 continue;
1268
1269 rcu_nocb_lock_irqsave(rdp, flags);
1270 /*
1271 * Recheck under the nocb lock. Since we are not holding the bypass
1272 * lock we may still race with increments from the enqueuer but still
1273 * we know for sure if there is at least one lazy callback.
1274 */
1275 _count = READ_ONCE(rdp->lazy_len);
1276 if (!_count) {
1277 rcu_nocb_unlock_irqrestore(rdp, flags);
1278 continue;
1279 }
1280 rcu_nocb_try_flush_bypass(rdp, jiffies);
1281 rcu_nocb_unlock_irqrestore(rdp, flags);
1282 wake_nocb_gp(rdp, false);
1283 sc->nr_to_scan -= _count;
1284 count += _count;
1285 if (sc->nr_to_scan <= 0)
1286 break;
1287 }
1288
1289 mutex_unlock(&rcu_state.nocb_mutex);
1290
1291 return count ? count : SHRINK_STOP;
1292}
1293#endif // #ifdef CONFIG_RCU_LAZY
1294
1295void __init rcu_init_nohz(void)
1296{
1297 int cpu;
1298 struct rcu_data *rdp;
1299 const struct cpumask *cpumask = NULL;
1300 struct shrinker * __maybe_unused lazy_rcu_shrinker;
1301
1302#if defined(CONFIG_NO_HZ_FULL)
1303 if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
1304 cpumask = tick_nohz_full_mask;
1305#endif
1306
1307 if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) &&
1308 !rcu_state.nocb_is_setup && !cpumask)
1309 cpumask = cpu_possible_mask;
1310
1311 if (cpumask) {
1312 if (!cpumask_available(rcu_nocb_mask)) {
1313 if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
1314 pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
1315 return;
1316 }
1317 }
1318
1319 cpumask_or(rcu_nocb_mask, rcu_nocb_mask, cpumask);
1320 rcu_state.nocb_is_setup = true;
1321 }
1322
1323 if (!rcu_state.nocb_is_setup)
1324 return;
1325
1326#ifdef CONFIG_RCU_LAZY
1327 lazy_rcu_shrinker = shrinker_alloc(0, "rcu-lazy");
1328 if (!lazy_rcu_shrinker) {
1329 pr_err("Failed to allocate lazy_rcu shrinker!\n");
1330 } else {
1331 lazy_rcu_shrinker->count_objects = lazy_rcu_shrink_count;
1332 lazy_rcu_shrinker->scan_objects = lazy_rcu_shrink_scan;
1333
1334 shrinker_register(lazy_rcu_shrinker);
1335 }
1336#endif // #ifdef CONFIG_RCU_LAZY
1337
1338 if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
1339 pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
1340 cpumask_and(rcu_nocb_mask, cpu_possible_mask,
1341 rcu_nocb_mask);
1342 }
1343 if (cpumask_empty(rcu_nocb_mask))
1344 pr_info("\tOffload RCU callbacks from CPUs: (none).\n");
1345 else
1346 pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
1347 cpumask_pr_args(rcu_nocb_mask));
1348 if (rcu_nocb_poll)
1349 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
1350
1351 for_each_cpu(cpu, rcu_nocb_mask) {
1352 rdp = per_cpu_ptr(&rcu_data, cpu);
1353 if (rcu_segcblist_empty(&rdp->cblist))
1354 rcu_segcblist_init(&rdp->cblist);
1355 rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_OFFLOADED);
1356 }
1357 rcu_organize_nocb_kthreads();
1358}
1359
1360/* Initialize per-rcu_data variables for no-CBs CPUs. */
1361static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
1362{
1363 init_swait_queue_head(&rdp->nocb_cb_wq);
1364 init_swait_queue_head(&rdp->nocb_gp_wq);
1365 init_swait_queue_head(&rdp->nocb_state_wq);
1366 raw_spin_lock_init(&rdp->nocb_lock);
1367 raw_spin_lock_init(&rdp->nocb_bypass_lock);
1368 raw_spin_lock_init(&rdp->nocb_gp_lock);
1369 timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
1370 rcu_cblist_init(&rdp->nocb_bypass);
1371 WRITE_ONCE(rdp->lazy_len, 0);
1372 mutex_init(&rdp->nocb_gp_kthread_mutex);
1373}
1374
1375/*
1376 * If the specified CPU is a no-CBs CPU that does not already have its
1377 * rcuo CB kthread, spawn it. Additionally, if the rcuo GP kthread
1378 * for this CPU's group has not yet been created, spawn it as well.
1379 */
1380static void rcu_spawn_cpu_nocb_kthread(int cpu)
1381{
1382 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
1383 struct rcu_data *rdp_gp;
1384 struct task_struct *t;
1385 struct sched_param sp;
1386
1387 if (!rcu_scheduler_fully_active || !rcu_state.nocb_is_setup)
1388 return;
1389
1390 /* If there already is an rcuo kthread, then nothing to do. */
1391 if (rdp->nocb_cb_kthread)
1392 return;
1393
1394 /* If we didn't spawn the GP kthread first, reorganize! */
1395 sp.sched_priority = kthread_prio;
1396 rdp_gp = rdp->nocb_gp_rdp;
1397 mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
1398 if (!rdp_gp->nocb_gp_kthread) {
1399 t = kthread_run(rcu_nocb_gp_kthread, rdp_gp,
1400 "rcuog/%d", rdp_gp->cpu);
1401 if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__)) {
1402 mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex);
1403 goto err;
1404 }
1405 WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);
1406 if (kthread_prio)
1407 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1408 }
1409 mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex);
1410
1411 /* Spawn the kthread for this CPU. */
1412 t = kthread_create(rcu_nocb_cb_kthread, rdp,
1413 "rcuo%c/%d", rcu_state.abbr, cpu);
1414 if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__))
1415 goto err;
1416
1417 if (rcu_rdp_is_offloaded(rdp))
1418 wake_up_process(t);
1419 else
1420 kthread_park(t);
1421
1422 if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_CB_BOOST) && kthread_prio)
1423 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1424
1425 WRITE_ONCE(rdp->nocb_cb_kthread, t);
1426 WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread);
1427 return;
1428
1429err:
1430 /*
1431 * No need to protect against concurrent rcu_barrier()
1432 * because the number of callbacks should be 0 for a non-boot CPU,
1433 * therefore rcu_barrier() shouldn't even try to grab the nocb_lock.
1434 * But hold nocb_mutex to avoid nocb_lock imbalance from shrinker.
1435 */
1436 WARN_ON_ONCE(system_state > SYSTEM_BOOTING && rcu_segcblist_n_cbs(&rdp->cblist));
1437 mutex_lock(&rcu_state.nocb_mutex);
1438 if (rcu_rdp_is_offloaded(rdp)) {
1439 rcu_nocb_rdp_deoffload(rdp);
1440 cpumask_clear_cpu(cpu, rcu_nocb_mask);
1441 }
1442 mutex_unlock(&rcu_state.nocb_mutex);
1443}
1444
1445/* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */
1446static int rcu_nocb_gp_stride = -1;
1447module_param(rcu_nocb_gp_stride, int, 0444);
1448
1449/*
1450 * Initialize GP-CB relationships for all no-CBs CPU.
1451 */
1452static void __init rcu_organize_nocb_kthreads(void)
1453{
1454 int cpu;
1455 bool firsttime = true;
1456 bool gotnocbs = false;
1457 bool gotnocbscbs = true;
1458 int ls = rcu_nocb_gp_stride;
1459 int nl = 0; /* Next GP kthread. */
1460 struct rcu_data *rdp;
1461 struct rcu_data *rdp_gp = NULL; /* Suppress misguided gcc warn. */
1462
1463 if (!cpumask_available(rcu_nocb_mask))
1464 return;
1465 if (ls == -1) {
1466 ls = nr_cpu_ids / int_sqrt(nr_cpu_ids);
1467 rcu_nocb_gp_stride = ls;
1468 }
1469
1470 /*
1471 * Each pass through this loop sets up one rcu_data structure.
1472 * Should the corresponding CPU come online in the future, then
1473 * we will spawn the needed set of rcu_nocb_kthread() kthreads.
1474 */
1475 for_each_possible_cpu(cpu) {
1476 rdp = per_cpu_ptr(&rcu_data, cpu);
1477 if (rdp->cpu >= nl) {
1478 /* New GP kthread, set up for CBs & next GP. */
1479 gotnocbs = true;
1480 nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
1481 rdp_gp = rdp;
1482 INIT_LIST_HEAD(&rdp->nocb_head_rdp);
1483 if (dump_tree) {
1484 if (!firsttime)
1485 pr_cont("%s\n", gotnocbscbs
1486 ? "" : " (self only)");
1487 gotnocbscbs = false;
1488 firsttime = false;
1489 pr_alert("%s: No-CB GP kthread CPU %d:",
1490 __func__, cpu);
1491 }
1492 } else {
1493 /* Another CB kthread, link to previous GP kthread. */
1494 gotnocbscbs = true;
1495 if (dump_tree)
1496 pr_cont(" %d", cpu);
1497 }
1498 rdp->nocb_gp_rdp = rdp_gp;
1499 if (cpumask_test_cpu(cpu, rcu_nocb_mask))
1500 list_add_tail(&rdp->nocb_entry_rdp, &rdp_gp->nocb_head_rdp);
1501 }
1502 if (gotnocbs && dump_tree)
1503 pr_cont("%s\n", gotnocbscbs ? "" : " (self only)");
1504}
1505
1506/*
1507 * Bind the current task to the offloaded CPUs. If there are no offloaded
1508 * CPUs, leave the task unbound. Splat if the bind attempt fails.
1509 */
1510void rcu_bind_current_to_nocb(void)
1511{
1512 if (cpumask_available(rcu_nocb_mask) && !cpumask_empty(rcu_nocb_mask))
1513 WARN_ON(sched_setaffinity(current->pid, rcu_nocb_mask));
1514}
1515EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb);
1516
1517// The ->on_cpu field is available only in CONFIG_SMP=y, so...
1518#ifdef CONFIG_SMP
1519static char *show_rcu_should_be_on_cpu(struct task_struct *tsp)
1520{
1521 return tsp && task_is_running(tsp) && !tsp->on_cpu ? "!" : "";
1522}
1523#else // #ifdef CONFIG_SMP
1524static char *show_rcu_should_be_on_cpu(struct task_struct *tsp)
1525{
1526 return "";
1527}
1528#endif // #else #ifdef CONFIG_SMP
1529
1530/*
1531 * Dump out nocb grace-period kthread state for the specified rcu_data
1532 * structure.
1533 */
1534static void show_rcu_nocb_gp_state(struct rcu_data *rdp)
1535{
1536 struct rcu_node *rnp = rdp->mynode;
1537
1538 pr_info("nocb GP %d %c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu %c CPU %d%s\n",
1539 rdp->cpu,
1540 "kK"[!!rdp->nocb_gp_kthread],
1541 "lL"[raw_spin_is_locked(&rdp->nocb_gp_lock)],
1542 "dD"[!!rdp->nocb_defer_wakeup],
1543 "tT"[timer_pending(&rdp->nocb_timer)],
1544 "sS"[!!rdp->nocb_gp_sleep],
1545 ".W"[swait_active(&rdp->nocb_gp_wq)],
1546 ".W"[swait_active(&rnp->nocb_gp_wq[0])],
1547 ".W"[swait_active(&rnp->nocb_gp_wq[1])],
1548 ".B"[!!rdp->nocb_gp_bypass],
1549 ".G"[!!rdp->nocb_gp_gp],
1550 (long)rdp->nocb_gp_seq,
1551 rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops),
1552 rdp->nocb_gp_kthread ? task_state_to_char(rdp->nocb_gp_kthread) : '.',
1553 rdp->nocb_gp_kthread ? (int)task_cpu(rdp->nocb_gp_kthread) : -1,
1554 show_rcu_should_be_on_cpu(rdp->nocb_gp_kthread));
1555}
1556
1557/* Dump out nocb kthread state for the specified rcu_data structure. */
1558static void show_rcu_nocb_state(struct rcu_data *rdp)
1559{
1560 char bufw[20];
1561 char bufr[20];
1562 struct rcu_data *nocb_next_rdp;
1563 struct rcu_segcblist *rsclp = &rdp->cblist;
1564 bool waslocked;
1565 bool wassleep;
1566
1567 if (rdp->nocb_gp_rdp == rdp)
1568 show_rcu_nocb_gp_state(rdp);
1569
1570 nocb_next_rdp = list_next_or_null_rcu(&rdp->nocb_gp_rdp->nocb_head_rdp,
1571 &rdp->nocb_entry_rdp,
1572 typeof(*rdp),
1573 nocb_entry_rdp);
1574
1575 sprintf(bufw, "%ld", rsclp->gp_seq[RCU_WAIT_TAIL]);
1576 sprintf(bufr, "%ld", rsclp->gp_seq[RCU_NEXT_READY_TAIL]);
1577 pr_info(" CB %d^%d->%d %c%c%c%c%c F%ld L%ld C%d %c%c%s%c%s%c%c q%ld %c CPU %d%s\n",
1578 rdp->cpu, rdp->nocb_gp_rdp->cpu,
1579 nocb_next_rdp ? nocb_next_rdp->cpu : -1,
1580 "kK"[!!rdp->nocb_cb_kthread],
1581 "bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)],
1582 "lL"[raw_spin_is_locked(&rdp->nocb_lock)],
1583 "sS"[!!rdp->nocb_cb_sleep],
1584 ".W"[swait_active(&rdp->nocb_cb_wq)],
1585 jiffies - rdp->nocb_bypass_first,
1586 jiffies - rdp->nocb_nobypass_last,
1587 rdp->nocb_nobypass_count,
1588 ".D"[rcu_segcblist_ready_cbs(rsclp)],
1589 ".W"[!rcu_segcblist_segempty(rsclp, RCU_WAIT_TAIL)],
1590 rcu_segcblist_segempty(rsclp, RCU_WAIT_TAIL) ? "" : bufw,
1591 ".R"[!rcu_segcblist_segempty(rsclp, RCU_NEXT_READY_TAIL)],
1592 rcu_segcblist_segempty(rsclp, RCU_NEXT_READY_TAIL) ? "" : bufr,
1593 ".N"[!rcu_segcblist_segempty(rsclp, RCU_NEXT_TAIL)],
1594 ".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)],
1595 rcu_segcblist_n_cbs(&rdp->cblist),
1596 rdp->nocb_cb_kthread ? task_state_to_char(rdp->nocb_cb_kthread) : '.',
1597 rdp->nocb_cb_kthread ? (int)task_cpu(rdp->nocb_cb_kthread) : -1,
1598 show_rcu_should_be_on_cpu(rdp->nocb_cb_kthread));
1599
1600 /* It is OK for GP kthreads to have GP state. */
1601 if (rdp->nocb_gp_rdp == rdp)
1602 return;
1603
1604 waslocked = raw_spin_is_locked(&rdp->nocb_gp_lock);
1605 wassleep = swait_active(&rdp->nocb_gp_wq);
1606 if (!rdp->nocb_gp_sleep && !waslocked && !wassleep)
1607 return; /* Nothing untoward. */
1608
1609 pr_info(" nocb GP activity on CB-only CPU!!! %c%c%c %c\n",
1610 "lL"[waslocked],
1611 "dD"[!!rdp->nocb_defer_wakeup],
1612 "sS"[!!rdp->nocb_gp_sleep],
1613 ".W"[wassleep]);
1614}
1615
1616#else /* #ifdef CONFIG_RCU_NOCB_CPU */
1617
1618/* No ->nocb_lock to acquire. */
1619static void rcu_nocb_lock(struct rcu_data *rdp)
1620{
1621}
1622
1623/* No ->nocb_lock to release. */
1624static void rcu_nocb_unlock(struct rcu_data *rdp)
1625{
1626}
1627
1628/* No ->nocb_lock to release. */
1629static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
1630 unsigned long flags)
1631{
1632 local_irq_restore(flags);
1633}
1634
1635/* Lockdep check that ->cblist may be safely accessed. */
1636static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
1637{
1638 lockdep_assert_irqs_disabled();
1639}
1640
1641static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
1642{
1643}
1644
1645static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
1646{
1647 return NULL;
1648}
1649
1650static void rcu_init_one_nocb(struct rcu_node *rnp)
1651{
1652}
1653
1654static bool wake_nocb_gp(struct rcu_data *rdp, bool force)
1655{
1656 return false;
1657}
1658
1659static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
1660 unsigned long j, bool lazy)
1661{
1662 return true;
1663}
1664
1665static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head,
1666 rcu_callback_t func, unsigned long flags, bool lazy)
1667{
1668 WARN_ON_ONCE(1); /* Should be dead code! */
1669}
1670
1671static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
1672 unsigned long flags)
1673{
1674 WARN_ON_ONCE(1); /* Should be dead code! */
1675}
1676
1677static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
1678{
1679}
1680
1681static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level)
1682{
1683 return false;
1684}
1685
1686static bool do_nocb_deferred_wakeup(struct rcu_data *rdp)
1687{
1688 return false;
1689}
1690
1691static void rcu_spawn_cpu_nocb_kthread(int cpu)
1692{
1693}
1694
1695static void show_rcu_nocb_state(struct rcu_data *rdp)
1696{
1697}
1698
1699#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */