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(mask: &rcu_nocb_mask);
62 if (*str == '=') {
63 if (cpulist_parse(buf: ++str, dstp: rcu_nocb_mask)) {
64 pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
65 cpumask_setall(dstp: 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(q: 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(s: 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(rcuname: rcu_state.name, cpu: 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 timer_delete(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(rcuname: rcu_state.name, cpu: rdp->cpu, TPS("DoWake"));
219 swake_up_one(q: &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_gp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) {
280 mod_timer(timer: &rdp_gp->nocb_timer, expires: 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(timer: &rdp_gp->nocb_timer, expires: 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(timer: &rdp_gp->nocb_timer, expires: 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(rcuname: rcu_state.name, cpu: 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(rclp: &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(rsclp: &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(rclp: &rdp->nocb_bypass, rhp);
333 rhp = NULL;
334 }
335 rcu_cblist_flush_enqueue(drclp: &rcl, srclp: &rdp->nocb_bypass, rhp);
336 WRITE_ONCE(rdp->lazy_len, 0);
337
338 rcu_segcblist_insert_pend_cbs(rsclp: &rdp->cblist, rclp: &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_in: 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(rclp: &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(rsclp: &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(rsclp: &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(rsclp: &rdp->cblist);
442 if (*was_alldone)
443 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu: 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(rsclp: &rdp->cblist);
459
460 if (!rcu_nocb_flush_bypass(rdp, rhp, j, lazy)) {
461 if (*was_alldone)
462 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu: 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(rsclp: &rdp->cblist, lp: &cur_gp_seq) &&
469 rcu_seq_done(sp: &rdp->mynode->gp_seq, s: cur_gp_seq)) {
470 rcu_advance_cbs_nowake(rnp: 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_empty: *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(rclp: &rdp->nocb_bypass);
485 rcu_segcblist_inc_len(rsclp: &rdp->cblist); /* Must precede enqueue. */
486 rcu_cblist_enqueue(rclp: &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(rcuname: rcu_state.name, cpu: 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(rsclp: &rdp->cblist)) {
508 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu: rdp->cpu,
509 TPS("FirstBQwake"));
510 __call_rcu_nocb_wake(rdp, was_empty: true, flags);
511 } else {
512 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu: 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(rcuname: rcu_state.name, cpu: rdp->cpu,
543 TPS("WakeNotPoll"));
544 return;
545 }
546 // Need to actually to a wakeup.
547 len = rcu_segcblist_n_cbs(rsclp: &rdp->cblist);
548 bypass_len = rcu_cblist_n_cbs(rclp: &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)) {
558 /* ... if queue was empty ... */
559 rcu_nocb_unlock(rdp);
560 wake_nocb_gp(rdp, force: false);
561 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu: rdp->cpu,
562 TPS("WakeEmpty"));
563 } else {
564 rcu_nocb_unlock(rdp);
565 wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE,
566 TPS("WakeEmptyIsDeferred"));
567 }
568 } else if (len > rdp->qlen_last_fqs_check + qhimark) {
569 /* ... or if many callbacks queued. */
570 rdp->qlen_last_fqs_check = len;
571 j = jiffies;
572 if (j != rdp->nocb_gp_adv_time &&
573 rcu_segcblist_nextgp(rsclp: &rdp->cblist, lp: &cur_gp_seq) &&
574 rcu_seq_done(sp: &rdp->mynode->gp_seq, s: cur_gp_seq)) {
575 rcu_advance_cbs_nowake(rnp: rdp->mynode, rdp);
576 rdp->nocb_gp_adv_time = j;
577 }
578 smp_mb(); /* Enqueue before timer_pending(). */
579 if ((rdp->nocb_cb_sleep ||
580 !rcu_segcblist_ready_cbs(rsclp: &rdp->cblist)) &&
581 !timer_pending(timer: &rdp_gp->nocb_timer)) {
582 rcu_nocb_unlock(rdp);
583 wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
584 TPS("WakeOvfIsDeferred"));
585 } else {
586 rcu_nocb_unlock(rdp);
587 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu: rdp->cpu, TPS("WakeNot"));
588 }
589 } else {
590 rcu_nocb_unlock(rdp);
591 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu: rdp->cpu, TPS("WakeNot"));
592 }
593}
594
595static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head,
596 rcu_callback_t func, unsigned long flags, bool lazy)
597{
598 bool was_alldone;
599
600 if (!rcu_nocb_try_bypass(rdp, rhp: head, was_alldone: &was_alldone, flags, lazy)) {
601 /* Not enqueued on bypass but locked, do regular enqueue */
602 rcutree_enqueue(rdp, head, func);
603 __call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */
604 }
605}
606
607static void nocb_gp_toggle_rdp(struct rcu_data *rdp_gp, struct rcu_data *rdp)
608{
609 struct rcu_segcblist *cblist = &rdp->cblist;
610 unsigned long flags;
611
612 /*
613 * Locking orders future de-offloaded callbacks enqueue against previous
614 * handling of this rdp. Ie: Make sure rcuog is done with this rdp before
615 * deoffloaded callbacks can be enqueued.
616 */
617 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
618 if (!rcu_segcblist_test_flags(rsclp: cblist, SEGCBLIST_OFFLOADED)) {
619 /*
620 * Offloading. Set our flag and notify the offload worker.
621 * We will handle this rdp until it ever gets de-offloaded.
622 */
623 list_add_tail(new: &rdp->nocb_entry_rdp, head: &rdp_gp->nocb_head_rdp);
624 rcu_segcblist_set_flags(rsclp: cblist, SEGCBLIST_OFFLOADED);
625 } else {
626 /*
627 * De-offloading. Clear our flag and notify the de-offload worker.
628 * We will ignore this rdp until it ever gets re-offloaded.
629 */
630 list_del(entry: &rdp->nocb_entry_rdp);
631 rcu_segcblist_clear_flags(rsclp: cblist, SEGCBLIST_OFFLOADED);
632 }
633 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
634}
635
636static void nocb_gp_sleep(struct rcu_data *my_rdp, int cpu)
637{
638 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu, TPS("Sleep"));
639 swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq,
640 !READ_ONCE(my_rdp->nocb_gp_sleep));
641 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu, TPS("EndSleep"));
642}
643
644/*
645 * No-CBs GP kthreads come here to wait for additional callbacks to show up
646 * or for grace periods to end.
647 */
648static void nocb_gp_wait(struct rcu_data *my_rdp)
649{
650 bool bypass = false;
651 int __maybe_unused cpu = my_rdp->cpu;
652 unsigned long cur_gp_seq;
653 unsigned long flags;
654 bool gotcbs = false;
655 unsigned long j = jiffies;
656 bool lazy = false;
657 bool needwait_gp = false; // This prevents actual uninitialized use.
658 bool needwake;
659 bool needwake_gp;
660 struct rcu_data *rdp, *rdp_toggling = NULL;
661 struct rcu_node *rnp;
662 unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning.
663 bool wasempty = false;
664
665 /*
666 * Each pass through the following loop checks for CBs and for the
667 * nearest grace period (if any) to wait for next. The CB kthreads
668 * and the global grace-period kthread are awakened if needed.
669 */
670 WARN_ON_ONCE(my_rdp->nocb_gp_rdp != my_rdp);
671 /*
672 * An rcu_data structure is removed from the list after its
673 * CPU is de-offloaded and added to the list before that CPU is
674 * (re-)offloaded. If the following loop happens to be referencing
675 * that rcu_data structure during the time that the corresponding
676 * CPU is de-offloaded and then immediately re-offloaded, this
677 * loop's rdp pointer will be carried to the end of the list by
678 * the resulting pair of list operations. This can cause the loop
679 * to skip over some of the rcu_data structures that were supposed
680 * to have been scanned. Fortunately a new iteration through the
681 * entire loop is forced after a given CPU's rcu_data structure
682 * is added to the list, so the skipped-over rcu_data structures
683 * won't be ignored for long.
684 */
685 list_for_each_entry(rdp, &my_rdp->nocb_head_rdp, nocb_entry_rdp) {
686 long bypass_ncbs;
687 bool flush_bypass = false;
688 long lazy_ncbs;
689
690 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu: rdp->cpu, TPS("Check"));
691 rcu_nocb_lock_irqsave(rdp, flags);
692 lockdep_assert_held(&rdp->nocb_lock);
693 bypass_ncbs = rcu_cblist_n_cbs(rclp: &rdp->nocb_bypass);
694 lazy_ncbs = READ_ONCE(rdp->lazy_len);
695
696 if (bypass_ncbs && (lazy_ncbs == bypass_ncbs) &&
697 (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + rcu_get_jiffies_lazy_flush()) ||
698 bypass_ncbs > 2 * qhimark)) {
699 flush_bypass = true;
700 } else if (bypass_ncbs && (lazy_ncbs != bypass_ncbs) &&
701 (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) ||
702 bypass_ncbs > 2 * qhimark)) {
703 flush_bypass = true;
704 } else if (!bypass_ncbs && rcu_segcblist_empty(rsclp: &rdp->cblist)) {
705 rcu_nocb_unlock_irqrestore(rdp, flags);
706 continue; /* No callbacks here, try next. */
707 }
708
709 if (flush_bypass) {
710 // Bypass full or old, so flush it.
711 (void)rcu_nocb_try_flush_bypass(rdp, j);
712 bypass_ncbs = rcu_cblist_n_cbs(rclp: &rdp->nocb_bypass);
713 lazy_ncbs = READ_ONCE(rdp->lazy_len);
714 }
715
716 if (bypass_ncbs) {
717 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu: rdp->cpu,
718 reason: bypass_ncbs == lazy_ncbs ? TPS("Lazy") : TPS("Bypass"));
719 if (bypass_ncbs == lazy_ncbs)
720 lazy = true;
721 else
722 bypass = true;
723 }
724 rnp = rdp->mynode;
725
726 // Advance callbacks if helpful and low contention.
727 needwake_gp = false;
728 if (!rcu_segcblist_restempty(rsclp: &rdp->cblist,
729 RCU_NEXT_READY_TAIL) ||
730 (rcu_segcblist_nextgp(rsclp: &rdp->cblist, lp: &cur_gp_seq) &&
731 rcu_seq_done(sp: &rnp->gp_seq, s: cur_gp_seq))) {
732 raw_spin_lock_rcu_node(rnp); /* irqs disabled. */
733 needwake_gp = rcu_advance_cbs(rnp, rdp);
734 wasempty = rcu_segcblist_restempty(rsclp: &rdp->cblist,
735 RCU_NEXT_READY_TAIL);
736 raw_spin_unlock_rcu_node(rnp); /* irqs disabled. */
737 }
738 // Need to wait on some grace period?
739 WARN_ON_ONCE(wasempty &&
740 !rcu_segcblist_restempty(&rdp->cblist,
741 RCU_NEXT_READY_TAIL));
742 if (rcu_segcblist_nextgp(rsclp: &rdp->cblist, lp: &cur_gp_seq)) {
743 if (!needwait_gp ||
744 ULONG_CMP_LT(cur_gp_seq, wait_gp_seq))
745 wait_gp_seq = cur_gp_seq;
746 needwait_gp = true;
747 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu: rdp->cpu,
748 TPS("NeedWaitGP"));
749 }
750 if (rcu_segcblist_ready_cbs(rsclp: &rdp->cblist)) {
751 needwake = rdp->nocb_cb_sleep;
752 WRITE_ONCE(rdp->nocb_cb_sleep, false);
753 } else {
754 needwake = false;
755 }
756 rcu_nocb_unlock_irqrestore(rdp, flags);
757 if (needwake) {
758 swake_up_one(q: &rdp->nocb_cb_wq);
759 gotcbs = true;
760 }
761 if (needwake_gp)
762 rcu_gp_kthread_wake();
763 }
764
765 my_rdp->nocb_gp_bypass = bypass;
766 my_rdp->nocb_gp_gp = needwait_gp;
767 my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;
768
769 // At least one child with non-empty ->nocb_bypass, so set
770 // timer in order to avoid stranding its callbacks.
771 if (!rcu_nocb_poll) {
772 // If bypass list only has lazy CBs. Add a deferred lazy wake up.
773 if (lazy && !bypass) {
774 wake_nocb_gp_defer(rdp: my_rdp, RCU_NOCB_WAKE_LAZY,
775 TPS("WakeLazyIsDeferred"));
776 // Otherwise add a deferred bypass wake up.
777 } else if (bypass) {
778 wake_nocb_gp_defer(rdp: my_rdp, RCU_NOCB_WAKE_BYPASS,
779 TPS("WakeBypassIsDeferred"));
780 }
781 }
782
783 if (rcu_nocb_poll) {
784 /* Polling, so trace if first poll in the series. */
785 if (gotcbs)
786 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu, TPS("Poll"));
787 if (list_empty(head: &my_rdp->nocb_head_rdp)) {
788 raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
789 if (!my_rdp->nocb_toggling_rdp)
790 WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
791 raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
792 /* Wait for any offloading rdp */
793 nocb_gp_sleep(my_rdp, cpu);
794 } else {
795 schedule_timeout_idle(timeout: 1);
796 }
797 } else if (!needwait_gp) {
798 /* Wait for callbacks to appear. */
799 nocb_gp_sleep(my_rdp, cpu);
800 } else {
801 rnp = my_rdp->mynode;
802 trace_rcu_this_gp(rnp, rdp: my_rdp, gp_seq_req: wait_gp_seq, TPS("StartWait"));
803 swait_event_interruptible_exclusive(
804 rnp->nocb_gp_wq[rcu_seq_ctr(wait_gp_seq) & 0x1],
805 rcu_seq_done(&rnp->gp_seq, wait_gp_seq) ||
806 !READ_ONCE(my_rdp->nocb_gp_sleep));
807 trace_rcu_this_gp(rnp, rdp: my_rdp, gp_seq_req: wait_gp_seq, TPS("EndWait"));
808 }
809
810 if (!rcu_nocb_poll) {
811 raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
812 // (De-)queue an rdp to/from the group if its nocb state is changing
813 rdp_toggling = my_rdp->nocb_toggling_rdp;
814 if (rdp_toggling)
815 my_rdp->nocb_toggling_rdp = NULL;
816
817 if (my_rdp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) {
818 WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
819 timer_delete(timer: &my_rdp->nocb_timer);
820 }
821 WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
822 raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
823 } else {
824 rdp_toggling = READ_ONCE(my_rdp->nocb_toggling_rdp);
825 if (rdp_toggling) {
826 /*
827 * Paranoid locking to make sure nocb_toggling_rdp is well
828 * reset *before* we (re)set SEGCBLIST_KTHREAD_GP or we could
829 * race with another round of nocb toggling for this rdp.
830 * Nocb locking should prevent from that already but we stick
831 * to paranoia, especially in rare path.
832 */
833 raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
834 my_rdp->nocb_toggling_rdp = NULL;
835 raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
836 }
837 }
838
839 if (rdp_toggling) {
840 nocb_gp_toggle_rdp(rdp_gp: my_rdp, rdp: rdp_toggling);
841 swake_up_one(q: &rdp_toggling->nocb_state_wq);
842 }
843
844 my_rdp->nocb_gp_seq = -1;
845 WARN_ON(signal_pending(current));
846}
847
848/*
849 * No-CBs grace-period-wait kthread. There is one of these per group
850 * of CPUs, but only once at least one CPU in that group has come online
851 * at least once since boot. This kthread checks for newly posted
852 * callbacks from any of the CPUs it is responsible for, waits for a
853 * grace period, then awakens all of the rcu_nocb_cb_kthread() instances
854 * that then have callback-invocation work to do.
855 */
856static int rcu_nocb_gp_kthread(void *arg)
857{
858 struct rcu_data *rdp = arg;
859
860 for (;;) {
861 WRITE_ONCE(rdp->nocb_gp_loops, rdp->nocb_gp_loops + 1);
862 nocb_gp_wait(my_rdp: rdp);
863 cond_resched_tasks_rcu_qs();
864 }
865 return 0;
866}
867
868static inline bool nocb_cb_wait_cond(struct rcu_data *rdp)
869{
870 return !READ_ONCE(rdp->nocb_cb_sleep) || kthread_should_park();
871}
872
873/*
874 * Invoke any ready callbacks from the corresponding no-CBs CPU,
875 * then, if there are no more, wait for more to appear.
876 */
877static void nocb_cb_wait(struct rcu_data *rdp)
878{
879 struct rcu_segcblist *cblist = &rdp->cblist;
880 unsigned long cur_gp_seq;
881 unsigned long flags;
882 bool needwake_gp = false;
883 struct rcu_node *rnp = rdp->mynode;
884
885 swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
886 nocb_cb_wait_cond(rdp));
887 if (kthread_should_park()) {
888 /*
889 * kthread_park() must be preceded by an rcu_barrier().
890 * But yet another rcu_barrier() might have sneaked in between
891 * the barrier callback execution and the callbacks counter
892 * decrement.
893 */
894 if (rdp->nocb_cb_sleep) {
895 rcu_nocb_lock_irqsave(rdp, flags);
896 WARN_ON_ONCE(rcu_segcblist_n_cbs(&rdp->cblist));
897 rcu_nocb_unlock_irqrestore(rdp, flags);
898 kthread_parkme();
899 }
900 } else if (READ_ONCE(rdp->nocb_cb_sleep)) {
901 WARN_ON(signal_pending(current));
902 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu: rdp->cpu, TPS("WokeEmpty"));
903 }
904
905 WARN_ON_ONCE(!rcu_rdp_is_offloaded(rdp));
906
907 local_irq_save(flags);
908 rcu_momentary_eqs();
909 local_irq_restore(flags);
910 /*
911 * Disable BH to provide the expected environment. Also, when
912 * transitioning to/from NOCB mode, a self-requeuing callback might
913 * be invoked from softirq. A short grace period could cause both
914 * instances of this callback would execute concurrently.
915 */
916 local_bh_disable();
917 rcu_do_batch(rdp);
918 local_bh_enable();
919 lockdep_assert_irqs_enabled();
920 rcu_nocb_lock_irqsave(rdp, flags);
921 if (rcu_segcblist_nextgp(rsclp: cblist, lp: &cur_gp_seq) &&
922 rcu_seq_done(sp: &rnp->gp_seq, s: cur_gp_seq) &&
923 raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */
924 needwake_gp = rcu_advance_cbs(rnp: rdp->mynode, rdp);
925 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
926 }
927
928 if (!rcu_segcblist_ready_cbs(rsclp: cblist)) {
929 WRITE_ONCE(rdp->nocb_cb_sleep, true);
930 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu: rdp->cpu, TPS("CBSleep"));
931 } else {
932 WRITE_ONCE(rdp->nocb_cb_sleep, false);
933 }
934
935 rcu_nocb_unlock_irqrestore(rdp, flags);
936 if (needwake_gp)
937 rcu_gp_kthread_wake();
938}
939
940/*
941 * Per-rcu_data kthread, but only for no-CBs CPUs. Repeatedly invoke
942 * nocb_cb_wait() to do the dirty work.
943 */
944static int rcu_nocb_cb_kthread(void *arg)
945{
946 struct rcu_data *rdp = arg;
947
948 // Each pass through this loop does one callback batch, and,
949 // if there are no more ready callbacks, waits for them.
950 for (;;) {
951 nocb_cb_wait(rdp);
952 cond_resched_tasks_rcu_qs();
953 }
954 return 0;
955}
956
957/* Is a deferred wakeup of rcu_nocb_kthread() required? */
958static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level)
959{
960 return READ_ONCE(rdp->nocb_defer_wakeup) >= level;
961}
962
963/* Do a deferred wakeup of rcu_nocb_kthread(). */
964static bool do_nocb_deferred_wakeup_common(struct rcu_data *rdp_gp,
965 struct rcu_data *rdp, int level,
966 unsigned long flags)
967 __releases(rdp_gp->nocb_gp_lock)
968{
969 int ndw;
970 int ret;
971
972 if (!rcu_nocb_need_deferred_wakeup(rdp: rdp_gp, level)) {
973 raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
974 return false;
975 }
976
977 ndw = rdp_gp->nocb_defer_wakeup;
978 ret = __wake_nocb_gp(rdp_gp, rdp, force: ndw == RCU_NOCB_WAKE_FORCE, flags);
979 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu: rdp->cpu, TPS("DeferredWake"));
980
981 return ret;
982}
983
984/* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
985static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
986{
987 unsigned long flags;
988 struct rcu_data *rdp = timer_container_of(rdp, t, nocb_timer);
989
990 WARN_ON_ONCE(rdp->nocb_gp_rdp != rdp);
991 trace_rcu_nocb_wake(rcuname: rcu_state.name, cpu: rdp->cpu, TPS("Timer"));
992
993 raw_spin_lock_irqsave(&rdp->nocb_gp_lock, flags);
994 smp_mb__after_spinlock(); /* Timer expire before wakeup. */
995 do_nocb_deferred_wakeup_common(rdp_gp: rdp, rdp, RCU_NOCB_WAKE_BYPASS, flags);
996}
997
998/*
999 * Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
1000 * This means we do an inexact common-case check. Note that if
1001 * we miss, ->nocb_timer will eventually clean things up.
1002 */
1003static bool do_nocb_deferred_wakeup(struct rcu_data *rdp)
1004{
1005 unsigned long flags;
1006 struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
1007
1008 if (!rdp_gp || !rcu_nocb_need_deferred_wakeup(rdp: rdp_gp, RCU_NOCB_WAKE))
1009 return false;
1010
1011 raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
1012 return do_nocb_deferred_wakeup_common(rdp_gp, rdp, RCU_NOCB_WAKE, flags);
1013}
1014
1015void rcu_nocb_flush_deferred_wakeup(void)
1016{
1017 do_nocb_deferred_wakeup(this_cpu_ptr(&rcu_data));
1018}
1019EXPORT_SYMBOL_GPL(rcu_nocb_flush_deferred_wakeup);
1020
1021static int rcu_nocb_queue_toggle_rdp(struct rcu_data *rdp)
1022{
1023 struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
1024 bool wake_gp = false;
1025 unsigned long flags;
1026
1027 raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
1028 // Queue this rdp for add/del to/from the list to iterate on rcuog
1029 WRITE_ONCE(rdp_gp->nocb_toggling_rdp, rdp);
1030 if (rdp_gp->nocb_gp_sleep) {
1031 rdp_gp->nocb_gp_sleep = false;
1032 wake_gp = true;
1033 }
1034 raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
1035
1036 return wake_gp;
1037}
1038
1039static bool rcu_nocb_rdp_deoffload_wait_cond(struct rcu_data *rdp)
1040{
1041 unsigned long flags;
1042 bool ret;
1043
1044 /*
1045 * Locking makes sure rcuog is done handling this rdp before deoffloaded
1046 * enqueue can happen. Also it keeps the SEGCBLIST_OFFLOADED flag stable
1047 * while the ->nocb_lock is held.
1048 */
1049 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
1050 ret = !rcu_segcblist_test_flags(rsclp: &rdp->cblist, SEGCBLIST_OFFLOADED);
1051 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1052
1053 return ret;
1054}
1055
1056static int rcu_nocb_rdp_deoffload(struct rcu_data *rdp)
1057{
1058 unsigned long flags;
1059 int wake_gp;
1060 struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
1061
1062 /* CPU must be offline, unless it's early boot */
1063 WARN_ON_ONCE(cpu_online(rdp->cpu) && rdp->cpu != raw_smp_processor_id());
1064
1065 pr_info("De-offloading %d\n", rdp->cpu);
1066
1067 /* Flush all callbacks from segcblist and bypass */
1068 rcu_barrier();
1069
1070 /*
1071 * Make sure the rcuoc kthread isn't in the middle of a nocb locked
1072 * sequence while offloading is deactivated, along with nocb locking.
1073 */
1074 if (rdp->nocb_cb_kthread)
1075 kthread_park(k: rdp->nocb_cb_kthread);
1076
1077 rcu_nocb_lock_irqsave(rdp, flags);
1078 WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
1079 WARN_ON_ONCE(rcu_segcblist_n_cbs(&rdp->cblist));
1080 rcu_nocb_unlock_irqrestore(rdp, flags);
1081
1082 wake_gp = rcu_nocb_queue_toggle_rdp(rdp);
1083
1084 mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
1085
1086 if (rdp_gp->nocb_gp_kthread) {
1087 if (wake_gp)
1088 wake_up_process(tsk: rdp_gp->nocb_gp_kthread);
1089
1090 swait_event_exclusive(rdp->nocb_state_wq,
1091 rcu_nocb_rdp_deoffload_wait_cond(rdp));
1092 } else {
1093 /*
1094 * No kthread to clear the flags for us or remove the rdp from the nocb list
1095 * to iterate. Do it here instead. Locking doesn't look stricly necessary
1096 * but we stick to paranoia in this rare path.
1097 */
1098 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
1099 rcu_segcblist_clear_flags(rsclp: &rdp->cblist, SEGCBLIST_OFFLOADED);
1100 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1101
1102 list_del(entry: &rdp->nocb_entry_rdp);
1103 }
1104
1105 mutex_unlock(lock: &rdp_gp->nocb_gp_kthread_mutex);
1106
1107 return 0;
1108}
1109
1110int rcu_nocb_cpu_deoffload(int cpu)
1111{
1112 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
1113 int ret = 0;
1114
1115 cpus_read_lock();
1116 mutex_lock(&rcu_state.nocb_mutex);
1117 if (rcu_rdp_is_offloaded(rdp)) {
1118 if (!cpu_online(cpu)) {
1119 ret = rcu_nocb_rdp_deoffload(rdp);
1120 if (!ret)
1121 cpumask_clear_cpu(cpu, dstp: rcu_nocb_mask);
1122 } else {
1123 pr_info("NOCB: Cannot CB-deoffload online CPU %d\n", rdp->cpu);
1124 ret = -EINVAL;
1125 }
1126 }
1127 mutex_unlock(lock: &rcu_state.nocb_mutex);
1128 cpus_read_unlock();
1129
1130 return ret;
1131}
1132EXPORT_SYMBOL_GPL(rcu_nocb_cpu_deoffload);
1133
1134static bool rcu_nocb_rdp_offload_wait_cond(struct rcu_data *rdp)
1135{
1136 unsigned long flags;
1137 bool ret;
1138
1139 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
1140 ret = rcu_segcblist_test_flags(rsclp: &rdp->cblist, SEGCBLIST_OFFLOADED);
1141 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1142
1143 return ret;
1144}
1145
1146static int rcu_nocb_rdp_offload(struct rcu_data *rdp)
1147{
1148 int wake_gp;
1149
1150 WARN_ON_ONCE(cpu_online(rdp->cpu));
1151 /*
1152 * For now we only support re-offload, ie: the rdp must have been
1153 * offloaded on boot first.
1154 */
1155 if (!rdp->nocb_gp_rdp)
1156 return -EINVAL;
1157
1158 if (WARN_ON_ONCE(!rdp->nocb_gp_kthread))
1159 return -EINVAL;
1160
1161 pr_info("Offloading %d\n", rdp->cpu);
1162
1163 WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
1164 WARN_ON_ONCE(rcu_segcblist_n_cbs(&rdp->cblist));
1165
1166 wake_gp = rcu_nocb_queue_toggle_rdp(rdp);
1167 if (wake_gp)
1168 wake_up_process(tsk: rdp->nocb_gp_kthread);
1169
1170 swait_event_exclusive(rdp->nocb_state_wq,
1171 rcu_nocb_rdp_offload_wait_cond(rdp));
1172
1173 kthread_unpark(k: rdp->nocb_cb_kthread);
1174
1175 return 0;
1176}
1177
1178int rcu_nocb_cpu_offload(int cpu)
1179{
1180 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
1181 int ret = 0;
1182
1183 cpus_read_lock();
1184 mutex_lock(&rcu_state.nocb_mutex);
1185 if (!rcu_rdp_is_offloaded(rdp)) {
1186 if (!cpu_online(cpu)) {
1187 ret = rcu_nocb_rdp_offload(rdp);
1188 if (!ret)
1189 cpumask_set_cpu(cpu, dstp: rcu_nocb_mask);
1190 } else {
1191 pr_info("NOCB: Cannot CB-offload online CPU %d\n", rdp->cpu);
1192 ret = -EINVAL;
1193 }
1194 }
1195 mutex_unlock(lock: &rcu_state.nocb_mutex);
1196 cpus_read_unlock();
1197
1198 return ret;
1199}
1200EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload);
1201
1202#ifdef CONFIG_RCU_LAZY
1203static unsigned long
1204lazy_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
1205{
1206 int cpu;
1207 unsigned long count = 0;
1208
1209 if (WARN_ON_ONCE(!cpumask_available(rcu_nocb_mask)))
1210 return 0;
1211
1212 /* Protect rcu_nocb_mask against concurrent (de-)offloading. */
1213 if (!mutex_trylock(&rcu_state.nocb_mutex))
1214 return 0;
1215
1216 /* Snapshot count of all CPUs */
1217 for_each_cpu(cpu, rcu_nocb_mask) {
1218 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
1219
1220 count += READ_ONCE(rdp->lazy_len);
1221 }
1222
1223 mutex_unlock(lock: &rcu_state.nocb_mutex);
1224
1225 return count ? count : SHRINK_EMPTY;
1226}
1227
1228static unsigned long
1229lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
1230{
1231 int cpu;
1232 unsigned long flags;
1233 unsigned long count = 0;
1234
1235 if (WARN_ON_ONCE(!cpumask_available(rcu_nocb_mask)))
1236 return 0;
1237 /*
1238 * Protect against concurrent (de-)offloading. Otherwise nocb locking
1239 * may be ignored or imbalanced.
1240 */
1241 if (!mutex_trylock(&rcu_state.nocb_mutex)) {
1242 /*
1243 * But really don't insist if nocb_mutex is contended since we
1244 * can't guarantee that it will never engage in a dependency
1245 * chain involving memory allocation. The lock is seldom contended
1246 * anyway.
1247 */
1248 return 0;
1249 }
1250
1251 /* Snapshot count of all CPUs */
1252 for_each_cpu(cpu, rcu_nocb_mask) {
1253 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
1254 int _count;
1255
1256 if (WARN_ON_ONCE(!rcu_rdp_is_offloaded(rdp)))
1257 continue;
1258
1259 if (!READ_ONCE(rdp->lazy_len))
1260 continue;
1261
1262 rcu_nocb_lock_irqsave(rdp, flags);
1263 /*
1264 * Recheck under the nocb lock. Since we are not holding the bypass
1265 * lock we may still race with increments from the enqueuer but still
1266 * we know for sure if there is at least one lazy callback.
1267 */
1268 _count = READ_ONCE(rdp->lazy_len);
1269 if (!_count) {
1270 rcu_nocb_unlock_irqrestore(rdp, flags);
1271 continue;
1272 }
1273 rcu_nocb_try_flush_bypass(rdp, j: jiffies);
1274 rcu_nocb_unlock_irqrestore(rdp, flags);
1275 wake_nocb_gp(rdp, force: false);
1276 sc->nr_to_scan -= _count;
1277 count += _count;
1278 if (sc->nr_to_scan <= 0)
1279 break;
1280 }
1281
1282 mutex_unlock(lock: &rcu_state.nocb_mutex);
1283
1284 return count ? count : SHRINK_STOP;
1285}
1286#endif // #ifdef CONFIG_RCU_LAZY
1287
1288void __init rcu_init_nohz(void)
1289{
1290 int cpu;
1291 struct rcu_data *rdp;
1292 const struct cpumask *cpumask = NULL;
1293 struct shrinker * __maybe_unused lazy_rcu_shrinker;
1294
1295#if defined(CONFIG_NO_HZ_FULL)
1296 if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
1297 cpumask = tick_nohz_full_mask;
1298#endif
1299
1300 if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) &&
1301 !rcu_state.nocb_is_setup && !cpumask)
1302 cpumask = cpu_possible_mask;
1303
1304 if (cpumask) {
1305 if (!cpumask_available(mask: rcu_nocb_mask)) {
1306 if (!zalloc_cpumask_var(mask: &rcu_nocb_mask, GFP_KERNEL)) {
1307 pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
1308 return;
1309 }
1310 }
1311
1312 cpumask_or(dstp: rcu_nocb_mask, src1p: rcu_nocb_mask, src2p: cpumask);
1313 rcu_state.nocb_is_setup = true;
1314 }
1315
1316 if (!rcu_state.nocb_is_setup)
1317 return;
1318
1319#ifdef CONFIG_RCU_LAZY
1320 lazy_rcu_shrinker = shrinker_alloc(flags: 0, fmt: "rcu-lazy");
1321 if (!lazy_rcu_shrinker) {
1322 pr_err("Failed to allocate lazy_rcu shrinker!\n");
1323 } else {
1324 lazy_rcu_shrinker->count_objects = lazy_rcu_shrink_count;
1325 lazy_rcu_shrinker->scan_objects = lazy_rcu_shrink_scan;
1326
1327 shrinker_register(shrinker: lazy_rcu_shrinker);
1328 }
1329#endif // #ifdef CONFIG_RCU_LAZY
1330
1331 if (!cpumask_subset(src1p: rcu_nocb_mask, cpu_possible_mask)) {
1332 pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
1333 cpumask_and(dstp: rcu_nocb_mask, cpu_possible_mask,
1334 src2p: rcu_nocb_mask);
1335 }
1336 if (cpumask_empty(srcp: rcu_nocb_mask))
1337 pr_info("\tOffload RCU callbacks from CPUs: (none).\n");
1338 else
1339 pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
1340 cpumask_pr_args(rcu_nocb_mask));
1341 if (rcu_nocb_poll)
1342 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
1343
1344 for_each_cpu(cpu, rcu_nocb_mask) {
1345 rdp = per_cpu_ptr(&rcu_data, cpu);
1346 if (rcu_segcblist_empty(rsclp: &rdp->cblist))
1347 rcu_segcblist_init(rsclp: &rdp->cblist);
1348 rcu_segcblist_set_flags(rsclp: &rdp->cblist, SEGCBLIST_OFFLOADED);
1349 }
1350 rcu_organize_nocb_kthreads();
1351}
1352
1353/* Initialize per-rcu_data variables for no-CBs CPUs. */
1354static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
1355{
1356 init_swait_queue_head(&rdp->nocb_cb_wq);
1357 init_swait_queue_head(&rdp->nocb_gp_wq);
1358 init_swait_queue_head(&rdp->nocb_state_wq);
1359 raw_spin_lock_init(&rdp->nocb_lock);
1360 raw_spin_lock_init(&rdp->nocb_bypass_lock);
1361 raw_spin_lock_init(&rdp->nocb_gp_lock);
1362 timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
1363 rcu_cblist_init(rclp: &rdp->nocb_bypass);
1364 WRITE_ONCE(rdp->lazy_len, 0);
1365 mutex_init(&rdp->nocb_gp_kthread_mutex);
1366}
1367
1368/*
1369 * If the specified CPU is a no-CBs CPU that does not already have its
1370 * rcuo CB kthread, spawn it. Additionally, if the rcuo GP kthread
1371 * for this CPU's group has not yet been created, spawn it as well.
1372 */
1373static void rcu_spawn_cpu_nocb_kthread(int cpu)
1374{
1375 struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
1376 struct rcu_data *rdp_gp;
1377 struct task_struct *t;
1378 struct sched_param sp;
1379
1380 if (!rcu_scheduler_fully_active || !rcu_state.nocb_is_setup)
1381 return;
1382
1383 /* If there already is an rcuo kthread, then nothing to do. */
1384 if (rdp->nocb_cb_kthread)
1385 return;
1386
1387 /* If we didn't spawn the GP kthread first, reorganize! */
1388 sp.sched_priority = kthread_prio;
1389 rdp_gp = rdp->nocb_gp_rdp;
1390 mutex_lock(&rdp_gp->nocb_gp_kthread_mutex);
1391 if (!rdp_gp->nocb_gp_kthread) {
1392 t = kthread_run(rcu_nocb_gp_kthread, rdp_gp,
1393 "rcuog/%d", rdp_gp->cpu);
1394 if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__)) {
1395 mutex_unlock(lock: &rdp_gp->nocb_gp_kthread_mutex);
1396 goto err;
1397 }
1398 WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);
1399 if (kthread_prio)
1400 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1401 }
1402 mutex_unlock(lock: &rdp_gp->nocb_gp_kthread_mutex);
1403
1404 /* Spawn the kthread for this CPU. */
1405 t = kthread_create(rcu_nocb_cb_kthread, rdp,
1406 "rcuo%c/%d", rcu_state.abbr, cpu);
1407 if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__))
1408 goto err;
1409
1410 if (rcu_rdp_is_offloaded(rdp))
1411 wake_up_process(tsk: t);
1412 else
1413 kthread_park(k: t);
1414
1415 if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_CB_BOOST) && kthread_prio)
1416 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1417
1418 WRITE_ONCE(rdp->nocb_cb_kthread, t);
1419 WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread);
1420 return;
1421
1422err:
1423 /*
1424 * No need to protect against concurrent rcu_barrier()
1425 * because the number of callbacks should be 0 for a non-boot CPU,
1426 * therefore rcu_barrier() shouldn't even try to grab the nocb_lock.
1427 * But hold nocb_mutex to avoid nocb_lock imbalance from shrinker.
1428 */
1429 WARN_ON_ONCE(system_state > SYSTEM_BOOTING && rcu_segcblist_n_cbs(&rdp->cblist));
1430 mutex_lock(&rcu_state.nocb_mutex);
1431 if (rcu_rdp_is_offloaded(rdp)) {
1432 rcu_nocb_rdp_deoffload(rdp);
1433 cpumask_clear_cpu(cpu, dstp: rcu_nocb_mask);
1434 }
1435 mutex_unlock(lock: &rcu_state.nocb_mutex);
1436}
1437
1438/* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */
1439static int rcu_nocb_gp_stride = -1;
1440module_param(rcu_nocb_gp_stride, int, 0444);
1441
1442/*
1443 * Initialize GP-CB relationships for all no-CBs CPU.
1444 */
1445static void __init rcu_organize_nocb_kthreads(void)
1446{
1447 int cpu;
1448 bool firsttime = true;
1449 bool gotnocbs = false;
1450 bool gotnocbscbs = true;
1451 int ls = rcu_nocb_gp_stride;
1452 int nl = 0; /* Next GP kthread. */
1453 struct rcu_data *rdp;
1454 struct rcu_data *rdp_gp = NULL; /* Suppress misguided gcc warn. */
1455
1456 if (!cpumask_available(mask: rcu_nocb_mask))
1457 return;
1458 if (ls == -1) {
1459 ls = nr_cpu_ids / int_sqrt(nr_cpu_ids);
1460 rcu_nocb_gp_stride = ls;
1461 }
1462
1463 /*
1464 * Each pass through this loop sets up one rcu_data structure.
1465 * Should the corresponding CPU come online in the future, then
1466 * we will spawn the needed set of rcu_nocb_kthread() kthreads.
1467 */
1468 for_each_possible_cpu(cpu) {
1469 rdp = per_cpu_ptr(&rcu_data, cpu);
1470 if (rdp->cpu >= nl) {
1471 /* New GP kthread, set up for CBs & next GP. */
1472 gotnocbs = true;
1473 nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
1474 rdp_gp = rdp;
1475 INIT_LIST_HEAD(list: &rdp->nocb_head_rdp);
1476 if (dump_tree) {
1477 if (!firsttime)
1478 pr_cont("%s\n", gotnocbscbs
1479 ? "" : " (self only)");
1480 gotnocbscbs = false;
1481 firsttime = false;
1482 pr_alert("%s: No-CB GP kthread CPU %d:",
1483 __func__, cpu);
1484 }
1485 } else {
1486 /* Another CB kthread, link to previous GP kthread. */
1487 gotnocbscbs = true;
1488 if (dump_tree)
1489 pr_cont(" %d", cpu);
1490 }
1491 rdp->nocb_gp_rdp = rdp_gp;
1492 if (cpumask_test_cpu(cpu, cpumask: rcu_nocb_mask))
1493 list_add_tail(new: &rdp->nocb_entry_rdp, head: &rdp_gp->nocb_head_rdp);
1494 }
1495 if (gotnocbs && dump_tree)
1496 pr_cont("%s\n", gotnocbscbs ? "" : " (self only)");
1497}
1498
1499/*
1500 * Bind the current task to the offloaded CPUs. If there are no offloaded
1501 * CPUs, leave the task unbound. Splat if the bind attempt fails.
1502 */
1503void rcu_bind_current_to_nocb(void)
1504{
1505 if (cpumask_available(mask: rcu_nocb_mask) && !cpumask_empty(srcp: rcu_nocb_mask))
1506 WARN_ON(sched_setaffinity(current->pid, rcu_nocb_mask));
1507}
1508EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb);
1509
1510// The ->on_cpu field is available only in CONFIG_SMP=y, so...
1511#ifdef CONFIG_SMP
1512static char *show_rcu_should_be_on_cpu(struct task_struct *tsp)
1513{
1514 return tsp && task_is_running(tsp) && !tsp->on_cpu ? "!" : "";
1515}
1516#else // #ifdef CONFIG_SMP
1517static char *show_rcu_should_be_on_cpu(struct task_struct *tsp)
1518{
1519 return "";
1520}
1521#endif // #else #ifdef CONFIG_SMP
1522
1523/*
1524 * Dump out nocb grace-period kthread state for the specified rcu_data
1525 * structure.
1526 */
1527static void show_rcu_nocb_gp_state(struct rcu_data *rdp)
1528{
1529 struct rcu_node *rnp = rdp->mynode;
1530
1531 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",
1532 rdp->cpu,
1533 "kK"[!!rdp->nocb_gp_kthread],
1534 "lL"[raw_spin_is_locked(&rdp->nocb_gp_lock)],
1535 "dD"[!!rdp->nocb_defer_wakeup],
1536 "tT"[timer_pending(&rdp->nocb_timer)],
1537 "sS"[!!rdp->nocb_gp_sleep],
1538 ".W"[swait_active(&rdp->nocb_gp_wq)],
1539 ".W"[swait_active(&rnp->nocb_gp_wq[0])],
1540 ".W"[swait_active(&rnp->nocb_gp_wq[1])],
1541 ".B"[!!rdp->nocb_gp_bypass],
1542 ".G"[!!rdp->nocb_gp_gp],
1543 (long)rdp->nocb_gp_seq,
1544 rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops),
1545 rdp->nocb_gp_kthread ? task_state_to_char(rdp->nocb_gp_kthread) : '.',
1546 rdp->nocb_gp_kthread ? (int)task_cpu(rdp->nocb_gp_kthread) : -1,
1547 show_rcu_should_be_on_cpu(rdp->nocb_gp_kthread));
1548}
1549
1550/* Dump out nocb kthread state for the specified rcu_data structure. */
1551static void show_rcu_nocb_state(struct rcu_data *rdp)
1552{
1553 char bufd[22];
1554 char bufw[45];
1555 char bufr[45];
1556 char bufn[22];
1557 char bufb[22];
1558 struct rcu_data *nocb_next_rdp;
1559 struct rcu_segcblist *rsclp = &rdp->cblist;
1560 bool waslocked;
1561 bool wassleep;
1562
1563 if (rdp->nocb_gp_rdp == rdp)
1564 show_rcu_nocb_gp_state(rdp);
1565
1566 if (!rcu_segcblist_is_offloaded(rsclp: &rdp->cblist))
1567 return;
1568
1569 nocb_next_rdp = list_next_or_null_rcu(&rdp->nocb_gp_rdp->nocb_head_rdp,
1570 &rdp->nocb_entry_rdp,
1571 typeof(*rdp),
1572 nocb_entry_rdp);
1573
1574 sprintf(buf: bufd, fmt: "%ld", rsclp->seglen[RCU_DONE_TAIL]);
1575 sprintf(buf: bufw, fmt: "%ld(%ld)", rsclp->seglen[RCU_WAIT_TAIL], rsclp->gp_seq[RCU_WAIT_TAIL]);
1576 sprintf(buf: bufr, fmt: "%ld(%ld)", rsclp->seglen[RCU_NEXT_READY_TAIL],
1577 rsclp->gp_seq[RCU_NEXT_READY_TAIL]);
1578 sprintf(buf: bufn, fmt: "%ld", rsclp->seglen[RCU_NEXT_TAIL]);
1579 sprintf(buf: bufb, fmt: "%ld", rcu_cblist_n_cbs(rclp: &rdp->nocb_bypass));
1580 pr_info(" CB %d^%d->%d %c%c%c%c%c F%ld L%ld C%d %c%s%c%s%c%s%c%s%c%s q%ld %c CPU %d%s\n",
1581 rdp->cpu, rdp->nocb_gp_rdp->cpu,
1582 nocb_next_rdp ? nocb_next_rdp->cpu : -1,
1583 "kK"[!!rdp->nocb_cb_kthread],
1584 "bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)],
1585 "lL"[raw_spin_is_locked(&rdp->nocb_lock)],
1586 "sS"[!!rdp->nocb_cb_sleep],
1587 ".W"[swait_active(&rdp->nocb_cb_wq)],
1588 jiffies - rdp->nocb_bypass_first,
1589 jiffies - rdp->nocb_nobypass_last,
1590 rdp->nocb_nobypass_count,
1591 ".D"[rcu_segcblist_ready_cbs(rsclp)],
1592 rcu_segcblist_segempty(rsclp, RCU_DONE_TAIL) ? "" : bufd,
1593 ".W"[!rcu_segcblist_segempty(rsclp, RCU_WAIT_TAIL)],
1594 rcu_segcblist_segempty(rsclp, RCU_WAIT_TAIL) ? "" : bufw,
1595 ".R"[!rcu_segcblist_segempty(rsclp, RCU_NEXT_READY_TAIL)],
1596 rcu_segcblist_segempty(rsclp, RCU_NEXT_READY_TAIL) ? "" : bufr,
1597 ".N"[!rcu_segcblist_segempty(rsclp, RCU_NEXT_TAIL)],
1598 rcu_segcblist_segempty(rsclp, RCU_NEXT_TAIL) ? "" : bufn,
1599 ".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)],
1600 !rcu_cblist_n_cbs(&rdp->nocb_bypass) ? "" : bufb,
1601 rcu_segcblist_n_cbs(&rdp->cblist),
1602 rdp->nocb_cb_kthread ? task_state_to_char(rdp->nocb_cb_kthread) : '.',
1603 rdp->nocb_cb_kthread ? (int)task_cpu(rdp->nocb_cb_kthread) : -1,
1604 show_rcu_should_be_on_cpu(rdp->nocb_cb_kthread));
1605
1606 /* It is OK for GP kthreads to have GP state. */
1607 if (rdp->nocb_gp_rdp == rdp)
1608 return;
1609
1610 waslocked = raw_spin_is_locked(&rdp->nocb_gp_lock);
1611 wassleep = swait_active(wq: &rdp->nocb_gp_wq);
1612 if (!rdp->nocb_gp_sleep && !waslocked && !wassleep)
1613 return; /* Nothing untoward. */
1614
1615 pr_info(" nocb GP activity on CB-only CPU!!! %c%c%c %c\n",
1616 "lL"[waslocked],
1617 "dD"[!!rdp->nocb_defer_wakeup],
1618 "sS"[!!rdp->nocb_gp_sleep],
1619 ".W"[wassleep]);
1620}
1621
1622#else /* #ifdef CONFIG_RCU_NOCB_CPU */
1623
1624/* No ->nocb_lock to acquire. */
1625static void rcu_nocb_lock(struct rcu_data *rdp)
1626{
1627}
1628
1629/* No ->nocb_lock to release. */
1630static void rcu_nocb_unlock(struct rcu_data *rdp)
1631{
1632}
1633
1634/* No ->nocb_lock to release. */
1635static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
1636 unsigned long flags)
1637{
1638 local_irq_restore(flags);
1639}
1640
1641/* Lockdep check that ->cblist may be safely accessed. */
1642static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
1643{
1644 lockdep_assert_irqs_disabled();
1645}
1646
1647static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
1648{
1649}
1650
1651static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
1652{
1653 return NULL;
1654}
1655
1656static void rcu_init_one_nocb(struct rcu_node *rnp)
1657{
1658}
1659
1660static bool wake_nocb_gp(struct rcu_data *rdp, bool force)
1661{
1662 return false;
1663}
1664
1665static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
1666 unsigned long j, bool lazy)
1667{
1668 return true;
1669}
1670
1671static void call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *head,
1672 rcu_callback_t func, unsigned long flags, bool lazy)
1673{
1674 WARN_ON_ONCE(1); /* Should be dead code! */
1675}
1676
1677static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
1678 unsigned long flags)
1679{
1680 WARN_ON_ONCE(1); /* Should be dead code! */
1681}
1682
1683static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
1684{
1685}
1686
1687static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level)
1688{
1689 return false;
1690}
1691
1692static bool do_nocb_deferred_wakeup(struct rcu_data *rdp)
1693{
1694 return false;
1695}
1696
1697static void rcu_spawn_cpu_nocb_kthread(int cpu)
1698{
1699}
1700
1701static void show_rcu_nocb_state(struct rcu_data *rdp)
1702{
1703}
1704
1705#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
1706

source code of linux/kernel/rcu/tree_nocb.h