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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 : : *
10 : : * Author: Ingo Molnar <mingo@elte.hu>
11 : : * Paul E. McKenney <paulmck@linux.ibm.com>
12 : : */
13 : :
14 : : #include "../locking/rtmutex_common.h"
15 : :
16 : : #ifdef CONFIG_RCU_NOCB_CPU
17 : : static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
18 : : static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
19 : : #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
20 : :
21 : : /*
22 : : * Check the RCU kernel configuration parameters and print informative
23 : : * messages about anything out of the ordinary.
24 : : */
25 : 207 : static void __init rcu_bootup_announce_oddness(void)
26 : : {
27 : : if (IS_ENABLED(CONFIG_RCU_TRACE))
28 : : pr_info("\tRCU event tracing is enabled.\n");
29 : : if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||
30 : : (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))
31 : : pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d.\n",
32 : : RCU_FANOUT);
33 [ - + ]: 207 : if (rcu_fanout_exact)
34 : 0 : pr_info("\tHierarchical RCU autobalancing is disabled.\n");
35 : : if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ))
36 : : pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
37 : : if (IS_ENABLED(CONFIG_PROVE_RCU))
38 : : pr_info("\tRCU lockdep checking is enabled.\n");
39 : : if (RCU_NUM_LVLS >= 4)
40 : : pr_info("\tFour(or more)-level hierarchy is enabled.\n");
41 : : if (RCU_FANOUT_LEAF != 16)
42 : : pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
43 : : RCU_FANOUT_LEAF);
44 [ - + ]: 207 : if (rcu_fanout_leaf != RCU_FANOUT_LEAF)
45 : 0 : pr_info("\tBoot-time adjustment of leaf fanout to %d.\n",
46 : : rcu_fanout_leaf);
47 [ - + ]: 207 : if (nr_cpu_ids != NR_CPUS)
48 : 0 : pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%u.\n", NR_CPUS, nr_cpu_ids);
49 : : #ifdef CONFIG_RCU_BOOST
50 : : pr_info("\tRCU priority boosting: priority %d delay %d ms.\n",
51 : : kthread_prio, CONFIG_RCU_BOOST_DELAY);
52 : : #endif
53 [ - + ]: 207 : if (blimit != DEFAULT_RCU_BLIMIT)
54 : 0 : pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit);
55 [ - + ]: 207 : if (qhimark != DEFAULT_RCU_QHIMARK)
56 : 0 : pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark);
57 [ - + ]: 207 : if (qlowmark != DEFAULT_RCU_QLOMARK)
58 : 0 : pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark);
59 [ - + ]: 207 : if (jiffies_till_first_fqs != ULONG_MAX)
60 : 0 : pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs);
61 [ - + ]: 207 : if (jiffies_till_next_fqs != ULONG_MAX)
62 : 0 : pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs);
63 [ - + ]: 207 : if (jiffies_till_sched_qs != ULONG_MAX)
64 : 0 : pr_info("\tBoot-time adjustment of scheduler-enlistment delay to %ld jiffies.\n", jiffies_till_sched_qs);
65 [ - + ]: 207 : if (rcu_kick_kthreads)
66 : 0 : pr_info("\tKick kthreads if too-long grace period.\n");
67 : : if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD))
68 : : pr_info("\tRCU callback double-/use-after-free debug enabled.\n");
69 [ - + ]: 207 : if (gp_preinit_delay)
70 : 0 : pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay);
71 [ - + ]: 207 : if (gp_init_delay)
72 : 0 : pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay);
73 [ - + ]: 207 : if (gp_cleanup_delay)
74 : 0 : pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay);
75 [ - + ]: 207 : if (!use_softirq)
76 : 0 : pr_info("\tRCU_SOFTIRQ processing moved to rcuc kthreads.\n");
77 : : if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))
78 : : pr_info("\tRCU debug extended QS entry/exit.\n");
79 : 207 : rcupdate_announce_bootup_oddness();
80 : 207 : }
81 : :
82 : : #ifdef CONFIG_PREEMPT_RCU
83 : :
84 : : static void rcu_report_exp_rnp(struct rcu_node *rnp, bool wake);
85 : : static void rcu_read_unlock_special(struct task_struct *t);
86 : :
87 : : /*
88 : : * Tell them what RCU they are running.
89 : : */
90 : : static void __init rcu_bootup_announce(void)
91 : : {
92 : : pr_info("Preemptible hierarchical RCU implementation.\n");
93 : : rcu_bootup_announce_oddness();
94 : : }
95 : :
96 : : /* Flags for rcu_preempt_ctxt_queue() decision table. */
97 : : #define RCU_GP_TASKS 0x8
98 : : #define RCU_EXP_TASKS 0x4
99 : : #define RCU_GP_BLKD 0x2
100 : : #define RCU_EXP_BLKD 0x1
101 : :
102 : : /*
103 : : * Queues a task preempted within an RCU-preempt read-side critical
104 : : * section into the appropriate location within the ->blkd_tasks list,
105 : : * depending on the states of any ongoing normal and expedited grace
106 : : * periods. The ->gp_tasks pointer indicates which element the normal
107 : : * grace period is waiting on (NULL if none), and the ->exp_tasks pointer
108 : : * indicates which element the expedited grace period is waiting on (again,
109 : : * NULL if none). If a grace period is waiting on a given element in the
110 : : * ->blkd_tasks list, it also waits on all subsequent elements. Thus,
111 : : * adding a task to the tail of the list blocks any grace period that is
112 : : * already waiting on one of the elements. In contrast, adding a task
113 : : * to the head of the list won't block any grace period that is already
114 : : * waiting on one of the elements.
115 : : *
116 : : * This queuing is imprecise, and can sometimes make an ongoing grace
117 : : * period wait for a task that is not strictly speaking blocking it.
118 : : * Given the choice, we needlessly block a normal grace period rather than
119 : : * blocking an expedited grace period.
120 : : *
121 : : * Note that an endless sequence of expedited grace periods still cannot
122 : : * indefinitely postpone a normal grace period. Eventually, all of the
123 : : * fixed number of preempted tasks blocking the normal grace period that are
124 : : * not also blocking the expedited grace period will resume and complete
125 : : * their RCU read-side critical sections. At that point, the ->gp_tasks
126 : : * pointer will equal the ->exp_tasks pointer, at which point the end of
127 : : * the corresponding expedited grace period will also be the end of the
128 : : * normal grace period.
129 : : */
130 : : static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
131 : : __releases(rnp->lock) /* But leaves rrupts disabled. */
132 : : {
133 : : int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) +
134 : : (rnp->exp_tasks ? RCU_EXP_TASKS : 0) +
135 : : (rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) +
136 : : (rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0);
137 : : struct task_struct *t = current;
138 : :
139 : : raw_lockdep_assert_held_rcu_node(rnp);
140 : : WARN_ON_ONCE(rdp->mynode != rnp);
141 : : WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
142 : : /* RCU better not be waiting on newly onlined CPUs! */
143 : : WARN_ON_ONCE(rnp->qsmaskinitnext & ~rnp->qsmaskinit & rnp->qsmask &
144 : : rdp->grpmask);
145 : :
146 : : /*
147 : : * Decide where to queue the newly blocked task. In theory,
148 : : * this could be an if-statement. In practice, when I tried
149 : : * that, it was quite messy.
150 : : */
151 : : switch (blkd_state) {
152 : : case 0:
153 : : case RCU_EXP_TASKS:
154 : : case RCU_EXP_TASKS + RCU_GP_BLKD:
155 : : case RCU_GP_TASKS:
156 : : case RCU_GP_TASKS + RCU_EXP_TASKS:
157 : :
158 : : /*
159 : : * Blocking neither GP, or first task blocking the normal
160 : : * GP but not blocking the already-waiting expedited GP.
161 : : * Queue at the head of the list to avoid unnecessarily
162 : : * blocking the already-waiting GPs.
163 : : */
164 : : list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
165 : : break;
166 : :
167 : : case RCU_EXP_BLKD:
168 : : case RCU_GP_BLKD:
169 : : case RCU_GP_BLKD + RCU_EXP_BLKD:
170 : : case RCU_GP_TASKS + RCU_EXP_BLKD:
171 : : case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
172 : : case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
173 : :
174 : : /*
175 : : * First task arriving that blocks either GP, or first task
176 : : * arriving that blocks the expedited GP (with the normal
177 : : * GP already waiting), or a task arriving that blocks
178 : : * both GPs with both GPs already waiting. Queue at the
179 : : * tail of the list to avoid any GP waiting on any of the
180 : : * already queued tasks that are not blocking it.
181 : : */
182 : : list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);
183 : : break;
184 : :
185 : : case RCU_EXP_TASKS + RCU_EXP_BLKD:
186 : : case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
187 : : case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD:
188 : :
189 : : /*
190 : : * Second or subsequent task blocking the expedited GP.
191 : : * The task either does not block the normal GP, or is the
192 : : * first task blocking the normal GP. Queue just after
193 : : * the first task blocking the expedited GP.
194 : : */
195 : : list_add(&t->rcu_node_entry, rnp->exp_tasks);
196 : : break;
197 : :
198 : : case RCU_GP_TASKS + RCU_GP_BLKD:
199 : : case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD:
200 : :
201 : : /*
202 : : * Second or subsequent task blocking the normal GP.
203 : : * The task does not block the expedited GP. Queue just
204 : : * after the first task blocking the normal GP.
205 : : */
206 : : list_add(&t->rcu_node_entry, rnp->gp_tasks);
207 : : break;
208 : :
209 : : default:
210 : :
211 : : /* Yet another exercise in excessive paranoia. */
212 : : WARN_ON_ONCE(1);
213 : : break;
214 : : }
215 : :
216 : : /*
217 : : * We have now queued the task. If it was the first one to
218 : : * block either grace period, update the ->gp_tasks and/or
219 : : * ->exp_tasks pointers, respectively, to reference the newly
220 : : * blocked tasks.
221 : : */
222 : : if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) {
223 : : WRITE_ONCE(rnp->gp_tasks, &t->rcu_node_entry);
224 : : WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq);
225 : : }
226 : : if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
227 : : rnp->exp_tasks = &t->rcu_node_entry;
228 : : WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=
229 : : !(rnp->qsmask & rdp->grpmask));
230 : : WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) !=
231 : : !(rnp->expmask & rdp->grpmask));
232 : : raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */
233 : :
234 : : /*
235 : : * Report the quiescent state for the expedited GP. This expedited
236 : : * GP should not be able to end until we report, so there should be
237 : : * no need to check for a subsequent expedited GP. (Though we are
238 : : * still in a quiescent state in any case.)
239 : : */
240 : : if (blkd_state & RCU_EXP_BLKD && rdp->exp_deferred_qs)
241 : : rcu_report_exp_rdp(rdp);
242 : : else
243 : : WARN_ON_ONCE(rdp->exp_deferred_qs);
244 : : }
245 : :
246 : : /*
247 : : * Record a preemptible-RCU quiescent state for the specified CPU.
248 : : * Note that this does not necessarily mean that the task currently running
249 : : * on the CPU is in a quiescent state: Instead, it means that the current
250 : : * grace period need not wait on any RCU read-side critical section that
251 : : * starts later on this CPU. It also means that if the current task is
252 : : * in an RCU read-side critical section, it has already added itself to
253 : : * some leaf rcu_node structure's ->blkd_tasks list. In addition to the
254 : : * current task, there might be any number of other tasks blocked while
255 : : * in an RCU read-side critical section.
256 : : *
257 : : * Callers to this function must disable preemption.
258 : : */
259 : : static void rcu_qs(void)
260 : : {
261 : : RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n");
262 : : if (__this_cpu_read(rcu_data.cpu_no_qs.s)) {
263 : : trace_rcu_grace_period(TPS("rcu_preempt"),
264 : : __this_cpu_read(rcu_data.gp_seq),
265 : : TPS("cpuqs"));
266 : : __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
267 : : barrier(); /* Coordinate with rcu_flavor_sched_clock_irq(). */
268 : : WRITE_ONCE(current->rcu_read_unlock_special.b.need_qs, false);
269 : : }
270 : : }
271 : :
272 : : /*
273 : : * We have entered the scheduler, and the current task might soon be
274 : : * context-switched away from. If this task is in an RCU read-side
275 : : * critical section, we will no longer be able to rely on the CPU to
276 : : * record that fact, so we enqueue the task on the blkd_tasks list.
277 : : * The task will dequeue itself when it exits the outermost enclosing
278 : : * RCU read-side critical section. Therefore, the current grace period
279 : : * cannot be permitted to complete until the blkd_tasks list entries
280 : : * predating the current grace period drain, in other words, until
281 : : * rnp->gp_tasks becomes NULL.
282 : : *
283 : : * Caller must disable interrupts.
284 : : */
285 : : void rcu_note_context_switch(bool preempt)
286 : : {
287 : : struct task_struct *t = current;
288 : : struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
289 : : struct rcu_node *rnp;
290 : :
291 : : trace_rcu_utilization(TPS("Start context switch"));
292 : : lockdep_assert_irqs_disabled();
293 : : WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0);
294 : : if (t->rcu_read_lock_nesting > 0 &&
295 : : !t->rcu_read_unlock_special.b.blocked) {
296 : :
297 : : /* Possibly blocking in an RCU read-side critical section. */
298 : : rnp = rdp->mynode;
299 : : raw_spin_lock_rcu_node(rnp);
300 : : t->rcu_read_unlock_special.b.blocked = true;
301 : : t->rcu_blocked_node = rnp;
302 : :
303 : : /*
304 : : * Verify the CPU's sanity, trace the preemption, and
305 : : * then queue the task as required based on the states
306 : : * of any ongoing and expedited grace periods.
307 : : */
308 : : WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);
309 : : WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
310 : : trace_rcu_preempt_task(rcu_state.name,
311 : : t->pid,
312 : : (rnp->qsmask & rdp->grpmask)
313 : : ? rnp->gp_seq
314 : : : rcu_seq_snap(&rnp->gp_seq));
315 : : rcu_preempt_ctxt_queue(rnp, rdp);
316 : : } else {
317 : : rcu_preempt_deferred_qs(t);
318 : : }
319 : :
320 : : /*
321 : : * Either we were not in an RCU read-side critical section to
322 : : * begin with, or we have now recorded that critical section
323 : : * globally. Either way, we can now note a quiescent state
324 : : * for this CPU. Again, if we were in an RCU read-side critical
325 : : * section, and if that critical section was blocking the current
326 : : * grace period, then the fact that the task has been enqueued
327 : : * means that we continue to block the current grace period.
328 : : */
329 : : rcu_qs();
330 : : if (rdp->exp_deferred_qs)
331 : : rcu_report_exp_rdp(rdp);
332 : : trace_rcu_utilization(TPS("End context switch"));
333 : : }
334 : : EXPORT_SYMBOL_GPL(rcu_note_context_switch);
335 : :
336 : : /*
337 : : * Check for preempted RCU readers blocking the current grace period
338 : : * for the specified rcu_node structure. If the caller needs a reliable
339 : : * answer, it must hold the rcu_node's ->lock.
340 : : */
341 : : static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
342 : : {
343 : : return READ_ONCE(rnp->gp_tasks) != NULL;
344 : : }
345 : :
346 : : /* Bias and limit values for ->rcu_read_lock_nesting. */
347 : : #define RCU_NEST_BIAS INT_MAX
348 : : #define RCU_NEST_NMAX (-INT_MAX / 2)
349 : : #define RCU_NEST_PMAX (INT_MAX / 2)
350 : :
351 : : /*
352 : : * Preemptible RCU implementation for rcu_read_lock().
353 : : * Just increment ->rcu_read_lock_nesting, shared state will be updated
354 : : * if we block.
355 : : */
356 : : void __rcu_read_lock(void)
357 : : {
358 : : current->rcu_read_lock_nesting++;
359 : : if (IS_ENABLED(CONFIG_PROVE_LOCKING))
360 : : WARN_ON_ONCE(current->rcu_read_lock_nesting > RCU_NEST_PMAX);
361 : : barrier(); /* critical section after entry code. */
362 : : }
363 : : EXPORT_SYMBOL_GPL(__rcu_read_lock);
364 : :
365 : : /*
366 : : * Preemptible RCU implementation for rcu_read_unlock().
367 : : * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
368 : : * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
369 : : * invoke rcu_read_unlock_special() to clean up after a context switch
370 : : * in an RCU read-side critical section and other special cases.
371 : : */
372 : : void __rcu_read_unlock(void)
373 : : {
374 : : struct task_struct *t = current;
375 : :
376 : : if (t->rcu_read_lock_nesting != 1) {
377 : : --t->rcu_read_lock_nesting;
378 : : } else {
379 : : barrier(); /* critical section before exit code. */
380 : : t->rcu_read_lock_nesting = -RCU_NEST_BIAS;
381 : : barrier(); /* assign before ->rcu_read_unlock_special load */
382 : : if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
383 : : rcu_read_unlock_special(t);
384 : : barrier(); /* ->rcu_read_unlock_special load before assign */
385 : : t->rcu_read_lock_nesting = 0;
386 : : }
387 : : if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
388 : : int rrln = t->rcu_read_lock_nesting;
389 : :
390 : : WARN_ON_ONCE(rrln < 0 && rrln > RCU_NEST_NMAX);
391 : : }
392 : : }
393 : : EXPORT_SYMBOL_GPL(__rcu_read_unlock);
394 : :
395 : : /*
396 : : * Advance a ->blkd_tasks-list pointer to the next entry, instead
397 : : * returning NULL if at the end of the list.
398 : : */
399 : : static struct list_head *rcu_next_node_entry(struct task_struct *t,
400 : : struct rcu_node *rnp)
401 : : {
402 : : struct list_head *np;
403 : :
404 : : np = t->rcu_node_entry.next;
405 : : if (np == &rnp->blkd_tasks)
406 : : np = NULL;
407 : : return np;
408 : : }
409 : :
410 : : /*
411 : : * Return true if the specified rcu_node structure has tasks that were
412 : : * preempted within an RCU read-side critical section.
413 : : */
414 : : static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
415 : : {
416 : : return !list_empty(&rnp->blkd_tasks);
417 : : }
418 : :
419 : : /*
420 : : * Report deferred quiescent states. The deferral time can
421 : : * be quite short, for example, in the case of the call from
422 : : * rcu_read_unlock_special().
423 : : */
424 : : static void
425 : : rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
426 : : {
427 : : bool empty_exp;
428 : : bool empty_norm;
429 : : bool empty_exp_now;
430 : : struct list_head *np;
431 : : bool drop_boost_mutex = false;
432 : : struct rcu_data *rdp;
433 : : struct rcu_node *rnp;
434 : : union rcu_special special;
435 : :
436 : : /*
437 : : * If RCU core is waiting for this CPU to exit its critical section,
438 : : * report the fact that it has exited. Because irqs are disabled,
439 : : * t->rcu_read_unlock_special cannot change.
440 : : */
441 : : special = t->rcu_read_unlock_special;
442 : : rdp = this_cpu_ptr(&rcu_data);
443 : : if (!special.s && !rdp->exp_deferred_qs) {
444 : : local_irq_restore(flags);
445 : : return;
446 : : }
447 : : t->rcu_read_unlock_special.b.deferred_qs = false;
448 : : if (special.b.need_qs) {
449 : : rcu_qs();
450 : : t->rcu_read_unlock_special.b.need_qs = false;
451 : : if (!t->rcu_read_unlock_special.s && !rdp->exp_deferred_qs) {
452 : : local_irq_restore(flags);
453 : : return;
454 : : }
455 : : }
456 : :
457 : : /*
458 : : * Respond to a request by an expedited grace period for a
459 : : * quiescent state from this CPU. Note that requests from
460 : : * tasks are handled when removing the task from the
461 : : * blocked-tasks list below.
462 : : */
463 : : if (rdp->exp_deferred_qs) {
464 : : rcu_report_exp_rdp(rdp);
465 : : if (!t->rcu_read_unlock_special.s) {
466 : : local_irq_restore(flags);
467 : : return;
468 : : }
469 : : }
470 : :
471 : : /* Clean up if blocked during RCU read-side critical section. */
472 : : if (special.b.blocked) {
473 : : t->rcu_read_unlock_special.b.blocked = false;
474 : :
475 : : /*
476 : : * Remove this task from the list it blocked on. The task
477 : : * now remains queued on the rcu_node corresponding to the
478 : : * CPU it first blocked on, so there is no longer any need
479 : : * to loop. Retain a WARN_ON_ONCE() out of sheer paranoia.
480 : : */
481 : : rnp = t->rcu_blocked_node;
482 : : raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
483 : : WARN_ON_ONCE(rnp != t->rcu_blocked_node);
484 : : WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
485 : : empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
486 : : WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq &&
487 : : (!empty_norm || rnp->qsmask));
488 : : empty_exp = sync_rcu_preempt_exp_done(rnp);
489 : : smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
490 : : np = rcu_next_node_entry(t, rnp);
491 : : list_del_init(&t->rcu_node_entry);
492 : : t->rcu_blocked_node = NULL;
493 : : trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
494 : : rnp->gp_seq, t->pid);
495 : : if (&t->rcu_node_entry == rnp->gp_tasks)
496 : : WRITE_ONCE(rnp->gp_tasks, np);
497 : : if (&t->rcu_node_entry == rnp->exp_tasks)
498 : : rnp->exp_tasks = np;
499 : : if (IS_ENABLED(CONFIG_RCU_BOOST)) {
500 : : /* Snapshot ->boost_mtx ownership w/rnp->lock held. */
501 : : drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
502 : : if (&t->rcu_node_entry == rnp->boost_tasks)
503 : : rnp->boost_tasks = np;
504 : : }
505 : :
506 : : /*
507 : : * If this was the last task on the current list, and if
508 : : * we aren't waiting on any CPUs, report the quiescent state.
509 : : * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
510 : : * so we must take a snapshot of the expedited state.
511 : : */
512 : : empty_exp_now = sync_rcu_preempt_exp_done(rnp);
513 : : if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
514 : : trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
515 : : rnp->gp_seq,
516 : : 0, rnp->qsmask,
517 : : rnp->level,
518 : : rnp->grplo,
519 : : rnp->grphi,
520 : : !!rnp->gp_tasks);
521 : : rcu_report_unblock_qs_rnp(rnp, flags);
522 : : } else {
523 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
524 : : }
525 : :
526 : : /* Unboost if we were boosted. */
527 : : if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
528 : : rt_mutex_futex_unlock(&rnp->boost_mtx);
529 : :
530 : : /*
531 : : * If this was the last task on the expedited lists,
532 : : * then we need to report up the rcu_node hierarchy.
533 : : */
534 : : if (!empty_exp && empty_exp_now)
535 : : rcu_report_exp_rnp(rnp, true);
536 : : } else {
537 : : local_irq_restore(flags);
538 : : }
539 : : }
540 : :
541 : : /*
542 : : * Is a deferred quiescent-state pending, and are we also not in
543 : : * an RCU read-side critical section? It is the caller's responsibility
544 : : * to ensure it is otherwise safe to report any deferred quiescent
545 : : * states. The reason for this is that it is safe to report a
546 : : * quiescent state during context switch even though preemption
547 : : * is disabled. This function cannot be expected to understand these
548 : : * nuances, so the caller must handle them.
549 : : */
550 : : static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
551 : : {
552 : : return (__this_cpu_read(rcu_data.exp_deferred_qs) ||
553 : : READ_ONCE(t->rcu_read_unlock_special.s)) &&
554 : : t->rcu_read_lock_nesting <= 0;
555 : : }
556 : :
557 : : /*
558 : : * Report a deferred quiescent state if needed and safe to do so.
559 : : * As with rcu_preempt_need_deferred_qs(), "safe" involves only
560 : : * not being in an RCU read-side critical section. The caller must
561 : : * evaluate safety in terms of interrupt, softirq, and preemption
562 : : * disabling.
563 : : */
564 : : static void rcu_preempt_deferred_qs(struct task_struct *t)
565 : : {
566 : : unsigned long flags;
567 : : bool couldrecurse = t->rcu_read_lock_nesting >= 0;
568 : :
569 : : if (!rcu_preempt_need_deferred_qs(t))
570 : : return;
571 : : if (couldrecurse)
572 : : t->rcu_read_lock_nesting -= RCU_NEST_BIAS;
573 : : local_irq_save(flags);
574 : : rcu_preempt_deferred_qs_irqrestore(t, flags);
575 : : if (couldrecurse)
576 : : t->rcu_read_lock_nesting += RCU_NEST_BIAS;
577 : : }
578 : :
579 : : /*
580 : : * Minimal handler to give the scheduler a chance to re-evaluate.
581 : : */
582 : : static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp)
583 : : {
584 : : struct rcu_data *rdp;
585 : :
586 : : rdp = container_of(iwp, struct rcu_data, defer_qs_iw);
587 : : rdp->defer_qs_iw_pending = false;
588 : : }
589 : :
590 : : /*
591 : : * Handle special cases during rcu_read_unlock(), such as needing to
592 : : * notify RCU core processing or task having blocked during the RCU
593 : : * read-side critical section.
594 : : */
595 : : static void rcu_read_unlock_special(struct task_struct *t)
596 : : {
597 : : unsigned long flags;
598 : : bool preempt_bh_were_disabled =
599 : : !!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK));
600 : : bool irqs_were_disabled;
601 : :
602 : : /* NMI handlers cannot block and cannot safely manipulate state. */
603 : : if (in_nmi())
604 : : return;
605 : :
606 : : local_irq_save(flags);
607 : : irqs_were_disabled = irqs_disabled_flags(flags);
608 : : if (preempt_bh_were_disabled || irqs_were_disabled) {
609 : : bool exp;
610 : : struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
611 : : struct rcu_node *rnp = rdp->mynode;
612 : :
613 : : t->rcu_read_unlock_special.b.exp_hint = false;
614 : : exp = (t->rcu_blocked_node && t->rcu_blocked_node->exp_tasks) ||
615 : : (rdp->grpmask & READ_ONCE(rnp->expmask)) ||
616 : : tick_nohz_full_cpu(rdp->cpu);
617 : : // Need to defer quiescent state until everything is enabled.
618 : : if (irqs_were_disabled && use_softirq &&
619 : : (in_interrupt() ||
620 : : (exp && !t->rcu_read_unlock_special.b.deferred_qs))) {
621 : : // Using softirq, safe to awaken, and we get
622 : : // no help from enabling irqs, unlike bh/preempt.
623 : : raise_softirq_irqoff(RCU_SOFTIRQ);
624 : : } else {
625 : : // Enabling BH or preempt does reschedule, so...
626 : : // Also if no expediting or NO_HZ_FULL, slow is OK.
627 : : set_tsk_need_resched(current);
628 : : set_preempt_need_resched();
629 : : if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled &&
630 : : !rdp->defer_qs_iw_pending && exp) {
631 : : // Get scheduler to re-evaluate and call hooks.
632 : : // If !IRQ_WORK, FQS scan will eventually IPI.
633 : : init_irq_work(&rdp->defer_qs_iw,
634 : : rcu_preempt_deferred_qs_handler);
635 : : rdp->defer_qs_iw_pending = true;
636 : : irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
637 : : }
638 : : }
639 : : t->rcu_read_unlock_special.b.deferred_qs = true;
640 : : local_irq_restore(flags);
641 : : return;
642 : : }
643 : : WRITE_ONCE(t->rcu_read_unlock_special.b.exp_hint, false);
644 : : rcu_preempt_deferred_qs_irqrestore(t, flags);
645 : : }
646 : :
647 : : /*
648 : : * Check that the list of blocked tasks for the newly completed grace
649 : : * period is in fact empty. It is a serious bug to complete a grace
650 : : * period that still has RCU readers blocked! This function must be
651 : : * invoked -before- updating this rnp's ->gp_seq, and the rnp's ->lock
652 : : * must be held by the caller.
653 : : *
654 : : * Also, if there are blocked tasks on the list, they automatically
655 : : * block the newly created grace period, so set up ->gp_tasks accordingly.
656 : : */
657 : : static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
658 : : {
659 : : struct task_struct *t;
660 : :
661 : : RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
662 : : if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
663 : : dump_blkd_tasks(rnp, 10);
664 : : if (rcu_preempt_has_tasks(rnp) &&
665 : : (rnp->qsmaskinit || rnp->wait_blkd_tasks)) {
666 : : WRITE_ONCE(rnp->gp_tasks, rnp->blkd_tasks.next);
667 : : t = container_of(rnp->gp_tasks, struct task_struct,
668 : : rcu_node_entry);
669 : : trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
670 : : rnp->gp_seq, t->pid);
671 : : }
672 : : WARN_ON_ONCE(rnp->qsmask);
673 : : }
674 : :
675 : : /*
676 : : * Check for a quiescent state from the current CPU, including voluntary
677 : : * context switches for Tasks RCU. When a task blocks, the task is
678 : : * recorded in the corresponding CPU's rcu_node structure, which is checked
679 : : * elsewhere, hence this function need only check for quiescent states
680 : : * related to the current CPU, not to those related to tasks.
681 : : */
682 : : static void rcu_flavor_sched_clock_irq(int user)
683 : : {
684 : : struct task_struct *t = current;
685 : :
686 : : if (user || rcu_is_cpu_rrupt_from_idle()) {
687 : : rcu_note_voluntary_context_switch(current);
688 : : }
689 : : if (t->rcu_read_lock_nesting > 0 ||
690 : : (preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) {
691 : : /* No QS, force context switch if deferred. */
692 : : if (rcu_preempt_need_deferred_qs(t)) {
693 : : set_tsk_need_resched(t);
694 : : set_preempt_need_resched();
695 : : }
696 : : } else if (rcu_preempt_need_deferred_qs(t)) {
697 : : rcu_preempt_deferred_qs(t); /* Report deferred QS. */
698 : : return;
699 : : } else if (!t->rcu_read_lock_nesting) {
700 : : rcu_qs(); /* Report immediate QS. */
701 : : return;
702 : : }
703 : :
704 : : /* If GP is oldish, ask for help from rcu_read_unlock_special(). */
705 : : if (t->rcu_read_lock_nesting > 0 &&
706 : : __this_cpu_read(rcu_data.core_needs_qs) &&
707 : : __this_cpu_read(rcu_data.cpu_no_qs.b.norm) &&
708 : : !t->rcu_read_unlock_special.b.need_qs &&
709 : : time_after(jiffies, rcu_state.gp_start + HZ))
710 : : t->rcu_read_unlock_special.b.need_qs = true;
711 : : }
712 : :
713 : : /*
714 : : * Check for a task exiting while in a preemptible-RCU read-side
715 : : * critical section, clean up if so. No need to issue warnings, as
716 : : * debug_check_no_locks_held() already does this if lockdep is enabled.
717 : : * Besides, if this function does anything other than just immediately
718 : : * return, there was a bug of some sort. Spewing warnings from this
719 : : * function is like as not to simply obscure important prior warnings.
720 : : */
721 : : void exit_rcu(void)
722 : : {
723 : : struct task_struct *t = current;
724 : :
725 : : if (unlikely(!list_empty(¤t->rcu_node_entry))) {
726 : : t->rcu_read_lock_nesting = 1;
727 : : barrier();
728 : : WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true);
729 : : } else if (unlikely(t->rcu_read_lock_nesting)) {
730 : : t->rcu_read_lock_nesting = 1;
731 : : } else {
732 : : return;
733 : : }
734 : : __rcu_read_unlock();
735 : : rcu_preempt_deferred_qs(current);
736 : : }
737 : :
738 : : /*
739 : : * Dump the blocked-tasks state, but limit the list dump to the
740 : : * specified number of elements.
741 : : */
742 : : static void
743 : : dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
744 : : {
745 : : int cpu;
746 : : int i;
747 : : struct list_head *lhp;
748 : : bool onl;
749 : : struct rcu_data *rdp;
750 : : struct rcu_node *rnp1;
751 : :
752 : : raw_lockdep_assert_held_rcu_node(rnp);
753 : : pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
754 : : __func__, rnp->grplo, rnp->grphi, rnp->level,
755 : : (long)rnp->gp_seq, (long)rnp->completedqs);
756 : : for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
757 : : pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n",
758 : : __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext);
759 : : pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n",
760 : : __func__, READ_ONCE(rnp->gp_tasks), rnp->boost_tasks,
761 : : rnp->exp_tasks);
762 : : pr_info("%s: ->blkd_tasks", __func__);
763 : : i = 0;
764 : : list_for_each(lhp, &rnp->blkd_tasks) {
765 : : pr_cont(" %p", lhp);
766 : : if (++i >= ncheck)
767 : : break;
768 : : }
769 : : pr_cont("\n");
770 : : for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
771 : : rdp = per_cpu_ptr(&rcu_data, cpu);
772 : : onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
773 : : pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n",
774 : : cpu, ".o"[onl],
775 : : (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
776 : : (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
777 : : }
778 : : }
779 : :
780 : : #else /* #ifdef CONFIG_PREEMPT_RCU */
781 : :
782 : : /*
783 : : * Tell them what RCU they are running.
784 : : */
785 : 207 : static void __init rcu_bootup_announce(void)
786 : : {
787 : 207 : pr_info("Hierarchical RCU implementation.\n");
788 : 207 : rcu_bootup_announce_oddness();
789 : 207 : }
790 : :
791 : : /*
792 : : * Note a quiescent state for PREEMPT=n. Because we do not need to know
793 : : * how many quiescent states passed, just if there was at least one since
794 : : * the start of the grace period, this just sets a flag. The caller must
795 : : * have disabled preemption.
796 : : */
797 : 15481466 : static void rcu_qs(void)
798 : : {
799 : : RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!");
800 [ + + ]: 30962932 : if (!__this_cpu_read(rcu_data.cpu_no_qs.s))
801 : : return;
802 : : trace_rcu_grace_period(TPS("rcu_sched"),
803 : 987427 : __this_cpu_read(rcu_data.gp_seq), TPS("cpuqs"));
804 : 1974854 : __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
805 [ + + ]: 1974854 : if (!__this_cpu_read(rcu_data.cpu_no_qs.b.exp))
806 : : return;
807 : 4866 : __this_cpu_write(rcu_data.cpu_no_qs.b.exp, false);
808 : 4866 : rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
809 : : }
810 : :
811 : : /*
812 : : * Register an urgently needed quiescent state. If there is an
813 : : * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
814 : : * dyntick-idle quiescent state visible to other CPUs, which will in
815 : : * some cases serve for expedited as well as normal grace periods.
816 : : * Either way, register a lightweight quiescent state.
817 : : */
818 : 762694400 : void rcu_all_qs(void)
819 : : {
820 : : unsigned long flags;
821 : :
822 [ + + ]: 1525388800 : if (!raw_cpu_read(rcu_data.rcu_urgent_qs))
823 : : return;
824 : 682 : preempt_disable();
825 : : /* Load rcu_urgent_qs before other flags. */
826 [ - + ]: 2046 : if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
827 : 0 : preempt_enable();
828 : 0 : return;
829 : : }
830 : 1364 : this_cpu_write(rcu_data.rcu_urgent_qs, false);
831 [ + + ]: 1364 : if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) {
832 : 22 : local_irq_save(flags);
833 : 22 : rcu_momentary_dyntick_idle();
834 [ - + ]: 22 : local_irq_restore(flags);
835 : : }
836 : 682 : rcu_qs();
837 : 682 : preempt_enable();
838 : : }
839 : : EXPORT_SYMBOL_GPL(rcu_all_qs);
840 : :
841 : : /*
842 : : * Note a PREEMPT=n context switch. The caller must have disabled interrupts.
843 : : */
844 : 11985287 : void rcu_note_context_switch(bool preempt)
845 : : {
846 : 11985287 : trace_rcu_utilization(TPS("Start context switch"));
847 : 11979115 : rcu_qs();
848 : : /* Load rcu_urgent_qs before other flags. */
849 [ + + ]: 35951427 : if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs)))
850 : : goto out;
851 : 5130 : this_cpu_write(rcu_data.rcu_urgent_qs, false);
852 [ + + ]: 5124 : if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs)))
853 : 175 : rcu_momentary_dyntick_idle();
854 : : if (!preempt)
855 : : rcu_tasks_qs(current);
856 : : out:
857 : 11984938 : trace_rcu_utilization(TPS("End context switch"));
858 : 11987676 : }
859 : : EXPORT_SYMBOL_GPL(rcu_note_context_switch);
860 : :
861 : : /*
862 : : * Because preemptible RCU does not exist, there are never any preempted
863 : : * RCU readers.
864 : : */
865 : : static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
866 : : {
867 : : return 0;
868 : : }
869 : :
870 : : /*
871 : : * Because there is no preemptible RCU, there can be no readers blocked.
872 : : */
873 : : static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
874 : : {
875 : : return false;
876 : : }
877 : :
878 : : /*
879 : : * Because there is no preemptible RCU, there can be no deferred quiescent
880 : : * states.
881 : : */
882 : : static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
883 : : {
884 : : return false;
885 : : }
886 : : static void rcu_preempt_deferred_qs(struct task_struct *t) { }
887 : :
888 : : /*
889 : : * Because there is no preemptible RCU, there can be no readers blocked,
890 : : * so there is no need to check for blocked tasks. So check only for
891 : : * bogus qsmask values.
892 : : */
893 : 280204 : static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
894 : : {
895 [ - + # # ]: 280204 : WARN_ON_ONCE(rnp->qsmask);
896 : 280204 : }
897 : :
898 : : /*
899 : : * Check to see if this CPU is in a non-context-switch quiescent state,
900 : : * namely user mode and idle loop.
901 : : */
902 : 2881156 : static void rcu_flavor_sched_clock_irq(int user)
903 : : {
904 [ + + + + ]: 4913600 : if (user || rcu_is_cpu_rrupt_from_idle()) {
905 : :
906 : : /*
907 : : * Get here if this CPU took its interrupt from user
908 : : * mode or from the idle loop, and if this is not a
909 : : * nested interrupt. In this case, the CPU is in
910 : : * a quiescent state, so note it.
911 : : *
912 : : * No memory barrier is required here because rcu_qs()
913 : : * references only CPU-local variables that other CPUs
914 : : * neither access nor modify, at least not while the
915 : : * corresponding CPU is online.
916 : : */
917 : :
918 : 1666717 : rcu_qs();
919 : : }
920 : 2949494 : }
921 : :
922 : : /*
923 : : * Because preemptible RCU does not exist, tasks cannot possibly exit
924 : : * while in preemptible RCU read-side critical sections.
925 : : */
926 : 199287 : void exit_rcu(void)
927 : : {
928 : 199287 : }
929 : :
930 : : /*
931 : : * Dump the guaranteed-empty blocked-tasks state. Trust but verify.
932 : : */
933 : : static void
934 : : dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
935 : : {
936 : : WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));
937 : : }
938 : :
939 : : #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
940 : :
941 : : /*
942 : : * If boosting, set rcuc kthreads to realtime priority.
943 : : */
944 : 0 : static void rcu_cpu_kthread_setup(unsigned int cpu)
945 : : {
946 : : #ifdef CONFIG_RCU_BOOST
947 : : struct sched_param sp;
948 : :
949 : : sp.sched_priority = kthread_prio;
950 : : sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
951 : : #endif /* #ifdef CONFIG_RCU_BOOST */
952 : 0 : }
953 : :
954 : : #ifdef CONFIG_RCU_BOOST
955 : :
956 : : /*
957 : : * Carry out RCU priority boosting on the task indicated by ->exp_tasks
958 : : * or ->boost_tasks, advancing the pointer to the next task in the
959 : : * ->blkd_tasks list.
960 : : *
961 : : * Note that irqs must be enabled: boosting the task can block.
962 : : * Returns 1 if there are more tasks needing to be boosted.
963 : : */
964 : : static int rcu_boost(struct rcu_node *rnp)
965 : : {
966 : : unsigned long flags;
967 : : struct task_struct *t;
968 : : struct list_head *tb;
969 : :
970 : : if (READ_ONCE(rnp->exp_tasks) == NULL &&
971 : : READ_ONCE(rnp->boost_tasks) == NULL)
972 : : return 0; /* Nothing left to boost. */
973 : :
974 : : raw_spin_lock_irqsave_rcu_node(rnp, flags);
975 : :
976 : : /*
977 : : * Recheck under the lock: all tasks in need of boosting
978 : : * might exit their RCU read-side critical sections on their own.
979 : : */
980 : : if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
981 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
982 : : return 0;
983 : : }
984 : :
985 : : /*
986 : : * Preferentially boost tasks blocking expedited grace periods.
987 : : * This cannot starve the normal grace periods because a second
988 : : * expedited grace period must boost all blocked tasks, including
989 : : * those blocking the pre-existing normal grace period.
990 : : */
991 : : if (rnp->exp_tasks != NULL)
992 : : tb = rnp->exp_tasks;
993 : : else
994 : : tb = rnp->boost_tasks;
995 : :
996 : : /*
997 : : * We boost task t by manufacturing an rt_mutex that appears to
998 : : * be held by task t. We leave a pointer to that rt_mutex where
999 : : * task t can find it, and task t will release the mutex when it
1000 : : * exits its outermost RCU read-side critical section. Then
1001 : : * simply acquiring this artificial rt_mutex will boost task
1002 : : * t's priority. (Thanks to tglx for suggesting this approach!)
1003 : : *
1004 : : * Note that task t must acquire rnp->lock to remove itself from
1005 : : * the ->blkd_tasks list, which it will do from exit() if from
1006 : : * nowhere else. We therefore are guaranteed that task t will
1007 : : * stay around at least until we drop rnp->lock. Note that
1008 : : * rnp->lock also resolves races between our priority boosting
1009 : : * and task t's exiting its outermost RCU read-side critical
1010 : : * section.
1011 : : */
1012 : : t = container_of(tb, struct task_struct, rcu_node_entry);
1013 : : rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
1014 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1015 : : /* Lock only for side effect: boosts task t's priority. */
1016 : : rt_mutex_lock(&rnp->boost_mtx);
1017 : : rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
1018 : :
1019 : : return READ_ONCE(rnp->exp_tasks) != NULL ||
1020 : : READ_ONCE(rnp->boost_tasks) != NULL;
1021 : : }
1022 : :
1023 : : /*
1024 : : * Priority-boosting kthread, one per leaf rcu_node.
1025 : : */
1026 : : static int rcu_boost_kthread(void *arg)
1027 : : {
1028 : : struct rcu_node *rnp = (struct rcu_node *)arg;
1029 : : int spincnt = 0;
1030 : : int more2boost;
1031 : :
1032 : : trace_rcu_utilization(TPS("Start boost kthread@init"));
1033 : : for (;;) {
1034 : : rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1035 : : trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1036 : : rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1037 : : trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1038 : : rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1039 : : more2boost = rcu_boost(rnp);
1040 : : if (more2boost)
1041 : : spincnt++;
1042 : : else
1043 : : spincnt = 0;
1044 : : if (spincnt > 10) {
1045 : : rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1046 : : trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1047 : : schedule_timeout_interruptible(2);
1048 : : trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1049 : : spincnt = 0;
1050 : : }
1051 : : }
1052 : : /* NOTREACHED */
1053 : : trace_rcu_utilization(TPS("End boost kthread@notreached"));
1054 : : return 0;
1055 : : }
1056 : :
1057 : : /*
1058 : : * Check to see if it is time to start boosting RCU readers that are
1059 : : * blocking the current grace period, and, if so, tell the per-rcu_node
1060 : : * kthread to start boosting them. If there is an expedited grace
1061 : : * period in progress, it is always time to boost.
1062 : : *
1063 : : * The caller must hold rnp->lock, which this function releases.
1064 : : * The ->boost_kthread_task is immortal, so we don't need to worry
1065 : : * about it going away.
1066 : : */
1067 : : static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1068 : : __releases(rnp->lock)
1069 : : {
1070 : : raw_lockdep_assert_held_rcu_node(rnp);
1071 : : if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1072 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1073 : : return;
1074 : : }
1075 : : if (rnp->exp_tasks != NULL ||
1076 : : (rnp->gp_tasks != NULL &&
1077 : : rnp->boost_tasks == NULL &&
1078 : : rnp->qsmask == 0 &&
1079 : : ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1080 : : if (rnp->exp_tasks == NULL)
1081 : : rnp->boost_tasks = rnp->gp_tasks;
1082 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1083 : : rcu_wake_cond(rnp->boost_kthread_task,
1084 : : rnp->boost_kthread_status);
1085 : : } else {
1086 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1087 : : }
1088 : : }
1089 : :
1090 : : /*
1091 : : * Is the current CPU running the RCU-callbacks kthread?
1092 : : * Caller must have preemption disabled.
1093 : : */
1094 : : static bool rcu_is_callbacks_kthread(void)
1095 : : {
1096 : : return __this_cpu_read(rcu_data.rcu_cpu_kthread_task) == current;
1097 : : }
1098 : :
1099 : : #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1100 : :
1101 : : /*
1102 : : * Do priority-boost accounting for the start of a new grace period.
1103 : : */
1104 : : static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1105 : : {
1106 : : rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1107 : : }
1108 : :
1109 : : /*
1110 : : * Create an RCU-boost kthread for the specified node if one does not
1111 : : * already exist. We only create this kthread for preemptible RCU.
1112 : : * Returns zero if all is well, a negated errno otherwise.
1113 : : */
1114 : : static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
1115 : : {
1116 : : int rnp_index = rnp - rcu_get_root();
1117 : : unsigned long flags;
1118 : : struct sched_param sp;
1119 : : struct task_struct *t;
1120 : :
1121 : : if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
1122 : : return;
1123 : :
1124 : : if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
1125 : : return;
1126 : :
1127 : : rcu_state.boost = 1;
1128 : :
1129 : : if (rnp->boost_kthread_task != NULL)
1130 : : return;
1131 : :
1132 : : t = kthread_create(rcu_boost_kthread, (void *)rnp,
1133 : : "rcub/%d", rnp_index);
1134 : : if (WARN_ON_ONCE(IS_ERR(t)))
1135 : : return;
1136 : :
1137 : : raw_spin_lock_irqsave_rcu_node(rnp, flags);
1138 : : rnp->boost_kthread_task = t;
1139 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1140 : : sp.sched_priority = kthread_prio;
1141 : : sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1142 : : wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1143 : : }
1144 : :
1145 : : /*
1146 : : * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1147 : : * served by the rcu_node in question. The CPU hotplug lock is still
1148 : : * held, so the value of rnp->qsmaskinit will be stable.
1149 : : *
1150 : : * We don't include outgoingcpu in the affinity set, use -1 if there is
1151 : : * no outgoing CPU. If there are no CPUs left in the affinity set,
1152 : : * this function allows the kthread to execute on any CPU.
1153 : : */
1154 : : static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1155 : : {
1156 : : struct task_struct *t = rnp->boost_kthread_task;
1157 : : unsigned long mask = rcu_rnp_online_cpus(rnp);
1158 : : cpumask_var_t cm;
1159 : : int cpu;
1160 : :
1161 : : if (!t)
1162 : : return;
1163 : : if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1164 : : return;
1165 : : for_each_leaf_node_possible_cpu(rnp, cpu)
1166 : : if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
1167 : : cpu != outgoingcpu)
1168 : : cpumask_set_cpu(cpu, cm);
1169 : : if (cpumask_weight(cm) == 0)
1170 : : cpumask_setall(cm);
1171 : : set_cpus_allowed_ptr(t, cm);
1172 : : free_cpumask_var(cm);
1173 : : }
1174 : :
1175 : : /*
1176 : : * Spawn boost kthreads -- called as soon as the scheduler is running.
1177 : : */
1178 : : static void __init rcu_spawn_boost_kthreads(void)
1179 : : {
1180 : : struct rcu_node *rnp;
1181 : :
1182 : : rcu_for_each_leaf_node(rnp)
1183 : : rcu_spawn_one_boost_kthread(rnp);
1184 : : }
1185 : :
1186 : : static void rcu_prepare_kthreads(int cpu)
1187 : : {
1188 : : struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
1189 : : struct rcu_node *rnp = rdp->mynode;
1190 : :
1191 : : /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1192 : : if (rcu_scheduler_fully_active)
1193 : : rcu_spawn_one_boost_kthread(rnp);
1194 : : }
1195 : :
1196 : : #else /* #ifdef CONFIG_RCU_BOOST */
1197 : :
1198 : : static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1199 : : __releases(rnp->lock)
1200 : : {
1201 : 523 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1202 : : }
1203 : :
1204 : : static bool rcu_is_callbacks_kthread(void)
1205 : : {
1206 : : return false;
1207 : : }
1208 : :
1209 : : static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1210 : : {
1211 : : }
1212 : :
1213 : : static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1214 : : {
1215 : : }
1216 : :
1217 : : static void __init rcu_spawn_boost_kthreads(void)
1218 : : {
1219 : : }
1220 : :
1221 : : static void rcu_prepare_kthreads(int cpu)
1222 : : {
1223 : : }
1224 : :
1225 : : #endif /* #else #ifdef CONFIG_RCU_BOOST */
1226 : :
1227 : : #if !defined(CONFIG_RCU_FAST_NO_HZ)
1228 : :
1229 : : /*
1230 : : * Check to see if any future non-offloaded RCU-related work will need
1231 : : * to be done by the current CPU, even if none need be done immediately,
1232 : : * returning 1 if so. This function is part of the RCU implementation;
1233 : : * it is -not- an exported member of the RCU API.
1234 : : *
1235 : : * Because we not have RCU_FAST_NO_HZ, just check whether or not this
1236 : : * CPU has RCU callbacks queued.
1237 : : */
1238 : 118208999 : int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1239 : : {
1240 : 118208999 : *nextevt = KTIME_MAX;
1241 [ + + + + ]: 376751744 : return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) &&
1242 : 44249494 : !rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist);
1243 : : }
1244 : :
1245 : : /*
1246 : : * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1247 : : * after it.
1248 : : */
1249 : 11565411 : static void rcu_cleanup_after_idle(void)
1250 : : {
1251 : 11565411 : }
1252 : :
1253 : : /*
1254 : : * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1255 : : * is nothing.
1256 : : */
1257 : 11563745 : static void rcu_prepare_for_idle(void)
1258 : : {
1259 : 11563745 : }
1260 : :
1261 : : #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1262 : :
1263 : : /*
1264 : : * This code is invoked when a CPU goes idle, at which point we want
1265 : : * to have the CPU do everything required for RCU so that it can enter
1266 : : * the energy-efficient dyntick-idle mode. This is handled by a
1267 : : * state machine implemented by rcu_prepare_for_idle() below.
1268 : : *
1269 : : * The following three proprocessor symbols control this state machine:
1270 : : *
1271 : : * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1272 : : * to sleep in dyntick-idle mode with RCU callbacks pending. This
1273 : : * is sized to be roughly one RCU grace period. Those energy-efficiency
1274 : : * benchmarkers who might otherwise be tempted to set this to a large
1275 : : * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1276 : : * system. And if you are -that- concerned about energy efficiency,
1277 : : * just power the system down and be done with it!
1278 : : * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1279 : : * permitted to sleep in dyntick-idle mode with only lazy RCU
1280 : : * callbacks pending. Setting this too high can OOM your system.
1281 : : *
1282 : : * The values below work well in practice. If future workloads require
1283 : : * adjustment, they can be converted into kernel config parameters, though
1284 : : * making the state machine smarter might be a better option.
1285 : : */
1286 : : #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1287 : : #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1288 : :
1289 : : static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
1290 : : module_param(rcu_idle_gp_delay, int, 0644);
1291 : : static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
1292 : : module_param(rcu_idle_lazy_gp_delay, int, 0644);
1293 : :
1294 : : /*
1295 : : * Try to advance callbacks on the current CPU, but only if it has been
1296 : : * awhile since the last time we did so. Afterwards, if there are any
1297 : : * callbacks ready for immediate invocation, return true.
1298 : : */
1299 : : static bool __maybe_unused rcu_try_advance_all_cbs(void)
1300 : : {
1301 : : bool cbs_ready = false;
1302 : : struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1303 : : struct rcu_node *rnp;
1304 : :
1305 : : /* Exit early if we advanced recently. */
1306 : : if (jiffies == rdp->last_advance_all)
1307 : : return false;
1308 : : rdp->last_advance_all = jiffies;
1309 : :
1310 : : rnp = rdp->mynode;
1311 : :
1312 : : /*
1313 : : * Don't bother checking unless a grace period has
1314 : : * completed since we last checked and there are
1315 : : * callbacks not yet ready to invoke.
1316 : : */
1317 : : if ((rcu_seq_completed_gp(rdp->gp_seq,
1318 : : rcu_seq_current(&rnp->gp_seq)) ||
1319 : : unlikely(READ_ONCE(rdp->gpwrap))) &&
1320 : : rcu_segcblist_pend_cbs(&rdp->cblist))
1321 : : note_gp_changes(rdp);
1322 : :
1323 : : if (rcu_segcblist_ready_cbs(&rdp->cblist))
1324 : : cbs_ready = true;
1325 : : return cbs_ready;
1326 : : }
1327 : :
1328 : : /*
1329 : : * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1330 : : * to invoke. If the CPU has callbacks, try to advance them. Tell the
1331 : : * caller to set the timeout based on whether or not there are non-lazy
1332 : : * callbacks.
1333 : : *
1334 : : * The caller must have disabled interrupts.
1335 : : */
1336 : : int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1337 : : {
1338 : : struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1339 : : unsigned long dj;
1340 : :
1341 : : lockdep_assert_irqs_disabled();
1342 : :
1343 : : /* If no non-offloaded callbacks, RCU doesn't need the CPU. */
1344 : : if (rcu_segcblist_empty(&rdp->cblist) ||
1345 : : rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist)) {
1346 : : *nextevt = KTIME_MAX;
1347 : : return 0;
1348 : : }
1349 : :
1350 : : /* Attempt to advance callbacks. */
1351 : : if (rcu_try_advance_all_cbs()) {
1352 : : /* Some ready to invoke, so initiate later invocation. */
1353 : : invoke_rcu_core();
1354 : : return 1;
1355 : : }
1356 : : rdp->last_accelerate = jiffies;
1357 : :
1358 : : /* Request timer delay depending on laziness, and round. */
1359 : : rdp->all_lazy = !rcu_segcblist_n_nonlazy_cbs(&rdp->cblist);
1360 : : if (rdp->all_lazy) {
1361 : : dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1362 : : } else {
1363 : : dj = round_up(rcu_idle_gp_delay + jiffies,
1364 : : rcu_idle_gp_delay) - jiffies;
1365 : : }
1366 : : *nextevt = basemono + dj * TICK_NSEC;
1367 : : return 0;
1368 : : }
1369 : :
1370 : : /*
1371 : : * Prepare a CPU for idle from an RCU perspective. The first major task
1372 : : * is to sense whether nohz mode has been enabled or disabled via sysfs.
1373 : : * The second major task is to check to see if a non-lazy callback has
1374 : : * arrived at a CPU that previously had only lazy callbacks. The third
1375 : : * major task is to accelerate (that is, assign grace-period numbers to)
1376 : : * any recently arrived callbacks.
1377 : : *
1378 : : * The caller must have disabled interrupts.
1379 : : */
1380 : : static void rcu_prepare_for_idle(void)
1381 : : {
1382 : : bool needwake;
1383 : : struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1384 : : struct rcu_node *rnp;
1385 : : int tne;
1386 : :
1387 : : lockdep_assert_irqs_disabled();
1388 : : if (rcu_segcblist_is_offloaded(&rdp->cblist))
1389 : : return;
1390 : :
1391 : : /* Handle nohz enablement switches conservatively. */
1392 : : tne = READ_ONCE(tick_nohz_active);
1393 : : if (tne != rdp->tick_nohz_enabled_snap) {
1394 : : if (!rcu_segcblist_empty(&rdp->cblist))
1395 : : invoke_rcu_core(); /* force nohz to see update. */
1396 : : rdp->tick_nohz_enabled_snap = tne;
1397 : : return;
1398 : : }
1399 : : if (!tne)
1400 : : return;
1401 : :
1402 : : /*
1403 : : * If a non-lazy callback arrived at a CPU having only lazy
1404 : : * callbacks, invoke RCU core for the side-effect of recalculating
1405 : : * idle duration on re-entry to idle.
1406 : : */
1407 : : if (rdp->all_lazy && rcu_segcblist_n_nonlazy_cbs(&rdp->cblist)) {
1408 : : rdp->all_lazy = false;
1409 : : invoke_rcu_core();
1410 : : return;
1411 : : }
1412 : :
1413 : : /*
1414 : : * If we have not yet accelerated this jiffy, accelerate all
1415 : : * callbacks on this CPU.
1416 : : */
1417 : : if (rdp->last_accelerate == jiffies)
1418 : : return;
1419 : : rdp->last_accelerate = jiffies;
1420 : : if (rcu_segcblist_pend_cbs(&rdp->cblist)) {
1421 : : rnp = rdp->mynode;
1422 : : raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
1423 : : needwake = rcu_accelerate_cbs(rnp, rdp);
1424 : : raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
1425 : : if (needwake)
1426 : : rcu_gp_kthread_wake();
1427 : : }
1428 : : }
1429 : :
1430 : : /*
1431 : : * Clean up for exit from idle. Attempt to advance callbacks based on
1432 : : * any grace periods that elapsed while the CPU was idle, and if any
1433 : : * callbacks are now ready to invoke, initiate invocation.
1434 : : */
1435 : : static void rcu_cleanup_after_idle(void)
1436 : : {
1437 : : struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1438 : :
1439 : : lockdep_assert_irqs_disabled();
1440 : : if (rcu_segcblist_is_offloaded(&rdp->cblist))
1441 : : return;
1442 : : if (rcu_try_advance_all_cbs())
1443 : : invoke_rcu_core();
1444 : : }
1445 : :
1446 : : #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1447 : :
1448 : : #ifdef CONFIG_RCU_NOCB_CPU
1449 : :
1450 : : /*
1451 : : * Offload callback processing from the boot-time-specified set of CPUs
1452 : : * specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads
1453 : : * created that pull the callbacks from the corresponding CPU, wait for
1454 : : * a grace period to elapse, and invoke the callbacks. These kthreads
1455 : : * are organized into GP kthreads, which manage incoming callbacks, wait for
1456 : : * grace periods, and awaken CB kthreads, and the CB kthreads, which only
1457 : : * invoke callbacks. Each GP kthread invokes its own CBs. The no-CBs CPUs
1458 : : * do a wake_up() on their GP kthread when they insert a callback into any
1459 : : * empty list, unless the rcu_nocb_poll boot parameter has been specified,
1460 : : * in which case each kthread actively polls its CPU. (Which isn't so great
1461 : : * for energy efficiency, but which does reduce RCU's overhead on that CPU.)
1462 : : *
1463 : : * This is intended to be used in conjunction with Frederic Weisbecker's
1464 : : * adaptive-idle work, which would seriously reduce OS jitter on CPUs
1465 : : * running CPU-bound user-mode computations.
1466 : : *
1467 : : * Offloading of callbacks can also be used as an energy-efficiency
1468 : : * measure because CPUs with no RCU callbacks queued are more aggressive
1469 : : * about entering dyntick-idle mode.
1470 : : */
1471 : :
1472 : :
1473 : : /*
1474 : : * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters.
1475 : : * The string after the "rcu_nocbs=" is either "all" for all CPUs, or a
1476 : : * comma-separated list of CPUs and/or CPU ranges. If an invalid list is
1477 : : * given, a warning is emitted and all CPUs are offloaded.
1478 : : */
1479 : : static int __init rcu_nocb_setup(char *str)
1480 : : {
1481 : : alloc_bootmem_cpumask_var(&rcu_nocb_mask);
1482 : : if (!strcasecmp(str, "all"))
1483 : : cpumask_setall(rcu_nocb_mask);
1484 : : else
1485 : : if (cpulist_parse(str, rcu_nocb_mask)) {
1486 : : pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
1487 : : cpumask_setall(rcu_nocb_mask);
1488 : : }
1489 : : return 1;
1490 : : }
1491 : : __setup("rcu_nocbs=", rcu_nocb_setup);
1492 : :
1493 : : static int __init parse_rcu_nocb_poll(char *arg)
1494 : : {
1495 : : rcu_nocb_poll = true;
1496 : : return 0;
1497 : : }
1498 : : early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
1499 : :
1500 : : /*
1501 : : * Don't bother bypassing ->cblist if the call_rcu() rate is low.
1502 : : * After all, the main point of bypassing is to avoid lock contention
1503 : : * on ->nocb_lock, which only can happen at high call_rcu() rates.
1504 : : */
1505 : : int nocb_nobypass_lim_per_jiffy = 16 * 1000 / HZ;
1506 : : module_param(nocb_nobypass_lim_per_jiffy, int, 0);
1507 : :
1508 : : /*
1509 : : * Acquire the specified rcu_data structure's ->nocb_bypass_lock. If the
1510 : : * lock isn't immediately available, increment ->nocb_lock_contended to
1511 : : * flag the contention.
1512 : : */
1513 : : static void rcu_nocb_bypass_lock(struct rcu_data *rdp)
1514 : : {
1515 : : lockdep_assert_irqs_disabled();
1516 : : if (raw_spin_trylock(&rdp->nocb_bypass_lock))
1517 : : return;
1518 : : atomic_inc(&rdp->nocb_lock_contended);
1519 : : WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
1520 : : smp_mb__after_atomic(); /* atomic_inc() before lock. */
1521 : : raw_spin_lock(&rdp->nocb_bypass_lock);
1522 : : smp_mb__before_atomic(); /* atomic_dec() after lock. */
1523 : : atomic_dec(&rdp->nocb_lock_contended);
1524 : : }
1525 : :
1526 : : /*
1527 : : * Spinwait until the specified rcu_data structure's ->nocb_lock is
1528 : : * not contended. Please note that this is extremely special-purpose,
1529 : : * relying on the fact that at most two kthreads and one CPU contend for
1530 : : * this lock, and also that the two kthreads are guaranteed to have frequent
1531 : : * grace-period-duration time intervals between successive acquisitions
1532 : : * of the lock. This allows us to use an extremely simple throttling
1533 : : * mechanism, and further to apply it only to the CPU doing floods of
1534 : : * call_rcu() invocations. Don't try this at home!
1535 : : */
1536 : : static void rcu_nocb_wait_contended(struct rcu_data *rdp)
1537 : : {
1538 : : WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
1539 : : while (WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended)))
1540 : : cpu_relax();
1541 : : }
1542 : :
1543 : : /*
1544 : : * Conditionally acquire the specified rcu_data structure's
1545 : : * ->nocb_bypass_lock.
1546 : : */
1547 : : static bool rcu_nocb_bypass_trylock(struct rcu_data *rdp)
1548 : : {
1549 : : lockdep_assert_irqs_disabled();
1550 : : return raw_spin_trylock(&rdp->nocb_bypass_lock);
1551 : : }
1552 : :
1553 : : /*
1554 : : * Release the specified rcu_data structure's ->nocb_bypass_lock.
1555 : : */
1556 : : static void rcu_nocb_bypass_unlock(struct rcu_data *rdp)
1557 : : {
1558 : : lockdep_assert_irqs_disabled();
1559 : : raw_spin_unlock(&rdp->nocb_bypass_lock);
1560 : : }
1561 : :
1562 : : /*
1563 : : * Acquire the specified rcu_data structure's ->nocb_lock, but only
1564 : : * if it corresponds to a no-CBs CPU.
1565 : : */
1566 : : static void rcu_nocb_lock(struct rcu_data *rdp)
1567 : : {
1568 : : lockdep_assert_irqs_disabled();
1569 : : if (!rcu_segcblist_is_offloaded(&rdp->cblist))
1570 : : return;
1571 : : raw_spin_lock(&rdp->nocb_lock);
1572 : : }
1573 : :
1574 : : /*
1575 : : * Release the specified rcu_data structure's ->nocb_lock, but only
1576 : : * if it corresponds to a no-CBs CPU.
1577 : : */
1578 : : static void rcu_nocb_unlock(struct rcu_data *rdp)
1579 : : {
1580 : : if (rcu_segcblist_is_offloaded(&rdp->cblist)) {
1581 : : lockdep_assert_irqs_disabled();
1582 : : raw_spin_unlock(&rdp->nocb_lock);
1583 : : }
1584 : : }
1585 : :
1586 : : /*
1587 : : * Release the specified rcu_data structure's ->nocb_lock and restore
1588 : : * interrupts, but only if it corresponds to a no-CBs CPU.
1589 : : */
1590 : : static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
1591 : : unsigned long flags)
1592 : : {
1593 : : if (rcu_segcblist_is_offloaded(&rdp->cblist)) {
1594 : : lockdep_assert_irqs_disabled();
1595 : : raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1596 : : } else {
1597 : : local_irq_restore(flags);
1598 : : }
1599 : : }
1600 : :
1601 : : /* Lockdep check that ->cblist may be safely accessed. */
1602 : : static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
1603 : : {
1604 : : lockdep_assert_irqs_disabled();
1605 : : if (rcu_segcblist_is_offloaded(&rdp->cblist) &&
1606 : : cpu_online(rdp->cpu))
1607 : : lockdep_assert_held(&rdp->nocb_lock);
1608 : : }
1609 : :
1610 : : /*
1611 : : * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
1612 : : * grace period.
1613 : : */
1614 : : static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
1615 : : {
1616 : : swake_up_all(sq);
1617 : : }
1618 : :
1619 : : static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
1620 : : {
1621 : : return &rnp->nocb_gp_wq[rcu_seq_ctr(rnp->gp_seq) & 0x1];
1622 : : }
1623 : :
1624 : : static void rcu_init_one_nocb(struct rcu_node *rnp)
1625 : : {
1626 : : init_swait_queue_head(&rnp->nocb_gp_wq[0]);
1627 : : init_swait_queue_head(&rnp->nocb_gp_wq[1]);
1628 : : }
1629 : :
1630 : : /* Is the specified CPU a no-CBs CPU? */
1631 : : bool rcu_is_nocb_cpu(int cpu)
1632 : : {
1633 : : if (cpumask_available(rcu_nocb_mask))
1634 : : return cpumask_test_cpu(cpu, rcu_nocb_mask);
1635 : : return false;
1636 : : }
1637 : :
1638 : : /*
1639 : : * Kick the GP kthread for this NOCB group. Caller holds ->nocb_lock
1640 : : * and this function releases it.
1641 : : */
1642 : : static void wake_nocb_gp(struct rcu_data *rdp, bool force,
1643 : : unsigned long flags)
1644 : : __releases(rdp->nocb_lock)
1645 : : {
1646 : : bool needwake = false;
1647 : : struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
1648 : :
1649 : : lockdep_assert_held(&rdp->nocb_lock);
1650 : : if (!READ_ONCE(rdp_gp->nocb_gp_kthread)) {
1651 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1652 : : TPS("AlreadyAwake"));
1653 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1654 : : return;
1655 : : }
1656 : : del_timer(&rdp->nocb_timer);
1657 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1658 : : raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
1659 : : if (force || READ_ONCE(rdp_gp->nocb_gp_sleep)) {
1660 : : WRITE_ONCE(rdp_gp->nocb_gp_sleep, false);
1661 : : needwake = true;
1662 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DoWake"));
1663 : : }
1664 : : raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
1665 : : if (needwake)
1666 : : wake_up_process(rdp_gp->nocb_gp_kthread);
1667 : : }
1668 : :
1669 : : /*
1670 : : * Arrange to wake the GP kthread for this NOCB group at some future
1671 : : * time when it is safe to do so.
1672 : : */
1673 : : static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
1674 : : const char *reason)
1675 : : {
1676 : : if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
1677 : : mod_timer(&rdp->nocb_timer, jiffies + 1);
1678 : : if (rdp->nocb_defer_wakeup < waketype)
1679 : : WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
1680 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason);
1681 : : }
1682 : :
1683 : : /*
1684 : : * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
1685 : : * However, if there is a callback to be enqueued and if ->nocb_bypass
1686 : : * proves to be initially empty, just return false because the no-CB GP
1687 : : * kthread may need to be awakened in this case.
1688 : : *
1689 : : * Note that this function always returns true if rhp is NULL.
1690 : : */
1691 : : static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
1692 : : unsigned long j)
1693 : : {
1694 : : struct rcu_cblist rcl;
1695 : :
1696 : : WARN_ON_ONCE(!rcu_segcblist_is_offloaded(&rdp->cblist));
1697 : : rcu_lockdep_assert_cblist_protected(rdp);
1698 : : lockdep_assert_held(&rdp->nocb_bypass_lock);
1699 : : if (rhp && !rcu_cblist_n_cbs(&rdp->nocb_bypass)) {
1700 : : raw_spin_unlock(&rdp->nocb_bypass_lock);
1701 : : return false;
1702 : : }
1703 : : /* Note: ->cblist.len already accounts for ->nocb_bypass contents. */
1704 : : if (rhp)
1705 : : rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
1706 : : rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp);
1707 : : rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl);
1708 : : WRITE_ONCE(rdp->nocb_bypass_first, j);
1709 : : rcu_nocb_bypass_unlock(rdp);
1710 : : return true;
1711 : : }
1712 : :
1713 : : /*
1714 : : * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
1715 : : * However, if there is a callback to be enqueued and if ->nocb_bypass
1716 : : * proves to be initially empty, just return false because the no-CB GP
1717 : : * kthread may need to be awakened in this case.
1718 : : *
1719 : : * Note that this function always returns true if rhp is NULL.
1720 : : */
1721 : : static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
1722 : : unsigned long j)
1723 : : {
1724 : : if (!rcu_segcblist_is_offloaded(&rdp->cblist))
1725 : : return true;
1726 : : rcu_lockdep_assert_cblist_protected(rdp);
1727 : : rcu_nocb_bypass_lock(rdp);
1728 : : return rcu_nocb_do_flush_bypass(rdp, rhp, j);
1729 : : }
1730 : :
1731 : : /*
1732 : : * If the ->nocb_bypass_lock is immediately available, flush the
1733 : : * ->nocb_bypass queue into ->cblist.
1734 : : */
1735 : : static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j)
1736 : : {
1737 : : rcu_lockdep_assert_cblist_protected(rdp);
1738 : : if (!rcu_segcblist_is_offloaded(&rdp->cblist) ||
1739 : : !rcu_nocb_bypass_trylock(rdp))
1740 : : return;
1741 : : WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j));
1742 : : }
1743 : :
1744 : : /*
1745 : : * See whether it is appropriate to use the ->nocb_bypass list in order
1746 : : * to control contention on ->nocb_lock. A limited number of direct
1747 : : * enqueues are permitted into ->cblist per jiffy. If ->nocb_bypass
1748 : : * is non-empty, further callbacks must be placed into ->nocb_bypass,
1749 : : * otherwise rcu_barrier() breaks. Use rcu_nocb_flush_bypass() to switch
1750 : : * back to direct use of ->cblist. However, ->nocb_bypass should not be
1751 : : * used if ->cblist is empty, because otherwise callbacks can be stranded
1752 : : * on ->nocb_bypass because we cannot count on the current CPU ever again
1753 : : * invoking call_rcu(). The general rule is that if ->nocb_bypass is
1754 : : * non-empty, the corresponding no-CBs grace-period kthread must not be
1755 : : * in an indefinite sleep state.
1756 : : *
1757 : : * Finally, it is not permitted to use the bypass during early boot,
1758 : : * as doing so would confuse the auto-initialization code. Besides
1759 : : * which, there is no point in worrying about lock contention while
1760 : : * there is only one CPU in operation.
1761 : : */
1762 : : static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
1763 : : bool *was_alldone, unsigned long flags)
1764 : : {
1765 : : unsigned long c;
1766 : : unsigned long cur_gp_seq;
1767 : : unsigned long j = jiffies;
1768 : : long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
1769 : :
1770 : : if (!rcu_segcblist_is_offloaded(&rdp->cblist)) {
1771 : : *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
1772 : : return false; /* Not offloaded, no bypassing. */
1773 : : }
1774 : : lockdep_assert_irqs_disabled();
1775 : :
1776 : : // Don't use ->nocb_bypass during early boot.
1777 : : if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING) {
1778 : : rcu_nocb_lock(rdp);
1779 : : WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
1780 : : *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
1781 : : return false;
1782 : : }
1783 : :
1784 : : // If we have advanced to a new jiffy, reset counts to allow
1785 : : // moving back from ->nocb_bypass to ->cblist.
1786 : : if (j == rdp->nocb_nobypass_last) {
1787 : : c = rdp->nocb_nobypass_count + 1;
1788 : : } else {
1789 : : WRITE_ONCE(rdp->nocb_nobypass_last, j);
1790 : : c = rdp->nocb_nobypass_count - nocb_nobypass_lim_per_jiffy;
1791 : : if (ULONG_CMP_LT(rdp->nocb_nobypass_count,
1792 : : nocb_nobypass_lim_per_jiffy))
1793 : : c = 0;
1794 : : else if (c > nocb_nobypass_lim_per_jiffy)
1795 : : c = nocb_nobypass_lim_per_jiffy;
1796 : : }
1797 : : WRITE_ONCE(rdp->nocb_nobypass_count, c);
1798 : :
1799 : : // If there hasn't yet been all that many ->cblist enqueues
1800 : : // this jiffy, tell the caller to enqueue onto ->cblist. But flush
1801 : : // ->nocb_bypass first.
1802 : : if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy) {
1803 : : rcu_nocb_lock(rdp);
1804 : : *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
1805 : : if (*was_alldone)
1806 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1807 : : TPS("FirstQ"));
1808 : : WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j));
1809 : : WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
1810 : : return false; // Caller must enqueue the callback.
1811 : : }
1812 : :
1813 : : // If ->nocb_bypass has been used too long or is too full,
1814 : : // flush ->nocb_bypass to ->cblist.
1815 : : if ((ncbs && j != READ_ONCE(rdp->nocb_bypass_first)) ||
1816 : : ncbs >= qhimark) {
1817 : : rcu_nocb_lock(rdp);
1818 : : if (!rcu_nocb_flush_bypass(rdp, rhp, j)) {
1819 : : *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
1820 : : if (*was_alldone)
1821 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1822 : : TPS("FirstQ"));
1823 : : WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
1824 : : return false; // Caller must enqueue the callback.
1825 : : }
1826 : : if (j != rdp->nocb_gp_adv_time &&
1827 : : rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
1828 : : rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
1829 : : rcu_advance_cbs_nowake(rdp->mynode, rdp);
1830 : : rdp->nocb_gp_adv_time = j;
1831 : : }
1832 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1833 : : return true; // Callback already enqueued.
1834 : : }
1835 : :
1836 : : // We need to use the bypass.
1837 : : rcu_nocb_wait_contended(rdp);
1838 : : rcu_nocb_bypass_lock(rdp);
1839 : : ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
1840 : : rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
1841 : : rcu_cblist_enqueue(&rdp->nocb_bypass, rhp);
1842 : : if (!ncbs) {
1843 : : WRITE_ONCE(rdp->nocb_bypass_first, j);
1844 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstBQ"));
1845 : : }
1846 : : rcu_nocb_bypass_unlock(rdp);
1847 : : smp_mb(); /* Order enqueue before wake. */
1848 : : if (ncbs) {
1849 : : local_irq_restore(flags);
1850 : : } else {
1851 : : // No-CBs GP kthread might be indefinitely asleep, if so, wake.
1852 : : rcu_nocb_lock(rdp); // Rare during call_rcu() flood.
1853 : : if (!rcu_segcblist_pend_cbs(&rdp->cblist)) {
1854 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1855 : : TPS("FirstBQwake"));
1856 : : __call_rcu_nocb_wake(rdp, true, flags);
1857 : : } else {
1858 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1859 : : TPS("FirstBQnoWake"));
1860 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1861 : : }
1862 : : }
1863 : : return true; // Callback already enqueued.
1864 : : }
1865 : :
1866 : : /*
1867 : : * Awaken the no-CBs grace-period kthead if needed, either due to it
1868 : : * legitimately being asleep or due to overload conditions.
1869 : : *
1870 : : * If warranted, also wake up the kthread servicing this CPUs queues.
1871 : : */
1872 : : static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
1873 : : unsigned long flags)
1874 : : __releases(rdp->nocb_lock)
1875 : : {
1876 : : unsigned long cur_gp_seq;
1877 : : unsigned long j;
1878 : : long len;
1879 : : struct task_struct *t;
1880 : :
1881 : : // If we are being polled or there is no kthread, just leave.
1882 : : t = READ_ONCE(rdp->nocb_gp_kthread);
1883 : : if (rcu_nocb_poll || !t) {
1884 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1885 : : TPS("WakeNotPoll"));
1886 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1887 : : return;
1888 : : }
1889 : : // Need to actually to a wakeup.
1890 : : len = rcu_segcblist_n_cbs(&rdp->cblist);
1891 : : if (was_alldone) {
1892 : : rdp->qlen_last_fqs_check = len;
1893 : : if (!irqs_disabled_flags(flags)) {
1894 : : /* ... if queue was empty ... */
1895 : : wake_nocb_gp(rdp, false, flags);
1896 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1897 : : TPS("WakeEmpty"));
1898 : : } else {
1899 : : wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE,
1900 : : TPS("WakeEmptyIsDeferred"));
1901 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1902 : : }
1903 : : } else if (len > rdp->qlen_last_fqs_check + qhimark) {
1904 : : /* ... or if many callbacks queued. */
1905 : : rdp->qlen_last_fqs_check = len;
1906 : : j = jiffies;
1907 : : if (j != rdp->nocb_gp_adv_time &&
1908 : : rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
1909 : : rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
1910 : : rcu_advance_cbs_nowake(rdp->mynode, rdp);
1911 : : rdp->nocb_gp_adv_time = j;
1912 : : }
1913 : : smp_mb(); /* Enqueue before timer_pending(). */
1914 : : if ((rdp->nocb_cb_sleep ||
1915 : : !rcu_segcblist_ready_cbs(&rdp->cblist)) &&
1916 : : !timer_pending(&rdp->nocb_bypass_timer))
1917 : : wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
1918 : : TPS("WakeOvfIsDeferred"));
1919 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1920 : : } else {
1921 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
1922 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1923 : : }
1924 : : return;
1925 : : }
1926 : :
1927 : : /* Wake up the no-CBs GP kthread to flush ->nocb_bypass. */
1928 : : static void do_nocb_bypass_wakeup_timer(struct timer_list *t)
1929 : : {
1930 : : unsigned long flags;
1931 : : struct rcu_data *rdp = from_timer(rdp, t, nocb_bypass_timer);
1932 : :
1933 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Timer"));
1934 : : rcu_nocb_lock_irqsave(rdp, flags);
1935 : : smp_mb__after_spinlock(); /* Timer expire before wakeup. */
1936 : : __call_rcu_nocb_wake(rdp, true, flags);
1937 : : }
1938 : :
1939 : : /*
1940 : : * No-CBs GP kthreads come here to wait for additional callbacks to show up
1941 : : * or for grace periods to end.
1942 : : */
1943 : : static void nocb_gp_wait(struct rcu_data *my_rdp)
1944 : : {
1945 : : bool bypass = false;
1946 : : long bypass_ncbs;
1947 : : int __maybe_unused cpu = my_rdp->cpu;
1948 : : unsigned long cur_gp_seq;
1949 : : unsigned long flags;
1950 : : bool gotcbs = false;
1951 : : unsigned long j = jiffies;
1952 : : bool needwait_gp = false; // This prevents actual uninitialized use.
1953 : : bool needwake;
1954 : : bool needwake_gp;
1955 : : struct rcu_data *rdp;
1956 : : struct rcu_node *rnp;
1957 : : unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning.
1958 : :
1959 : : /*
1960 : : * Each pass through the following loop checks for CBs and for the
1961 : : * nearest grace period (if any) to wait for next. The CB kthreads
1962 : : * and the global grace-period kthread are awakened if needed.
1963 : : */
1964 : : for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_cb_rdp) {
1965 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check"));
1966 : : rcu_nocb_lock_irqsave(rdp, flags);
1967 : : bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
1968 : : if (bypass_ncbs &&
1969 : : (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) ||
1970 : : bypass_ncbs > 2 * qhimark)) {
1971 : : // Bypass full or old, so flush it.
1972 : : (void)rcu_nocb_try_flush_bypass(rdp, j);
1973 : : bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
1974 : : } else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) {
1975 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1976 : : continue; /* No callbacks here, try next. */
1977 : : }
1978 : : if (bypass_ncbs) {
1979 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1980 : : TPS("Bypass"));
1981 : : bypass = true;
1982 : : }
1983 : : rnp = rdp->mynode;
1984 : : if (bypass) { // Avoid race with first bypass CB.
1985 : : WRITE_ONCE(my_rdp->nocb_defer_wakeup,
1986 : : RCU_NOCB_WAKE_NOT);
1987 : : del_timer(&my_rdp->nocb_timer);
1988 : : }
1989 : : // Advance callbacks if helpful and low contention.
1990 : : needwake_gp = false;
1991 : : if (!rcu_segcblist_restempty(&rdp->cblist,
1992 : : RCU_NEXT_READY_TAIL) ||
1993 : : (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
1994 : : rcu_seq_done(&rnp->gp_seq, cur_gp_seq))) {
1995 : : raw_spin_lock_rcu_node(rnp); /* irqs disabled. */
1996 : : needwake_gp = rcu_advance_cbs(rnp, rdp);
1997 : : raw_spin_unlock_rcu_node(rnp); /* irqs disabled. */
1998 : : }
1999 : : // Need to wait on some grace period?
2000 : : WARN_ON_ONCE(!rcu_segcblist_restempty(&rdp->cblist,
2001 : : RCU_NEXT_READY_TAIL));
2002 : : if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq)) {
2003 : : if (!needwait_gp ||
2004 : : ULONG_CMP_LT(cur_gp_seq, wait_gp_seq))
2005 : : wait_gp_seq = cur_gp_seq;
2006 : : needwait_gp = true;
2007 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
2008 : : TPS("NeedWaitGP"));
2009 : : }
2010 : : if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
2011 : : needwake = rdp->nocb_cb_sleep;
2012 : : WRITE_ONCE(rdp->nocb_cb_sleep, false);
2013 : : smp_mb(); /* CB invocation -after- GP end. */
2014 : : } else {
2015 : : needwake = false;
2016 : : }
2017 : : rcu_nocb_unlock_irqrestore(rdp, flags);
2018 : : if (needwake) {
2019 : : swake_up_one(&rdp->nocb_cb_wq);
2020 : : gotcbs = true;
2021 : : }
2022 : : if (needwake_gp)
2023 : : rcu_gp_kthread_wake();
2024 : : }
2025 : :
2026 : : my_rdp->nocb_gp_bypass = bypass;
2027 : : my_rdp->nocb_gp_gp = needwait_gp;
2028 : : my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;
2029 : : if (bypass && !rcu_nocb_poll) {
2030 : : // At least one child with non-empty ->nocb_bypass, so set
2031 : : // timer in order to avoid stranding its callbacks.
2032 : : raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
2033 : : mod_timer(&my_rdp->nocb_bypass_timer, j + 2);
2034 : : raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
2035 : : }
2036 : : if (rcu_nocb_poll) {
2037 : : /* Polling, so trace if first poll in the series. */
2038 : : if (gotcbs)
2039 : : trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
2040 : : schedule_timeout_interruptible(1);
2041 : : } else if (!needwait_gp) {
2042 : : /* Wait for callbacks to appear. */
2043 : : trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
2044 : : swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq,
2045 : : !READ_ONCE(my_rdp->nocb_gp_sleep));
2046 : : trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep"));
2047 : : } else {
2048 : : rnp = my_rdp->mynode;
2049 : : trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("StartWait"));
2050 : : swait_event_interruptible_exclusive(
2051 : : rnp->nocb_gp_wq[rcu_seq_ctr(wait_gp_seq) & 0x1],
2052 : : rcu_seq_done(&rnp->gp_seq, wait_gp_seq) ||
2053 : : !READ_ONCE(my_rdp->nocb_gp_sleep));
2054 : : trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("EndWait"));
2055 : : }
2056 : : if (!rcu_nocb_poll) {
2057 : : raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
2058 : : if (bypass)
2059 : : del_timer(&my_rdp->nocb_bypass_timer);
2060 : : WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
2061 : : raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
2062 : : }
2063 : : my_rdp->nocb_gp_seq = -1;
2064 : : WARN_ON(signal_pending(current));
2065 : : }
2066 : :
2067 : : /*
2068 : : * No-CBs grace-period-wait kthread. There is one of these per group
2069 : : * of CPUs, but only once at least one CPU in that group has come online
2070 : : * at least once since boot. This kthread checks for newly posted
2071 : : * callbacks from any of the CPUs it is responsible for, waits for a
2072 : : * grace period, then awakens all of the rcu_nocb_cb_kthread() instances
2073 : : * that then have callback-invocation work to do.
2074 : : */
2075 : : static int rcu_nocb_gp_kthread(void *arg)
2076 : : {
2077 : : struct rcu_data *rdp = arg;
2078 : :
2079 : : for (;;) {
2080 : : WRITE_ONCE(rdp->nocb_gp_loops, rdp->nocb_gp_loops + 1);
2081 : : nocb_gp_wait(rdp);
2082 : : cond_resched_tasks_rcu_qs();
2083 : : }
2084 : : return 0;
2085 : : }
2086 : :
2087 : : /*
2088 : : * Invoke any ready callbacks from the corresponding no-CBs CPU,
2089 : : * then, if there are no more, wait for more to appear.
2090 : : */
2091 : : static void nocb_cb_wait(struct rcu_data *rdp)
2092 : : {
2093 : : unsigned long cur_gp_seq;
2094 : : unsigned long flags;
2095 : : bool needwake_gp = false;
2096 : : struct rcu_node *rnp = rdp->mynode;
2097 : :
2098 : : local_irq_save(flags);
2099 : : rcu_momentary_dyntick_idle();
2100 : : local_irq_restore(flags);
2101 : : local_bh_disable();
2102 : : rcu_do_batch(rdp);
2103 : : local_bh_enable();
2104 : : lockdep_assert_irqs_enabled();
2105 : : rcu_nocb_lock_irqsave(rdp, flags);
2106 : : if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
2107 : : rcu_seq_done(&rnp->gp_seq, cur_gp_seq) &&
2108 : : raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */
2109 : : needwake_gp = rcu_advance_cbs(rdp->mynode, rdp);
2110 : : raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2111 : : }
2112 : : if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
2113 : : rcu_nocb_unlock_irqrestore(rdp, flags);
2114 : : if (needwake_gp)
2115 : : rcu_gp_kthread_wake();
2116 : : return;
2117 : : }
2118 : :
2119 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("CBSleep"));
2120 : : WRITE_ONCE(rdp->nocb_cb_sleep, true);
2121 : : rcu_nocb_unlock_irqrestore(rdp, flags);
2122 : : if (needwake_gp)
2123 : : rcu_gp_kthread_wake();
2124 : : swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
2125 : : !READ_ONCE(rdp->nocb_cb_sleep));
2126 : : if (!smp_load_acquire(&rdp->nocb_cb_sleep)) { /* VVV */
2127 : : /* ^^^ Ensure CB invocation follows _sleep test. */
2128 : : return;
2129 : : }
2130 : : WARN_ON(signal_pending(current));
2131 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty"));
2132 : : }
2133 : :
2134 : : /*
2135 : : * Per-rcu_data kthread, but only for no-CBs CPUs. Repeatedly invoke
2136 : : * nocb_cb_wait() to do the dirty work.
2137 : : */
2138 : : static int rcu_nocb_cb_kthread(void *arg)
2139 : : {
2140 : : struct rcu_data *rdp = arg;
2141 : :
2142 : : // Each pass through this loop does one callback batch, and,
2143 : : // if there are no more ready callbacks, waits for them.
2144 : : for (;;) {
2145 : : nocb_cb_wait(rdp);
2146 : : cond_resched_tasks_rcu_qs();
2147 : : }
2148 : : return 0;
2149 : : }
2150 : :
2151 : : /* Is a deferred wakeup of rcu_nocb_kthread() required? */
2152 : : static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2153 : : {
2154 : : return READ_ONCE(rdp->nocb_defer_wakeup);
2155 : : }
2156 : :
2157 : : /* Do a deferred wakeup of rcu_nocb_kthread(). */
2158 : : static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
2159 : : {
2160 : : unsigned long flags;
2161 : : int ndw;
2162 : :
2163 : : rcu_nocb_lock_irqsave(rdp, flags);
2164 : : if (!rcu_nocb_need_deferred_wakeup(rdp)) {
2165 : : rcu_nocb_unlock_irqrestore(rdp, flags);
2166 : : return;
2167 : : }
2168 : : ndw = READ_ONCE(rdp->nocb_defer_wakeup);
2169 : : WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
2170 : : wake_nocb_gp(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
2171 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DeferredWake"));
2172 : : }
2173 : :
2174 : : /* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
2175 : : static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
2176 : : {
2177 : : struct rcu_data *rdp = from_timer(rdp, t, nocb_timer);
2178 : :
2179 : : do_nocb_deferred_wakeup_common(rdp);
2180 : : }
2181 : :
2182 : : /*
2183 : : * Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
2184 : : * This means we do an inexact common-case check. Note that if
2185 : : * we miss, ->nocb_timer will eventually clean things up.
2186 : : */
2187 : : static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2188 : : {
2189 : : if (rcu_nocb_need_deferred_wakeup(rdp))
2190 : : do_nocb_deferred_wakeup_common(rdp);
2191 : : }
2192 : :
2193 : : void __init rcu_init_nohz(void)
2194 : : {
2195 : : int cpu;
2196 : : bool need_rcu_nocb_mask = false;
2197 : : struct rcu_data *rdp;
2198 : :
2199 : : #if defined(CONFIG_NO_HZ_FULL)
2200 : : if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
2201 : : need_rcu_nocb_mask = true;
2202 : : #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2203 : :
2204 : : if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) {
2205 : : if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
2206 : : pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
2207 : : return;
2208 : : }
2209 : : }
2210 : : if (!cpumask_available(rcu_nocb_mask))
2211 : : return;
2212 : :
2213 : : #if defined(CONFIG_NO_HZ_FULL)
2214 : : if (tick_nohz_full_running)
2215 : : cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
2216 : : #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2217 : :
2218 : : if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
2219 : : pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
2220 : : cpumask_and(rcu_nocb_mask, cpu_possible_mask,
2221 : : rcu_nocb_mask);
2222 : : }
2223 : : if (cpumask_empty(rcu_nocb_mask))
2224 : : pr_info("\tOffload RCU callbacks from CPUs: (none).\n");
2225 : : else
2226 : : pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
2227 : : cpumask_pr_args(rcu_nocb_mask));
2228 : : if (rcu_nocb_poll)
2229 : : pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
2230 : :
2231 : : for_each_cpu(cpu, rcu_nocb_mask) {
2232 : : rdp = per_cpu_ptr(&rcu_data, cpu);
2233 : : if (rcu_segcblist_empty(&rdp->cblist))
2234 : : rcu_segcblist_init(&rdp->cblist);
2235 : : rcu_segcblist_offload(&rdp->cblist);
2236 : : }
2237 : : rcu_organize_nocb_kthreads();
2238 : : }
2239 : :
2240 : : /* Initialize per-rcu_data variables for no-CBs CPUs. */
2241 : : static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2242 : : {
2243 : : init_swait_queue_head(&rdp->nocb_cb_wq);
2244 : : init_swait_queue_head(&rdp->nocb_gp_wq);
2245 : : raw_spin_lock_init(&rdp->nocb_lock);
2246 : : raw_spin_lock_init(&rdp->nocb_bypass_lock);
2247 : : raw_spin_lock_init(&rdp->nocb_gp_lock);
2248 : : timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
2249 : : timer_setup(&rdp->nocb_bypass_timer, do_nocb_bypass_wakeup_timer, 0);
2250 : : rcu_cblist_init(&rdp->nocb_bypass);
2251 : : }
2252 : :
2253 : : /*
2254 : : * If the specified CPU is a no-CBs CPU that does not already have its
2255 : : * rcuo CB kthread, spawn it. Additionally, if the rcuo GP kthread
2256 : : * for this CPU's group has not yet been created, spawn it as well.
2257 : : */
2258 : : static void rcu_spawn_one_nocb_kthread(int cpu)
2259 : : {
2260 : : struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
2261 : : struct rcu_data *rdp_gp;
2262 : : struct task_struct *t;
2263 : :
2264 : : /*
2265 : : * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
2266 : : * then nothing to do.
2267 : : */
2268 : : if (!rcu_is_nocb_cpu(cpu) || rdp->nocb_cb_kthread)
2269 : : return;
2270 : :
2271 : : /* If we didn't spawn the GP kthread first, reorganize! */
2272 : : rdp_gp = rdp->nocb_gp_rdp;
2273 : : if (!rdp_gp->nocb_gp_kthread) {
2274 : : t = kthread_run(rcu_nocb_gp_kthread, rdp_gp,
2275 : : "rcuog/%d", rdp_gp->cpu);
2276 : : if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__))
2277 : : return;
2278 : : WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);
2279 : : }
2280 : :
2281 : : /* Spawn the kthread for this CPU. */
2282 : : t = kthread_run(rcu_nocb_cb_kthread, rdp,
2283 : : "rcuo%c/%d", rcu_state.abbr, cpu);
2284 : : if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__))
2285 : : return;
2286 : : WRITE_ONCE(rdp->nocb_cb_kthread, t);
2287 : : WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread);
2288 : : }
2289 : :
2290 : : /*
2291 : : * If the specified CPU is a no-CBs CPU that does not already have its
2292 : : * rcuo kthread, spawn it.
2293 : : */
2294 : : static void rcu_spawn_cpu_nocb_kthread(int cpu)
2295 : : {
2296 : : if (rcu_scheduler_fully_active)
2297 : : rcu_spawn_one_nocb_kthread(cpu);
2298 : : }
2299 : :
2300 : : /*
2301 : : * Once the scheduler is running, spawn rcuo kthreads for all online
2302 : : * no-CBs CPUs. This assumes that the early_initcall()s happen before
2303 : : * non-boot CPUs come online -- if this changes, we will need to add
2304 : : * some mutual exclusion.
2305 : : */
2306 : : static void __init rcu_spawn_nocb_kthreads(void)
2307 : : {
2308 : : int cpu;
2309 : :
2310 : : for_each_online_cpu(cpu)
2311 : : rcu_spawn_cpu_nocb_kthread(cpu);
2312 : : }
2313 : :
2314 : : /* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */
2315 : : static int rcu_nocb_gp_stride = -1;
2316 : : module_param(rcu_nocb_gp_stride, int, 0444);
2317 : :
2318 : : /*
2319 : : * Initialize GP-CB relationships for all no-CBs CPU.
2320 : : */
2321 : : static void __init rcu_organize_nocb_kthreads(void)
2322 : : {
2323 : : int cpu;
2324 : : bool firsttime = true;
2325 : : bool gotnocbs = false;
2326 : : bool gotnocbscbs = true;
2327 : : int ls = rcu_nocb_gp_stride;
2328 : : int nl = 0; /* Next GP kthread. */
2329 : : struct rcu_data *rdp;
2330 : : struct rcu_data *rdp_gp = NULL; /* Suppress misguided gcc warn. */
2331 : : struct rcu_data *rdp_prev = NULL;
2332 : :
2333 : : if (!cpumask_available(rcu_nocb_mask))
2334 : : return;
2335 : : if (ls == -1) {
2336 : : ls = nr_cpu_ids / int_sqrt(nr_cpu_ids);
2337 : : rcu_nocb_gp_stride = ls;
2338 : : }
2339 : :
2340 : : /*
2341 : : * Each pass through this loop sets up one rcu_data structure.
2342 : : * Should the corresponding CPU come online in the future, then
2343 : : * we will spawn the needed set of rcu_nocb_kthread() kthreads.
2344 : : */
2345 : : for_each_cpu(cpu, rcu_nocb_mask) {
2346 : : rdp = per_cpu_ptr(&rcu_data, cpu);
2347 : : if (rdp->cpu >= nl) {
2348 : : /* New GP kthread, set up for CBs & next GP. */
2349 : : gotnocbs = true;
2350 : : nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
2351 : : rdp->nocb_gp_rdp = rdp;
2352 : : rdp_gp = rdp;
2353 : : if (dump_tree) {
2354 : : if (!firsttime)
2355 : : pr_cont("%s\n", gotnocbscbs
2356 : : ? "" : " (self only)");
2357 : : gotnocbscbs = false;
2358 : : firsttime = false;
2359 : : pr_alert("%s: No-CB GP kthread CPU %d:",
2360 : : __func__, cpu);
2361 : : }
2362 : : } else {
2363 : : /* Another CB kthread, link to previous GP kthread. */
2364 : : gotnocbscbs = true;
2365 : : rdp->nocb_gp_rdp = rdp_gp;
2366 : : rdp_prev->nocb_next_cb_rdp = rdp;
2367 : : if (dump_tree)
2368 : : pr_cont(" %d", cpu);
2369 : : }
2370 : : rdp_prev = rdp;
2371 : : }
2372 : : if (gotnocbs && dump_tree)
2373 : : pr_cont("%s\n", gotnocbscbs ? "" : " (self only)");
2374 : : }
2375 : :
2376 : : /*
2377 : : * Bind the current task to the offloaded CPUs. If there are no offloaded
2378 : : * CPUs, leave the task unbound. Splat if the bind attempt fails.
2379 : : */
2380 : : void rcu_bind_current_to_nocb(void)
2381 : : {
2382 : : if (cpumask_available(rcu_nocb_mask) && cpumask_weight(rcu_nocb_mask))
2383 : : WARN_ON(sched_setaffinity(current->pid, rcu_nocb_mask));
2384 : : }
2385 : : EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb);
2386 : :
2387 : : /*
2388 : : * Dump out nocb grace-period kthread state for the specified rcu_data
2389 : : * structure.
2390 : : */
2391 : : static void show_rcu_nocb_gp_state(struct rcu_data *rdp)
2392 : : {
2393 : : struct rcu_node *rnp = rdp->mynode;
2394 : :
2395 : : pr_info("nocb GP %d %c%c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu\n",
2396 : : rdp->cpu,
2397 : : "kK"[!!rdp->nocb_gp_kthread],
2398 : : "lL"[raw_spin_is_locked(&rdp->nocb_gp_lock)],
2399 : : "dD"[!!rdp->nocb_defer_wakeup],
2400 : : "tT"[timer_pending(&rdp->nocb_timer)],
2401 : : "bB"[timer_pending(&rdp->nocb_bypass_timer)],
2402 : : "sS"[!!rdp->nocb_gp_sleep],
2403 : : ".W"[swait_active(&rdp->nocb_gp_wq)],
2404 : : ".W"[swait_active(&rnp->nocb_gp_wq[0])],
2405 : : ".W"[swait_active(&rnp->nocb_gp_wq[1])],
2406 : : ".B"[!!rdp->nocb_gp_bypass],
2407 : : ".G"[!!rdp->nocb_gp_gp],
2408 : : (long)rdp->nocb_gp_seq,
2409 : : rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops));
2410 : : }
2411 : :
2412 : : /* Dump out nocb kthread state for the specified rcu_data structure. */
2413 : : static void show_rcu_nocb_state(struct rcu_data *rdp)
2414 : : {
2415 : : struct rcu_segcblist *rsclp = &rdp->cblist;
2416 : : bool waslocked;
2417 : : bool wastimer;
2418 : : bool wassleep;
2419 : :
2420 : : if (rdp->nocb_gp_rdp == rdp)
2421 : : show_rcu_nocb_gp_state(rdp);
2422 : :
2423 : : pr_info(" CB %d->%d %c%c%c%c%c%c F%ld L%ld C%d %c%c%c%c%c q%ld\n",
2424 : : rdp->cpu, rdp->nocb_gp_rdp->cpu,
2425 : : "kK"[!!rdp->nocb_cb_kthread],
2426 : : "bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)],
2427 : : "cC"[!!atomic_read(&rdp->nocb_lock_contended)],
2428 : : "lL"[raw_spin_is_locked(&rdp->nocb_lock)],
2429 : : "sS"[!!rdp->nocb_cb_sleep],
2430 : : ".W"[swait_active(&rdp->nocb_cb_wq)],
2431 : : jiffies - rdp->nocb_bypass_first,
2432 : : jiffies - rdp->nocb_nobypass_last,
2433 : : rdp->nocb_nobypass_count,
2434 : : ".D"[rcu_segcblist_ready_cbs(rsclp)],
2435 : : ".W"[!rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL)],
2436 : : ".R"[!rcu_segcblist_restempty(rsclp, RCU_WAIT_TAIL)],
2437 : : ".N"[!rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL)],
2438 : : ".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)],
2439 : : rcu_segcblist_n_cbs(&rdp->cblist));
2440 : :
2441 : : /* It is OK for GP kthreads to have GP state. */
2442 : : if (rdp->nocb_gp_rdp == rdp)
2443 : : return;
2444 : :
2445 : : waslocked = raw_spin_is_locked(&rdp->nocb_gp_lock);
2446 : : wastimer = timer_pending(&rdp->nocb_timer);
2447 : : wassleep = swait_active(&rdp->nocb_gp_wq);
2448 : : if (!rdp->nocb_defer_wakeup && !rdp->nocb_gp_sleep &&
2449 : : !waslocked && !wastimer && !wassleep)
2450 : : return; /* Nothing untowards. */
2451 : :
2452 : : pr_info(" !!! %c%c%c%c %c\n",
2453 : : "lL"[waslocked],
2454 : : "dD"[!!rdp->nocb_defer_wakeup],
2455 : : "tT"[wastimer],
2456 : : "sS"[!!rdp->nocb_gp_sleep],
2457 : : ".W"[wassleep]);
2458 : : }
2459 : :
2460 : : #else /* #ifdef CONFIG_RCU_NOCB_CPU */
2461 : :
2462 : : /* No ->nocb_lock to acquire. */
2463 : : static void rcu_nocb_lock(struct rcu_data *rdp)
2464 : : {
2465 : : }
2466 : :
2467 : : /* No ->nocb_lock to release. */
2468 : : static void rcu_nocb_unlock(struct rcu_data *rdp)
2469 : : {
2470 : : }
2471 : :
2472 : : /* No ->nocb_lock to release. */
2473 : 5533610 : static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
2474 : : unsigned long flags)
2475 : : {
2476 [ - + ]: 5533610 : local_irq_restore(flags);
2477 : 5533720 : }
2478 : :
2479 : : /* Lockdep check that ->cblist may be safely accessed. */
2480 : : static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
2481 : : {
2482 : : lockdep_assert_irqs_disabled();
2483 : : }
2484 : :
2485 : : static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
2486 : : {
2487 : : }
2488 : :
2489 : : static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
2490 : : {
2491 : : return NULL;
2492 : : }
2493 : :
2494 : : static void rcu_init_one_nocb(struct rcu_node *rnp)
2495 : : {
2496 : : }
2497 : :
2498 : : static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
2499 : : unsigned long j)
2500 : : {
2501 : : return true;
2502 : : }
2503 : :
2504 : : static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
2505 : : bool *was_alldone, unsigned long flags)
2506 : : {
2507 : : return false;
2508 : : }
2509 : :
2510 : : static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
2511 : : unsigned long flags)
2512 : : {
2513 : : WARN_ON_ONCE(1); /* Should be dead code! */
2514 : : }
2515 : :
2516 : : static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2517 : : {
2518 : : }
2519 : :
2520 : : static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2521 : : {
2522 : : return false;
2523 : : }
2524 : :
2525 : : static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2526 : : {
2527 : : }
2528 : :
2529 : : static void rcu_spawn_cpu_nocb_kthread(int cpu)
2530 : : {
2531 : : }
2532 : :
2533 : : static void __init rcu_spawn_nocb_kthreads(void)
2534 : : {
2535 : : }
2536 : :
2537 : : static void show_rcu_nocb_state(struct rcu_data *rdp)
2538 : : {
2539 : : }
2540 : :
2541 : : #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2542 : :
2543 : : /*
2544 : : * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
2545 : : * grace-period kthread will do force_quiescent_state() processing?
2546 : : * The idea is to avoid waking up RCU core processing on such a
2547 : : * CPU unless the grace period has extended for too long.
2548 : : *
2549 : : * This code relies on the fact that all NO_HZ_FULL CPUs are also
2550 : : * CONFIG_RCU_NOCB_CPU CPUs.
2551 : : */
2552 : : static bool rcu_nohz_full_cpu(void)
2553 : : {
2554 : : #ifdef CONFIG_NO_HZ_FULL
2555 : : if (tick_nohz_full_cpu(smp_processor_id()) &&
2556 : : (!rcu_gp_in_progress() ||
2557 : : ULONG_CMP_LT(jiffies, READ_ONCE(rcu_state.gp_start) + HZ)))
2558 : : return true;
2559 : : #endif /* #ifdef CONFIG_NO_HZ_FULL */
2560 : : return false;
2561 : : }
2562 : :
2563 : : /*
2564 : : * Bind the RCU grace-period kthreads to the housekeeping CPU.
2565 : : */
2566 : : static void rcu_bind_gp_kthread(void)
2567 : : {
2568 : : if (!tick_nohz_full_enabled())
2569 : : return;
2570 : : housekeeping_affine(current, HK_FLAG_RCU);
2571 : : }
2572 : :
2573 : : /* Record the current task on dyntick-idle entry. */
2574 : 11579739 : static void rcu_dynticks_task_enter(void)
2575 : : {
2576 : : #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2577 : : WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
2578 : : #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
2579 : 11579739 : }
2580 : :
2581 : : /* Record no current task on dyntick-idle exit. */
2582 : 11555680 : static void rcu_dynticks_task_exit(void)
2583 : : {
2584 : : #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2585 : : WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
2586 : : #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
2587 : 11555680 : }
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