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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 : 30 : static void __init rcu_bootup_announce_oddness(void)
26 : : {
27 : 30 : if (IS_ENABLED(CONFIG_RCU_TRACE))
28 : 30 : pr_info("\tRCU event tracing is enabled.\n");
29 : 30 : 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 [ - + ]: 30 : if (rcu_fanout_exact)
34 : 0 : pr_info("\tHierarchical RCU autobalancing is disabled.\n");
35 : 30 : if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ))
36 : : pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
37 : 30 : if (IS_ENABLED(CONFIG_PROVE_RCU))
38 : : pr_info("\tRCU lockdep checking is enabled.\n");
39 : 30 : if (RCU_NUM_LVLS >= 4)
40 : : pr_info("\tFour(or more)-level hierarchy is enabled.\n");
41 : 30 : if (RCU_FANOUT_LEAF != 16)
42 : : pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
43 : : RCU_FANOUT_LEAF);
44 [ - + ]: 30 : 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 [ + - ]: 30 : if (nr_cpu_ids != NR_CPUS)
48 : 30 : 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 [ - + ]: 30 : if (blimit != DEFAULT_RCU_BLIMIT)
54 : 0 : pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit);
55 [ - + ]: 30 : if (qhimark != DEFAULT_RCU_QHIMARK)
56 : 0 : pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark);
57 [ - + ]: 30 : if (qlowmark != DEFAULT_RCU_QLOMARK)
58 : 0 : pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark);
59 [ - + ]: 30 : 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 [ - + ]: 30 : 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 [ - + ]: 30 : 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 [ - + ]: 30 : if (rcu_kick_kthreads)
66 : 0 : pr_info("\tKick kthreads if too-long grace period.\n");
67 : 30 : if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD))
68 : : pr_info("\tRCU callback double-/use-after-free debug enabled.\n");
69 [ - + ]: 30 : if (gp_preinit_delay)
70 : 0 : pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay);
71 [ - + ]: 30 : if (gp_init_delay)
72 : 0 : pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay);
73 [ - + ]: 30 : if (gp_cleanup_delay)
74 : 0 : pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay);
75 [ - + ]: 30 : if (!use_softirq)
76 : 0 : pr_info("\tRCU_SOFTIRQ processing moved to rcuc kthreads.\n");
77 : 30 : if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))
78 : : pr_info("\tRCU debug extended QS entry/exit.\n");
79 : 30 : rcupdate_announce_bootup_oddness();
80 : 30 : }
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 && rcu_preempt_depth() > 0);
294 : : if (rcu_preempt_depth() > 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 : : static void rcu_preempt_read_enter(void)
352 : : {
353 : : current->rcu_read_lock_nesting++;
354 : : }
355 : :
356 : : static void rcu_preempt_read_exit(void)
357 : : {
358 : : current->rcu_read_lock_nesting--;
359 : : }
360 : :
361 : : static void rcu_preempt_depth_set(int val)
362 : : {
363 : : current->rcu_read_lock_nesting = val;
364 : : }
365 : :
366 : : /*
367 : : * Preemptible RCU implementation for rcu_read_lock().
368 : : * Just increment ->rcu_read_lock_nesting, shared state will be updated
369 : : * if we block.
370 : : */
371 : : void __rcu_read_lock(void)
372 : : {
373 : : rcu_preempt_read_enter();
374 : : if (IS_ENABLED(CONFIG_PROVE_LOCKING))
375 : : WARN_ON_ONCE(rcu_preempt_depth() > RCU_NEST_PMAX);
376 : : barrier(); /* critical section after entry code. */
377 : : }
378 : : EXPORT_SYMBOL_GPL(__rcu_read_lock);
379 : :
380 : : /*
381 : : * Preemptible RCU implementation for rcu_read_unlock().
382 : : * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
383 : : * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
384 : : * invoke rcu_read_unlock_special() to clean up after a context switch
385 : : * in an RCU read-side critical section and other special cases.
386 : : */
387 : : void __rcu_read_unlock(void)
388 : : {
389 : : struct task_struct *t = current;
390 : :
391 : : if (rcu_preempt_depth() != 1) {
392 : : rcu_preempt_read_exit();
393 : : } else {
394 : : barrier(); /* critical section before exit code. */
395 : : rcu_preempt_depth_set(-RCU_NEST_BIAS);
396 : : barrier(); /* assign before ->rcu_read_unlock_special load */
397 : : if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
398 : : rcu_read_unlock_special(t);
399 : : barrier(); /* ->rcu_read_unlock_special load before assign */
400 : : rcu_preempt_depth_set(0);
401 : : }
402 : : if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
403 : : int rrln = rcu_preempt_depth();
404 : :
405 : : WARN_ON_ONCE(rrln < 0 && rrln > RCU_NEST_NMAX);
406 : : }
407 : : }
408 : : EXPORT_SYMBOL_GPL(__rcu_read_unlock);
409 : :
410 : : /*
411 : : * Advance a ->blkd_tasks-list pointer to the next entry, instead
412 : : * returning NULL if at the end of the list.
413 : : */
414 : : static struct list_head *rcu_next_node_entry(struct task_struct *t,
415 : : struct rcu_node *rnp)
416 : : {
417 : : struct list_head *np;
418 : :
419 : : np = t->rcu_node_entry.next;
420 : : if (np == &rnp->blkd_tasks)
421 : : np = NULL;
422 : : return np;
423 : : }
424 : :
425 : : /*
426 : : * Return true if the specified rcu_node structure has tasks that were
427 : : * preempted within an RCU read-side critical section.
428 : : */
429 : : static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
430 : : {
431 : : return !list_empty(&rnp->blkd_tasks);
432 : : }
433 : :
434 : : /*
435 : : * Report deferred quiescent states. The deferral time can
436 : : * be quite short, for example, in the case of the call from
437 : : * rcu_read_unlock_special().
438 : : */
439 : : static void
440 : : rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
441 : : {
442 : : bool empty_exp;
443 : : bool empty_norm;
444 : : bool empty_exp_now;
445 : : struct list_head *np;
446 : : bool drop_boost_mutex = false;
447 : : struct rcu_data *rdp;
448 : : struct rcu_node *rnp;
449 : : union rcu_special special;
450 : :
451 : : /*
452 : : * If RCU core is waiting for this CPU to exit its critical section,
453 : : * report the fact that it has exited. Because irqs are disabled,
454 : : * t->rcu_read_unlock_special cannot change.
455 : : */
456 : : special = t->rcu_read_unlock_special;
457 : : rdp = this_cpu_ptr(&rcu_data);
458 : : if (!special.s && !rdp->exp_deferred_qs) {
459 : : local_irq_restore(flags);
460 : : return;
461 : : }
462 : : t->rcu_read_unlock_special.s = 0;
463 : : if (special.b.need_qs)
464 : : rcu_qs();
465 : :
466 : : /*
467 : : * Respond to a request by an expedited grace period for a
468 : : * quiescent state from this CPU. Note that requests from
469 : : * tasks are handled when removing the task from the
470 : : * blocked-tasks list below.
471 : : */
472 : : if (rdp->exp_deferred_qs)
473 : : rcu_report_exp_rdp(rdp);
474 : :
475 : : /* Clean up if blocked during RCU read-side critical section. */
476 : : if (special.b.blocked) {
477 : :
478 : : /*
479 : : * Remove this task from the list it blocked on. The task
480 : : * now remains queued on the rcu_node corresponding to the
481 : : * CPU it first blocked on, so there is no longer any need
482 : : * to loop. Retain a WARN_ON_ONCE() out of sheer paranoia.
483 : : */
484 : : rnp = t->rcu_blocked_node;
485 : : raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
486 : : WARN_ON_ONCE(rnp != t->rcu_blocked_node);
487 : : WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
488 : : empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
489 : : WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq &&
490 : : (!empty_norm || rnp->qsmask));
491 : : empty_exp = sync_rcu_exp_done(rnp);
492 : : smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
493 : : np = rcu_next_node_entry(t, rnp);
494 : : list_del_init(&t->rcu_node_entry);
495 : : t->rcu_blocked_node = NULL;
496 : : trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
497 : : rnp->gp_seq, t->pid);
498 : : if (&t->rcu_node_entry == rnp->gp_tasks)
499 : : WRITE_ONCE(rnp->gp_tasks, np);
500 : : if (&t->rcu_node_entry == rnp->exp_tasks)
501 : : rnp->exp_tasks = np;
502 : : if (IS_ENABLED(CONFIG_RCU_BOOST)) {
503 : : /* Snapshot ->boost_mtx ownership w/rnp->lock held. */
504 : : drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
505 : : if (&t->rcu_node_entry == rnp->boost_tasks)
506 : : rnp->boost_tasks = np;
507 : : }
508 : :
509 : : /*
510 : : * If this was the last task on the current list, and if
511 : : * we aren't waiting on any CPUs, report the quiescent state.
512 : : * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
513 : : * so we must take a snapshot of the expedited state.
514 : : */
515 : : empty_exp_now = sync_rcu_exp_done(rnp);
516 : : if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
517 : : trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
518 : : rnp->gp_seq,
519 : : 0, rnp->qsmask,
520 : : rnp->level,
521 : : rnp->grplo,
522 : : rnp->grphi,
523 : : !!rnp->gp_tasks);
524 : : rcu_report_unblock_qs_rnp(rnp, flags);
525 : : } else {
526 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
527 : : }
528 : :
529 : : /* Unboost if we were boosted. */
530 : : if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
531 : : rt_mutex_futex_unlock(&rnp->boost_mtx);
532 : :
533 : : /*
534 : : * If this was the last task on the expedited lists,
535 : : * then we need to report up the rcu_node hierarchy.
536 : : */
537 : : if (!empty_exp && empty_exp_now)
538 : : rcu_report_exp_rnp(rnp, true);
539 : : } else {
540 : : local_irq_restore(flags);
541 : : }
542 : : }
543 : :
544 : : /*
545 : : * Is a deferred quiescent-state pending, and are we also not in
546 : : * an RCU read-side critical section? It is the caller's responsibility
547 : : * to ensure it is otherwise safe to report any deferred quiescent
548 : : * states. The reason for this is that it is safe to report a
549 : : * quiescent state during context switch even though preemption
550 : : * is disabled. This function cannot be expected to understand these
551 : : * nuances, so the caller must handle them.
552 : : */
553 : : static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
554 : : {
555 : : return (__this_cpu_read(rcu_data.exp_deferred_qs) ||
556 : : READ_ONCE(t->rcu_read_unlock_special.s)) &&
557 : : rcu_preempt_depth() <= 0;
558 : : }
559 : :
560 : : /*
561 : : * Report a deferred quiescent state if needed and safe to do so.
562 : : * As with rcu_preempt_need_deferred_qs(), "safe" involves only
563 : : * not being in an RCU read-side critical section. The caller must
564 : : * evaluate safety in terms of interrupt, softirq, and preemption
565 : : * disabling.
566 : : */
567 : : static void rcu_preempt_deferred_qs(struct task_struct *t)
568 : : {
569 : : unsigned long flags;
570 : : bool couldrecurse = rcu_preempt_depth() >= 0;
571 : :
572 : : if (!rcu_preempt_need_deferred_qs(t))
573 : : return;
574 : : if (couldrecurse)
575 : : rcu_preempt_depth_set(rcu_preempt_depth() - RCU_NEST_BIAS);
576 : : local_irq_save(flags);
577 : : rcu_preempt_deferred_qs_irqrestore(t, flags);
578 : : if (couldrecurse)
579 : : rcu_preempt_depth_set(rcu_preempt_depth() + RCU_NEST_BIAS);
580 : : }
581 : :
582 : : /*
583 : : * Minimal handler to give the scheduler a chance to re-evaluate.
584 : : */
585 : : static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp)
586 : : {
587 : : struct rcu_data *rdp;
588 : :
589 : : rdp = container_of(iwp, struct rcu_data, defer_qs_iw);
590 : : rdp->defer_qs_iw_pending = false;
591 : : }
592 : :
593 : : /*
594 : : * Handle special cases during rcu_read_unlock(), such as needing to
595 : : * notify RCU core processing or task having blocked during the RCU
596 : : * read-side critical section.
597 : : */
598 : : static void rcu_read_unlock_special(struct task_struct *t)
599 : : {
600 : : unsigned long flags;
601 : : bool preempt_bh_were_disabled =
602 : : !!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK));
603 : : bool irqs_were_disabled;
604 : :
605 : : /* NMI handlers cannot block and cannot safely manipulate state. */
606 : : if (in_nmi())
607 : : return;
608 : :
609 : : local_irq_save(flags);
610 : : irqs_were_disabled = irqs_disabled_flags(flags);
611 : : if (preempt_bh_were_disabled || irqs_were_disabled) {
612 : : bool exp;
613 : : struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
614 : : struct rcu_node *rnp = rdp->mynode;
615 : :
616 : : exp = (t->rcu_blocked_node && t->rcu_blocked_node->exp_tasks) ||
617 : : (rdp->grpmask & READ_ONCE(rnp->expmask)) ||
618 : : tick_nohz_full_cpu(rdp->cpu);
619 : : // Need to defer quiescent state until everything is enabled.
620 : : if (irqs_were_disabled && use_softirq &&
621 : : (in_interrupt() ||
622 : : (exp && !t->rcu_read_unlock_special.b.deferred_qs))) {
623 : : // Using softirq, safe to awaken, and we get
624 : : // no help from enabling irqs, unlike bh/preempt.
625 : : raise_softirq_irqoff(RCU_SOFTIRQ);
626 : : } else {
627 : : // Enabling BH or preempt does reschedule, so...
628 : : // Also if no expediting or NO_HZ_FULL, slow is OK.
629 : : set_tsk_need_resched(current);
630 : : set_preempt_need_resched();
631 : : if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled &&
632 : : !rdp->defer_qs_iw_pending && exp) {
633 : : // Get scheduler to re-evaluate and call hooks.
634 : : // If !IRQ_WORK, FQS scan will eventually IPI.
635 : : init_irq_work(&rdp->defer_qs_iw,
636 : : rcu_preempt_deferred_qs_handler);
637 : : rdp->defer_qs_iw_pending = true;
638 : : irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu);
639 : : }
640 : : }
641 : : t->rcu_read_unlock_special.b.deferred_qs = true;
642 : : local_irq_restore(flags);
643 : : return;
644 : : }
645 : : rcu_preempt_deferred_qs_irqrestore(t, flags);
646 : : }
647 : :
648 : : /*
649 : : * Check that the list of blocked tasks for the newly completed grace
650 : : * period is in fact empty. It is a serious bug to complete a grace
651 : : * period that still has RCU readers blocked! This function must be
652 : : * invoked -before- updating this rnp's ->gp_seq.
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 : : raw_lockdep_assert_held_rcu_node(rnp);
663 : : if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
664 : : dump_blkd_tasks(rnp, 10);
665 : : if (rcu_preempt_has_tasks(rnp) &&
666 : : (rnp->qsmaskinit || rnp->wait_blkd_tasks)) {
667 : : WRITE_ONCE(rnp->gp_tasks, rnp->blkd_tasks.next);
668 : : t = container_of(rnp->gp_tasks, struct task_struct,
669 : : rcu_node_entry);
670 : : trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
671 : : rnp->gp_seq, t->pid);
672 : : }
673 : : WARN_ON_ONCE(rnp->qsmask);
674 : : }
675 : :
676 : : /*
677 : : * Check for a quiescent state from the current CPU, including voluntary
678 : : * context switches for Tasks RCU. When a task blocks, the task is
679 : : * recorded in the corresponding CPU's rcu_node structure, which is checked
680 : : * elsewhere, hence this function need only check for quiescent states
681 : : * related to the current CPU, not to those related to tasks.
682 : : */
683 : : static void rcu_flavor_sched_clock_irq(int user)
684 : : {
685 : : struct task_struct *t = current;
686 : :
687 : : if (user || rcu_is_cpu_rrupt_from_idle()) {
688 : : rcu_note_voluntary_context_switch(current);
689 : : }
690 : : if (rcu_preempt_depth() > 0 ||
691 : : (preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) {
692 : : /* No QS, force context switch if deferred. */
693 : : if (rcu_preempt_need_deferred_qs(t)) {
694 : : set_tsk_need_resched(t);
695 : : set_preempt_need_resched();
696 : : }
697 : : } else if (rcu_preempt_need_deferred_qs(t)) {
698 : : rcu_preempt_deferred_qs(t); /* Report deferred QS. */
699 : : return;
700 : : } else if (!rcu_preempt_depth()) {
701 : : rcu_qs(); /* Report immediate QS. */
702 : : return;
703 : : }
704 : :
705 : : /* If GP is oldish, ask for help from rcu_read_unlock_special(). */
706 : : if (rcu_preempt_depth() > 0 &&
707 : : __this_cpu_read(rcu_data.core_needs_qs) &&
708 : : __this_cpu_read(rcu_data.cpu_no_qs.b.norm) &&
709 : : !t->rcu_read_unlock_special.b.need_qs &&
710 : : time_after(jiffies, rcu_state.gp_start + HZ))
711 : : t->rcu_read_unlock_special.b.need_qs = true;
712 : : }
713 : :
714 : : /*
715 : : * Check for a task exiting while in a preemptible-RCU read-side
716 : : * critical section, clean up if so. No need to issue warnings, as
717 : : * debug_check_no_locks_held() already does this if lockdep is enabled.
718 : : * Besides, if this function does anything other than just immediately
719 : : * return, there was a bug of some sort. Spewing warnings from this
720 : : * function is like as not to simply obscure important prior warnings.
721 : : */
722 : : void exit_rcu(void)
723 : : {
724 : : struct task_struct *t = current;
725 : :
726 : : if (unlikely(!list_empty(¤t->rcu_node_entry))) {
727 : : rcu_preempt_depth_set(1);
728 : : barrier();
729 : : WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true);
730 : : } else if (unlikely(rcu_preempt_depth())) {
731 : : rcu_preempt_depth_set(1);
732 : : } else {
733 : : return;
734 : : }
735 : : __rcu_read_unlock();
736 : : rcu_preempt_deferred_qs(current);
737 : : }
738 : :
739 : : /*
740 : : * Dump the blocked-tasks state, but limit the list dump to the
741 : : * specified number of elements.
742 : : */
743 : : static void
744 : : dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
745 : : {
746 : : int cpu;
747 : : int i;
748 : : struct list_head *lhp;
749 : : bool onl;
750 : : struct rcu_data *rdp;
751 : : struct rcu_node *rnp1;
752 : :
753 : : raw_lockdep_assert_held_rcu_node(rnp);
754 : : pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n",
755 : : __func__, rnp->grplo, rnp->grphi, rnp->level,
756 : : (long)rnp->gp_seq, (long)rnp->completedqs);
757 : : for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent)
758 : : pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n",
759 : : __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext);
760 : : pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n",
761 : : __func__, READ_ONCE(rnp->gp_tasks), rnp->boost_tasks,
762 : : rnp->exp_tasks);
763 : : pr_info("%s: ->blkd_tasks", __func__);
764 : : i = 0;
765 : : list_for_each(lhp, &rnp->blkd_tasks) {
766 : : pr_cont(" %p", lhp);
767 : : if (++i >= ncheck)
768 : : break;
769 : : }
770 : : pr_cont("\n");
771 : : for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) {
772 : : rdp = per_cpu_ptr(&rcu_data, cpu);
773 : : onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp));
774 : : pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n",
775 : : cpu, ".o"[onl],
776 : : (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags,
777 : : (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags);
778 : : }
779 : : }
780 : :
781 : : #else /* #ifdef CONFIG_PREEMPT_RCU */
782 : :
783 : : /*
784 : : * Tell them what RCU they are running.
785 : : */
786 : 30 : static void __init rcu_bootup_announce(void)
787 : : {
788 : 30 : pr_info("Hierarchical RCU implementation.\n");
789 : 30 : rcu_bootup_announce_oddness();
790 : 30 : }
791 : :
792 : : /*
793 : : * Note a quiescent state for PREEMPTION=n. Because we do not need to know
794 : : * how many quiescent states passed, just if there was at least one since
795 : : * the start of the grace period, this just sets a flag. The caller must
796 : : * have disabled preemption.
797 : : */
798 : 519847 : static void rcu_qs(void)
799 : : {
800 : 519847 : RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!");
801 [ + + ]: 519847 : if (!__this_cpu_read(rcu_data.cpu_no_qs.s))
802 : : return;
803 : 67577 : trace_rcu_grace_period(TPS("rcu_sched"),
804 : 67577 : __this_cpu_read(rcu_data.gp_seq), TPS("cpuqs"));
805 [ - + ]: 67577 : __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false);
806 [ - + ]: 67577 : if (!__this_cpu_read(rcu_data.cpu_no_qs.b.exp))
807 : : return;
808 : 0 : __this_cpu_write(rcu_data.cpu_no_qs.b.exp, false);
809 : 0 : rcu_report_exp_rdp(this_cpu_ptr(&rcu_data));
810 : : }
811 : :
812 : : /*
813 : : * Register an urgently needed quiescent state. If there is an
814 : : * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
815 : : * dyntick-idle quiescent state visible to other CPUs, which will in
816 : : * some cases serve for expedited as well as normal grace periods.
817 : : * Either way, register a lightweight quiescent state.
818 : : */
819 : 68388520 : void rcu_all_qs(void)
820 : : {
821 : 68388520 : unsigned long flags;
822 : :
823 [ - + ]: 68388520 : if (!raw_cpu_read(rcu_data.rcu_urgent_qs))
824 : : return;
825 : 0 : preempt_disable();
826 : : /* Load rcu_urgent_qs before other flags. */
827 [ # # ]: 0 : if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) {
828 : 0 : preempt_enable();
829 : 0 : return;
830 : : }
831 : 0 : this_cpu_write(rcu_data.rcu_urgent_qs, false);
832 [ # # ]: 0 : if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) {
833 : 0 : local_irq_save(flags);
834 : 0 : rcu_momentary_dyntick_idle();
835 : 0 : local_irq_restore(flags);
836 : : }
837 : 0 : rcu_qs();
838 : 0 : preempt_enable();
839 : : }
840 : : EXPORT_SYMBOL_GPL(rcu_all_qs);
841 : :
842 : : /*
843 : : * Note a PREEMPTION=n context switch. The caller must have disabled interrupts.
844 : : */
845 : 315502 : void rcu_note_context_switch(bool preempt)
846 : : {
847 : 315502 : trace_rcu_utilization(TPS("Start context switch"));
848 : 315502 : rcu_qs();
849 : : /* Load rcu_urgent_qs before other flags. */
850 [ + - ]: 315502 : if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs)))
851 : 315502 : goto out;
852 : 0 : this_cpu_write(rcu_data.rcu_urgent_qs, false);
853 [ # # ]: 0 : if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs)))
854 : 0 : rcu_momentary_dyntick_idle();
855 : 0 : if (!preempt)
856 : 315502 : rcu_tasks_qs(current);
857 : 0 : out:
858 : 315502 : trace_rcu_utilization(TPS("End context switch"));
859 : 315502 : }
860 : : EXPORT_SYMBOL_GPL(rcu_note_context_switch);
861 : :
862 : : /*
863 : : * Because preemptible RCU does not exist, there are never any preempted
864 : : * RCU readers.
865 : : */
866 : 202563 : static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
867 : : {
868 [ - + - + ]: 135042 : return 0;
869 : : }
870 : :
871 : : /*
872 : : * Because there is no preemptible RCU, there can be no readers blocked.
873 : : */
874 : 0 : static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
875 : : {
876 [ # # ]: 0 : return false;
877 : : }
878 : :
879 : : /*
880 : : * Because there is no preemptible RCU, there can be no deferred quiescent
881 : : * states.
882 : : */
883 : 52 : static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
884 : : {
885 : 52 : return false;
886 : : }
887 : 258992 : static void rcu_preempt_deferred_qs(struct task_struct *t) { }
888 : :
889 : : /*
890 : : * Because there is no preemptible RCU, there can be no readers blocked,
891 : : * so there is no need to check for blocked tasks. So check only for
892 : : * bogus qsmask values.
893 : : */
894 : 67551 : static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
895 : : {
896 [ - + + - ]: 67551 : WARN_ON_ONCE(rnp->qsmask);
897 : : }
898 : :
899 : : /*
900 : : * Check to see if this CPU is in a non-context-switch quiescent state,
901 : : * namely user mode and idle loop.
902 : : */
903 : 97198 : static void rcu_flavor_sched_clock_irq(int user)
904 : : {
905 [ + + + - ]: 99291 : if (user || rcu_is_cpu_rrupt_from_idle()) {
906 : :
907 : : /*
908 : : * Get here if this CPU took its interrupt from user
909 : : * mode or from the idle loop, and if this is not a
910 : : * nested interrupt. In this case, the CPU is in
911 : : * a quiescent state, so note it.
912 : : *
913 : : * No memory barrier is required here because rcu_qs()
914 : : * references only CPU-local variables that other CPUs
915 : : * neither access nor modify, at least not while the
916 : : * corresponding CPU is online.
917 : : */
918 : :
919 : 10305 : rcu_qs();
920 : : }
921 : 97198 : }
922 : :
923 : : /*
924 : : * Because preemptible RCU does not exist, tasks cannot possibly exit
925 : : * while in preemptible RCU read-side critical sections.
926 : : */
927 : 17730 : void exit_rcu(void)
928 : : {
929 : 17730 : }
930 : :
931 : : /*
932 : : * Dump the guaranteed-empty blocked-tasks state. Trust but verify.
933 : : */
934 : : static void
935 : : dump_blkd_tasks(struct rcu_node *rnp, int ncheck)
936 : : {
937 : : WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks));
938 : : }
939 : :
940 : : #endif /* #else #ifdef CONFIG_PREEMPT_RCU */
941 : :
942 : : /*
943 : : * If boosting, set rcuc kthreads to realtime priority.
944 : : */
945 : 0 : static void rcu_cpu_kthread_setup(unsigned int cpu)
946 : : {
947 : : #ifdef CONFIG_RCU_BOOST
948 : : struct sched_param sp;
949 : :
950 : : sp.sched_priority = kthread_prio;
951 : : sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
952 : : #endif /* #ifdef CONFIG_RCU_BOOST */
953 : 0 : }
954 : :
955 : : #ifdef CONFIG_RCU_BOOST
956 : :
957 : : /*
958 : : * Carry out RCU priority boosting on the task indicated by ->exp_tasks
959 : : * or ->boost_tasks, advancing the pointer to the next task in the
960 : : * ->blkd_tasks list.
961 : : *
962 : : * Note that irqs must be enabled: boosting the task can block.
963 : : * Returns 1 if there are more tasks needing to be boosted.
964 : : */
965 : : static int rcu_boost(struct rcu_node *rnp)
966 : : {
967 : : unsigned long flags;
968 : : struct task_struct *t;
969 : : struct list_head *tb;
970 : :
971 : : if (READ_ONCE(rnp->exp_tasks) == NULL &&
972 : : READ_ONCE(rnp->boost_tasks) == NULL)
973 : : return 0; /* Nothing left to boost. */
974 : :
975 : : raw_spin_lock_irqsave_rcu_node(rnp, flags);
976 : :
977 : : /*
978 : : * Recheck under the lock: all tasks in need of boosting
979 : : * might exit their RCU read-side critical sections on their own.
980 : : */
981 : : if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
982 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
983 : : return 0;
984 : : }
985 : :
986 : : /*
987 : : * Preferentially boost tasks blocking expedited grace periods.
988 : : * This cannot starve the normal grace periods because a second
989 : : * expedited grace period must boost all blocked tasks, including
990 : : * those blocking the pre-existing normal grace period.
991 : : */
992 : : if (rnp->exp_tasks != NULL)
993 : : tb = rnp->exp_tasks;
994 : : else
995 : : tb = rnp->boost_tasks;
996 : :
997 : : /*
998 : : * We boost task t by manufacturing an rt_mutex that appears to
999 : : * be held by task t. We leave a pointer to that rt_mutex where
1000 : : * task t can find it, and task t will release the mutex when it
1001 : : * exits its outermost RCU read-side critical section. Then
1002 : : * simply acquiring this artificial rt_mutex will boost task
1003 : : * t's priority. (Thanks to tglx for suggesting this approach!)
1004 : : *
1005 : : * Note that task t must acquire rnp->lock to remove itself from
1006 : : * the ->blkd_tasks list, which it will do from exit() if from
1007 : : * nowhere else. We therefore are guaranteed that task t will
1008 : : * stay around at least until we drop rnp->lock. Note that
1009 : : * rnp->lock also resolves races between our priority boosting
1010 : : * and task t's exiting its outermost RCU read-side critical
1011 : : * section.
1012 : : */
1013 : : t = container_of(tb, struct task_struct, rcu_node_entry);
1014 : : rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
1015 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1016 : : /* Lock only for side effect: boosts task t's priority. */
1017 : : rt_mutex_lock(&rnp->boost_mtx);
1018 : : rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
1019 : :
1020 : : return READ_ONCE(rnp->exp_tasks) != NULL ||
1021 : : READ_ONCE(rnp->boost_tasks) != NULL;
1022 : : }
1023 : :
1024 : : /*
1025 : : * Priority-boosting kthread, one per leaf rcu_node.
1026 : : */
1027 : : static int rcu_boost_kthread(void *arg)
1028 : : {
1029 : : struct rcu_node *rnp = (struct rcu_node *)arg;
1030 : : int spincnt = 0;
1031 : : int more2boost;
1032 : :
1033 : : trace_rcu_utilization(TPS("Start boost kthread@init"));
1034 : : for (;;) {
1035 : : rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1036 : : trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1037 : : rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1038 : : trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1039 : : rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1040 : : more2boost = rcu_boost(rnp);
1041 : : if (more2boost)
1042 : : spincnt++;
1043 : : else
1044 : : spincnt = 0;
1045 : : if (spincnt > 10) {
1046 : : rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1047 : : trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1048 : : schedule_timeout_interruptible(2);
1049 : : trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1050 : : spincnt = 0;
1051 : : }
1052 : : }
1053 : : /* NOTREACHED */
1054 : : trace_rcu_utilization(TPS("End boost kthread@notreached"));
1055 : : return 0;
1056 : : }
1057 : :
1058 : : /*
1059 : : * Check to see if it is time to start boosting RCU readers that are
1060 : : * blocking the current grace period, and, if so, tell the per-rcu_node
1061 : : * kthread to start boosting them. If there is an expedited grace
1062 : : * period in progress, it is always time to boost.
1063 : : *
1064 : : * The caller must hold rnp->lock, which this function releases.
1065 : : * The ->boost_kthread_task is immortal, so we don't need to worry
1066 : : * about it going away.
1067 : : */
1068 : : static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1069 : : __releases(rnp->lock)
1070 : : {
1071 : : raw_lockdep_assert_held_rcu_node(rnp);
1072 : : if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1073 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1074 : : return;
1075 : : }
1076 : : if (rnp->exp_tasks != NULL ||
1077 : : (rnp->gp_tasks != NULL &&
1078 : : rnp->boost_tasks == NULL &&
1079 : : rnp->qsmask == 0 &&
1080 : : ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1081 : : if (rnp->exp_tasks == NULL)
1082 : : rnp->boost_tasks = rnp->gp_tasks;
1083 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1084 : : rcu_wake_cond(rnp->boost_kthread_task,
1085 : : rnp->boost_kthread_status);
1086 : : } else {
1087 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1088 : : }
1089 : : }
1090 : :
1091 : : /*
1092 : : * Is the current CPU running the RCU-callbacks kthread?
1093 : : * Caller must have preemption disabled.
1094 : : */
1095 : : static bool rcu_is_callbacks_kthread(void)
1096 : : {
1097 : : return __this_cpu_read(rcu_data.rcu_cpu_kthread_task) == current;
1098 : : }
1099 : :
1100 : : #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1101 : :
1102 : : /*
1103 : : * Do priority-boost accounting for the start of a new grace period.
1104 : : */
1105 : : static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1106 : : {
1107 : : rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1108 : : }
1109 : :
1110 : : /*
1111 : : * Create an RCU-boost kthread for the specified node if one does not
1112 : : * already exist. We only create this kthread for preemptible RCU.
1113 : : * Returns zero if all is well, a negated errno otherwise.
1114 : : */
1115 : : static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp)
1116 : : {
1117 : : int rnp_index = rnp - rcu_get_root();
1118 : : unsigned long flags;
1119 : : struct sched_param sp;
1120 : : struct task_struct *t;
1121 : :
1122 : : if (!IS_ENABLED(CONFIG_PREEMPT_RCU))
1123 : : return;
1124 : :
1125 : : if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
1126 : : return;
1127 : :
1128 : : rcu_state.boost = 1;
1129 : :
1130 : : if (rnp->boost_kthread_task != NULL)
1131 : : return;
1132 : :
1133 : : t = kthread_create(rcu_boost_kthread, (void *)rnp,
1134 : : "rcub/%d", rnp_index);
1135 : : if (WARN_ON_ONCE(IS_ERR(t)))
1136 : : return;
1137 : :
1138 : : raw_spin_lock_irqsave_rcu_node(rnp, flags);
1139 : : rnp->boost_kthread_task = t;
1140 : : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1141 : : sp.sched_priority = kthread_prio;
1142 : : sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1143 : : wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1144 : : }
1145 : :
1146 : : /*
1147 : : * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1148 : : * served by the rcu_node in question. The CPU hotplug lock is still
1149 : : * held, so the value of rnp->qsmaskinit will be stable.
1150 : : *
1151 : : * We don't include outgoingcpu in the affinity set, use -1 if there is
1152 : : * no outgoing CPU. If there are no CPUs left in the affinity set,
1153 : : * this function allows the kthread to execute on any CPU.
1154 : : */
1155 : : static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1156 : : {
1157 : : struct task_struct *t = rnp->boost_kthread_task;
1158 : : unsigned long mask = rcu_rnp_online_cpus(rnp);
1159 : : cpumask_var_t cm;
1160 : : int cpu;
1161 : :
1162 : : if (!t)
1163 : : return;
1164 : : if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1165 : : return;
1166 : : for_each_leaf_node_possible_cpu(rnp, cpu)
1167 : : if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
1168 : : cpu != outgoingcpu)
1169 : : cpumask_set_cpu(cpu, cm);
1170 : : if (cpumask_weight(cm) == 0)
1171 : : cpumask_setall(cm);
1172 : : set_cpus_allowed_ptr(t, cm);
1173 : : free_cpumask_var(cm);
1174 : : }
1175 : :
1176 : : /*
1177 : : * Spawn boost kthreads -- called as soon as the scheduler is running.
1178 : : */
1179 : : static void __init rcu_spawn_boost_kthreads(void)
1180 : : {
1181 : : struct rcu_node *rnp;
1182 : :
1183 : : rcu_for_each_leaf_node(rnp)
1184 : : rcu_spawn_one_boost_kthread(rnp);
1185 : : }
1186 : :
1187 : : static void rcu_prepare_kthreads(int cpu)
1188 : : {
1189 : : struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
1190 : : struct rcu_node *rnp = rdp->mynode;
1191 : :
1192 : : /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1193 : : if (rcu_scheduler_fully_active)
1194 : : rcu_spawn_one_boost_kthread(rnp);
1195 : : }
1196 : :
1197 : : #else /* #ifdef CONFIG_RCU_BOOST */
1198 : :
1199 : 0 : static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1200 : : __releases(rnp->lock)
1201 : : {
1202 : 0 : raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1203 : 0 : }
1204 : :
1205 : 238839 : static bool rcu_is_callbacks_kthread(void)
1206 : : {
1207 : 238839 : return false;
1208 : : }
1209 : :
1210 : 67551 : static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1211 : : {
1212 : 67551 : }
1213 : :
1214 : 0 : static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1215 : : {
1216 : 0 : }
1217 : :
1218 : 30 : static void __init rcu_spawn_boost_kthreads(void)
1219 : : {
1220 : 30 : }
1221 : :
1222 : 30 : static void rcu_prepare_kthreads(int cpu)
1223 : : {
1224 : 30 : }
1225 : :
1226 : : #endif /* #else #ifdef CONFIG_RCU_BOOST */
1227 : :
1228 : : #if !defined(CONFIG_RCU_FAST_NO_HZ)
1229 : :
1230 : : /*
1231 : : * Check to see if any future non-offloaded RCU-related work will need
1232 : : * to be done by the current CPU, even if none need be done immediately,
1233 : : * returning 1 if so. This function is part of the RCU implementation;
1234 : : * it is -not- an exported member of the RCU API.
1235 : : *
1236 : : * Because we not have RCU_FAST_NO_HZ, just check whether or not this
1237 : : * CPU has RCU callbacks queued.
1238 : : */
1239 : 11058 : int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1240 : : {
1241 : 11058 : *nextevt = KTIME_MAX;
1242 [ + + - + ]: 21281 : return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) &&
1243 [ - + ]: 10223 : !rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist);
1244 : : }
1245 : :
1246 : : /*
1247 : : * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1248 : : * after it.
1249 : : */
1250 : 11058 : static void rcu_cleanup_after_idle(void)
1251 : : {
1252 : 11058 : }
1253 : :
1254 : : /*
1255 : : * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1256 : : * is nothing.
1257 : : */
1258 : 22123 : static void rcu_prepare_for_idle(void)
1259 : : {
1260 : 22123 : }
1261 : :
1262 : : #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1263 : :
1264 : : /*
1265 : : * This code is invoked when a CPU goes idle, at which point we want
1266 : : * to have the CPU do everything required for RCU so that it can enter
1267 : : * the energy-efficient dyntick-idle mode.
1268 : : *
1269 : : * The following preprocessor symbol controls this:
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 : : *
1279 : : * The value below works well in practice. If future workloads require
1280 : : * adjustment, they can be converted into kernel config parameters, though
1281 : : * making the state machine smarter might be a better option.
1282 : : */
1283 : : #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1284 : :
1285 : : static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
1286 : : module_param(rcu_idle_gp_delay, int, 0644);
1287 : :
1288 : : /*
1289 : : * Try to advance callbacks on the current CPU, but only if it has been
1290 : : * awhile since the last time we did so. Afterwards, if there are any
1291 : : * callbacks ready for immediate invocation, return true.
1292 : : */
1293 : : static bool __maybe_unused rcu_try_advance_all_cbs(void)
1294 : : {
1295 : : bool cbs_ready = false;
1296 : : struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1297 : : struct rcu_node *rnp;
1298 : :
1299 : : /* Exit early if we advanced recently. */
1300 : : if (jiffies == rdp->last_advance_all)
1301 : : return false;
1302 : : rdp->last_advance_all = jiffies;
1303 : :
1304 : : rnp = rdp->mynode;
1305 : :
1306 : : /*
1307 : : * Don't bother checking unless a grace period has
1308 : : * completed since we last checked and there are
1309 : : * callbacks not yet ready to invoke.
1310 : : */
1311 : : if ((rcu_seq_completed_gp(rdp->gp_seq,
1312 : : rcu_seq_current(&rnp->gp_seq)) ||
1313 : : unlikely(READ_ONCE(rdp->gpwrap))) &&
1314 : : rcu_segcblist_pend_cbs(&rdp->cblist))
1315 : : note_gp_changes(rdp);
1316 : :
1317 : : if (rcu_segcblist_ready_cbs(&rdp->cblist))
1318 : : cbs_ready = true;
1319 : : return cbs_ready;
1320 : : }
1321 : :
1322 : : /*
1323 : : * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1324 : : * to invoke. If the CPU has callbacks, try to advance them. Tell the
1325 : : * caller about what to set the timeout.
1326 : : *
1327 : : * The caller must have disabled interrupts.
1328 : : */
1329 : : int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1330 : : {
1331 : : struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1332 : : unsigned long dj;
1333 : :
1334 : : lockdep_assert_irqs_disabled();
1335 : :
1336 : : /* If no non-offloaded callbacks, RCU doesn't need the CPU. */
1337 : : if (rcu_segcblist_empty(&rdp->cblist) ||
1338 : : rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist)) {
1339 : : *nextevt = KTIME_MAX;
1340 : : return 0;
1341 : : }
1342 : :
1343 : : /* Attempt to advance callbacks. */
1344 : : if (rcu_try_advance_all_cbs()) {
1345 : : /* Some ready to invoke, so initiate later invocation. */
1346 : : invoke_rcu_core();
1347 : : return 1;
1348 : : }
1349 : : rdp->last_accelerate = jiffies;
1350 : :
1351 : : /* Request timer and round. */
1352 : : dj = round_up(rcu_idle_gp_delay + jiffies, rcu_idle_gp_delay) - jiffies;
1353 : :
1354 : : *nextevt = basemono + dj * TICK_NSEC;
1355 : : return 0;
1356 : : }
1357 : :
1358 : : /*
1359 : : * Prepare a CPU for idle from an RCU perspective. The first major task is to
1360 : : * sense whether nohz mode has been enabled or disabled via sysfs. The second
1361 : : * major task is to accelerate (that is, assign grace-period numbers to) any
1362 : : * recently arrived callbacks.
1363 : : *
1364 : : * The caller must have disabled interrupts.
1365 : : */
1366 : : static void rcu_prepare_for_idle(void)
1367 : : {
1368 : : bool needwake;
1369 : : struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1370 : : struct rcu_node *rnp;
1371 : : int tne;
1372 : :
1373 : : lockdep_assert_irqs_disabled();
1374 : : if (rcu_segcblist_is_offloaded(&rdp->cblist))
1375 : : return;
1376 : :
1377 : : /* Handle nohz enablement switches conservatively. */
1378 : : tne = READ_ONCE(tick_nohz_active);
1379 : : if (tne != rdp->tick_nohz_enabled_snap) {
1380 : : if (!rcu_segcblist_empty(&rdp->cblist))
1381 : : invoke_rcu_core(); /* force nohz to see update. */
1382 : : rdp->tick_nohz_enabled_snap = tne;
1383 : : return;
1384 : : }
1385 : : if (!tne)
1386 : : return;
1387 : :
1388 : : /*
1389 : : * If we have not yet accelerated this jiffy, accelerate all
1390 : : * callbacks on this CPU.
1391 : : */
1392 : : if (rdp->last_accelerate == jiffies)
1393 : : return;
1394 : : rdp->last_accelerate = jiffies;
1395 : : if (rcu_segcblist_pend_cbs(&rdp->cblist)) {
1396 : : rnp = rdp->mynode;
1397 : : raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
1398 : : needwake = rcu_accelerate_cbs(rnp, rdp);
1399 : : raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
1400 : : if (needwake)
1401 : : rcu_gp_kthread_wake();
1402 : : }
1403 : : }
1404 : :
1405 : : /*
1406 : : * Clean up for exit from idle. Attempt to advance callbacks based on
1407 : : * any grace periods that elapsed while the CPU was idle, and if any
1408 : : * callbacks are now ready to invoke, initiate invocation.
1409 : : */
1410 : : static void rcu_cleanup_after_idle(void)
1411 : : {
1412 : : struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
1413 : :
1414 : : lockdep_assert_irqs_disabled();
1415 : : if (rcu_segcblist_is_offloaded(&rdp->cblist))
1416 : : return;
1417 : : if (rcu_try_advance_all_cbs())
1418 : : invoke_rcu_core();
1419 : : }
1420 : :
1421 : : #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1422 : :
1423 : : #ifdef CONFIG_RCU_NOCB_CPU
1424 : :
1425 : : /*
1426 : : * Offload callback processing from the boot-time-specified set of CPUs
1427 : : * specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads
1428 : : * created that pull the callbacks from the corresponding CPU, wait for
1429 : : * a grace period to elapse, and invoke the callbacks. These kthreads
1430 : : * are organized into GP kthreads, which manage incoming callbacks, wait for
1431 : : * grace periods, and awaken CB kthreads, and the CB kthreads, which only
1432 : : * invoke callbacks. Each GP kthread invokes its own CBs. The no-CBs CPUs
1433 : : * do a wake_up() on their GP kthread when they insert a callback into any
1434 : : * empty list, unless the rcu_nocb_poll boot parameter has been specified,
1435 : : * in which case each kthread actively polls its CPU. (Which isn't so great
1436 : : * for energy efficiency, but which does reduce RCU's overhead on that CPU.)
1437 : : *
1438 : : * This is intended to be used in conjunction with Frederic Weisbecker's
1439 : : * adaptive-idle work, which would seriously reduce OS jitter on CPUs
1440 : : * running CPU-bound user-mode computations.
1441 : : *
1442 : : * Offloading of callbacks can also be used as an energy-efficiency
1443 : : * measure because CPUs with no RCU callbacks queued are more aggressive
1444 : : * about entering dyntick-idle mode.
1445 : : */
1446 : :
1447 : :
1448 : : /*
1449 : : * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters.
1450 : : * The string after the "rcu_nocbs=" is either "all" for all CPUs, or a
1451 : : * comma-separated list of CPUs and/or CPU ranges. If an invalid list is
1452 : : * given, a warning is emitted and all CPUs are offloaded.
1453 : : */
1454 : : static int __init rcu_nocb_setup(char *str)
1455 : : {
1456 : : alloc_bootmem_cpumask_var(&rcu_nocb_mask);
1457 : : if (!strcasecmp(str, "all"))
1458 : : cpumask_setall(rcu_nocb_mask);
1459 : : else
1460 : : if (cpulist_parse(str, rcu_nocb_mask)) {
1461 : : pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n");
1462 : : cpumask_setall(rcu_nocb_mask);
1463 : : }
1464 : : return 1;
1465 : : }
1466 : : __setup("rcu_nocbs=", rcu_nocb_setup);
1467 : :
1468 : : static int __init parse_rcu_nocb_poll(char *arg)
1469 : : {
1470 : : rcu_nocb_poll = true;
1471 : : return 0;
1472 : : }
1473 : : early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
1474 : :
1475 : : /*
1476 : : * Don't bother bypassing ->cblist if the call_rcu() rate is low.
1477 : : * After all, the main point of bypassing is to avoid lock contention
1478 : : * on ->nocb_lock, which only can happen at high call_rcu() rates.
1479 : : */
1480 : : int nocb_nobypass_lim_per_jiffy = 16 * 1000 / HZ;
1481 : : module_param(nocb_nobypass_lim_per_jiffy, int, 0);
1482 : :
1483 : : /*
1484 : : * Acquire the specified rcu_data structure's ->nocb_bypass_lock. If the
1485 : : * lock isn't immediately available, increment ->nocb_lock_contended to
1486 : : * flag the contention.
1487 : : */
1488 : : static void rcu_nocb_bypass_lock(struct rcu_data *rdp)
1489 : : {
1490 : : lockdep_assert_irqs_disabled();
1491 : : if (raw_spin_trylock(&rdp->nocb_bypass_lock))
1492 : : return;
1493 : : atomic_inc(&rdp->nocb_lock_contended);
1494 : : WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
1495 : : smp_mb__after_atomic(); /* atomic_inc() before lock. */
1496 : : raw_spin_lock(&rdp->nocb_bypass_lock);
1497 : : smp_mb__before_atomic(); /* atomic_dec() after lock. */
1498 : : atomic_dec(&rdp->nocb_lock_contended);
1499 : : }
1500 : :
1501 : : /*
1502 : : * Spinwait until the specified rcu_data structure's ->nocb_lock is
1503 : : * not contended. Please note that this is extremely special-purpose,
1504 : : * relying on the fact that at most two kthreads and one CPU contend for
1505 : : * this lock, and also that the two kthreads are guaranteed to have frequent
1506 : : * grace-period-duration time intervals between successive acquisitions
1507 : : * of the lock. This allows us to use an extremely simple throttling
1508 : : * mechanism, and further to apply it only to the CPU doing floods of
1509 : : * call_rcu() invocations. Don't try this at home!
1510 : : */
1511 : : static void rcu_nocb_wait_contended(struct rcu_data *rdp)
1512 : : {
1513 : : WARN_ON_ONCE(smp_processor_id() != rdp->cpu);
1514 : : while (WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended)))
1515 : : cpu_relax();
1516 : : }
1517 : :
1518 : : /*
1519 : : * Conditionally acquire the specified rcu_data structure's
1520 : : * ->nocb_bypass_lock.
1521 : : */
1522 : : static bool rcu_nocb_bypass_trylock(struct rcu_data *rdp)
1523 : : {
1524 : : lockdep_assert_irqs_disabled();
1525 : : return raw_spin_trylock(&rdp->nocb_bypass_lock);
1526 : : }
1527 : :
1528 : : /*
1529 : : * Release the specified rcu_data structure's ->nocb_bypass_lock.
1530 : : */
1531 : : static void rcu_nocb_bypass_unlock(struct rcu_data *rdp)
1532 : : {
1533 : : lockdep_assert_irqs_disabled();
1534 : : raw_spin_unlock(&rdp->nocb_bypass_lock);
1535 : : }
1536 : :
1537 : : /*
1538 : : * Acquire the specified rcu_data structure's ->nocb_lock, but only
1539 : : * if it corresponds to a no-CBs CPU.
1540 : : */
1541 : : static void rcu_nocb_lock(struct rcu_data *rdp)
1542 : : {
1543 : : lockdep_assert_irqs_disabled();
1544 : : if (!rcu_segcblist_is_offloaded(&rdp->cblist))
1545 : : return;
1546 : : raw_spin_lock(&rdp->nocb_lock);
1547 : : }
1548 : :
1549 : : /*
1550 : : * Release the specified rcu_data structure's ->nocb_lock, but only
1551 : : * if it corresponds to a no-CBs CPU.
1552 : : */
1553 : : static void rcu_nocb_unlock(struct rcu_data *rdp)
1554 : : {
1555 : : if (rcu_segcblist_is_offloaded(&rdp->cblist)) {
1556 : : lockdep_assert_irqs_disabled();
1557 : : raw_spin_unlock(&rdp->nocb_lock);
1558 : : }
1559 : : }
1560 : :
1561 : : /*
1562 : : * Release the specified rcu_data structure's ->nocb_lock and restore
1563 : : * interrupts, but only if it corresponds to a no-CBs CPU.
1564 : : */
1565 : : static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
1566 : : unsigned long flags)
1567 : : {
1568 : : if (rcu_segcblist_is_offloaded(&rdp->cblist)) {
1569 : : lockdep_assert_irqs_disabled();
1570 : : raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1571 : : } else {
1572 : : local_irq_restore(flags);
1573 : : }
1574 : : }
1575 : :
1576 : : /* Lockdep check that ->cblist may be safely accessed. */
1577 : : static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
1578 : : {
1579 : : lockdep_assert_irqs_disabled();
1580 : : if (rcu_segcblist_is_offloaded(&rdp->cblist) &&
1581 : : cpu_online(rdp->cpu))
1582 : : lockdep_assert_held(&rdp->nocb_lock);
1583 : : }
1584 : :
1585 : : /*
1586 : : * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
1587 : : * grace period.
1588 : : */
1589 : : static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
1590 : : {
1591 : : swake_up_all(sq);
1592 : : }
1593 : :
1594 : : static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
1595 : : {
1596 : : return &rnp->nocb_gp_wq[rcu_seq_ctr(rnp->gp_seq) & 0x1];
1597 : : }
1598 : :
1599 : : static void rcu_init_one_nocb(struct rcu_node *rnp)
1600 : : {
1601 : : init_swait_queue_head(&rnp->nocb_gp_wq[0]);
1602 : : init_swait_queue_head(&rnp->nocb_gp_wq[1]);
1603 : : }
1604 : :
1605 : : /* Is the specified CPU a no-CBs CPU? */
1606 : : bool rcu_is_nocb_cpu(int cpu)
1607 : : {
1608 : : if (cpumask_available(rcu_nocb_mask))
1609 : : return cpumask_test_cpu(cpu, rcu_nocb_mask);
1610 : : return false;
1611 : : }
1612 : :
1613 : : /*
1614 : : * Kick the GP kthread for this NOCB group. Caller holds ->nocb_lock
1615 : : * and this function releases it.
1616 : : */
1617 : : static void wake_nocb_gp(struct rcu_data *rdp, bool force,
1618 : : unsigned long flags)
1619 : : __releases(rdp->nocb_lock)
1620 : : {
1621 : : bool needwake = false;
1622 : : struct rcu_data *rdp_gp = rdp->nocb_gp_rdp;
1623 : :
1624 : : lockdep_assert_held(&rdp->nocb_lock);
1625 : : if (!READ_ONCE(rdp_gp->nocb_gp_kthread)) {
1626 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1627 : : TPS("AlreadyAwake"));
1628 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1629 : : return;
1630 : : }
1631 : : del_timer(&rdp->nocb_timer);
1632 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1633 : : raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags);
1634 : : if (force || READ_ONCE(rdp_gp->nocb_gp_sleep)) {
1635 : : WRITE_ONCE(rdp_gp->nocb_gp_sleep, false);
1636 : : needwake = true;
1637 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DoWake"));
1638 : : }
1639 : : raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags);
1640 : : if (needwake)
1641 : : wake_up_process(rdp_gp->nocb_gp_kthread);
1642 : : }
1643 : :
1644 : : /*
1645 : : * Arrange to wake the GP kthread for this NOCB group at some future
1646 : : * time when it is safe to do so.
1647 : : */
1648 : : static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype,
1649 : : const char *reason)
1650 : : {
1651 : : if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
1652 : : mod_timer(&rdp->nocb_timer, jiffies + 1);
1653 : : if (rdp->nocb_defer_wakeup < waketype)
1654 : : WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
1655 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason);
1656 : : }
1657 : :
1658 : : /*
1659 : : * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
1660 : : * However, if there is a callback to be enqueued and if ->nocb_bypass
1661 : : * proves to be initially empty, just return false because the no-CB GP
1662 : : * kthread may need to be awakened in this case.
1663 : : *
1664 : : * Note that this function always returns true if rhp is NULL.
1665 : : */
1666 : : static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
1667 : : unsigned long j)
1668 : : {
1669 : : struct rcu_cblist rcl;
1670 : :
1671 : : WARN_ON_ONCE(!rcu_segcblist_is_offloaded(&rdp->cblist));
1672 : : rcu_lockdep_assert_cblist_protected(rdp);
1673 : : lockdep_assert_held(&rdp->nocb_bypass_lock);
1674 : : if (rhp && !rcu_cblist_n_cbs(&rdp->nocb_bypass)) {
1675 : : raw_spin_unlock(&rdp->nocb_bypass_lock);
1676 : : return false;
1677 : : }
1678 : : /* Note: ->cblist.len already accounts for ->nocb_bypass contents. */
1679 : : if (rhp)
1680 : : rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
1681 : : rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp);
1682 : : rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl);
1683 : : WRITE_ONCE(rdp->nocb_bypass_first, j);
1684 : : rcu_nocb_bypass_unlock(rdp);
1685 : : return true;
1686 : : }
1687 : :
1688 : : /*
1689 : : * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL.
1690 : : * However, if there is a callback to be enqueued and if ->nocb_bypass
1691 : : * proves to be initially empty, just return false because the no-CB GP
1692 : : * kthread may need to be awakened in this case.
1693 : : *
1694 : : * Note that this function always returns true if rhp is NULL.
1695 : : */
1696 : : static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
1697 : : unsigned long j)
1698 : : {
1699 : : if (!rcu_segcblist_is_offloaded(&rdp->cblist))
1700 : : return true;
1701 : : rcu_lockdep_assert_cblist_protected(rdp);
1702 : : rcu_nocb_bypass_lock(rdp);
1703 : : return rcu_nocb_do_flush_bypass(rdp, rhp, j);
1704 : : }
1705 : :
1706 : : /*
1707 : : * If the ->nocb_bypass_lock is immediately available, flush the
1708 : : * ->nocb_bypass queue into ->cblist.
1709 : : */
1710 : : static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j)
1711 : : {
1712 : : rcu_lockdep_assert_cblist_protected(rdp);
1713 : : if (!rcu_segcblist_is_offloaded(&rdp->cblist) ||
1714 : : !rcu_nocb_bypass_trylock(rdp))
1715 : : return;
1716 : : WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j));
1717 : : }
1718 : :
1719 : : /*
1720 : : * See whether it is appropriate to use the ->nocb_bypass list in order
1721 : : * to control contention on ->nocb_lock. A limited number of direct
1722 : : * enqueues are permitted into ->cblist per jiffy. If ->nocb_bypass
1723 : : * is non-empty, further callbacks must be placed into ->nocb_bypass,
1724 : : * otherwise rcu_barrier() breaks. Use rcu_nocb_flush_bypass() to switch
1725 : : * back to direct use of ->cblist. However, ->nocb_bypass should not be
1726 : : * used if ->cblist is empty, because otherwise callbacks can be stranded
1727 : : * on ->nocb_bypass because we cannot count on the current CPU ever again
1728 : : * invoking call_rcu(). The general rule is that if ->nocb_bypass is
1729 : : * non-empty, the corresponding no-CBs grace-period kthread must not be
1730 : : * in an indefinite sleep state.
1731 : : *
1732 : : * Finally, it is not permitted to use the bypass during early boot,
1733 : : * as doing so would confuse the auto-initialization code. Besides
1734 : : * which, there is no point in worrying about lock contention while
1735 : : * there is only one CPU in operation.
1736 : : */
1737 : : static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
1738 : : bool *was_alldone, unsigned long flags)
1739 : : {
1740 : : unsigned long c;
1741 : : unsigned long cur_gp_seq;
1742 : : unsigned long j = jiffies;
1743 : : long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
1744 : :
1745 : : if (!rcu_segcblist_is_offloaded(&rdp->cblist)) {
1746 : : *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
1747 : : return false; /* Not offloaded, no bypassing. */
1748 : : }
1749 : : lockdep_assert_irqs_disabled();
1750 : :
1751 : : // Don't use ->nocb_bypass during early boot.
1752 : : if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING) {
1753 : : rcu_nocb_lock(rdp);
1754 : : WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
1755 : : *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
1756 : : return false;
1757 : : }
1758 : :
1759 : : // If we have advanced to a new jiffy, reset counts to allow
1760 : : // moving back from ->nocb_bypass to ->cblist.
1761 : : if (j == rdp->nocb_nobypass_last) {
1762 : : c = rdp->nocb_nobypass_count + 1;
1763 : : } else {
1764 : : WRITE_ONCE(rdp->nocb_nobypass_last, j);
1765 : : c = rdp->nocb_nobypass_count - nocb_nobypass_lim_per_jiffy;
1766 : : if (ULONG_CMP_LT(rdp->nocb_nobypass_count,
1767 : : nocb_nobypass_lim_per_jiffy))
1768 : : c = 0;
1769 : : else if (c > nocb_nobypass_lim_per_jiffy)
1770 : : c = nocb_nobypass_lim_per_jiffy;
1771 : : }
1772 : : WRITE_ONCE(rdp->nocb_nobypass_count, c);
1773 : :
1774 : : // If there hasn't yet been all that many ->cblist enqueues
1775 : : // this jiffy, tell the caller to enqueue onto ->cblist. But flush
1776 : : // ->nocb_bypass first.
1777 : : if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy) {
1778 : : rcu_nocb_lock(rdp);
1779 : : *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
1780 : : if (*was_alldone)
1781 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1782 : : TPS("FirstQ"));
1783 : : WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j));
1784 : : WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
1785 : : return false; // Caller must enqueue the callback.
1786 : : }
1787 : :
1788 : : // If ->nocb_bypass has been used too long or is too full,
1789 : : // flush ->nocb_bypass to ->cblist.
1790 : : if ((ncbs && j != READ_ONCE(rdp->nocb_bypass_first)) ||
1791 : : ncbs >= qhimark) {
1792 : : rcu_nocb_lock(rdp);
1793 : : if (!rcu_nocb_flush_bypass(rdp, rhp, j)) {
1794 : : *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist);
1795 : : if (*was_alldone)
1796 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1797 : : TPS("FirstQ"));
1798 : : WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass));
1799 : : return false; // Caller must enqueue the callback.
1800 : : }
1801 : : if (j != rdp->nocb_gp_adv_time &&
1802 : : rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
1803 : : rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
1804 : : rcu_advance_cbs_nowake(rdp->mynode, rdp);
1805 : : rdp->nocb_gp_adv_time = j;
1806 : : }
1807 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1808 : : return true; // Callback already enqueued.
1809 : : }
1810 : :
1811 : : // We need to use the bypass.
1812 : : rcu_nocb_wait_contended(rdp);
1813 : : rcu_nocb_bypass_lock(rdp);
1814 : : ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
1815 : : rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */
1816 : : rcu_cblist_enqueue(&rdp->nocb_bypass, rhp);
1817 : : if (!ncbs) {
1818 : : WRITE_ONCE(rdp->nocb_bypass_first, j);
1819 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstBQ"));
1820 : : }
1821 : : rcu_nocb_bypass_unlock(rdp);
1822 : : smp_mb(); /* Order enqueue before wake. */
1823 : : if (ncbs) {
1824 : : local_irq_restore(flags);
1825 : : } else {
1826 : : // No-CBs GP kthread might be indefinitely asleep, if so, wake.
1827 : : rcu_nocb_lock(rdp); // Rare during call_rcu() flood.
1828 : : if (!rcu_segcblist_pend_cbs(&rdp->cblist)) {
1829 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1830 : : TPS("FirstBQwake"));
1831 : : __call_rcu_nocb_wake(rdp, true, flags);
1832 : : } else {
1833 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1834 : : TPS("FirstBQnoWake"));
1835 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1836 : : }
1837 : : }
1838 : : return true; // Callback already enqueued.
1839 : : }
1840 : :
1841 : : /*
1842 : : * Awaken the no-CBs grace-period kthead if needed, either due to it
1843 : : * legitimately being asleep or due to overload conditions.
1844 : : *
1845 : : * If warranted, also wake up the kthread servicing this CPUs queues.
1846 : : */
1847 : : static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone,
1848 : : unsigned long flags)
1849 : : __releases(rdp->nocb_lock)
1850 : : {
1851 : : unsigned long cur_gp_seq;
1852 : : unsigned long j;
1853 : : long len;
1854 : : struct task_struct *t;
1855 : :
1856 : : // If we are being polled or there is no kthread, just leave.
1857 : : t = READ_ONCE(rdp->nocb_gp_kthread);
1858 : : if (rcu_nocb_poll || !t) {
1859 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1860 : : TPS("WakeNotPoll"));
1861 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1862 : : return;
1863 : : }
1864 : : // Need to actually to a wakeup.
1865 : : len = rcu_segcblist_n_cbs(&rdp->cblist);
1866 : : if (was_alldone) {
1867 : : rdp->qlen_last_fqs_check = len;
1868 : : if (!irqs_disabled_flags(flags)) {
1869 : : /* ... if queue was empty ... */
1870 : : wake_nocb_gp(rdp, false, flags);
1871 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1872 : : TPS("WakeEmpty"));
1873 : : } else {
1874 : : wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE,
1875 : : TPS("WakeEmptyIsDeferred"));
1876 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1877 : : }
1878 : : } else if (len > rdp->qlen_last_fqs_check + qhimark) {
1879 : : /* ... or if many callbacks queued. */
1880 : : rdp->qlen_last_fqs_check = len;
1881 : : j = jiffies;
1882 : : if (j != rdp->nocb_gp_adv_time &&
1883 : : rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
1884 : : rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) {
1885 : : rcu_advance_cbs_nowake(rdp->mynode, rdp);
1886 : : rdp->nocb_gp_adv_time = j;
1887 : : }
1888 : : smp_mb(); /* Enqueue before timer_pending(). */
1889 : : if ((rdp->nocb_cb_sleep ||
1890 : : !rcu_segcblist_ready_cbs(&rdp->cblist)) &&
1891 : : !timer_pending(&rdp->nocb_bypass_timer))
1892 : : wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE,
1893 : : TPS("WakeOvfIsDeferred"));
1894 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1895 : : } else {
1896 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot"));
1897 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1898 : : }
1899 : : return;
1900 : : }
1901 : :
1902 : : /* Wake up the no-CBs GP kthread to flush ->nocb_bypass. */
1903 : : static void do_nocb_bypass_wakeup_timer(struct timer_list *t)
1904 : : {
1905 : : unsigned long flags;
1906 : : struct rcu_data *rdp = from_timer(rdp, t, nocb_bypass_timer);
1907 : :
1908 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Timer"));
1909 : : rcu_nocb_lock_irqsave(rdp, flags);
1910 : : smp_mb__after_spinlock(); /* Timer expire before wakeup. */
1911 : : __call_rcu_nocb_wake(rdp, true, flags);
1912 : : }
1913 : :
1914 : : /*
1915 : : * No-CBs GP kthreads come here to wait for additional callbacks to show up
1916 : : * or for grace periods to end.
1917 : : */
1918 : : static void nocb_gp_wait(struct rcu_data *my_rdp)
1919 : : {
1920 : : bool bypass = false;
1921 : : long bypass_ncbs;
1922 : : int __maybe_unused cpu = my_rdp->cpu;
1923 : : unsigned long cur_gp_seq;
1924 : : unsigned long flags;
1925 : : bool gotcbs = false;
1926 : : unsigned long j = jiffies;
1927 : : bool needwait_gp = false; // This prevents actual uninitialized use.
1928 : : bool needwake;
1929 : : bool needwake_gp;
1930 : : struct rcu_data *rdp;
1931 : : struct rcu_node *rnp;
1932 : : unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning.
1933 : :
1934 : : /*
1935 : : * Each pass through the following loop checks for CBs and for the
1936 : : * nearest grace period (if any) to wait for next. The CB kthreads
1937 : : * and the global grace-period kthread are awakened if needed.
1938 : : */
1939 : : for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_cb_rdp) {
1940 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check"));
1941 : : rcu_nocb_lock_irqsave(rdp, flags);
1942 : : bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
1943 : : if (bypass_ncbs &&
1944 : : (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) ||
1945 : : bypass_ncbs > 2 * qhimark)) {
1946 : : // Bypass full or old, so flush it.
1947 : : (void)rcu_nocb_try_flush_bypass(rdp, j);
1948 : : bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass);
1949 : : } else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) {
1950 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1951 : : continue; /* No callbacks here, try next. */
1952 : : }
1953 : : if (bypass_ncbs) {
1954 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1955 : : TPS("Bypass"));
1956 : : bypass = true;
1957 : : }
1958 : : rnp = rdp->mynode;
1959 : : if (bypass) { // Avoid race with first bypass CB.
1960 : : WRITE_ONCE(my_rdp->nocb_defer_wakeup,
1961 : : RCU_NOCB_WAKE_NOT);
1962 : : del_timer(&my_rdp->nocb_timer);
1963 : : }
1964 : : // Advance callbacks if helpful and low contention.
1965 : : needwake_gp = false;
1966 : : if (!rcu_segcblist_restempty(&rdp->cblist,
1967 : : RCU_NEXT_READY_TAIL) ||
1968 : : (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
1969 : : rcu_seq_done(&rnp->gp_seq, cur_gp_seq))) {
1970 : : raw_spin_lock_rcu_node(rnp); /* irqs disabled. */
1971 : : needwake_gp = rcu_advance_cbs(rnp, rdp);
1972 : : raw_spin_unlock_rcu_node(rnp); /* irqs disabled. */
1973 : : }
1974 : : // Need to wait on some grace period?
1975 : : WARN_ON_ONCE(!rcu_segcblist_restempty(&rdp->cblist,
1976 : : RCU_NEXT_READY_TAIL));
1977 : : if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq)) {
1978 : : if (!needwait_gp ||
1979 : : ULONG_CMP_LT(cur_gp_seq, wait_gp_seq))
1980 : : wait_gp_seq = cur_gp_seq;
1981 : : needwait_gp = true;
1982 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu,
1983 : : TPS("NeedWaitGP"));
1984 : : }
1985 : : if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
1986 : : needwake = rdp->nocb_cb_sleep;
1987 : : WRITE_ONCE(rdp->nocb_cb_sleep, false);
1988 : : smp_mb(); /* CB invocation -after- GP end. */
1989 : : } else {
1990 : : needwake = false;
1991 : : }
1992 : : rcu_nocb_unlock_irqrestore(rdp, flags);
1993 : : if (needwake) {
1994 : : swake_up_one(&rdp->nocb_cb_wq);
1995 : : gotcbs = true;
1996 : : }
1997 : : if (needwake_gp)
1998 : : rcu_gp_kthread_wake();
1999 : : }
2000 : :
2001 : : my_rdp->nocb_gp_bypass = bypass;
2002 : : my_rdp->nocb_gp_gp = needwait_gp;
2003 : : my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0;
2004 : : if (bypass && !rcu_nocb_poll) {
2005 : : // At least one child with non-empty ->nocb_bypass, so set
2006 : : // timer in order to avoid stranding its callbacks.
2007 : : raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
2008 : : mod_timer(&my_rdp->nocb_bypass_timer, j + 2);
2009 : : raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
2010 : : }
2011 : : if (rcu_nocb_poll) {
2012 : : /* Polling, so trace if first poll in the series. */
2013 : : if (gotcbs)
2014 : : trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll"));
2015 : : schedule_timeout_interruptible(1);
2016 : : } else if (!needwait_gp) {
2017 : : /* Wait for callbacks to appear. */
2018 : : trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep"));
2019 : : swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq,
2020 : : !READ_ONCE(my_rdp->nocb_gp_sleep));
2021 : : trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep"));
2022 : : } else {
2023 : : rnp = my_rdp->mynode;
2024 : : trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("StartWait"));
2025 : : swait_event_interruptible_exclusive(
2026 : : rnp->nocb_gp_wq[rcu_seq_ctr(wait_gp_seq) & 0x1],
2027 : : rcu_seq_done(&rnp->gp_seq, wait_gp_seq) ||
2028 : : !READ_ONCE(my_rdp->nocb_gp_sleep));
2029 : : trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("EndWait"));
2030 : : }
2031 : : if (!rcu_nocb_poll) {
2032 : : raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
2033 : : if (bypass)
2034 : : del_timer(&my_rdp->nocb_bypass_timer);
2035 : : WRITE_ONCE(my_rdp->nocb_gp_sleep, true);
2036 : : raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
2037 : : }
2038 : : my_rdp->nocb_gp_seq = -1;
2039 : : WARN_ON(signal_pending(current));
2040 : : }
2041 : :
2042 : : /*
2043 : : * No-CBs grace-period-wait kthread. There is one of these per group
2044 : : * of CPUs, but only once at least one CPU in that group has come online
2045 : : * at least once since boot. This kthread checks for newly posted
2046 : : * callbacks from any of the CPUs it is responsible for, waits for a
2047 : : * grace period, then awakens all of the rcu_nocb_cb_kthread() instances
2048 : : * that then have callback-invocation work to do.
2049 : : */
2050 : : static int rcu_nocb_gp_kthread(void *arg)
2051 : : {
2052 : : struct rcu_data *rdp = arg;
2053 : :
2054 : : for (;;) {
2055 : : WRITE_ONCE(rdp->nocb_gp_loops, rdp->nocb_gp_loops + 1);
2056 : : nocb_gp_wait(rdp);
2057 : : cond_resched_tasks_rcu_qs();
2058 : : }
2059 : : return 0;
2060 : : }
2061 : :
2062 : : /*
2063 : : * Invoke any ready callbacks from the corresponding no-CBs CPU,
2064 : : * then, if there are no more, wait for more to appear.
2065 : : */
2066 : : static void nocb_cb_wait(struct rcu_data *rdp)
2067 : : {
2068 : : unsigned long cur_gp_seq;
2069 : : unsigned long flags;
2070 : : bool needwake_gp = false;
2071 : : struct rcu_node *rnp = rdp->mynode;
2072 : :
2073 : : local_irq_save(flags);
2074 : : rcu_momentary_dyntick_idle();
2075 : : local_irq_restore(flags);
2076 : : local_bh_disable();
2077 : : rcu_do_batch(rdp);
2078 : : local_bh_enable();
2079 : : lockdep_assert_irqs_enabled();
2080 : : rcu_nocb_lock_irqsave(rdp, flags);
2081 : : if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) &&
2082 : : rcu_seq_done(&rnp->gp_seq, cur_gp_seq) &&
2083 : : raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */
2084 : : needwake_gp = rcu_advance_cbs(rdp->mynode, rdp);
2085 : : raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2086 : : }
2087 : : if (rcu_segcblist_ready_cbs(&rdp->cblist)) {
2088 : : rcu_nocb_unlock_irqrestore(rdp, flags);
2089 : : if (needwake_gp)
2090 : : rcu_gp_kthread_wake();
2091 : : return;
2092 : : }
2093 : :
2094 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("CBSleep"));
2095 : : WRITE_ONCE(rdp->nocb_cb_sleep, true);
2096 : : rcu_nocb_unlock_irqrestore(rdp, flags);
2097 : : if (needwake_gp)
2098 : : rcu_gp_kthread_wake();
2099 : : swait_event_interruptible_exclusive(rdp->nocb_cb_wq,
2100 : : !READ_ONCE(rdp->nocb_cb_sleep));
2101 : : if (!smp_load_acquire(&rdp->nocb_cb_sleep)) { /* VVV */
2102 : : /* ^^^ Ensure CB invocation follows _sleep test. */
2103 : : return;
2104 : : }
2105 : : WARN_ON(signal_pending(current));
2106 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty"));
2107 : : }
2108 : :
2109 : : /*
2110 : : * Per-rcu_data kthread, but only for no-CBs CPUs. Repeatedly invoke
2111 : : * nocb_cb_wait() to do the dirty work.
2112 : : */
2113 : : static int rcu_nocb_cb_kthread(void *arg)
2114 : : {
2115 : : struct rcu_data *rdp = arg;
2116 : :
2117 : : // Each pass through this loop does one callback batch, and,
2118 : : // if there are no more ready callbacks, waits for them.
2119 : : for (;;) {
2120 : : nocb_cb_wait(rdp);
2121 : : cond_resched_tasks_rcu_qs();
2122 : : }
2123 : : return 0;
2124 : : }
2125 : :
2126 : : /* Is a deferred wakeup of rcu_nocb_kthread() required? */
2127 : : static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2128 : : {
2129 : : return READ_ONCE(rdp->nocb_defer_wakeup);
2130 : : }
2131 : :
2132 : : /* Do a deferred wakeup of rcu_nocb_kthread(). */
2133 : : static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
2134 : : {
2135 : : unsigned long flags;
2136 : : int ndw;
2137 : :
2138 : : rcu_nocb_lock_irqsave(rdp, flags);
2139 : : if (!rcu_nocb_need_deferred_wakeup(rdp)) {
2140 : : rcu_nocb_unlock_irqrestore(rdp, flags);
2141 : : return;
2142 : : }
2143 : : ndw = READ_ONCE(rdp->nocb_defer_wakeup);
2144 : : WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
2145 : : wake_nocb_gp(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
2146 : : trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DeferredWake"));
2147 : : }
2148 : :
2149 : : /* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
2150 : : static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
2151 : : {
2152 : : struct rcu_data *rdp = from_timer(rdp, t, nocb_timer);
2153 : :
2154 : : do_nocb_deferred_wakeup_common(rdp);
2155 : : }
2156 : :
2157 : : /*
2158 : : * Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
2159 : : * This means we do an inexact common-case check. Note that if
2160 : : * we miss, ->nocb_timer will eventually clean things up.
2161 : : */
2162 : : static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2163 : : {
2164 : : if (rcu_nocb_need_deferred_wakeup(rdp))
2165 : : do_nocb_deferred_wakeup_common(rdp);
2166 : : }
2167 : :
2168 : : void __init rcu_init_nohz(void)
2169 : : {
2170 : : int cpu;
2171 : : bool need_rcu_nocb_mask = false;
2172 : : struct rcu_data *rdp;
2173 : :
2174 : : #if defined(CONFIG_NO_HZ_FULL)
2175 : : if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
2176 : : need_rcu_nocb_mask = true;
2177 : : #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2178 : :
2179 : : if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) {
2180 : : if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
2181 : : pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
2182 : : return;
2183 : : }
2184 : : }
2185 : : if (!cpumask_available(rcu_nocb_mask))
2186 : : return;
2187 : :
2188 : : #if defined(CONFIG_NO_HZ_FULL)
2189 : : if (tick_nohz_full_running)
2190 : : cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
2191 : : #endif /* #if defined(CONFIG_NO_HZ_FULL) */
2192 : :
2193 : : if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
2194 : : pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
2195 : : cpumask_and(rcu_nocb_mask, cpu_possible_mask,
2196 : : rcu_nocb_mask);
2197 : : }
2198 : : if (cpumask_empty(rcu_nocb_mask))
2199 : : pr_info("\tOffload RCU callbacks from CPUs: (none).\n");
2200 : : else
2201 : : pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
2202 : : cpumask_pr_args(rcu_nocb_mask));
2203 : : if (rcu_nocb_poll)
2204 : : pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
2205 : :
2206 : : for_each_cpu(cpu, rcu_nocb_mask) {
2207 : : rdp = per_cpu_ptr(&rcu_data, cpu);
2208 : : if (rcu_segcblist_empty(&rdp->cblist))
2209 : : rcu_segcblist_init(&rdp->cblist);
2210 : : rcu_segcblist_offload(&rdp->cblist);
2211 : : }
2212 : : rcu_organize_nocb_kthreads();
2213 : : }
2214 : :
2215 : : /* Initialize per-rcu_data variables for no-CBs CPUs. */
2216 : : static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2217 : : {
2218 : : init_swait_queue_head(&rdp->nocb_cb_wq);
2219 : : init_swait_queue_head(&rdp->nocb_gp_wq);
2220 : : raw_spin_lock_init(&rdp->nocb_lock);
2221 : : raw_spin_lock_init(&rdp->nocb_bypass_lock);
2222 : : raw_spin_lock_init(&rdp->nocb_gp_lock);
2223 : : timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
2224 : : timer_setup(&rdp->nocb_bypass_timer, do_nocb_bypass_wakeup_timer, 0);
2225 : : rcu_cblist_init(&rdp->nocb_bypass);
2226 : : }
2227 : :
2228 : : /*
2229 : : * If the specified CPU is a no-CBs CPU that does not already have its
2230 : : * rcuo CB kthread, spawn it. Additionally, if the rcuo GP kthread
2231 : : * for this CPU's group has not yet been created, spawn it as well.
2232 : : */
2233 : : static void rcu_spawn_one_nocb_kthread(int cpu)
2234 : : {
2235 : : struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
2236 : : struct rcu_data *rdp_gp;
2237 : : struct task_struct *t;
2238 : :
2239 : : /*
2240 : : * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
2241 : : * then nothing to do.
2242 : : */
2243 : : if (!rcu_is_nocb_cpu(cpu) || rdp->nocb_cb_kthread)
2244 : : return;
2245 : :
2246 : : /* If we didn't spawn the GP kthread first, reorganize! */
2247 : : rdp_gp = rdp->nocb_gp_rdp;
2248 : : if (!rdp_gp->nocb_gp_kthread) {
2249 : : t = kthread_run(rcu_nocb_gp_kthread, rdp_gp,
2250 : : "rcuog/%d", rdp_gp->cpu);
2251 : : if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__))
2252 : : return;
2253 : : WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);
2254 : : }
2255 : :
2256 : : /* Spawn the kthread for this CPU. */
2257 : : t = kthread_run(rcu_nocb_cb_kthread, rdp,
2258 : : "rcuo%c/%d", rcu_state.abbr, cpu);
2259 : : if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__))
2260 : : return;
2261 : : WRITE_ONCE(rdp->nocb_cb_kthread, t);
2262 : : WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread);
2263 : : }
2264 : :
2265 : : /*
2266 : : * If the specified CPU is a no-CBs CPU that does not already have its
2267 : : * rcuo kthread, spawn it.
2268 : : */
2269 : : static void rcu_spawn_cpu_nocb_kthread(int cpu)
2270 : : {
2271 : : if (rcu_scheduler_fully_active)
2272 : : rcu_spawn_one_nocb_kthread(cpu);
2273 : : }
2274 : :
2275 : : /*
2276 : : * Once the scheduler is running, spawn rcuo kthreads for all online
2277 : : * no-CBs CPUs. This assumes that the early_initcall()s happen before
2278 : : * non-boot CPUs come online -- if this changes, we will need to add
2279 : : * some mutual exclusion.
2280 : : */
2281 : : static void __init rcu_spawn_nocb_kthreads(void)
2282 : : {
2283 : : int cpu;
2284 : :
2285 : : for_each_online_cpu(cpu)
2286 : : rcu_spawn_cpu_nocb_kthread(cpu);
2287 : : }
2288 : :
2289 : : /* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */
2290 : : static int rcu_nocb_gp_stride = -1;
2291 : : module_param(rcu_nocb_gp_stride, int, 0444);
2292 : :
2293 : : /*
2294 : : * Initialize GP-CB relationships for all no-CBs CPU.
2295 : : */
2296 : : static void __init rcu_organize_nocb_kthreads(void)
2297 : : {
2298 : : int cpu;
2299 : : bool firsttime = true;
2300 : : bool gotnocbs = false;
2301 : : bool gotnocbscbs = true;
2302 : : int ls = rcu_nocb_gp_stride;
2303 : : int nl = 0; /* Next GP kthread. */
2304 : : struct rcu_data *rdp;
2305 : : struct rcu_data *rdp_gp = NULL; /* Suppress misguided gcc warn. */
2306 : : struct rcu_data *rdp_prev = NULL;
2307 : :
2308 : : if (!cpumask_available(rcu_nocb_mask))
2309 : : return;
2310 : : if (ls == -1) {
2311 : : ls = nr_cpu_ids / int_sqrt(nr_cpu_ids);
2312 : : rcu_nocb_gp_stride = ls;
2313 : : }
2314 : :
2315 : : /*
2316 : : * Each pass through this loop sets up one rcu_data structure.
2317 : : * Should the corresponding CPU come online in the future, then
2318 : : * we will spawn the needed set of rcu_nocb_kthread() kthreads.
2319 : : */
2320 : : for_each_cpu(cpu, rcu_nocb_mask) {
2321 : : rdp = per_cpu_ptr(&rcu_data, cpu);
2322 : : if (rdp->cpu >= nl) {
2323 : : /* New GP kthread, set up for CBs & next GP. */
2324 : : gotnocbs = true;
2325 : : nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
2326 : : rdp->nocb_gp_rdp = rdp;
2327 : : rdp_gp = rdp;
2328 : : if (dump_tree) {
2329 : : if (!firsttime)
2330 : : pr_cont("%s\n", gotnocbscbs
2331 : : ? "" : " (self only)");
2332 : : gotnocbscbs = false;
2333 : : firsttime = false;
2334 : : pr_alert("%s: No-CB GP kthread CPU %d:",
2335 : : __func__, cpu);
2336 : : }
2337 : : } else {
2338 : : /* Another CB kthread, link to previous GP kthread. */
2339 : : gotnocbscbs = true;
2340 : : rdp->nocb_gp_rdp = rdp_gp;
2341 : : rdp_prev->nocb_next_cb_rdp = rdp;
2342 : : if (dump_tree)
2343 : : pr_cont(" %d", cpu);
2344 : : }
2345 : : rdp_prev = rdp;
2346 : : }
2347 : : if (gotnocbs && dump_tree)
2348 : : pr_cont("%s\n", gotnocbscbs ? "" : " (self only)");
2349 : : }
2350 : :
2351 : : /*
2352 : : * Bind the current task to the offloaded CPUs. If there are no offloaded
2353 : : * CPUs, leave the task unbound. Splat if the bind attempt fails.
2354 : : */
2355 : : void rcu_bind_current_to_nocb(void)
2356 : : {
2357 : : if (cpumask_available(rcu_nocb_mask) && cpumask_weight(rcu_nocb_mask))
2358 : : WARN_ON(sched_setaffinity(current->pid, rcu_nocb_mask));
2359 : : }
2360 : : EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb);
2361 : :
2362 : : /*
2363 : : * Dump out nocb grace-period kthread state for the specified rcu_data
2364 : : * structure.
2365 : : */
2366 : : static void show_rcu_nocb_gp_state(struct rcu_data *rdp)
2367 : : {
2368 : : struct rcu_node *rnp = rdp->mynode;
2369 : :
2370 : : pr_info("nocb GP %d %c%c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu\n",
2371 : : rdp->cpu,
2372 : : "kK"[!!rdp->nocb_gp_kthread],
2373 : : "lL"[raw_spin_is_locked(&rdp->nocb_gp_lock)],
2374 : : "dD"[!!rdp->nocb_defer_wakeup],
2375 : : "tT"[timer_pending(&rdp->nocb_timer)],
2376 : : "bB"[timer_pending(&rdp->nocb_bypass_timer)],
2377 : : "sS"[!!rdp->nocb_gp_sleep],
2378 : : ".W"[swait_active(&rdp->nocb_gp_wq)],
2379 : : ".W"[swait_active(&rnp->nocb_gp_wq[0])],
2380 : : ".W"[swait_active(&rnp->nocb_gp_wq[1])],
2381 : : ".B"[!!rdp->nocb_gp_bypass],
2382 : : ".G"[!!rdp->nocb_gp_gp],
2383 : : (long)rdp->nocb_gp_seq,
2384 : : rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops));
2385 : : }
2386 : :
2387 : : /* Dump out nocb kthread state for the specified rcu_data structure. */
2388 : : static void show_rcu_nocb_state(struct rcu_data *rdp)
2389 : : {
2390 : : struct rcu_segcblist *rsclp = &rdp->cblist;
2391 : : bool waslocked;
2392 : : bool wastimer;
2393 : : bool wassleep;
2394 : :
2395 : : if (rdp->nocb_gp_rdp == rdp)
2396 : : show_rcu_nocb_gp_state(rdp);
2397 : :
2398 : : 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",
2399 : : rdp->cpu, rdp->nocb_gp_rdp->cpu,
2400 : : "kK"[!!rdp->nocb_cb_kthread],
2401 : : "bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)],
2402 : : "cC"[!!atomic_read(&rdp->nocb_lock_contended)],
2403 : : "lL"[raw_spin_is_locked(&rdp->nocb_lock)],
2404 : : "sS"[!!rdp->nocb_cb_sleep],
2405 : : ".W"[swait_active(&rdp->nocb_cb_wq)],
2406 : : jiffies - rdp->nocb_bypass_first,
2407 : : jiffies - rdp->nocb_nobypass_last,
2408 : : rdp->nocb_nobypass_count,
2409 : : ".D"[rcu_segcblist_ready_cbs(rsclp)],
2410 : : ".W"[!rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL)],
2411 : : ".R"[!rcu_segcblist_restempty(rsclp, RCU_WAIT_TAIL)],
2412 : : ".N"[!rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL)],
2413 : : ".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)],
2414 : : rcu_segcblist_n_cbs(&rdp->cblist));
2415 : :
2416 : : /* It is OK for GP kthreads to have GP state. */
2417 : : if (rdp->nocb_gp_rdp == rdp)
2418 : : return;
2419 : :
2420 : : waslocked = raw_spin_is_locked(&rdp->nocb_gp_lock);
2421 : : wastimer = timer_pending(&rdp->nocb_timer);
2422 : : wassleep = swait_active(&rdp->nocb_gp_wq);
2423 : : if (!rdp->nocb_defer_wakeup && !rdp->nocb_gp_sleep &&
2424 : : !waslocked && !wastimer && !wassleep)
2425 : : return; /* Nothing untowards. */
2426 : :
2427 : : pr_info(" !!! %c%c%c%c %c\n",
2428 : : "lL"[waslocked],
2429 : : "dD"[!!rdp->nocb_defer_wakeup],
2430 : : "tT"[wastimer],
2431 : : "sS"[!!rdp->nocb_gp_sleep],
2432 : : ".W"[wassleep]);
2433 : : }
2434 : :
2435 : : #else /* #ifdef CONFIG_RCU_NOCB_CPU */
2436 : :
2437 : : /* No ->nocb_lock to acquire. */
2438 : 477704 : static void rcu_nocb_lock(struct rcu_data *rdp)
2439 : : {
2440 : 477704 : }
2441 : :
2442 : : /* No ->nocb_lock to release. */
2443 : 26 : static void rcu_nocb_unlock(struct rcu_data *rdp)
2444 : : {
2445 : 0 : }
2446 : :
2447 : : /* No ->nocb_lock to release. */
2448 : 477678 : static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
2449 : : unsigned long flags)
2450 : : {
2451 : 477678 : local_irq_restore(flags);
2452 : : }
2453 : :
2454 : : /* Lockdep check that ->cblist may be safely accessed. */
2455 : 340208 : static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
2456 : : {
2457 : 340208 : lockdep_assert_irqs_disabled();
2458 : : }
2459 : :
2460 : 67521 : static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
2461 : : {
2462 : 67521 : }
2463 : :
2464 : 67521 : static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
2465 : : {
2466 : 67521 : return NULL;
2467 : : }
2468 : :
2469 : 30 : static void rcu_init_one_nocb(struct rcu_node *rnp)
2470 : : {
2471 : 30 : }
2472 : :
2473 : 26 : static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
2474 : : unsigned long j)
2475 : : {
2476 : 26 : return true;
2477 : : }
2478 : :
2479 : 2219838 : static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
2480 : : bool *was_alldone, unsigned long flags)
2481 : : {
2482 : 2219838 : return false;
2483 : : }
2484 : :
2485 : 0 : static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty,
2486 : : unsigned long flags)
2487 : : {
2488 : 0 : WARN_ON_ONCE(1); /* Should be dead code! */
2489 : 0 : }
2490 : :
2491 : 30 : static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2492 : : {
2493 : 30 : }
2494 : :
2495 : 97200 : static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2496 : : {
2497 [ + + ]: 97200 : return false;
2498 : : }
2499 : :
2500 : 259044 : static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2501 : : {
2502 : 259044 : }
2503 : :
2504 : 30 : static void rcu_spawn_cpu_nocb_kthread(int cpu)
2505 : : {
2506 : 30 : }
2507 : :
2508 : 30 : static void __init rcu_spawn_nocb_kthreads(void)
2509 : : {
2510 : 30 : }
2511 : :
2512 : : static void show_rcu_nocb_state(struct rcu_data *rdp)
2513 : : {
2514 : : }
2515 : :
2516 : : #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2517 : :
2518 : : /*
2519 : : * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
2520 : : * grace-period kthread will do force_quiescent_state() processing?
2521 : : * The idea is to avoid waking up RCU core processing on such a
2522 : : * CPU unless the grace period has extended for too long.
2523 : : *
2524 : : * This code relies on the fact that all NO_HZ_FULL CPUs are also
2525 : : * CONFIG_RCU_NOCB_CPU CPUs.
2526 : : */
2527 : : static bool rcu_nohz_full_cpu(void)
2528 : : {
2529 : : #ifdef CONFIG_NO_HZ_FULL
2530 : : if (tick_nohz_full_cpu(smp_processor_id()) &&
2531 : : (!rcu_gp_in_progress() ||
2532 : : ULONG_CMP_LT(jiffies, READ_ONCE(rcu_state.gp_start) + HZ)))
2533 : : return true;
2534 : : #endif /* #ifdef CONFIG_NO_HZ_FULL */
2535 : : return false;
2536 : : }
2537 : :
2538 : : /*
2539 : : * Bind the RCU grace-period kthreads to the housekeeping CPU.
2540 : : */
2541 : 30 : static void rcu_bind_gp_kthread(void)
2542 : : {
2543 : 30 : if (!tick_nohz_full_enabled())
2544 : 30 : return;
2545 : : housekeeping_affine(current, HK_FLAG_RCU);
2546 : : }
2547 : :
2548 : : /* Record the current task on dyntick-idle entry. */
2549 : : static void rcu_dynticks_task_enter(void)
2550 : : {
2551 : : #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2552 : : WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
2553 : : #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
2554 : : }
2555 : :
2556 : : /* Record no current task on dyntick-idle exit. */
2557 : 22123 : static void rcu_dynticks_task_exit(void)
2558 : : {
2559 : : #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2560 : : WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
2561 : : #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
2562 : 22123 : }
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