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1/*
2 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
3 * Internal non-public definitions that provide either classic
4 * or preemptible semantics.
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, you can access it online at
18 * http://www.gnu.org/licenses/gpl-2.0.html.
19 *
20 * Copyright Red Hat, 2009
21 * Copyright IBM Corporation, 2009
22 *
23 * Author: Ingo Molnar <mingo@elte.hu>
24 * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
25 */
26
27#include <linux/delay.h>
28#include <linux/gfp.h>
29#include <linux/oom.h>
30#include <linux/smpboot.h>
31#include "../time/tick-internal.h"
32
33#define RCU_KTHREAD_PRIO 1
34
35#ifdef CONFIG_RCU_BOOST
36#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
37#else
38#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
39#endif
40
41#ifdef CONFIG_RCU_NOCB_CPU
42static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
43static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */
44static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
45static char __initdata nocb_buf[NR_CPUS * 5];
46#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
47
48/*
49 * Check the RCU kernel configuration parameters and print informative
50 * messages about anything out of the ordinary. If you like #ifdef, you
51 * will love this function.
52 */
53static void __init rcu_bootup_announce_oddness(void)
54{
55#ifdef CONFIG_RCU_TRACE
56 pr_info("\tRCU debugfs-based tracing is enabled.\n");
57#endif
58#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
59 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
60 CONFIG_RCU_FANOUT);
61#endif
62#ifdef CONFIG_RCU_FANOUT_EXACT
63 pr_info("\tHierarchical RCU autobalancing is disabled.\n");
64#endif
65#ifdef CONFIG_RCU_FAST_NO_HZ
66 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
67#endif
68#ifdef CONFIG_PROVE_RCU
69 pr_info("\tRCU lockdep checking is enabled.\n");
70#endif
71#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
72 pr_info("\tRCU torture testing starts during boot.\n");
73#endif
74#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
75 pr_info("\tDump stacks of tasks blocking RCU-preempt GP.\n");
76#endif
77#if defined(CONFIG_RCU_CPU_STALL_INFO)
78 pr_info("\tAdditional per-CPU info printed with stalls.\n");
79#endif
80#if NUM_RCU_LVL_4 != 0
81 pr_info("\tFour-level hierarchy is enabled.\n");
82#endif
83 if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
84 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
85 if (nr_cpu_ids != NR_CPUS)
86 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
87#ifdef CONFIG_RCU_NOCB_CPU
88#ifndef CONFIG_RCU_NOCB_CPU_NONE
89 if (!have_rcu_nocb_mask) {
90 zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL);
91 have_rcu_nocb_mask = true;
92 }
93#ifdef CONFIG_RCU_NOCB_CPU_ZERO
94 pr_info("\tOffload RCU callbacks from CPU 0\n");
95 cpumask_set_cpu(0, rcu_nocb_mask);
96#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
97#ifdef CONFIG_RCU_NOCB_CPU_ALL
98 pr_info("\tOffload RCU callbacks from all CPUs\n");
99 cpumask_copy(rcu_nocb_mask, cpu_possible_mask);
100#endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
101#endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
102 if (have_rcu_nocb_mask) {
103 if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
104 pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
105 cpumask_and(rcu_nocb_mask, cpu_possible_mask,
106 rcu_nocb_mask);
107 }
108 cpulist_scnprintf(nocb_buf, sizeof(nocb_buf), rcu_nocb_mask);
109 pr_info("\tOffload RCU callbacks from CPUs: %s.\n", nocb_buf);
110 if (rcu_nocb_poll)
111 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
112 }
113#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
114}
115
116#ifdef CONFIG_TREE_PREEMPT_RCU
117
118RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
119static struct rcu_state *rcu_state = &rcu_preempt_state;
120
121static int rcu_preempted_readers_exp(struct rcu_node *rnp);
122
123/*
124 * Tell them what RCU they are running.
125 */
126static void __init rcu_bootup_announce(void)
127{
128 pr_info("Preemptible hierarchical RCU implementation.\n");
129 rcu_bootup_announce_oddness();
130}
131
132/*
133 * Return the number of RCU-preempt batches processed thus far
134 * for debug and statistics.
135 */
136long rcu_batches_completed_preempt(void)
137{
138 return rcu_preempt_state.completed;
139}
140EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
141
142/*
143 * Return the number of RCU batches processed thus far for debug & stats.
144 */
145long rcu_batches_completed(void)
146{
147 return rcu_batches_completed_preempt();
148}
149EXPORT_SYMBOL_GPL(rcu_batches_completed);
150
151/*
152 * Force a quiescent state for preemptible RCU.
153 */
154void rcu_force_quiescent_state(void)
155{
156 force_quiescent_state(&rcu_preempt_state);
157}
158EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
159
160/*
161 * Record a preemptible-RCU quiescent state for the specified CPU. Note
162 * that this just means that the task currently running on the CPU is
163 * not in a quiescent state. There might be any number of tasks blocked
164 * while in an RCU read-side critical section.
165 *
166 * Unlike the other rcu_*_qs() functions, callers to this function
167 * must disable irqs in order to protect the assignment to
168 * ->rcu_read_unlock_special.
169 */
170static void rcu_preempt_qs(int cpu)
171{
172 struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
173
174 if (rdp->passed_quiesce == 0)
175 trace_rcu_grace_period(TPS("rcu_preempt"), rdp->gpnum, TPS("cpuqs"));
176 rdp->passed_quiesce = 1;
177 current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
178}
179
180/*
181 * We have entered the scheduler, and the current task might soon be
182 * context-switched away from. If this task is in an RCU read-side
183 * critical section, we will no longer be able to rely on the CPU to
184 * record that fact, so we enqueue the task on the blkd_tasks list.
185 * The task will dequeue itself when it exits the outermost enclosing
186 * RCU read-side critical section. Therefore, the current grace period
187 * cannot be permitted to complete until the blkd_tasks list entries
188 * predating the current grace period drain, in other words, until
189 * rnp->gp_tasks becomes NULL.
190 *
191 * Caller must disable preemption.
192 */
193static void rcu_preempt_note_context_switch(int cpu)
194{
195 struct task_struct *t = current;
196 unsigned long flags;
197 struct rcu_data *rdp;
198 struct rcu_node *rnp;
199
200 if (t->rcu_read_lock_nesting > 0 &&
201 (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
202
203 /* Possibly blocking in an RCU read-side critical section. */
204 rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
205 rnp = rdp->mynode;
206 raw_spin_lock_irqsave(&rnp->lock, flags);
207 smp_mb__after_unlock_lock();
208 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
209 t->rcu_blocked_node = rnp;
210
211 /*
212 * If this CPU has already checked in, then this task
213 * will hold up the next grace period rather than the
214 * current grace period. Queue the task accordingly.
215 * If the task is queued for the current grace period
216 * (i.e., this CPU has not yet passed through a quiescent
217 * state for the current grace period), then as long
218 * as that task remains queued, the current grace period
219 * cannot end. Note that there is some uncertainty as
220 * to exactly when the current grace period started.
221 * We take a conservative approach, which can result
222 * in unnecessarily waiting on tasks that started very
223 * slightly after the current grace period began. C'est
224 * la vie!!!
225 *
226 * But first, note that the current CPU must still be
227 * on line!
228 */
229 WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
230 WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
231 if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
232 list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
233 rnp->gp_tasks = &t->rcu_node_entry;
234#ifdef CONFIG_RCU_BOOST
235 if (rnp->boost_tasks != NULL)
236 rnp->boost_tasks = rnp->gp_tasks;
237#endif /* #ifdef CONFIG_RCU_BOOST */
238 } else {
239 list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
240 if (rnp->qsmask & rdp->grpmask)
241 rnp->gp_tasks = &t->rcu_node_entry;
242 }
243 trace_rcu_preempt_task(rdp->rsp->name,
244 t->pid,
245 (rnp->qsmask & rdp->grpmask)
246 ? rnp->gpnum
247 : rnp->gpnum + 1);
248 raw_spin_unlock_irqrestore(&rnp->lock, flags);
249 } else if (t->rcu_read_lock_nesting < 0 &&
250 t->rcu_read_unlock_special) {
251
252 /*
253 * Complete exit from RCU read-side critical section on
254 * behalf of preempted instance of __rcu_read_unlock().
255 */
256 rcu_read_unlock_special(t);
257 }
258
259 /*
260 * Either we were not in an RCU read-side critical section to
261 * begin with, or we have now recorded that critical section
262 * globally. Either way, we can now note a quiescent state
263 * for this CPU. Again, if we were in an RCU read-side critical
264 * section, and if that critical section was blocking the current
265 * grace period, then the fact that the task has been enqueued
266 * means that we continue to block the current grace period.
267 */
268 local_irq_save(flags);
269 rcu_preempt_qs(cpu);
270 local_irq_restore(flags);
271}
272
273/*
274 * Check for preempted RCU readers blocking the current grace period
275 * for the specified rcu_node structure. If the caller needs a reliable
276 * answer, it must hold the rcu_node's ->lock.
277 */
278static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
279{
280 return rnp->gp_tasks != NULL;
281}
282
283/*
284 * Record a quiescent state for all tasks that were previously queued
285 * on the specified rcu_node structure and that were blocking the current
286 * RCU grace period. The caller must hold the specified rnp->lock with
287 * irqs disabled, and this lock is released upon return, but irqs remain
288 * disabled.
289 */
290static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
291 __releases(rnp->lock)
292{
293 unsigned long mask;
294 struct rcu_node *rnp_p;
295
296 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
297 raw_spin_unlock_irqrestore(&rnp->lock, flags);
298 return; /* Still need more quiescent states! */
299 }
300
301 rnp_p = rnp->parent;
302 if (rnp_p == NULL) {
303 /*
304 * Either there is only one rcu_node in the tree,
305 * or tasks were kicked up to root rcu_node due to
306 * CPUs going offline.
307 */
308 rcu_report_qs_rsp(&rcu_preempt_state, flags);
309 return;
310 }
311
312 /* Report up the rest of the hierarchy. */
313 mask = rnp->grpmask;
314 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
315 raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */
316 smp_mb__after_unlock_lock();
317 rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
318}
319
320/*
321 * Advance a ->blkd_tasks-list pointer to the next entry, instead
322 * returning NULL if at the end of the list.
323 */
324static struct list_head *rcu_next_node_entry(struct task_struct *t,
325 struct rcu_node *rnp)
326{
327 struct list_head *np;
328
329 np = t->rcu_node_entry.next;
330 if (np == &rnp->blkd_tasks)
331 np = NULL;
332 return np;
333}
334
335/*
336 * Handle special cases during rcu_read_unlock(), such as needing to
337 * notify RCU core processing or task having blocked during the RCU
338 * read-side critical section.
339 */
340void rcu_read_unlock_special(struct task_struct *t)
341{
342 int empty;
343 int empty_exp;
344 int empty_exp_now;
345 unsigned long flags;
346 struct list_head *np;
347#ifdef CONFIG_RCU_BOOST
348 struct rt_mutex *rbmp = NULL;
349#endif /* #ifdef CONFIG_RCU_BOOST */
350 struct rcu_node *rnp;
351 int special;
352
353 /* NMI handlers cannot block and cannot safely manipulate state. */
354 if (in_nmi())
355 return;
356
357 local_irq_save(flags);
358
359 /*
360 * If RCU core is waiting for this CPU to exit critical section,
361 * let it know that we have done so.
362 */
363 special = t->rcu_read_unlock_special;
364 if (special & RCU_READ_UNLOCK_NEED_QS) {
365 rcu_preempt_qs(smp_processor_id());
366 if (!t->rcu_read_unlock_special) {
367 local_irq_restore(flags);
368 return;
369 }
370 }
371
372 /* Hardware IRQ handlers cannot block, complain if they get here. */
373 if (WARN_ON_ONCE(in_irq() || in_serving_softirq())) {
374 local_irq_restore(flags);
375 return;
376 }
377
378 /* Clean up if blocked during RCU read-side critical section. */
379 if (special & RCU_READ_UNLOCK_BLOCKED) {
380 t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
381
382 /*
383 * Remove this task from the list it blocked on. The
384 * task can migrate while we acquire the lock, but at
385 * most one time. So at most two passes through loop.
386 */
387 for (;;) {
388 rnp = t->rcu_blocked_node;
389 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
390 smp_mb__after_unlock_lock();
391 if (rnp == t->rcu_blocked_node)
392 break;
393 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
394 }
395 empty = !rcu_preempt_blocked_readers_cgp(rnp);
396 empty_exp = !rcu_preempted_readers_exp(rnp);
397 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
398 np = rcu_next_node_entry(t, rnp);
399 list_del_init(&t->rcu_node_entry);
400 t->rcu_blocked_node = NULL;
401 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
402 rnp->gpnum, t->pid);
403 if (&t->rcu_node_entry == rnp->gp_tasks)
404 rnp->gp_tasks = np;
405 if (&t->rcu_node_entry == rnp->exp_tasks)
406 rnp->exp_tasks = np;
407#ifdef CONFIG_RCU_BOOST
408 if (&t->rcu_node_entry == rnp->boost_tasks)
409 rnp->boost_tasks = np;
410 /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
411 if (t->rcu_boost_mutex) {
412 rbmp = t->rcu_boost_mutex;
413 t->rcu_boost_mutex = NULL;
414 }
415#endif /* #ifdef CONFIG_RCU_BOOST */
416
417 /*
418 * If this was the last task on the current list, and if
419 * we aren't waiting on any CPUs, report the quiescent state.
420 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
421 * so we must take a snapshot of the expedited state.
422 */
423 empty_exp_now = !rcu_preempted_readers_exp(rnp);
424 if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
425 trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
426 rnp->gpnum,
427 0, rnp->qsmask,
428 rnp->level,
429 rnp->grplo,
430 rnp->grphi,
431 !!rnp->gp_tasks);
432 rcu_report_unblock_qs_rnp(rnp, flags);
433 } else {
434 raw_spin_unlock_irqrestore(&rnp->lock, flags);
435 }
436
437#ifdef CONFIG_RCU_BOOST
438 /* Unboost if we were boosted. */
439 if (rbmp)
440 rt_mutex_unlock(rbmp);
441#endif /* #ifdef CONFIG_RCU_BOOST */
442
443 /*
444 * If this was the last task on the expedited lists,
445 * then we need to report up the rcu_node hierarchy.
446 */
447 if (!empty_exp && empty_exp_now)
448 rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
449 } else {
450 local_irq_restore(flags);
451 }
452}
453
454#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
455
456/*
457 * Dump detailed information for all tasks blocking the current RCU
458 * grace period on the specified rcu_node structure.
459 */
460static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
461{
462 unsigned long flags;
463 struct task_struct *t;
464
465 raw_spin_lock_irqsave(&rnp->lock, flags);
466 if (!rcu_preempt_blocked_readers_cgp(rnp)) {
467 raw_spin_unlock_irqrestore(&rnp->lock, flags);
468 return;
469 }
470 t = list_entry(rnp->gp_tasks,
471 struct task_struct, rcu_node_entry);
472 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
473 sched_show_task(t);
474 raw_spin_unlock_irqrestore(&rnp->lock, flags);
475}
476
477/*
478 * Dump detailed information for all tasks blocking the current RCU
479 * grace period.
480 */
481static void rcu_print_detail_task_stall(struct rcu_state *rsp)
482{
483 struct rcu_node *rnp = rcu_get_root(rsp);
484
485 rcu_print_detail_task_stall_rnp(rnp);
486 rcu_for_each_leaf_node(rsp, rnp)
487 rcu_print_detail_task_stall_rnp(rnp);
488}
489
490#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
491
492static void rcu_print_detail_task_stall(struct rcu_state *rsp)
493{
494}
495
496#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
497
498#ifdef CONFIG_RCU_CPU_STALL_INFO
499
500static void rcu_print_task_stall_begin(struct rcu_node *rnp)
501{
502 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
503 rnp->level, rnp->grplo, rnp->grphi);
504}
505
506static void rcu_print_task_stall_end(void)
507{
508 pr_cont("\n");
509}
510
511#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
512
513static void rcu_print_task_stall_begin(struct rcu_node *rnp)
514{
515}
516
517static void rcu_print_task_stall_end(void)
518{
519}
520
521#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
522
523/*
524 * Scan the current list of tasks blocked within RCU read-side critical
525 * sections, printing out the tid of each.
526 */
527static int rcu_print_task_stall(struct rcu_node *rnp)
528{
529 struct task_struct *t;
530 int ndetected = 0;
531
532 if (!rcu_preempt_blocked_readers_cgp(rnp))
533 return 0;
534 rcu_print_task_stall_begin(rnp);
535 t = list_entry(rnp->gp_tasks,
536 struct task_struct, rcu_node_entry);
537 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
538 pr_cont(" P%d", t->pid);
539 ndetected++;
540 }
541 rcu_print_task_stall_end();
542 return ndetected;
543}
544
545/*
546 * Check that the list of blocked tasks for the newly completed grace
547 * period is in fact empty. It is a serious bug to complete a grace
548 * period that still has RCU readers blocked! This function must be
549 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
550 * must be held by the caller.
551 *
552 * Also, if there are blocked tasks on the list, they automatically
553 * block the newly created grace period, so set up ->gp_tasks accordingly.
554 */
555static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
556{
557 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
558 if (!list_empty(&rnp->blkd_tasks))
559 rnp->gp_tasks = rnp->blkd_tasks.next;
560 WARN_ON_ONCE(rnp->qsmask);
561}
562
563#ifdef CONFIG_HOTPLUG_CPU
564
565/*
566 * Handle tasklist migration for case in which all CPUs covered by the
567 * specified rcu_node have gone offline. Move them up to the root
568 * rcu_node. The reason for not just moving them to the immediate
569 * parent is to remove the need for rcu_read_unlock_special() to
570 * make more than two attempts to acquire the target rcu_node's lock.
571 * Returns true if there were tasks blocking the current RCU grace
572 * period.
573 *
574 * Returns 1 if there was previously a task blocking the current grace
575 * period on the specified rcu_node structure.
576 *
577 * The caller must hold rnp->lock with irqs disabled.
578 */
579static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
580 struct rcu_node *rnp,
581 struct rcu_data *rdp)
582{
583 struct list_head *lp;
584 struct list_head *lp_root;
585 int retval = 0;
586 struct rcu_node *rnp_root = rcu_get_root(rsp);
587 struct task_struct *t;
588
589 if (rnp == rnp_root) {
590 WARN_ONCE(1, "Last CPU thought to be offlined?");
591 return 0; /* Shouldn't happen: at least one CPU online. */
592 }
593
594 /* If we are on an internal node, complain bitterly. */
595 WARN_ON_ONCE(rnp != rdp->mynode);
596
597 /*
598 * Move tasks up to root rcu_node. Don't try to get fancy for
599 * this corner-case operation -- just put this node's tasks
600 * at the head of the root node's list, and update the root node's
601 * ->gp_tasks and ->exp_tasks pointers to those of this node's,
602 * if non-NULL. This might result in waiting for more tasks than
603 * absolutely necessary, but this is a good performance/complexity
604 * tradeoff.
605 */
606 if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
607 retval |= RCU_OFL_TASKS_NORM_GP;
608 if (rcu_preempted_readers_exp(rnp))
609 retval |= RCU_OFL_TASKS_EXP_GP;
610 lp = &rnp->blkd_tasks;
611 lp_root = &rnp_root->blkd_tasks;
612 while (!list_empty(lp)) {
613 t = list_entry(lp->next, typeof(*t), rcu_node_entry);
614 raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
615 smp_mb__after_unlock_lock();
616 list_del(&t->rcu_node_entry);
617 t->rcu_blocked_node = rnp_root;
618 list_add(&t->rcu_node_entry, lp_root);
619 if (&t->rcu_node_entry == rnp->gp_tasks)
620 rnp_root->gp_tasks = rnp->gp_tasks;
621 if (&t->rcu_node_entry == rnp->exp_tasks)
622 rnp_root->exp_tasks = rnp->exp_tasks;
623#ifdef CONFIG_RCU_BOOST
624 if (&t->rcu_node_entry == rnp->boost_tasks)
625 rnp_root->boost_tasks = rnp->boost_tasks;
626#endif /* #ifdef CONFIG_RCU_BOOST */
627 raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
628 }
629
630 rnp->gp_tasks = NULL;
631 rnp->exp_tasks = NULL;
632#ifdef CONFIG_RCU_BOOST
633 rnp->boost_tasks = NULL;
634 /*
635 * In case root is being boosted and leaf was not. Make sure
636 * that we boost the tasks blocking the current grace period
637 * in this case.
638 */
639 raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
640 smp_mb__after_unlock_lock();
641 if (rnp_root->boost_tasks != NULL &&
642 rnp_root->boost_tasks != rnp_root->gp_tasks &&
643 rnp_root->boost_tasks != rnp_root->exp_tasks)
644 rnp_root->boost_tasks = rnp_root->gp_tasks;
645 raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
646#endif /* #ifdef CONFIG_RCU_BOOST */
647
648 return retval;
649}
650
651#endif /* #ifdef CONFIG_HOTPLUG_CPU */
652
653/*
654 * Check for a quiescent state from the current CPU. When a task blocks,
655 * the task is recorded in the corresponding CPU's rcu_node structure,
656 * which is checked elsewhere.
657 *
658 * Caller must disable hard irqs.
659 */
660static void rcu_preempt_check_callbacks(int cpu)
661{
662 struct task_struct *t = current;
663
664 if (t->rcu_read_lock_nesting == 0) {
665 rcu_preempt_qs(cpu);
666 return;
667 }
668 if (t->rcu_read_lock_nesting > 0 &&
669 per_cpu(rcu_preempt_data, cpu).qs_pending)
670 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
671}
672
673#ifdef CONFIG_RCU_BOOST
674
675static void rcu_preempt_do_callbacks(void)
676{
677 rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data));
678}
679
680#endif /* #ifdef CONFIG_RCU_BOOST */
681
682/*
683 * Queue a preemptible-RCU callback for invocation after a grace period.
684 */
685void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
686{
687 __call_rcu(head, func, &rcu_preempt_state, -1, 0);
688}
689EXPORT_SYMBOL_GPL(call_rcu);
690
691/*
692 * Queue an RCU callback for lazy invocation after a grace period.
693 * This will likely be later named something like "call_rcu_lazy()",
694 * but this change will require some way of tagging the lazy RCU
695 * callbacks in the list of pending callbacks. Until then, this
696 * function may only be called from __kfree_rcu().
697 */
698void kfree_call_rcu(struct rcu_head *head,
699 void (*func)(struct rcu_head *rcu))
700{
701 __call_rcu(head, func, &rcu_preempt_state, -1, 1);
702}
703EXPORT_SYMBOL_GPL(kfree_call_rcu);
704
705/**
706 * synchronize_rcu - wait until a grace period has elapsed.
707 *
708 * Control will return to the caller some time after a full grace
709 * period has elapsed, in other words after all currently executing RCU
710 * read-side critical sections have completed. Note, however, that
711 * upon return from synchronize_rcu(), the caller might well be executing
712 * concurrently with new RCU read-side critical sections that began while
713 * synchronize_rcu() was waiting. RCU read-side critical sections are
714 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
715 *
716 * See the description of synchronize_sched() for more detailed information
717 * on memory ordering guarantees.
718 */
719void synchronize_rcu(void)
720{
721 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
722 !lock_is_held(&rcu_lock_map) &&
723 !lock_is_held(&rcu_sched_lock_map),
724 "Illegal synchronize_rcu() in RCU read-side critical section");
725 if (!rcu_scheduler_active)
726 return;
727 if (rcu_expedited)
728 synchronize_rcu_expedited();
729 else
730 wait_rcu_gp(call_rcu);
731}
732EXPORT_SYMBOL_GPL(synchronize_rcu);
733
734static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
735static unsigned long sync_rcu_preempt_exp_count;
736static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
737
738/*
739 * Return non-zero if there are any tasks in RCU read-side critical
740 * sections blocking the current preemptible-RCU expedited grace period.
741 * If there is no preemptible-RCU expedited grace period currently in
742 * progress, returns zero unconditionally.
743 */
744static int rcu_preempted_readers_exp(struct rcu_node *rnp)
745{
746 return rnp->exp_tasks != NULL;
747}
748
749/*
750 * return non-zero if there is no RCU expedited grace period in progress
751 * for the specified rcu_node structure, in other words, if all CPUs and
752 * tasks covered by the specified rcu_node structure have done their bit
753 * for the current expedited grace period. Works only for preemptible
754 * RCU -- other RCU implementation use other means.
755 *
756 * Caller must hold sync_rcu_preempt_exp_mutex.
757 */
758static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
759{
760 return !rcu_preempted_readers_exp(rnp) &&
761 ACCESS_ONCE(rnp->expmask) == 0;
762}
763
764/*
765 * Report the exit from RCU read-side critical section for the last task
766 * that queued itself during or before the current expedited preemptible-RCU
767 * grace period. This event is reported either to the rcu_node structure on
768 * which the task was queued or to one of that rcu_node structure's ancestors,
769 * recursively up the tree. (Calm down, calm down, we do the recursion
770 * iteratively!)
771 *
772 * Most callers will set the "wake" flag, but the task initiating the
773 * expedited grace period need not wake itself.
774 *
775 * Caller must hold sync_rcu_preempt_exp_mutex.
776 */
777static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
778 bool wake)
779{
780 unsigned long flags;
781 unsigned long mask;
782
783 raw_spin_lock_irqsave(&rnp->lock, flags);
784 smp_mb__after_unlock_lock();
785 for (;;) {
786 if (!sync_rcu_preempt_exp_done(rnp)) {
787 raw_spin_unlock_irqrestore(&rnp->lock, flags);
788 break;
789 }
790 if (rnp->parent == NULL) {
791 raw_spin_unlock_irqrestore(&rnp->lock, flags);
792 if (wake) {
793 smp_mb(); /* EGP done before wake_up(). */
794 wake_up(&sync_rcu_preempt_exp_wq);
795 }
796 break;
797 }
798 mask = rnp->grpmask;
799 raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
800 rnp = rnp->parent;
801 raw_spin_lock(&rnp->lock); /* irqs already disabled */
802 smp_mb__after_unlock_lock();
803 rnp->expmask &= ~mask;
804 }
805}
806
807/*
808 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
809 * grace period for the specified rcu_node structure. If there are no such
810 * tasks, report it up the rcu_node hierarchy.
811 *
812 * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
813 * CPU hotplug operations.
814 */
815static void
816sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
817{
818 unsigned long flags;
819 int must_wait = 0;
820
821 raw_spin_lock_irqsave(&rnp->lock, flags);
822 smp_mb__after_unlock_lock();
823 if (list_empty(&rnp->blkd_tasks)) {
824 raw_spin_unlock_irqrestore(&rnp->lock, flags);
825 } else {
826 rnp->exp_tasks = rnp->blkd_tasks.next;
827 rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
828 must_wait = 1;
829 }
830 if (!must_wait)
831 rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
832}
833
834/**
835 * synchronize_rcu_expedited - Brute-force RCU grace period
836 *
837 * Wait for an RCU-preempt grace period, but expedite it. The basic
838 * idea is to invoke synchronize_sched_expedited() to push all the tasks to
839 * the ->blkd_tasks lists and wait for this list to drain. This consumes
840 * significant time on all CPUs and is unfriendly to real-time workloads,
841 * so is thus not recommended for any sort of common-case code.
842 * In fact, if you are using synchronize_rcu_expedited() in a loop,
843 * please restructure your code to batch your updates, and then Use a
844 * single synchronize_rcu() instead.
845 *
846 * Note that it is illegal to call this function while holding any lock
847 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
848 * to call this function from a CPU-hotplug notifier. Failing to observe
849 * these restriction will result in deadlock.
850 */
851void synchronize_rcu_expedited(void)
852{
853 unsigned long flags;
854 struct rcu_node *rnp;
855 struct rcu_state *rsp = &rcu_preempt_state;
856 unsigned long snap;
857 int trycount = 0;
858
859 smp_mb(); /* Caller's modifications seen first by other CPUs. */
860 snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
861 smp_mb(); /* Above access cannot bleed into critical section. */
862
863 /*
864 * Block CPU-hotplug operations. This means that any CPU-hotplug
865 * operation that finds an rcu_node structure with tasks in the
866 * process of being boosted will know that all tasks blocking
867 * this expedited grace period will already be in the process of
868 * being boosted. This simplifies the process of moving tasks
869 * from leaf to root rcu_node structures.
870 */
871 get_online_cpus();
872
873 /*
874 * Acquire lock, falling back to synchronize_rcu() if too many
875 * lock-acquisition failures. Of course, if someone does the
876 * expedited grace period for us, just leave.
877 */
878 while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
879 if (ULONG_CMP_LT(snap,
880 ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
881 put_online_cpus();
882 goto mb_ret; /* Others did our work for us. */
883 }
884 if (trycount++ < 10) {
885 udelay(trycount * num_online_cpus());
886 } else {
887 put_online_cpus();
888 wait_rcu_gp(call_rcu);
889 return;
890 }
891 }
892 if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) {
893 put_online_cpus();
894 goto unlock_mb_ret; /* Others did our work for us. */
895 }
896
897 /* force all RCU readers onto ->blkd_tasks lists. */
898 synchronize_sched_expedited();
899
900 /* Initialize ->expmask for all non-leaf rcu_node structures. */
901 rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
902 raw_spin_lock_irqsave(&rnp->lock, flags);
903 smp_mb__after_unlock_lock();
904 rnp->expmask = rnp->qsmaskinit;
905 raw_spin_unlock_irqrestore(&rnp->lock, flags);
906 }
907
908 /* Snapshot current state of ->blkd_tasks lists. */
909 rcu_for_each_leaf_node(rsp, rnp)
910 sync_rcu_preempt_exp_init(rsp, rnp);
911 if (NUM_RCU_NODES > 1)
912 sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
913
914 put_online_cpus();
915
916 /* Wait for snapshotted ->blkd_tasks lists to drain. */
917 rnp = rcu_get_root(rsp);
918 wait_event(sync_rcu_preempt_exp_wq,
919 sync_rcu_preempt_exp_done(rnp));
920
921 /* Clean up and exit. */
922 smp_mb(); /* ensure expedited GP seen before counter increment. */
923 ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
924unlock_mb_ret:
925 mutex_unlock(&sync_rcu_preempt_exp_mutex);
926mb_ret:
927 smp_mb(); /* ensure subsequent action seen after grace period. */
928}
929EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
930
931/**
932 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
933 *
934 * Note that this primitive does not necessarily wait for an RCU grace period
935 * to complete. For example, if there are no RCU callbacks queued anywhere
936 * in the system, then rcu_barrier() is within its rights to return
937 * immediately, without waiting for anything, much less an RCU grace period.
938 */
939void rcu_barrier(void)
940{
941 _rcu_barrier(&rcu_preempt_state);
942}
943EXPORT_SYMBOL_GPL(rcu_barrier);
944
945/*
946 * Initialize preemptible RCU's state structures.
947 */
948static void __init __rcu_init_preempt(void)
949{
950 rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
951}
952
953/*
954 * Check for a task exiting while in a preemptible-RCU read-side
955 * critical section, clean up if so. No need to issue warnings,
956 * as debug_check_no_locks_held() already does this if lockdep
957 * is enabled.
958 */
959void exit_rcu(void)
960{
961 struct task_struct *t = current;
962
963 if (likely(list_empty(¤t->rcu_node_entry)))
964 return;
965 t->rcu_read_lock_nesting = 1;
966 barrier();
967 t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
968 __rcu_read_unlock();
969}
970
971#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
972
973static struct rcu_state *rcu_state = &rcu_sched_state;
974
975/*
976 * Tell them what RCU they are running.
977 */
978static void __init rcu_bootup_announce(void)
979{
980 pr_info("Hierarchical RCU implementation.\n");
981 rcu_bootup_announce_oddness();
982}
983
984/*
985 * Return the number of RCU batches processed thus far for debug & stats.
986 */
987long rcu_batches_completed(void)
988{
989 return rcu_batches_completed_sched();
990}
991EXPORT_SYMBOL_GPL(rcu_batches_completed);
992
993/*
994 * Force a quiescent state for RCU, which, because there is no preemptible
995 * RCU, becomes the same as rcu-sched.
996 */
997void rcu_force_quiescent_state(void)
998{
999 rcu_sched_force_quiescent_state();
1000}
1001EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
1002
1003/*
1004 * Because preemptible RCU does not exist, we never have to check for
1005 * CPUs being in quiescent states.
1006 */
1007static void rcu_preempt_note_context_switch(int cpu)
1008{
1009}
1010
1011/*
1012 * Because preemptible RCU does not exist, there are never any preempted
1013 * RCU readers.
1014 */
1015static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
1016{
1017 return 0;
1018}
1019
1020#ifdef CONFIG_HOTPLUG_CPU
1021
1022/* Because preemptible RCU does not exist, no quieting of tasks. */
1023static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
1024{
1025 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1026}
1027
1028#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1029
1030/*
1031 * Because preemptible RCU does not exist, we never have to check for
1032 * tasks blocked within RCU read-side critical sections.
1033 */
1034static void rcu_print_detail_task_stall(struct rcu_state *rsp)
1035{
1036}
1037
1038/*
1039 * Because preemptible RCU does not exist, we never have to check for
1040 * tasks blocked within RCU read-side critical sections.
1041 */
1042static int rcu_print_task_stall(struct rcu_node *rnp)
1043{
1044 return 0;
1045}
1046
1047/*
1048 * Because there is no preemptible RCU, there can be no readers blocked,
1049 * so there is no need to check for blocked tasks. So check only for
1050 * bogus qsmask values.
1051 */
1052static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
1053{
1054 WARN_ON_ONCE(rnp->qsmask);
1055}
1056
1057#ifdef CONFIG_HOTPLUG_CPU
1058
1059/*
1060 * Because preemptible RCU does not exist, it never needs to migrate
1061 * tasks that were blocked within RCU read-side critical sections, and
1062 * such non-existent tasks cannot possibly have been blocking the current
1063 * grace period.
1064 */
1065static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
1066 struct rcu_node *rnp,
1067 struct rcu_data *rdp)
1068{
1069 return 0;
1070}
1071
1072#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1073
1074/*
1075 * Because preemptible RCU does not exist, it never has any callbacks
1076 * to check.
1077 */
1078static void rcu_preempt_check_callbacks(int cpu)
1079{
1080}
1081
1082/*
1083 * Queue an RCU callback for lazy invocation after a grace period.
1084 * This will likely be later named something like "call_rcu_lazy()",
1085 * but this change will require some way of tagging the lazy RCU
1086 * callbacks in the list of pending callbacks. Until then, this
1087 * function may only be called from __kfree_rcu().
1088 *
1089 * Because there is no preemptible RCU, we use RCU-sched instead.
1090 */
1091void kfree_call_rcu(struct rcu_head *head,
1092 void (*func)(struct rcu_head *rcu))
1093{
1094 __call_rcu(head, func, &rcu_sched_state, -1, 1);
1095}
1096EXPORT_SYMBOL_GPL(kfree_call_rcu);
1097
1098/*
1099 * Wait for an rcu-preempt grace period, but make it happen quickly.
1100 * But because preemptible RCU does not exist, map to rcu-sched.
1101 */
1102void synchronize_rcu_expedited(void)
1103{
1104 synchronize_sched_expedited();
1105}
1106EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
1107
1108#ifdef CONFIG_HOTPLUG_CPU
1109
1110/*
1111 * Because preemptible RCU does not exist, there is never any need to
1112 * report on tasks preempted in RCU read-side critical sections during
1113 * expedited RCU grace periods.
1114 */
1115static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
1116 bool wake)
1117{
1118}
1119
1120#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1121
1122/*
1123 * Because preemptible RCU does not exist, rcu_barrier() is just
1124 * another name for rcu_barrier_sched().
1125 */
1126void rcu_barrier(void)
1127{
1128 rcu_barrier_sched();
1129}
1130EXPORT_SYMBOL_GPL(rcu_barrier);
1131
1132/*
1133 * Because preemptible RCU does not exist, it need not be initialized.
1134 */
1135static void __init __rcu_init_preempt(void)
1136{
1137}
1138
1139/*
1140 * Because preemptible RCU does not exist, tasks cannot possibly exit
1141 * while in preemptible RCU read-side critical sections.
1142 */
1143void exit_rcu(void)
1144{
1145}
1146
1147#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1148
1149#ifdef CONFIG_RCU_BOOST
1150
1151#include "../locking/rtmutex_common.h"
1152
1153#ifdef CONFIG_RCU_TRACE
1154
1155static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1156{
1157 if (list_empty(&rnp->blkd_tasks))
1158 rnp->n_balk_blkd_tasks++;
1159 else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
1160 rnp->n_balk_exp_gp_tasks++;
1161 else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
1162 rnp->n_balk_boost_tasks++;
1163 else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
1164 rnp->n_balk_notblocked++;
1165 else if (rnp->gp_tasks != NULL &&
1166 ULONG_CMP_LT(jiffies, rnp->boost_time))
1167 rnp->n_balk_notyet++;
1168 else
1169 rnp->n_balk_nos++;
1170}
1171
1172#else /* #ifdef CONFIG_RCU_TRACE */
1173
1174static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1175{
1176}
1177
1178#endif /* #else #ifdef CONFIG_RCU_TRACE */
1179
1180static void rcu_wake_cond(struct task_struct *t, int status)
1181{
1182 /*
1183 * If the thread is yielding, only wake it when this
1184 * is invoked from idle
1185 */
1186 if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
1187 wake_up_process(t);
1188}
1189
1190/*
1191 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
1192 * or ->boost_tasks, advancing the pointer to the next task in the
1193 * ->blkd_tasks list.
1194 *
1195 * Note that irqs must be enabled: boosting the task can block.
1196 * Returns 1 if there are more tasks needing to be boosted.
1197 */
1198static int rcu_boost(struct rcu_node *rnp)
1199{
1200 unsigned long flags;
1201 struct rt_mutex mtx;
1202 struct task_struct *t;
1203 struct list_head *tb;
1204
1205 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
1206 return 0; /* Nothing left to boost. */
1207
1208 raw_spin_lock_irqsave(&rnp->lock, flags);
1209 smp_mb__after_unlock_lock();
1210
1211 /*
1212 * Recheck under the lock: all tasks in need of boosting
1213 * might exit their RCU read-side critical sections on their own.
1214 */
1215 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
1216 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1217 return 0;
1218 }
1219
1220 /*
1221 * Preferentially boost tasks blocking expedited grace periods.
1222 * This cannot starve the normal grace periods because a second
1223 * expedited grace period must boost all blocked tasks, including
1224 * those blocking the pre-existing normal grace period.
1225 */
1226 if (rnp->exp_tasks != NULL) {
1227 tb = rnp->exp_tasks;
1228 rnp->n_exp_boosts++;
1229 } else {
1230 tb = rnp->boost_tasks;
1231 rnp->n_normal_boosts++;
1232 }
1233 rnp->n_tasks_boosted++;
1234
1235 /*
1236 * We boost task t by manufacturing an rt_mutex that appears to
1237 * be held by task t. We leave a pointer to that rt_mutex where
1238 * task t can find it, and task t will release the mutex when it
1239 * exits its outermost RCU read-side critical section. Then
1240 * simply acquiring this artificial rt_mutex will boost task
1241 * t's priority. (Thanks to tglx for suggesting this approach!)
1242 *
1243 * Note that task t must acquire rnp->lock to remove itself from
1244 * the ->blkd_tasks list, which it will do from exit() if from
1245 * nowhere else. We therefore are guaranteed that task t will
1246 * stay around at least until we drop rnp->lock. Note that
1247 * rnp->lock also resolves races between our priority boosting
1248 * and task t's exiting its outermost RCU read-side critical
1249 * section.
1250 */
1251 t = container_of(tb, struct task_struct, rcu_node_entry);
1252 rt_mutex_init_proxy_locked(&mtx, t);
1253 t->rcu_boost_mutex = &mtx;
1254 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1255 rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */
1256 rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
1257
1258 return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
1259 ACCESS_ONCE(rnp->boost_tasks) != NULL;
1260}
1261
1262/*
1263 * Priority-boosting kthread. One per leaf rcu_node and one for the
1264 * root rcu_node.
1265 */
1266static int rcu_boost_kthread(void *arg)
1267{
1268 struct rcu_node *rnp = (struct rcu_node *)arg;
1269 int spincnt = 0;
1270 int more2boost;
1271
1272 trace_rcu_utilization(TPS("Start boost kthread@init"));
1273 for (;;) {
1274 rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1275 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1276 rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1277 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1278 rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1279 more2boost = rcu_boost(rnp);
1280 if (more2boost)
1281 spincnt++;
1282 else
1283 spincnt = 0;
1284 if (spincnt > 10) {
1285 rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1286 trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1287 schedule_timeout_interruptible(2);
1288 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1289 spincnt = 0;
1290 }
1291 }
1292 /* NOTREACHED */
1293 trace_rcu_utilization(TPS("End boost kthread@notreached"));
1294 return 0;
1295}
1296
1297/*
1298 * Check to see if it is time to start boosting RCU readers that are
1299 * blocking the current grace period, and, if so, tell the per-rcu_node
1300 * kthread to start boosting them. If there is an expedited grace
1301 * period in progress, it is always time to boost.
1302 *
1303 * The caller must hold rnp->lock, which this function releases.
1304 * The ->boost_kthread_task is immortal, so we don't need to worry
1305 * about it going away.
1306 */
1307static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1308{
1309 struct task_struct *t;
1310
1311 if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1312 rnp->n_balk_exp_gp_tasks++;
1313 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1314 return;
1315 }
1316 if (rnp->exp_tasks != NULL ||
1317 (rnp->gp_tasks != NULL &&
1318 rnp->boost_tasks == NULL &&
1319 rnp->qsmask == 0 &&
1320 ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1321 if (rnp->exp_tasks == NULL)
1322 rnp->boost_tasks = rnp->gp_tasks;
1323 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1324 t = rnp->boost_kthread_task;
1325 if (t)
1326 rcu_wake_cond(t, rnp->boost_kthread_status);
1327 } else {
1328 rcu_initiate_boost_trace(rnp);
1329 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1330 }
1331}
1332
1333/*
1334 * Wake up the per-CPU kthread to invoke RCU callbacks.
1335 */
1336static void invoke_rcu_callbacks_kthread(void)
1337{
1338 unsigned long flags;
1339
1340 local_irq_save(flags);
1341 __this_cpu_write(rcu_cpu_has_work, 1);
1342 if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
1343 current != __this_cpu_read(rcu_cpu_kthread_task)) {
1344 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
1345 __this_cpu_read(rcu_cpu_kthread_status));
1346 }
1347 local_irq_restore(flags);
1348}
1349
1350/*
1351 * Is the current CPU running the RCU-callbacks kthread?
1352 * Caller must have preemption disabled.
1353 */
1354static bool rcu_is_callbacks_kthread(void)
1355{
1356 return __this_cpu_read(rcu_cpu_kthread_task) == current;
1357}
1358
1359#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1360
1361/*
1362 * Do priority-boost accounting for the start of a new grace period.
1363 */
1364static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1365{
1366 rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1367}
1368
1369/*
1370 * Create an RCU-boost kthread for the specified node if one does not
1371 * already exist. We only create this kthread for preemptible RCU.
1372 * Returns zero if all is well, a negated errno otherwise.
1373 */
1374static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
1375 struct rcu_node *rnp)
1376{
1377 int rnp_index = rnp - &rsp->node[0];
1378 unsigned long flags;
1379 struct sched_param sp;
1380 struct task_struct *t;
1381
1382 if (&rcu_preempt_state != rsp)
1383 return 0;
1384
1385 if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0)
1386 return 0;
1387
1388 rsp->boost = 1;
1389 if (rnp->boost_kthread_task != NULL)
1390 return 0;
1391 t = kthread_create(rcu_boost_kthread, (void *)rnp,
1392 "rcub/%d", rnp_index);
1393 if (IS_ERR(t))
1394 return PTR_ERR(t);
1395 raw_spin_lock_irqsave(&rnp->lock, flags);
1396 smp_mb__after_unlock_lock();
1397 rnp->boost_kthread_task = t;
1398 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1399 sp.sched_priority = RCU_BOOST_PRIO;
1400 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1401 wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1402 return 0;
1403}
1404
1405static void rcu_kthread_do_work(void)
1406{
1407 rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
1408 rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
1409 rcu_preempt_do_callbacks();
1410}
1411
1412static void rcu_cpu_kthread_setup(unsigned int cpu)
1413{
1414 struct sched_param sp;
1415
1416 sp.sched_priority = RCU_KTHREAD_PRIO;
1417 sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
1418}
1419
1420static void rcu_cpu_kthread_park(unsigned int cpu)
1421{
1422 per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1423}
1424
1425static int rcu_cpu_kthread_should_run(unsigned int cpu)
1426{
1427 return __this_cpu_read(rcu_cpu_has_work);
1428}
1429
1430/*
1431 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
1432 * RCU softirq used in flavors and configurations of RCU that do not
1433 * support RCU priority boosting.
1434 */
1435static void rcu_cpu_kthread(unsigned int cpu)
1436{
1437 unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
1438 char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
1439 int spincnt;
1440
1441 for (spincnt = 0; spincnt < 10; spincnt++) {
1442 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1443 local_bh_disable();
1444 *statusp = RCU_KTHREAD_RUNNING;
1445 this_cpu_inc(rcu_cpu_kthread_loops);
1446 local_irq_disable();
1447 work = *workp;
1448 *workp = 0;
1449 local_irq_enable();
1450 if (work)
1451 rcu_kthread_do_work();
1452 local_bh_enable();
1453 if (*workp == 0) {
1454 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1455 *statusp = RCU_KTHREAD_WAITING;
1456 return;
1457 }
1458 }
1459 *statusp = RCU_KTHREAD_YIELDING;
1460 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1461 schedule_timeout_interruptible(2);
1462 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1463 *statusp = RCU_KTHREAD_WAITING;
1464}
1465
1466/*
1467 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1468 * served by the rcu_node in question. The CPU hotplug lock is still
1469 * held, so the value of rnp->qsmaskinit will be stable.
1470 *
1471 * We don't include outgoingcpu in the affinity set, use -1 if there is
1472 * no outgoing CPU. If there are no CPUs left in the affinity set,
1473 * this function allows the kthread to execute on any CPU.
1474 */
1475static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1476{
1477 struct task_struct *t = rnp->boost_kthread_task;
1478 unsigned long mask = rnp->qsmaskinit;
1479 cpumask_var_t cm;
1480 int cpu;
1481
1482 if (!t)
1483 return;
1484 if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1485 return;
1486 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
1487 if ((mask & 0x1) && cpu != outgoingcpu)
1488 cpumask_set_cpu(cpu, cm);
1489 if (cpumask_weight(cm) == 0) {
1490 cpumask_setall(cm);
1491 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
1492 cpumask_clear_cpu(cpu, cm);
1493 WARN_ON_ONCE(cpumask_weight(cm) == 0);
1494 }
1495 set_cpus_allowed_ptr(t, cm);
1496 free_cpumask_var(cm);
1497}
1498
1499static struct smp_hotplug_thread rcu_cpu_thread_spec = {
1500 .store = &rcu_cpu_kthread_task,
1501 .thread_should_run = rcu_cpu_kthread_should_run,
1502 .thread_fn = rcu_cpu_kthread,
1503 .thread_comm = "rcuc/%u",
1504 .setup = rcu_cpu_kthread_setup,
1505 .park = rcu_cpu_kthread_park,
1506};
1507
1508/*
1509 * Spawn all kthreads -- called as soon as the scheduler is running.
1510 */
1511static int __init rcu_spawn_kthreads(void)
1512{
1513 struct rcu_node *rnp;
1514 int cpu;
1515
1516 rcu_scheduler_fully_active = 1;
1517 for_each_possible_cpu(cpu)
1518 per_cpu(rcu_cpu_has_work, cpu) = 0;
1519 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
1520 rnp = rcu_get_root(rcu_state);
1521 (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1522 if (NUM_RCU_NODES > 1) {
1523 rcu_for_each_leaf_node(rcu_state, rnp)
1524 (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1525 }
1526 return 0;
1527}
1528early_initcall(rcu_spawn_kthreads);
1529
1530static void rcu_prepare_kthreads(int cpu)
1531{
1532 struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
1533 struct rcu_node *rnp = rdp->mynode;
1534
1535 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1536 if (rcu_scheduler_fully_active)
1537 (void)rcu_spawn_one_boost_kthread(rcu_state, rnp);
1538}
1539
1540#else /* #ifdef CONFIG_RCU_BOOST */
1541
1542static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1543{
1544 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1545}
1546
1547static void invoke_rcu_callbacks_kthread(void)
1548{
1549 WARN_ON_ONCE(1);
1550}
1551
1552static bool rcu_is_callbacks_kthread(void)
1553{
1554 return false;
1555}
1556
1557static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1558{
1559}
1560
1561static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1562{
1563}
1564
1565static int __init rcu_scheduler_really_started(void)
1566{
1567 rcu_scheduler_fully_active = 1;
1568 return 0;
1569}
1570early_initcall(rcu_scheduler_really_started);
1571
1572static void rcu_prepare_kthreads(int cpu)
1573{
1574}
1575
1576#endif /* #else #ifdef CONFIG_RCU_BOOST */
1577
1578#if !defined(CONFIG_RCU_FAST_NO_HZ)
1579
1580/*
1581 * Check to see if any future RCU-related work will need to be done
1582 * by the current CPU, even if none need be done immediately, returning
1583 * 1 if so. This function is part of the RCU implementation; it is -not-
1584 * an exported member of the RCU API.
1585 *
1586 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1587 * any flavor of RCU.
1588 */
1589#ifndef CONFIG_RCU_NOCB_CPU_ALL
1590int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
1591{
1592 *delta_jiffies = ULONG_MAX;
1593 return rcu_cpu_has_callbacks(cpu, NULL);
1594}
1595#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1596
1597/*
1598 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1599 * after it.
1600 */
1601static void rcu_cleanup_after_idle(int cpu)
1602{
1603}
1604
1605/*
1606 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1607 * is nothing.
1608 */
1609static void rcu_prepare_for_idle(int cpu)
1610{
1611}
1612
1613/*
1614 * Don't bother keeping a running count of the number of RCU callbacks
1615 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1616 */
1617static void rcu_idle_count_callbacks_posted(void)
1618{
1619}
1620
1621#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1622
1623/*
1624 * This code is invoked when a CPU goes idle, at which point we want
1625 * to have the CPU do everything required for RCU so that it can enter
1626 * the energy-efficient dyntick-idle mode. This is handled by a
1627 * state machine implemented by rcu_prepare_for_idle() below.
1628 *
1629 * The following three proprocessor symbols control this state machine:
1630 *
1631 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1632 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1633 * is sized to be roughly one RCU grace period. Those energy-efficiency
1634 * benchmarkers who might otherwise be tempted to set this to a large
1635 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1636 * system. And if you are -that- concerned about energy efficiency,
1637 * just power the system down and be done with it!
1638 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1639 * permitted to sleep in dyntick-idle mode with only lazy RCU
1640 * callbacks pending. Setting this too high can OOM your system.
1641 *
1642 * The values below work well in practice. If future workloads require
1643 * adjustment, they can be converted into kernel config parameters, though
1644 * making the state machine smarter might be a better option.
1645 */
1646#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1647#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1648
1649static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
1650module_param(rcu_idle_gp_delay, int, 0644);
1651static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
1652module_param(rcu_idle_lazy_gp_delay, int, 0644);
1653
1654extern int tick_nohz_active;
1655
1656/*
1657 * Try to advance callbacks for all flavors of RCU on the current CPU, but
1658 * only if it has been awhile since the last time we did so. Afterwards,
1659 * if there are any callbacks ready for immediate invocation, return true.
1660 */
1661static bool __maybe_unused rcu_try_advance_all_cbs(void)
1662{
1663 bool cbs_ready = false;
1664 struct rcu_data *rdp;
1665 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1666 struct rcu_node *rnp;
1667 struct rcu_state *rsp;
1668
1669 /* Exit early if we advanced recently. */
1670 if (jiffies == rdtp->last_advance_all)
1671 return 0;
1672 rdtp->last_advance_all = jiffies;
1673
1674 for_each_rcu_flavor(rsp) {
1675 rdp = this_cpu_ptr(rsp->rda);
1676 rnp = rdp->mynode;
1677
1678 /*
1679 * Don't bother checking unless a grace period has
1680 * completed since we last checked and there are
1681 * callbacks not yet ready to invoke.
1682 */
1683 if (rdp->completed != rnp->completed &&
1684 rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL])
1685 note_gp_changes(rsp, rdp);
1686
1687 if (cpu_has_callbacks_ready_to_invoke(rdp))
1688 cbs_ready = true;
1689 }
1690 return cbs_ready;
1691}
1692
1693/*
1694 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1695 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1696 * caller to set the timeout based on whether or not there are non-lazy
1697 * callbacks.
1698 *
1699 * The caller must have disabled interrupts.
1700 */
1701#ifndef CONFIG_RCU_NOCB_CPU_ALL
1702int rcu_needs_cpu(int cpu, unsigned long *dj)
1703{
1704 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1705
1706 /* Snapshot to detect later posting of non-lazy callback. */
1707 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1708
1709 /* If no callbacks, RCU doesn't need the CPU. */
1710 if (!rcu_cpu_has_callbacks(cpu, &rdtp->all_lazy)) {
1711 *dj = ULONG_MAX;
1712 return 0;
1713 }
1714
1715 /* Attempt to advance callbacks. */
1716 if (rcu_try_advance_all_cbs()) {
1717 /* Some ready to invoke, so initiate later invocation. */
1718 invoke_rcu_core();
1719 return 1;
1720 }
1721 rdtp->last_accelerate = jiffies;
1722
1723 /* Request timer delay depending on laziness, and round. */
1724 if (!rdtp->all_lazy) {
1725 *dj = round_up(rcu_idle_gp_delay + jiffies,
1726 rcu_idle_gp_delay) - jiffies;
1727 } else {
1728 *dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1729 }
1730 return 0;
1731}
1732#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1733
1734/*
1735 * Prepare a CPU for idle from an RCU perspective. The first major task
1736 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1737 * The second major task is to check to see if a non-lazy callback has
1738 * arrived at a CPU that previously had only lazy callbacks. The third
1739 * major task is to accelerate (that is, assign grace-period numbers to)
1740 * any recently arrived callbacks.
1741 *
1742 * The caller must have disabled interrupts.
1743 */
1744static void rcu_prepare_for_idle(int cpu)
1745{
1746#ifndef CONFIG_RCU_NOCB_CPU_ALL
1747 struct rcu_data *rdp;
1748 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1749 struct rcu_node *rnp;
1750 struct rcu_state *rsp;
1751 int tne;
1752
1753 /* Handle nohz enablement switches conservatively. */
1754 tne = ACCESS_ONCE(tick_nohz_active);
1755 if (tne != rdtp->tick_nohz_enabled_snap) {
1756 if (rcu_cpu_has_callbacks(cpu, NULL))
1757 invoke_rcu_core(); /* force nohz to see update. */
1758 rdtp->tick_nohz_enabled_snap = tne;
1759 return;
1760 }
1761 if (!tne)
1762 return;
1763
1764 /* If this is a no-CBs CPU, no callbacks, just return. */
1765 if (rcu_is_nocb_cpu(cpu))
1766 return;
1767
1768 /*
1769 * If a non-lazy callback arrived at a CPU having only lazy
1770 * callbacks, invoke RCU core for the side-effect of recalculating
1771 * idle duration on re-entry to idle.
1772 */
1773 if (rdtp->all_lazy &&
1774 rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
1775 rdtp->all_lazy = false;
1776 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1777 invoke_rcu_core();
1778 return;
1779 }
1780
1781 /*
1782 * If we have not yet accelerated this jiffy, accelerate all
1783 * callbacks on this CPU.
1784 */
1785 if (rdtp->last_accelerate == jiffies)
1786 return;
1787 rdtp->last_accelerate = jiffies;
1788 for_each_rcu_flavor(rsp) {
1789 rdp = per_cpu_ptr(rsp->rda, cpu);
1790 if (!*rdp->nxttail[RCU_DONE_TAIL])
1791 continue;
1792 rnp = rdp->mynode;
1793 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
1794 smp_mb__after_unlock_lock();
1795 rcu_accelerate_cbs(rsp, rnp, rdp);
1796 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1797 }
1798#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1799}
1800
1801/*
1802 * Clean up for exit from idle. Attempt to advance callbacks based on
1803 * any grace periods that elapsed while the CPU was idle, and if any
1804 * callbacks are now ready to invoke, initiate invocation.
1805 */
1806static void rcu_cleanup_after_idle(int cpu)
1807{
1808#ifndef CONFIG_RCU_NOCB_CPU_ALL
1809 if (rcu_is_nocb_cpu(cpu))
1810 return;
1811 if (rcu_try_advance_all_cbs())
1812 invoke_rcu_core();
1813#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
1814}
1815
1816/*
1817 * Keep a running count of the number of non-lazy callbacks posted
1818 * on this CPU. This running counter (which is never decremented) allows
1819 * rcu_prepare_for_idle() to detect when something out of the idle loop
1820 * posts a callback, even if an equal number of callbacks are invoked.
1821 * Of course, callbacks should only be posted from within a trace event
1822 * designed to be called from idle or from within RCU_NONIDLE().
1823 */
1824static void rcu_idle_count_callbacks_posted(void)
1825{
1826 __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
1827}
1828
1829/*
1830 * Data for flushing lazy RCU callbacks at OOM time.
1831 */
1832static atomic_t oom_callback_count;
1833static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
1834
1835/*
1836 * RCU OOM callback -- decrement the outstanding count and deliver the
1837 * wake-up if we are the last one.
1838 */
1839static void rcu_oom_callback(struct rcu_head *rhp)
1840{
1841 if (atomic_dec_and_test(&oom_callback_count))
1842 wake_up(&oom_callback_wq);
1843}
1844
1845/*
1846 * Post an rcu_oom_notify callback on the current CPU if it has at
1847 * least one lazy callback. This will unnecessarily post callbacks
1848 * to CPUs that already have a non-lazy callback at the end of their
1849 * callback list, but this is an infrequent operation, so accept some
1850 * extra overhead to keep things simple.
1851 */
1852static void rcu_oom_notify_cpu(void *unused)
1853{
1854 struct rcu_state *rsp;
1855 struct rcu_data *rdp;
1856
1857 for_each_rcu_flavor(rsp) {
1858 rdp = __this_cpu_ptr(rsp->rda);
1859 if (rdp->qlen_lazy != 0) {
1860 atomic_inc(&oom_callback_count);
1861 rsp->call(&rdp->oom_head, rcu_oom_callback);
1862 }
1863 }
1864}
1865
1866/*
1867 * If low on memory, ensure that each CPU has a non-lazy callback.
1868 * This will wake up CPUs that have only lazy callbacks, in turn
1869 * ensuring that they free up the corresponding memory in a timely manner.
1870 * Because an uncertain amount of memory will be freed in some uncertain
1871 * timeframe, we do not claim to have freed anything.
1872 */
1873static int rcu_oom_notify(struct notifier_block *self,
1874 unsigned long notused, void *nfreed)
1875{
1876 int cpu;
1877
1878 /* Wait for callbacks from earlier instance to complete. */
1879 wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
1880 smp_mb(); /* Ensure callback reuse happens after callback invocation. */
1881
1882 /*
1883 * Prevent premature wakeup: ensure that all increments happen
1884 * before there is a chance of the counter reaching zero.
1885 */
1886 atomic_set(&oom_callback_count, 1);
1887
1888 get_online_cpus();
1889 for_each_online_cpu(cpu) {
1890 smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
1891 cond_resched();
1892 }
1893 put_online_cpus();
1894
1895 /* Unconditionally decrement: no need to wake ourselves up. */
1896 atomic_dec(&oom_callback_count);
1897
1898 return NOTIFY_OK;
1899}
1900
1901static struct notifier_block rcu_oom_nb = {
1902 .notifier_call = rcu_oom_notify
1903};
1904
1905static int __init rcu_register_oom_notifier(void)
1906{
1907 register_oom_notifier(&rcu_oom_nb);
1908 return 0;
1909}
1910early_initcall(rcu_register_oom_notifier);
1911
1912#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1913
1914#ifdef CONFIG_RCU_CPU_STALL_INFO
1915
1916#ifdef CONFIG_RCU_FAST_NO_HZ
1917
1918static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1919{
1920 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1921 unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
1922
1923 sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1924 rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
1925 ulong2long(nlpd),
1926 rdtp->all_lazy ? 'L' : '.',
1927 rdtp->tick_nohz_enabled_snap ? '.' : 'D');
1928}
1929
1930#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1931
1932static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1933{
1934 *cp = '\0';
1935}
1936
1937#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1938
1939/* Initiate the stall-info list. */
1940static void print_cpu_stall_info_begin(void)
1941{
1942 pr_cont("\n");
1943}
1944
1945/*
1946 * Print out diagnostic information for the specified stalled CPU.
1947 *
1948 * If the specified CPU is aware of the current RCU grace period
1949 * (flavor specified by rsp), then print the number of scheduling
1950 * clock interrupts the CPU has taken during the time that it has
1951 * been aware. Otherwise, print the number of RCU grace periods
1952 * that this CPU is ignorant of, for example, "1" if the CPU was
1953 * aware of the previous grace period.
1954 *
1955 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1956 */
1957static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1958{
1959 char fast_no_hz[72];
1960 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1961 struct rcu_dynticks *rdtp = rdp->dynticks;
1962 char *ticks_title;
1963 unsigned long ticks_value;
1964
1965 if (rsp->gpnum == rdp->gpnum) {
1966 ticks_title = "ticks this GP";
1967 ticks_value = rdp->ticks_this_gp;
1968 } else {
1969 ticks_title = "GPs behind";
1970 ticks_value = rsp->gpnum - rdp->gpnum;
1971 }
1972 print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
1973 pr_err("\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
1974 cpu, ticks_value, ticks_title,
1975 atomic_read(&rdtp->dynticks) & 0xfff,
1976 rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
1977 rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
1978 fast_no_hz);
1979}
1980
1981/* Terminate the stall-info list. */
1982static void print_cpu_stall_info_end(void)
1983{
1984 pr_err("\t");
1985}
1986
1987/* Zero ->ticks_this_gp for all flavors of RCU. */
1988static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1989{
1990 rdp->ticks_this_gp = 0;
1991 rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
1992}
1993
1994/* Increment ->ticks_this_gp for all flavors of RCU. */
1995static void increment_cpu_stall_ticks(void)
1996{
1997 struct rcu_state *rsp;
1998
1999 for_each_rcu_flavor(rsp)
2000 __this_cpu_ptr(rsp->rda)->ticks_this_gp++;
2001}
2002
2003#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
2004
2005static void print_cpu_stall_info_begin(void)
2006{
2007 pr_cont(" {");
2008}
2009
2010static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
2011{
2012 pr_cont(" %d", cpu);
2013}
2014
2015static void print_cpu_stall_info_end(void)
2016{
2017 pr_cont("} ");
2018}
2019
2020static void zero_cpu_stall_ticks(struct rcu_data *rdp)
2021{
2022}
2023
2024static void increment_cpu_stall_ticks(void)
2025{
2026}
2027
2028#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
2029
2030#ifdef CONFIG_RCU_NOCB_CPU
2031
2032/*
2033 * Offload callback processing from the boot-time-specified set of CPUs
2034 * specified by rcu_nocb_mask. For each CPU in the set, there is a
2035 * kthread created that pulls the callbacks from the corresponding CPU,
2036 * waits for a grace period to elapse, and invokes the callbacks.
2037 * The no-CBs CPUs do a wake_up() on their kthread when they insert
2038 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
2039 * has been specified, in which case each kthread actively polls its
2040 * CPU. (Which isn't so great for energy efficiency, but which does
2041 * reduce RCU's overhead on that CPU.)
2042 *
2043 * This is intended to be used in conjunction with Frederic Weisbecker's
2044 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
2045 * running CPU-bound user-mode computations.
2046 *
2047 * Offloading of callback processing could also in theory be used as
2048 * an energy-efficiency measure because CPUs with no RCU callbacks
2049 * queued are more aggressive about entering dyntick-idle mode.
2050 */
2051
2052
2053/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
2054static int __init rcu_nocb_setup(char *str)
2055{
2056 alloc_bootmem_cpumask_var(&rcu_nocb_mask);
2057 have_rcu_nocb_mask = true;
2058 cpulist_parse(str, rcu_nocb_mask);
2059 return 1;
2060}
2061__setup("rcu_nocbs=", rcu_nocb_setup);
2062
2063static int __init parse_rcu_nocb_poll(char *arg)
2064{
2065 rcu_nocb_poll = 1;
2066 return 0;
2067}
2068early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
2069
2070/*
2071 * Do any no-CBs CPUs need another grace period?
2072 *
2073 * Interrupts must be disabled. If the caller does not hold the root
2074 * rnp_node structure's ->lock, the results are advisory only.
2075 */
2076static int rcu_nocb_needs_gp(struct rcu_state *rsp)
2077{
2078 struct rcu_node *rnp = rcu_get_root(rsp);
2079
2080 return rnp->need_future_gp[(ACCESS_ONCE(rnp->completed) + 1) & 0x1];
2081}
2082
2083/*
2084 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
2085 * grace period.
2086 */
2087static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2088{
2089 wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]);
2090}
2091
2092/*
2093 * Set the root rcu_node structure's ->need_future_gp field
2094 * based on the sum of those of all rcu_node structures. This does
2095 * double-count the root rcu_node structure's requests, but this
2096 * is necessary to handle the possibility of a rcu_nocb_kthread()
2097 * having awakened during the time that the rcu_node structures
2098 * were being updated for the end of the previous grace period.
2099 */
2100static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2101{
2102 rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
2103}
2104
2105static void rcu_init_one_nocb(struct rcu_node *rnp)
2106{
2107 init_waitqueue_head(&rnp->nocb_gp_wq[0]);
2108 init_waitqueue_head(&rnp->nocb_gp_wq[1]);
2109}
2110
2111#ifndef CONFIG_RCU_NOCB_CPU_ALL
2112/* Is the specified CPU a no-CPUs CPU? */
2113bool rcu_is_nocb_cpu(int cpu)
2114{
2115 if (have_rcu_nocb_mask)
2116 return cpumask_test_cpu(cpu, rcu_nocb_mask);
2117 return false;
2118}
2119#endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */
2120
2121/*
2122 * Enqueue the specified string of rcu_head structures onto the specified
2123 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
2124 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
2125 * counts are supplied by rhcount and rhcount_lazy.
2126 *
2127 * If warranted, also wake up the kthread servicing this CPUs queues.
2128 */
2129static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
2130 struct rcu_head *rhp,
2131 struct rcu_head **rhtp,
2132 int rhcount, int rhcount_lazy,
2133 unsigned long flags)
2134{
2135 int len;
2136 struct rcu_head **old_rhpp;
2137 struct task_struct *t;
2138
2139 /* Enqueue the callback on the nocb list and update counts. */
2140 old_rhpp = xchg(&rdp->nocb_tail, rhtp);
2141 ACCESS_ONCE(*old_rhpp) = rhp;
2142 atomic_long_add(rhcount, &rdp->nocb_q_count);
2143 atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
2144
2145 /* If we are not being polled and there is a kthread, awaken it ... */
2146 t = ACCESS_ONCE(rdp->nocb_kthread);
2147 if (rcu_nocb_poll || !t) {
2148 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2149 TPS("WakeNotPoll"));
2150 return;
2151 }
2152 len = atomic_long_read(&rdp->nocb_q_count);
2153 if (old_rhpp == &rdp->nocb_head) {
2154 if (!irqs_disabled_flags(flags)) {
2155 wake_up(&rdp->nocb_wq); /* ... if queue was empty ... */
2156 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2157 TPS("WakeEmpty"));
2158 } else {
2159 rdp->nocb_defer_wakeup = true;
2160 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2161 TPS("WakeEmptyIsDeferred"));
2162 }
2163 rdp->qlen_last_fqs_check = 0;
2164 } else if (len > rdp->qlen_last_fqs_check + qhimark) {
2165 wake_up_process(t); /* ... or if many callbacks queued. */
2166 rdp->qlen_last_fqs_check = LONG_MAX / 2;
2167 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeOvf"));
2168 } else {
2169 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
2170 }
2171 return;
2172}
2173
2174/*
2175 * This is a helper for __call_rcu(), which invokes this when the normal
2176 * callback queue is inoperable. If this is not a no-CBs CPU, this
2177 * function returns failure back to __call_rcu(), which can complain
2178 * appropriately.
2179 *
2180 * Otherwise, this function queues the callback where the corresponding
2181 * "rcuo" kthread can find it.
2182 */
2183static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2184 bool lazy, unsigned long flags)
2185{
2186
2187 if (!rcu_is_nocb_cpu(rdp->cpu))
2188 return 0;
2189 __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
2190 if (__is_kfree_rcu_offset((unsigned long)rhp->func))
2191 trace_rcu_kfree_callback(rdp->rsp->name, rhp,
2192 (unsigned long)rhp->func,
2193 -atomic_long_read(&rdp->nocb_q_count_lazy),
2194 -atomic_long_read(&rdp->nocb_q_count));
2195 else
2196 trace_rcu_callback(rdp->rsp->name, rhp,
2197 -atomic_long_read(&rdp->nocb_q_count_lazy),
2198 -atomic_long_read(&rdp->nocb_q_count));
2199 return 1;
2200}
2201
2202/*
2203 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2204 * not a no-CBs CPU.
2205 */
2206static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2207 struct rcu_data *rdp,
2208 unsigned long flags)
2209{
2210 long ql = rsp->qlen;
2211 long qll = rsp->qlen_lazy;
2212
2213 /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
2214 if (!rcu_is_nocb_cpu(smp_processor_id()))
2215 return 0;
2216 rsp->qlen = 0;
2217 rsp->qlen_lazy = 0;
2218
2219 /* First, enqueue the donelist, if any. This preserves CB ordering. */
2220 if (rsp->orphan_donelist != NULL) {
2221 __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist,
2222 rsp->orphan_donetail, ql, qll, flags);
2223 ql = qll = 0;
2224 rsp->orphan_donelist = NULL;
2225 rsp->orphan_donetail = &rsp->orphan_donelist;
2226 }
2227 if (rsp->orphan_nxtlist != NULL) {
2228 __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist,
2229 rsp->orphan_nxttail, ql, qll, flags);
2230 ql = qll = 0;
2231 rsp->orphan_nxtlist = NULL;
2232 rsp->orphan_nxttail = &rsp->orphan_nxtlist;
2233 }
2234 return 1;
2235}
2236
2237/*
2238 * If necessary, kick off a new grace period, and either way wait
2239 * for a subsequent grace period to complete.
2240 */
2241static void rcu_nocb_wait_gp(struct rcu_data *rdp)
2242{
2243 unsigned long c;
2244 bool d;
2245 unsigned long flags;
2246 struct rcu_node *rnp = rdp->mynode;
2247
2248 raw_spin_lock_irqsave(&rnp->lock, flags);
2249 smp_mb__after_unlock_lock();
2250 c = rcu_start_future_gp(rnp, rdp);
2251 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2252
2253 /*
2254 * Wait for the grace period. Do so interruptibly to avoid messing
2255 * up the load average.
2256 */
2257 trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
2258 for (;;) {
2259 wait_event_interruptible(
2260 rnp->nocb_gp_wq[c & 0x1],
2261 (d = ULONG_CMP_GE(ACCESS_ONCE(rnp->completed), c)));
2262 if (likely(d))
2263 break;
2264 flush_signals(current);
2265 trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
2266 }
2267 trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
2268 smp_mb(); /* Ensure that CB invocation happens after GP end. */
2269}
2270
2271/*
2272 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
2273 * callbacks queued by the corresponding no-CBs CPU.
2274 */
2275static int rcu_nocb_kthread(void *arg)
2276{
2277 int c, cl;
2278 bool firsttime = 1;
2279 struct rcu_head *list;
2280 struct rcu_head *next;
2281 struct rcu_head **tail;
2282 struct rcu_data *rdp = arg;
2283
2284 /* Each pass through this loop invokes one batch of callbacks */
2285 for (;;) {
2286 /* If not polling, wait for next batch of callbacks. */
2287 if (!rcu_nocb_poll) {
2288 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2289 TPS("Sleep"));
2290 wait_event_interruptible(rdp->nocb_wq, rdp->nocb_head);
2291 /* Memory barrier provide by xchg() below. */
2292 } else if (firsttime) {
2293 firsttime = 0;
2294 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2295 TPS("Poll"));
2296 }
2297 list = ACCESS_ONCE(rdp->nocb_head);
2298 if (!list) {
2299 if (!rcu_nocb_poll)
2300 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2301 TPS("WokeEmpty"));
2302 schedule_timeout_interruptible(1);
2303 flush_signals(current);
2304 continue;
2305 }
2306 firsttime = 1;
2307 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2308 TPS("WokeNonEmpty"));
2309
2310 /*
2311 * Extract queued callbacks, update counts, and wait
2312 * for a grace period to elapse.
2313 */
2314 ACCESS_ONCE(rdp->nocb_head) = NULL;
2315 tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
2316 c = atomic_long_xchg(&rdp->nocb_q_count, 0);
2317 cl = atomic_long_xchg(&rdp->nocb_q_count_lazy, 0);
2318 ACCESS_ONCE(rdp->nocb_p_count) += c;
2319 ACCESS_ONCE(rdp->nocb_p_count_lazy) += cl;
2320 rcu_nocb_wait_gp(rdp);
2321
2322 /* Each pass through the following loop invokes a callback. */
2323 trace_rcu_batch_start(rdp->rsp->name, cl, c, -1);
2324 c = cl = 0;
2325 while (list) {
2326 next = list->next;
2327 /* Wait for enqueuing to complete, if needed. */
2328 while (next == NULL && &list->next != tail) {
2329 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2330 TPS("WaitQueue"));
2331 schedule_timeout_interruptible(1);
2332 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2333 TPS("WokeQueue"));
2334 next = list->next;
2335 }
2336 debug_rcu_head_unqueue(list);
2337 local_bh_disable();
2338 if (__rcu_reclaim(rdp->rsp->name, list))
2339 cl++;
2340 c++;
2341 local_bh_enable();
2342 list = next;
2343 }
2344 trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
2345 ACCESS_ONCE(rdp->nocb_p_count) -= c;
2346 ACCESS_ONCE(rdp->nocb_p_count_lazy) -= cl;
2347 rdp->n_nocbs_invoked += c;
2348 }
2349 return 0;
2350}
2351
2352/* Is a deferred wakeup of rcu_nocb_kthread() required? */
2353static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2354{
2355 return ACCESS_ONCE(rdp->nocb_defer_wakeup);
2356}
2357
2358/* Do a deferred wakeup of rcu_nocb_kthread(). */
2359static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2360{
2361 if (!rcu_nocb_need_deferred_wakeup(rdp))
2362 return;
2363 ACCESS_ONCE(rdp->nocb_defer_wakeup) = false;
2364 wake_up(&rdp->nocb_wq);
2365 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWakeEmpty"));
2366}
2367
2368/* Initialize per-rcu_data variables for no-CBs CPUs. */
2369static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2370{
2371 rdp->nocb_tail = &rdp->nocb_head;
2372 init_waitqueue_head(&rdp->nocb_wq);
2373}
2374
2375/* Create a kthread for each RCU flavor for each no-CBs CPU. */
2376static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
2377{
2378 int cpu;
2379 struct rcu_data *rdp;
2380 struct task_struct *t;
2381
2382 if (rcu_nocb_mask == NULL)
2383 return;
2384 for_each_cpu(cpu, rcu_nocb_mask) {
2385 rdp = per_cpu_ptr(rsp->rda, cpu);
2386 t = kthread_run(rcu_nocb_kthread, rdp,
2387 "rcuo%c/%d", rsp->abbr, cpu);
2388 BUG_ON(IS_ERR(t));
2389 ACCESS_ONCE(rdp->nocb_kthread) = t;
2390 }
2391}
2392
2393/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2394static bool init_nocb_callback_list(struct rcu_data *rdp)
2395{
2396 if (rcu_nocb_mask == NULL ||
2397 !cpumask_test_cpu(rdp->cpu, rcu_nocb_mask))
2398 return false;
2399 rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2400 return true;
2401}
2402
2403#else /* #ifdef CONFIG_RCU_NOCB_CPU */
2404
2405static int rcu_nocb_needs_gp(struct rcu_state *rsp)
2406{
2407 return 0;
2408}
2409
2410static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
2411{
2412}
2413
2414static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2415{
2416}
2417
2418static void rcu_init_one_nocb(struct rcu_node *rnp)
2419{
2420}
2421
2422static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2423 bool lazy, unsigned long flags)
2424{
2425 return 0;
2426}
2427
2428static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
2429 struct rcu_data *rdp,
2430 unsigned long flags)
2431{
2432 return 0;
2433}
2434
2435static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2436{
2437}
2438
2439static bool rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2440{
2441 return false;
2442}
2443
2444static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2445{
2446}
2447
2448static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
2449{
2450}
2451
2452static bool init_nocb_callback_list(struct rcu_data *rdp)
2453{
2454 return false;
2455}
2456
2457#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2458
2459/*
2460 * An adaptive-ticks CPU can potentially execute in kernel mode for an
2461 * arbitrarily long period of time with the scheduling-clock tick turned
2462 * off. RCU will be paying attention to this CPU because it is in the
2463 * kernel, but the CPU cannot be guaranteed to be executing the RCU state
2464 * machine because the scheduling-clock tick has been disabled. Therefore,
2465 * if an adaptive-ticks CPU is failing to respond to the current grace
2466 * period and has not be idle from an RCU perspective, kick it.
2467 */
2468static void rcu_kick_nohz_cpu(int cpu)
2469{
2470#ifdef CONFIG_NO_HZ_FULL
2471 if (tick_nohz_full_cpu(cpu))
2472 smp_send_reschedule(cpu);
2473#endif /* #ifdef CONFIG_NO_HZ_FULL */
2474}
2475
2476
2477#ifdef CONFIG_NO_HZ_FULL_SYSIDLE
2478
2479/*
2480 * Define RCU flavor that holds sysidle state. This needs to be the
2481 * most active flavor of RCU.
2482 */
2483#ifdef CONFIG_PREEMPT_RCU
2484static struct rcu_state *rcu_sysidle_state = &rcu_preempt_state;
2485#else /* #ifdef CONFIG_PREEMPT_RCU */
2486static struct rcu_state *rcu_sysidle_state = &rcu_sched_state;
2487#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
2488
2489static int full_sysidle_state; /* Current system-idle state. */
2490#define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */
2491#define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */
2492#define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */
2493#define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */
2494#define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */
2495
2496/*
2497 * Invoked to note exit from irq or task transition to idle. Note that
2498 * usermode execution does -not- count as idle here! After all, we want
2499 * to detect full-system idle states, not RCU quiescent states and grace
2500 * periods. The caller must have disabled interrupts.
2501 */
2502static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
2503{
2504 unsigned long j;
2505
2506 /* Adjust nesting, check for fully idle. */
2507 if (irq) {
2508 rdtp->dynticks_idle_nesting--;
2509 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
2510 if (rdtp->dynticks_idle_nesting != 0)
2511 return; /* Still not fully idle. */
2512 } else {
2513 if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) ==
2514 DYNTICK_TASK_NEST_VALUE) {
2515 rdtp->dynticks_idle_nesting = 0;
2516 } else {
2517 rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE;
2518 WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0);
2519 return; /* Still not fully idle. */
2520 }
2521 }
2522
2523 /* Record start of fully idle period. */
2524 j = jiffies;
2525 ACCESS_ONCE(rdtp->dynticks_idle_jiffies) = j;
2526 smp_mb__before_atomic_inc();
2527 atomic_inc(&rdtp->dynticks_idle);
2528 smp_mb__after_atomic_inc();
2529 WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1);
2530}
2531
2532/*
2533 * Unconditionally force exit from full system-idle state. This is
2534 * invoked when a normal CPU exits idle, but must be called separately
2535 * for the timekeeping CPU (tick_do_timer_cpu). The reason for this
2536 * is that the timekeeping CPU is permitted to take scheduling-clock
2537 * interrupts while the system is in system-idle state, and of course
2538 * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock
2539 * interrupt from any other type of interrupt.
2540 */
2541void rcu_sysidle_force_exit(void)
2542{
2543 int oldstate = ACCESS_ONCE(full_sysidle_state);
2544 int newoldstate;
2545
2546 /*
2547 * Each pass through the following loop attempts to exit full
2548 * system-idle state. If contention proves to be a problem,
2549 * a trylock-based contention tree could be used here.
2550 */
2551 while (oldstate > RCU_SYSIDLE_SHORT) {
2552 newoldstate = cmpxchg(&full_sysidle_state,
2553 oldstate, RCU_SYSIDLE_NOT);
2554 if (oldstate == newoldstate &&
2555 oldstate == RCU_SYSIDLE_FULL_NOTED) {
2556 rcu_kick_nohz_cpu(tick_do_timer_cpu);
2557 return; /* We cleared it, done! */
2558 }
2559 oldstate = newoldstate;
2560 }
2561 smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */
2562}
2563
2564/*
2565 * Invoked to note entry to irq or task transition from idle. Note that
2566 * usermode execution does -not- count as idle here! The caller must
2567 * have disabled interrupts.
2568 */
2569static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
2570{
2571 /* Adjust nesting, check for already non-idle. */
2572 if (irq) {
2573 rdtp->dynticks_idle_nesting++;
2574 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
2575 if (rdtp->dynticks_idle_nesting != 1)
2576 return; /* Already non-idle. */
2577 } else {
2578 /*
2579 * Allow for irq misnesting. Yes, it really is possible
2580 * to enter an irq handler then never leave it, and maybe
2581 * also vice versa. Handle both possibilities.
2582 */
2583 if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) {
2584 rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE;
2585 WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0);
2586 return; /* Already non-idle. */
2587 } else {
2588 rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE;
2589 }
2590 }
2591
2592 /* Record end of idle period. */
2593 smp_mb__before_atomic_inc();
2594 atomic_inc(&rdtp->dynticks_idle);
2595 smp_mb__after_atomic_inc();
2596 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1));
2597
2598 /*
2599 * If we are the timekeeping CPU, we are permitted to be non-idle
2600 * during a system-idle state. This must be the case, because
2601 * the timekeeping CPU has to take scheduling-clock interrupts
2602 * during the time that the system is transitioning to full
2603 * system-idle state. This means that the timekeeping CPU must
2604 * invoke rcu_sysidle_force_exit() directly if it does anything
2605 * more than take a scheduling-clock interrupt.
2606 */
2607 if (smp_processor_id() == tick_do_timer_cpu)
2608 return;
2609
2610 /* Update system-idle state: We are clearly no longer fully idle! */
2611 rcu_sysidle_force_exit();
2612}
2613
2614/*
2615 * Check to see if the current CPU is idle. Note that usermode execution
2616 * does not count as idle. The caller must have disabled interrupts.
2617 */
2618static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
2619 unsigned long *maxj)
2620{
2621 int cur;
2622 unsigned long j;
2623 struct rcu_dynticks *rdtp = rdp->dynticks;
2624
2625 /*
2626 * If some other CPU has already reported non-idle, if this is
2627 * not the flavor of RCU that tracks sysidle state, or if this
2628 * is an offline or the timekeeping CPU, nothing to do.
2629 */
2630 if (!*isidle || rdp->rsp != rcu_sysidle_state ||
2631 cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu)
2632 return;
2633 if (rcu_gp_in_progress(rdp->rsp))
2634 WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu);
2635
2636 /* Pick up current idle and NMI-nesting counter and check. */
2637 cur = atomic_read(&rdtp->dynticks_idle);
2638 if (cur & 0x1) {
2639 *isidle = false; /* We are not idle! */
2640 return;
2641 }
2642 smp_mb(); /* Read counters before timestamps. */
2643
2644 /* Pick up timestamps. */
2645 j = ACCESS_ONCE(rdtp->dynticks_idle_jiffies);
2646 /* If this CPU entered idle more recently, update maxj timestamp. */
2647 if (ULONG_CMP_LT(*maxj, j))
2648 *maxj = j;
2649}
2650
2651/*
2652 * Is this the flavor of RCU that is handling full-system idle?
2653 */
2654static bool is_sysidle_rcu_state(struct rcu_state *rsp)
2655{
2656 return rsp == rcu_sysidle_state;
2657}
2658
2659/*
2660 * Bind the grace-period kthread for the sysidle flavor of RCU to the
2661 * timekeeping CPU.
2662 */
2663static void rcu_bind_gp_kthread(void)
2664{
2665 int cpu = ACCESS_ONCE(tick_do_timer_cpu);
2666
2667 if (cpu < 0 || cpu >= nr_cpu_ids)
2668 return;
2669 if (raw_smp_processor_id() != cpu)
2670 set_cpus_allowed_ptr(current, cpumask_of(cpu));
2671}
2672
2673/*
2674 * Return a delay in jiffies based on the number of CPUs, rcu_node
2675 * leaf fanout, and jiffies tick rate. The idea is to allow larger
2676 * systems more time to transition to full-idle state in order to
2677 * avoid the cache thrashing that otherwise occur on the state variable.
2678 * Really small systems (less than a couple of tens of CPUs) should
2679 * instead use a single global atomically incremented counter, and later
2680 * versions of this will automatically reconfigure themselves accordingly.
2681 */
2682static unsigned long rcu_sysidle_delay(void)
2683{
2684 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
2685 return 0;
2686 return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000);
2687}
2688
2689/*
2690 * Advance the full-system-idle state. This is invoked when all of
2691 * the non-timekeeping CPUs are idle.
2692 */
2693static void rcu_sysidle(unsigned long j)
2694{
2695 /* Check the current state. */
2696 switch (ACCESS_ONCE(full_sysidle_state)) {
2697 case RCU_SYSIDLE_NOT:
2698
2699 /* First time all are idle, so note a short idle period. */
2700 ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_SHORT;
2701 break;
2702
2703 case RCU_SYSIDLE_SHORT:
2704
2705 /*
2706 * Idle for a bit, time to advance to next state?
2707 * cmpxchg failure means race with non-idle, let them win.
2708 */
2709 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
2710 (void)cmpxchg(&full_sysidle_state,
2711 RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG);
2712 break;
2713
2714 case RCU_SYSIDLE_LONG:
2715
2716 /*
2717 * Do an additional check pass before advancing to full.
2718 * cmpxchg failure means race with non-idle, let them win.
2719 */
2720 if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay()))
2721 (void)cmpxchg(&full_sysidle_state,
2722 RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL);
2723 break;
2724
2725 default:
2726 break;
2727 }
2728}
2729
2730/*
2731 * Found a non-idle non-timekeeping CPU, so kick the system-idle state
2732 * back to the beginning.
2733 */
2734static void rcu_sysidle_cancel(void)
2735{
2736 smp_mb();
2737 ACCESS_ONCE(full_sysidle_state) = RCU_SYSIDLE_NOT;
2738}
2739
2740/*
2741 * Update the sysidle state based on the results of a force-quiescent-state
2742 * scan of the CPUs' dyntick-idle state.
2743 */
2744static void rcu_sysidle_report(struct rcu_state *rsp, int isidle,
2745 unsigned long maxj, bool gpkt)
2746{
2747 if (rsp != rcu_sysidle_state)
2748 return; /* Wrong flavor, ignore. */
2749 if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL)
2750 return; /* Running state machine from timekeeping CPU. */
2751 if (isidle)
2752 rcu_sysidle(maxj); /* More idle! */
2753 else
2754 rcu_sysidle_cancel(); /* Idle is over. */
2755}
2756
2757/*
2758 * Wrapper for rcu_sysidle_report() when called from the grace-period
2759 * kthread's context.
2760 */
2761static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
2762 unsigned long maxj)
2763{
2764 rcu_sysidle_report(rsp, isidle, maxj, true);
2765}
2766
2767/* Callback and function for forcing an RCU grace period. */
2768struct rcu_sysidle_head {
2769 struct rcu_head rh;
2770 int inuse;
2771};
2772
2773static void rcu_sysidle_cb(struct rcu_head *rhp)
2774{
2775 struct rcu_sysidle_head *rshp;
2776
2777 /*
2778 * The following memory barrier is needed to replace the
2779 * memory barriers that would normally be in the memory
2780 * allocator.
2781 */
2782 smp_mb(); /* grace period precedes setting inuse. */
2783
2784 rshp = container_of(rhp, struct rcu_sysidle_head, rh);
2785 ACCESS_ONCE(rshp->inuse) = 0;
2786}
2787
2788/*
2789 * Check to see if the system is fully idle, other than the timekeeping CPU.
2790 * The caller must have disabled interrupts.
2791 */
2792bool rcu_sys_is_idle(void)
2793{
2794 static struct rcu_sysidle_head rsh;
2795 int rss = ACCESS_ONCE(full_sysidle_state);
2796
2797 if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu))
2798 return false;
2799
2800 /* Handle small-system case by doing a full scan of CPUs. */
2801 if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) {
2802 int oldrss = rss - 1;
2803
2804 /*
2805 * One pass to advance to each state up to _FULL.
2806 * Give up if any pass fails to advance the state.
2807 */
2808 while (rss < RCU_SYSIDLE_FULL && oldrss < rss) {
2809 int cpu;
2810 bool isidle = true;
2811 unsigned long maxj = jiffies - ULONG_MAX / 4;
2812 struct rcu_data *rdp;
2813
2814 /* Scan all the CPUs looking for nonidle CPUs. */
2815 for_each_possible_cpu(cpu) {
2816 rdp = per_cpu_ptr(rcu_sysidle_state->rda, cpu);
2817 rcu_sysidle_check_cpu(rdp, &isidle, &maxj);
2818 if (!isidle)
2819 break;
2820 }
2821 rcu_sysidle_report(rcu_sysidle_state,
2822 isidle, maxj, false);
2823 oldrss = rss;
2824 rss = ACCESS_ONCE(full_sysidle_state);
2825 }
2826 }
2827
2828 /* If this is the first observation of an idle period, record it. */
2829 if (rss == RCU_SYSIDLE_FULL) {
2830 rss = cmpxchg(&full_sysidle_state,
2831 RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED);
2832 return rss == RCU_SYSIDLE_FULL;
2833 }
2834
2835 smp_mb(); /* ensure rss load happens before later caller actions. */
2836
2837 /* If already fully idle, tell the caller (in case of races). */
2838 if (rss == RCU_SYSIDLE_FULL_NOTED)
2839 return true;
2840
2841 /*
2842 * If we aren't there yet, and a grace period is not in flight,
2843 * initiate a grace period. Either way, tell the caller that
2844 * we are not there yet. We use an xchg() rather than an assignment
2845 * to make up for the memory barriers that would otherwise be
2846 * provided by the memory allocator.
2847 */
2848 if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL &&
2849 !rcu_gp_in_progress(rcu_sysidle_state) &&
2850 !rsh.inuse && xchg(&rsh.inuse, 1) == 0)
2851 call_rcu(&rsh.rh, rcu_sysidle_cb);
2852 return false;
2853}
2854
2855/*
2856 * Initialize dynticks sysidle state for CPUs coming online.
2857 */
2858static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
2859{
2860 rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE;
2861}
2862
2863#else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
2864
2865static void rcu_sysidle_enter(struct rcu_dynticks *rdtp, int irq)
2866{
2867}
2868
2869static void rcu_sysidle_exit(struct rcu_dynticks *rdtp, int irq)
2870{
2871}
2872
2873static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle,
2874 unsigned long *maxj)
2875{
2876}
2877
2878static bool is_sysidle_rcu_state(struct rcu_state *rsp)
2879{
2880 return false;
2881}
2882
2883static void rcu_bind_gp_kthread(void)
2884{
2885}
2886
2887static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,
2888 unsigned long maxj)
2889{
2890}
2891
2892static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp)
2893{
2894}
2895
2896#endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
2897
2898/*
2899 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
2900 * grace-period kthread will do force_quiescent_state() processing?
2901 * The idea is to avoid waking up RCU core processing on such a
2902 * CPU unless the grace period has extended for too long.
2903 *
2904 * This code relies on the fact that all NO_HZ_FULL CPUs are also
2905 * CONFIG_RCU_NOCB_CPU CPUs.
2906 */
2907static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
2908{
2909#ifdef CONFIG_NO_HZ_FULL
2910 if (tick_nohz_full_cpu(smp_processor_id()) &&
2911 (!rcu_gp_in_progress(rsp) ||
2912 ULONG_CMP_LT(jiffies, ACCESS_ONCE(rsp->gp_start) + HZ)))
2913 return 1;
2914#endif /* #ifdef CONFIG_NO_HZ_FULL */
2915 return 0;
2916}
1/*
2 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
3 * Internal non-public definitions that provide either classic
4 * or preemptible semantics.
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, you can access it online at
18 * http://www.gnu.org/licenses/gpl-2.0.html.
19 *
20 * Copyright Red Hat, 2009
21 * Copyright IBM Corporation, 2009
22 *
23 * Author: Ingo Molnar <mingo@elte.hu>
24 * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
25 */
26
27#include <linux/delay.h>
28#include <linux/gfp.h>
29#include <linux/oom.h>
30#include <linux/sched/debug.h>
31#include <linux/smpboot.h>
32#include <linux/sched/isolation.h>
33#include <uapi/linux/sched/types.h>
34#include "../time/tick-internal.h"
35
36#ifdef CONFIG_RCU_BOOST
37
38#include "../locking/rtmutex_common.h"
39
40/*
41 * Control variables for per-CPU and per-rcu_node kthreads. These
42 * handle all flavors of RCU.
43 */
44static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
45DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
46DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
47DEFINE_PER_CPU(char, rcu_cpu_has_work);
48
49#else /* #ifdef CONFIG_RCU_BOOST */
50
51/*
52 * Some architectures do not define rt_mutexes, but if !CONFIG_RCU_BOOST,
53 * all uses are in dead code. Provide a definition to keep the compiler
54 * happy, but add WARN_ON_ONCE() to complain if used in the wrong place.
55 * This probably needs to be excluded from -rt builds.
56 */
57#define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; })
58#define rt_mutex_futex_unlock(x) WARN_ON_ONCE(1)
59
60#endif /* #else #ifdef CONFIG_RCU_BOOST */
61
62#ifdef CONFIG_RCU_NOCB_CPU
63static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
64static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
65#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
66
67/*
68 * Check the RCU kernel configuration parameters and print informative
69 * messages about anything out of the ordinary.
70 */
71static void __init rcu_bootup_announce_oddness(void)
72{
73 if (IS_ENABLED(CONFIG_RCU_TRACE))
74 pr_info("\tRCU event tracing is enabled.\n");
75 if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||
76 (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))
77 pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
78 RCU_FANOUT);
79 if (rcu_fanout_exact)
80 pr_info("\tHierarchical RCU autobalancing is disabled.\n");
81 if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ))
82 pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
83 if (IS_ENABLED(CONFIG_PROVE_RCU))
84 pr_info("\tRCU lockdep checking is enabled.\n");
85 if (RCU_NUM_LVLS >= 4)
86 pr_info("\tFour(or more)-level hierarchy is enabled.\n");
87 if (RCU_FANOUT_LEAF != 16)
88 pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
89 RCU_FANOUT_LEAF);
90 if (rcu_fanout_leaf != RCU_FANOUT_LEAF)
91 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
92 if (nr_cpu_ids != NR_CPUS)
93 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%u.\n", NR_CPUS, nr_cpu_ids);
94#ifdef CONFIG_RCU_BOOST
95 pr_info("\tRCU priority boosting: priority %d delay %d ms.\n", kthread_prio, CONFIG_RCU_BOOST_DELAY);
96#endif
97 if (blimit != DEFAULT_RCU_BLIMIT)
98 pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit);
99 if (qhimark != DEFAULT_RCU_QHIMARK)
100 pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark);
101 if (qlowmark != DEFAULT_RCU_QLOMARK)
102 pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark);
103 if (jiffies_till_first_fqs != ULONG_MAX)
104 pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs);
105 if (jiffies_till_next_fqs != ULONG_MAX)
106 pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs);
107 if (rcu_kick_kthreads)
108 pr_info("\tKick kthreads if too-long grace period.\n");
109 if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD))
110 pr_info("\tRCU callback double-/use-after-free debug enabled.\n");
111 if (gp_preinit_delay)
112 pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay);
113 if (gp_init_delay)
114 pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay);
115 if (gp_cleanup_delay)
116 pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay);
117 if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))
118 pr_info("\tRCU debug extended QS entry/exit.\n");
119 rcupdate_announce_bootup_oddness();
120}
121
122#ifdef CONFIG_PREEMPT_RCU
123
124RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
125static struct rcu_state *const rcu_state_p = &rcu_preempt_state;
126static struct rcu_data __percpu *const rcu_data_p = &rcu_preempt_data;
127
128static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
129 bool wake);
130
131/*
132 * Tell them what RCU they are running.
133 */
134static void __init rcu_bootup_announce(void)
135{
136 pr_info("Preemptible hierarchical RCU implementation.\n");
137 rcu_bootup_announce_oddness();
138}
139
140/* Flags for rcu_preempt_ctxt_queue() decision table. */
141#define RCU_GP_TASKS 0x8
142#define RCU_EXP_TASKS 0x4
143#define RCU_GP_BLKD 0x2
144#define RCU_EXP_BLKD 0x1
145
146/*
147 * Queues a task preempted within an RCU-preempt read-side critical
148 * section into the appropriate location within the ->blkd_tasks list,
149 * depending on the states of any ongoing normal and expedited grace
150 * periods. The ->gp_tasks pointer indicates which element the normal
151 * grace period is waiting on (NULL if none), and the ->exp_tasks pointer
152 * indicates which element the expedited grace period is waiting on (again,
153 * NULL if none). If a grace period is waiting on a given element in the
154 * ->blkd_tasks list, it also waits on all subsequent elements. Thus,
155 * adding a task to the tail of the list blocks any grace period that is
156 * already waiting on one of the elements. In contrast, adding a task
157 * to the head of the list won't block any grace period that is already
158 * waiting on one of the elements.
159 *
160 * This queuing is imprecise, and can sometimes make an ongoing grace
161 * period wait for a task that is not strictly speaking blocking it.
162 * Given the choice, we needlessly block a normal grace period rather than
163 * blocking an expedited grace period.
164 *
165 * Note that an endless sequence of expedited grace periods still cannot
166 * indefinitely postpone a normal grace period. Eventually, all of the
167 * fixed number of preempted tasks blocking the normal grace period that are
168 * not also blocking the expedited grace period will resume and complete
169 * their RCU read-side critical sections. At that point, the ->gp_tasks
170 * pointer will equal the ->exp_tasks pointer, at which point the end of
171 * the corresponding expedited grace period will also be the end of the
172 * normal grace period.
173 */
174static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
175 __releases(rnp->lock) /* But leaves rrupts disabled. */
176{
177 int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) +
178 (rnp->exp_tasks ? RCU_EXP_TASKS : 0) +
179 (rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) +
180 (rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0);
181 struct task_struct *t = current;
182
183 raw_lockdep_assert_held_rcu_node(rnp);
184 WARN_ON_ONCE(rdp->mynode != rnp);
185 WARN_ON_ONCE(rnp->level != rcu_num_lvls - 1);
186
187 /*
188 * Decide where to queue the newly blocked task. In theory,
189 * this could be an if-statement. In practice, when I tried
190 * that, it was quite messy.
191 */
192 switch (blkd_state) {
193 case 0:
194 case RCU_EXP_TASKS:
195 case RCU_EXP_TASKS + RCU_GP_BLKD:
196 case RCU_GP_TASKS:
197 case RCU_GP_TASKS + RCU_EXP_TASKS:
198
199 /*
200 * Blocking neither GP, or first task blocking the normal
201 * GP but not blocking the already-waiting expedited GP.
202 * Queue at the head of the list to avoid unnecessarily
203 * blocking the already-waiting GPs.
204 */
205 list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
206 break;
207
208 case RCU_EXP_BLKD:
209 case RCU_GP_BLKD:
210 case RCU_GP_BLKD + RCU_EXP_BLKD:
211 case RCU_GP_TASKS + RCU_EXP_BLKD:
212 case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
213 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
214
215 /*
216 * First task arriving that blocks either GP, or first task
217 * arriving that blocks the expedited GP (with the normal
218 * GP already waiting), or a task arriving that blocks
219 * both GPs with both GPs already waiting. Queue at the
220 * tail of the list to avoid any GP waiting on any of the
221 * already queued tasks that are not blocking it.
222 */
223 list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);
224 break;
225
226 case RCU_EXP_TASKS + RCU_EXP_BLKD:
227 case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
228 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD:
229
230 /*
231 * Second or subsequent task blocking the expedited GP.
232 * The task either does not block the normal GP, or is the
233 * first task blocking the normal GP. Queue just after
234 * the first task blocking the expedited GP.
235 */
236 list_add(&t->rcu_node_entry, rnp->exp_tasks);
237 break;
238
239 case RCU_GP_TASKS + RCU_GP_BLKD:
240 case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD:
241
242 /*
243 * Second or subsequent task blocking the normal GP.
244 * The task does not block the expedited GP. Queue just
245 * after the first task blocking the normal GP.
246 */
247 list_add(&t->rcu_node_entry, rnp->gp_tasks);
248 break;
249
250 default:
251
252 /* Yet another exercise in excessive paranoia. */
253 WARN_ON_ONCE(1);
254 break;
255 }
256
257 /*
258 * We have now queued the task. If it was the first one to
259 * block either grace period, update the ->gp_tasks and/or
260 * ->exp_tasks pointers, respectively, to reference the newly
261 * blocked tasks.
262 */
263 if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD))
264 rnp->gp_tasks = &t->rcu_node_entry;
265 if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
266 rnp->exp_tasks = &t->rcu_node_entry;
267 WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=
268 !(rnp->qsmask & rdp->grpmask));
269 WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) !=
270 !(rnp->expmask & rdp->grpmask));
271 raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */
272
273 /*
274 * Report the quiescent state for the expedited GP. This expedited
275 * GP should not be able to end until we report, so there should be
276 * no need to check for a subsequent expedited GP. (Though we are
277 * still in a quiescent state in any case.)
278 */
279 if (blkd_state & RCU_EXP_BLKD &&
280 t->rcu_read_unlock_special.b.exp_need_qs) {
281 t->rcu_read_unlock_special.b.exp_need_qs = false;
282 rcu_report_exp_rdp(rdp->rsp, rdp, true);
283 } else {
284 WARN_ON_ONCE(t->rcu_read_unlock_special.b.exp_need_qs);
285 }
286}
287
288/*
289 * Record a preemptible-RCU quiescent state for the specified CPU. Note
290 * that this just means that the task currently running on the CPU is
291 * not in a quiescent state. There might be any number of tasks blocked
292 * while in an RCU read-side critical section.
293 *
294 * As with the other rcu_*_qs() functions, callers to this function
295 * must disable preemption.
296 */
297static void rcu_preempt_qs(void)
298{
299 RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_qs() invoked with preemption enabled!!!\n");
300 if (__this_cpu_read(rcu_data_p->cpu_no_qs.s)) {
301 trace_rcu_grace_period(TPS("rcu_preempt"),
302 __this_cpu_read(rcu_data_p->gpnum),
303 TPS("cpuqs"));
304 __this_cpu_write(rcu_data_p->cpu_no_qs.b.norm, false);
305 barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
306 current->rcu_read_unlock_special.b.need_qs = false;
307 }
308}
309
310/*
311 * We have entered the scheduler, and the current task might soon be
312 * context-switched away from. If this task is in an RCU read-side
313 * critical section, we will no longer be able to rely on the CPU to
314 * record that fact, so we enqueue the task on the blkd_tasks list.
315 * The task will dequeue itself when it exits the outermost enclosing
316 * RCU read-side critical section. Therefore, the current grace period
317 * cannot be permitted to complete until the blkd_tasks list entries
318 * predating the current grace period drain, in other words, until
319 * rnp->gp_tasks becomes NULL.
320 *
321 * Caller must disable interrupts.
322 */
323static void rcu_preempt_note_context_switch(bool preempt)
324{
325 struct task_struct *t = current;
326 struct rcu_data *rdp;
327 struct rcu_node *rnp;
328
329 lockdep_assert_irqs_disabled();
330 WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0);
331 if (t->rcu_read_lock_nesting > 0 &&
332 !t->rcu_read_unlock_special.b.blocked) {
333
334 /* Possibly blocking in an RCU read-side critical section. */
335 rdp = this_cpu_ptr(rcu_state_p->rda);
336 rnp = rdp->mynode;
337 raw_spin_lock_rcu_node(rnp);
338 t->rcu_read_unlock_special.b.blocked = true;
339 t->rcu_blocked_node = rnp;
340
341 /*
342 * Verify the CPU's sanity, trace the preemption, and
343 * then queue the task as required based on the states
344 * of any ongoing and expedited grace periods.
345 */
346 WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);
347 WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
348 trace_rcu_preempt_task(rdp->rsp->name,
349 t->pid,
350 (rnp->qsmask & rdp->grpmask)
351 ? rnp->gpnum
352 : rnp->gpnum + 1);
353 rcu_preempt_ctxt_queue(rnp, rdp);
354 } else if (t->rcu_read_lock_nesting < 0 &&
355 t->rcu_read_unlock_special.s) {
356
357 /*
358 * Complete exit from RCU read-side critical section on
359 * behalf of preempted instance of __rcu_read_unlock().
360 */
361 rcu_read_unlock_special(t);
362 }
363
364 /*
365 * Either we were not in an RCU read-side critical section to
366 * begin with, or we have now recorded that critical section
367 * globally. Either way, we can now note a quiescent state
368 * for this CPU. Again, if we were in an RCU read-side critical
369 * section, and if that critical section was blocking the current
370 * grace period, then the fact that the task has been enqueued
371 * means that we continue to block the current grace period.
372 */
373 rcu_preempt_qs();
374}
375
376/*
377 * Check for preempted RCU readers blocking the current grace period
378 * for the specified rcu_node structure. If the caller needs a reliable
379 * answer, it must hold the rcu_node's ->lock.
380 */
381static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
382{
383 return rnp->gp_tasks != NULL;
384}
385
386/*
387 * Advance a ->blkd_tasks-list pointer to the next entry, instead
388 * returning NULL if at the end of the list.
389 */
390static struct list_head *rcu_next_node_entry(struct task_struct *t,
391 struct rcu_node *rnp)
392{
393 struct list_head *np;
394
395 np = t->rcu_node_entry.next;
396 if (np == &rnp->blkd_tasks)
397 np = NULL;
398 return np;
399}
400
401/*
402 * Return true if the specified rcu_node structure has tasks that were
403 * preempted within an RCU read-side critical section.
404 */
405static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
406{
407 return !list_empty(&rnp->blkd_tasks);
408}
409
410/*
411 * Handle special cases during rcu_read_unlock(), such as needing to
412 * notify RCU core processing or task having blocked during the RCU
413 * read-side critical section.
414 */
415void rcu_read_unlock_special(struct task_struct *t)
416{
417 bool empty_exp;
418 bool empty_norm;
419 bool empty_exp_now;
420 unsigned long flags;
421 struct list_head *np;
422 bool drop_boost_mutex = false;
423 struct rcu_data *rdp;
424 struct rcu_node *rnp;
425 union rcu_special special;
426
427 /* NMI handlers cannot block and cannot safely manipulate state. */
428 if (in_nmi())
429 return;
430
431 local_irq_save(flags);
432
433 /*
434 * If RCU core is waiting for this CPU to exit its critical section,
435 * report the fact that it has exited. Because irqs are disabled,
436 * t->rcu_read_unlock_special cannot change.
437 */
438 special = t->rcu_read_unlock_special;
439 if (special.b.need_qs) {
440 rcu_preempt_qs();
441 t->rcu_read_unlock_special.b.need_qs = false;
442 if (!t->rcu_read_unlock_special.s) {
443 local_irq_restore(flags);
444 return;
445 }
446 }
447
448 /*
449 * Respond to a request for an expedited grace period, but only if
450 * we were not preempted, meaning that we were running on the same
451 * CPU throughout. If we were preempted, the exp_need_qs flag
452 * would have been cleared at the time of the first preemption,
453 * and the quiescent state would be reported when we were dequeued.
454 */
455 if (special.b.exp_need_qs) {
456 WARN_ON_ONCE(special.b.blocked);
457 t->rcu_read_unlock_special.b.exp_need_qs = false;
458 rdp = this_cpu_ptr(rcu_state_p->rda);
459 rcu_report_exp_rdp(rcu_state_p, rdp, true);
460 if (!t->rcu_read_unlock_special.s) {
461 local_irq_restore(flags);
462 return;
463 }
464 }
465
466 /* Hardware IRQ handlers cannot block, complain if they get here. */
467 if (in_irq() || in_serving_softirq()) {
468 lockdep_rcu_suspicious(__FILE__, __LINE__,
469 "rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n");
470 pr_alert("->rcu_read_unlock_special: %#x (b: %d, enq: %d nq: %d)\n",
471 t->rcu_read_unlock_special.s,
472 t->rcu_read_unlock_special.b.blocked,
473 t->rcu_read_unlock_special.b.exp_need_qs,
474 t->rcu_read_unlock_special.b.need_qs);
475 local_irq_restore(flags);
476 return;
477 }
478
479 /* Clean up if blocked during RCU read-side critical section. */
480 if (special.b.blocked) {
481 t->rcu_read_unlock_special.b.blocked = false;
482
483 /*
484 * Remove this task from the list it blocked on. The task
485 * now remains queued on the rcu_node corresponding to the
486 * CPU it first blocked on, so there is no longer any need
487 * to loop. Retain a WARN_ON_ONCE() out of sheer paranoia.
488 */
489 rnp = t->rcu_blocked_node;
490 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
491 WARN_ON_ONCE(rnp != t->rcu_blocked_node);
492 WARN_ON_ONCE(rnp->level != rcu_num_lvls - 1);
493 empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
494 empty_exp = sync_rcu_preempt_exp_done(rnp);
495 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
496 np = rcu_next_node_entry(t, rnp);
497 list_del_init(&t->rcu_node_entry);
498 t->rcu_blocked_node = NULL;
499 trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
500 rnp->gpnum, t->pid);
501 if (&t->rcu_node_entry == rnp->gp_tasks)
502 rnp->gp_tasks = np;
503 if (&t->rcu_node_entry == rnp->exp_tasks)
504 rnp->exp_tasks = np;
505 if (IS_ENABLED(CONFIG_RCU_BOOST)) {
506 /* Snapshot ->boost_mtx ownership w/rnp->lock held. */
507 drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
508 if (&t->rcu_node_entry == rnp->boost_tasks)
509 rnp->boost_tasks = np;
510 }
511
512 /*
513 * If this was the last task on the current list, and if
514 * we aren't waiting on any CPUs, report the quiescent state.
515 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
516 * so we must take a snapshot of the expedited state.
517 */
518 empty_exp_now = sync_rcu_preempt_exp_done(rnp);
519 if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
520 trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
521 rnp->gpnum,
522 0, rnp->qsmask,
523 rnp->level,
524 rnp->grplo,
525 rnp->grphi,
526 !!rnp->gp_tasks);
527 rcu_report_unblock_qs_rnp(rcu_state_p, rnp, flags);
528 } else {
529 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
530 }
531
532 /* Unboost if we were boosted. */
533 if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
534 rt_mutex_futex_unlock(&rnp->boost_mtx);
535
536 /*
537 * If this was the last task on the expedited lists,
538 * then we need to report up the rcu_node hierarchy.
539 */
540 if (!empty_exp && empty_exp_now)
541 rcu_report_exp_rnp(rcu_state_p, rnp, true);
542 } else {
543 local_irq_restore(flags);
544 }
545}
546
547/*
548 * Dump detailed information for all tasks blocking the current RCU
549 * grace period on the specified rcu_node structure.
550 */
551static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
552{
553 unsigned long flags;
554 struct task_struct *t;
555
556 raw_spin_lock_irqsave_rcu_node(rnp, flags);
557 if (!rcu_preempt_blocked_readers_cgp(rnp)) {
558 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
559 return;
560 }
561 t = list_entry(rnp->gp_tasks->prev,
562 struct task_struct, rcu_node_entry);
563 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
564 /*
565 * We could be printing a lot while holding a spinlock.
566 * Avoid triggering hard lockup.
567 */
568 touch_nmi_watchdog();
569 sched_show_task(t);
570 }
571 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
572}
573
574/*
575 * Dump detailed information for all tasks blocking the current RCU
576 * grace period.
577 */
578static void rcu_print_detail_task_stall(struct rcu_state *rsp)
579{
580 struct rcu_node *rnp = rcu_get_root(rsp);
581
582 rcu_print_detail_task_stall_rnp(rnp);
583 rcu_for_each_leaf_node(rsp, rnp)
584 rcu_print_detail_task_stall_rnp(rnp);
585}
586
587static void rcu_print_task_stall_begin(struct rcu_node *rnp)
588{
589 pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
590 rnp->level, rnp->grplo, rnp->grphi);
591}
592
593static void rcu_print_task_stall_end(void)
594{
595 pr_cont("\n");
596}
597
598/*
599 * Scan the current list of tasks blocked within RCU read-side critical
600 * sections, printing out the tid of each.
601 */
602static int rcu_print_task_stall(struct rcu_node *rnp)
603{
604 struct task_struct *t;
605 int ndetected = 0;
606
607 if (!rcu_preempt_blocked_readers_cgp(rnp))
608 return 0;
609 rcu_print_task_stall_begin(rnp);
610 t = list_entry(rnp->gp_tasks->prev,
611 struct task_struct, rcu_node_entry);
612 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
613 pr_cont(" P%d", t->pid);
614 ndetected++;
615 }
616 rcu_print_task_stall_end();
617 return ndetected;
618}
619
620/*
621 * Scan the current list of tasks blocked within RCU read-side critical
622 * sections, printing out the tid of each that is blocking the current
623 * expedited grace period.
624 */
625static int rcu_print_task_exp_stall(struct rcu_node *rnp)
626{
627 struct task_struct *t;
628 int ndetected = 0;
629
630 if (!rnp->exp_tasks)
631 return 0;
632 t = list_entry(rnp->exp_tasks->prev,
633 struct task_struct, rcu_node_entry);
634 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
635 pr_cont(" P%d", t->pid);
636 ndetected++;
637 }
638 return ndetected;
639}
640
641/*
642 * Check that the list of blocked tasks for the newly completed grace
643 * period is in fact empty. It is a serious bug to complete a grace
644 * period that still has RCU readers blocked! This function must be
645 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
646 * must be held by the caller.
647 *
648 * Also, if there are blocked tasks on the list, they automatically
649 * block the newly created grace period, so set up ->gp_tasks accordingly.
650 */
651static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
652{
653 struct task_struct *t;
654
655 RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
656 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
657 if (rcu_preempt_has_tasks(rnp)) {
658 rnp->gp_tasks = rnp->blkd_tasks.next;
659 t = container_of(rnp->gp_tasks, struct task_struct,
660 rcu_node_entry);
661 trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
662 rnp->gpnum, t->pid);
663 }
664 WARN_ON_ONCE(rnp->qsmask);
665}
666
667/*
668 * Check for a quiescent state from the current CPU. When a task blocks,
669 * the task is recorded in the corresponding CPU's rcu_node structure,
670 * which is checked elsewhere.
671 *
672 * Caller must disable hard irqs.
673 */
674static void rcu_preempt_check_callbacks(void)
675{
676 struct task_struct *t = current;
677
678 if (t->rcu_read_lock_nesting == 0) {
679 rcu_preempt_qs();
680 return;
681 }
682 if (t->rcu_read_lock_nesting > 0 &&
683 __this_cpu_read(rcu_data_p->core_needs_qs) &&
684 __this_cpu_read(rcu_data_p->cpu_no_qs.b.norm))
685 t->rcu_read_unlock_special.b.need_qs = true;
686}
687
688#ifdef CONFIG_RCU_BOOST
689
690static void rcu_preempt_do_callbacks(void)
691{
692 rcu_do_batch(rcu_state_p, this_cpu_ptr(rcu_data_p));
693}
694
695#endif /* #ifdef CONFIG_RCU_BOOST */
696
697/**
698 * call_rcu() - Queue an RCU callback for invocation after a grace period.
699 * @head: structure to be used for queueing the RCU updates.
700 * @func: actual callback function to be invoked after the grace period
701 *
702 * The callback function will be invoked some time after a full grace
703 * period elapses, in other words after all pre-existing RCU read-side
704 * critical sections have completed. However, the callback function
705 * might well execute concurrently with RCU read-side critical sections
706 * that started after call_rcu() was invoked. RCU read-side critical
707 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
708 * and may be nested.
709 *
710 * Note that all CPUs must agree that the grace period extended beyond
711 * all pre-existing RCU read-side critical section. On systems with more
712 * than one CPU, this means that when "func()" is invoked, each CPU is
713 * guaranteed to have executed a full memory barrier since the end of its
714 * last RCU read-side critical section whose beginning preceded the call
715 * to call_rcu(). It also means that each CPU executing an RCU read-side
716 * critical section that continues beyond the start of "func()" must have
717 * executed a memory barrier after the call_rcu() but before the beginning
718 * of that RCU read-side critical section. Note that these guarantees
719 * include CPUs that are offline, idle, or executing in user mode, as
720 * well as CPUs that are executing in the kernel.
721 *
722 * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
723 * resulting RCU callback function "func()", then both CPU A and CPU B are
724 * guaranteed to execute a full memory barrier during the time interval
725 * between the call to call_rcu() and the invocation of "func()" -- even
726 * if CPU A and CPU B are the same CPU (but again only if the system has
727 * more than one CPU).
728 */
729void call_rcu(struct rcu_head *head, rcu_callback_t func)
730{
731 __call_rcu(head, func, rcu_state_p, -1, 0);
732}
733EXPORT_SYMBOL_GPL(call_rcu);
734
735/**
736 * synchronize_rcu - wait until a grace period has elapsed.
737 *
738 * Control will return to the caller some time after a full grace
739 * period has elapsed, in other words after all currently executing RCU
740 * read-side critical sections have completed. Note, however, that
741 * upon return from synchronize_rcu(), the caller might well be executing
742 * concurrently with new RCU read-side critical sections that began while
743 * synchronize_rcu() was waiting. RCU read-side critical sections are
744 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
745 *
746 * See the description of synchronize_sched() for more detailed
747 * information on memory-ordering guarantees. However, please note
748 * that -only- the memory-ordering guarantees apply. For example,
749 * synchronize_rcu() is -not- guaranteed to wait on things like code
750 * protected by preempt_disable(), instead, synchronize_rcu() is -only-
751 * guaranteed to wait on RCU read-side critical sections, that is, sections
752 * of code protected by rcu_read_lock().
753 */
754void synchronize_rcu(void)
755{
756 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
757 lock_is_held(&rcu_lock_map) ||
758 lock_is_held(&rcu_sched_lock_map),
759 "Illegal synchronize_rcu() in RCU read-side critical section");
760 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
761 return;
762 if (rcu_gp_is_expedited())
763 synchronize_rcu_expedited();
764 else
765 wait_rcu_gp(call_rcu);
766}
767EXPORT_SYMBOL_GPL(synchronize_rcu);
768
769/**
770 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
771 *
772 * Note that this primitive does not necessarily wait for an RCU grace period
773 * to complete. For example, if there are no RCU callbacks queued anywhere
774 * in the system, then rcu_barrier() is within its rights to return
775 * immediately, without waiting for anything, much less an RCU grace period.
776 */
777void rcu_barrier(void)
778{
779 _rcu_barrier(rcu_state_p);
780}
781EXPORT_SYMBOL_GPL(rcu_barrier);
782
783/*
784 * Initialize preemptible RCU's state structures.
785 */
786static void __init __rcu_init_preempt(void)
787{
788 rcu_init_one(rcu_state_p);
789}
790
791/*
792 * Check for a task exiting while in a preemptible-RCU read-side
793 * critical section, clean up if so. No need to issue warnings,
794 * as debug_check_no_locks_held() already does this if lockdep
795 * is enabled.
796 */
797void exit_rcu(void)
798{
799 struct task_struct *t = current;
800
801 if (likely(list_empty(¤t->rcu_node_entry)))
802 return;
803 t->rcu_read_lock_nesting = 1;
804 barrier();
805 t->rcu_read_unlock_special.b.blocked = true;
806 __rcu_read_unlock();
807}
808
809#else /* #ifdef CONFIG_PREEMPT_RCU */
810
811static struct rcu_state *const rcu_state_p = &rcu_sched_state;
812
813/*
814 * Tell them what RCU they are running.
815 */
816static void __init rcu_bootup_announce(void)
817{
818 pr_info("Hierarchical RCU implementation.\n");
819 rcu_bootup_announce_oddness();
820}
821
822/*
823 * Because preemptible RCU does not exist, we never have to check for
824 * CPUs being in quiescent states.
825 */
826static void rcu_preempt_note_context_switch(bool preempt)
827{
828}
829
830/*
831 * Because preemptible RCU does not exist, there are never any preempted
832 * RCU readers.
833 */
834static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
835{
836 return 0;
837}
838
839/*
840 * Because there is no preemptible RCU, there can be no readers blocked.
841 */
842static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
843{
844 return false;
845}
846
847/*
848 * Because preemptible RCU does not exist, we never have to check for
849 * tasks blocked within RCU read-side critical sections.
850 */
851static void rcu_print_detail_task_stall(struct rcu_state *rsp)
852{
853}
854
855/*
856 * Because preemptible RCU does not exist, we never have to check for
857 * tasks blocked within RCU read-side critical sections.
858 */
859static int rcu_print_task_stall(struct rcu_node *rnp)
860{
861 return 0;
862}
863
864/*
865 * Because preemptible RCU does not exist, we never have to check for
866 * tasks blocked within RCU read-side critical sections that are
867 * blocking the current expedited grace period.
868 */
869static int rcu_print_task_exp_stall(struct rcu_node *rnp)
870{
871 return 0;
872}
873
874/*
875 * Because there is no preemptible RCU, there can be no readers blocked,
876 * so there is no need to check for blocked tasks. So check only for
877 * bogus qsmask values.
878 */
879static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
880{
881 WARN_ON_ONCE(rnp->qsmask);
882}
883
884/*
885 * Because preemptible RCU does not exist, it never has any callbacks
886 * to check.
887 */
888static void rcu_preempt_check_callbacks(void)
889{
890}
891
892/*
893 * Because preemptible RCU does not exist, rcu_barrier() is just
894 * another name for rcu_barrier_sched().
895 */
896void rcu_barrier(void)
897{
898 rcu_barrier_sched();
899}
900EXPORT_SYMBOL_GPL(rcu_barrier);
901
902/*
903 * Because preemptible RCU does not exist, it need not be initialized.
904 */
905static void __init __rcu_init_preempt(void)
906{
907}
908
909/*
910 * Because preemptible RCU does not exist, tasks cannot possibly exit
911 * while in preemptible RCU read-side critical sections.
912 */
913void exit_rcu(void)
914{
915}
916
917#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
918
919#ifdef CONFIG_RCU_BOOST
920
921static void rcu_wake_cond(struct task_struct *t, int status)
922{
923 /*
924 * If the thread is yielding, only wake it when this
925 * is invoked from idle
926 */
927 if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
928 wake_up_process(t);
929}
930
931/*
932 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
933 * or ->boost_tasks, advancing the pointer to the next task in the
934 * ->blkd_tasks list.
935 *
936 * Note that irqs must be enabled: boosting the task can block.
937 * Returns 1 if there are more tasks needing to be boosted.
938 */
939static int rcu_boost(struct rcu_node *rnp)
940{
941 unsigned long flags;
942 struct task_struct *t;
943 struct list_head *tb;
944
945 if (READ_ONCE(rnp->exp_tasks) == NULL &&
946 READ_ONCE(rnp->boost_tasks) == NULL)
947 return 0; /* Nothing left to boost. */
948
949 raw_spin_lock_irqsave_rcu_node(rnp, flags);
950
951 /*
952 * Recheck under the lock: all tasks in need of boosting
953 * might exit their RCU read-side critical sections on their own.
954 */
955 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
956 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
957 return 0;
958 }
959
960 /*
961 * Preferentially boost tasks blocking expedited grace periods.
962 * This cannot starve the normal grace periods because a second
963 * expedited grace period must boost all blocked tasks, including
964 * those blocking the pre-existing normal grace period.
965 */
966 if (rnp->exp_tasks != NULL)
967 tb = rnp->exp_tasks;
968 else
969 tb = rnp->boost_tasks;
970
971 /*
972 * We boost task t by manufacturing an rt_mutex that appears to
973 * be held by task t. We leave a pointer to that rt_mutex where
974 * task t can find it, and task t will release the mutex when it
975 * exits its outermost RCU read-side critical section. Then
976 * simply acquiring this artificial rt_mutex will boost task
977 * t's priority. (Thanks to tglx for suggesting this approach!)
978 *
979 * Note that task t must acquire rnp->lock to remove itself from
980 * the ->blkd_tasks list, which it will do from exit() if from
981 * nowhere else. We therefore are guaranteed that task t will
982 * stay around at least until we drop rnp->lock. Note that
983 * rnp->lock also resolves races between our priority boosting
984 * and task t's exiting its outermost RCU read-side critical
985 * section.
986 */
987 t = container_of(tb, struct task_struct, rcu_node_entry);
988 rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
989 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
990 /* Lock only for side effect: boosts task t's priority. */
991 rt_mutex_lock(&rnp->boost_mtx);
992 rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
993
994 return READ_ONCE(rnp->exp_tasks) != NULL ||
995 READ_ONCE(rnp->boost_tasks) != NULL;
996}
997
998/*
999 * Priority-boosting kthread, one per leaf rcu_node.
1000 */
1001static int rcu_boost_kthread(void *arg)
1002{
1003 struct rcu_node *rnp = (struct rcu_node *)arg;
1004 int spincnt = 0;
1005 int more2boost;
1006
1007 trace_rcu_utilization(TPS("Start boost kthread@init"));
1008 for (;;) {
1009 rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
1010 trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
1011 rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
1012 trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
1013 rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
1014 more2boost = rcu_boost(rnp);
1015 if (more2boost)
1016 spincnt++;
1017 else
1018 spincnt = 0;
1019 if (spincnt > 10) {
1020 rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
1021 trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
1022 schedule_timeout_interruptible(2);
1023 trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
1024 spincnt = 0;
1025 }
1026 }
1027 /* NOTREACHED */
1028 trace_rcu_utilization(TPS("End boost kthread@notreached"));
1029 return 0;
1030}
1031
1032/*
1033 * Check to see if it is time to start boosting RCU readers that are
1034 * blocking the current grace period, and, if so, tell the per-rcu_node
1035 * kthread to start boosting them. If there is an expedited grace
1036 * period in progress, it is always time to boost.
1037 *
1038 * The caller must hold rnp->lock, which this function releases.
1039 * The ->boost_kthread_task is immortal, so we don't need to worry
1040 * about it going away.
1041 */
1042static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1043 __releases(rnp->lock)
1044{
1045 struct task_struct *t;
1046
1047 raw_lockdep_assert_held_rcu_node(rnp);
1048 if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1049 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1050 return;
1051 }
1052 if (rnp->exp_tasks != NULL ||
1053 (rnp->gp_tasks != NULL &&
1054 rnp->boost_tasks == NULL &&
1055 rnp->qsmask == 0 &&
1056 ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1057 if (rnp->exp_tasks == NULL)
1058 rnp->boost_tasks = rnp->gp_tasks;
1059 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1060 t = rnp->boost_kthread_task;
1061 if (t)
1062 rcu_wake_cond(t, rnp->boost_kthread_status);
1063 } else {
1064 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1065 }
1066}
1067
1068/*
1069 * Wake up the per-CPU kthread to invoke RCU callbacks.
1070 */
1071static void invoke_rcu_callbacks_kthread(void)
1072{
1073 unsigned long flags;
1074
1075 local_irq_save(flags);
1076 __this_cpu_write(rcu_cpu_has_work, 1);
1077 if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
1078 current != __this_cpu_read(rcu_cpu_kthread_task)) {
1079 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
1080 __this_cpu_read(rcu_cpu_kthread_status));
1081 }
1082 local_irq_restore(flags);
1083}
1084
1085/*
1086 * Is the current CPU running the RCU-callbacks kthread?
1087 * Caller must have preemption disabled.
1088 */
1089static bool rcu_is_callbacks_kthread(void)
1090{
1091 return __this_cpu_read(rcu_cpu_kthread_task) == current;
1092}
1093
1094#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1095
1096/*
1097 * Do priority-boost accounting for the start of a new grace period.
1098 */
1099static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1100{
1101 rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1102}
1103
1104/*
1105 * Create an RCU-boost kthread for the specified node if one does not
1106 * already exist. We only create this kthread for preemptible RCU.
1107 * Returns zero if all is well, a negated errno otherwise.
1108 */
1109static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
1110 struct rcu_node *rnp)
1111{
1112 int rnp_index = rnp - &rsp->node[0];
1113 unsigned long flags;
1114 struct sched_param sp;
1115 struct task_struct *t;
1116
1117 if (rcu_state_p != rsp)
1118 return 0;
1119
1120 if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
1121 return 0;
1122
1123 rsp->boost = 1;
1124 if (rnp->boost_kthread_task != NULL)
1125 return 0;
1126 t = kthread_create(rcu_boost_kthread, (void *)rnp,
1127 "rcub/%d", rnp_index);
1128 if (IS_ERR(t))
1129 return PTR_ERR(t);
1130 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1131 rnp->boost_kthread_task = t;
1132 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1133 sp.sched_priority = kthread_prio;
1134 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1135 wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1136 return 0;
1137}
1138
1139static void rcu_kthread_do_work(void)
1140{
1141 rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
1142 rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
1143 rcu_preempt_do_callbacks();
1144}
1145
1146static void rcu_cpu_kthread_setup(unsigned int cpu)
1147{
1148 struct sched_param sp;
1149
1150 sp.sched_priority = kthread_prio;
1151 sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
1152}
1153
1154static void rcu_cpu_kthread_park(unsigned int cpu)
1155{
1156 per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1157}
1158
1159static int rcu_cpu_kthread_should_run(unsigned int cpu)
1160{
1161 return __this_cpu_read(rcu_cpu_has_work);
1162}
1163
1164/*
1165 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
1166 * RCU softirq used in flavors and configurations of RCU that do not
1167 * support RCU priority boosting.
1168 */
1169static void rcu_cpu_kthread(unsigned int cpu)
1170{
1171 unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
1172 char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
1173 int spincnt;
1174
1175 for (spincnt = 0; spincnt < 10; spincnt++) {
1176 trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
1177 local_bh_disable();
1178 *statusp = RCU_KTHREAD_RUNNING;
1179 this_cpu_inc(rcu_cpu_kthread_loops);
1180 local_irq_disable();
1181 work = *workp;
1182 *workp = 0;
1183 local_irq_enable();
1184 if (work)
1185 rcu_kthread_do_work();
1186 local_bh_enable();
1187 if (*workp == 0) {
1188 trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
1189 *statusp = RCU_KTHREAD_WAITING;
1190 return;
1191 }
1192 }
1193 *statusp = RCU_KTHREAD_YIELDING;
1194 trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
1195 schedule_timeout_interruptible(2);
1196 trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
1197 *statusp = RCU_KTHREAD_WAITING;
1198}
1199
1200/*
1201 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1202 * served by the rcu_node in question. The CPU hotplug lock is still
1203 * held, so the value of rnp->qsmaskinit will be stable.
1204 *
1205 * We don't include outgoingcpu in the affinity set, use -1 if there is
1206 * no outgoing CPU. If there are no CPUs left in the affinity set,
1207 * this function allows the kthread to execute on any CPU.
1208 */
1209static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1210{
1211 struct task_struct *t = rnp->boost_kthread_task;
1212 unsigned long mask = rcu_rnp_online_cpus(rnp);
1213 cpumask_var_t cm;
1214 int cpu;
1215
1216 if (!t)
1217 return;
1218 if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
1219 return;
1220 for_each_leaf_node_possible_cpu(rnp, cpu)
1221 if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
1222 cpu != outgoingcpu)
1223 cpumask_set_cpu(cpu, cm);
1224 if (cpumask_weight(cm) == 0)
1225 cpumask_setall(cm);
1226 set_cpus_allowed_ptr(t, cm);
1227 free_cpumask_var(cm);
1228}
1229
1230static struct smp_hotplug_thread rcu_cpu_thread_spec = {
1231 .store = &rcu_cpu_kthread_task,
1232 .thread_should_run = rcu_cpu_kthread_should_run,
1233 .thread_fn = rcu_cpu_kthread,
1234 .thread_comm = "rcuc/%u",
1235 .setup = rcu_cpu_kthread_setup,
1236 .park = rcu_cpu_kthread_park,
1237};
1238
1239/*
1240 * Spawn boost kthreads -- called as soon as the scheduler is running.
1241 */
1242static void __init rcu_spawn_boost_kthreads(void)
1243{
1244 struct rcu_node *rnp;
1245 int cpu;
1246
1247 for_each_possible_cpu(cpu)
1248 per_cpu(rcu_cpu_has_work, cpu) = 0;
1249 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
1250 rcu_for_each_leaf_node(rcu_state_p, rnp)
1251 (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1252}
1253
1254static void rcu_prepare_kthreads(int cpu)
1255{
1256 struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
1257 struct rcu_node *rnp = rdp->mynode;
1258
1259 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1260 if (rcu_scheduler_fully_active)
1261 (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
1262}
1263
1264#else /* #ifdef CONFIG_RCU_BOOST */
1265
1266static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
1267 __releases(rnp->lock)
1268{
1269 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1270}
1271
1272static void invoke_rcu_callbacks_kthread(void)
1273{
1274 WARN_ON_ONCE(1);
1275}
1276
1277static bool rcu_is_callbacks_kthread(void)
1278{
1279 return false;
1280}
1281
1282static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1283{
1284}
1285
1286static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1287{
1288}
1289
1290static void __init rcu_spawn_boost_kthreads(void)
1291{
1292}
1293
1294static void rcu_prepare_kthreads(int cpu)
1295{
1296}
1297
1298#endif /* #else #ifdef CONFIG_RCU_BOOST */
1299
1300#if !defined(CONFIG_RCU_FAST_NO_HZ)
1301
1302/*
1303 * Check to see if any future RCU-related work will need to be done
1304 * by the current CPU, even if none need be done immediately, returning
1305 * 1 if so. This function is part of the RCU implementation; it is -not-
1306 * an exported member of the RCU API.
1307 *
1308 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1309 * any flavor of RCU.
1310 */
1311int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1312{
1313 *nextevt = KTIME_MAX;
1314 return rcu_cpu_has_callbacks(NULL);
1315}
1316
1317/*
1318 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1319 * after it.
1320 */
1321static void rcu_cleanup_after_idle(void)
1322{
1323}
1324
1325/*
1326 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1327 * is nothing.
1328 */
1329static void rcu_prepare_for_idle(void)
1330{
1331}
1332
1333/*
1334 * Don't bother keeping a running count of the number of RCU callbacks
1335 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1336 */
1337static void rcu_idle_count_callbacks_posted(void)
1338{
1339}
1340
1341#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1342
1343/*
1344 * This code is invoked when a CPU goes idle, at which point we want
1345 * to have the CPU do everything required for RCU so that it can enter
1346 * the energy-efficient dyntick-idle mode. This is handled by a
1347 * state machine implemented by rcu_prepare_for_idle() below.
1348 *
1349 * The following three proprocessor symbols control this state machine:
1350 *
1351 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1352 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1353 * is sized to be roughly one RCU grace period. Those energy-efficiency
1354 * benchmarkers who might otherwise be tempted to set this to a large
1355 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1356 * system. And if you are -that- concerned about energy efficiency,
1357 * just power the system down and be done with it!
1358 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1359 * permitted to sleep in dyntick-idle mode with only lazy RCU
1360 * callbacks pending. Setting this too high can OOM your system.
1361 *
1362 * The values below work well in practice. If future workloads require
1363 * adjustment, they can be converted into kernel config parameters, though
1364 * making the state machine smarter might be a better option.
1365 */
1366#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1367#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1368
1369static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
1370module_param(rcu_idle_gp_delay, int, 0644);
1371static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
1372module_param(rcu_idle_lazy_gp_delay, int, 0644);
1373
1374/*
1375 * Try to advance callbacks for all flavors of RCU on the current CPU, but
1376 * only if it has been awhile since the last time we did so. Afterwards,
1377 * if there are any callbacks ready for immediate invocation, return true.
1378 */
1379static bool __maybe_unused rcu_try_advance_all_cbs(void)
1380{
1381 bool cbs_ready = false;
1382 struct rcu_data *rdp;
1383 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1384 struct rcu_node *rnp;
1385 struct rcu_state *rsp;
1386
1387 /* Exit early if we advanced recently. */
1388 if (jiffies == rdtp->last_advance_all)
1389 return false;
1390 rdtp->last_advance_all = jiffies;
1391
1392 for_each_rcu_flavor(rsp) {
1393 rdp = this_cpu_ptr(rsp->rda);
1394 rnp = rdp->mynode;
1395
1396 /*
1397 * Don't bother checking unless a grace period has
1398 * completed since we last checked and there are
1399 * callbacks not yet ready to invoke.
1400 */
1401 if ((rdp->completed != rnp->completed ||
1402 unlikely(READ_ONCE(rdp->gpwrap))) &&
1403 rcu_segcblist_pend_cbs(&rdp->cblist))
1404 note_gp_changes(rsp, rdp);
1405
1406 if (rcu_segcblist_ready_cbs(&rdp->cblist))
1407 cbs_ready = true;
1408 }
1409 return cbs_ready;
1410}
1411
1412/*
1413 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1414 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1415 * caller to set the timeout based on whether or not there are non-lazy
1416 * callbacks.
1417 *
1418 * The caller must have disabled interrupts.
1419 */
1420int rcu_needs_cpu(u64 basemono, u64 *nextevt)
1421{
1422 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1423 unsigned long dj;
1424
1425 lockdep_assert_irqs_disabled();
1426
1427 /* Snapshot to detect later posting of non-lazy callback. */
1428 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1429
1430 /* If no callbacks, RCU doesn't need the CPU. */
1431 if (!rcu_cpu_has_callbacks(&rdtp->all_lazy)) {
1432 *nextevt = KTIME_MAX;
1433 return 0;
1434 }
1435
1436 /* Attempt to advance callbacks. */
1437 if (rcu_try_advance_all_cbs()) {
1438 /* Some ready to invoke, so initiate later invocation. */
1439 invoke_rcu_core();
1440 return 1;
1441 }
1442 rdtp->last_accelerate = jiffies;
1443
1444 /* Request timer delay depending on laziness, and round. */
1445 if (!rdtp->all_lazy) {
1446 dj = round_up(rcu_idle_gp_delay + jiffies,
1447 rcu_idle_gp_delay) - jiffies;
1448 } else {
1449 dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
1450 }
1451 *nextevt = basemono + dj * TICK_NSEC;
1452 return 0;
1453}
1454
1455/*
1456 * Prepare a CPU for idle from an RCU perspective. The first major task
1457 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1458 * The second major task is to check to see if a non-lazy callback has
1459 * arrived at a CPU that previously had only lazy callbacks. The third
1460 * major task is to accelerate (that is, assign grace-period numbers to)
1461 * any recently arrived callbacks.
1462 *
1463 * The caller must have disabled interrupts.
1464 */
1465static void rcu_prepare_for_idle(void)
1466{
1467 bool needwake;
1468 struct rcu_data *rdp;
1469 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
1470 struct rcu_node *rnp;
1471 struct rcu_state *rsp;
1472 int tne;
1473
1474 lockdep_assert_irqs_disabled();
1475 if (rcu_is_nocb_cpu(smp_processor_id()))
1476 return;
1477
1478 /* Handle nohz enablement switches conservatively. */
1479 tne = READ_ONCE(tick_nohz_active);
1480 if (tne != rdtp->tick_nohz_enabled_snap) {
1481 if (rcu_cpu_has_callbacks(NULL))
1482 invoke_rcu_core(); /* force nohz to see update. */
1483 rdtp->tick_nohz_enabled_snap = tne;
1484 return;
1485 }
1486 if (!tne)
1487 return;
1488
1489 /*
1490 * If a non-lazy callback arrived at a CPU having only lazy
1491 * callbacks, invoke RCU core for the side-effect of recalculating
1492 * idle duration on re-entry to idle.
1493 */
1494 if (rdtp->all_lazy &&
1495 rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
1496 rdtp->all_lazy = false;
1497 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
1498 invoke_rcu_core();
1499 return;
1500 }
1501
1502 /*
1503 * If we have not yet accelerated this jiffy, accelerate all
1504 * callbacks on this CPU.
1505 */
1506 if (rdtp->last_accelerate == jiffies)
1507 return;
1508 rdtp->last_accelerate = jiffies;
1509 for_each_rcu_flavor(rsp) {
1510 rdp = this_cpu_ptr(rsp->rda);
1511 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1512 continue;
1513 rnp = rdp->mynode;
1514 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
1515 needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
1516 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
1517 if (needwake)
1518 rcu_gp_kthread_wake(rsp);
1519 }
1520}
1521
1522/*
1523 * Clean up for exit from idle. Attempt to advance callbacks based on
1524 * any grace periods that elapsed while the CPU was idle, and if any
1525 * callbacks are now ready to invoke, initiate invocation.
1526 */
1527static void rcu_cleanup_after_idle(void)
1528{
1529 lockdep_assert_irqs_disabled();
1530 if (rcu_is_nocb_cpu(smp_processor_id()))
1531 return;
1532 if (rcu_try_advance_all_cbs())
1533 invoke_rcu_core();
1534}
1535
1536/*
1537 * Keep a running count of the number of non-lazy callbacks posted
1538 * on this CPU. This running counter (which is never decremented) allows
1539 * rcu_prepare_for_idle() to detect when something out of the idle loop
1540 * posts a callback, even if an equal number of callbacks are invoked.
1541 * Of course, callbacks should only be posted from within a trace event
1542 * designed to be called from idle or from within RCU_NONIDLE().
1543 */
1544static void rcu_idle_count_callbacks_posted(void)
1545{
1546 __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
1547}
1548
1549/*
1550 * Data for flushing lazy RCU callbacks at OOM time.
1551 */
1552static atomic_t oom_callback_count;
1553static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
1554
1555/*
1556 * RCU OOM callback -- decrement the outstanding count and deliver the
1557 * wake-up if we are the last one.
1558 */
1559static void rcu_oom_callback(struct rcu_head *rhp)
1560{
1561 if (atomic_dec_and_test(&oom_callback_count))
1562 wake_up(&oom_callback_wq);
1563}
1564
1565/*
1566 * Post an rcu_oom_notify callback on the current CPU if it has at
1567 * least one lazy callback. This will unnecessarily post callbacks
1568 * to CPUs that already have a non-lazy callback at the end of their
1569 * callback list, but this is an infrequent operation, so accept some
1570 * extra overhead to keep things simple.
1571 */
1572static void rcu_oom_notify_cpu(void *unused)
1573{
1574 struct rcu_state *rsp;
1575 struct rcu_data *rdp;
1576
1577 for_each_rcu_flavor(rsp) {
1578 rdp = raw_cpu_ptr(rsp->rda);
1579 if (rcu_segcblist_n_lazy_cbs(&rdp->cblist)) {
1580 atomic_inc(&oom_callback_count);
1581 rsp->call(&rdp->oom_head, rcu_oom_callback);
1582 }
1583 }
1584}
1585
1586/*
1587 * If low on memory, ensure that each CPU has a non-lazy callback.
1588 * This will wake up CPUs that have only lazy callbacks, in turn
1589 * ensuring that they free up the corresponding memory in a timely manner.
1590 * Because an uncertain amount of memory will be freed in some uncertain
1591 * timeframe, we do not claim to have freed anything.
1592 */
1593static int rcu_oom_notify(struct notifier_block *self,
1594 unsigned long notused, void *nfreed)
1595{
1596 int cpu;
1597
1598 /* Wait for callbacks from earlier instance to complete. */
1599 wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
1600 smp_mb(); /* Ensure callback reuse happens after callback invocation. */
1601
1602 /*
1603 * Prevent premature wakeup: ensure that all increments happen
1604 * before there is a chance of the counter reaching zero.
1605 */
1606 atomic_set(&oom_callback_count, 1);
1607
1608 for_each_online_cpu(cpu) {
1609 smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
1610 cond_resched_rcu_qs();
1611 }
1612
1613 /* Unconditionally decrement: no need to wake ourselves up. */
1614 atomic_dec(&oom_callback_count);
1615
1616 return NOTIFY_OK;
1617}
1618
1619static struct notifier_block rcu_oom_nb = {
1620 .notifier_call = rcu_oom_notify
1621};
1622
1623static int __init rcu_register_oom_notifier(void)
1624{
1625 register_oom_notifier(&rcu_oom_nb);
1626 return 0;
1627}
1628early_initcall(rcu_register_oom_notifier);
1629
1630#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1631
1632#ifdef CONFIG_RCU_FAST_NO_HZ
1633
1634static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1635{
1636 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1637 unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
1638
1639 sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1640 rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
1641 ulong2long(nlpd),
1642 rdtp->all_lazy ? 'L' : '.',
1643 rdtp->tick_nohz_enabled_snap ? '.' : 'D');
1644}
1645
1646#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1647
1648static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
1649{
1650 *cp = '\0';
1651}
1652
1653#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1654
1655/* Initiate the stall-info list. */
1656static void print_cpu_stall_info_begin(void)
1657{
1658 pr_cont("\n");
1659}
1660
1661/*
1662 * Print out diagnostic information for the specified stalled CPU.
1663 *
1664 * If the specified CPU is aware of the current RCU grace period
1665 * (flavor specified by rsp), then print the number of scheduling
1666 * clock interrupts the CPU has taken during the time that it has
1667 * been aware. Otherwise, print the number of RCU grace periods
1668 * that this CPU is ignorant of, for example, "1" if the CPU was
1669 * aware of the previous grace period.
1670 *
1671 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1672 */
1673static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
1674{
1675 unsigned long delta;
1676 char fast_no_hz[72];
1677 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1678 struct rcu_dynticks *rdtp = rdp->dynticks;
1679 char *ticks_title;
1680 unsigned long ticks_value;
1681
1682 /*
1683 * We could be printing a lot while holding a spinlock. Avoid
1684 * triggering hard lockup.
1685 */
1686 touch_nmi_watchdog();
1687
1688 if (rsp->gpnum == rdp->gpnum) {
1689 ticks_title = "ticks this GP";
1690 ticks_value = rdp->ticks_this_gp;
1691 } else {
1692 ticks_title = "GPs behind";
1693 ticks_value = rsp->gpnum - rdp->gpnum;
1694 }
1695 print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
1696 delta = rdp->mynode->gpnum - rdp->rcu_iw_gpnum;
1697 pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%ld softirq=%u/%u fqs=%ld %s\n",
1698 cpu,
1699 "O."[!!cpu_online(cpu)],
1700 "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
1701 "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
1702 !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
1703 rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
1704 "!."[!delta],
1705 ticks_value, ticks_title,
1706 rcu_dynticks_snap(rdtp) & 0xfff,
1707 rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
1708 rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
1709 READ_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart,
1710 fast_no_hz);
1711}
1712
1713/* Terminate the stall-info list. */
1714static void print_cpu_stall_info_end(void)
1715{
1716 pr_err("\t");
1717}
1718
1719/* Zero ->ticks_this_gp for all flavors of RCU. */
1720static void zero_cpu_stall_ticks(struct rcu_data *rdp)
1721{
1722 rdp->ticks_this_gp = 0;
1723 rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
1724}
1725
1726/* Increment ->ticks_this_gp for all flavors of RCU. */
1727static void increment_cpu_stall_ticks(void)
1728{
1729 struct rcu_state *rsp;
1730
1731 for_each_rcu_flavor(rsp)
1732 raw_cpu_inc(rsp->rda->ticks_this_gp);
1733}
1734
1735#ifdef CONFIG_RCU_NOCB_CPU
1736
1737/*
1738 * Offload callback processing from the boot-time-specified set of CPUs
1739 * specified by rcu_nocb_mask. For each CPU in the set, there is a
1740 * kthread created that pulls the callbacks from the corresponding CPU,
1741 * waits for a grace period to elapse, and invokes the callbacks.
1742 * The no-CBs CPUs do a wake_up() on their kthread when they insert
1743 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
1744 * has been specified, in which case each kthread actively polls its
1745 * CPU. (Which isn't so great for energy efficiency, but which does
1746 * reduce RCU's overhead on that CPU.)
1747 *
1748 * This is intended to be used in conjunction with Frederic Weisbecker's
1749 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
1750 * running CPU-bound user-mode computations.
1751 *
1752 * Offloading of callback processing could also in theory be used as
1753 * an energy-efficiency measure because CPUs with no RCU callbacks
1754 * queued are more aggressive about entering dyntick-idle mode.
1755 */
1756
1757
1758/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
1759static int __init rcu_nocb_setup(char *str)
1760{
1761 alloc_bootmem_cpumask_var(&rcu_nocb_mask);
1762 cpulist_parse(str, rcu_nocb_mask);
1763 return 1;
1764}
1765__setup("rcu_nocbs=", rcu_nocb_setup);
1766
1767static int __init parse_rcu_nocb_poll(char *arg)
1768{
1769 rcu_nocb_poll = true;
1770 return 0;
1771}
1772early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
1773
1774/*
1775 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
1776 * grace period.
1777 */
1778static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
1779{
1780 swake_up_all(sq);
1781}
1782
1783/*
1784 * Set the root rcu_node structure's ->need_future_gp field
1785 * based on the sum of those of all rcu_node structures. This does
1786 * double-count the root rcu_node structure's requests, but this
1787 * is necessary to handle the possibility of a rcu_nocb_kthread()
1788 * having awakened during the time that the rcu_node structures
1789 * were being updated for the end of the previous grace period.
1790 */
1791static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
1792{
1793 rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
1794}
1795
1796static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
1797{
1798 return &rnp->nocb_gp_wq[rnp->completed & 0x1];
1799}
1800
1801static void rcu_init_one_nocb(struct rcu_node *rnp)
1802{
1803 init_swait_queue_head(&rnp->nocb_gp_wq[0]);
1804 init_swait_queue_head(&rnp->nocb_gp_wq[1]);
1805}
1806
1807/* Is the specified CPU a no-CBs CPU? */
1808bool rcu_is_nocb_cpu(int cpu)
1809{
1810 if (cpumask_available(rcu_nocb_mask))
1811 return cpumask_test_cpu(cpu, rcu_nocb_mask);
1812 return false;
1813}
1814
1815/*
1816 * Kick the leader kthread for this NOCB group. Caller holds ->nocb_lock
1817 * and this function releases it.
1818 */
1819static void __wake_nocb_leader(struct rcu_data *rdp, bool force,
1820 unsigned long flags)
1821 __releases(rdp->nocb_lock)
1822{
1823 struct rcu_data *rdp_leader = rdp->nocb_leader;
1824
1825 lockdep_assert_held(&rdp->nocb_lock);
1826 if (!READ_ONCE(rdp_leader->nocb_kthread)) {
1827 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1828 return;
1829 }
1830 if (rdp_leader->nocb_leader_sleep || force) {
1831 /* Prior smp_mb__after_atomic() orders against prior enqueue. */
1832 WRITE_ONCE(rdp_leader->nocb_leader_sleep, false);
1833 del_timer(&rdp->nocb_timer);
1834 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1835 smp_mb(); /* ->nocb_leader_sleep before swake_up(). */
1836 swake_up(&rdp_leader->nocb_wq);
1837 } else {
1838 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1839 }
1840}
1841
1842/*
1843 * Kick the leader kthread for this NOCB group, but caller has not
1844 * acquired locks.
1845 */
1846static void wake_nocb_leader(struct rcu_data *rdp, bool force)
1847{
1848 unsigned long flags;
1849
1850 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
1851 __wake_nocb_leader(rdp, force, flags);
1852}
1853
1854/*
1855 * Arrange to wake the leader kthread for this NOCB group at some
1856 * future time when it is safe to do so.
1857 */
1858static void wake_nocb_leader_defer(struct rcu_data *rdp, int waketype,
1859 const char *reason)
1860{
1861 unsigned long flags;
1862
1863 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
1864 if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
1865 mod_timer(&rdp->nocb_timer, jiffies + 1);
1866 WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
1867 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, reason);
1868 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
1869}
1870
1871/*
1872 * Does the specified CPU need an RCU callback for the specified flavor
1873 * of rcu_barrier()?
1874 */
1875static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
1876{
1877 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1878 unsigned long ret;
1879#ifdef CONFIG_PROVE_RCU
1880 struct rcu_head *rhp;
1881#endif /* #ifdef CONFIG_PROVE_RCU */
1882
1883 /*
1884 * Check count of all no-CBs callbacks awaiting invocation.
1885 * There needs to be a barrier before this function is called,
1886 * but associated with a prior determination that no more
1887 * callbacks would be posted. In the worst case, the first
1888 * barrier in _rcu_barrier() suffices (but the caller cannot
1889 * necessarily rely on this, not a substitute for the caller
1890 * getting the concurrency design right!). There must also be
1891 * a barrier between the following load an posting of a callback
1892 * (if a callback is in fact needed). This is associated with an
1893 * atomic_inc() in the caller.
1894 */
1895 ret = atomic_long_read(&rdp->nocb_q_count);
1896
1897#ifdef CONFIG_PROVE_RCU
1898 rhp = READ_ONCE(rdp->nocb_head);
1899 if (!rhp)
1900 rhp = READ_ONCE(rdp->nocb_gp_head);
1901 if (!rhp)
1902 rhp = READ_ONCE(rdp->nocb_follower_head);
1903
1904 /* Having no rcuo kthread but CBs after scheduler starts is bad! */
1905 if (!READ_ONCE(rdp->nocb_kthread) && rhp &&
1906 rcu_scheduler_fully_active) {
1907 /* RCU callback enqueued before CPU first came online??? */
1908 pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
1909 cpu, rhp->func);
1910 WARN_ON_ONCE(1);
1911 }
1912#endif /* #ifdef CONFIG_PROVE_RCU */
1913
1914 return !!ret;
1915}
1916
1917/*
1918 * Enqueue the specified string of rcu_head structures onto the specified
1919 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
1920 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
1921 * counts are supplied by rhcount and rhcount_lazy.
1922 *
1923 * If warranted, also wake up the kthread servicing this CPUs queues.
1924 */
1925static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
1926 struct rcu_head *rhp,
1927 struct rcu_head **rhtp,
1928 int rhcount, int rhcount_lazy,
1929 unsigned long flags)
1930{
1931 int len;
1932 struct rcu_head **old_rhpp;
1933 struct task_struct *t;
1934
1935 /* Enqueue the callback on the nocb list and update counts. */
1936 atomic_long_add(rhcount, &rdp->nocb_q_count);
1937 /* rcu_barrier() relies on ->nocb_q_count add before xchg. */
1938 old_rhpp = xchg(&rdp->nocb_tail, rhtp);
1939 WRITE_ONCE(*old_rhpp, rhp);
1940 atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
1941 smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
1942
1943 /* If we are not being polled and there is a kthread, awaken it ... */
1944 t = READ_ONCE(rdp->nocb_kthread);
1945 if (rcu_nocb_poll || !t) {
1946 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
1947 TPS("WakeNotPoll"));
1948 return;
1949 }
1950 len = atomic_long_read(&rdp->nocb_q_count);
1951 if (old_rhpp == &rdp->nocb_head) {
1952 if (!irqs_disabled_flags(flags)) {
1953 /* ... if queue was empty ... */
1954 wake_nocb_leader(rdp, false);
1955 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
1956 TPS("WakeEmpty"));
1957 } else {
1958 wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE,
1959 TPS("WakeEmptyIsDeferred"));
1960 }
1961 rdp->qlen_last_fqs_check = 0;
1962 } else if (len > rdp->qlen_last_fqs_check + qhimark) {
1963 /* ... or if many callbacks queued. */
1964 if (!irqs_disabled_flags(flags)) {
1965 wake_nocb_leader(rdp, true);
1966 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
1967 TPS("WakeOvf"));
1968 } else {
1969 wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE,
1970 TPS("WakeOvfIsDeferred"));
1971 }
1972 rdp->qlen_last_fqs_check = LONG_MAX / 2;
1973 } else {
1974 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
1975 }
1976 return;
1977}
1978
1979/*
1980 * This is a helper for __call_rcu(), which invokes this when the normal
1981 * callback queue is inoperable. If this is not a no-CBs CPU, this
1982 * function returns failure back to __call_rcu(), which can complain
1983 * appropriately.
1984 *
1985 * Otherwise, this function queues the callback where the corresponding
1986 * "rcuo" kthread can find it.
1987 */
1988static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
1989 bool lazy, unsigned long flags)
1990{
1991
1992 if (!rcu_is_nocb_cpu(rdp->cpu))
1993 return false;
1994 __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
1995 if (__is_kfree_rcu_offset((unsigned long)rhp->func))
1996 trace_rcu_kfree_callback(rdp->rsp->name, rhp,
1997 (unsigned long)rhp->func,
1998 -atomic_long_read(&rdp->nocb_q_count_lazy),
1999 -atomic_long_read(&rdp->nocb_q_count));
2000 else
2001 trace_rcu_callback(rdp->rsp->name, rhp,
2002 -atomic_long_read(&rdp->nocb_q_count_lazy),
2003 -atomic_long_read(&rdp->nocb_q_count));
2004
2005 /*
2006 * If called from an extended quiescent state with interrupts
2007 * disabled, invoke the RCU core in order to allow the idle-entry
2008 * deferred-wakeup check to function.
2009 */
2010 if (irqs_disabled_flags(flags) &&
2011 !rcu_is_watching() &&
2012 cpu_online(smp_processor_id()))
2013 invoke_rcu_core();
2014
2015 return true;
2016}
2017
2018/*
2019 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2020 * not a no-CBs CPU.
2021 */
2022static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
2023 struct rcu_data *rdp,
2024 unsigned long flags)
2025{
2026 lockdep_assert_irqs_disabled();
2027 if (!rcu_is_nocb_cpu(smp_processor_id()))
2028 return false; /* Not NOCBs CPU, caller must migrate CBs. */
2029 __call_rcu_nocb_enqueue(my_rdp, rcu_segcblist_head(&rdp->cblist),
2030 rcu_segcblist_tail(&rdp->cblist),
2031 rcu_segcblist_n_cbs(&rdp->cblist),
2032 rcu_segcblist_n_lazy_cbs(&rdp->cblist), flags);
2033 rcu_segcblist_init(&rdp->cblist);
2034 rcu_segcblist_disable(&rdp->cblist);
2035 return true;
2036}
2037
2038/*
2039 * If necessary, kick off a new grace period, and either way wait
2040 * for a subsequent grace period to complete.
2041 */
2042static void rcu_nocb_wait_gp(struct rcu_data *rdp)
2043{
2044 unsigned long c;
2045 bool d;
2046 unsigned long flags;
2047 bool needwake;
2048 struct rcu_node *rnp = rdp->mynode;
2049
2050 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2051 needwake = rcu_start_future_gp(rnp, rdp, &c);
2052 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2053 if (needwake)
2054 rcu_gp_kthread_wake(rdp->rsp);
2055
2056 /*
2057 * Wait for the grace period. Do so interruptibly to avoid messing
2058 * up the load average.
2059 */
2060 trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
2061 for (;;) {
2062 swait_event_interruptible(
2063 rnp->nocb_gp_wq[c & 0x1],
2064 (d = ULONG_CMP_GE(READ_ONCE(rnp->completed), c)));
2065 if (likely(d))
2066 break;
2067 WARN_ON(signal_pending(current));
2068 trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
2069 }
2070 trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
2071 smp_mb(); /* Ensure that CB invocation happens after GP end. */
2072}
2073
2074/*
2075 * Leaders come here to wait for additional callbacks to show up.
2076 * This function does not return until callbacks appear.
2077 */
2078static void nocb_leader_wait(struct rcu_data *my_rdp)
2079{
2080 bool firsttime = true;
2081 unsigned long flags;
2082 bool gotcbs;
2083 struct rcu_data *rdp;
2084 struct rcu_head **tail;
2085
2086wait_again:
2087
2088 /* Wait for callbacks to appear. */
2089 if (!rcu_nocb_poll) {
2090 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, TPS("Sleep"));
2091 swait_event_interruptible(my_rdp->nocb_wq,
2092 !READ_ONCE(my_rdp->nocb_leader_sleep));
2093 raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags);
2094 my_rdp->nocb_leader_sleep = true;
2095 WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
2096 del_timer(&my_rdp->nocb_timer);
2097 raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags);
2098 } else if (firsttime) {
2099 firsttime = false; /* Don't drown trace log with "Poll"! */
2100 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, TPS("Poll"));
2101 }
2102
2103 /*
2104 * Each pass through the following loop checks a follower for CBs.
2105 * We are our own first follower. Any CBs found are moved to
2106 * nocb_gp_head, where they await a grace period.
2107 */
2108 gotcbs = false;
2109 smp_mb(); /* wakeup and _sleep before ->nocb_head reads. */
2110 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
2111 rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head);
2112 if (!rdp->nocb_gp_head)
2113 continue; /* No CBs here, try next follower. */
2114
2115 /* Move callbacks to wait-for-GP list, which is empty. */
2116 WRITE_ONCE(rdp->nocb_head, NULL);
2117 rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
2118 gotcbs = true;
2119 }
2120
2121 /* No callbacks? Sleep a bit if polling, and go retry. */
2122 if (unlikely(!gotcbs)) {
2123 WARN_ON(signal_pending(current));
2124 if (rcu_nocb_poll) {
2125 schedule_timeout_interruptible(1);
2126 } else {
2127 trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
2128 TPS("WokeEmpty"));
2129 }
2130 goto wait_again;
2131 }
2132
2133 /* Wait for one grace period. */
2134 rcu_nocb_wait_gp(my_rdp);
2135
2136 /* Each pass through the following loop wakes a follower, if needed. */
2137 for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
2138 if (!rcu_nocb_poll &&
2139 READ_ONCE(rdp->nocb_head) &&
2140 READ_ONCE(my_rdp->nocb_leader_sleep)) {
2141 raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags);
2142 my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/
2143 raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags);
2144 }
2145 if (!rdp->nocb_gp_head)
2146 continue; /* No CBs, so no need to wake follower. */
2147
2148 /* Append callbacks to follower's "done" list. */
2149 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
2150 tail = rdp->nocb_follower_tail;
2151 rdp->nocb_follower_tail = rdp->nocb_gp_tail;
2152 *tail = rdp->nocb_gp_head;
2153 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
2154 if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
2155 /* List was empty, so wake up the follower. */
2156 swake_up(&rdp->nocb_wq);
2157 }
2158 }
2159
2160 /* If we (the leader) don't have CBs, go wait some more. */
2161 if (!my_rdp->nocb_follower_head)
2162 goto wait_again;
2163}
2164
2165/*
2166 * Followers come here to wait for additional callbacks to show up.
2167 * This function does not return until callbacks appear.
2168 */
2169static void nocb_follower_wait(struct rcu_data *rdp)
2170{
2171 for (;;) {
2172 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("FollowerSleep"));
2173 swait_event_interruptible(rdp->nocb_wq,
2174 READ_ONCE(rdp->nocb_follower_head));
2175 if (smp_load_acquire(&rdp->nocb_follower_head)) {
2176 /* ^^^ Ensure CB invocation follows _head test. */
2177 return;
2178 }
2179 WARN_ON(signal_pending(current));
2180 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeEmpty"));
2181 }
2182}
2183
2184/*
2185 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
2186 * callbacks queued by the corresponding no-CBs CPU, however, there is
2187 * an optional leader-follower relationship so that the grace-period
2188 * kthreads don't have to do quite so many wakeups.
2189 */
2190static int rcu_nocb_kthread(void *arg)
2191{
2192 int c, cl;
2193 unsigned long flags;
2194 struct rcu_head *list;
2195 struct rcu_head *next;
2196 struct rcu_head **tail;
2197 struct rcu_data *rdp = arg;
2198
2199 /* Each pass through this loop invokes one batch of callbacks */
2200 for (;;) {
2201 /* Wait for callbacks. */
2202 if (rdp->nocb_leader == rdp)
2203 nocb_leader_wait(rdp);
2204 else
2205 nocb_follower_wait(rdp);
2206
2207 /* Pull the ready-to-invoke callbacks onto local list. */
2208 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
2209 list = rdp->nocb_follower_head;
2210 rdp->nocb_follower_head = NULL;
2211 tail = rdp->nocb_follower_tail;
2212 rdp->nocb_follower_tail = &rdp->nocb_follower_head;
2213 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
2214 BUG_ON(!list);
2215 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeNonEmpty"));
2216
2217 /* Each pass through the following loop invokes a callback. */
2218 trace_rcu_batch_start(rdp->rsp->name,
2219 atomic_long_read(&rdp->nocb_q_count_lazy),
2220 atomic_long_read(&rdp->nocb_q_count), -1);
2221 c = cl = 0;
2222 while (list) {
2223 next = list->next;
2224 /* Wait for enqueuing to complete, if needed. */
2225 while (next == NULL && &list->next != tail) {
2226 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2227 TPS("WaitQueue"));
2228 schedule_timeout_interruptible(1);
2229 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
2230 TPS("WokeQueue"));
2231 next = list->next;
2232 }
2233 debug_rcu_head_unqueue(list);
2234 local_bh_disable();
2235 if (__rcu_reclaim(rdp->rsp->name, list))
2236 cl++;
2237 c++;
2238 local_bh_enable();
2239 cond_resched_rcu_qs();
2240 list = next;
2241 }
2242 trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
2243 smp_mb__before_atomic(); /* _add after CB invocation. */
2244 atomic_long_add(-c, &rdp->nocb_q_count);
2245 atomic_long_add(-cl, &rdp->nocb_q_count_lazy);
2246 }
2247 return 0;
2248}
2249
2250/* Is a deferred wakeup of rcu_nocb_kthread() required? */
2251static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2252{
2253 return READ_ONCE(rdp->nocb_defer_wakeup);
2254}
2255
2256/* Do a deferred wakeup of rcu_nocb_kthread(). */
2257static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
2258{
2259 unsigned long flags;
2260 int ndw;
2261
2262 raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
2263 if (!rcu_nocb_need_deferred_wakeup(rdp)) {
2264 raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
2265 return;
2266 }
2267 ndw = READ_ONCE(rdp->nocb_defer_wakeup);
2268 WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
2269 __wake_nocb_leader(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
2270 trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake"));
2271}
2272
2273/* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
2274static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
2275{
2276 struct rcu_data *rdp = from_timer(rdp, t, nocb_timer);
2277
2278 do_nocb_deferred_wakeup_common(rdp);
2279}
2280
2281/*
2282 * Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
2283 * This means we do an inexact common-case check. Note that if
2284 * we miss, ->nocb_timer will eventually clean things up.
2285 */
2286static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2287{
2288 if (rcu_nocb_need_deferred_wakeup(rdp))
2289 do_nocb_deferred_wakeup_common(rdp);
2290}
2291
2292void __init rcu_init_nohz(void)
2293{
2294 int cpu;
2295 bool need_rcu_nocb_mask = true;
2296 struct rcu_state *rsp;
2297
2298#if defined(CONFIG_NO_HZ_FULL)
2299 if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
2300 need_rcu_nocb_mask = true;
2301#endif /* #if defined(CONFIG_NO_HZ_FULL) */
2302
2303 if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) {
2304 if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
2305 pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
2306 return;
2307 }
2308 }
2309 if (!cpumask_available(rcu_nocb_mask))
2310 return;
2311
2312#if defined(CONFIG_NO_HZ_FULL)
2313 if (tick_nohz_full_running)
2314 cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
2315#endif /* #if defined(CONFIG_NO_HZ_FULL) */
2316
2317 if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
2318 pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
2319 cpumask_and(rcu_nocb_mask, cpu_possible_mask,
2320 rcu_nocb_mask);
2321 }
2322 if (cpumask_empty(rcu_nocb_mask))
2323 pr_info("\tOffload RCU callbacks from CPUs: (none).\n");
2324 else
2325 pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
2326 cpumask_pr_args(rcu_nocb_mask));
2327 if (rcu_nocb_poll)
2328 pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
2329
2330 for_each_rcu_flavor(rsp) {
2331 for_each_cpu(cpu, rcu_nocb_mask)
2332 init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu));
2333 rcu_organize_nocb_kthreads(rsp);
2334 }
2335}
2336
2337/* Initialize per-rcu_data variables for no-CBs CPUs. */
2338static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2339{
2340 rdp->nocb_tail = &rdp->nocb_head;
2341 init_swait_queue_head(&rdp->nocb_wq);
2342 rdp->nocb_follower_tail = &rdp->nocb_follower_head;
2343 raw_spin_lock_init(&rdp->nocb_lock);
2344 timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
2345}
2346
2347/*
2348 * If the specified CPU is a no-CBs CPU that does not already have its
2349 * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are
2350 * brought online out of order, this can require re-organizing the
2351 * leader-follower relationships.
2352 */
2353static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu)
2354{
2355 struct rcu_data *rdp;
2356 struct rcu_data *rdp_last;
2357 struct rcu_data *rdp_old_leader;
2358 struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu);
2359 struct task_struct *t;
2360
2361 /*
2362 * If this isn't a no-CBs CPU or if it already has an rcuo kthread,
2363 * then nothing to do.
2364 */
2365 if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread)
2366 return;
2367
2368 /* If we didn't spawn the leader first, reorganize! */
2369 rdp_old_leader = rdp_spawn->nocb_leader;
2370 if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) {
2371 rdp_last = NULL;
2372 rdp = rdp_old_leader;
2373 do {
2374 rdp->nocb_leader = rdp_spawn;
2375 if (rdp_last && rdp != rdp_spawn)
2376 rdp_last->nocb_next_follower = rdp;
2377 if (rdp == rdp_spawn) {
2378 rdp = rdp->nocb_next_follower;
2379 } else {
2380 rdp_last = rdp;
2381 rdp = rdp->nocb_next_follower;
2382 rdp_last->nocb_next_follower = NULL;
2383 }
2384 } while (rdp);
2385 rdp_spawn->nocb_next_follower = rdp_old_leader;
2386 }
2387
2388 /* Spawn the kthread for this CPU and RCU flavor. */
2389 t = kthread_run(rcu_nocb_kthread, rdp_spawn,
2390 "rcuo%c/%d", rsp->abbr, cpu);
2391 BUG_ON(IS_ERR(t));
2392 WRITE_ONCE(rdp_spawn->nocb_kthread, t);
2393}
2394
2395/*
2396 * If the specified CPU is a no-CBs CPU that does not already have its
2397 * rcuo kthreads, spawn them.
2398 */
2399static void rcu_spawn_all_nocb_kthreads(int cpu)
2400{
2401 struct rcu_state *rsp;
2402
2403 if (rcu_scheduler_fully_active)
2404 for_each_rcu_flavor(rsp)
2405 rcu_spawn_one_nocb_kthread(rsp, cpu);
2406}
2407
2408/*
2409 * Once the scheduler is running, spawn rcuo kthreads for all online
2410 * no-CBs CPUs. This assumes that the early_initcall()s happen before
2411 * non-boot CPUs come online -- if this changes, we will need to add
2412 * some mutual exclusion.
2413 */
2414static void __init rcu_spawn_nocb_kthreads(void)
2415{
2416 int cpu;
2417
2418 for_each_online_cpu(cpu)
2419 rcu_spawn_all_nocb_kthreads(cpu);
2420}
2421
2422/* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */
2423static int rcu_nocb_leader_stride = -1;
2424module_param(rcu_nocb_leader_stride, int, 0444);
2425
2426/*
2427 * Initialize leader-follower relationships for all no-CBs CPU.
2428 */
2429static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp)
2430{
2431 int cpu;
2432 int ls = rcu_nocb_leader_stride;
2433 int nl = 0; /* Next leader. */
2434 struct rcu_data *rdp;
2435 struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */
2436 struct rcu_data *rdp_prev = NULL;
2437
2438 if (!cpumask_available(rcu_nocb_mask))
2439 return;
2440 if (ls == -1) {
2441 ls = int_sqrt(nr_cpu_ids);
2442 rcu_nocb_leader_stride = ls;
2443 }
2444
2445 /*
2446 * Each pass through this loop sets up one rcu_data structure.
2447 * Should the corresponding CPU come online in the future, then
2448 * we will spawn the needed set of rcu_nocb_kthread() kthreads.
2449 */
2450 for_each_cpu(cpu, rcu_nocb_mask) {
2451 rdp = per_cpu_ptr(rsp->rda, cpu);
2452 if (rdp->cpu >= nl) {
2453 /* New leader, set up for followers & next leader. */
2454 nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
2455 rdp->nocb_leader = rdp;
2456 rdp_leader = rdp;
2457 } else {
2458 /* Another follower, link to previous leader. */
2459 rdp->nocb_leader = rdp_leader;
2460 rdp_prev->nocb_next_follower = rdp;
2461 }
2462 rdp_prev = rdp;
2463 }
2464}
2465
2466/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2467static bool init_nocb_callback_list(struct rcu_data *rdp)
2468{
2469 if (!rcu_is_nocb_cpu(rdp->cpu))
2470 return false;
2471
2472 /* If there are early-boot callbacks, move them to nocb lists. */
2473 if (!rcu_segcblist_empty(&rdp->cblist)) {
2474 rdp->nocb_head = rcu_segcblist_head(&rdp->cblist);
2475 rdp->nocb_tail = rcu_segcblist_tail(&rdp->cblist);
2476 atomic_long_set(&rdp->nocb_q_count,
2477 rcu_segcblist_n_cbs(&rdp->cblist));
2478 atomic_long_set(&rdp->nocb_q_count_lazy,
2479 rcu_segcblist_n_lazy_cbs(&rdp->cblist));
2480 rcu_segcblist_init(&rdp->cblist);
2481 }
2482 rcu_segcblist_disable(&rdp->cblist);
2483 return true;
2484}
2485
2486#else /* #ifdef CONFIG_RCU_NOCB_CPU */
2487
2488static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
2489{
2490 WARN_ON_ONCE(1); /* Should be dead code. */
2491 return false;
2492}
2493
2494static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
2495{
2496}
2497
2498static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
2499{
2500}
2501
2502static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
2503{
2504 return NULL;
2505}
2506
2507static void rcu_init_one_nocb(struct rcu_node *rnp)
2508{
2509}
2510
2511static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
2512 bool lazy, unsigned long flags)
2513{
2514 return false;
2515}
2516
2517static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
2518 struct rcu_data *rdp,
2519 unsigned long flags)
2520{
2521 return false;
2522}
2523
2524static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
2525{
2526}
2527
2528static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
2529{
2530 return false;
2531}
2532
2533static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
2534{
2535}
2536
2537static void rcu_spawn_all_nocb_kthreads(int cpu)
2538{
2539}
2540
2541static void __init rcu_spawn_nocb_kthreads(void)
2542{
2543}
2544
2545static bool init_nocb_callback_list(struct rcu_data *rdp)
2546{
2547 return false;
2548}
2549
2550#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
2551
2552/*
2553 * An adaptive-ticks CPU can potentially execute in kernel mode for an
2554 * arbitrarily long period of time with the scheduling-clock tick turned
2555 * off. RCU will be paying attention to this CPU because it is in the
2556 * kernel, but the CPU cannot be guaranteed to be executing the RCU state
2557 * machine because the scheduling-clock tick has been disabled. Therefore,
2558 * if an adaptive-ticks CPU is failing to respond to the current grace
2559 * period and has not be idle from an RCU perspective, kick it.
2560 */
2561static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
2562{
2563#ifdef CONFIG_NO_HZ_FULL
2564 if (tick_nohz_full_cpu(cpu))
2565 smp_send_reschedule(cpu);
2566#endif /* #ifdef CONFIG_NO_HZ_FULL */
2567}
2568
2569/*
2570 * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
2571 * grace-period kthread will do force_quiescent_state() processing?
2572 * The idea is to avoid waking up RCU core processing on such a
2573 * CPU unless the grace period has extended for too long.
2574 *
2575 * This code relies on the fact that all NO_HZ_FULL CPUs are also
2576 * CONFIG_RCU_NOCB_CPU CPUs.
2577 */
2578static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
2579{
2580#ifdef CONFIG_NO_HZ_FULL
2581 if (tick_nohz_full_cpu(smp_processor_id()) &&
2582 (!rcu_gp_in_progress(rsp) ||
2583 ULONG_CMP_LT(jiffies, READ_ONCE(rsp->gp_start) + HZ)))
2584 return true;
2585#endif /* #ifdef CONFIG_NO_HZ_FULL */
2586 return false;
2587}
2588
2589/*
2590 * Bind the grace-period kthread for the sysidle flavor of RCU to the
2591 * timekeeping CPU.
2592 */
2593static void rcu_bind_gp_kthread(void)
2594{
2595 int __maybe_unused cpu;
2596
2597 if (!tick_nohz_full_enabled())
2598 return;
2599 housekeeping_affine(current, HK_FLAG_RCU);
2600}
2601
2602/* Record the current task on dyntick-idle entry. */
2603static void rcu_dynticks_task_enter(void)
2604{
2605#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2606 WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
2607#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
2608}
2609
2610/* Record no current task on dyntick-idle exit. */
2611static void rcu_dynticks_task_exit(void)
2612{
2613#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
2614 WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
2615#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
2616}