1 /* SPDX-License-Identifier: GPL-2.0+ */
3 * Task-based RCU implementations.
5 * Copyright (C) 2020 Paul E. McKenney
8 #ifdef CONFIG_TASKS_RCU_GENERIC
10 ////////////////////////////////////////////////////////////////////////
12 // Generic data structures.
15 typedef void (*rcu_tasks_gp_func_t)(struct rcu_tasks *rtp);
16 typedef void (*pregp_func_t)(void);
17 typedef void (*pertask_func_t)(struct task_struct *t, struct list_head *hop);
18 typedef void (*postscan_func_t)(struct list_head *hop);
19 typedef void (*holdouts_func_t)(struct list_head *hop, bool ndrpt, bool *frptp);
20 typedef void (*postgp_func_t)(struct rcu_tasks *rtp);
23 * struct rcu_tasks - Definition for a Tasks-RCU-like mechanism.
24 * @cbs_head: Head of callback list.
25 * @cbs_tail: Tail pointer for callback list.
26 * @cbs_wq: Wait queue allowing new callback to get kthread's attention.
27 * @cbs_lock: Lock protecting callback list.
28 * @kthread_ptr: This flavor's grace-period/callback-invocation kthread.
29 * @gp_func: This flavor's grace-period-wait function.
30 * @gp_state: Grace period's most recent state transition (debugging).
31 * @gp_sleep: Per-grace-period sleep to prevent CPU-bound looping.
32 * @init_fract: Initial backoff sleep interval.
33 * @gp_jiffies: Time of last @gp_state transition.
34 * @gp_start: Most recent grace-period start in jiffies.
35 * @n_gps: Number of grace periods completed since boot.
36 * @n_ipis: Number of IPIs sent to encourage grace periods to end.
37 * @n_ipis_fails: Number of IPI-send failures.
38 * @pregp_func: This flavor's pre-grace-period function (optional).
39 * @pertask_func: This flavor's per-task scan function (optional).
40 * @postscan_func: This flavor's post-task scan function (optional).
41 * @holdouts_func: This flavor's holdout-list scan function (optional).
42 * @postgp_func: This flavor's post-grace-period function (optional).
43 * @call_func: This flavor's call_rcu()-equivalent function.
44 * @name: This flavor's textual name.
45 * @kname: This flavor's kthread name.
48 struct rcu_head *cbs_head;
49 struct rcu_head **cbs_tail;
50 struct wait_queue_head cbs_wq;
51 raw_spinlock_t cbs_lock;
55 unsigned long gp_jiffies;
56 unsigned long gp_start;
59 unsigned long n_ipis_fails;
60 struct task_struct *kthread_ptr;
61 rcu_tasks_gp_func_t gp_func;
62 pregp_func_t pregp_func;
63 pertask_func_t pertask_func;
64 postscan_func_t postscan_func;
65 holdouts_func_t holdouts_func;
66 postgp_func_t postgp_func;
67 call_rcu_func_t call_func;
72 #define DEFINE_RCU_TASKS(rt_name, gp, call, n) \
73 static struct rcu_tasks rt_name = \
75 .cbs_tail = &rt_name.cbs_head, \
76 .cbs_wq = __WAIT_QUEUE_HEAD_INITIALIZER(rt_name.cbs_wq), \
77 .cbs_lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name.cbs_lock), \
84 /* Track exiting tasks in order to allow them to be waited for. */
85 DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu);
87 /* Avoid IPIing CPUs early in the grace period. */
88 #define RCU_TASK_IPI_DELAY (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) ? HZ / 2 : 0)
89 static int rcu_task_ipi_delay __read_mostly = RCU_TASK_IPI_DELAY;
90 module_param(rcu_task_ipi_delay, int, 0644);
92 /* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */
93 #define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10)
94 static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT;
95 module_param(rcu_task_stall_timeout, int, 0644);
97 /* RCU tasks grace-period state for debugging. */
99 #define RTGS_WAIT_WAIT_CBS 1
100 #define RTGS_WAIT_GP 2
101 #define RTGS_PRE_WAIT_GP 3
102 #define RTGS_SCAN_TASKLIST 4
103 #define RTGS_POST_SCAN_TASKLIST 5
104 #define RTGS_WAIT_SCAN_HOLDOUTS 6
105 #define RTGS_SCAN_HOLDOUTS 7
106 #define RTGS_POST_GP 8
107 #define RTGS_WAIT_READERS 9
108 #define RTGS_INVOKE_CBS 10
109 #define RTGS_WAIT_CBS 11
110 #ifndef CONFIG_TINY_RCU
111 static const char * const rcu_tasks_gp_state_names[] = {
113 "RTGS_WAIT_WAIT_CBS",
116 "RTGS_SCAN_TASKLIST",
117 "RTGS_POST_SCAN_TASKLIST",
118 "RTGS_WAIT_SCAN_HOLDOUTS",
119 "RTGS_SCAN_HOLDOUTS",
125 #endif /* #ifndef CONFIG_TINY_RCU */
127 ////////////////////////////////////////////////////////////////////////
131 /* Record grace-period phase and time. */
132 static void set_tasks_gp_state(struct rcu_tasks *rtp, int newstate)
134 rtp->gp_state = newstate;
135 rtp->gp_jiffies = jiffies;
138 #ifndef CONFIG_TINY_RCU
139 /* Return state name. */
140 static const char *tasks_gp_state_getname(struct rcu_tasks *rtp)
142 int i = data_race(rtp->gp_state); // Let KCSAN detect update races
143 int j = READ_ONCE(i); // Prevent the compiler from reading twice
145 if (j >= ARRAY_SIZE(rcu_tasks_gp_state_names))
147 return rcu_tasks_gp_state_names[j];
149 #endif /* #ifndef CONFIG_TINY_RCU */
151 // Enqueue a callback for the specified flavor of Tasks RCU.
152 static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
153 struct rcu_tasks *rtp)
160 raw_spin_lock_irqsave(&rtp->cbs_lock, flags);
161 needwake = !rtp->cbs_head;
162 WRITE_ONCE(*rtp->cbs_tail, rhp);
163 rtp->cbs_tail = &rhp->next;
164 raw_spin_unlock_irqrestore(&rtp->cbs_lock, flags);
165 /* We can't create the thread unless interrupts are enabled. */
166 if (needwake && READ_ONCE(rtp->kthread_ptr))
167 wake_up(&rtp->cbs_wq);
170 // Wait for a grace period for the specified flavor of Tasks RCU.
171 static void synchronize_rcu_tasks_generic(struct rcu_tasks *rtp)
173 /* Complain if the scheduler has not started. */
174 RCU_LOCKDEP_WARN(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
175 "synchronize_rcu_tasks called too soon");
177 /* Wait for the grace period. */
178 wait_rcu_gp(rtp->call_func);
181 /* RCU-tasks kthread that detects grace periods and invokes callbacks. */
182 static int __noreturn rcu_tasks_kthread(void *arg)
185 struct rcu_head *list;
186 struct rcu_head *next;
187 struct rcu_tasks *rtp = arg;
189 /* Run on housekeeping CPUs by default. Sysadm can move if desired. */
190 housekeeping_affine(current, HK_FLAG_RCU);
191 WRITE_ONCE(rtp->kthread_ptr, current); // Let GPs start!
194 * Each pass through the following loop makes one check for
195 * newly arrived callbacks, and, if there are some, waits for
196 * one RCU-tasks grace period and then invokes the callbacks.
197 * This loop is terminated by the system going down. ;-)
200 set_tasks_gp_state(rtp, RTGS_WAIT_CBS);
202 /* Pick up any new callbacks. */
203 raw_spin_lock_irqsave(&rtp->cbs_lock, flags);
204 smp_mb__after_spinlock(); // Order updates vs. GP.
205 list = rtp->cbs_head;
206 rtp->cbs_head = NULL;
207 rtp->cbs_tail = &rtp->cbs_head;
208 raw_spin_unlock_irqrestore(&rtp->cbs_lock, flags);
210 /* If there were none, wait a bit and start over. */
212 wait_event_interruptible(rtp->cbs_wq,
213 READ_ONCE(rtp->cbs_head));
214 if (!rtp->cbs_head) {
215 WARN_ON(signal_pending(current));
216 set_tasks_gp_state(rtp, RTGS_WAIT_WAIT_CBS);
217 schedule_timeout_idle(HZ/10);
222 // Wait for one grace period.
223 set_tasks_gp_state(rtp, RTGS_WAIT_GP);
224 rtp->gp_start = jiffies;
228 /* Invoke the callbacks. */
229 set_tasks_gp_state(rtp, RTGS_INVOKE_CBS);
238 /* Paranoid sleep to keep this from entering a tight loop */
239 schedule_timeout_idle(rtp->gp_sleep);
243 /* Spawn RCU-tasks grace-period kthread. */
244 static void __init rcu_spawn_tasks_kthread_generic(struct rcu_tasks *rtp)
246 struct task_struct *t;
248 t = kthread_run(rcu_tasks_kthread, rtp, "%s_kthread", rtp->kname);
249 if (WARN_ONCE(IS_ERR(t), "%s: Could not start %s grace-period kthread, OOM is now expected behavior\n", __func__, rtp->name))
251 smp_mb(); /* Ensure others see full kthread. */
254 #ifndef CONFIG_TINY_RCU
257 * Print any non-default Tasks RCU settings.
259 static void __init rcu_tasks_bootup_oddness(void)
261 #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU)
262 if (rcu_task_stall_timeout != RCU_TASK_STALL_TIMEOUT)
263 pr_info("\tTasks-RCU CPU stall warnings timeout set to %d (rcu_task_stall_timeout).\n", rcu_task_stall_timeout);
264 #endif /* #ifdef CONFIG_TASKS_RCU */
265 #ifdef CONFIG_TASKS_RCU
266 pr_info("\tTrampoline variant of Tasks RCU enabled.\n");
267 #endif /* #ifdef CONFIG_TASKS_RCU */
268 #ifdef CONFIG_TASKS_RUDE_RCU
269 pr_info("\tRude variant of Tasks RCU enabled.\n");
270 #endif /* #ifdef CONFIG_TASKS_RUDE_RCU */
271 #ifdef CONFIG_TASKS_TRACE_RCU
272 pr_info("\tTracing variant of Tasks RCU enabled.\n");
273 #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
276 #endif /* #ifndef CONFIG_TINY_RCU */
278 #ifndef CONFIG_TINY_RCU
279 /* Dump out rcutorture-relevant state common to all RCU-tasks flavors. */
280 static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s)
282 pr_info("%s: %s(%d) since %lu g:%lu i:%lu/%lu %c%c %s\n",
284 tasks_gp_state_getname(rtp), data_race(rtp->gp_state),
285 jiffies - data_race(rtp->gp_jiffies),
286 data_race(rtp->n_gps),
287 data_race(rtp->n_ipis_fails), data_race(rtp->n_ipis),
288 ".k"[!!data_race(rtp->kthread_ptr)],
289 ".C"[!!data_race(rtp->cbs_head)],
292 #endif // #ifndef CONFIG_TINY_RCU
294 static void exit_tasks_rcu_finish_trace(struct task_struct *t);
296 #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU)
298 ////////////////////////////////////////////////////////////////////////
300 // Shared code between task-list-scanning variants of Tasks RCU.
302 /* Wait for one RCU-tasks grace period. */
303 static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
305 struct task_struct *g, *t;
306 unsigned long lastreport;
310 set_tasks_gp_state(rtp, RTGS_PRE_WAIT_GP);
314 * There were callbacks, so we need to wait for an RCU-tasks
315 * grace period. Start off by scanning the task list for tasks
316 * that are not already voluntarily blocked. Mark these tasks
317 * and make a list of them in holdouts.
319 set_tasks_gp_state(rtp, RTGS_SCAN_TASKLIST);
321 for_each_process_thread(g, t)
322 rtp->pertask_func(t, &holdouts);
325 set_tasks_gp_state(rtp, RTGS_POST_SCAN_TASKLIST);
326 rtp->postscan_func(&holdouts);
329 * Each pass through the following loop scans the list of holdout
330 * tasks, removing any that are no longer holdouts. When the list
331 * is empty, we are done.
333 lastreport = jiffies;
335 // Start off with initial wait and slowly back off to 1 HZ wait.
336 fract = rtp->init_fract;
338 while (!list_empty(&holdouts)) {
343 /* Slowly back off waiting for holdouts */
344 set_tasks_gp_state(rtp, RTGS_WAIT_SCAN_HOLDOUTS);
345 schedule_timeout_idle(fract);
350 rtst = READ_ONCE(rcu_task_stall_timeout);
351 needreport = rtst > 0 && time_after(jiffies, lastreport + rtst);
353 lastreport = jiffies;
355 WARN_ON(signal_pending(current));
356 set_tasks_gp_state(rtp, RTGS_SCAN_HOLDOUTS);
357 rtp->holdouts_func(&holdouts, needreport, &firstreport);
360 set_tasks_gp_state(rtp, RTGS_POST_GP);
361 rtp->postgp_func(rtp);
364 #endif /* #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU) */
366 #ifdef CONFIG_TASKS_RCU
368 ////////////////////////////////////////////////////////////////////////
370 // Simple variant of RCU whose quiescent states are voluntary context
371 // switch, cond_resched_tasks_rcu_qs(), user-space execution, and idle.
372 // As such, grace periods can take one good long time. There are no
373 // read-side primitives similar to rcu_read_lock() and rcu_read_unlock()
374 // because this implementation is intended to get the system into a safe
375 // state for some of the manipulations involved in tracing and the like.
376 // Finally, this implementation does not support high call_rcu_tasks()
377 // rates from multiple CPUs. If this is required, per-CPU callback lists
380 // The implementation uses rcu_tasks_wait_gp(), which relies on function
381 // pointers in the rcu_tasks structure. The rcu_spawn_tasks_kthread()
382 // function sets these function pointers up so that rcu_tasks_wait_gp()
383 // invokes these functions in this order:
385 // rcu_tasks_pregp_step():
386 // Invokes synchronize_rcu() in order to wait for all in-flight
387 // t->on_rq and t->nvcsw transitions to complete. This works because
388 // all such transitions are carried out with interrupts disabled.
389 // rcu_tasks_pertask(), invoked on every non-idle task:
390 // For every runnable non-idle task other than the current one, use
391 // get_task_struct() to pin down that task, snapshot that task's
392 // number of voluntary context switches, and add that task to the
394 // rcu_tasks_postscan():
395 // Invoke synchronize_srcu() to ensure that all tasks that were
396 // in the process of exiting (and which thus might not know to
397 // synchronize with this RCU Tasks grace period) have completed
399 // check_all_holdout_tasks(), repeatedly until holdout list is empty:
400 // Scans the holdout list, attempting to identify a quiescent state
401 // for each task on the list. If there is a quiescent state, the
402 // corresponding task is removed from the holdout list.
403 // rcu_tasks_postgp():
404 // Invokes synchronize_rcu() in order to ensure that all prior
405 // t->on_rq and t->nvcsw transitions are seen by all CPUs and tasks
406 // to have happened before the end of this RCU Tasks grace period.
407 // Again, this works because all such transitions are carried out
408 // with interrupts disabled.
410 // For each exiting task, the exit_tasks_rcu_start() and
411 // exit_tasks_rcu_finish() functions begin and end, respectively, the SRCU
412 // read-side critical sections waited for by rcu_tasks_postscan().
414 // Pre-grace-period update-side code is ordered before the grace via the
415 // ->cbs_lock and the smp_mb__after_spinlock(). Pre-grace-period read-side
416 // code is ordered before the grace period via synchronize_rcu() call
417 // in rcu_tasks_pregp_step() and by the scheduler's locks and interrupt
420 /* Pre-grace-period preparation. */
421 static void rcu_tasks_pregp_step(void)
424 * Wait for all pre-existing t->on_rq and t->nvcsw transitions
425 * to complete. Invoking synchronize_rcu() suffices because all
426 * these transitions occur with interrupts disabled. Without this
427 * synchronize_rcu(), a read-side critical section that started
428 * before the grace period might be incorrectly seen as having
429 * started after the grace period.
431 * This synchronize_rcu() also dispenses with the need for a
432 * memory barrier on the first store to t->rcu_tasks_holdout,
433 * as it forces the store to happen after the beginning of the
439 /* Per-task initial processing. */
440 static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop)
442 if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) {
444 t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);
445 WRITE_ONCE(t->rcu_tasks_holdout, true);
446 list_add(&t->rcu_tasks_holdout_list, hop);
450 /* Processing between scanning taskslist and draining the holdout list. */
451 static void rcu_tasks_postscan(struct list_head *hop)
454 * Wait for tasks that are in the process of exiting. This
455 * does only part of the job, ensuring that all tasks that were
456 * previously exiting reach the point where they have disabled
457 * preemption, allowing the later synchronize_rcu() to finish
460 synchronize_srcu(&tasks_rcu_exit_srcu);
463 /* See if tasks are still holding out, complain if so. */
464 static void check_holdout_task(struct task_struct *t,
465 bool needreport, bool *firstreport)
469 if (!READ_ONCE(t->rcu_tasks_holdout) ||
470 t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||
471 !READ_ONCE(t->on_rq) ||
472 (IS_ENABLED(CONFIG_NO_HZ_FULL) &&
473 !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
474 WRITE_ONCE(t->rcu_tasks_holdout, false);
475 list_del_init(&t->rcu_tasks_holdout_list);
479 rcu_request_urgent_qs_task(t);
483 pr_err("INFO: rcu_tasks detected stalls on tasks:\n");
484 *firstreport = false;
487 pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n",
488 t, ".I"[is_idle_task(t)],
489 "N."[cpu < 0 || !tick_nohz_full_cpu(cpu)],
490 t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout,
491 t->rcu_tasks_idle_cpu, cpu);
495 /* Scan the holdout lists for tasks no longer holding out. */
496 static void check_all_holdout_tasks(struct list_head *hop,
497 bool needreport, bool *firstreport)
499 struct task_struct *t, *t1;
501 list_for_each_entry_safe(t, t1, hop, rcu_tasks_holdout_list) {
502 check_holdout_task(t, needreport, firstreport);
507 /* Finish off the Tasks-RCU grace period. */
508 static void rcu_tasks_postgp(struct rcu_tasks *rtp)
511 * Because ->on_rq and ->nvcsw are not guaranteed to have a full
512 * memory barriers prior to them in the schedule() path, memory
513 * reordering on other CPUs could cause their RCU-tasks read-side
514 * critical sections to extend past the end of the grace period.
515 * However, because these ->nvcsw updates are carried out with
516 * interrupts disabled, we can use synchronize_rcu() to force the
517 * needed ordering on all such CPUs.
519 * This synchronize_rcu() also confines all ->rcu_tasks_holdout
520 * accesses to be within the grace period, avoiding the need for
521 * memory barriers for ->rcu_tasks_holdout accesses.
523 * In addition, this synchronize_rcu() waits for exiting tasks
524 * to complete their final preempt_disable() region of execution,
525 * cleaning up after the synchronize_srcu() above.
530 void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func);
531 DEFINE_RCU_TASKS(rcu_tasks, rcu_tasks_wait_gp, call_rcu_tasks, "RCU Tasks");
534 * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
535 * @rhp: structure to be used for queueing the RCU updates.
536 * @func: actual callback function to be invoked after the grace period
538 * The callback function will be invoked some time after a full grace
539 * period elapses, in other words after all currently executing RCU
540 * read-side critical sections have completed. call_rcu_tasks() assumes
541 * that the read-side critical sections end at a voluntary context
542 * switch (not a preemption!), cond_resched_tasks_rcu_qs(), entry into idle,
543 * or transition to usermode execution. As such, there are no read-side
544 * primitives analogous to rcu_read_lock() and rcu_read_unlock() because
545 * this primitive is intended to determine that all tasks have passed
546 * through a safe state, not so much for data-structure synchronization.
548 * See the description of call_rcu() for more detailed information on
549 * memory ordering guarantees.
551 void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func)
553 call_rcu_tasks_generic(rhp, func, &rcu_tasks);
555 EXPORT_SYMBOL_GPL(call_rcu_tasks);
558 * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed.
560 * Control will return to the caller some time after a full rcu-tasks
561 * grace period has elapsed, in other words after all currently
562 * executing rcu-tasks read-side critical sections have elapsed. These
563 * read-side critical sections are delimited by calls to schedule(),
564 * cond_resched_tasks_rcu_qs(), idle execution, userspace execution, calls
565 * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched().
567 * This is a very specialized primitive, intended only for a few uses in
568 * tracing and other situations requiring manipulation of function
569 * preambles and profiling hooks. The synchronize_rcu_tasks() function
570 * is not (yet) intended for heavy use from multiple CPUs.
572 * See the description of synchronize_rcu() for more detailed information
573 * on memory ordering guarantees.
575 void synchronize_rcu_tasks(void)
577 synchronize_rcu_tasks_generic(&rcu_tasks);
579 EXPORT_SYMBOL_GPL(synchronize_rcu_tasks);
582 * rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks.
584 * Although the current implementation is guaranteed to wait, it is not
585 * obligated to, for example, if there are no pending callbacks.
587 void rcu_barrier_tasks(void)
589 /* There is only one callback queue, so this is easy. ;-) */
590 synchronize_rcu_tasks();
592 EXPORT_SYMBOL_GPL(rcu_barrier_tasks);
594 static int __init rcu_spawn_tasks_kthread(void)
596 rcu_tasks.gp_sleep = HZ / 10;
597 rcu_tasks.init_fract = HZ / 10;
598 rcu_tasks.pregp_func = rcu_tasks_pregp_step;
599 rcu_tasks.pertask_func = rcu_tasks_pertask;
600 rcu_tasks.postscan_func = rcu_tasks_postscan;
601 rcu_tasks.holdouts_func = check_all_holdout_tasks;
602 rcu_tasks.postgp_func = rcu_tasks_postgp;
603 rcu_spawn_tasks_kthread_generic(&rcu_tasks);
607 #if !defined(CONFIG_TINY_RCU)
608 void show_rcu_tasks_classic_gp_kthread(void)
610 show_rcu_tasks_generic_gp_kthread(&rcu_tasks, "");
612 EXPORT_SYMBOL_GPL(show_rcu_tasks_classic_gp_kthread);
613 #endif // !defined(CONFIG_TINY_RCU)
615 /* Do the srcu_read_lock() for the above synchronize_srcu(). */
616 void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu)
619 current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
623 /* Do the srcu_read_unlock() for the above synchronize_srcu(). */
624 void exit_tasks_rcu_finish(void) __releases(&tasks_rcu_exit_srcu)
626 struct task_struct *t = current;
629 __srcu_read_unlock(&tasks_rcu_exit_srcu, t->rcu_tasks_idx);
631 exit_tasks_rcu_finish_trace(t);
634 #else /* #ifdef CONFIG_TASKS_RCU */
635 void exit_tasks_rcu_start(void) { }
636 void exit_tasks_rcu_finish(void) { exit_tasks_rcu_finish_trace(current); }
637 #endif /* #else #ifdef CONFIG_TASKS_RCU */
639 #ifdef CONFIG_TASKS_RUDE_RCU
641 ////////////////////////////////////////////////////////////////////////
643 // "Rude" variant of Tasks RCU, inspired by Steve Rostedt's trick of
644 // passing an empty function to schedule_on_each_cpu(). This approach
645 // provides an asynchronous call_rcu_tasks_rude() API and batching of
646 // concurrent calls to the synchronous synchronize_rcu_tasks_rude() API.
647 // This invokes schedule_on_each_cpu() in order to send IPIs far and wide
648 // and induces otherwise unnecessary context switches on all online CPUs,
649 // whether idle or not.
651 // Callback handling is provided by the rcu_tasks_kthread() function.
653 // Ordering is provided by the scheduler's context-switch code.
655 // Empty function to allow workqueues to force a context switch.
656 static void rcu_tasks_be_rude(struct work_struct *work)
660 // Wait for one rude RCU-tasks grace period.
661 static void rcu_tasks_rude_wait_gp(struct rcu_tasks *rtp)
663 rtp->n_ipis += cpumask_weight(cpu_online_mask);
664 schedule_on_each_cpu(rcu_tasks_be_rude);
667 void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func);
668 DEFINE_RCU_TASKS(rcu_tasks_rude, rcu_tasks_rude_wait_gp, call_rcu_tasks_rude,
672 * call_rcu_tasks_rude() - Queue a callback rude task-based grace period
673 * @rhp: structure to be used for queueing the RCU updates.
674 * @func: actual callback function to be invoked after the grace period
676 * The callback function will be invoked some time after a full grace
677 * period elapses, in other words after all currently executing RCU
678 * read-side critical sections have completed. call_rcu_tasks_rude()
679 * assumes that the read-side critical sections end at context switch,
680 * cond_resched_tasks_rcu_qs(), or transition to usermode execution (as
681 * usermode execution is schedulable). As such, there are no read-side
682 * primitives analogous to rcu_read_lock() and rcu_read_unlock() because
683 * this primitive is intended to determine that all tasks have passed
684 * through a safe state, not so much for data-structure synchronization.
686 * See the description of call_rcu() for more detailed information on
687 * memory ordering guarantees.
689 void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func)
691 call_rcu_tasks_generic(rhp, func, &rcu_tasks_rude);
693 EXPORT_SYMBOL_GPL(call_rcu_tasks_rude);
696 * synchronize_rcu_tasks_rude - wait for a rude rcu-tasks grace period
698 * Control will return to the caller some time after a rude rcu-tasks
699 * grace period has elapsed, in other words after all currently
700 * executing rcu-tasks read-side critical sections have elapsed. These
701 * read-side critical sections are delimited by calls to schedule(),
702 * cond_resched_tasks_rcu_qs(), userspace execution (which is a schedulable
703 * context), and (in theory, anyway) cond_resched().
705 * This is a very specialized primitive, intended only for a few uses in
706 * tracing and other situations requiring manipulation of function preambles
707 * and profiling hooks. The synchronize_rcu_tasks_rude() function is not
708 * (yet) intended for heavy use from multiple CPUs.
710 * See the description of synchronize_rcu() for more detailed information
711 * on memory ordering guarantees.
713 void synchronize_rcu_tasks_rude(void)
715 synchronize_rcu_tasks_generic(&rcu_tasks_rude);
717 EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_rude);
720 * rcu_barrier_tasks_rude - Wait for in-flight call_rcu_tasks_rude() callbacks.
722 * Although the current implementation is guaranteed to wait, it is not
723 * obligated to, for example, if there are no pending callbacks.
725 void rcu_barrier_tasks_rude(void)
727 /* There is only one callback queue, so this is easy. ;-) */
728 synchronize_rcu_tasks_rude();
730 EXPORT_SYMBOL_GPL(rcu_barrier_tasks_rude);
732 static int __init rcu_spawn_tasks_rude_kthread(void)
734 rcu_tasks_rude.gp_sleep = HZ / 10;
735 rcu_spawn_tasks_kthread_generic(&rcu_tasks_rude);
739 #if !defined(CONFIG_TINY_RCU)
740 void show_rcu_tasks_rude_gp_kthread(void)
742 show_rcu_tasks_generic_gp_kthread(&rcu_tasks_rude, "");
744 EXPORT_SYMBOL_GPL(show_rcu_tasks_rude_gp_kthread);
745 #endif // !defined(CONFIG_TINY_RCU)
746 #endif /* #ifdef CONFIG_TASKS_RUDE_RCU */
748 ////////////////////////////////////////////////////////////////////////
750 // Tracing variant of Tasks RCU. This variant is designed to be used
751 // to protect tracing hooks, including those of BPF. This variant
754 // 1. Has explicit read-side markers to allow finite grace periods
755 // in the face of in-kernel loops for PREEMPT=n builds.
757 // 2. Protects code in the idle loop, exception entry/exit, and
758 // CPU-hotplug code paths, similar to the capabilities of SRCU.
760 // 3. Avoids expensive read-side instructions, having overhead similar
761 // to that of Preemptible RCU.
763 // There are of course downsides. The grace-period code can send IPIs to
764 // CPUs, even when those CPUs are in the idle loop or in nohz_full userspace.
765 // It is necessary to scan the full tasklist, much as for Tasks RCU. There
766 // is a single callback queue guarded by a single lock, again, much as for
767 // Tasks RCU. If needed, these downsides can be at least partially remedied.
769 // Perhaps most important, this variant of RCU does not affect the vanilla
770 // flavors, rcu_preempt and rcu_sched. The fact that RCU Tasks Trace
771 // readers can operate from idle, offline, and exception entry/exit in no
772 // way allows rcu_preempt and rcu_sched readers to also do so.
774 // The implementation uses rcu_tasks_wait_gp(), which relies on function
775 // pointers in the rcu_tasks structure. The rcu_spawn_tasks_trace_kthread()
776 // function sets these function pointers up so that rcu_tasks_wait_gp()
777 // invokes these functions in this order:
779 // rcu_tasks_trace_pregp_step():
780 // Initialize the count of readers and block CPU-hotplug operations.
781 // rcu_tasks_trace_pertask(), invoked on every non-idle task:
782 // Initialize per-task state and attempt to identify an immediate
783 // quiescent state for that task, or, failing that, attempt to
784 // set that task's .need_qs flag so that task's next outermost
785 // rcu_read_unlock_trace() will report the quiescent state (in which
786 // case the count of readers is incremented). If both attempts fail,
787 // the task is added to a "holdout" list. Note that IPIs are used
788 // to invoke trc_read_check_handler() in the context of running tasks
789 // in order to avoid ordering overhead on common-case shared-variable
791 // rcu_tasks_trace_postscan():
792 // Initialize state and attempt to identify an immediate quiescent
793 // state as above (but only for idle tasks), unblock CPU-hotplug
794 // operations, and wait for an RCU grace period to avoid races with
795 // tasks that are in the process of exiting.
796 // check_all_holdout_tasks_trace(), repeatedly until holdout list is empty:
797 // Scans the holdout list, attempting to identify a quiescent state
798 // for each task on the list. If there is a quiescent state, the
799 // corresponding task is removed from the holdout list.
800 // rcu_tasks_trace_postgp():
801 // Wait for the count of readers do drop to zero, reporting any stalls.
802 // Also execute full memory barriers to maintain ordering with code
803 // executing after the grace period.
805 // The exit_tasks_rcu_finish_trace() synchronizes with exiting tasks.
807 // Pre-grace-period update-side code is ordered before the grace
808 // period via the ->cbs_lock and barriers in rcu_tasks_kthread().
809 // Pre-grace-period read-side code is ordered before the grace period by
810 // atomic_dec_and_test() of the count of readers (for IPIed readers) and by
811 // scheduler context-switch ordering (for locked-down non-running readers).
813 // The lockdep state must be outside of #ifdef to be useful.
814 #ifdef CONFIG_DEBUG_LOCK_ALLOC
815 static struct lock_class_key rcu_lock_trace_key;
816 struct lockdep_map rcu_trace_lock_map =
817 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_trace", &rcu_lock_trace_key);
818 EXPORT_SYMBOL_GPL(rcu_trace_lock_map);
819 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
821 #ifdef CONFIG_TASKS_TRACE_RCU
823 static atomic_t trc_n_readers_need_end; // Number of waited-for readers.
824 static DECLARE_WAIT_QUEUE_HEAD(trc_wait); // List of holdout tasks.
826 // Record outstanding IPIs to each CPU. No point in sending two...
827 static DEFINE_PER_CPU(bool, trc_ipi_to_cpu);
829 // The number of detections of task quiescent state relying on
830 // heavyweight readers executing explicit memory barriers.
831 static unsigned long n_heavy_reader_attempts;
832 static unsigned long n_heavy_reader_updates;
833 static unsigned long n_heavy_reader_ofl_updates;
835 void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func);
836 DEFINE_RCU_TASKS(rcu_tasks_trace, rcu_tasks_wait_gp, call_rcu_tasks_trace,
840 * This irq_work handler allows rcu_read_unlock_trace() to be invoked
841 * while the scheduler locks are held.
843 static void rcu_read_unlock_iw(struct irq_work *iwp)
847 static DEFINE_IRQ_WORK(rcu_tasks_trace_iw, rcu_read_unlock_iw);
849 /* If we are the last reader, wake up the grace-period kthread. */
850 void rcu_read_unlock_trace_special(struct task_struct *t)
852 int nq = READ_ONCE(t->trc_reader_special.b.need_qs);
854 if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) &&
855 t->trc_reader_special.b.need_mb)
856 smp_mb(); // Pairs with update-side barriers.
857 // Update .need_qs before ->trc_reader_nesting for irq/NMI handlers.
859 WRITE_ONCE(t->trc_reader_special.b.need_qs, false);
860 WRITE_ONCE(t->trc_reader_nesting, 0);
861 if (nq && atomic_dec_and_test(&trc_n_readers_need_end))
862 irq_work_queue(&rcu_tasks_trace_iw);
864 EXPORT_SYMBOL_GPL(rcu_read_unlock_trace_special);
866 /* Add a task to the holdout list, if it is not already on the list. */
867 static void trc_add_holdout(struct task_struct *t, struct list_head *bhp)
869 if (list_empty(&t->trc_holdout_list)) {
871 list_add(&t->trc_holdout_list, bhp);
875 /* Remove a task from the holdout list, if it is in fact present. */
876 static void trc_del_holdout(struct task_struct *t)
878 if (!list_empty(&t->trc_holdout_list)) {
879 list_del_init(&t->trc_holdout_list);
884 /* IPI handler to check task state. */
885 static void trc_read_check_handler(void *t_in)
887 struct task_struct *t = current;
888 struct task_struct *texp = t_in;
890 // If the task is no longer running on this CPU, leave.
891 if (unlikely(texp != t)) {
892 goto reset_ipi; // Already on holdout list, so will check later.
895 // If the task is not in a read-side critical section, and
896 // if this is the last reader, awaken the grace-period kthread.
897 if (likely(!READ_ONCE(t->trc_reader_nesting))) {
898 WRITE_ONCE(t->trc_reader_checked, true);
901 // If we are racing with an rcu_read_unlock_trace(), try again later.
902 if (unlikely(READ_ONCE(t->trc_reader_nesting) < 0))
904 WRITE_ONCE(t->trc_reader_checked, true);
906 // Get here if the task is in a read-side critical section. Set
907 // its state so that it will awaken the grace-period kthread upon
908 // exit from that critical section.
909 atomic_inc(&trc_n_readers_need_end); // One more to wait on.
910 WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs));
911 WRITE_ONCE(t->trc_reader_special.b.need_qs, true);
914 // Allow future IPIs to be sent on CPU and for task.
915 // Also order this IPI handler against any later manipulations of
916 // the intended task.
917 smp_store_release(per_cpu_ptr(&trc_ipi_to_cpu, smp_processor_id()), false); // ^^^
918 smp_store_release(&texp->trc_ipi_to_cpu, -1); // ^^^
921 /* Callback function for scheduler to check locked-down task. */
922 static int trc_inspect_reader(struct task_struct *t, void *arg)
924 int cpu = task_cpu(t);
926 bool ofl = cpu_is_offline(cpu);
929 WARN_ON_ONCE(ofl && !is_idle_task(t));
931 // If no chance of heavyweight readers, do it the hard way.
932 if (!ofl && !IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
935 // If heavyweight readers are enabled on the remote task,
936 // we can inspect its state despite its currently running.
937 // However, we cannot safely change its state.
938 n_heavy_reader_attempts++;
939 if (!ofl && // Check for "running" idle tasks on offline CPUs.
940 !rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting))
941 return -EINVAL; // No quiescent state, do it the hard way.
942 n_heavy_reader_updates++;
944 n_heavy_reader_ofl_updates++;
947 // The task is not running, so C-language access is safe.
948 nesting = t->trc_reader_nesting;
951 // If not exiting a read-side critical section, mark as checked
952 // so that the grace-period kthread will remove it from the
954 t->trc_reader_checked = nesting >= 0;
956 return nesting ? -EINVAL : 0; // If in QS, done, otherwise try again later.
958 // The task is in a read-side critical section, so set up its
959 // state so that it will awaken the grace-period kthread upon exit
960 // from that critical section.
961 atomic_inc(&trc_n_readers_need_end); // One more to wait on.
962 WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs));
963 WRITE_ONCE(t->trc_reader_special.b.need_qs, true);
967 /* Attempt to extract the state for the specified task. */
968 static void trc_wait_for_one_reader(struct task_struct *t,
969 struct list_head *bhp)
973 // If a previous IPI is still in flight, let it complete.
974 if (smp_load_acquire(&t->trc_ipi_to_cpu) != -1) // Order IPI
977 // The current task had better be in a quiescent state.
979 t->trc_reader_checked = true;
980 WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting));
984 // Attempt to nail down the task for inspection.
986 if (!task_call_func(t, trc_inspect_reader, NULL)) {
992 // If this task is not yet on the holdout list, then we are in
993 // an RCU read-side critical section. Otherwise, the invocation of
994 // trc_add_holdout() that added it to the list did the necessary
995 // get_task_struct(). Either way, the task cannot be freed out
996 // from under this code.
998 // If currently running, send an IPI, either way, add to list.
999 trc_add_holdout(t, bhp);
1001 time_after(jiffies + 1, rcu_tasks_trace.gp_start + rcu_task_ipi_delay)) {
1002 // The task is currently running, so try IPIing it.
1005 // If there is already an IPI outstanding, let it happen.
1006 if (per_cpu(trc_ipi_to_cpu, cpu) || t->trc_ipi_to_cpu >= 0)
1009 per_cpu(trc_ipi_to_cpu, cpu) = true;
1010 t->trc_ipi_to_cpu = cpu;
1011 rcu_tasks_trace.n_ipis++;
1012 if (smp_call_function_single(cpu, trc_read_check_handler, t, 0)) {
1013 // Just in case there is some other reason for
1014 // failure than the target CPU being offline.
1015 WARN_ONCE(1, "%s(): smp_call_function_single() failed for CPU: %d\n",
1017 rcu_tasks_trace.n_ipis_fails++;
1018 per_cpu(trc_ipi_to_cpu, cpu) = false;
1019 t->trc_ipi_to_cpu = -1;
1024 /* Initialize for a new RCU-tasks-trace grace period. */
1025 static void rcu_tasks_trace_pregp_step(void)
1029 // Allow for fast-acting IPIs.
1030 atomic_set(&trc_n_readers_need_end, 1);
1032 // There shouldn't be any old IPIs, but...
1033 for_each_possible_cpu(cpu)
1034 WARN_ON_ONCE(per_cpu(trc_ipi_to_cpu, cpu));
1036 // Disable CPU hotplug across the tasklist scan.
1037 // This also waits for all readers in CPU-hotplug code paths.
1041 /* Do first-round processing for the specified task. */
1042 static void rcu_tasks_trace_pertask(struct task_struct *t,
1043 struct list_head *hop)
1045 // During early boot when there is only the one boot CPU, there
1046 // is no idle task for the other CPUs. Just return.
1047 if (unlikely(t == NULL))
1050 WRITE_ONCE(t->trc_reader_special.b.need_qs, false);
1051 WRITE_ONCE(t->trc_reader_checked, false);
1052 t->trc_ipi_to_cpu = -1;
1053 trc_wait_for_one_reader(t, hop);
1057 * Do intermediate processing between task and holdout scans and
1058 * pick up the idle tasks.
1060 static void rcu_tasks_trace_postscan(struct list_head *hop)
1064 for_each_possible_cpu(cpu)
1065 rcu_tasks_trace_pertask(idle_task(cpu), hop);
1067 // Re-enable CPU hotplug now that the tasklist scan has completed.
1070 // Wait for late-stage exiting tasks to finish exiting.
1071 // These might have passed the call to exit_tasks_rcu_finish().
1073 // Any tasks that exit after this point will set ->trc_reader_checked.
1076 /* Show the state of a task stalling the current RCU tasks trace GP. */
1077 static void show_stalled_task_trace(struct task_struct *t, bool *firstreport)
1082 pr_err("INFO: rcu_tasks_trace detected stalls on tasks:\n");
1083 *firstreport = false;
1085 // FIXME: This should attempt to use try_invoke_on_nonrunning_task().
1087 pr_alert("P%d: %c%c%c nesting: %d%c cpu: %d\n",
1089 ".I"[READ_ONCE(t->trc_ipi_to_cpu) >= 0],
1090 ".i"[is_idle_task(t)],
1091 ".N"[cpu >= 0 && tick_nohz_full_cpu(cpu)],
1092 READ_ONCE(t->trc_reader_nesting),
1093 " N"[!!READ_ONCE(t->trc_reader_special.b.need_qs)],
1098 /* List stalled IPIs for RCU tasks trace. */
1099 static void show_stalled_ipi_trace(void)
1103 for_each_possible_cpu(cpu)
1104 if (per_cpu(trc_ipi_to_cpu, cpu))
1105 pr_alert("\tIPI outstanding to CPU %d\n", cpu);
1108 /* Do one scan of the holdout list. */
1109 static void check_all_holdout_tasks_trace(struct list_head *hop,
1110 bool needreport, bool *firstreport)
1112 struct task_struct *g, *t;
1114 // Disable CPU hotplug across the holdout list scan.
1117 list_for_each_entry_safe(t, g, hop, trc_holdout_list) {
1118 // If safe and needed, try to check the current task.
1119 if (READ_ONCE(t->trc_ipi_to_cpu) == -1 &&
1120 !READ_ONCE(t->trc_reader_checked))
1121 trc_wait_for_one_reader(t, hop);
1123 // If check succeeded, remove this task from the list.
1124 if (READ_ONCE(t->trc_reader_checked))
1126 else if (needreport)
1127 show_stalled_task_trace(t, firstreport);
1130 // Re-enable CPU hotplug now that the holdout list scan has completed.
1135 pr_err("INFO: rcu_tasks_trace detected stalls? (Late IPI?)\n");
1136 show_stalled_ipi_trace();
1140 static void rcu_tasks_trace_empty_fn(void *unused)
1144 /* Wait for grace period to complete and provide ordering. */
1145 static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp)
1149 struct task_struct *g, *t;
1150 LIST_HEAD(holdouts);
1153 // Wait for any lingering IPI handlers to complete. Note that
1154 // if a CPU has gone offline or transitioned to userspace in the
1155 // meantime, all IPI handlers should have been drained beforehand.
1156 // Yes, this assumes that CPUs process IPIs in order. If that ever
1157 // changes, there will need to be a recheck and/or timed wait.
1158 for_each_online_cpu(cpu)
1159 if (smp_load_acquire(per_cpu_ptr(&trc_ipi_to_cpu, cpu)))
1160 smp_call_function_single(cpu, rcu_tasks_trace_empty_fn, NULL, 1);
1162 // Remove the safety count.
1163 smp_mb__before_atomic(); // Order vs. earlier atomics
1164 atomic_dec(&trc_n_readers_need_end);
1165 smp_mb__after_atomic(); // Order vs. later atomics
1167 // Wait for readers.
1168 set_tasks_gp_state(rtp, RTGS_WAIT_READERS);
1170 ret = wait_event_idle_exclusive_timeout(
1172 atomic_read(&trc_n_readers_need_end) == 0,
1173 READ_ONCE(rcu_task_stall_timeout));
1175 break; // Count reached zero.
1176 // Stall warning time, so make a list of the offenders.
1178 for_each_process_thread(g, t)
1179 if (READ_ONCE(t->trc_reader_special.b.need_qs))
1180 trc_add_holdout(t, &holdouts);
1183 list_for_each_entry_safe(t, g, &holdouts, trc_holdout_list) {
1184 if (READ_ONCE(t->trc_reader_special.b.need_qs))
1185 show_stalled_task_trace(t, &firstreport);
1186 trc_del_holdout(t); // Release task_struct reference.
1189 pr_err("INFO: rcu_tasks_trace detected stalls? (Counter/taskslist mismatch?)\n");
1190 show_stalled_ipi_trace();
1191 pr_err("\t%d holdouts\n", atomic_read(&trc_n_readers_need_end));
1193 smp_mb(); // Caller's code must be ordered after wakeup.
1194 // Pairs with pretty much every ordering primitive.
1197 /* Report any needed quiescent state for this exiting task. */
1198 static void exit_tasks_rcu_finish_trace(struct task_struct *t)
1200 WRITE_ONCE(t->trc_reader_checked, true);
1201 WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting));
1202 WRITE_ONCE(t->trc_reader_nesting, 0);
1203 if (WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs)))
1204 rcu_read_unlock_trace_special(t);
1208 * call_rcu_tasks_trace() - Queue a callback trace task-based grace period
1209 * @rhp: structure to be used for queueing the RCU updates.
1210 * @func: actual callback function to be invoked after the grace period
1212 * The callback function will be invoked some time after a trace rcu-tasks
1213 * grace period elapses, in other words after all currently executing
1214 * trace rcu-tasks read-side critical sections have completed. These
1215 * read-side critical sections are delimited by calls to rcu_read_lock_trace()
1216 * and rcu_read_unlock_trace().
1218 * See the description of call_rcu() for more detailed information on
1219 * memory ordering guarantees.
1221 void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func)
1223 call_rcu_tasks_generic(rhp, func, &rcu_tasks_trace);
1225 EXPORT_SYMBOL_GPL(call_rcu_tasks_trace);
1228 * synchronize_rcu_tasks_trace - wait for a trace rcu-tasks grace period
1230 * Control will return to the caller some time after a trace rcu-tasks
1231 * grace period has elapsed, in other words after all currently executing
1232 * trace rcu-tasks read-side critical sections have elapsed. These read-side
1233 * critical sections are delimited by calls to rcu_read_lock_trace()
1234 * and rcu_read_unlock_trace().
1236 * This is a very specialized primitive, intended only for a few uses in
1237 * tracing and other situations requiring manipulation of function preambles
1238 * and profiling hooks. The synchronize_rcu_tasks_trace() function is not
1239 * (yet) intended for heavy use from multiple CPUs.
1241 * See the description of synchronize_rcu() for more detailed information
1242 * on memory ordering guarantees.
1244 void synchronize_rcu_tasks_trace(void)
1246 RCU_LOCKDEP_WARN(lock_is_held(&rcu_trace_lock_map), "Illegal synchronize_rcu_tasks_trace() in RCU Tasks Trace read-side critical section");
1247 synchronize_rcu_tasks_generic(&rcu_tasks_trace);
1249 EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_trace);
1252 * rcu_barrier_tasks_trace - Wait for in-flight call_rcu_tasks_trace() callbacks.
1254 * Although the current implementation is guaranteed to wait, it is not
1255 * obligated to, for example, if there are no pending callbacks.
1257 void rcu_barrier_tasks_trace(void)
1259 /* There is only one callback queue, so this is easy. ;-) */
1260 synchronize_rcu_tasks_trace();
1262 EXPORT_SYMBOL_GPL(rcu_barrier_tasks_trace);
1264 static int __init rcu_spawn_tasks_trace_kthread(void)
1266 if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) {
1267 rcu_tasks_trace.gp_sleep = HZ / 10;
1268 rcu_tasks_trace.init_fract = HZ / 10;
1270 rcu_tasks_trace.gp_sleep = HZ / 200;
1271 if (rcu_tasks_trace.gp_sleep <= 0)
1272 rcu_tasks_trace.gp_sleep = 1;
1273 rcu_tasks_trace.init_fract = HZ / 200;
1274 if (rcu_tasks_trace.init_fract <= 0)
1275 rcu_tasks_trace.init_fract = 1;
1277 rcu_tasks_trace.pregp_func = rcu_tasks_trace_pregp_step;
1278 rcu_tasks_trace.pertask_func = rcu_tasks_trace_pertask;
1279 rcu_tasks_trace.postscan_func = rcu_tasks_trace_postscan;
1280 rcu_tasks_trace.holdouts_func = check_all_holdout_tasks_trace;
1281 rcu_tasks_trace.postgp_func = rcu_tasks_trace_postgp;
1282 rcu_spawn_tasks_kthread_generic(&rcu_tasks_trace);
1286 #if !defined(CONFIG_TINY_RCU)
1287 void show_rcu_tasks_trace_gp_kthread(void)
1291 sprintf(buf, "N%d h:%lu/%lu/%lu", atomic_read(&trc_n_readers_need_end),
1292 data_race(n_heavy_reader_ofl_updates),
1293 data_race(n_heavy_reader_updates),
1294 data_race(n_heavy_reader_attempts));
1295 show_rcu_tasks_generic_gp_kthread(&rcu_tasks_trace, buf);
1297 EXPORT_SYMBOL_GPL(show_rcu_tasks_trace_gp_kthread);
1298 #endif // !defined(CONFIG_TINY_RCU)
1300 #else /* #ifdef CONFIG_TASKS_TRACE_RCU */
1301 static void exit_tasks_rcu_finish_trace(struct task_struct *t) { }
1302 #endif /* #else #ifdef CONFIG_TASKS_TRACE_RCU */
1304 #ifndef CONFIG_TINY_RCU
1305 void show_rcu_tasks_gp_kthreads(void)
1307 show_rcu_tasks_classic_gp_kthread();
1308 show_rcu_tasks_rude_gp_kthread();
1309 show_rcu_tasks_trace_gp_kthread();
1311 #endif /* #ifndef CONFIG_TINY_RCU */
1313 #ifdef CONFIG_PROVE_RCU
1314 struct rcu_tasks_test_desc {
1320 static struct rcu_tasks_test_desc tests[] = {
1322 .name = "call_rcu_tasks()",
1323 /* If not defined, the test is skipped. */
1324 .notrun = !IS_ENABLED(CONFIG_TASKS_RCU),
1327 .name = "call_rcu_tasks_rude()",
1328 /* If not defined, the test is skipped. */
1329 .notrun = !IS_ENABLED(CONFIG_TASKS_RUDE_RCU),
1332 .name = "call_rcu_tasks_trace()",
1333 /* If not defined, the test is skipped. */
1334 .notrun = !IS_ENABLED(CONFIG_TASKS_TRACE_RCU)
1338 static void test_rcu_tasks_callback(struct rcu_head *rhp)
1340 struct rcu_tasks_test_desc *rttd =
1341 container_of(rhp, struct rcu_tasks_test_desc, rh);
1343 pr_info("Callback from %s invoked.\n", rttd->name);
1345 rttd->notrun = true;
1348 static void rcu_tasks_initiate_self_tests(void)
1350 pr_info("Running RCU-tasks wait API self tests\n");
1351 #ifdef CONFIG_TASKS_RCU
1352 synchronize_rcu_tasks();
1353 call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback);
1356 #ifdef CONFIG_TASKS_RUDE_RCU
1357 synchronize_rcu_tasks_rude();
1358 call_rcu_tasks_rude(&tests[1].rh, test_rcu_tasks_callback);
1361 #ifdef CONFIG_TASKS_TRACE_RCU
1362 synchronize_rcu_tasks_trace();
1363 call_rcu_tasks_trace(&tests[2].rh, test_rcu_tasks_callback);
1367 static int rcu_tasks_verify_self_tests(void)
1372 for (i = 0; i < ARRAY_SIZE(tests); i++) {
1373 if (!tests[i].notrun) { // still hanging.
1374 pr_err("%s has been failed.\n", tests[i].name);
1384 late_initcall(rcu_tasks_verify_self_tests);
1385 #else /* #ifdef CONFIG_PROVE_RCU */
1386 static void rcu_tasks_initiate_self_tests(void) { }
1387 #endif /* #else #ifdef CONFIG_PROVE_RCU */
1389 void __init rcu_init_tasks_generic(void)
1391 #ifdef CONFIG_TASKS_RCU
1392 rcu_spawn_tasks_kthread();
1395 #ifdef CONFIG_TASKS_RUDE_RCU
1396 rcu_spawn_tasks_rude_kthread();
1399 #ifdef CONFIG_TASKS_TRACE_RCU
1400 rcu_spawn_tasks_trace_kthread();
1403 // Run the self-tests.
1404 rcu_tasks_initiate_self_tests();
1407 #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
1408 static inline void rcu_tasks_bootup_oddness(void) {}
1409 #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */