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
9 #include "rcu_segcblist.h"
11 ////////////////////////////////////////////////////////////////////////
13 // Generic data structures.
16 typedef void (*rcu_tasks_gp_func_t)(struct rcu_tasks *rtp);
17 typedef void (*pregp_func_t)(struct list_head *hop);
18 typedef void (*pertask_func_t)(struct task_struct *t, struct list_head *hop);
19 typedef void (*postscan_func_t)(struct list_head *hop);
20 typedef void (*holdouts_func_t)(struct list_head *hop, bool ndrpt, bool *frptp);
21 typedef void (*postgp_func_t)(struct rcu_tasks *rtp);
24 * struct rcu_tasks_percpu - Per-CPU component of definition for a Tasks-RCU-like mechanism.
25 * @cblist: Callback list.
26 * @lock: Lock protecting per-CPU callback list.
27 * @rtp_jiffies: Jiffies counter value for statistics.
28 * @rtp_n_lock_retries: Rough lock-contention statistic.
29 * @rtp_work: Work queue for invoking callbacks.
30 * @rtp_irq_work: IRQ work queue for deferred wakeups.
31 * @barrier_q_head: RCU callback for barrier operation.
32 * @rtp_blkd_tasks: List of tasks blocked as readers.
33 * @cpu: CPU number corresponding to this entry.
34 * @rtpp: Pointer to the rcu_tasks structure.
36 struct rcu_tasks_percpu {
37 struct rcu_segcblist cblist;
38 raw_spinlock_t __private lock;
39 unsigned long rtp_jiffies;
40 unsigned long rtp_n_lock_retries;
41 struct work_struct rtp_work;
42 struct irq_work rtp_irq_work;
43 struct rcu_head barrier_q_head;
44 struct list_head rtp_blkd_tasks;
46 struct rcu_tasks *rtpp;
50 * struct rcu_tasks - Definition for a Tasks-RCU-like mechanism.
51 * @cbs_wait: RCU wait allowing a new callback to get kthread's attention.
52 * @cbs_gbl_lock: Lock protecting callback list.
53 * @tasks_gp_mutex: Mutex protecting grace period, needed during mid-boot dead zone.
54 * @kthread_ptr: This flavor's grace-period/callback-invocation kthread.
55 * @gp_func: This flavor's grace-period-wait function.
56 * @gp_state: Grace period's most recent state transition (debugging).
57 * @gp_sleep: Per-grace-period sleep to prevent CPU-bound looping.
58 * @init_fract: Initial backoff sleep interval.
59 * @gp_jiffies: Time of last @gp_state transition.
60 * @gp_start: Most recent grace-period start in jiffies.
61 * @tasks_gp_seq: Number of grace periods completed since boot.
62 * @n_ipis: Number of IPIs sent to encourage grace periods to end.
63 * @n_ipis_fails: Number of IPI-send failures.
64 * @pregp_func: This flavor's pre-grace-period function (optional).
65 * @pertask_func: This flavor's per-task scan function (optional).
66 * @postscan_func: This flavor's post-task scan function (optional).
67 * @holdouts_func: This flavor's holdout-list scan function (optional).
68 * @postgp_func: This flavor's post-grace-period function (optional).
69 * @call_func: This flavor's call_rcu()-equivalent function.
70 * @rtpcpu: This flavor's rcu_tasks_percpu structure.
71 * @percpu_enqueue_shift: Shift down CPU ID this much when enqueuing callbacks.
72 * @percpu_enqueue_lim: Number of per-CPU callback queues in use for enqueuing.
73 * @percpu_dequeue_lim: Number of per-CPU callback queues in use for dequeuing.
74 * @percpu_dequeue_gpseq: RCU grace-period number to propagate enqueue limit to dequeuers.
75 * @barrier_q_mutex: Serialize barrier operations.
76 * @barrier_q_count: Number of queues being waited on.
77 * @barrier_q_completion: Barrier wait/wakeup mechanism.
78 * @barrier_q_seq: Sequence number for barrier operations.
79 * @name: This flavor's textual name.
80 * @kname: This flavor's kthread name.
83 struct rcuwait cbs_wait;
84 raw_spinlock_t cbs_gbl_lock;
85 struct mutex tasks_gp_mutex;
89 unsigned long gp_jiffies;
90 unsigned long gp_start;
91 unsigned long tasks_gp_seq;
93 unsigned long n_ipis_fails;
94 struct task_struct *kthread_ptr;
95 rcu_tasks_gp_func_t gp_func;
96 pregp_func_t pregp_func;
97 pertask_func_t pertask_func;
98 postscan_func_t postscan_func;
99 holdouts_func_t holdouts_func;
100 postgp_func_t postgp_func;
101 call_rcu_func_t call_func;
102 struct rcu_tasks_percpu __percpu *rtpcpu;
103 int percpu_enqueue_shift;
104 int percpu_enqueue_lim;
105 int percpu_dequeue_lim;
106 unsigned long percpu_dequeue_gpseq;
107 struct mutex barrier_q_mutex;
108 atomic_t barrier_q_count;
109 struct completion barrier_q_completion;
110 unsigned long barrier_q_seq;
115 static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp);
117 #define DEFINE_RCU_TASKS(rt_name, gp, call, n) \
118 static DEFINE_PER_CPU(struct rcu_tasks_percpu, rt_name ## __percpu) = { \
119 .lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name ## __percpu.cbs_pcpu_lock), \
120 .rtp_irq_work = IRQ_WORK_INIT_HARD(call_rcu_tasks_iw_wakeup), \
122 static struct rcu_tasks rt_name = \
124 .cbs_wait = __RCUWAIT_INITIALIZER(rt_name.wait), \
125 .cbs_gbl_lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name.cbs_gbl_lock), \
126 .tasks_gp_mutex = __MUTEX_INITIALIZER(rt_name.tasks_gp_mutex), \
129 .rtpcpu = &rt_name ## __percpu, \
131 .percpu_enqueue_shift = order_base_2(CONFIG_NR_CPUS), \
132 .percpu_enqueue_lim = 1, \
133 .percpu_dequeue_lim = 1, \
134 .barrier_q_mutex = __MUTEX_INITIALIZER(rt_name.barrier_q_mutex), \
135 .barrier_q_seq = (0UL - 50UL) << RCU_SEQ_CTR_SHIFT, \
139 #ifdef CONFIG_TASKS_RCU
140 /* Track exiting tasks in order to allow them to be waited for. */
141 DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu);
144 #ifdef CONFIG_TASKS_RCU
145 /* Report delay in synchronize_srcu() completion in rcu_tasks_postscan(). */
146 static void tasks_rcu_exit_srcu_stall(struct timer_list *unused);
147 static DEFINE_TIMER(tasks_rcu_exit_srcu_stall_timer, tasks_rcu_exit_srcu_stall);
150 /* Avoid IPIing CPUs early in the grace period. */
151 #define RCU_TASK_IPI_DELAY (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) ? HZ / 2 : 0)
152 static int rcu_task_ipi_delay __read_mostly = RCU_TASK_IPI_DELAY;
153 module_param(rcu_task_ipi_delay, int, 0644);
155 /* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */
156 #define RCU_TASK_BOOT_STALL_TIMEOUT (HZ * 30)
157 #define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10)
158 static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT;
159 module_param(rcu_task_stall_timeout, int, 0644);
160 #define RCU_TASK_STALL_INFO (HZ * 10)
161 static int rcu_task_stall_info __read_mostly = RCU_TASK_STALL_INFO;
162 module_param(rcu_task_stall_info, int, 0644);
163 static int rcu_task_stall_info_mult __read_mostly = 3;
164 module_param(rcu_task_stall_info_mult, int, 0444);
166 static int rcu_task_enqueue_lim __read_mostly = -1;
167 module_param(rcu_task_enqueue_lim, int, 0444);
169 static bool rcu_task_cb_adjust;
170 static int rcu_task_contend_lim __read_mostly = 100;
171 module_param(rcu_task_contend_lim, int, 0444);
172 static int rcu_task_collapse_lim __read_mostly = 10;
173 module_param(rcu_task_collapse_lim, int, 0444);
175 /* RCU tasks grace-period state for debugging. */
177 #define RTGS_WAIT_WAIT_CBS 1
178 #define RTGS_WAIT_GP 2
179 #define RTGS_PRE_WAIT_GP 3
180 #define RTGS_SCAN_TASKLIST 4
181 #define RTGS_POST_SCAN_TASKLIST 5
182 #define RTGS_WAIT_SCAN_HOLDOUTS 6
183 #define RTGS_SCAN_HOLDOUTS 7
184 #define RTGS_POST_GP 8
185 #define RTGS_WAIT_READERS 9
186 #define RTGS_INVOKE_CBS 10
187 #define RTGS_WAIT_CBS 11
188 #ifndef CONFIG_TINY_RCU
189 static const char * const rcu_tasks_gp_state_names[] = {
191 "RTGS_WAIT_WAIT_CBS",
194 "RTGS_SCAN_TASKLIST",
195 "RTGS_POST_SCAN_TASKLIST",
196 "RTGS_WAIT_SCAN_HOLDOUTS",
197 "RTGS_SCAN_HOLDOUTS",
203 #endif /* #ifndef CONFIG_TINY_RCU */
205 ////////////////////////////////////////////////////////////////////////
209 static void rcu_tasks_invoke_cbs_wq(struct work_struct *wp);
211 /* Record grace-period phase and time. */
212 static void set_tasks_gp_state(struct rcu_tasks *rtp, int newstate)
214 rtp->gp_state = newstate;
215 rtp->gp_jiffies = jiffies;
218 #ifndef CONFIG_TINY_RCU
219 /* Return state name. */
220 static const char *tasks_gp_state_getname(struct rcu_tasks *rtp)
222 int i = data_race(rtp->gp_state); // Let KCSAN detect update races
223 int j = READ_ONCE(i); // Prevent the compiler from reading twice
225 if (j >= ARRAY_SIZE(rcu_tasks_gp_state_names))
227 return rcu_tasks_gp_state_names[j];
229 #endif /* #ifndef CONFIG_TINY_RCU */
231 // Initialize per-CPU callback lists for the specified flavor of
233 static void cblist_init_generic(struct rcu_tasks *rtp)
240 raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags);
241 if (rcu_task_enqueue_lim < 0) {
242 rcu_task_enqueue_lim = 1;
243 rcu_task_cb_adjust = true;
244 } else if (rcu_task_enqueue_lim == 0) {
245 rcu_task_enqueue_lim = 1;
247 lim = rcu_task_enqueue_lim;
249 if (lim > nr_cpu_ids)
251 shift = ilog2(nr_cpu_ids / lim);
252 if (((nr_cpu_ids - 1) >> shift) >= lim)
254 WRITE_ONCE(rtp->percpu_enqueue_shift, shift);
255 WRITE_ONCE(rtp->percpu_dequeue_lim, lim);
256 smp_store_release(&rtp->percpu_enqueue_lim, lim);
257 for_each_possible_cpu(cpu) {
258 struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
260 WARN_ON_ONCE(!rtpcp);
262 raw_spin_lock_init(&ACCESS_PRIVATE(rtpcp, lock));
263 raw_spin_lock_rcu_node(rtpcp); // irqs already disabled.
264 if (rcu_segcblist_empty(&rtpcp->cblist))
265 rcu_segcblist_init(&rtpcp->cblist);
266 INIT_WORK(&rtpcp->rtp_work, rcu_tasks_invoke_cbs_wq);
269 if (!rtpcp->rtp_blkd_tasks.next)
270 INIT_LIST_HEAD(&rtpcp->rtp_blkd_tasks);
271 raw_spin_unlock_rcu_node(rtpcp); // irqs remain disabled.
273 raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
275 pr_info("%s: Setting shift to %d and lim to %d rcu_task_cb_adjust=%d.\n", rtp->name,
276 data_race(rtp->percpu_enqueue_shift), data_race(rtp->percpu_enqueue_lim), rcu_task_cb_adjust);
279 // IRQ-work handler that does deferred wakeup for call_rcu_tasks_generic().
280 static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp)
282 struct rcu_tasks *rtp;
283 struct rcu_tasks_percpu *rtpcp = container_of(iwp, struct rcu_tasks_percpu, rtp_irq_work);
286 rcuwait_wake_up(&rtp->cbs_wait);
289 // Enqueue a callback for the specified flavor of Tasks RCU.
290 static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
291 struct rcu_tasks *rtp)
297 bool needadjust = false;
299 struct rcu_tasks_percpu *rtpcp;
303 local_irq_save(flags);
305 ideal_cpu = smp_processor_id() >> READ_ONCE(rtp->percpu_enqueue_shift);
306 chosen_cpu = cpumask_next(ideal_cpu - 1, cpu_possible_mask);
307 rtpcp = per_cpu_ptr(rtp->rtpcpu, chosen_cpu);
308 if (!raw_spin_trylock_rcu_node(rtpcp)) { // irqs already disabled.
309 raw_spin_lock_rcu_node(rtpcp); // irqs already disabled.
311 if (rtpcp->rtp_jiffies != j) {
312 rtpcp->rtp_jiffies = j;
313 rtpcp->rtp_n_lock_retries = 0;
315 if (rcu_task_cb_adjust && ++rtpcp->rtp_n_lock_retries > rcu_task_contend_lim &&
316 READ_ONCE(rtp->percpu_enqueue_lim) != nr_cpu_ids)
317 needadjust = true; // Defer adjustment to avoid deadlock.
319 if (!rcu_segcblist_is_enabled(&rtpcp->cblist)) {
320 raw_spin_unlock_rcu_node(rtpcp); // irqs remain disabled.
321 cblist_init_generic(rtp);
322 raw_spin_lock_rcu_node(rtpcp); // irqs already disabled.
324 needwake = rcu_segcblist_empty(&rtpcp->cblist);
325 rcu_segcblist_enqueue(&rtpcp->cblist, rhp);
326 raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
327 if (unlikely(needadjust)) {
328 raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags);
329 if (rtp->percpu_enqueue_lim != nr_cpu_ids) {
330 WRITE_ONCE(rtp->percpu_enqueue_shift, 0);
331 WRITE_ONCE(rtp->percpu_dequeue_lim, nr_cpu_ids);
332 smp_store_release(&rtp->percpu_enqueue_lim, nr_cpu_ids);
333 pr_info("Switching %s to per-CPU callback queuing.\n", rtp->name);
335 raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
338 /* We can't create the thread unless interrupts are enabled. */
339 if (needwake && READ_ONCE(rtp->kthread_ptr))
340 irq_work_queue(&rtpcp->rtp_irq_work);
343 // RCU callback function for rcu_barrier_tasks_generic().
344 static void rcu_barrier_tasks_generic_cb(struct rcu_head *rhp)
346 struct rcu_tasks *rtp;
347 struct rcu_tasks_percpu *rtpcp;
349 rtpcp = container_of(rhp, struct rcu_tasks_percpu, barrier_q_head);
351 if (atomic_dec_and_test(&rtp->barrier_q_count))
352 complete(&rtp->barrier_q_completion);
355 // Wait for all in-flight callbacks for the specified RCU Tasks flavor.
356 // Operates in a manner similar to rcu_barrier().
357 static void rcu_barrier_tasks_generic(struct rcu_tasks *rtp)
361 struct rcu_tasks_percpu *rtpcp;
362 unsigned long s = rcu_seq_snap(&rtp->barrier_q_seq);
364 mutex_lock(&rtp->barrier_q_mutex);
365 if (rcu_seq_done(&rtp->barrier_q_seq, s)) {
367 mutex_unlock(&rtp->barrier_q_mutex);
370 rcu_seq_start(&rtp->barrier_q_seq);
371 init_completion(&rtp->barrier_q_completion);
372 atomic_set(&rtp->barrier_q_count, 2);
373 for_each_possible_cpu(cpu) {
374 if (cpu >= smp_load_acquire(&rtp->percpu_dequeue_lim))
376 rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
377 rtpcp->barrier_q_head.func = rcu_barrier_tasks_generic_cb;
378 raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
379 if (rcu_segcblist_entrain(&rtpcp->cblist, &rtpcp->barrier_q_head))
380 atomic_inc(&rtp->barrier_q_count);
381 raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
383 if (atomic_sub_and_test(2, &rtp->barrier_q_count))
384 complete(&rtp->barrier_q_completion);
385 wait_for_completion(&rtp->barrier_q_completion);
386 rcu_seq_end(&rtp->barrier_q_seq);
387 mutex_unlock(&rtp->barrier_q_mutex);
390 // Advance callbacks and indicate whether either a grace period or
391 // callback invocation is needed.
392 static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp)
396 bool gpdone = poll_state_synchronize_rcu(rtp->percpu_dequeue_gpseq);
402 for (cpu = 0; cpu < smp_load_acquire(&rtp->percpu_dequeue_lim); cpu++) {
403 struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
405 /* Advance and accelerate any new callbacks. */
406 if (!rcu_segcblist_n_cbs(&rtpcp->cblist))
408 raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
409 // Should we shrink down to a single callback queue?
410 n = rcu_segcblist_n_cbs(&rtpcp->cblist);
416 rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq));
417 (void)rcu_segcblist_accelerate(&rtpcp->cblist, rcu_seq_snap(&rtp->tasks_gp_seq));
418 if (rcu_segcblist_pend_cbs(&rtpcp->cblist))
420 if (!rcu_segcblist_empty(&rtpcp->cblist))
422 raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
425 // Shrink down to a single callback queue if appropriate.
426 // This is done in two stages: (1) If there are no more than
427 // rcu_task_collapse_lim callbacks on CPU 0 and none on any other
428 // CPU, limit enqueueing to CPU 0. (2) After an RCU grace period,
429 // if there has not been an increase in callbacks, limit dequeuing
430 // to CPU 0. Note the matching RCU read-side critical section in
431 // call_rcu_tasks_generic().
432 if (rcu_task_cb_adjust && ncbs <= rcu_task_collapse_lim) {
433 raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags);
434 if (rtp->percpu_enqueue_lim > 1) {
435 WRITE_ONCE(rtp->percpu_enqueue_shift, order_base_2(nr_cpu_ids));
436 smp_store_release(&rtp->percpu_enqueue_lim, 1);
437 rtp->percpu_dequeue_gpseq = get_state_synchronize_rcu();
439 pr_info("Starting switch %s to CPU-0 callback queuing.\n", rtp->name);
441 raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
443 if (rcu_task_cb_adjust && !ncbsnz && gpdone) {
444 raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags);
445 if (rtp->percpu_enqueue_lim < rtp->percpu_dequeue_lim) {
446 WRITE_ONCE(rtp->percpu_dequeue_lim, 1);
447 pr_info("Completing switch %s to CPU-0 callback queuing.\n", rtp->name);
449 if (rtp->percpu_dequeue_lim == 1) {
450 for (cpu = rtp->percpu_dequeue_lim; cpu < nr_cpu_ids; cpu++) {
451 struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
453 WARN_ON_ONCE(rcu_segcblist_n_cbs(&rtpcp->cblist));
456 raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags);
462 // Advance callbacks and invoke any that are ready.
463 static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp, struct rcu_tasks_percpu *rtpcp)
470 struct rcu_head *rhp;
471 struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
472 struct rcu_tasks_percpu *rtpcp_next;
475 cpunext = cpu * 2 + 1;
476 if (cpunext < smp_load_acquire(&rtp->percpu_dequeue_lim)) {
477 rtpcp_next = per_cpu_ptr(rtp->rtpcpu, cpunext);
478 cpuwq = rcu_cpu_beenfullyonline(cpunext) ? cpunext : WORK_CPU_UNBOUND;
479 queue_work_on(cpuwq, system_wq, &rtpcp_next->rtp_work);
481 if (cpunext < smp_load_acquire(&rtp->percpu_dequeue_lim)) {
482 rtpcp_next = per_cpu_ptr(rtp->rtpcpu, cpunext);
483 cpuwq = rcu_cpu_beenfullyonline(cpunext) ? cpunext : WORK_CPU_UNBOUND;
484 queue_work_on(cpuwq, system_wq, &rtpcp_next->rtp_work);
488 if (rcu_segcblist_empty(&rtpcp->cblist) || !cpu_possible(cpu))
490 raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
491 rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq));
492 rcu_segcblist_extract_done_cbs(&rtpcp->cblist, &rcl);
493 raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
495 for (rhp = rcu_cblist_dequeue(&rcl); rhp; rhp = rcu_cblist_dequeue(&rcl)) {
501 raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
502 rcu_segcblist_add_len(&rtpcp->cblist, -len);
503 (void)rcu_segcblist_accelerate(&rtpcp->cblist, rcu_seq_snap(&rtp->tasks_gp_seq));
504 raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
507 // Workqueue flood to advance callbacks and invoke any that are ready.
508 static void rcu_tasks_invoke_cbs_wq(struct work_struct *wp)
510 struct rcu_tasks *rtp;
511 struct rcu_tasks_percpu *rtpcp = container_of(wp, struct rcu_tasks_percpu, rtp_work);
514 rcu_tasks_invoke_cbs(rtp, rtpcp);
517 // Wait for one grace period.
518 static void rcu_tasks_one_gp(struct rcu_tasks *rtp, bool midboot)
522 mutex_lock(&rtp->tasks_gp_mutex);
524 // If there were none, wait a bit and start over.
525 if (unlikely(midboot)) {
528 set_tasks_gp_state(rtp, RTGS_WAIT_CBS);
529 rcuwait_wait_event(&rtp->cbs_wait,
530 (needgpcb = rcu_tasks_need_gpcb(rtp)),
534 if (needgpcb & 0x2) {
535 // Wait for one grace period.
536 set_tasks_gp_state(rtp, RTGS_WAIT_GP);
537 rtp->gp_start = jiffies;
538 rcu_seq_start(&rtp->tasks_gp_seq);
540 rcu_seq_end(&rtp->tasks_gp_seq);
544 set_tasks_gp_state(rtp, RTGS_INVOKE_CBS);
545 rcu_tasks_invoke_cbs(rtp, per_cpu_ptr(rtp->rtpcpu, 0));
546 mutex_unlock(&rtp->tasks_gp_mutex);
549 // RCU-tasks kthread that detects grace periods and invokes callbacks.
550 static int __noreturn rcu_tasks_kthread(void *arg)
552 struct rcu_tasks *rtp = arg;
554 /* Run on housekeeping CPUs by default. Sysadm can move if desired. */
555 housekeeping_affine(current, HK_TYPE_RCU);
556 WRITE_ONCE(rtp->kthread_ptr, current); // Let GPs start!
559 * Each pass through the following loop makes one check for
560 * newly arrived callbacks, and, if there are some, waits for
561 * one RCU-tasks grace period and then invokes the callbacks.
562 * This loop is terminated by the system going down. ;-)
565 // Wait for one grace period and invoke any callbacks
567 rcu_tasks_one_gp(rtp, false);
569 // Paranoid sleep to keep this from entering a tight loop.
570 schedule_timeout_idle(rtp->gp_sleep);
574 // Wait for a grace period for the specified flavor of Tasks RCU.
575 static void synchronize_rcu_tasks_generic(struct rcu_tasks *rtp)
577 /* Complain if the scheduler has not started. */
578 if (WARN_ONCE(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
579 "synchronize_%s() called too soon", rtp->name))
582 // If the grace-period kthread is running, use it.
583 if (READ_ONCE(rtp->kthread_ptr)) {
584 wait_rcu_gp(rtp->call_func);
587 rcu_tasks_one_gp(rtp, true);
590 /* Spawn RCU-tasks grace-period kthread. */
591 static void __init rcu_spawn_tasks_kthread_generic(struct rcu_tasks *rtp)
593 struct task_struct *t;
595 t = kthread_run(rcu_tasks_kthread, rtp, "%s_kthread", rtp->kname);
596 if (WARN_ONCE(IS_ERR(t), "%s: Could not start %s grace-period kthread, OOM is now expected behavior\n", __func__, rtp->name))
598 smp_mb(); /* Ensure others see full kthread. */
601 #ifndef CONFIG_TINY_RCU
604 * Print any non-default Tasks RCU settings.
606 static void __init rcu_tasks_bootup_oddness(void)
608 #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU)
611 if (rcu_task_stall_timeout != RCU_TASK_STALL_TIMEOUT)
612 pr_info("\tTasks-RCU CPU stall warnings timeout set to %d (rcu_task_stall_timeout).\n", rcu_task_stall_timeout);
613 rtsimc = clamp(rcu_task_stall_info_mult, 1, 10);
614 if (rtsimc != rcu_task_stall_info_mult) {
615 pr_info("\tTasks-RCU CPU stall info multiplier clamped to %d (rcu_task_stall_info_mult).\n", rtsimc);
616 rcu_task_stall_info_mult = rtsimc;
618 #endif /* #ifdef CONFIG_TASKS_RCU */
619 #ifdef CONFIG_TASKS_RCU
620 pr_info("\tTrampoline variant of Tasks RCU enabled.\n");
621 #endif /* #ifdef CONFIG_TASKS_RCU */
622 #ifdef CONFIG_TASKS_RUDE_RCU
623 pr_info("\tRude variant of Tasks RCU enabled.\n");
624 #endif /* #ifdef CONFIG_TASKS_RUDE_RCU */
625 #ifdef CONFIG_TASKS_TRACE_RCU
626 pr_info("\tTracing variant of Tasks RCU enabled.\n");
627 #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */
630 #endif /* #ifndef CONFIG_TINY_RCU */
632 #ifndef CONFIG_TINY_RCU
633 /* Dump out rcutorture-relevant state common to all RCU-tasks flavors. */
634 static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s)
637 bool havecbs = false;
639 for_each_possible_cpu(cpu) {
640 struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
642 if (!data_race(rcu_segcblist_empty(&rtpcp->cblist))) {
647 pr_info("%s: %s(%d) since %lu g:%lu i:%lu/%lu %c%c %s\n",
649 tasks_gp_state_getname(rtp), data_race(rtp->gp_state),
650 jiffies - data_race(rtp->gp_jiffies),
651 data_race(rcu_seq_current(&rtp->tasks_gp_seq)),
652 data_race(rtp->n_ipis_fails), data_race(rtp->n_ipis),
653 ".k"[!!data_race(rtp->kthread_ptr)],
657 #endif // #ifndef CONFIG_TINY_RCU
659 static void exit_tasks_rcu_finish_trace(struct task_struct *t);
661 #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU)
663 ////////////////////////////////////////////////////////////////////////
665 // Shared code between task-list-scanning variants of Tasks RCU.
667 /* Wait for one RCU-tasks grace period. */
668 static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
670 struct task_struct *g;
674 unsigned long lastinfo;
675 unsigned long lastreport;
676 bool reported = false;
678 struct task_struct *t;
680 set_tasks_gp_state(rtp, RTGS_PRE_WAIT_GP);
681 rtp->pregp_func(&holdouts);
684 * There were callbacks, so we need to wait for an RCU-tasks
685 * grace period. Start off by scanning the task list for tasks
686 * that are not already voluntarily blocked. Mark these tasks
687 * and make a list of them in holdouts.
689 set_tasks_gp_state(rtp, RTGS_SCAN_TASKLIST);
690 if (rtp->pertask_func) {
692 for_each_process_thread(g, t)
693 rtp->pertask_func(t, &holdouts);
697 set_tasks_gp_state(rtp, RTGS_POST_SCAN_TASKLIST);
698 rtp->postscan_func(&holdouts);
701 * Each pass through the following loop scans the list of holdout
702 * tasks, removing any that are no longer holdouts. When the list
703 * is empty, we are done.
705 lastreport = jiffies;
706 lastinfo = lastreport;
707 rtsi = READ_ONCE(rcu_task_stall_info);
709 // Start off with initial wait and slowly back off to 1 HZ wait.
710 fract = rtp->init_fract;
712 while (!list_empty(&holdouts)) {
718 // Slowly back off waiting for holdouts
719 set_tasks_gp_state(rtp, RTGS_WAIT_SCAN_HOLDOUTS);
720 if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
721 schedule_timeout_idle(fract);
723 exp = jiffies_to_nsecs(fract);
724 __set_current_state(TASK_IDLE);
725 schedule_hrtimeout_range(&exp, jiffies_to_nsecs(HZ / 2), HRTIMER_MODE_REL_HARD);
731 rtst = READ_ONCE(rcu_task_stall_timeout);
732 needreport = rtst > 0 && time_after(jiffies, lastreport + rtst);
734 lastreport = jiffies;
738 WARN_ON(signal_pending(current));
739 set_tasks_gp_state(rtp, RTGS_SCAN_HOLDOUTS);
740 rtp->holdouts_func(&holdouts, needreport, &firstreport);
742 // Print pre-stall informational messages if needed.
744 if (rtsi > 0 && !reported && time_after(j, lastinfo + rtsi)) {
746 rtsi = rtsi * rcu_task_stall_info_mult;
747 pr_info("%s: %s grace period number %lu (since boot) is %lu jiffies old.\n",
748 __func__, rtp->kname, rtp->tasks_gp_seq, j - rtp->gp_start);
752 set_tasks_gp_state(rtp, RTGS_POST_GP);
753 rtp->postgp_func(rtp);
756 #endif /* #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU) */
758 #ifdef CONFIG_TASKS_RCU
760 ////////////////////////////////////////////////////////////////////////
762 // Simple variant of RCU whose quiescent states are voluntary context
763 // switch, cond_resched_tasks_rcu_qs(), user-space execution, and idle.
764 // As such, grace periods can take one good long time. There are no
765 // read-side primitives similar to rcu_read_lock() and rcu_read_unlock()
766 // because this implementation is intended to get the system into a safe
767 // state for some of the manipulations involved in tracing and the like.
768 // Finally, this implementation does not support high call_rcu_tasks()
769 // rates from multiple CPUs. If this is required, per-CPU callback lists
772 // The implementation uses rcu_tasks_wait_gp(), which relies on function
773 // pointers in the rcu_tasks structure. The rcu_spawn_tasks_kthread()
774 // function sets these function pointers up so that rcu_tasks_wait_gp()
775 // invokes these functions in this order:
777 // rcu_tasks_pregp_step():
778 // Invokes synchronize_rcu() in order to wait for all in-flight
779 // t->on_rq and t->nvcsw transitions to complete. This works because
780 // all such transitions are carried out with interrupts disabled.
781 // rcu_tasks_pertask(), invoked on every non-idle task:
782 // For every runnable non-idle task other than the current one, use
783 // get_task_struct() to pin down that task, snapshot that task's
784 // number of voluntary context switches, and add that task to the
786 // rcu_tasks_postscan():
787 // Invoke synchronize_srcu() to ensure that all tasks that were
788 // in the process of exiting (and which thus might not know to
789 // synchronize with this RCU Tasks grace period) have completed
791 // check_all_holdout_tasks(), repeatedly until holdout list is empty:
792 // Scans the holdout list, attempting to identify a quiescent state
793 // for each task on the list. If there is a quiescent state, the
794 // corresponding task is removed from the holdout list.
795 // rcu_tasks_postgp():
796 // Invokes synchronize_rcu() in order to ensure that all prior
797 // t->on_rq and t->nvcsw transitions are seen by all CPUs and tasks
798 // to have happened before the end of this RCU Tasks grace period.
799 // Again, this works because all such transitions are carried out
800 // with interrupts disabled.
802 // For each exiting task, the exit_tasks_rcu_start() and
803 // exit_tasks_rcu_finish() functions begin and end, respectively, the SRCU
804 // read-side critical sections waited for by rcu_tasks_postscan().
806 // Pre-grace-period update-side code is ordered before the grace
807 // via the raw_spin_lock.*rcu_node(). Pre-grace-period read-side code
808 // is ordered before the grace period via synchronize_rcu() call in
809 // rcu_tasks_pregp_step() and by the scheduler's locks and interrupt
812 /* Pre-grace-period preparation. */
813 static void rcu_tasks_pregp_step(struct list_head *hop)
816 * Wait for all pre-existing t->on_rq and t->nvcsw transitions
817 * to complete. Invoking synchronize_rcu() suffices because all
818 * these transitions occur with interrupts disabled. Without this
819 * synchronize_rcu(), a read-side critical section that started
820 * before the grace period might be incorrectly seen as having
821 * started after the grace period.
823 * This synchronize_rcu() also dispenses with the need for a
824 * memory barrier on the first store to t->rcu_tasks_holdout,
825 * as it forces the store to happen after the beginning of the
831 /* Per-task initial processing. */
832 static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop)
834 if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) {
836 t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);
837 WRITE_ONCE(t->rcu_tasks_holdout, true);
838 list_add(&t->rcu_tasks_holdout_list, hop);
842 /* Processing between scanning taskslist and draining the holdout list. */
843 static void rcu_tasks_postscan(struct list_head *hop)
845 int rtsi = READ_ONCE(rcu_task_stall_info);
847 if (!IS_ENABLED(CONFIG_TINY_RCU)) {
848 tasks_rcu_exit_srcu_stall_timer.expires = jiffies + rtsi;
849 add_timer(&tasks_rcu_exit_srcu_stall_timer);
853 * Exiting tasks may escape the tasklist scan. Those are vulnerable
854 * until their final schedule() with TASK_DEAD state. To cope with
855 * this, divide the fragile exit path part in two intersecting
856 * read side critical sections:
858 * 1) An _SRCU_ read side starting before calling exit_notify(),
859 * which may remove the task from the tasklist, and ending after
860 * the final preempt_disable() call in do_exit().
862 * 2) An _RCU_ read side starting with the final preempt_disable()
863 * call in do_exit() and ending with the final call to schedule()
864 * with TASK_DEAD state.
866 * This handles the part 1). And postgp will handle part 2) with a
867 * call to synchronize_rcu().
869 synchronize_srcu(&tasks_rcu_exit_srcu);
871 if (!IS_ENABLED(CONFIG_TINY_RCU))
872 del_timer_sync(&tasks_rcu_exit_srcu_stall_timer);
875 /* See if tasks are still holding out, complain if so. */
876 static void check_holdout_task(struct task_struct *t,
877 bool needreport, bool *firstreport)
881 if (!READ_ONCE(t->rcu_tasks_holdout) ||
882 t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||
883 !READ_ONCE(t->on_rq) ||
884 (IS_ENABLED(CONFIG_NO_HZ_FULL) &&
885 !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
886 WRITE_ONCE(t->rcu_tasks_holdout, false);
887 list_del_init(&t->rcu_tasks_holdout_list);
891 rcu_request_urgent_qs_task(t);
895 pr_err("INFO: rcu_tasks detected stalls on tasks:\n");
896 *firstreport = false;
899 pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n",
900 t, ".I"[is_idle_task(t)],
901 "N."[cpu < 0 || !tick_nohz_full_cpu(cpu)],
902 t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout,
903 t->rcu_tasks_idle_cpu, cpu);
907 /* Scan the holdout lists for tasks no longer holding out. */
908 static void check_all_holdout_tasks(struct list_head *hop,
909 bool needreport, bool *firstreport)
911 struct task_struct *t, *t1;
913 list_for_each_entry_safe(t, t1, hop, rcu_tasks_holdout_list) {
914 check_holdout_task(t, needreport, firstreport);
919 /* Finish off the Tasks-RCU grace period. */
920 static void rcu_tasks_postgp(struct rcu_tasks *rtp)
923 * Because ->on_rq and ->nvcsw are not guaranteed to have a full
924 * memory barriers prior to them in the schedule() path, memory
925 * reordering on other CPUs could cause their RCU-tasks read-side
926 * critical sections to extend past the end of the grace period.
927 * However, because these ->nvcsw updates are carried out with
928 * interrupts disabled, we can use synchronize_rcu() to force the
929 * needed ordering on all such CPUs.
931 * This synchronize_rcu() also confines all ->rcu_tasks_holdout
932 * accesses to be within the grace period, avoiding the need for
933 * memory barriers for ->rcu_tasks_holdout accesses.
935 * In addition, this synchronize_rcu() waits for exiting tasks
936 * to complete their final preempt_disable() region of execution,
937 * cleaning up after synchronize_srcu(&tasks_rcu_exit_srcu),
938 * enforcing the whole region before tasklist removal until
939 * the final schedule() with TASK_DEAD state to be an RCU TASKS
940 * read side critical section.
945 void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func);
946 DEFINE_RCU_TASKS(rcu_tasks, rcu_tasks_wait_gp, call_rcu_tasks, "RCU Tasks");
948 static void tasks_rcu_exit_srcu_stall(struct timer_list *unused)
950 #ifndef CONFIG_TINY_RCU
953 rtsi = READ_ONCE(rcu_task_stall_info);
954 pr_info("%s: %s grace period number %lu (since boot) gp_state: %s is %lu jiffies old.\n",
955 __func__, rcu_tasks.kname, rcu_tasks.tasks_gp_seq,
956 tasks_gp_state_getname(&rcu_tasks), jiffies - rcu_tasks.gp_jiffies);
957 pr_info("Please check any exiting tasks stuck between calls to exit_tasks_rcu_start() and exit_tasks_rcu_finish()\n");
958 tasks_rcu_exit_srcu_stall_timer.expires = jiffies + rtsi;
959 add_timer(&tasks_rcu_exit_srcu_stall_timer);
960 #endif // #ifndef CONFIG_TINY_RCU
964 * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
965 * @rhp: structure to be used for queueing the RCU updates.
966 * @func: actual callback function to be invoked after the grace period
968 * The callback function will be invoked some time after a full grace
969 * period elapses, in other words after all currently executing RCU
970 * read-side critical sections have completed. call_rcu_tasks() assumes
971 * that the read-side critical sections end at a voluntary context
972 * switch (not a preemption!), cond_resched_tasks_rcu_qs(), entry into idle,
973 * or transition to usermode execution. As such, there are no read-side
974 * primitives analogous to rcu_read_lock() and rcu_read_unlock() because
975 * this primitive is intended to determine that all tasks have passed
976 * through a safe state, not so much for data-structure synchronization.
978 * See the description of call_rcu() for more detailed information on
979 * memory ordering guarantees.
981 void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func)
983 call_rcu_tasks_generic(rhp, func, &rcu_tasks);
985 EXPORT_SYMBOL_GPL(call_rcu_tasks);
988 * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed.
990 * Control will return to the caller some time after a full rcu-tasks
991 * grace period has elapsed, in other words after all currently
992 * executing rcu-tasks read-side critical sections have elapsed. These
993 * read-side critical sections are delimited by calls to schedule(),
994 * cond_resched_tasks_rcu_qs(), idle execution, userspace execution, calls
995 * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched().
997 * This is a very specialized primitive, intended only for a few uses in
998 * tracing and other situations requiring manipulation of function
999 * preambles and profiling hooks. The synchronize_rcu_tasks() function
1000 * is not (yet) intended for heavy use from multiple CPUs.
1002 * See the description of synchronize_rcu() for more detailed information
1003 * on memory ordering guarantees.
1005 void synchronize_rcu_tasks(void)
1007 synchronize_rcu_tasks_generic(&rcu_tasks);
1009 EXPORT_SYMBOL_GPL(synchronize_rcu_tasks);
1012 * rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks.
1014 * Although the current implementation is guaranteed to wait, it is not
1015 * obligated to, for example, if there are no pending callbacks.
1017 void rcu_barrier_tasks(void)
1019 rcu_barrier_tasks_generic(&rcu_tasks);
1021 EXPORT_SYMBOL_GPL(rcu_barrier_tasks);
1023 static int __init rcu_spawn_tasks_kthread(void)
1025 cblist_init_generic(&rcu_tasks);
1026 rcu_tasks.gp_sleep = HZ / 10;
1027 rcu_tasks.init_fract = HZ / 10;
1028 rcu_tasks.pregp_func = rcu_tasks_pregp_step;
1029 rcu_tasks.pertask_func = rcu_tasks_pertask;
1030 rcu_tasks.postscan_func = rcu_tasks_postscan;
1031 rcu_tasks.holdouts_func = check_all_holdout_tasks;
1032 rcu_tasks.postgp_func = rcu_tasks_postgp;
1033 rcu_spawn_tasks_kthread_generic(&rcu_tasks);
1037 #if !defined(CONFIG_TINY_RCU)
1038 void show_rcu_tasks_classic_gp_kthread(void)
1040 show_rcu_tasks_generic_gp_kthread(&rcu_tasks, "");
1042 EXPORT_SYMBOL_GPL(show_rcu_tasks_classic_gp_kthread);
1043 #endif // !defined(CONFIG_TINY_RCU)
1046 * Contribute to protect against tasklist scan blind spot while the
1047 * task is exiting and may be removed from the tasklist. See
1048 * corresponding synchronize_srcu() for further details.
1050 void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu)
1052 current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
1056 * Contribute to protect against tasklist scan blind spot while the
1057 * task is exiting and may be removed from the tasklist. See
1058 * corresponding synchronize_srcu() for further details.
1060 void exit_tasks_rcu_stop(void) __releases(&tasks_rcu_exit_srcu)
1062 struct task_struct *t = current;
1064 __srcu_read_unlock(&tasks_rcu_exit_srcu, t->rcu_tasks_idx);
1068 * Contribute to protect against tasklist scan blind spot while the
1069 * task is exiting and may be removed from the tasklist. See
1070 * corresponding synchronize_srcu() for further details.
1072 void exit_tasks_rcu_finish(void)
1074 exit_tasks_rcu_stop();
1075 exit_tasks_rcu_finish_trace(current);
1078 #else /* #ifdef CONFIG_TASKS_RCU */
1079 void exit_tasks_rcu_start(void) { }
1080 void exit_tasks_rcu_stop(void) { }
1081 void exit_tasks_rcu_finish(void) { exit_tasks_rcu_finish_trace(current); }
1082 #endif /* #else #ifdef CONFIG_TASKS_RCU */
1084 #ifdef CONFIG_TASKS_RUDE_RCU
1086 ////////////////////////////////////////////////////////////////////////
1088 // "Rude" variant of Tasks RCU, inspired by Steve Rostedt's trick of
1089 // passing an empty function to schedule_on_each_cpu(). This approach
1090 // provides an asynchronous call_rcu_tasks_rude() API and batching of
1091 // concurrent calls to the synchronous synchronize_rcu_tasks_rude() API.
1092 // This invokes schedule_on_each_cpu() in order to send IPIs far and wide
1093 // and induces otherwise unnecessary context switches on all online CPUs,
1094 // whether idle or not.
1096 // Callback handling is provided by the rcu_tasks_kthread() function.
1098 // Ordering is provided by the scheduler's context-switch code.
1100 // Empty function to allow workqueues to force a context switch.
1101 static void rcu_tasks_be_rude(struct work_struct *work)
1105 // Wait for one rude RCU-tasks grace period.
1106 static void rcu_tasks_rude_wait_gp(struct rcu_tasks *rtp)
1108 rtp->n_ipis += cpumask_weight(cpu_online_mask);
1109 schedule_on_each_cpu(rcu_tasks_be_rude);
1112 void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func);
1113 DEFINE_RCU_TASKS(rcu_tasks_rude, rcu_tasks_rude_wait_gp, call_rcu_tasks_rude,
1117 * call_rcu_tasks_rude() - Queue a callback rude task-based grace period
1118 * @rhp: structure to be used for queueing the RCU updates.
1119 * @func: actual callback function to be invoked after the grace period
1121 * The callback function will be invoked some time after a full grace
1122 * period elapses, in other words after all currently executing RCU
1123 * read-side critical sections have completed. call_rcu_tasks_rude()
1124 * assumes that the read-side critical sections end at context switch,
1125 * cond_resched_tasks_rcu_qs(), or transition to usermode execution (as
1126 * usermode execution is schedulable). As such, there are no read-side
1127 * primitives analogous to rcu_read_lock() and rcu_read_unlock() because
1128 * this primitive is intended to determine that all tasks have passed
1129 * through a safe state, not so much for data-structure synchronization.
1131 * See the description of call_rcu() for more detailed information on
1132 * memory ordering guarantees.
1134 void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func)
1136 call_rcu_tasks_generic(rhp, func, &rcu_tasks_rude);
1138 EXPORT_SYMBOL_GPL(call_rcu_tasks_rude);
1141 * synchronize_rcu_tasks_rude - wait for a rude rcu-tasks grace period
1143 * Control will return to the caller some time after a rude rcu-tasks
1144 * grace period has elapsed, in other words after all currently
1145 * executing rcu-tasks read-side critical sections have elapsed. These
1146 * read-side critical sections are delimited by calls to schedule(),
1147 * cond_resched_tasks_rcu_qs(), userspace execution (which is a schedulable
1148 * context), and (in theory, anyway) cond_resched().
1150 * This is a very specialized primitive, intended only for a few uses in
1151 * tracing and other situations requiring manipulation of function preambles
1152 * and profiling hooks. The synchronize_rcu_tasks_rude() function is not
1153 * (yet) intended for heavy use from multiple CPUs.
1155 * See the description of synchronize_rcu() for more detailed information
1156 * on memory ordering guarantees.
1158 void synchronize_rcu_tasks_rude(void)
1160 synchronize_rcu_tasks_generic(&rcu_tasks_rude);
1162 EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_rude);
1165 * rcu_barrier_tasks_rude - Wait for in-flight call_rcu_tasks_rude() callbacks.
1167 * Although the current implementation is guaranteed to wait, it is not
1168 * obligated to, for example, if there are no pending callbacks.
1170 void rcu_barrier_tasks_rude(void)
1172 rcu_barrier_tasks_generic(&rcu_tasks_rude);
1174 EXPORT_SYMBOL_GPL(rcu_barrier_tasks_rude);
1176 static int __init rcu_spawn_tasks_rude_kthread(void)
1178 cblist_init_generic(&rcu_tasks_rude);
1179 rcu_tasks_rude.gp_sleep = HZ / 10;
1180 rcu_spawn_tasks_kthread_generic(&rcu_tasks_rude);
1184 #if !defined(CONFIG_TINY_RCU)
1185 void show_rcu_tasks_rude_gp_kthread(void)
1187 show_rcu_tasks_generic_gp_kthread(&rcu_tasks_rude, "");
1189 EXPORT_SYMBOL_GPL(show_rcu_tasks_rude_gp_kthread);
1190 #endif // !defined(CONFIG_TINY_RCU)
1191 #endif /* #ifdef CONFIG_TASKS_RUDE_RCU */
1193 ////////////////////////////////////////////////////////////////////////
1195 // Tracing variant of Tasks RCU. This variant is designed to be used
1196 // to protect tracing hooks, including those of BPF. This variant
1199 // 1. Has explicit read-side markers to allow finite grace periods
1200 // in the face of in-kernel loops for PREEMPT=n builds.
1202 // 2. Protects code in the idle loop, exception entry/exit, and
1203 // CPU-hotplug code paths, similar to the capabilities of SRCU.
1205 // 3. Avoids expensive read-side instructions, having overhead similar
1206 // to that of Preemptible RCU.
1208 // There are of course downsides. For example, the grace-period code
1209 // can send IPIs to CPUs, even when those CPUs are in the idle loop or
1210 // in nohz_full userspace. If needed, these downsides can be at least
1211 // partially remedied.
1213 // Perhaps most important, this variant of RCU does not affect the vanilla
1214 // flavors, rcu_preempt and rcu_sched. The fact that RCU Tasks Trace
1215 // readers can operate from idle, offline, and exception entry/exit in no
1216 // way allows rcu_preempt and rcu_sched readers to also do so.
1218 // The implementation uses rcu_tasks_wait_gp(), which relies on function
1219 // pointers in the rcu_tasks structure. The rcu_spawn_tasks_trace_kthread()
1220 // function sets these function pointers up so that rcu_tasks_wait_gp()
1221 // invokes these functions in this order:
1223 // rcu_tasks_trace_pregp_step():
1224 // Disables CPU hotplug, adds all currently executing tasks to the
1225 // holdout list, then checks the state of all tasks that blocked
1226 // or were preempted within their current RCU Tasks Trace read-side
1227 // critical section, adding them to the holdout list if appropriate.
1228 // Finally, this function re-enables CPU hotplug.
1229 // The ->pertask_func() pointer is NULL, so there is no per-task processing.
1230 // rcu_tasks_trace_postscan():
1231 // Invokes synchronize_rcu() to wait for late-stage exiting tasks
1232 // to finish exiting.
1233 // check_all_holdout_tasks_trace(), repeatedly until holdout list is empty:
1234 // Scans the holdout list, attempting to identify a quiescent state
1235 // for each task on the list. If there is a quiescent state, the
1236 // corresponding task is removed from the holdout list. Once this
1237 // list is empty, the grace period has completed.
1238 // rcu_tasks_trace_postgp():
1239 // Provides the needed full memory barrier and does debug checks.
1241 // The exit_tasks_rcu_finish_trace() synchronizes with exiting tasks.
1243 // Pre-grace-period update-side code is ordered before the grace period
1244 // via the ->cbs_lock and barriers in rcu_tasks_kthread(). Pre-grace-period
1245 // read-side code is ordered before the grace period by atomic operations
1246 // on .b.need_qs flag of each task involved in this process, or by scheduler
1247 // context-switch ordering (for locked-down non-running readers).
1249 // The lockdep state must be outside of #ifdef to be useful.
1250 #ifdef CONFIG_DEBUG_LOCK_ALLOC
1251 static struct lock_class_key rcu_lock_trace_key;
1252 struct lockdep_map rcu_trace_lock_map =
1253 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_trace", &rcu_lock_trace_key);
1254 EXPORT_SYMBOL_GPL(rcu_trace_lock_map);
1255 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
1257 #ifdef CONFIG_TASKS_TRACE_RCU
1259 // Record outstanding IPIs to each CPU. No point in sending two...
1260 static DEFINE_PER_CPU(bool, trc_ipi_to_cpu);
1262 // The number of detections of task quiescent state relying on
1263 // heavyweight readers executing explicit memory barriers.
1264 static unsigned long n_heavy_reader_attempts;
1265 static unsigned long n_heavy_reader_updates;
1266 static unsigned long n_heavy_reader_ofl_updates;
1267 static unsigned long n_trc_holdouts;
1269 void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func);
1270 DEFINE_RCU_TASKS(rcu_tasks_trace, rcu_tasks_wait_gp, call_rcu_tasks_trace,
1273 /* Load from ->trc_reader_special.b.need_qs with proper ordering. */
1274 static u8 rcu_ld_need_qs(struct task_struct *t)
1276 smp_mb(); // Enforce full grace-period ordering.
1277 return smp_load_acquire(&t->trc_reader_special.b.need_qs);
1280 /* Store to ->trc_reader_special.b.need_qs with proper ordering. */
1281 static void rcu_st_need_qs(struct task_struct *t, u8 v)
1283 smp_store_release(&t->trc_reader_special.b.need_qs, v);
1284 smp_mb(); // Enforce full grace-period ordering.
1288 * Do a cmpxchg() on ->trc_reader_special.b.need_qs, allowing for
1289 * the four-byte operand-size restriction of some platforms.
1290 * Returns the old value, which is often ignored.
1292 u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new)
1294 union rcu_special ret;
1295 union rcu_special trs_old = READ_ONCE(t->trc_reader_special);
1296 union rcu_special trs_new = trs_old;
1298 if (trs_old.b.need_qs != old)
1299 return trs_old.b.need_qs;
1300 trs_new.b.need_qs = new;
1301 ret.s = cmpxchg(&t->trc_reader_special.s, trs_old.s, trs_new.s);
1302 return ret.b.need_qs;
1304 EXPORT_SYMBOL_GPL(rcu_trc_cmpxchg_need_qs);
1307 * If we are the last reader, signal the grace-period kthread.
1308 * Also remove from the per-CPU list of blocked tasks.
1310 void rcu_read_unlock_trace_special(struct task_struct *t)
1312 unsigned long flags;
1313 struct rcu_tasks_percpu *rtpcp;
1314 union rcu_special trs;
1316 // Open-coded full-word version of rcu_ld_need_qs().
1317 smp_mb(); // Enforce full grace-period ordering.
1318 trs = smp_load_acquire(&t->trc_reader_special);
1320 if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && t->trc_reader_special.b.need_mb)
1321 smp_mb(); // Pairs with update-side barriers.
1322 // Update .need_qs before ->trc_reader_nesting for irq/NMI handlers.
1323 if (trs.b.need_qs == (TRC_NEED_QS_CHECKED | TRC_NEED_QS)) {
1324 u8 result = rcu_trc_cmpxchg_need_qs(t, TRC_NEED_QS_CHECKED | TRC_NEED_QS,
1325 TRC_NEED_QS_CHECKED);
1327 WARN_ONCE(result != trs.b.need_qs, "%s: result = %d", __func__, result);
1329 if (trs.b.blocked) {
1330 rtpcp = per_cpu_ptr(rcu_tasks_trace.rtpcpu, t->trc_blkd_cpu);
1331 raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
1332 list_del_init(&t->trc_blkd_node);
1333 WRITE_ONCE(t->trc_reader_special.b.blocked, false);
1334 raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
1336 WRITE_ONCE(t->trc_reader_nesting, 0);
1338 EXPORT_SYMBOL_GPL(rcu_read_unlock_trace_special);
1340 /* Add a newly blocked reader task to its CPU's list. */
1341 void rcu_tasks_trace_qs_blkd(struct task_struct *t)
1343 unsigned long flags;
1344 struct rcu_tasks_percpu *rtpcp;
1346 local_irq_save(flags);
1347 rtpcp = this_cpu_ptr(rcu_tasks_trace.rtpcpu);
1348 raw_spin_lock_rcu_node(rtpcp); // irqs already disabled
1349 t->trc_blkd_cpu = smp_processor_id();
1350 if (!rtpcp->rtp_blkd_tasks.next)
1351 INIT_LIST_HEAD(&rtpcp->rtp_blkd_tasks);
1352 list_add(&t->trc_blkd_node, &rtpcp->rtp_blkd_tasks);
1353 WRITE_ONCE(t->trc_reader_special.b.blocked, true);
1354 raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
1356 EXPORT_SYMBOL_GPL(rcu_tasks_trace_qs_blkd);
1358 /* Add a task to the holdout list, if it is not already on the list. */
1359 static void trc_add_holdout(struct task_struct *t, struct list_head *bhp)
1361 if (list_empty(&t->trc_holdout_list)) {
1363 list_add(&t->trc_holdout_list, bhp);
1368 /* Remove a task from the holdout list, if it is in fact present. */
1369 static void trc_del_holdout(struct task_struct *t)
1371 if (!list_empty(&t->trc_holdout_list)) {
1372 list_del_init(&t->trc_holdout_list);
1378 /* IPI handler to check task state. */
1379 static void trc_read_check_handler(void *t_in)
1382 struct task_struct *t = current;
1383 struct task_struct *texp = t_in;
1385 // If the task is no longer running on this CPU, leave.
1386 if (unlikely(texp != t))
1387 goto reset_ipi; // Already on holdout list, so will check later.
1389 // If the task is not in a read-side critical section, and
1390 // if this is the last reader, awaken the grace-period kthread.
1391 nesting = READ_ONCE(t->trc_reader_nesting);
1392 if (likely(!nesting)) {
1393 rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED);
1396 // If we are racing with an rcu_read_unlock_trace(), try again later.
1397 if (unlikely(nesting < 0))
1400 // Get here if the task is in a read-side critical section.
1401 // Set its state so that it will update state for the grace-period
1402 // kthread upon exit from that critical section.
1403 rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS | TRC_NEED_QS_CHECKED);
1406 // Allow future IPIs to be sent on CPU and for task.
1407 // Also order this IPI handler against any later manipulations of
1408 // the intended task.
1409 smp_store_release(per_cpu_ptr(&trc_ipi_to_cpu, smp_processor_id()), false); // ^^^
1410 smp_store_release(&texp->trc_ipi_to_cpu, -1); // ^^^
1413 /* Callback function for scheduler to check locked-down task. */
1414 static int trc_inspect_reader(struct task_struct *t, void *bhp_in)
1416 struct list_head *bhp = bhp_in;
1417 int cpu = task_cpu(t);
1419 bool ofl = cpu_is_offline(cpu);
1421 if (task_curr(t) && !ofl) {
1422 // If no chance of heavyweight readers, do it the hard way.
1423 if (!IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB))
1426 // If heavyweight readers are enabled on the remote task,
1427 // we can inspect its state despite its currently running.
1428 // However, we cannot safely change its state.
1429 n_heavy_reader_attempts++;
1430 // Check for "running" idle tasks on offline CPUs.
1431 if (!rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting))
1432 return -EINVAL; // No quiescent state, do it the hard way.
1433 n_heavy_reader_updates++;
1436 // The task is not running, so C-language access is safe.
1437 nesting = t->trc_reader_nesting;
1438 WARN_ON_ONCE(ofl && task_curr(t) && !is_idle_task(t));
1439 if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && ofl)
1440 n_heavy_reader_ofl_updates++;
1443 // If not exiting a read-side critical section, mark as checked
1444 // so that the grace-period kthread will remove it from the
1447 rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED);
1448 return 0; // In QS, so done.
1451 return -EINVAL; // Reader transitioning, try again later.
1453 // The task is in a read-side critical section, so set up its
1454 // state so that it will update state upon exit from that critical
1456 if (!rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS | TRC_NEED_QS_CHECKED))
1457 trc_add_holdout(t, bhp);
1461 /* Attempt to extract the state for the specified task. */
1462 static void trc_wait_for_one_reader(struct task_struct *t,
1463 struct list_head *bhp)
1467 // If a previous IPI is still in flight, let it complete.
1468 if (smp_load_acquire(&t->trc_ipi_to_cpu) != -1) // Order IPI
1471 // The current task had better be in a quiescent state.
1473 rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED);
1474 WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting));
1478 // Attempt to nail down the task for inspection.
1480 if (!task_call_func(t, trc_inspect_reader, bhp)) {
1486 // If this task is not yet on the holdout list, then we are in
1487 // an RCU read-side critical section. Otherwise, the invocation of
1488 // trc_add_holdout() that added it to the list did the necessary
1489 // get_task_struct(). Either way, the task cannot be freed out
1490 // from under this code.
1492 // If currently running, send an IPI, either way, add to list.
1493 trc_add_holdout(t, bhp);
1495 time_after(jiffies + 1, rcu_tasks_trace.gp_start + rcu_task_ipi_delay)) {
1496 // The task is currently running, so try IPIing it.
1499 // If there is already an IPI outstanding, let it happen.
1500 if (per_cpu(trc_ipi_to_cpu, cpu) || t->trc_ipi_to_cpu >= 0)
1503 per_cpu(trc_ipi_to_cpu, cpu) = true;
1504 t->trc_ipi_to_cpu = cpu;
1505 rcu_tasks_trace.n_ipis++;
1506 if (smp_call_function_single(cpu, trc_read_check_handler, t, 0)) {
1507 // Just in case there is some other reason for
1508 // failure than the target CPU being offline.
1509 WARN_ONCE(1, "%s(): smp_call_function_single() failed for CPU: %d\n",
1511 rcu_tasks_trace.n_ipis_fails++;
1512 per_cpu(trc_ipi_to_cpu, cpu) = false;
1513 t->trc_ipi_to_cpu = -1;
1519 * Initialize for first-round processing for the specified task.
1520 * Return false if task is NULL or already taken care of, true otherwise.
1522 static bool rcu_tasks_trace_pertask_prep(struct task_struct *t, bool notself)
1524 // During early boot when there is only the one boot CPU, there
1525 // is no idle task for the other CPUs. Also, the grace-period
1526 // kthread is always in a quiescent state. In addition, just return
1527 // if this task is already on the list.
1528 if (unlikely(t == NULL) || (t == current && notself) || !list_empty(&t->trc_holdout_list))
1531 rcu_st_need_qs(t, 0);
1532 t->trc_ipi_to_cpu = -1;
1536 /* Do first-round processing for the specified task. */
1537 static void rcu_tasks_trace_pertask(struct task_struct *t, struct list_head *hop)
1539 if (rcu_tasks_trace_pertask_prep(t, true))
1540 trc_wait_for_one_reader(t, hop);
1543 /* Initialize for a new RCU-tasks-trace grace period. */
1544 static void rcu_tasks_trace_pregp_step(struct list_head *hop)
1546 LIST_HEAD(blkd_tasks);
1548 unsigned long flags;
1549 struct rcu_tasks_percpu *rtpcp;
1550 struct task_struct *t;
1552 // There shouldn't be any old IPIs, but...
1553 for_each_possible_cpu(cpu)
1554 WARN_ON_ONCE(per_cpu(trc_ipi_to_cpu, cpu));
1556 // Disable CPU hotplug across the CPU scan for the benefit of
1557 // any IPIs that might be needed. This also waits for all readers
1558 // in CPU-hotplug code paths.
1561 // These rcu_tasks_trace_pertask_prep() calls are serialized to
1562 // allow safe access to the hop list.
1563 for_each_online_cpu(cpu) {
1565 t = cpu_curr_snapshot(cpu);
1566 if (rcu_tasks_trace_pertask_prep(t, true))
1567 trc_add_holdout(t, hop);
1569 cond_resched_tasks_rcu_qs();
1572 // Only after all running tasks have been accounted for is it
1573 // safe to take care of the tasks that have blocked within their
1574 // current RCU tasks trace read-side critical section.
1575 for_each_possible_cpu(cpu) {
1576 rtpcp = per_cpu_ptr(rcu_tasks_trace.rtpcpu, cpu);
1577 raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
1578 list_splice_init(&rtpcp->rtp_blkd_tasks, &blkd_tasks);
1579 while (!list_empty(&blkd_tasks)) {
1581 t = list_first_entry(&blkd_tasks, struct task_struct, trc_blkd_node);
1582 list_del_init(&t->trc_blkd_node);
1583 list_add(&t->trc_blkd_node, &rtpcp->rtp_blkd_tasks);
1584 raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
1585 rcu_tasks_trace_pertask(t, hop);
1587 raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
1589 raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
1590 cond_resched_tasks_rcu_qs();
1593 // Re-enable CPU hotplug now that the holdout list is populated.
1598 * Do intermediate processing between task and holdout scans.
1600 static void rcu_tasks_trace_postscan(struct list_head *hop)
1602 // Wait for late-stage exiting tasks to finish exiting.
1603 // These might have passed the call to exit_tasks_rcu_finish().
1605 // If you remove the following line, update rcu_trace_implies_rcu_gp()!!!
1607 // Any tasks that exit after this point will set
1608 // TRC_NEED_QS_CHECKED in ->trc_reader_special.b.need_qs.
1611 /* Communicate task state back to the RCU tasks trace stall warning request. */
1612 struct trc_stall_chk_rdr {
1618 static int trc_check_slow_task(struct task_struct *t, void *arg)
1620 struct trc_stall_chk_rdr *trc_rdrp = arg;
1622 if (task_curr(t) && cpu_online(task_cpu(t)))
1623 return false; // It is running, so decline to inspect it.
1624 trc_rdrp->nesting = READ_ONCE(t->trc_reader_nesting);
1625 trc_rdrp->ipi_to_cpu = READ_ONCE(t->trc_ipi_to_cpu);
1626 trc_rdrp->needqs = rcu_ld_need_qs(t);
1630 /* Show the state of a task stalling the current RCU tasks trace GP. */
1631 static void show_stalled_task_trace(struct task_struct *t, bool *firstreport)
1634 struct trc_stall_chk_rdr trc_rdr;
1635 bool is_idle_tsk = is_idle_task(t);
1638 pr_err("INFO: rcu_tasks_trace detected stalls on tasks:\n");
1639 *firstreport = false;
1642 if (!task_call_func(t, trc_check_slow_task, &trc_rdr))
1643 pr_alert("P%d: %c%c\n",
1645 ".I"[t->trc_ipi_to_cpu >= 0],
1648 pr_alert("P%d: %c%c%c%c nesting: %d%c%c cpu: %d%s\n",
1650 ".I"[trc_rdr.ipi_to_cpu >= 0],
1652 ".N"[cpu >= 0 && tick_nohz_full_cpu(cpu)],
1653 ".B"[!!data_race(t->trc_reader_special.b.blocked)],
1655 " !CN"[trc_rdr.needqs & 0x3],
1656 " ?"[trc_rdr.needqs > 0x3],
1657 cpu, cpu_online(cpu) ? "" : "(offline)");
1661 /* List stalled IPIs for RCU tasks trace. */
1662 static void show_stalled_ipi_trace(void)
1666 for_each_possible_cpu(cpu)
1667 if (per_cpu(trc_ipi_to_cpu, cpu))
1668 pr_alert("\tIPI outstanding to CPU %d\n", cpu);
1671 /* Do one scan of the holdout list. */
1672 static void check_all_holdout_tasks_trace(struct list_head *hop,
1673 bool needreport, bool *firstreport)
1675 struct task_struct *g, *t;
1677 // Disable CPU hotplug across the holdout list scan for IPIs.
1680 list_for_each_entry_safe(t, g, hop, trc_holdout_list) {
1681 // If safe and needed, try to check the current task.
1682 if (READ_ONCE(t->trc_ipi_to_cpu) == -1 &&
1683 !(rcu_ld_need_qs(t) & TRC_NEED_QS_CHECKED))
1684 trc_wait_for_one_reader(t, hop);
1686 // If check succeeded, remove this task from the list.
1687 if (smp_load_acquire(&t->trc_ipi_to_cpu) == -1 &&
1688 rcu_ld_need_qs(t) == TRC_NEED_QS_CHECKED)
1690 else if (needreport)
1691 show_stalled_task_trace(t, firstreport);
1692 cond_resched_tasks_rcu_qs();
1695 // Re-enable CPU hotplug now that the holdout list scan has completed.
1700 pr_err("INFO: rcu_tasks_trace detected stalls? (Late IPI?)\n");
1701 show_stalled_ipi_trace();
1705 static void rcu_tasks_trace_empty_fn(void *unused)
1709 /* Wait for grace period to complete and provide ordering. */
1710 static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp)
1714 // Wait for any lingering IPI handlers to complete. Note that
1715 // if a CPU has gone offline or transitioned to userspace in the
1716 // meantime, all IPI handlers should have been drained beforehand.
1717 // Yes, this assumes that CPUs process IPIs in order. If that ever
1718 // changes, there will need to be a recheck and/or timed wait.
1719 for_each_online_cpu(cpu)
1720 if (WARN_ON_ONCE(smp_load_acquire(per_cpu_ptr(&trc_ipi_to_cpu, cpu))))
1721 smp_call_function_single(cpu, rcu_tasks_trace_empty_fn, NULL, 1);
1723 smp_mb(); // Caller's code must be ordered after wakeup.
1724 // Pairs with pretty much every ordering primitive.
1727 /* Report any needed quiescent state for this exiting task. */
1728 static void exit_tasks_rcu_finish_trace(struct task_struct *t)
1730 union rcu_special trs = READ_ONCE(t->trc_reader_special);
1732 rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED);
1733 WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting));
1734 if (WARN_ON_ONCE(rcu_ld_need_qs(t) & TRC_NEED_QS || trs.b.blocked))
1735 rcu_read_unlock_trace_special(t);
1737 WRITE_ONCE(t->trc_reader_nesting, 0);
1741 * call_rcu_tasks_trace() - Queue a callback trace task-based grace period
1742 * @rhp: structure to be used for queueing the RCU updates.
1743 * @func: actual callback function to be invoked after the grace period
1745 * The callback function will be invoked some time after a trace rcu-tasks
1746 * grace period elapses, in other words after all currently executing
1747 * trace rcu-tasks read-side critical sections have completed. These
1748 * read-side critical sections are delimited by calls to rcu_read_lock_trace()
1749 * and rcu_read_unlock_trace().
1751 * See the description of call_rcu() for more detailed information on
1752 * memory ordering guarantees.
1754 void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func)
1756 call_rcu_tasks_generic(rhp, func, &rcu_tasks_trace);
1758 EXPORT_SYMBOL_GPL(call_rcu_tasks_trace);
1761 * synchronize_rcu_tasks_trace - wait for a trace rcu-tasks grace period
1763 * Control will return to the caller some time after a trace rcu-tasks
1764 * grace period has elapsed, in other words after all currently executing
1765 * trace rcu-tasks read-side critical sections have elapsed. These read-side
1766 * critical sections are delimited by calls to rcu_read_lock_trace()
1767 * and rcu_read_unlock_trace().
1769 * This is a very specialized primitive, intended only for a few uses in
1770 * tracing and other situations requiring manipulation of function preambles
1771 * and profiling hooks. The synchronize_rcu_tasks_trace() function is not
1772 * (yet) intended for heavy use from multiple CPUs.
1774 * See the description of synchronize_rcu() for more detailed information
1775 * on memory ordering guarantees.
1777 void synchronize_rcu_tasks_trace(void)
1779 RCU_LOCKDEP_WARN(lock_is_held(&rcu_trace_lock_map), "Illegal synchronize_rcu_tasks_trace() in RCU Tasks Trace read-side critical section");
1780 synchronize_rcu_tasks_generic(&rcu_tasks_trace);
1782 EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_trace);
1785 * rcu_barrier_tasks_trace - Wait for in-flight call_rcu_tasks_trace() callbacks.
1787 * Although the current implementation is guaranteed to wait, it is not
1788 * obligated to, for example, if there are no pending callbacks.
1790 void rcu_barrier_tasks_trace(void)
1792 rcu_barrier_tasks_generic(&rcu_tasks_trace);
1794 EXPORT_SYMBOL_GPL(rcu_barrier_tasks_trace);
1796 static int __init rcu_spawn_tasks_trace_kthread(void)
1798 cblist_init_generic(&rcu_tasks_trace);
1799 if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) {
1800 rcu_tasks_trace.gp_sleep = HZ / 10;
1801 rcu_tasks_trace.init_fract = HZ / 10;
1803 rcu_tasks_trace.gp_sleep = HZ / 200;
1804 if (rcu_tasks_trace.gp_sleep <= 0)
1805 rcu_tasks_trace.gp_sleep = 1;
1806 rcu_tasks_trace.init_fract = HZ / 200;
1807 if (rcu_tasks_trace.init_fract <= 0)
1808 rcu_tasks_trace.init_fract = 1;
1810 rcu_tasks_trace.pregp_func = rcu_tasks_trace_pregp_step;
1811 rcu_tasks_trace.postscan_func = rcu_tasks_trace_postscan;
1812 rcu_tasks_trace.holdouts_func = check_all_holdout_tasks_trace;
1813 rcu_tasks_trace.postgp_func = rcu_tasks_trace_postgp;
1814 rcu_spawn_tasks_kthread_generic(&rcu_tasks_trace);
1818 #if !defined(CONFIG_TINY_RCU)
1819 void show_rcu_tasks_trace_gp_kthread(void)
1823 sprintf(buf, "N%lu h:%lu/%lu/%lu",
1824 data_race(n_trc_holdouts),
1825 data_race(n_heavy_reader_ofl_updates),
1826 data_race(n_heavy_reader_updates),
1827 data_race(n_heavy_reader_attempts));
1828 show_rcu_tasks_generic_gp_kthread(&rcu_tasks_trace, buf);
1830 EXPORT_SYMBOL_GPL(show_rcu_tasks_trace_gp_kthread);
1831 #endif // !defined(CONFIG_TINY_RCU)
1833 #else /* #ifdef CONFIG_TASKS_TRACE_RCU */
1834 static void exit_tasks_rcu_finish_trace(struct task_struct *t) { }
1835 #endif /* #else #ifdef CONFIG_TASKS_TRACE_RCU */
1837 #ifndef CONFIG_TINY_RCU
1838 void show_rcu_tasks_gp_kthreads(void)
1840 show_rcu_tasks_classic_gp_kthread();
1841 show_rcu_tasks_rude_gp_kthread();
1842 show_rcu_tasks_trace_gp_kthread();
1844 #endif /* #ifndef CONFIG_TINY_RCU */
1846 #ifdef CONFIG_PROVE_RCU
1847 struct rcu_tasks_test_desc {
1851 unsigned long runstart;
1854 static struct rcu_tasks_test_desc tests[] = {
1856 .name = "call_rcu_tasks()",
1857 /* If not defined, the test is skipped. */
1858 .notrun = IS_ENABLED(CONFIG_TASKS_RCU),
1861 .name = "call_rcu_tasks_rude()",
1862 /* If not defined, the test is skipped. */
1863 .notrun = IS_ENABLED(CONFIG_TASKS_RUDE_RCU),
1866 .name = "call_rcu_tasks_trace()",
1867 /* If not defined, the test is skipped. */
1868 .notrun = IS_ENABLED(CONFIG_TASKS_TRACE_RCU)
1872 static void test_rcu_tasks_callback(struct rcu_head *rhp)
1874 struct rcu_tasks_test_desc *rttd =
1875 container_of(rhp, struct rcu_tasks_test_desc, rh);
1877 pr_info("Callback from %s invoked.\n", rttd->name);
1879 rttd->notrun = false;
1882 static void rcu_tasks_initiate_self_tests(void)
1884 pr_info("Running RCU-tasks wait API self tests\n");
1885 #ifdef CONFIG_TASKS_RCU
1886 tests[0].runstart = jiffies;
1887 synchronize_rcu_tasks();
1888 call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback);
1891 #ifdef CONFIG_TASKS_RUDE_RCU
1892 tests[1].runstart = jiffies;
1893 synchronize_rcu_tasks_rude();
1894 call_rcu_tasks_rude(&tests[1].rh, test_rcu_tasks_callback);
1897 #ifdef CONFIG_TASKS_TRACE_RCU
1898 tests[2].runstart = jiffies;
1899 synchronize_rcu_tasks_trace();
1900 call_rcu_tasks_trace(&tests[2].rh, test_rcu_tasks_callback);
1905 * Return: 0 - test passed
1906 * 1 - test failed, but have not timed out yet
1907 * -1 - test failed and timed out
1909 static int rcu_tasks_verify_self_tests(void)
1913 unsigned long bst = rcu_task_stall_timeout;
1915 if (bst <= 0 || bst > RCU_TASK_BOOT_STALL_TIMEOUT)
1916 bst = RCU_TASK_BOOT_STALL_TIMEOUT;
1917 for (i = 0; i < ARRAY_SIZE(tests); i++) {
1918 while (tests[i].notrun) { // still hanging.
1919 if (time_after(jiffies, tests[i].runstart + bst)) {
1920 pr_err("%s has failed boot-time tests.\n", tests[i].name);
1934 * Repeat the rcu_tasks_verify_self_tests() call once every second until the
1935 * test passes or has timed out.
1937 static struct delayed_work rcu_tasks_verify_work;
1938 static void rcu_tasks_verify_work_fn(struct work_struct *work __maybe_unused)
1940 int ret = rcu_tasks_verify_self_tests();
1945 /* Test fails but not timed out yet, reschedule another check */
1946 schedule_delayed_work(&rcu_tasks_verify_work, HZ);
1949 static int rcu_tasks_verify_schedule_work(void)
1951 INIT_DELAYED_WORK(&rcu_tasks_verify_work, rcu_tasks_verify_work_fn);
1952 rcu_tasks_verify_work_fn(NULL);
1955 late_initcall(rcu_tasks_verify_schedule_work);
1956 #else /* #ifdef CONFIG_PROVE_RCU */
1957 static void rcu_tasks_initiate_self_tests(void) { }
1958 #endif /* #else #ifdef CONFIG_PROVE_RCU */
1960 void __init rcu_init_tasks_generic(void)
1962 #ifdef CONFIG_TASKS_RCU
1963 rcu_spawn_tasks_kthread();
1966 #ifdef CONFIG_TASKS_RUDE_RCU
1967 rcu_spawn_tasks_rude_kthread();
1970 #ifdef CONFIG_TASKS_TRACE_RCU
1971 rcu_spawn_tasks_trace_kthread();
1974 // Run the self-tests.
1975 rcu_tasks_initiate_self_tests();
1978 #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */
1979 static inline void rcu_tasks_bootup_oddness(void) {}
1980 #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */