1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * kernel/stop_machine.c
4 *
5 * Copyright (C) 2008, 2005 IBM Corporation.
6 * Copyright (C) 2008, 2005 Rusty Russell rusty@rustcorp.com.au
7 * Copyright (C) 2010 SUSE Linux Products GmbH
8 * Copyright (C) 2010 Tejun Heo <tj@kernel.org>
9 */
10#include <linux/compiler.h>
11#include <linux/completion.h>
12#include <linux/cpu.h>
13#include <linux/init.h>
14#include <linux/kthread.h>
15#include <linux/export.h>
16#include <linux/percpu.h>
17#include <linux/sched.h>
18#include <linux/stop_machine.h>
19#include <linux/interrupt.h>
20#include <linux/kallsyms.h>
21#include <linux/smpboot.h>
22#include <linux/atomic.h>
23#include <linux/nmi.h>
24#include <linux/sched/wake_q.h>
25
26/*
27 * Structure to determine completion condition and record errors. May
28 * be shared by works on different cpus.
29 */
30struct cpu_stop_done {
31 atomic_t nr_todo; /* nr left to execute */
32 int ret; /* collected return value */
33 struct completion completion; /* fired if nr_todo reaches 0 */
34};
35
36/* the actual stopper, one per every possible cpu, enabled on online cpus */
37struct cpu_stopper {
38 struct task_struct *thread;
39
40 raw_spinlock_t lock;
41 bool enabled; /* is this stopper enabled? */
42 struct list_head works; /* list of pending works */
43
44 struct cpu_stop_work stop_work; /* for stop_cpus */
45 unsigned long caller;
46 cpu_stop_fn_t fn;
47};
48
49static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
50static bool stop_machine_initialized = false;
51
52void print_stop_info(const char *log_lvl, struct task_struct *task)
53{
54 /*
55 * If @task is a stopper task, it cannot migrate and task_cpu() is
56 * stable.
57 */
58 struct cpu_stopper *stopper = per_cpu_ptr(&cpu_stopper, task_cpu(task));
59
60 if (task != stopper->thread)
61 return;
62
63 printk("%sStopper: %pS <- %pS\n", log_lvl, stopper->fn, (void *)stopper->caller);
64}
65
66/* static data for stop_cpus */
67static DEFINE_MUTEX(stop_cpus_mutex);
68static bool stop_cpus_in_progress;
69
70static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
71{
72 memset(done, 0, sizeof(*done));
73 atomic_set(v: &done->nr_todo, i: nr_todo);
74 init_completion(x: &done->completion);
75}
76
77/* signal completion unless @done is NULL */
78static void cpu_stop_signal_done(struct cpu_stop_done *done)
79{
80 if (atomic_dec_and_test(v: &done->nr_todo))
81 complete(&done->completion);
82}
83
84static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
85 struct cpu_stop_work *work,
86 struct wake_q_head *wakeq)
87{
88 list_add_tail(new: &work->list, head: &stopper->works);
89 wake_q_add(head: wakeq, task: stopper->thread);
90}
91
92/* queue @work to @stopper. if offline, @work is completed immediately */
93static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
94{
95 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
96 DEFINE_WAKE_Q(wakeq);
97 unsigned long flags;
98 bool enabled;
99
100 preempt_disable();
101 raw_spin_lock_irqsave(&stopper->lock, flags);
102 enabled = stopper->enabled;
103 if (enabled)
104 __cpu_stop_queue_work(stopper, work, wakeq: &wakeq);
105 else if (work->done)
106 cpu_stop_signal_done(done: work->done);
107 raw_spin_unlock_irqrestore(&stopper->lock, flags);
108
109 wake_up_q(head: &wakeq);
110 preempt_enable();
111
112 return enabled;
113}
114
115/**
116 * stop_one_cpu - stop a cpu
117 * @cpu: cpu to stop
118 * @fn: function to execute
119 * @arg: argument to @fn
120 *
121 * Execute @fn(@arg) on @cpu. @fn is run in a process context with
122 * the highest priority preempting any task on the cpu and
123 * monopolizing it. This function returns after the execution is
124 * complete.
125 *
126 * This function doesn't guarantee @cpu stays online till @fn
127 * completes. If @cpu goes down in the middle, execution may happen
128 * partially or fully on different cpus. @fn should either be ready
129 * for that or the caller should ensure that @cpu stays online until
130 * this function completes.
131 *
132 * CONTEXT:
133 * Might sleep.
134 *
135 * RETURNS:
136 * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
137 * otherwise, the return value of @fn.
138 */
139int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
140{
141 struct cpu_stop_done done;
142 struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done, .caller = _RET_IP_ };
143
144 cpu_stop_init_done(done: &done, nr_todo: 1);
145 if (!cpu_stop_queue_work(cpu, work: &work))
146 return -ENOENT;
147 /*
148 * In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup
149 * cycle by doing a preemption:
150 */
151 cond_resched();
152 wait_for_completion(&done.completion);
153 return done.ret;
154}
155
156/* This controls the threads on each CPU. */
157enum multi_stop_state {
158 /* Dummy starting state for thread. */
159 MULTI_STOP_NONE,
160 /* Awaiting everyone to be scheduled. */
161 MULTI_STOP_PREPARE,
162 /* Disable interrupts. */
163 MULTI_STOP_DISABLE_IRQ,
164 /* Run the function */
165 MULTI_STOP_RUN,
166 /* Exit */
167 MULTI_STOP_EXIT,
168};
169
170struct multi_stop_data {
171 cpu_stop_fn_t fn;
172 void *data;
173 /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
174 unsigned int num_threads;
175 const struct cpumask *active_cpus;
176
177 enum multi_stop_state state;
178 atomic_t thread_ack;
179};
180
181static void set_state(struct multi_stop_data *msdata,
182 enum multi_stop_state newstate)
183{
184 /* Reset ack counter. */
185 atomic_set(v: &msdata->thread_ack, i: msdata->num_threads);
186 smp_wmb();
187 WRITE_ONCE(msdata->state, newstate);
188}
189
190/* Last one to ack a state moves to the next state. */
191static void ack_state(struct multi_stop_data *msdata)
192{
193 if (atomic_dec_and_test(v: &msdata->thread_ack))
194 set_state(msdata, newstate: msdata->state + 1);
195}
196
197notrace void __weak stop_machine_yield(const struct cpumask *cpumask)
198{
199 cpu_relax();
200}
201
202/* This is the cpu_stop function which stops the CPU. */
203static int multi_cpu_stop(void *data)
204{
205 struct multi_stop_data *msdata = data;
206 enum multi_stop_state newstate, curstate = MULTI_STOP_NONE;
207 int cpu = smp_processor_id(), err = 0;
208 const struct cpumask *cpumask;
209 unsigned long flags;
210 bool is_active;
211
212 /*
213 * When called from stop_machine_from_inactive_cpu(), irq might
214 * already be disabled. Save the state and restore it on exit.
215 */
216 local_save_flags(flags);
217
218 if (!msdata->active_cpus) {
219 cpumask = cpu_online_mask;
220 is_active = cpu == cpumask_first(srcp: cpumask);
221 } else {
222 cpumask = msdata->active_cpus;
223 is_active = cpumask_test_cpu(cpu, cpumask);
224 }
225
226 /* Simple state machine */
227 do {
228 /* Chill out and ensure we re-read multi_stop_state. */
229 stop_machine_yield(cpumask);
230 newstate = READ_ONCE(msdata->state);
231 if (newstate != curstate) {
232 curstate = newstate;
233 switch (curstate) {
234 case MULTI_STOP_DISABLE_IRQ:
235 local_irq_disable();
236 hard_irq_disable();
237 break;
238 case MULTI_STOP_RUN:
239 if (is_active)
240 err = msdata->fn(msdata->data);
241 break;
242 default:
243 break;
244 }
245 ack_state(msdata);
246 } else if (curstate > MULTI_STOP_PREPARE) {
247 /*
248 * At this stage all other CPUs we depend on must spin
249 * in the same loop. Any reason for hard-lockup should
250 * be detected and reported on their side.
251 */
252 touch_nmi_watchdog();
253 /* Also suppress RCU CPU stall warnings. */
254 rcu_momentary_eqs();
255 }
256 } while (curstate != MULTI_STOP_EXIT);
257
258 local_irq_restore(flags);
259 return err;
260}
261
262static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
263 int cpu2, struct cpu_stop_work *work2)
264{
265 struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
266 struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
267 DEFINE_WAKE_Q(wakeq);
268 int err;
269
270retry:
271 /*
272 * The waking up of stopper threads has to happen in the same
273 * scheduling context as the queueing. Otherwise, there is a
274 * possibility of one of the above stoppers being woken up by another
275 * CPU, and preempting us. This will cause us to not wake up the other
276 * stopper forever.
277 */
278 preempt_disable();
279 raw_spin_lock_irq(&stopper1->lock);
280 raw_spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
281
282 if (!stopper1->enabled || !stopper2->enabled) {
283 err = -ENOENT;
284 goto unlock;
285 }
286
287 /*
288 * Ensure that if we race with __stop_cpus() the stoppers won't get
289 * queued up in reverse order leading to system deadlock.
290 *
291 * We can't miss stop_cpus_in_progress if queue_stop_cpus_work() has
292 * queued a work on cpu1 but not on cpu2, we hold both locks.
293 *
294 * It can be falsely true but it is safe to spin until it is cleared,
295 * queue_stop_cpus_work() does everything under preempt_disable().
296 */
297 if (unlikely(stop_cpus_in_progress)) {
298 err = -EDEADLK;
299 goto unlock;
300 }
301
302 err = 0;
303 __cpu_stop_queue_work(stopper: stopper1, work: work1, wakeq: &wakeq);
304 __cpu_stop_queue_work(stopper: stopper2, work: work2, wakeq: &wakeq);
305
306unlock:
307 raw_spin_unlock(&stopper2->lock);
308 raw_spin_unlock_irq(&stopper1->lock);
309
310 if (unlikely(err == -EDEADLK)) {
311 preempt_enable();
312
313 while (stop_cpus_in_progress)
314 cpu_relax();
315
316 goto retry;
317 }
318
319 wake_up_q(head: &wakeq);
320 preempt_enable();
321
322 return err;
323}
324/**
325 * stop_two_cpus - stops two cpus
326 * @cpu1: the cpu to stop
327 * @cpu2: the other cpu to stop
328 * @fn: function to execute
329 * @arg: argument to @fn
330 *
331 * Stops both the current and specified CPU and runs @fn on one of them.
332 *
333 * returns when both are completed.
334 */
335int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
336{
337 struct cpu_stop_done done;
338 struct cpu_stop_work work1, work2;
339 struct multi_stop_data msdata;
340
341 msdata = (struct multi_stop_data){
342 .fn = fn,
343 .data = arg,
344 .num_threads = 2,
345 .active_cpus = cpumask_of(cpu1),
346 };
347
348 work1 = work2 = (struct cpu_stop_work){
349 .fn = multi_cpu_stop,
350 .arg = &msdata,
351 .done = &done,
352 .caller = _RET_IP_,
353 };
354
355 cpu_stop_init_done(done: &done, nr_todo: 2);
356 set_state(msdata: &msdata, newstate: MULTI_STOP_PREPARE);
357
358 if (cpu1 > cpu2)
359 swap(cpu1, cpu2);
360 if (cpu_stop_queue_two_works(cpu1, work1: &work1, cpu2, work2: &work2))
361 return -ENOENT;
362
363 wait_for_completion(&done.completion);
364 return done.ret;
365}
366
367/**
368 * stop_one_cpu_nowait - stop a cpu but don't wait for completion
369 * @cpu: cpu to stop
370 * @fn: function to execute
371 * @arg: argument to @fn
372 * @work_buf: pointer to cpu_stop_work structure
373 *
374 * Similar to stop_one_cpu() but doesn't wait for completion. The
375 * caller is responsible for ensuring @work_buf is currently unused
376 * and will remain untouched until stopper starts executing @fn.
377 *
378 * CONTEXT:
379 * Don't care.
380 *
381 * RETURNS:
382 * true if cpu_stop_work was queued successfully and @fn will be called,
383 * false otherwise.
384 */
385bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
386 struct cpu_stop_work *work_buf)
387{
388 *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, .caller = _RET_IP_, };
389 return cpu_stop_queue_work(cpu, work: work_buf);
390}
391
392static bool queue_stop_cpus_work(const struct cpumask *cpumask,
393 cpu_stop_fn_t fn, void *arg,
394 struct cpu_stop_done *done)
395{
396 struct cpu_stop_work *work;
397 unsigned int cpu;
398 bool queued = false;
399
400 /*
401 * Disable preemption while queueing to avoid getting
402 * preempted by a stopper which might wait for other stoppers
403 * to enter @fn which can lead to deadlock.
404 */
405 preempt_disable();
406 stop_cpus_in_progress = true;
407 barrier();
408 for_each_cpu(cpu, cpumask) {
409 work = &per_cpu(cpu_stopper.stop_work, cpu);
410 work->fn = fn;
411 work->arg = arg;
412 work->done = done;
413 work->caller = _RET_IP_;
414 if (cpu_stop_queue_work(cpu, work))
415 queued = true;
416 }
417 barrier();
418 stop_cpus_in_progress = false;
419 preempt_enable();
420
421 return queued;
422}
423
424static int __stop_cpus(const struct cpumask *cpumask,
425 cpu_stop_fn_t fn, void *arg)
426{
427 struct cpu_stop_done done;
428
429 cpu_stop_init_done(done: &done, nr_todo: cpumask_weight(srcp: cpumask));
430 if (!queue_stop_cpus_work(cpumask, fn, arg, done: &done))
431 return -ENOENT;
432 wait_for_completion(&done.completion);
433 return done.ret;
434}
435
436/**
437 * stop_cpus - stop multiple cpus
438 * @cpumask: cpus to stop
439 * @fn: function to execute
440 * @arg: argument to @fn
441 *
442 * Execute @fn(@arg) on online cpus in @cpumask. On each target cpu,
443 * @fn is run in a process context with the highest priority
444 * preempting any task on the cpu and monopolizing it. This function
445 * returns after all executions are complete.
446 *
447 * This function doesn't guarantee the cpus in @cpumask stay online
448 * till @fn completes. If some cpus go down in the middle, execution
449 * on the cpu may happen partially or fully on different cpus. @fn
450 * should either be ready for that or the caller should ensure that
451 * the cpus stay online until this function completes.
452 *
453 * All stop_cpus() calls are serialized making it safe for @fn to wait
454 * for all cpus to start executing it.
455 *
456 * CONTEXT:
457 * Might sleep.
458 *
459 * RETURNS:
460 * -ENOENT if @fn(@arg) was not executed at all because all cpus in
461 * @cpumask were offline; otherwise, 0 if all executions of @fn
462 * returned 0, any non zero return value if any returned non zero.
463 */
464static int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
465{
466 int ret;
467
468 /* static works are used, process one request at a time */
469 mutex_lock(&stop_cpus_mutex);
470 ret = __stop_cpus(cpumask, fn, arg);
471 mutex_unlock(lock: &stop_cpus_mutex);
472 return ret;
473}
474
475static int cpu_stop_should_run(unsigned int cpu)
476{
477 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
478 unsigned long flags;
479 int run;
480
481 raw_spin_lock_irqsave(&stopper->lock, flags);
482 run = !list_empty(head: &stopper->works);
483 raw_spin_unlock_irqrestore(&stopper->lock, flags);
484 return run;
485}
486
487static void cpu_stopper_thread(unsigned int cpu)
488{
489 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
490 struct cpu_stop_work *work;
491
492repeat:
493 work = NULL;
494 raw_spin_lock_irq(&stopper->lock);
495 if (!list_empty(head: &stopper->works)) {
496 work = list_first_entry(&stopper->works,
497 struct cpu_stop_work, list);
498 list_del_init(entry: &work->list);
499 }
500 raw_spin_unlock_irq(&stopper->lock);
501
502 if (work) {
503 cpu_stop_fn_t fn = work->fn;
504 void *arg = work->arg;
505 struct cpu_stop_done *done = work->done;
506 int ret;
507
508 /* cpu stop callbacks must not sleep, make in_atomic() == T */
509 stopper->caller = work->caller;
510 stopper->fn = fn;
511 preempt_count_inc();
512 ret = fn(arg);
513 if (done) {
514 if (ret)
515 done->ret = ret;
516 cpu_stop_signal_done(done);
517 }
518 preempt_count_dec();
519 stopper->fn = NULL;
520 stopper->caller = 0;
521 WARN_ONCE(preempt_count(),
522 "cpu_stop: %ps(%p) leaked preempt count\n", fn, arg);
523 goto repeat;
524 }
525}
526
527void stop_machine_park(int cpu)
528{
529 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
530 /*
531 * Lockless. cpu_stopper_thread() will take stopper->lock and flush
532 * the pending works before it parks, until then it is fine to queue
533 * the new works.
534 */
535 stopper->enabled = false;
536 kthread_park(k: stopper->thread);
537}
538
539static void cpu_stop_create(unsigned int cpu)
540{
541 sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
542}
543
544static void cpu_stop_park(unsigned int cpu)
545{
546 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
547
548 WARN_ON(!list_empty(&stopper->works));
549}
550
551void stop_machine_unpark(int cpu)
552{
553 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
554
555 stopper->enabled = true;
556 kthread_unpark(k: stopper->thread);
557}
558
559static struct smp_hotplug_thread cpu_stop_threads = {
560 .store = &cpu_stopper.thread,
561 .thread_should_run = cpu_stop_should_run,
562 .thread_fn = cpu_stopper_thread,
563 .thread_comm = "migration/%u",
564 .create = cpu_stop_create,
565 .park = cpu_stop_park,
566 .selfparking = true,
567};
568
569static int __init cpu_stop_init(void)
570{
571 unsigned int cpu;
572
573 for_each_possible_cpu(cpu) {
574 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
575
576 raw_spin_lock_init(&stopper->lock);
577 INIT_LIST_HEAD(list: &stopper->works);
578 }
579
580 BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
581 stop_machine_unpark(raw_smp_processor_id());
582 stop_machine_initialized = true;
583 return 0;
584}
585early_initcall(cpu_stop_init);
586
587int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data,
588 const struct cpumask *cpus)
589{
590 struct multi_stop_data msdata = {
591 .fn = fn,
592 .data = data,
593 .num_threads = num_online_cpus(),
594 .active_cpus = cpus,
595 };
596
597 lockdep_assert_cpus_held();
598
599 if (!stop_machine_initialized) {
600 /*
601 * Handle the case where stop_machine() is called
602 * early in boot before stop_machine() has been
603 * initialized.
604 */
605 unsigned long flags;
606 int ret;
607
608 WARN_ON_ONCE(msdata.num_threads != 1);
609
610 local_irq_save(flags);
611 hard_irq_disable();
612 ret = (*fn)(data);
613 local_irq_restore(flags);
614
615 return ret;
616 }
617
618 /* Set the initial state and stop all online cpus. */
619 set_state(msdata: &msdata, newstate: MULTI_STOP_PREPARE);
620 return stop_cpus(cpu_online_mask, fn: multi_cpu_stop, arg: &msdata);
621}
622
623int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
624{
625 int ret;
626
627 /* No CPUs can come up or down during this. */
628 cpus_read_lock();
629 ret = stop_machine_cpuslocked(fn, data, cpus);
630 cpus_read_unlock();
631 return ret;
632}
633EXPORT_SYMBOL_GPL(stop_machine);
634
635#ifdef CONFIG_SCHED_SMT
636int stop_core_cpuslocked(unsigned int cpu, cpu_stop_fn_t fn, void *data)
637{
638 const struct cpumask *smt_mask = cpu_smt_mask(cpu);
639
640 struct multi_stop_data msdata = {
641 .fn = fn,
642 .data = data,
643 .num_threads = cpumask_weight(srcp: smt_mask),
644 .active_cpus = smt_mask,
645 };
646
647 lockdep_assert_cpus_held();
648
649 /* Set the initial state and stop all online cpus. */
650 set_state(msdata: &msdata, newstate: MULTI_STOP_PREPARE);
651 return stop_cpus(cpumask: smt_mask, fn: multi_cpu_stop, arg: &msdata);
652}
653EXPORT_SYMBOL_GPL(stop_core_cpuslocked);
654#endif
655
656/**
657 * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
658 * @fn: the function to run
659 * @data: the data ptr for the @fn()
660 * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
661 *
662 * This is identical to stop_machine() but can be called from a CPU which
663 * is not active. The local CPU is in the process of hotplug (so no other
664 * CPU hotplug can start) and not marked active and doesn't have enough
665 * context to sleep.
666 *
667 * This function provides stop_machine() functionality for such state by
668 * using busy-wait for synchronization and executing @fn directly for local
669 * CPU.
670 *
671 * CONTEXT:
672 * Local CPU is inactive. Temporarily stops all active CPUs.
673 *
674 * RETURNS:
675 * 0 if all executions of @fn returned 0, any non zero return value if any
676 * returned non zero.
677 */
678int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
679 const struct cpumask *cpus)
680{
681 struct multi_stop_data msdata = { .fn = fn, .data = data,
682 .active_cpus = cpus };
683 struct cpu_stop_done done;
684 int ret;
685
686 /* Local CPU must be inactive and CPU hotplug in progress. */
687 BUG_ON(cpu_active(raw_smp_processor_id()));
688 msdata.num_threads = num_active_cpus() + 1; /* +1 for local */
689
690 /* No proper task established and can't sleep - busy wait for lock. */
691 while (!mutex_trylock(&stop_cpus_mutex))
692 cpu_relax();
693
694 /* Schedule work on other CPUs and execute directly for local CPU */
695 set_state(msdata: &msdata, newstate: MULTI_STOP_PREPARE);
696 cpu_stop_init_done(done: &done, num_active_cpus());
697 queue_stop_cpus_work(cpu_active_mask, fn: multi_cpu_stop, arg: &msdata,
698 done: &done);
699 ret = multi_cpu_stop(data: &msdata);
700
701 /* Busy wait for completion. */
702 while (!completion_done(x: &done.completion))
703 cpu_relax();
704
705 mutex_unlock(lock: &stop_cpus_mutex);
706 return ret ?: done.ret;
707}
708

source code of linux/kernel/stop_machine.c

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