Loading...
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};
46
47static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
48static bool stop_machine_initialized = false;
49
50/* static data for stop_cpus */
51static DEFINE_MUTEX(stop_cpus_mutex);
52static bool stop_cpus_in_progress;
53
54static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
55{
56 memset(done, 0, sizeof(*done));
57 atomic_set(&done->nr_todo, nr_todo);
58 init_completion(&done->completion);
59}
60
61/* signal completion unless @done is NULL */
62static void cpu_stop_signal_done(struct cpu_stop_done *done)
63{
64 if (atomic_dec_and_test(&done->nr_todo))
65 complete(&done->completion);
66}
67
68static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
69 struct cpu_stop_work *work,
70 struct wake_q_head *wakeq)
71{
72 list_add_tail(&work->list, &stopper->works);
73 wake_q_add(wakeq, stopper->thread);
74}
75
76/* queue @work to @stopper. if offline, @work is completed immediately */
77static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
78{
79 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
80 DEFINE_WAKE_Q(wakeq);
81 unsigned long flags;
82 bool enabled;
83
84 preempt_disable();
85 raw_spin_lock_irqsave(&stopper->lock, flags);
86 enabled = stopper->enabled;
87 if (enabled)
88 __cpu_stop_queue_work(stopper, work, &wakeq);
89 else if (work->done)
90 cpu_stop_signal_done(work->done);
91 raw_spin_unlock_irqrestore(&stopper->lock, flags);
92
93 wake_up_q(&wakeq);
94 preempt_enable();
95
96 return enabled;
97}
98
99/**
100 * stop_one_cpu - stop a cpu
101 * @cpu: cpu to stop
102 * @fn: function to execute
103 * @arg: argument to @fn
104 *
105 * Execute @fn(@arg) on @cpu. @fn is run in a process context with
106 * the highest priority preempting any task on the cpu and
107 * monopolizing it. This function returns after the execution is
108 * complete.
109 *
110 * This function doesn't guarantee @cpu stays online till @fn
111 * completes. If @cpu goes down in the middle, execution may happen
112 * partially or fully on different cpus. @fn should either be ready
113 * for that or the caller should ensure that @cpu stays online until
114 * this function completes.
115 *
116 * CONTEXT:
117 * Might sleep.
118 *
119 * RETURNS:
120 * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
121 * otherwise, the return value of @fn.
122 */
123int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
124{
125 struct cpu_stop_done done;
126 struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
127
128 cpu_stop_init_done(&done, 1);
129 if (!cpu_stop_queue_work(cpu, &work))
130 return -ENOENT;
131 /*
132 * In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup
133 * cycle by doing a preemption:
134 */
135 cond_resched();
136 wait_for_completion(&done.completion);
137 return done.ret;
138}
139
140/* This controls the threads on each CPU. */
141enum multi_stop_state {
142 /* Dummy starting state for thread. */
143 MULTI_STOP_NONE,
144 /* Awaiting everyone to be scheduled. */
145 MULTI_STOP_PREPARE,
146 /* Disable interrupts. */
147 MULTI_STOP_DISABLE_IRQ,
148 /* Run the function */
149 MULTI_STOP_RUN,
150 /* Exit */
151 MULTI_STOP_EXIT,
152};
153
154struct multi_stop_data {
155 cpu_stop_fn_t fn;
156 void *data;
157 /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
158 unsigned int num_threads;
159 const struct cpumask *active_cpus;
160
161 enum multi_stop_state state;
162 atomic_t thread_ack;
163};
164
165static void set_state(struct multi_stop_data *msdata,
166 enum multi_stop_state newstate)
167{
168 /* Reset ack counter. */
169 atomic_set(&msdata->thread_ack, msdata->num_threads);
170 smp_wmb();
171 WRITE_ONCE(msdata->state, newstate);
172}
173
174/* Last one to ack a state moves to the next state. */
175static void ack_state(struct multi_stop_data *msdata)
176{
177 if (atomic_dec_and_test(&msdata->thread_ack))
178 set_state(msdata, msdata->state + 1);
179}
180
181void __weak stop_machine_yield(const struct cpumask *cpumask)
182{
183 cpu_relax();
184}
185
186/* This is the cpu_stop function which stops the CPU. */
187static int multi_cpu_stop(void *data)
188{
189 struct multi_stop_data *msdata = data;
190 enum multi_stop_state newstate, curstate = MULTI_STOP_NONE;
191 int cpu = smp_processor_id(), err = 0;
192 const struct cpumask *cpumask;
193 unsigned long flags;
194 bool is_active;
195
196 /*
197 * When called from stop_machine_from_inactive_cpu(), irq might
198 * already be disabled. Save the state and restore it on exit.
199 */
200 local_save_flags(flags);
201
202 if (!msdata->active_cpus) {
203 cpumask = cpu_online_mask;
204 is_active = cpu == cpumask_first(cpumask);
205 } else {
206 cpumask = msdata->active_cpus;
207 is_active = cpumask_test_cpu(cpu, cpumask);
208 }
209
210 /* Simple state machine */
211 do {
212 /* Chill out and ensure we re-read multi_stop_state. */
213 stop_machine_yield(cpumask);
214 newstate = READ_ONCE(msdata->state);
215 if (newstate != curstate) {
216 curstate = newstate;
217 switch (curstate) {
218 case MULTI_STOP_DISABLE_IRQ:
219 local_irq_disable();
220 hard_irq_disable();
221 break;
222 case MULTI_STOP_RUN:
223 if (is_active)
224 err = msdata->fn(msdata->data);
225 break;
226 default:
227 break;
228 }
229 ack_state(msdata);
230 } else if (curstate > MULTI_STOP_PREPARE) {
231 /*
232 * At this stage all other CPUs we depend on must spin
233 * in the same loop. Any reason for hard-lockup should
234 * be detected and reported on their side.
235 */
236 touch_nmi_watchdog();
237 }
238 } while (curstate != MULTI_STOP_EXIT);
239
240 local_irq_restore(flags);
241 return err;
242}
243
244static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
245 int cpu2, struct cpu_stop_work *work2)
246{
247 struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
248 struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
249 DEFINE_WAKE_Q(wakeq);
250 int err;
251
252retry:
253 /*
254 * The waking up of stopper threads has to happen in the same
255 * scheduling context as the queueing. Otherwise, there is a
256 * possibility of one of the above stoppers being woken up by another
257 * CPU, and preempting us. This will cause us to not wake up the other
258 * stopper forever.
259 */
260 preempt_disable();
261 raw_spin_lock_irq(&stopper1->lock);
262 raw_spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
263
264 if (!stopper1->enabled || !stopper2->enabled) {
265 err = -ENOENT;
266 goto unlock;
267 }
268
269 /*
270 * Ensure that if we race with __stop_cpus() the stoppers won't get
271 * queued up in reverse order leading to system deadlock.
272 *
273 * We can't miss stop_cpus_in_progress if queue_stop_cpus_work() has
274 * queued a work on cpu1 but not on cpu2, we hold both locks.
275 *
276 * It can be falsely true but it is safe to spin until it is cleared,
277 * queue_stop_cpus_work() does everything under preempt_disable().
278 */
279 if (unlikely(stop_cpus_in_progress)) {
280 err = -EDEADLK;
281 goto unlock;
282 }
283
284 err = 0;
285 __cpu_stop_queue_work(stopper1, work1, &wakeq);
286 __cpu_stop_queue_work(stopper2, work2, &wakeq);
287
288unlock:
289 raw_spin_unlock(&stopper2->lock);
290 raw_spin_unlock_irq(&stopper1->lock);
291
292 if (unlikely(err == -EDEADLK)) {
293 preempt_enable();
294
295 while (stop_cpus_in_progress)
296 cpu_relax();
297
298 goto retry;
299 }
300
301 wake_up_q(&wakeq);
302 preempt_enable();
303
304 return err;
305}
306/**
307 * stop_two_cpus - stops two cpus
308 * @cpu1: the cpu to stop
309 * @cpu2: the other cpu to stop
310 * @fn: function to execute
311 * @arg: argument to @fn
312 *
313 * Stops both the current and specified CPU and runs @fn on one of them.
314 *
315 * returns when both are completed.
316 */
317int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
318{
319 struct cpu_stop_done done;
320 struct cpu_stop_work work1, work2;
321 struct multi_stop_data msdata;
322
323 msdata = (struct multi_stop_data){
324 .fn = fn,
325 .data = arg,
326 .num_threads = 2,
327 .active_cpus = cpumask_of(cpu1),
328 };
329
330 work1 = work2 = (struct cpu_stop_work){
331 .fn = multi_cpu_stop,
332 .arg = &msdata,
333 .done = &done
334 };
335
336 cpu_stop_init_done(&done, 2);
337 set_state(&msdata, MULTI_STOP_PREPARE);
338
339 if (cpu1 > cpu2)
340 swap(cpu1, cpu2);
341 if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
342 return -ENOENT;
343
344 wait_for_completion(&done.completion);
345 return done.ret;
346}
347
348/**
349 * stop_one_cpu_nowait - stop a cpu but don't wait for completion
350 * @cpu: cpu to stop
351 * @fn: function to execute
352 * @arg: argument to @fn
353 * @work_buf: pointer to cpu_stop_work structure
354 *
355 * Similar to stop_one_cpu() but doesn't wait for completion. The
356 * caller is responsible for ensuring @work_buf is currently unused
357 * and will remain untouched until stopper starts executing @fn.
358 *
359 * CONTEXT:
360 * Don't care.
361 *
362 * RETURNS:
363 * true if cpu_stop_work was queued successfully and @fn will be called,
364 * false otherwise.
365 */
366bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
367 struct cpu_stop_work *work_buf)
368{
369 *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
370 return cpu_stop_queue_work(cpu, work_buf);
371}
372
373static bool queue_stop_cpus_work(const struct cpumask *cpumask,
374 cpu_stop_fn_t fn, void *arg,
375 struct cpu_stop_done *done)
376{
377 struct cpu_stop_work *work;
378 unsigned int cpu;
379 bool queued = false;
380
381 /*
382 * Disable preemption while queueing to avoid getting
383 * preempted by a stopper which might wait for other stoppers
384 * to enter @fn which can lead to deadlock.
385 */
386 preempt_disable();
387 stop_cpus_in_progress = true;
388 barrier();
389 for_each_cpu(cpu, cpumask) {
390 work = &per_cpu(cpu_stopper.stop_work, cpu);
391 work->fn = fn;
392 work->arg = arg;
393 work->done = done;
394 if (cpu_stop_queue_work(cpu, work))
395 queued = true;
396 }
397 barrier();
398 stop_cpus_in_progress = false;
399 preempt_enable();
400
401 return queued;
402}
403
404static int __stop_cpus(const struct cpumask *cpumask,
405 cpu_stop_fn_t fn, void *arg)
406{
407 struct cpu_stop_done done;
408
409 cpu_stop_init_done(&done, cpumask_weight(cpumask));
410 if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
411 return -ENOENT;
412 wait_for_completion(&done.completion);
413 return done.ret;
414}
415
416/**
417 * stop_cpus - stop multiple cpus
418 * @cpumask: cpus to stop
419 * @fn: function to execute
420 * @arg: argument to @fn
421 *
422 * Execute @fn(@arg) on online cpus in @cpumask. On each target cpu,
423 * @fn is run in a process context with the highest priority
424 * preempting any task on the cpu and monopolizing it. This function
425 * returns after all executions are complete.
426 *
427 * This function doesn't guarantee the cpus in @cpumask stay online
428 * till @fn completes. If some cpus go down in the middle, execution
429 * on the cpu may happen partially or fully on different cpus. @fn
430 * should either be ready for that or the caller should ensure that
431 * the cpus stay online until this function completes.
432 *
433 * All stop_cpus() calls are serialized making it safe for @fn to wait
434 * for all cpus to start executing it.
435 *
436 * CONTEXT:
437 * Might sleep.
438 *
439 * RETURNS:
440 * -ENOENT if @fn(@arg) was not executed at all because all cpus in
441 * @cpumask were offline; otherwise, 0 if all executions of @fn
442 * returned 0, any non zero return value if any returned non zero.
443 */
444int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
445{
446 int ret;
447
448 /* static works are used, process one request at a time */
449 mutex_lock(&stop_cpus_mutex);
450 ret = __stop_cpus(cpumask, fn, arg);
451 mutex_unlock(&stop_cpus_mutex);
452 return ret;
453}
454
455/**
456 * try_stop_cpus - try to stop multiple cpus
457 * @cpumask: cpus to stop
458 * @fn: function to execute
459 * @arg: argument to @fn
460 *
461 * Identical to stop_cpus() except that it fails with -EAGAIN if
462 * someone else is already using the facility.
463 *
464 * CONTEXT:
465 * Might sleep.
466 *
467 * RETURNS:
468 * -EAGAIN if someone else is already stopping cpus, -ENOENT if
469 * @fn(@arg) was not executed at all because all cpus in @cpumask were
470 * offline; otherwise, 0 if all executions of @fn returned 0, any non
471 * zero return value if any returned non zero.
472 */
473int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
474{
475 int ret;
476
477 /* static works are used, process one request at a time */
478 if (!mutex_trylock(&stop_cpus_mutex))
479 return -EAGAIN;
480 ret = __stop_cpus(cpumask, fn, arg);
481 mutex_unlock(&stop_cpus_mutex);
482 return ret;
483}
484
485static int cpu_stop_should_run(unsigned int cpu)
486{
487 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
488 unsigned long flags;
489 int run;
490
491 raw_spin_lock_irqsave(&stopper->lock, flags);
492 run = !list_empty(&stopper->works);
493 raw_spin_unlock_irqrestore(&stopper->lock, flags);
494 return run;
495}
496
497static void cpu_stopper_thread(unsigned int cpu)
498{
499 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
500 struct cpu_stop_work *work;
501
502repeat:
503 work = NULL;
504 raw_spin_lock_irq(&stopper->lock);
505 if (!list_empty(&stopper->works)) {
506 work = list_first_entry(&stopper->works,
507 struct cpu_stop_work, list);
508 list_del_init(&work->list);
509 }
510 raw_spin_unlock_irq(&stopper->lock);
511
512 if (work) {
513 cpu_stop_fn_t fn = work->fn;
514 void *arg = work->arg;
515 struct cpu_stop_done *done = work->done;
516 int ret;
517
518 /* cpu stop callbacks must not sleep, make in_atomic() == T */
519 preempt_count_inc();
520 ret = fn(arg);
521 if (done) {
522 if (ret)
523 done->ret = ret;
524 cpu_stop_signal_done(done);
525 }
526 preempt_count_dec();
527 WARN_ONCE(preempt_count(),
528 "cpu_stop: %ps(%p) leaked preempt count\n", fn, arg);
529 goto repeat;
530 }
531}
532
533void stop_machine_park(int cpu)
534{
535 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
536 /*
537 * Lockless. cpu_stopper_thread() will take stopper->lock and flush
538 * the pending works before it parks, until then it is fine to queue
539 * the new works.
540 */
541 stopper->enabled = false;
542 kthread_park(stopper->thread);
543}
544
545extern void sched_set_stop_task(int cpu, struct task_struct *stop);
546
547static void cpu_stop_create(unsigned int cpu)
548{
549 sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
550}
551
552static void cpu_stop_park(unsigned int cpu)
553{
554 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
555
556 WARN_ON(!list_empty(&stopper->works));
557}
558
559void stop_machine_unpark(int cpu)
560{
561 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
562
563 stopper->enabled = true;
564 kthread_unpark(stopper->thread);
565}
566
567static struct smp_hotplug_thread cpu_stop_threads = {
568 .store = &cpu_stopper.thread,
569 .thread_should_run = cpu_stop_should_run,
570 .thread_fn = cpu_stopper_thread,
571 .thread_comm = "migration/%u",
572 .create = cpu_stop_create,
573 .park = cpu_stop_park,
574 .selfparking = true,
575};
576
577static int __init cpu_stop_init(void)
578{
579 unsigned int cpu;
580
581 for_each_possible_cpu(cpu) {
582 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
583
584 raw_spin_lock_init(&stopper->lock);
585 INIT_LIST_HEAD(&stopper->works);
586 }
587
588 BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
589 stop_machine_unpark(raw_smp_processor_id());
590 stop_machine_initialized = true;
591 return 0;
592}
593early_initcall(cpu_stop_init);
594
595int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data,
596 const struct cpumask *cpus)
597{
598 struct multi_stop_data msdata = {
599 .fn = fn,
600 .data = data,
601 .num_threads = num_online_cpus(),
602 .active_cpus = cpus,
603 };
604
605 lockdep_assert_cpus_held();
606
607 if (!stop_machine_initialized) {
608 /*
609 * Handle the case where stop_machine() is called
610 * early in boot before stop_machine() has been
611 * initialized.
612 */
613 unsigned long flags;
614 int ret;
615
616 WARN_ON_ONCE(msdata.num_threads != 1);
617
618 local_irq_save(flags);
619 hard_irq_disable();
620 ret = (*fn)(data);
621 local_irq_restore(flags);
622
623 return ret;
624 }
625
626 /* Set the initial state and stop all online cpus. */
627 set_state(&msdata, MULTI_STOP_PREPARE);
628 return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
629}
630
631int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
632{
633 int ret;
634
635 /* No CPUs can come up or down during this. */
636 cpus_read_lock();
637 ret = stop_machine_cpuslocked(fn, data, cpus);
638 cpus_read_unlock();
639 return ret;
640}
641EXPORT_SYMBOL_GPL(stop_machine);
642
643/**
644 * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
645 * @fn: the function to run
646 * @data: the data ptr for the @fn()
647 * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
648 *
649 * This is identical to stop_machine() but can be called from a CPU which
650 * is not active. The local CPU is in the process of hotplug (so no other
651 * CPU hotplug can start) and not marked active and doesn't have enough
652 * context to sleep.
653 *
654 * This function provides stop_machine() functionality for such state by
655 * using busy-wait for synchronization and executing @fn directly for local
656 * CPU.
657 *
658 * CONTEXT:
659 * Local CPU is inactive. Temporarily stops all active CPUs.
660 *
661 * RETURNS:
662 * 0 if all executions of @fn returned 0, any non zero return value if any
663 * returned non zero.
664 */
665int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
666 const struct cpumask *cpus)
667{
668 struct multi_stop_data msdata = { .fn = fn, .data = data,
669 .active_cpus = cpus };
670 struct cpu_stop_done done;
671 int ret;
672
673 /* Local CPU must be inactive and CPU hotplug in progress. */
674 BUG_ON(cpu_active(raw_smp_processor_id()));
675 msdata.num_threads = num_active_cpus() + 1; /* +1 for local */
676
677 /* No proper task established and can't sleep - busy wait for lock. */
678 while (!mutex_trylock(&stop_cpus_mutex))
679 cpu_relax();
680
681 /* Schedule work on other CPUs and execute directly for local CPU */
682 set_state(&msdata, MULTI_STOP_PREPARE);
683 cpu_stop_init_done(&done, num_active_cpus());
684 queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
685 &done);
686 ret = multi_cpu_stop(&msdata);
687
688 /* Busy wait for completion. */
689 while (!completion_done(&done.completion))
690 cpu_relax();
691
692 mutex_unlock(&stop_cpus_mutex);
693 return ret ?: done.ret;
694}
1/*
2 * kernel/stop_machine.c
3 *
4 * Copyright (C) 2008, 2005 IBM Corporation.
5 * Copyright (C) 2008, 2005 Rusty Russell rusty@rustcorp.com.au
6 * Copyright (C) 2010 SUSE Linux Products GmbH
7 * Copyright (C) 2010 Tejun Heo <tj@kernel.org>
8 *
9 * This file is released under the GPLv2 and any later version.
10 */
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
25/*
26 * Structure to determine completion condition and record errors. May
27 * be shared by works on different cpus.
28 */
29struct cpu_stop_done {
30 atomic_t nr_todo; /* nr left to execute */
31 int ret; /* collected return value */
32 struct completion completion; /* fired if nr_todo reaches 0 */
33};
34
35/* the actual stopper, one per every possible cpu, enabled on online cpus */
36struct cpu_stopper {
37 struct task_struct *thread;
38
39 spinlock_t lock;
40 bool enabled; /* is this stopper enabled? */
41 struct list_head works; /* list of pending works */
42
43 struct cpu_stop_work stop_work; /* for stop_cpus */
44};
45
46static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
47static bool stop_machine_initialized = false;
48
49/* static data for stop_cpus */
50static DEFINE_MUTEX(stop_cpus_mutex);
51static bool stop_cpus_in_progress;
52
53static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
54{
55 memset(done, 0, sizeof(*done));
56 atomic_set(&done->nr_todo, nr_todo);
57 init_completion(&done->completion);
58}
59
60/* signal completion unless @done is NULL */
61static void cpu_stop_signal_done(struct cpu_stop_done *done)
62{
63 if (atomic_dec_and_test(&done->nr_todo))
64 complete(&done->completion);
65}
66
67static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
68 struct cpu_stop_work *work)
69{
70 list_add_tail(&work->list, &stopper->works);
71 wake_up_process(stopper->thread);
72}
73
74/* queue @work to @stopper. if offline, @work is completed immediately */
75static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
76{
77 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
78 unsigned long flags;
79 bool enabled;
80
81 spin_lock_irqsave(&stopper->lock, flags);
82 enabled = stopper->enabled;
83 if (enabled)
84 __cpu_stop_queue_work(stopper, work);
85 else if (work->done)
86 cpu_stop_signal_done(work->done);
87 spin_unlock_irqrestore(&stopper->lock, flags);
88
89 return enabled;
90}
91
92/**
93 * stop_one_cpu - stop a cpu
94 * @cpu: cpu to stop
95 * @fn: function to execute
96 * @arg: argument to @fn
97 *
98 * Execute @fn(@arg) on @cpu. @fn is run in a process context with
99 * the highest priority preempting any task on the cpu and
100 * monopolizing it. This function returns after the execution is
101 * complete.
102 *
103 * This function doesn't guarantee @cpu stays online till @fn
104 * completes. If @cpu goes down in the middle, execution may happen
105 * partially or fully on different cpus. @fn should either be ready
106 * for that or the caller should ensure that @cpu stays online until
107 * this function completes.
108 *
109 * CONTEXT:
110 * Might sleep.
111 *
112 * RETURNS:
113 * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
114 * otherwise, the return value of @fn.
115 */
116int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
117{
118 struct cpu_stop_done done;
119 struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
120
121 cpu_stop_init_done(&done, 1);
122 if (!cpu_stop_queue_work(cpu, &work))
123 return -ENOENT;
124 /*
125 * In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup
126 * cycle by doing a preemption:
127 */
128 cond_resched();
129 wait_for_completion(&done.completion);
130 return done.ret;
131}
132
133/* This controls the threads on each CPU. */
134enum multi_stop_state {
135 /* Dummy starting state for thread. */
136 MULTI_STOP_NONE,
137 /* Awaiting everyone to be scheduled. */
138 MULTI_STOP_PREPARE,
139 /* Disable interrupts. */
140 MULTI_STOP_DISABLE_IRQ,
141 /* Run the function */
142 MULTI_STOP_RUN,
143 /* Exit */
144 MULTI_STOP_EXIT,
145};
146
147struct multi_stop_data {
148 cpu_stop_fn_t fn;
149 void *data;
150 /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
151 unsigned int num_threads;
152 const struct cpumask *active_cpus;
153
154 enum multi_stop_state state;
155 atomic_t thread_ack;
156};
157
158static void set_state(struct multi_stop_data *msdata,
159 enum multi_stop_state newstate)
160{
161 /* Reset ack counter. */
162 atomic_set(&msdata->thread_ack, msdata->num_threads);
163 smp_wmb();
164 msdata->state = newstate;
165}
166
167/* Last one to ack a state moves to the next state. */
168static void ack_state(struct multi_stop_data *msdata)
169{
170 if (atomic_dec_and_test(&msdata->thread_ack))
171 set_state(msdata, msdata->state + 1);
172}
173
174/* This is the cpu_stop function which stops the CPU. */
175static int multi_cpu_stop(void *data)
176{
177 struct multi_stop_data *msdata = data;
178 enum multi_stop_state curstate = MULTI_STOP_NONE;
179 int cpu = smp_processor_id(), err = 0;
180 unsigned long flags;
181 bool is_active;
182
183 /*
184 * When called from stop_machine_from_inactive_cpu(), irq might
185 * already be disabled. Save the state and restore it on exit.
186 */
187 local_save_flags(flags);
188
189 if (!msdata->active_cpus)
190 is_active = cpu == cpumask_first(cpu_online_mask);
191 else
192 is_active = cpumask_test_cpu(cpu, msdata->active_cpus);
193
194 /* Simple state machine */
195 do {
196 /* Chill out and ensure we re-read multi_stop_state. */
197 cpu_relax_yield();
198 if (msdata->state != curstate) {
199 curstate = msdata->state;
200 switch (curstate) {
201 case MULTI_STOP_DISABLE_IRQ:
202 local_irq_disable();
203 hard_irq_disable();
204 break;
205 case MULTI_STOP_RUN:
206 if (is_active)
207 err = msdata->fn(msdata->data);
208 break;
209 default:
210 break;
211 }
212 ack_state(msdata);
213 } else if (curstate > MULTI_STOP_PREPARE) {
214 /*
215 * At this stage all other CPUs we depend on must spin
216 * in the same loop. Any reason for hard-lockup should
217 * be detected and reported on their side.
218 */
219 touch_nmi_watchdog();
220 }
221 } while (curstate != MULTI_STOP_EXIT);
222
223 local_irq_restore(flags);
224 return err;
225}
226
227static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
228 int cpu2, struct cpu_stop_work *work2)
229{
230 struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
231 struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
232 int err;
233retry:
234 spin_lock_irq(&stopper1->lock);
235 spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
236
237 err = -ENOENT;
238 if (!stopper1->enabled || !stopper2->enabled)
239 goto unlock;
240 /*
241 * Ensure that if we race with __stop_cpus() the stoppers won't get
242 * queued up in reverse order leading to system deadlock.
243 *
244 * We can't miss stop_cpus_in_progress if queue_stop_cpus_work() has
245 * queued a work on cpu1 but not on cpu2, we hold both locks.
246 *
247 * It can be falsely true but it is safe to spin until it is cleared,
248 * queue_stop_cpus_work() does everything under preempt_disable().
249 */
250 err = -EDEADLK;
251 if (unlikely(stop_cpus_in_progress))
252 goto unlock;
253
254 err = 0;
255 __cpu_stop_queue_work(stopper1, work1);
256 __cpu_stop_queue_work(stopper2, work2);
257unlock:
258 spin_unlock(&stopper2->lock);
259 spin_unlock_irq(&stopper1->lock);
260
261 if (unlikely(err == -EDEADLK)) {
262 while (stop_cpus_in_progress)
263 cpu_relax();
264 goto retry;
265 }
266 return err;
267}
268/**
269 * stop_two_cpus - stops two cpus
270 * @cpu1: the cpu to stop
271 * @cpu2: the other cpu to stop
272 * @fn: function to execute
273 * @arg: argument to @fn
274 *
275 * Stops both the current and specified CPU and runs @fn on one of them.
276 *
277 * returns when both are completed.
278 */
279int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
280{
281 struct cpu_stop_done done;
282 struct cpu_stop_work work1, work2;
283 struct multi_stop_data msdata;
284
285 msdata = (struct multi_stop_data){
286 .fn = fn,
287 .data = arg,
288 .num_threads = 2,
289 .active_cpus = cpumask_of(cpu1),
290 };
291
292 work1 = work2 = (struct cpu_stop_work){
293 .fn = multi_cpu_stop,
294 .arg = &msdata,
295 .done = &done
296 };
297
298 cpu_stop_init_done(&done, 2);
299 set_state(&msdata, MULTI_STOP_PREPARE);
300
301 if (cpu1 > cpu2)
302 swap(cpu1, cpu2);
303 if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
304 return -ENOENT;
305
306 wait_for_completion(&done.completion);
307 return done.ret;
308}
309
310/**
311 * stop_one_cpu_nowait - stop a cpu but don't wait for completion
312 * @cpu: cpu to stop
313 * @fn: function to execute
314 * @arg: argument to @fn
315 * @work_buf: pointer to cpu_stop_work structure
316 *
317 * Similar to stop_one_cpu() but doesn't wait for completion. The
318 * caller is responsible for ensuring @work_buf is currently unused
319 * and will remain untouched until stopper starts executing @fn.
320 *
321 * CONTEXT:
322 * Don't care.
323 *
324 * RETURNS:
325 * true if cpu_stop_work was queued successfully and @fn will be called,
326 * false otherwise.
327 */
328bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
329 struct cpu_stop_work *work_buf)
330{
331 *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
332 return cpu_stop_queue_work(cpu, work_buf);
333}
334
335static bool queue_stop_cpus_work(const struct cpumask *cpumask,
336 cpu_stop_fn_t fn, void *arg,
337 struct cpu_stop_done *done)
338{
339 struct cpu_stop_work *work;
340 unsigned int cpu;
341 bool queued = false;
342
343 /*
344 * Disable preemption while queueing to avoid getting
345 * preempted by a stopper which might wait for other stoppers
346 * to enter @fn which can lead to deadlock.
347 */
348 preempt_disable();
349 stop_cpus_in_progress = true;
350 for_each_cpu(cpu, cpumask) {
351 work = &per_cpu(cpu_stopper.stop_work, cpu);
352 work->fn = fn;
353 work->arg = arg;
354 work->done = done;
355 if (cpu_stop_queue_work(cpu, work))
356 queued = true;
357 }
358 stop_cpus_in_progress = false;
359 preempt_enable();
360
361 return queued;
362}
363
364static int __stop_cpus(const struct cpumask *cpumask,
365 cpu_stop_fn_t fn, void *arg)
366{
367 struct cpu_stop_done done;
368
369 cpu_stop_init_done(&done, cpumask_weight(cpumask));
370 if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
371 return -ENOENT;
372 wait_for_completion(&done.completion);
373 return done.ret;
374}
375
376/**
377 * stop_cpus - stop multiple cpus
378 * @cpumask: cpus to stop
379 * @fn: function to execute
380 * @arg: argument to @fn
381 *
382 * Execute @fn(@arg) on online cpus in @cpumask. On each target cpu,
383 * @fn is run in a process context with the highest priority
384 * preempting any task on the cpu and monopolizing it. This function
385 * returns after all executions are complete.
386 *
387 * This function doesn't guarantee the cpus in @cpumask stay online
388 * till @fn completes. If some cpus go down in the middle, execution
389 * on the cpu may happen partially or fully on different cpus. @fn
390 * should either be ready for that or the caller should ensure that
391 * the cpus stay online until this function completes.
392 *
393 * All stop_cpus() calls are serialized making it safe for @fn to wait
394 * for all cpus to start executing it.
395 *
396 * CONTEXT:
397 * Might sleep.
398 *
399 * RETURNS:
400 * -ENOENT if @fn(@arg) was not executed at all because all cpus in
401 * @cpumask were offline; otherwise, 0 if all executions of @fn
402 * returned 0, any non zero return value if any returned non zero.
403 */
404int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
405{
406 int ret;
407
408 /* static works are used, process one request at a time */
409 mutex_lock(&stop_cpus_mutex);
410 ret = __stop_cpus(cpumask, fn, arg);
411 mutex_unlock(&stop_cpus_mutex);
412 return ret;
413}
414
415/**
416 * try_stop_cpus - try to stop multiple cpus
417 * @cpumask: cpus to stop
418 * @fn: function to execute
419 * @arg: argument to @fn
420 *
421 * Identical to stop_cpus() except that it fails with -EAGAIN if
422 * someone else is already using the facility.
423 *
424 * CONTEXT:
425 * Might sleep.
426 *
427 * RETURNS:
428 * -EAGAIN if someone else is already stopping cpus, -ENOENT if
429 * @fn(@arg) was not executed at all because all cpus in @cpumask were
430 * offline; otherwise, 0 if all executions of @fn returned 0, any non
431 * zero return value if any returned non zero.
432 */
433int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
434{
435 int ret;
436
437 /* static works are used, process one request at a time */
438 if (!mutex_trylock(&stop_cpus_mutex))
439 return -EAGAIN;
440 ret = __stop_cpus(cpumask, fn, arg);
441 mutex_unlock(&stop_cpus_mutex);
442 return ret;
443}
444
445static int cpu_stop_should_run(unsigned int cpu)
446{
447 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
448 unsigned long flags;
449 int run;
450
451 spin_lock_irqsave(&stopper->lock, flags);
452 run = !list_empty(&stopper->works);
453 spin_unlock_irqrestore(&stopper->lock, flags);
454 return run;
455}
456
457static void cpu_stopper_thread(unsigned int cpu)
458{
459 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
460 struct cpu_stop_work *work;
461
462repeat:
463 work = NULL;
464 spin_lock_irq(&stopper->lock);
465 if (!list_empty(&stopper->works)) {
466 work = list_first_entry(&stopper->works,
467 struct cpu_stop_work, list);
468 list_del_init(&work->list);
469 }
470 spin_unlock_irq(&stopper->lock);
471
472 if (work) {
473 cpu_stop_fn_t fn = work->fn;
474 void *arg = work->arg;
475 struct cpu_stop_done *done = work->done;
476 int ret;
477
478 /* cpu stop callbacks must not sleep, make in_atomic() == T */
479 preempt_count_inc();
480 ret = fn(arg);
481 if (done) {
482 if (ret)
483 done->ret = ret;
484 cpu_stop_signal_done(done);
485 }
486 preempt_count_dec();
487 WARN_ONCE(preempt_count(),
488 "cpu_stop: %pf(%p) leaked preempt count\n", fn, arg);
489 goto repeat;
490 }
491}
492
493void stop_machine_park(int cpu)
494{
495 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
496 /*
497 * Lockless. cpu_stopper_thread() will take stopper->lock and flush
498 * the pending works before it parks, until then it is fine to queue
499 * the new works.
500 */
501 stopper->enabled = false;
502 kthread_park(stopper->thread);
503}
504
505extern void sched_set_stop_task(int cpu, struct task_struct *stop);
506
507static void cpu_stop_create(unsigned int cpu)
508{
509 sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
510}
511
512static void cpu_stop_park(unsigned int cpu)
513{
514 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
515
516 WARN_ON(!list_empty(&stopper->works));
517}
518
519void stop_machine_unpark(int cpu)
520{
521 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
522
523 stopper->enabled = true;
524 kthread_unpark(stopper->thread);
525}
526
527static struct smp_hotplug_thread cpu_stop_threads = {
528 .store = &cpu_stopper.thread,
529 .thread_should_run = cpu_stop_should_run,
530 .thread_fn = cpu_stopper_thread,
531 .thread_comm = "migration/%u",
532 .create = cpu_stop_create,
533 .park = cpu_stop_park,
534 .selfparking = true,
535};
536
537static int __init cpu_stop_init(void)
538{
539 unsigned int cpu;
540
541 for_each_possible_cpu(cpu) {
542 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
543
544 spin_lock_init(&stopper->lock);
545 INIT_LIST_HEAD(&stopper->works);
546 }
547
548 BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
549 stop_machine_unpark(raw_smp_processor_id());
550 stop_machine_initialized = true;
551 return 0;
552}
553early_initcall(cpu_stop_init);
554
555static int __stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
556{
557 struct multi_stop_data msdata = {
558 .fn = fn,
559 .data = data,
560 .num_threads = num_online_cpus(),
561 .active_cpus = cpus,
562 };
563
564 if (!stop_machine_initialized) {
565 /*
566 * Handle the case where stop_machine() is called
567 * early in boot before stop_machine() has been
568 * initialized.
569 */
570 unsigned long flags;
571 int ret;
572
573 WARN_ON_ONCE(msdata.num_threads != 1);
574
575 local_irq_save(flags);
576 hard_irq_disable();
577 ret = (*fn)(data);
578 local_irq_restore(flags);
579
580 return ret;
581 }
582
583 /* Set the initial state and stop all online cpus. */
584 set_state(&msdata, MULTI_STOP_PREPARE);
585 return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
586}
587
588int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
589{
590 int ret;
591
592 /* No CPUs can come up or down during this. */
593 get_online_cpus();
594 ret = __stop_machine(fn, data, cpus);
595 put_online_cpus();
596 return ret;
597}
598EXPORT_SYMBOL_GPL(stop_machine);
599
600/**
601 * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
602 * @fn: the function to run
603 * @data: the data ptr for the @fn()
604 * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
605 *
606 * This is identical to stop_machine() but can be called from a CPU which
607 * is not active. The local CPU is in the process of hotplug (so no other
608 * CPU hotplug can start) and not marked active and doesn't have enough
609 * context to sleep.
610 *
611 * This function provides stop_machine() functionality for such state by
612 * using busy-wait for synchronization and executing @fn directly for local
613 * CPU.
614 *
615 * CONTEXT:
616 * Local CPU is inactive. Temporarily stops all active CPUs.
617 *
618 * RETURNS:
619 * 0 if all executions of @fn returned 0, any non zero return value if any
620 * returned non zero.
621 */
622int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
623 const struct cpumask *cpus)
624{
625 struct multi_stop_data msdata = { .fn = fn, .data = data,
626 .active_cpus = cpus };
627 struct cpu_stop_done done;
628 int ret;
629
630 /* Local CPU must be inactive and CPU hotplug in progress. */
631 BUG_ON(cpu_active(raw_smp_processor_id()));
632 msdata.num_threads = num_active_cpus() + 1; /* +1 for local */
633
634 /* No proper task established and can't sleep - busy wait for lock. */
635 while (!mutex_trylock(&stop_cpus_mutex))
636 cpu_relax();
637
638 /* Schedule work on other CPUs and execute directly for local CPU */
639 set_state(&msdata, MULTI_STOP_PREPARE);
640 cpu_stop_init_done(&done, num_active_cpus());
641 queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
642 &done);
643 ret = multi_cpu_stop(&msdata);
644
645 /* Busy wait for completion. */
646 while (!completion_done(&done.completion))
647 cpu_relax();
648
649 mutex_unlock(&stop_cpus_mutex);
650 return ret ?: done.ret;
651}