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1/*
2 * kernel/stop_machine.c
3 *
4 * Copyright (C) 2008, 2005 IBM Corporation.
5 * Copyright (C) 2008, 2005 Rusty Russell [email protected]
6 * Copyright (C) 2010 SUSE Linux Products GmbH
7 * Copyright (C) 2010 Tejun Heo <[email protected]>
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/lglock.h>
24#include <linux/nmi.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 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/*
51 * Avoids a race between stop_two_cpus and global stop_cpus, where
52 * the stoppers could get queued up in reverse order, leading to
53 * system deadlock. Using an lglock means stop_two_cpus remains
54 * relatively cheap.
55 */
56DEFINE_STATIC_LGLOCK(stop_cpus_lock);
57
58static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
59{
60 memset(done, 0, sizeof(*done));
61 atomic_set(&done->nr_todo, nr_todo);
62 init_completion(&done->completion);
63}
64
65/* signal completion unless @done is NULL */
66static void cpu_stop_signal_done(struct cpu_stop_done *done)
67{
68 if (atomic_dec_and_test(&done->nr_todo))
69 complete(&done->completion);
70}
71
72static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
73 struct cpu_stop_work *work)
74{
75 list_add_tail(&work->list, &stopper->works);
76 wake_up_process(stopper->thread);
77}
78
79/* queue @work to @stopper. if offline, @work is completed immediately */
80static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
81{
82 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
83 unsigned long flags;
84 bool enabled;
85
86 spin_lock_irqsave(&stopper->lock, flags);
87 enabled = stopper->enabled;
88 if (enabled)
89 __cpu_stop_queue_work(stopper, work);
90 else if (work->done)
91 cpu_stop_signal_done(work->done);
92 spin_unlock_irqrestore(&stopper->lock, flags);
93
94 return enabled;
95}
96
97/**
98 * stop_one_cpu - stop a cpu
99 * @cpu: cpu to stop
100 * @fn: function to execute
101 * @arg: argument to @fn
102 *
103 * Execute @fn(@arg) on @cpu. @fn is run in a process context with
104 * the highest priority preempting any task on the cpu and
105 * monopolizing it. This function returns after the execution is
106 * complete.
107 *
108 * This function doesn't guarantee @cpu stays online till @fn
109 * completes. If @cpu goes down in the middle, execution may happen
110 * partially or fully on different cpus. @fn should either be ready
111 * for that or the caller should ensure that @cpu stays online until
112 * this function completes.
113 *
114 * CONTEXT:
115 * Might sleep.
116 *
117 * RETURNS:
118 * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
119 * otherwise, the return value of @fn.
120 */
121int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
122{
123 struct cpu_stop_done done;
124 struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
125
126 cpu_stop_init_done(&done, 1);
127 if (!cpu_stop_queue_work(cpu, &work))
128 return -ENOENT;
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();
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;
233
234 lg_double_lock(&stop_cpus_lock, cpu1, cpu2);
235 spin_lock_irq(&stopper1->lock);
236 spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
237
238 err = -ENOENT;
239 if (!stopper1->enabled || !stopper2->enabled)
240 goto unlock;
241
242 err = 0;
243 __cpu_stop_queue_work(stopper1, work1);
244 __cpu_stop_queue_work(stopper2, work2);
245unlock:
246 spin_unlock(&stopper2->lock);
247 spin_unlock_irq(&stopper1->lock);
248 lg_double_unlock(&stop_cpus_lock, cpu1, cpu2);
249
250 return err;
251}
252/**
253 * stop_two_cpus - stops two cpus
254 * @cpu1: the cpu to stop
255 * @cpu2: the other cpu to stop
256 * @fn: function to execute
257 * @arg: argument to @fn
258 *
259 * Stops both the current and specified CPU and runs @fn on one of them.
260 *
261 * returns when both are completed.
262 */
263int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
264{
265 struct cpu_stop_done done;
266 struct cpu_stop_work work1, work2;
267 struct multi_stop_data msdata;
268
269 msdata = (struct multi_stop_data){
270 .fn = fn,
271 .data = arg,
272 .num_threads = 2,
273 .active_cpus = cpumask_of(cpu1),
274 };
275
276 work1 = work2 = (struct cpu_stop_work){
277 .fn = multi_cpu_stop,
278 .arg = &msdata,
279 .done = &done
280 };
281
282 cpu_stop_init_done(&done, 2);
283 set_state(&msdata, MULTI_STOP_PREPARE);
284
285 if (cpu1 > cpu2)
286 swap(cpu1, cpu2);
287 if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
288 return -ENOENT;
289
290 wait_for_completion(&done.completion);
291 return done.ret;
292}
293
294/**
295 * stop_one_cpu_nowait - stop a cpu but don't wait for completion
296 * @cpu: cpu to stop
297 * @fn: function to execute
298 * @arg: argument to @fn
299 * @work_buf: pointer to cpu_stop_work structure
300 *
301 * Similar to stop_one_cpu() but doesn't wait for completion. The
302 * caller is responsible for ensuring @work_buf is currently unused
303 * and will remain untouched until stopper starts executing @fn.
304 *
305 * CONTEXT:
306 * Don't care.
307 *
308 * RETURNS:
309 * true if cpu_stop_work was queued successfully and @fn will be called,
310 * false otherwise.
311 */
312bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
313 struct cpu_stop_work *work_buf)
314{
315 *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
316 return cpu_stop_queue_work(cpu, work_buf);
317}
318
319/* static data for stop_cpus */
320static DEFINE_MUTEX(stop_cpus_mutex);
321
322static bool queue_stop_cpus_work(const struct cpumask *cpumask,
323 cpu_stop_fn_t fn, void *arg,
324 struct cpu_stop_done *done)
325{
326 struct cpu_stop_work *work;
327 unsigned int cpu;
328 bool queued = false;
329
330 /*
331 * Disable preemption while queueing to avoid getting
332 * preempted by a stopper which might wait for other stoppers
333 * to enter @fn which can lead to deadlock.
334 */
335 lg_global_lock(&stop_cpus_lock);
336 for_each_cpu(cpu, cpumask) {
337 work = &per_cpu(cpu_stopper.stop_work, cpu);
338 work->fn = fn;
339 work->arg = arg;
340 work->done = done;
341 if (cpu_stop_queue_work(cpu, work))
342 queued = true;
343 }
344 lg_global_unlock(&stop_cpus_lock);
345
346 return queued;
347}
348
349static int __stop_cpus(const struct cpumask *cpumask,
350 cpu_stop_fn_t fn, void *arg)
351{
352 struct cpu_stop_done done;
353
354 cpu_stop_init_done(&done, cpumask_weight(cpumask));
355 if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
356 return -ENOENT;
357 wait_for_completion(&done.completion);
358 return done.ret;
359}
360
361/**
362 * stop_cpus - stop multiple cpus
363 * @cpumask: cpus to stop
364 * @fn: function to execute
365 * @arg: argument to @fn
366 *
367 * Execute @fn(@arg) on online cpus in @cpumask. On each target cpu,
368 * @fn is run in a process context with the highest priority
369 * preempting any task on the cpu and monopolizing it. This function
370 * returns after all executions are complete.
371 *
372 * This function doesn't guarantee the cpus in @cpumask stay online
373 * till @fn completes. If some cpus go down in the middle, execution
374 * on the cpu may happen partially or fully on different cpus. @fn
375 * should either be ready for that or the caller should ensure that
376 * the cpus stay online until this function completes.
377 *
378 * All stop_cpus() calls are serialized making it safe for @fn to wait
379 * for all cpus to start executing it.
380 *
381 * CONTEXT:
382 * Might sleep.
383 *
384 * RETURNS:
385 * -ENOENT if @fn(@arg) was not executed at all because all cpus in
386 * @cpumask were offline; otherwise, 0 if all executions of @fn
387 * returned 0, any non zero return value if any returned non zero.
388 */
389int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
390{
391 int ret;
392
393 /* static works are used, process one request at a time */
394 mutex_lock(&stop_cpus_mutex);
395 ret = __stop_cpus(cpumask, fn, arg);
396 mutex_unlock(&stop_cpus_mutex);
397 return ret;
398}
399
400/**
401 * try_stop_cpus - try to stop multiple cpus
402 * @cpumask: cpus to stop
403 * @fn: function to execute
404 * @arg: argument to @fn
405 *
406 * Identical to stop_cpus() except that it fails with -EAGAIN if
407 * someone else is already using the facility.
408 *
409 * CONTEXT:
410 * Might sleep.
411 *
412 * RETURNS:
413 * -EAGAIN if someone else is already stopping cpus, -ENOENT if
414 * @fn(@arg) was not executed at all because all cpus in @cpumask were
415 * offline; otherwise, 0 if all executions of @fn returned 0, any non
416 * zero return value if any returned non zero.
417 */
418int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
419{
420 int ret;
421
422 /* static works are used, process one request at a time */
423 if (!mutex_trylock(&stop_cpus_mutex))
424 return -EAGAIN;
425 ret = __stop_cpus(cpumask, fn, arg);
426 mutex_unlock(&stop_cpus_mutex);
427 return ret;
428}
429
430static int cpu_stop_should_run(unsigned int cpu)
431{
432 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
433 unsigned long flags;
434 int run;
435
436 spin_lock_irqsave(&stopper->lock, flags);
437 run = !list_empty(&stopper->works);
438 spin_unlock_irqrestore(&stopper->lock, flags);
439 return run;
440}
441
442static void cpu_stopper_thread(unsigned int cpu)
443{
444 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
445 struct cpu_stop_work *work;
446
447repeat:
448 work = NULL;
449 spin_lock_irq(&stopper->lock);
450 if (!list_empty(&stopper->works)) {
451 work = list_first_entry(&stopper->works,
452 struct cpu_stop_work, list);
453 list_del_init(&work->list);
454 }
455 spin_unlock_irq(&stopper->lock);
456
457 if (work) {
458 cpu_stop_fn_t fn = work->fn;
459 void *arg = work->arg;
460 struct cpu_stop_done *done = work->done;
461 int ret;
462
463 /* cpu stop callbacks must not sleep, make in_atomic() == T */
464 preempt_count_inc();
465 ret = fn(arg);
466 if (done) {
467 if (ret)
468 done->ret = ret;
469 cpu_stop_signal_done(done);
470 }
471 preempt_count_dec();
472 WARN_ONCE(preempt_count(),
473 "cpu_stop: %pf(%p) leaked preempt count\n", fn, arg);
474 goto repeat;
475 }
476}
477
478void stop_machine_park(int cpu)
479{
480 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
481 /*
482 * Lockless. cpu_stopper_thread() will take stopper->lock and flush
483 * the pending works before it parks, until then it is fine to queue
484 * the new works.
485 */
486 stopper->enabled = false;
487 kthread_park(stopper->thread);
488}
489
490extern void sched_set_stop_task(int cpu, struct task_struct *stop);
491
492static void cpu_stop_create(unsigned int cpu)
493{
494 sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
495}
496
497static void cpu_stop_park(unsigned int cpu)
498{
499 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
500
501 WARN_ON(!list_empty(&stopper->works));
502}
503
504void stop_machine_unpark(int cpu)
505{
506 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
507
508 stopper->enabled = true;
509 kthread_unpark(stopper->thread);
510}
511
512static struct smp_hotplug_thread cpu_stop_threads = {
513 .store = &cpu_stopper.thread,
514 .thread_should_run = cpu_stop_should_run,
515 .thread_fn = cpu_stopper_thread,
516 .thread_comm = "migration/%u",
517 .create = cpu_stop_create,
518 .park = cpu_stop_park,
519 .selfparking = true,
520};
521
522static int __init cpu_stop_init(void)
523{
524 unsigned int cpu;
525
526 for_each_possible_cpu(cpu) {
527 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
528
529 spin_lock_init(&stopper->lock);
530 INIT_LIST_HEAD(&stopper->works);
531 }
532
533 BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
534 stop_machine_unpark(raw_smp_processor_id());
535 stop_machine_initialized = true;
536 return 0;
537}
538early_initcall(cpu_stop_init);
539
540static int __stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
541{
542 struct multi_stop_data msdata = {
543 .fn = fn,
544 .data = data,
545 .num_threads = num_online_cpus(),
546 .active_cpus = cpus,
547 };
548
549 if (!stop_machine_initialized) {
550 /*
551 * Handle the case where stop_machine() is called
552 * early in boot before stop_machine() has been
553 * initialized.
554 */
555 unsigned long flags;
556 int ret;
557
558 WARN_ON_ONCE(msdata.num_threads != 1);
559
560 local_irq_save(flags);
561 hard_irq_disable();
562 ret = (*fn)(data);
563 local_irq_restore(flags);
564
565 return ret;
566 }
567
568 /* Set the initial state and stop all online cpus. */
569 set_state(&msdata, MULTI_STOP_PREPARE);
570 return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
571}
572
573int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
574{
575 int ret;
576
577 /* No CPUs can come up or down during this. */
578 get_online_cpus();
579 ret = __stop_machine(fn, data, cpus);
580 put_online_cpus();
581 return ret;
582}
583EXPORT_SYMBOL_GPL(stop_machine);
584
585/**
586 * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
587 * @fn: the function to run
588 * @data: the data ptr for the @fn()
589 * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
590 *
591 * This is identical to stop_machine() but can be called from a CPU which
592 * is not active. The local CPU is in the process of hotplug (so no other
593 * CPU hotplug can start) and not marked active and doesn't have enough
594 * context to sleep.
595 *
596 * This function provides stop_machine() functionality for such state by
597 * using busy-wait for synchronization and executing @fn directly for local
598 * CPU.
599 *
600 * CONTEXT:
601 * Local CPU is inactive. Temporarily stops all active CPUs.
602 *
603 * RETURNS:
604 * 0 if all executions of @fn returned 0, any non zero return value if any
605 * returned non zero.
606 */
607int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
608 const struct cpumask *cpus)
609{
610 struct multi_stop_data msdata = { .fn = fn, .data = data,
611 .active_cpus = cpus };
612 struct cpu_stop_done done;
613 int ret;
614
615 /* Local CPU must be inactive and CPU hotplug in progress. */
616 BUG_ON(cpu_active(raw_smp_processor_id()));
617 msdata.num_threads = num_active_cpus() + 1; /* +1 for local */
618
619 /* No proper task established and can't sleep - busy wait for lock. */
620 while (!mutex_trylock(&stop_cpus_mutex))
621 cpu_relax();
622
623 /* Schedule work on other CPUs and execute directly for local CPU */
624 set_state(&msdata, MULTI_STOP_PREPARE);
625 cpu_stop_init_done(&done, num_active_cpus());
626 queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
627 &done);
628 ret = multi_cpu_stop(&msdata);
629
630 /* Busy wait for completion. */
631 while (!completion_done(&done.completion))
632 cpu_relax();
633
634 mutex_unlock(&stop_cpus_mutex);
635 return ret ?: done.ret;
636}