projects/linux·blob v4.1-rc7 · refs

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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
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 bool executed; /* actually executed? */
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 spinlock_t lock;
39 bool enabled; /* is this stopper enabled? */
40 struct list_head works; /* list of pending works */
41};
42
43static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
44static DEFINE_PER_CPU(struct task_struct *, cpu_stopper_task);
45static bool stop_machine_initialized = false;
46
47/*
48 * Avoids a race between stop_two_cpus and global stop_cpus, where
49 * the stoppers could get queued up in reverse order, leading to
50 * system deadlock. Using an lglock means stop_two_cpus remains
51 * relatively cheap.
52 */
53DEFINE_STATIC_LGLOCK(stop_cpus_lock);
54
55static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
56{
57 memset(done, 0, sizeof(*done));
58 atomic_set(&done->nr_todo, nr_todo);
59 init_completion(&done->completion);
60}
61
62/* signal completion unless @done is NULL */
63static void cpu_stop_signal_done(struct cpu_stop_done *done, bool executed)
64{
65 if (done) {
66 if (executed)
67 done->executed = true;
68 if (atomic_dec_and_test(&done->nr_todo))
69 complete(&done->completion);
70 }
71}
72
73/* queue @work to @stopper. if offline, @work is completed immediately */
74static void cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
75{
76 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
77 struct task_struct *p = per_cpu(cpu_stopper_task, cpu);
78
79 unsigned long flags;
80
81 spin_lock_irqsave(&stopper->lock, flags);
82
83 if (stopper->enabled) {
84 list_add_tail(&work->list, &stopper->works);
85 wake_up_process(p);
86 } else
87 cpu_stop_signal_done(work->done, false);
88
89 spin_unlock_irqrestore(&stopper->lock, flags);
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 cpu_stop_queue_work(cpu, &work);
123 wait_for_completion(&done.completion);
124 return done.executed ? done.ret : -ENOENT;
125}
126
127/* This controls the threads on each CPU. */
128enum multi_stop_state {
129 /* Dummy starting state for thread. */
130 MULTI_STOP_NONE,
131 /* Awaiting everyone to be scheduled. */
132 MULTI_STOP_PREPARE,
133 /* Disable interrupts. */
134 MULTI_STOP_DISABLE_IRQ,
135 /* Run the function */
136 MULTI_STOP_RUN,
137 /* Exit */
138 MULTI_STOP_EXIT,
139};
140
141struct multi_stop_data {
142 int (*fn)(void *);
143 void *data;
144 /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
145 unsigned int num_threads;
146 const struct cpumask *active_cpus;
147
148 enum multi_stop_state state;
149 atomic_t thread_ack;
150};
151
152static void set_state(struct multi_stop_data *msdata,
153 enum multi_stop_state newstate)
154{
155 /* Reset ack counter. */
156 atomic_set(&msdata->thread_ack, msdata->num_threads);
157 smp_wmb();
158 msdata->state = newstate;
159}
160
161/* Last one to ack a state moves to the next state. */
162static void ack_state(struct multi_stop_data *msdata)
163{
164 if (atomic_dec_and_test(&msdata->thread_ack))
165 set_state(msdata, msdata->state + 1);
166}
167
168/* This is the cpu_stop function which stops the CPU. */
169static int multi_cpu_stop(void *data)
170{
171 struct multi_stop_data *msdata = data;
172 enum multi_stop_state curstate = MULTI_STOP_NONE;
173 int cpu = smp_processor_id(), err = 0;
174 unsigned long flags;
175 bool is_active;
176
177 /*
178 * When called from stop_machine_from_inactive_cpu(), irq might
179 * already be disabled. Save the state and restore it on exit.
180 */
181 local_save_flags(flags);
182
183 if (!msdata->active_cpus)
184 is_active = cpu == cpumask_first(cpu_online_mask);
185 else
186 is_active = cpumask_test_cpu(cpu, msdata->active_cpus);
187
188 /* Simple state machine */
189 do {
190 /* Chill out and ensure we re-read multi_stop_state. */
191 cpu_relax();
192 if (msdata->state != curstate) {
193 curstate = msdata->state;
194 switch (curstate) {
195 case MULTI_STOP_DISABLE_IRQ:
196 local_irq_disable();
197 hard_irq_disable();
198 break;
199 case MULTI_STOP_RUN:
200 if (is_active)
201 err = msdata->fn(msdata->data);
202 break;
203 default:
204 break;
205 }
206 ack_state(msdata);
207 }
208 } while (curstate != MULTI_STOP_EXIT);
209
210 local_irq_restore(flags);
211 return err;
212}
213
214struct irq_cpu_stop_queue_work_info {
215 int cpu1;
216 int cpu2;
217 struct cpu_stop_work *work1;
218 struct cpu_stop_work *work2;
219};
220
221/*
222 * This function is always run with irqs and preemption disabled.
223 * This guarantees that both work1 and work2 get queued, before
224 * our local migrate thread gets the chance to preempt us.
225 */
226static void irq_cpu_stop_queue_work(void *arg)
227{
228 struct irq_cpu_stop_queue_work_info *info = arg;
229 cpu_stop_queue_work(info->cpu1, info->work1);
230 cpu_stop_queue_work(info->cpu2, info->work2);
231}
232
233/**
234 * stop_two_cpus - stops two cpus
235 * @cpu1: the cpu to stop
236 * @cpu2: the other cpu to stop
237 * @fn: function to execute
238 * @arg: argument to @fn
239 *
240 * Stops both the current and specified CPU and runs @fn on one of them.
241 *
242 * returns when both are completed.
243 */
244int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
245{
246 struct cpu_stop_done done;
247 struct cpu_stop_work work1, work2;
248 struct irq_cpu_stop_queue_work_info call_args;
249 struct multi_stop_data msdata;
250
251 preempt_disable();
252 msdata = (struct multi_stop_data){
253 .fn = fn,
254 .data = arg,
255 .num_threads = 2,
256 .active_cpus = cpumask_of(cpu1),
257 };
258
259 work1 = work2 = (struct cpu_stop_work){
260 .fn = multi_cpu_stop,
261 .arg = &msdata,
262 .done = &done
263 };
264
265 call_args = (struct irq_cpu_stop_queue_work_info){
266 .cpu1 = cpu1,
267 .cpu2 = cpu2,
268 .work1 = &work1,
269 .work2 = &work2,
270 };
271
272 cpu_stop_init_done(&done, 2);
273 set_state(&msdata, MULTI_STOP_PREPARE);
274
275 /*
276 * If we observe both CPUs active we know _cpu_down() cannot yet have
277 * queued its stop_machine works and therefore ours will get executed
278 * first. Or its not either one of our CPUs that's getting unplugged,
279 * in which case we don't care.
280 *
281 * This relies on the stopper workqueues to be FIFO.
282 */
283 if (!cpu_active(cpu1) || !cpu_active(cpu2)) {
284 preempt_enable();
285 return -ENOENT;
286 }
287
288 lg_local_lock(&stop_cpus_lock);
289 /*
290 * Queuing needs to be done by the lowest numbered CPU, to ensure
291 * that works are always queued in the same order on every CPU.
292 * This prevents deadlocks.
293 */
294 smp_call_function_single(min(cpu1, cpu2),
295 &irq_cpu_stop_queue_work,
296 &call_args, 1);
297 lg_local_unlock(&stop_cpus_lock);
298 preempt_enable();
299
300 wait_for_completion(&done.completion);
301
302 return done.executed ? done.ret : -ENOENT;
303}
304
305/**
306 * stop_one_cpu_nowait - stop a cpu but don't wait for completion
307 * @cpu: cpu to stop
308 * @fn: function to execute
309 * @arg: argument to @fn
310 * @work_buf: pointer to cpu_stop_work structure
311 *
312 * Similar to stop_one_cpu() but doesn't wait for completion. The
313 * caller is responsible for ensuring @work_buf is currently unused
314 * and will remain untouched until stopper starts executing @fn.
315 *
316 * CONTEXT:
317 * Don't care.
318 */
319void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
320 struct cpu_stop_work *work_buf)
321{
322 *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
323 cpu_stop_queue_work(cpu, work_buf);
324}
325
326/* static data for stop_cpus */
327static DEFINE_MUTEX(stop_cpus_mutex);
328static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work);
329
330static void queue_stop_cpus_work(const struct cpumask *cpumask,
331 cpu_stop_fn_t fn, void *arg,
332 struct cpu_stop_done *done)
333{
334 struct cpu_stop_work *work;
335 unsigned int cpu;
336
337 /* initialize works and done */
338 for_each_cpu(cpu, cpumask) {
339 work = &per_cpu(stop_cpus_work, cpu);
340 work->fn = fn;
341 work->arg = arg;
342 work->done = done;
343 }
344
345 /*
346 * Disable preemption while queueing to avoid getting
347 * preempted by a stopper which might wait for other stoppers
348 * to enter @fn which can lead to deadlock.
349 */
350 lg_global_lock(&stop_cpus_lock);
351 for_each_cpu(cpu, cpumask)
352 cpu_stop_queue_work(cpu, &per_cpu(stop_cpus_work, cpu));
353 lg_global_unlock(&stop_cpus_lock);
354}
355
356static int __stop_cpus(const struct cpumask *cpumask,
357 cpu_stop_fn_t fn, void *arg)
358{
359 struct cpu_stop_done done;
360
361 cpu_stop_init_done(&done, cpumask_weight(cpumask));
362 queue_stop_cpus_work(cpumask, fn, arg, &done);
363 wait_for_completion(&done.completion);
364 return done.executed ? done.ret : -ENOENT;
365}
366
367/**
368 * stop_cpus - stop multiple cpus
369 * @cpumask: cpus to stop
370 * @fn: function to execute
371 * @arg: argument to @fn
372 *
373 * Execute @fn(@arg) on online cpus in @cpumask. On each target cpu,
374 * @fn is run in a process context with the highest priority
375 * preempting any task on the cpu and monopolizing it. This function
376 * returns after all executions are complete.
377 *
378 * This function doesn't guarantee the cpus in @cpumask stay online
379 * till @fn completes. If some cpus go down in the middle, execution
380 * on the cpu may happen partially or fully on different cpus. @fn
381 * should either be ready for that or the caller should ensure that
382 * the cpus stay online until this function completes.
383 *
384 * All stop_cpus() calls are serialized making it safe for @fn to wait
385 * for all cpus to start executing it.
386 *
387 * CONTEXT:
388 * Might sleep.
389 *
390 * RETURNS:
391 * -ENOENT if @fn(@arg) was not executed at all because all cpus in
392 * @cpumask were offline; otherwise, 0 if all executions of @fn
393 * returned 0, any non zero return value if any returned non zero.
394 */
395int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
396{
397 int ret;
398
399 /* static works are used, process one request at a time */
400 mutex_lock(&stop_cpus_mutex);
401 ret = __stop_cpus(cpumask, fn, arg);
402 mutex_unlock(&stop_cpus_mutex);
403 return ret;
404}
405
406/**
407 * try_stop_cpus - try to stop multiple cpus
408 * @cpumask: cpus to stop
409 * @fn: function to execute
410 * @arg: argument to @fn
411 *
412 * Identical to stop_cpus() except that it fails with -EAGAIN if
413 * someone else is already using the facility.
414 *
415 * CONTEXT:
416 * Might sleep.
417 *
418 * RETURNS:
419 * -EAGAIN if someone else is already stopping cpus, -ENOENT if
420 * @fn(@arg) was not executed at all because all cpus in @cpumask were
421 * offline; otherwise, 0 if all executions of @fn returned 0, any non
422 * zero return value if any returned non zero.
423 */
424int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
425{
426 int ret;
427
428 /* static works are used, process one request at a time */
429 if (!mutex_trylock(&stop_cpus_mutex))
430 return -EAGAIN;
431 ret = __stop_cpus(cpumask, fn, arg);
432 mutex_unlock(&stop_cpus_mutex);
433 return ret;
434}
435
436static int cpu_stop_should_run(unsigned int cpu)
437{
438 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
439 unsigned long flags;
440 int run;
441
442 spin_lock_irqsave(&stopper->lock, flags);
443 run = !list_empty(&stopper->works);
444 spin_unlock_irqrestore(&stopper->lock, flags);
445 return run;
446}
447
448static void cpu_stopper_thread(unsigned int cpu)
449{
450 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
451 struct cpu_stop_work *work;
452 int ret;
453
454repeat:
455 work = NULL;
456 spin_lock_irq(&stopper->lock);
457 if (!list_empty(&stopper->works)) {
458 work = list_first_entry(&stopper->works,
459 struct cpu_stop_work, list);
460 list_del_init(&work->list);
461 }
462 spin_unlock_irq(&stopper->lock);
463
464 if (work) {
465 cpu_stop_fn_t fn = work->fn;
466 void *arg = work->arg;
467 struct cpu_stop_done *done = work->done;
468 char ksym_buf[KSYM_NAME_LEN] __maybe_unused;
469
470 /* cpu stop callbacks are not allowed to sleep */
471 preempt_disable();
472
473 ret = fn(arg);
474 if (ret)
475 done->ret = ret;
476
477 /* restore preemption and check it's still balanced */
478 preempt_enable();
479 WARN_ONCE(preempt_count(),
480 "cpu_stop: %s(%p) leaked preempt count\n",
481 kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
482 ksym_buf), arg);
483
484 cpu_stop_signal_done(done, true);
485 goto repeat;
486 }
487}
488
489extern void sched_set_stop_task(int cpu, struct task_struct *stop);
490
491static void cpu_stop_create(unsigned int cpu)
492{
493 sched_set_stop_task(cpu, per_cpu(cpu_stopper_task, cpu));
494}
495
496static void cpu_stop_park(unsigned int cpu)
497{
498 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
499 struct cpu_stop_work *work;
500 unsigned long flags;
501
502 /* drain remaining works */
503 spin_lock_irqsave(&stopper->lock, flags);
504 list_for_each_entry(work, &stopper->works, list)
505 cpu_stop_signal_done(work->done, false);
506 stopper->enabled = false;
507 spin_unlock_irqrestore(&stopper->lock, flags);
508}
509
510static void cpu_stop_unpark(unsigned int cpu)
511{
512 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
513
514 spin_lock_irq(&stopper->lock);
515 stopper->enabled = true;
516 spin_unlock_irq(&stopper->lock);
517}
518
519static struct smp_hotplug_thread cpu_stop_threads = {
520 .store = &cpu_stopper_task,
521 .thread_should_run = cpu_stop_should_run,
522 .thread_fn = cpu_stopper_thread,
523 .thread_comm = "migration/%u",
524 .create = cpu_stop_create,
525 .setup = cpu_stop_unpark,
526 .park = cpu_stop_park,
527 .pre_unpark = cpu_stop_unpark,
528 .selfparking = true,
529};
530
531static int __init cpu_stop_init(void)
532{
533 unsigned int cpu;
534
535 for_each_possible_cpu(cpu) {
536 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
537
538 spin_lock_init(&stopper->lock);
539 INIT_LIST_HEAD(&stopper->works);
540 }
541
542 BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
543 stop_machine_initialized = true;
544 return 0;
545}
546early_initcall(cpu_stop_init);
547
548#ifdef CONFIG_STOP_MACHINE
549
550int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
551{
552 struct multi_stop_data msdata = {
553 .fn = fn,
554 .data = data,
555 .num_threads = num_online_cpus(),
556 .active_cpus = cpus,
557 };
558
559 if (!stop_machine_initialized) {
560 /*
561 * Handle the case where stop_machine() is called
562 * early in boot before stop_machine() has been
563 * initialized.
564 */
565 unsigned long flags;
566 int ret;
567
568 WARN_ON_ONCE(msdata.num_threads != 1);
569
570 local_irq_save(flags);
571 hard_irq_disable();
572 ret = (*fn)(data);
573 local_irq_restore(flags);
574
575 return ret;
576 }
577
578 /* Set the initial state and stop all online cpus. */
579 set_state(&msdata, MULTI_STOP_PREPARE);
580 return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
581}
582
583int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
584{
585 int ret;
586
587 /* No CPUs can come up or down during this. */
588 get_online_cpus();
589 ret = __stop_machine(fn, data, cpus);
590 put_online_cpus();
591 return ret;
592}
593EXPORT_SYMBOL_GPL(stop_machine);
594
595/**
596 * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
597 * @fn: the function to run
598 * @data: the data ptr for the @fn()
599 * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
600 *
601 * This is identical to stop_machine() but can be called from a CPU which
602 * is not active. The local CPU is in the process of hotplug (so no other
603 * CPU hotplug can start) and not marked active and doesn't have enough
604 * context to sleep.
605 *
606 * This function provides stop_machine() functionality for such state by
607 * using busy-wait for synchronization and executing @fn directly for local
608 * CPU.
609 *
610 * CONTEXT:
611 * Local CPU is inactive. Temporarily stops all active CPUs.
612 *
613 * RETURNS:
614 * 0 if all executions of @fn returned 0, any non zero return value if any
615 * returned non zero.
616 */
617int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
618 const struct cpumask *cpus)
619{
620 struct multi_stop_data msdata = { .fn = fn, .data = data,
621 .active_cpus = cpus };
622 struct cpu_stop_done done;
623 int ret;
624
625 /* Local CPU must be inactive and CPU hotplug in progress. */
626 BUG_ON(cpu_active(raw_smp_processor_id()));
627 msdata.num_threads = num_active_cpus() + 1; /* +1 for local */
628
629 /* No proper task established and can't sleep - busy wait for lock. */
630 while (!mutex_trylock(&stop_cpus_mutex))
631 cpu_relax();
632
633 /* Schedule work on other CPUs and execute directly for local CPU */
634 set_state(&msdata, MULTI_STOP_PREPARE);
635 cpu_stop_init_done(&done, num_active_cpus());
636 queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
637 &done);
638 ret = multi_cpu_stop(&msdata);
639
640 /* Busy wait for completion. */
641 while (!completion_done(&done.completion))
642 cpu_relax();
643
644 mutex_unlock(&stop_cpus_mutex);
645 return ret ?: done.ret;
646}
647
648#endif /* CONFIG_STOP_MACHINE */