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[mirror_ubuntu-zesty-kernel.git] / kernel / stop_machine.c
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/lglock.h>
24
25 /*
26 * Structure to determine completion condition and record errors. May
27 * be shared by works on different cpus.
28 */
29 struct 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 */
37 struct 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
47 static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
48 static 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 */
56 DEFINE_STATIC_LGLOCK(stop_cpus_lock);
57
58 static 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 */
66 static void cpu_stop_signal_done(struct cpu_stop_done *done, bool executed)
67 {
68 if (done) {
69 if (executed)
70 done->executed = true;
71 if (atomic_dec_and_test(&done->nr_todo))
72 complete(&done->completion);
73 }
74 }
75
76 static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
77 struct cpu_stop_work *work)
78 {
79 list_add_tail(&work->list, &stopper->works);
80 wake_up_process(stopper->thread);
81 }
82
83 /* queue @work to @stopper. if offline, @work is completed immediately */
84 static void cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
85 {
86 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
87 unsigned long flags;
88
89 spin_lock_irqsave(&stopper->lock, flags);
90 if (stopper->enabled)
91 __cpu_stop_queue_work(stopper, work);
92 else
93 cpu_stop_signal_done(work->done, false);
94 spin_unlock_irqrestore(&stopper->lock, flags);
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 */
121 int 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 cpu_stop_queue_work(cpu, &work);
128 wait_for_completion(&done.completion);
129 return done.executed ? done.ret : -ENOENT;
130 }
131
132 /* This controls the threads on each CPU. */
133 enum multi_stop_state {
134 /* Dummy starting state for thread. */
135 MULTI_STOP_NONE,
136 /* Awaiting everyone to be scheduled. */
137 MULTI_STOP_PREPARE,
138 /* Disable interrupts. */
139 MULTI_STOP_DISABLE_IRQ,
140 /* Run the function */
141 MULTI_STOP_RUN,
142 /* Exit */
143 MULTI_STOP_EXIT,
144 };
145
146 struct multi_stop_data {
147 cpu_stop_fn_t fn;
148 void *data;
149 /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
150 unsigned int num_threads;
151 const struct cpumask *active_cpus;
152
153 enum multi_stop_state state;
154 atomic_t thread_ack;
155 };
156
157 static void set_state(struct multi_stop_data *msdata,
158 enum multi_stop_state newstate)
159 {
160 /* Reset ack counter. */
161 atomic_set(&msdata->thread_ack, msdata->num_threads);
162 smp_wmb();
163 msdata->state = newstate;
164 }
165
166 /* Last one to ack a state moves to the next state. */
167 static void ack_state(struct multi_stop_data *msdata)
168 {
169 if (atomic_dec_and_test(&msdata->thread_ack))
170 set_state(msdata, msdata->state + 1);
171 }
172
173 /* This is the cpu_stop function which stops the CPU. */
174 static int multi_cpu_stop(void *data)
175 {
176 struct multi_stop_data *msdata = data;
177 enum multi_stop_state curstate = MULTI_STOP_NONE;
178 int cpu = smp_processor_id(), err = 0;
179 unsigned long flags;
180 bool is_active;
181
182 /*
183 * When called from stop_machine_from_inactive_cpu(), irq might
184 * already be disabled. Save the state and restore it on exit.
185 */
186 local_save_flags(flags);
187
188 if (!msdata->active_cpus)
189 is_active = cpu == cpumask_first(cpu_online_mask);
190 else
191 is_active = cpumask_test_cpu(cpu, msdata->active_cpus);
192
193 /* Simple state machine */
194 do {
195 /* Chill out and ensure we re-read multi_stop_state. */
196 cpu_relax();
197 if (msdata->state != curstate) {
198 curstate = msdata->state;
199 switch (curstate) {
200 case MULTI_STOP_DISABLE_IRQ:
201 local_irq_disable();
202 hard_irq_disable();
203 break;
204 case MULTI_STOP_RUN:
205 if (is_active)
206 err = msdata->fn(msdata->data);
207 break;
208 default:
209 break;
210 }
211 ack_state(msdata);
212 }
213 } while (curstate != MULTI_STOP_EXIT);
214
215 local_irq_restore(flags);
216 return err;
217 }
218
219 static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
220 int cpu2, struct cpu_stop_work *work2)
221 {
222 struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
223 struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
224 int err;
225
226 lg_double_lock(&stop_cpus_lock, cpu1, cpu2);
227 spin_lock_irq(&stopper1->lock);
228 spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
229
230 err = -ENOENT;
231 if (!stopper1->enabled || !stopper2->enabled)
232 goto unlock;
233
234 err = 0;
235 __cpu_stop_queue_work(stopper1, work1);
236 __cpu_stop_queue_work(stopper2, work2);
237 unlock:
238 spin_unlock(&stopper2->lock);
239 spin_unlock_irq(&stopper1->lock);
240 lg_double_unlock(&stop_cpus_lock, cpu1, cpu2);
241
242 return err;
243 }
244 /**
245 * stop_two_cpus - stops two cpus
246 * @cpu1: the cpu to stop
247 * @cpu2: the other cpu to stop
248 * @fn: function to execute
249 * @arg: argument to @fn
250 *
251 * Stops both the current and specified CPU and runs @fn on one of them.
252 *
253 * returns when both are completed.
254 */
255 int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
256 {
257 struct cpu_stop_done done;
258 struct cpu_stop_work work1, work2;
259 struct multi_stop_data msdata;
260
261 preempt_disable();
262 msdata = (struct multi_stop_data){
263 .fn = fn,
264 .data = arg,
265 .num_threads = 2,
266 .active_cpus = cpumask_of(cpu1),
267 };
268
269 work1 = work2 = (struct cpu_stop_work){
270 .fn = multi_cpu_stop,
271 .arg = &msdata,
272 .done = &done
273 };
274
275 cpu_stop_init_done(&done, 2);
276 set_state(&msdata, MULTI_STOP_PREPARE);
277
278 if (cpu1 > cpu2)
279 swap(cpu1, cpu2);
280 if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2)) {
281 preempt_enable();
282 return -ENOENT;
283 }
284
285 preempt_enable();
286
287 wait_for_completion(&done.completion);
288
289 return done.executed ? done.ret : -ENOENT;
290 }
291
292 /**
293 * stop_one_cpu_nowait - stop a cpu but don't wait for completion
294 * @cpu: cpu to stop
295 * @fn: function to execute
296 * @arg: argument to @fn
297 * @work_buf: pointer to cpu_stop_work structure
298 *
299 * Similar to stop_one_cpu() but doesn't wait for completion. The
300 * caller is responsible for ensuring @work_buf is currently unused
301 * and will remain untouched until stopper starts executing @fn.
302 *
303 * CONTEXT:
304 * Don't care.
305 */
306 void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
307 struct cpu_stop_work *work_buf)
308 {
309 *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
310 cpu_stop_queue_work(cpu, work_buf);
311 }
312
313 /* static data for stop_cpus */
314 static DEFINE_MUTEX(stop_cpus_mutex);
315
316 static void queue_stop_cpus_work(const struct cpumask *cpumask,
317 cpu_stop_fn_t fn, void *arg,
318 struct cpu_stop_done *done)
319 {
320 struct cpu_stop_work *work;
321 unsigned int cpu;
322
323 /*
324 * Disable preemption while queueing to avoid getting
325 * preempted by a stopper which might wait for other stoppers
326 * to enter @fn which can lead to deadlock.
327 */
328 lg_global_lock(&stop_cpus_lock);
329 for_each_cpu(cpu, cpumask) {
330 work = &per_cpu(cpu_stopper.stop_work, cpu);
331 work->fn = fn;
332 work->arg = arg;
333 work->done = done;
334 cpu_stop_queue_work(cpu, work);
335 }
336 lg_global_unlock(&stop_cpus_lock);
337 }
338
339 static int __stop_cpus(const struct cpumask *cpumask,
340 cpu_stop_fn_t fn, void *arg)
341 {
342 struct cpu_stop_done done;
343
344 cpu_stop_init_done(&done, cpumask_weight(cpumask));
345 queue_stop_cpus_work(cpumask, fn, arg, &done);
346 wait_for_completion(&done.completion);
347 return done.executed ? done.ret : -ENOENT;
348 }
349
350 /**
351 * stop_cpus - stop multiple cpus
352 * @cpumask: cpus to stop
353 * @fn: function to execute
354 * @arg: argument to @fn
355 *
356 * Execute @fn(@arg) on online cpus in @cpumask. On each target cpu,
357 * @fn is run in a process context with the highest priority
358 * preempting any task on the cpu and monopolizing it. This function
359 * returns after all executions are complete.
360 *
361 * This function doesn't guarantee the cpus in @cpumask stay online
362 * till @fn completes. If some cpus go down in the middle, execution
363 * on the cpu may happen partially or fully on different cpus. @fn
364 * should either be ready for that or the caller should ensure that
365 * the cpus stay online until this function completes.
366 *
367 * All stop_cpus() calls are serialized making it safe for @fn to wait
368 * for all cpus to start executing it.
369 *
370 * CONTEXT:
371 * Might sleep.
372 *
373 * RETURNS:
374 * -ENOENT if @fn(@arg) was not executed at all because all cpus in
375 * @cpumask were offline; otherwise, 0 if all executions of @fn
376 * returned 0, any non zero return value if any returned non zero.
377 */
378 int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
379 {
380 int ret;
381
382 /* static works are used, process one request at a time */
383 mutex_lock(&stop_cpus_mutex);
384 ret = __stop_cpus(cpumask, fn, arg);
385 mutex_unlock(&stop_cpus_mutex);
386 return ret;
387 }
388
389 /**
390 * try_stop_cpus - try to stop multiple cpus
391 * @cpumask: cpus to stop
392 * @fn: function to execute
393 * @arg: argument to @fn
394 *
395 * Identical to stop_cpus() except that it fails with -EAGAIN if
396 * someone else is already using the facility.
397 *
398 * CONTEXT:
399 * Might sleep.
400 *
401 * RETURNS:
402 * -EAGAIN if someone else is already stopping cpus, -ENOENT if
403 * @fn(@arg) was not executed at all because all cpus in @cpumask were
404 * offline; otherwise, 0 if all executions of @fn returned 0, any non
405 * zero return value if any returned non zero.
406 */
407 int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
408 {
409 int ret;
410
411 /* static works are used, process one request at a time */
412 if (!mutex_trylock(&stop_cpus_mutex))
413 return -EAGAIN;
414 ret = __stop_cpus(cpumask, fn, arg);
415 mutex_unlock(&stop_cpus_mutex);
416 return ret;
417 }
418
419 static int cpu_stop_should_run(unsigned int cpu)
420 {
421 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
422 unsigned long flags;
423 int run;
424
425 spin_lock_irqsave(&stopper->lock, flags);
426 run = !list_empty(&stopper->works);
427 spin_unlock_irqrestore(&stopper->lock, flags);
428 return run;
429 }
430
431 static void cpu_stopper_thread(unsigned int cpu)
432 {
433 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
434 struct cpu_stop_work *work;
435 int ret;
436
437 repeat:
438 work = NULL;
439 spin_lock_irq(&stopper->lock);
440 if (!list_empty(&stopper->works)) {
441 work = list_first_entry(&stopper->works,
442 struct cpu_stop_work, list);
443 list_del_init(&work->list);
444 }
445 spin_unlock_irq(&stopper->lock);
446
447 if (work) {
448 cpu_stop_fn_t fn = work->fn;
449 void *arg = work->arg;
450 struct cpu_stop_done *done = work->done;
451 char ksym_buf[KSYM_NAME_LEN] __maybe_unused;
452
453 /* cpu stop callbacks are not allowed to sleep */
454 preempt_disable();
455
456 ret = fn(arg);
457 if (ret)
458 done->ret = ret;
459
460 /* restore preemption and check it's still balanced */
461 preempt_enable();
462 WARN_ONCE(preempt_count(),
463 "cpu_stop: %s(%p) leaked preempt count\n",
464 kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
465 ksym_buf), arg);
466
467 cpu_stop_signal_done(done, true);
468 goto repeat;
469 }
470 }
471
472 void stop_machine_park(int cpu)
473 {
474 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
475 /*
476 * Lockless. cpu_stopper_thread() will take stopper->lock and flush
477 * the pending works before it parks, until then it is fine to queue
478 * the new works.
479 */
480 stopper->enabled = false;
481 kthread_park(stopper->thread);
482 }
483
484 extern void sched_set_stop_task(int cpu, struct task_struct *stop);
485
486 static void cpu_stop_create(unsigned int cpu)
487 {
488 sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
489 }
490
491 static void cpu_stop_park(unsigned int cpu)
492 {
493 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
494
495 WARN_ON(!list_empty(&stopper->works));
496 }
497
498 void stop_machine_unpark(int cpu)
499 {
500 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
501
502 stopper->enabled = true;
503 kthread_unpark(stopper->thread);
504 }
505
506 static struct smp_hotplug_thread cpu_stop_threads = {
507 .store = &cpu_stopper.thread,
508 .thread_should_run = cpu_stop_should_run,
509 .thread_fn = cpu_stopper_thread,
510 .thread_comm = "migration/%u",
511 .create = cpu_stop_create,
512 .park = cpu_stop_park,
513 .selfparking = true,
514 };
515
516 static int __init cpu_stop_init(void)
517 {
518 unsigned int cpu;
519
520 for_each_possible_cpu(cpu) {
521 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
522
523 spin_lock_init(&stopper->lock);
524 INIT_LIST_HEAD(&stopper->works);
525 }
526
527 BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
528 stop_machine_unpark(raw_smp_processor_id());
529 stop_machine_initialized = true;
530 return 0;
531 }
532 early_initcall(cpu_stop_init);
533
534 #if defined(CONFIG_SMP) || defined(CONFIG_HOTPLUG_CPU)
535
536 static int __stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
537 {
538 struct multi_stop_data msdata = {
539 .fn = fn,
540 .data = data,
541 .num_threads = num_online_cpus(),
542 .active_cpus = cpus,
543 };
544
545 if (!stop_machine_initialized) {
546 /*
547 * Handle the case where stop_machine() is called
548 * early in boot before stop_machine() has been
549 * initialized.
550 */
551 unsigned long flags;
552 int ret;
553
554 WARN_ON_ONCE(msdata.num_threads != 1);
555
556 local_irq_save(flags);
557 hard_irq_disable();
558 ret = (*fn)(data);
559 local_irq_restore(flags);
560
561 return ret;
562 }
563
564 /* Set the initial state and stop all online cpus. */
565 set_state(&msdata, MULTI_STOP_PREPARE);
566 return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
567 }
568
569 int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
570 {
571 int ret;
572
573 /* No CPUs can come up or down during this. */
574 get_online_cpus();
575 ret = __stop_machine(fn, data, cpus);
576 put_online_cpus();
577 return ret;
578 }
579 EXPORT_SYMBOL_GPL(stop_machine);
580
581 /**
582 * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
583 * @fn: the function to run
584 * @data: the data ptr for the @fn()
585 * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
586 *
587 * This is identical to stop_machine() but can be called from a CPU which
588 * is not active. The local CPU is in the process of hotplug (so no other
589 * CPU hotplug can start) and not marked active and doesn't have enough
590 * context to sleep.
591 *
592 * This function provides stop_machine() functionality for such state by
593 * using busy-wait for synchronization and executing @fn directly for local
594 * CPU.
595 *
596 * CONTEXT:
597 * Local CPU is inactive. Temporarily stops all active CPUs.
598 *
599 * RETURNS:
600 * 0 if all executions of @fn returned 0, any non zero return value if any
601 * returned non zero.
602 */
603 int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
604 const struct cpumask *cpus)
605 {
606 struct multi_stop_data msdata = { .fn = fn, .data = data,
607 .active_cpus = cpus };
608 struct cpu_stop_done done;
609 int ret;
610
611 /* Local CPU must be inactive and CPU hotplug in progress. */
612 BUG_ON(cpu_active(raw_smp_processor_id()));
613 msdata.num_threads = num_active_cpus() + 1; /* +1 for local */
614
615 /* No proper task established and can't sleep - busy wait for lock. */
616 while (!mutex_trylock(&stop_cpus_mutex))
617 cpu_relax();
618
619 /* Schedule work on other CPUs and execute directly for local CPU */
620 set_state(&msdata, MULTI_STOP_PREPARE);
621 cpu_stop_init_done(&done, num_active_cpus());
622 queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
623 &done);
624 ret = multi_cpu_stop(&msdata);
625
626 /* Busy wait for completion. */
627 while (!completion_done(&done.completion))
628 cpu_relax();
629
630 mutex_unlock(&stop_cpus_mutex);
631 return ret ?: done.ret;
632 }
633
634 #endif /* CONFIG_SMP || CONFIG_HOTPLUG_CPU */