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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 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 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 */
36 struct 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
46 static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
47 static bool stop_machine_initialized = false;
48
49 /*
50 * Avoids a race between stop_two_cpus and global stop_cpus, where
51 * the stoppers could get queued up in reverse order, leading to
52 * system deadlock. Using an lglock means stop_two_cpus remains
53 * relatively cheap.
54 */
55 DEFINE_STATIC_LGLOCK(stop_cpus_lock);
56
57 static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
58 {
59 memset(done, 0, sizeof(*done));
60 atomic_set(&done->nr_todo, nr_todo);
61 init_completion(&done->completion);
62 }
63
64 /* signal completion unless @done is NULL */
65 static void cpu_stop_signal_done(struct cpu_stop_done *done)
66 {
67 if (atomic_dec_and_test(&done->nr_todo))
68 complete(&done->completion);
69 }
70
71 static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
72 struct cpu_stop_work *work)
73 {
74 list_add_tail(&work->list, &stopper->works);
75 wake_up_process(stopper->thread);
76 }
77
78 /* queue @work to @stopper. if offline, @work is completed immediately */
79 static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
80 {
81 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
82 unsigned long flags;
83 bool enabled;
84
85 spin_lock_irqsave(&stopper->lock, flags);
86 enabled = stopper->enabled;
87 if (enabled)
88 __cpu_stop_queue_work(stopper, work);
89 else if (work->done)
90 cpu_stop_signal_done(work->done);
91 spin_unlock_irqrestore(&stopper->lock, flags);
92
93 return enabled;
94 }
95
96 /**
97 * stop_one_cpu - stop a cpu
98 * @cpu: cpu to stop
99 * @fn: function to execute
100 * @arg: argument to @fn
101 *
102 * Execute @fn(@arg) on @cpu. @fn is run in a process context with
103 * the highest priority preempting any task on the cpu and
104 * monopolizing it. This function returns after the execution is
105 * complete.
106 *
107 * This function doesn't guarantee @cpu stays online till @fn
108 * completes. If @cpu goes down in the middle, execution may happen
109 * partially or fully on different cpus. @fn should either be ready
110 * for that or the caller should ensure that @cpu stays online until
111 * this function completes.
112 *
113 * CONTEXT:
114 * Might sleep.
115 *
116 * RETURNS:
117 * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
118 * otherwise, the return value of @fn.
119 */
120 int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
121 {
122 struct cpu_stop_done done;
123 struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
124
125 cpu_stop_init_done(&done, 1);
126 if (!cpu_stop_queue_work(cpu, &work))
127 return -ENOENT;
128 wait_for_completion(&done.completion);
129 return done.ret;
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 msdata = (struct multi_stop_data){
262 .fn = fn,
263 .data = arg,
264 .num_threads = 2,
265 .active_cpus = cpumask_of(cpu1),
266 };
267
268 work1 = work2 = (struct cpu_stop_work){
269 .fn = multi_cpu_stop,
270 .arg = &msdata,
271 .done = &done
272 };
273
274 cpu_stop_init_done(&done, 2);
275 set_state(&msdata, MULTI_STOP_PREPARE);
276
277 if (cpu1 > cpu2)
278 swap(cpu1, cpu2);
279 if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
280 return -ENOENT;
281
282 wait_for_completion(&done.completion);
283 return done.ret;
284 }
285
286 /**
287 * stop_one_cpu_nowait - stop a cpu but don't wait for completion
288 * @cpu: cpu to stop
289 * @fn: function to execute
290 * @arg: argument to @fn
291 * @work_buf: pointer to cpu_stop_work structure
292 *
293 * Similar to stop_one_cpu() but doesn't wait for completion. The
294 * caller is responsible for ensuring @work_buf is currently unused
295 * and will remain untouched until stopper starts executing @fn.
296 *
297 * CONTEXT:
298 * Don't care.
299 *
300 * RETURNS:
301 * true if cpu_stop_work was queued successfully and @fn will be called,
302 * false otherwise.
303 */
304 bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
305 struct cpu_stop_work *work_buf)
306 {
307 *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
308 return cpu_stop_queue_work(cpu, work_buf);
309 }
310
311 /* static data for stop_cpus */
312 static DEFINE_MUTEX(stop_cpus_mutex);
313
314 static bool queue_stop_cpus_work(const struct cpumask *cpumask,
315 cpu_stop_fn_t fn, void *arg,
316 struct cpu_stop_done *done)
317 {
318 struct cpu_stop_work *work;
319 unsigned int cpu;
320 bool queued = false;
321
322 /*
323 * Disable preemption while queueing to avoid getting
324 * preempted by a stopper which might wait for other stoppers
325 * to enter @fn which can lead to deadlock.
326 */
327 lg_global_lock(&stop_cpus_lock);
328 for_each_cpu(cpu, cpumask) {
329 work = &per_cpu(cpu_stopper.stop_work, cpu);
330 work->fn = fn;
331 work->arg = arg;
332 work->done = done;
333 if (cpu_stop_queue_work(cpu, work))
334 queued = true;
335 }
336 lg_global_unlock(&stop_cpus_lock);
337
338 return queued;
339 }
340
341 static int __stop_cpus(const struct cpumask *cpumask,
342 cpu_stop_fn_t fn, void *arg)
343 {
344 struct cpu_stop_done done;
345
346 cpu_stop_init_done(&done, cpumask_weight(cpumask));
347 if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
348 return -ENOENT;
349 wait_for_completion(&done.completion);
350 return done.ret;
351 }
352
353 /**
354 * stop_cpus - stop multiple cpus
355 * @cpumask: cpus to stop
356 * @fn: function to execute
357 * @arg: argument to @fn
358 *
359 * Execute @fn(@arg) on online cpus in @cpumask. On each target cpu,
360 * @fn is run in a process context with the highest priority
361 * preempting any task on the cpu and monopolizing it. This function
362 * returns after all executions are complete.
363 *
364 * This function doesn't guarantee the cpus in @cpumask stay online
365 * till @fn completes. If some cpus go down in the middle, execution
366 * on the cpu may happen partially or fully on different cpus. @fn
367 * should either be ready for that or the caller should ensure that
368 * the cpus stay online until this function completes.
369 *
370 * All stop_cpus() calls are serialized making it safe for @fn to wait
371 * for all cpus to start executing it.
372 *
373 * CONTEXT:
374 * Might sleep.
375 *
376 * RETURNS:
377 * -ENOENT if @fn(@arg) was not executed at all because all cpus in
378 * @cpumask were offline; otherwise, 0 if all executions of @fn
379 * returned 0, any non zero return value if any returned non zero.
380 */
381 int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
382 {
383 int ret;
384
385 /* static works are used, process one request at a time */
386 mutex_lock(&stop_cpus_mutex);
387 ret = __stop_cpus(cpumask, fn, arg);
388 mutex_unlock(&stop_cpus_mutex);
389 return ret;
390 }
391
392 /**
393 * try_stop_cpus - try to stop multiple cpus
394 * @cpumask: cpus to stop
395 * @fn: function to execute
396 * @arg: argument to @fn
397 *
398 * Identical to stop_cpus() except that it fails with -EAGAIN if
399 * someone else is already using the facility.
400 *
401 * CONTEXT:
402 * Might sleep.
403 *
404 * RETURNS:
405 * -EAGAIN if someone else is already stopping cpus, -ENOENT if
406 * @fn(@arg) was not executed at all because all cpus in @cpumask were
407 * offline; otherwise, 0 if all executions of @fn returned 0, any non
408 * zero return value if any returned non zero.
409 */
410 int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
411 {
412 int ret;
413
414 /* static works are used, process one request at a time */
415 if (!mutex_trylock(&stop_cpus_mutex))
416 return -EAGAIN;
417 ret = __stop_cpus(cpumask, fn, arg);
418 mutex_unlock(&stop_cpus_mutex);
419 return ret;
420 }
421
422 static int cpu_stop_should_run(unsigned int cpu)
423 {
424 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
425 unsigned long flags;
426 int run;
427
428 spin_lock_irqsave(&stopper->lock, flags);
429 run = !list_empty(&stopper->works);
430 spin_unlock_irqrestore(&stopper->lock, flags);
431 return run;
432 }
433
434 static void cpu_stopper_thread(unsigned int cpu)
435 {
436 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
437 struct cpu_stop_work *work;
438
439 repeat:
440 work = NULL;
441 spin_lock_irq(&stopper->lock);
442 if (!list_empty(&stopper->works)) {
443 work = list_first_entry(&stopper->works,
444 struct cpu_stop_work, list);
445 list_del_init(&work->list);
446 }
447 spin_unlock_irq(&stopper->lock);
448
449 if (work) {
450 cpu_stop_fn_t fn = work->fn;
451 void *arg = work->arg;
452 struct cpu_stop_done *done = work->done;
453 int ret;
454
455 /* cpu stop callbacks must not sleep, make in_atomic() == T */
456 preempt_count_inc();
457 ret = fn(arg);
458 if (done) {
459 if (ret)
460 done->ret = ret;
461 cpu_stop_signal_done(done);
462 }
463 preempt_count_dec();
464 WARN_ONCE(preempt_count(),
465 "cpu_stop: %pf(%p) leaked preempt count\n", fn, arg);
466 goto repeat;
467 }
468 }
469
470 void stop_machine_park(int cpu)
471 {
472 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
473 /*
474 * Lockless. cpu_stopper_thread() will take stopper->lock and flush
475 * the pending works before it parks, until then it is fine to queue
476 * the new works.
477 */
478 stopper->enabled = false;
479 kthread_park(stopper->thread);
480 }
481
482 extern void sched_set_stop_task(int cpu, struct task_struct *stop);
483
484 static void cpu_stop_create(unsigned int cpu)
485 {
486 sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
487 }
488
489 static void cpu_stop_park(unsigned int cpu)
490 {
491 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
492
493 WARN_ON(!list_empty(&stopper->works));
494 }
495
496 void stop_machine_unpark(int cpu)
497 {
498 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
499
500 stopper->enabled = true;
501 kthread_unpark(stopper->thread);
502 }
503
504 static struct smp_hotplug_thread cpu_stop_threads = {
505 .store = &cpu_stopper.thread,
506 .thread_should_run = cpu_stop_should_run,
507 .thread_fn = cpu_stopper_thread,
508 .thread_comm = "migration/%u",
509 .create = cpu_stop_create,
510 .park = cpu_stop_park,
511 .selfparking = true,
512 };
513
514 static int __init cpu_stop_init(void)
515 {
516 unsigned int cpu;
517
518 for_each_possible_cpu(cpu) {
519 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
520
521 spin_lock_init(&stopper->lock);
522 INIT_LIST_HEAD(&stopper->works);
523 }
524
525 BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
526 stop_machine_unpark(raw_smp_processor_id());
527 stop_machine_initialized = true;
528 return 0;
529 }
530 early_initcall(cpu_stop_init);
531
532 #if defined(CONFIG_SMP) || defined(CONFIG_HOTPLUG_CPU)
533
534 static int __stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
535 {
536 struct multi_stop_data msdata = {
537 .fn = fn,
538 .data = data,
539 .num_threads = num_online_cpus(),
540 .active_cpus = cpus,
541 };
542
543 if (!stop_machine_initialized) {
544 /*
545 * Handle the case where stop_machine() is called
546 * early in boot before stop_machine() has been
547 * initialized.
548 */
549 unsigned long flags;
550 int ret;
551
552 WARN_ON_ONCE(msdata.num_threads != 1);
553
554 local_irq_save(flags);
555 hard_irq_disable();
556 ret = (*fn)(data);
557 local_irq_restore(flags);
558
559 return ret;
560 }
561
562 /* Set the initial state and stop all online cpus. */
563 set_state(&msdata, MULTI_STOP_PREPARE);
564 return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
565 }
566
567 int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
568 {
569 int ret;
570
571 /* No CPUs can come up or down during this. */
572 get_online_cpus();
573 ret = __stop_machine(fn, data, cpus);
574 put_online_cpus();
575 return ret;
576 }
577 EXPORT_SYMBOL_GPL(stop_machine);
578
579 /**
580 * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
581 * @fn: the function to run
582 * @data: the data ptr for the @fn()
583 * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
584 *
585 * This is identical to stop_machine() but can be called from a CPU which
586 * is not active. The local CPU is in the process of hotplug (so no other
587 * CPU hotplug can start) and not marked active and doesn't have enough
588 * context to sleep.
589 *
590 * This function provides stop_machine() functionality for such state by
591 * using busy-wait for synchronization and executing @fn directly for local
592 * CPU.
593 *
594 * CONTEXT:
595 * Local CPU is inactive. Temporarily stops all active CPUs.
596 *
597 * RETURNS:
598 * 0 if all executions of @fn returned 0, any non zero return value if any
599 * returned non zero.
600 */
601 int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
602 const struct cpumask *cpus)
603 {
604 struct multi_stop_data msdata = { .fn = fn, .data = data,
605 .active_cpus = cpus };
606 struct cpu_stop_done done;
607 int ret;
608
609 /* Local CPU must be inactive and CPU hotplug in progress. */
610 BUG_ON(cpu_active(raw_smp_processor_id()));
611 msdata.num_threads = num_active_cpus() + 1; /* +1 for local */
612
613 /* No proper task established and can't sleep - busy wait for lock. */
614 while (!mutex_trylock(&stop_cpus_mutex))
615 cpu_relax();
616
617 /* Schedule work on other CPUs and execute directly for local CPU */
618 set_state(&msdata, MULTI_STOP_PREPARE);
619 cpu_stop_init_done(&done, num_active_cpus());
620 queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
621 &done);
622 ret = multi_cpu_stop(&msdata);
623
624 /* Busy wait for completion. */
625 while (!completion_done(&done.completion))
626 cpu_relax();
627
628 mutex_unlock(&stop_cpus_mutex);
629 return ret ?: done.ret;
630 }
631
632 #endif /* CONFIG_SMP || CONFIG_HOTPLUG_CPU */