xref: /openbmc/linux/kernel/stop_machine.c (revision abfbd895)
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 */
635