summaryrefslogtreecommitdiff
path: root/kernel/stop_machine.c
blob: ef51d1fcf5e6ddc818b5c85993801508e5ae9684 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
/*
 * kernel/stop_machine.c
 *
 * Copyright (C) 2008, 2005	IBM Corporation.
 * Copyright (C) 2008, 2005	Rusty Russell rusty@rustcorp.com.au
 * Copyright (C) 2010		SUSE Linux Products GmbH
 * Copyright (C) 2010		Tejun Heo <tj@kernel.org>
 *
 * This file is released under the GPLv2 and any later version.
 */
#include <linux/completion.h>
#include <linux/cpu.h>
#include <linux/init.h>
#include <linux/kthread.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/stop_machine.h>
#include <linux/interrupt.h>
#include <linux/kallsyms.h>

#include <asm/atomic.h>

/*
 * Structure to determine completion condition and record errors.  May
 * be shared by works on different cpus.
 */
struct cpu_stop_done {
	atomic_t		nr_todo;	/* nr left to execute */
	bool			executed;	/* actually executed? */
	int			ret;		/* collected return value */
	struct completion	completion;	/* fired if nr_todo reaches 0 */
};

/* the actual stopper, one per every possible cpu, enabled on online cpus */
struct cpu_stopper {
	spinlock_t		lock;
	struct list_head	works;		/* list of pending works */
	struct task_struct	*thread;	/* stopper thread */
	bool			enabled;	/* is this stopper enabled? */
};

static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);

static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
{
	memset(done, 0, sizeof(*done));
	atomic_set(&done->nr_todo, nr_todo);
	init_completion(&done->completion);
}

/* signal completion unless @done is NULL */
static void cpu_stop_signal_done(struct cpu_stop_done *done, bool executed)
{
	if (done) {
		if (executed)
			done->executed = true;
		if (atomic_dec_and_test(&done->nr_todo))
			complete(&done->completion);
	}
}

/* queue @work to @stopper.  if offline, @work is completed immediately */
static void cpu_stop_queue_work(struct cpu_stopper *stopper,
				struct cpu_stop_work *work)
{
	unsigned long flags;

	spin_lock_irqsave(&stopper->lock, flags);

	if (stopper->enabled) {
		list_add_tail(&work->list, &stopper->works);
		wake_up_process(stopper->thread);
	} else
		cpu_stop_signal_done(work->done, false);

	spin_unlock_irqrestore(&stopper->lock, flags);
}

/**
 * stop_one_cpu - stop a cpu
 * @cpu: cpu to stop
 * @fn: function to execute
 * @arg: argument to @fn
 *
 * Execute @fn(@arg) on @cpu.  @fn is run in a process context with
 * the highest priority preempting any task on the cpu and
 * monopolizing it.  This function returns after the execution is
 * complete.
 *
 * This function doesn't guarantee @cpu stays online till @fn
 * completes.  If @cpu goes down in the middle, execution may happen
 * partially or fully on different cpus.  @fn should either be ready
 * for that or the caller should ensure that @cpu stays online until
 * this function completes.
 *
 * CONTEXT:
 * Might sleep.
 *
 * RETURNS:
 * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
 * otherwise, the return value of @fn.
 */
int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
{
	struct cpu_stop_done done;
	struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };

	cpu_stop_init_done(&done, 1);
	cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), &work);
	wait_for_completion(&done.completion);
	return done.executed ? done.ret : -ENOENT;
}

/**
 * stop_one_cpu_nowait - stop a cpu but don't wait for completion
 * @cpu: cpu to stop
 * @fn: function to execute
 * @arg: argument to @fn
 *
 * Similar to stop_one_cpu() but doesn't wait for completion.  The
 * caller is responsible for ensuring @work_buf is currently unused
 * and will remain untouched until stopper starts executing @fn.
 *
 * CONTEXT:
 * Don't care.
 */
void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
			struct cpu_stop_work *work_buf)
{
	*work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
	cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), work_buf);
}

/* static data for stop_cpus */
static DEFINE_MUTEX(stop_cpus_mutex);
static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work);

int __stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
{
	struct cpu_stop_work *work;
	struct cpu_stop_done done;
	unsigned int cpu;

	/* initialize works and done */
	for_each_cpu(cpu, cpumask) {
		work = &per_cpu(stop_cpus_work, cpu);
		work->fn = fn;
		work->arg = arg;
		work->done = &done;
	}
	cpu_stop_init_done(&done, cpumask_weight(cpumask));

	/*
	 * Disable preemption while queueing to avoid getting
	 * preempted by a stopper which might wait for other stoppers
	 * to enter @fn which can lead to deadlock.
	 */
	preempt_disable();
	for_each_cpu(cpu, cpumask)
		cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu),
				    &per_cpu(stop_cpus_work, cpu));
	preempt_enable();

	wait_for_completion(&done.completion);
	return done.executed ? done.ret : -ENOENT;
}

/**
 * stop_cpus - stop multiple cpus
 * @cpumask: cpus to stop
 * @fn: function to execute
 * @arg: argument to @fn
 *
 * Execute @fn(@arg) on online cpus in @cpumask.  On each target cpu,
 * @fn is run in a process context with the highest priority
 * preempting any task on the cpu and monopolizing it.  This function
 * returns after all executions are complete.
 *
 * This function doesn't guarantee the cpus in @cpumask stay online
 * till @fn completes.  If some cpus go down in the middle, execution
 * on the cpu may happen partially or fully on different cpus.  @fn
 * should either be ready for that or the caller should ensure that
 * the cpus stay online until this function completes.
 *
 * All stop_cpus() calls are serialized making it safe for @fn to wait
 * for all cpus to start executing it.
 *
 * CONTEXT:
 * Might sleep.
 *
 * RETURNS:
 * -ENOENT if @fn(@arg) was not executed at all because all cpus in
 * @cpumask were offline; otherwise, 0 if all executions of @fn
 * returned 0, any non zero return value if any returned non zero.
 */
int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
{
	int ret;

	/* static works are used, process one request at a time */
	mutex_lock(&stop_cpus_mutex);
	ret = __stop_cpus(cpumask, fn, arg);
	mutex_unlock(&stop_cpus_mutex);
	return ret;
}

/**
 * try_stop_cpus - try to stop multiple cpus
 * @cpumask: cpus to stop
 * @fn: function to execute
 * @arg: argument to @fn
 *
 * Identical to stop_cpus() except that it fails with -EAGAIN if
 * someone else is already using the facility.
 *
 * CONTEXT:
 * Might sleep.
 *
 * RETURNS:
 * -EAGAIN if someone else is already stopping cpus, -ENOENT if
 * @fn(@arg) was not executed at all because all cpus in @cpumask were
 * offline; otherwise, 0 if all executions of @fn returned 0, any non
 * zero return value if any returned non zero.
 */
int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
{
	int ret;

	/* static works are used, process one request at a time */
	if (!mutex_trylock(&stop_cpus_mutex))
		return -EAGAIN;
	ret = __stop_cpus(cpumask, fn, arg);
	mutex_unlock(&stop_cpus_mutex);
	return ret;
}

static int cpu_stopper_thread(void *data)
{
	struct cpu_stopper *stopper = data;
	struct cpu_stop_work *work;
	int ret;

repeat:
	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */

	if (kthread_should_stop()) {
		__set_current_state(TASK_RUNNING);
		return 0;
	}

	work = NULL;
	spin_lock_irq(&stopper->lock);
	if (!list_empty(&stopper->works)) {
		work = list_first_entry(&stopper->works,
					struct cpu_stop_work, list);
		list_del_init(&work->list);
	}
	spin_unlock_irq(&stopper->lock);

	if (work) {
		cpu_stop_fn_t fn = work->fn;
		void *arg = work->arg;
		struct cpu_stop_done *done = work->done;
		char ksym_buf[KSYM_NAME_LEN];

		__set_current_state(TASK_RUNNING);

		/* cpu stop callbacks are not allowed to sleep */
		preempt_disable();

		ret = fn(arg);
		if (ret)
			done->ret = ret;

		/* restore preemption and check it's still balanced */
		preempt_enable();
		WARN_ONCE(preempt_count(),
			  "cpu_stop: %s(%p) leaked preempt count\n",
			  kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
					  ksym_buf), arg);

		cpu_stop_signal_done(done, true);
	} else
		schedule();

	goto repeat;
}

/* manage stopper for a cpu, mostly lifted from sched migration thread mgmt */
static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
					   unsigned long action, void *hcpu)
{
	struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
	unsigned int cpu = (unsigned long)hcpu;
	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
	struct cpu_stop_work *work;
	struct task_struct *p;

	switch (action & ~CPU_TASKS_FROZEN) {
	case CPU_UP_PREPARE:
		BUG_ON(stopper->thread || stopper->enabled ||
		       !list_empty(&stopper->works));
		p = kthread_create(cpu_stopper_thread, stopper, "migration/%d",
				   cpu);
		if (IS_ERR(p))
			return NOTIFY_BAD;
		sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
		get_task_struct(p);
		stopper->thread = p;
		break;

	case CPU_ONLINE:
		kthread_bind(stopper->thread, cpu);
		/* strictly unnecessary, as first user will wake it */
		wake_up_process(stopper->thread);
		/* mark enabled */
		spin_lock_irq(&stopper->lock);
		stopper->enabled = true;
		spin_unlock_irq(&stopper->lock);
		break;

#ifdef CONFIG_HOTPLUG_CPU
	case CPU_UP_CANCELED:
	case CPU_DEAD:
		/* kill the stopper */
		kthread_stop(stopper->thread);
		/* drain remaining works */
		spin_lock_irq(&stopper->lock);
		list_for_each_entry(work, &stopper->works, list)
			cpu_stop_signal_done(work->done, false);
		stopper->enabled = false;
		spin_unlock_irq(&stopper->lock);
		/* release the stopper */
		put_task_struct(stopper->thread);
		stopper->thread = NULL;
		break;
#endif
	}

	return NOTIFY_OK;
}

/*
 * Give it a higher priority so that cpu stopper is available to other
 * cpu notifiers.  It currently shares the same priority as sched
 * migration_notifier.
 */
static struct notifier_block __cpuinitdata cpu_stop_cpu_notifier = {
	.notifier_call	= cpu_stop_cpu_callback,
	.priority	= 10,
};

static int __init cpu_stop_init(void)
{
	void *bcpu = (void *)(long)smp_processor_id();
	unsigned int cpu;
	int err;

	for_each_possible_cpu(cpu) {
		struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

		spin_lock_init(&stopper->lock);
		INIT_LIST_HEAD(&stopper->works);
	}

	/* start one for the boot cpu */
	err = cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_UP_PREPARE,
				    bcpu);
	BUG_ON(err == NOTIFY_BAD);
	cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);
	register_cpu_notifier(&cpu_stop_cpu_notifier);

	return 0;
}
early_initcall(cpu_stop_init);

#ifdef CONFIG_STOP_MACHINE

/* This controls the threads on each CPU. */
enum stopmachine_state {
	/* Dummy starting state for thread. */
	STOPMACHINE_NONE,
	/* Awaiting everyone to be scheduled. */
	STOPMACHINE_PREPARE,
	/* Disable interrupts. */
	STOPMACHINE_DISABLE_IRQ,
	/* Run the function */
	STOPMACHINE_RUN,
	/* Exit */
	STOPMACHINE_EXIT,
};

struct stop_machine_data {
	int			(*fn)(void *);
	void			*data;
	/* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
	unsigned int		num_threads;
	const struct cpumask	*active_cpus;

	enum stopmachine_state	state;
	atomic_t		thread_ack;
};

static void set_state(struct stop_machine_data *smdata,
		      enum stopmachine_state newstate)
{
	/* Reset ack counter. */
	atomic_set(&smdata->thread_ack, smdata->num_threads);
	smp_wmb();
	smdata->state = newstate;
}

/* Last one to ack a state moves to the next state. */
static void ack_state(struct stop_machine_data *smdata)
{
	if (atomic_dec_and_test(&smdata->thread_ack))
		set_state(smdata, smdata->state + 1);
}

/* This is the cpu_stop function which stops the CPU. */
static int stop_machine_cpu_stop(void *data)
{
	struct stop_machine_data *smdata = data;
	enum stopmachine_state curstate = STOPMACHINE_NONE;
	int cpu = smp_processor_id(), err = 0;
	bool is_active;

	if (!smdata->active_cpus)
		is_active = cpu == cpumask_first(cpu_online_mask);
	else
		is_active = cpumask_test_cpu(cpu, smdata->active_cpus);

	/* Simple state machine */
	do {
		/* Chill out and ensure we re-read stopmachine_state. */
		cpu_relax();
		if (smdata->state != curstate) {
			curstate = smdata->state;
			switch (curstate) {
			case STOPMACHINE_DISABLE_IRQ:
				local_irq_disable();
				hard_irq_disable();
				break;
			case STOPMACHINE_RUN:
				if (is_active)
					err = smdata->fn(smdata->data);
				break;
			default:
				break;
			}
			ack_state(smdata);
		}
	} while (curstate != STOPMACHINE_EXIT);

	local_irq_enable();
	return err;
}

int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
{
	struct stop_machine_data smdata = { .fn = fn, .data = data,
					    .num_threads = num_online_cpus(),
					    .active_cpus = cpus };

	/* Set the initial state and stop all online cpus. */
	set_state(&smdata, STOPMACHINE_PREPARE);
	return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata);
}

int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
{
	int ret;

	/* No CPUs can come up or down during this. */
	get_online_cpus();
	ret = __stop_machine(fn, data, cpus);
	put_online_cpus();
	return ret;
}
EXPORT_SYMBOL_GPL(stop_machine);

#endif	/* CONFIG_STOP_MACHINE */