2 * kernel/stop_machine.c
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>
9 * This file is released under the GPLv2 and any later version.
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/nmi.h>
26 * Structure to determine completion condition and record errors. May
27 * be shared by works on different cpus.
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 */
35 /* the actual stopper, one per every possible cpu, enabled on online cpus */
37 struct task_struct *thread;
40 bool enabled; /* is this stopper enabled? */
41 struct list_head works; /* list of pending works */
43 struct cpu_stop_work stop_work; /* for stop_cpus */
46 static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
47 static bool stop_machine_initialized = false;
49 /* static data for stop_cpus */
50 static DEFINE_MUTEX(stop_cpus_mutex);
51 static bool stop_cpus_in_progress;
53 static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
55 memset(done, 0, sizeof(*done));
56 atomic_set(&done->nr_todo, nr_todo);
57 init_completion(&done->completion);
60 /* signal completion unless @done is NULL */
61 static void cpu_stop_signal_done(struct cpu_stop_done *done)
63 if (atomic_dec_and_test(&done->nr_todo))
64 complete(&done->completion);
67 static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
68 struct cpu_stop_work *work)
70 list_add_tail(&work->list, &stopper->works);
71 wake_up_process(stopper->thread);
74 /* queue @work to @stopper. if offline, @work is completed immediately */
75 static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
77 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
81 spin_lock_irqsave(&stopper->lock, flags);
82 enabled = stopper->enabled;
84 __cpu_stop_queue_work(stopper, work);
86 cpu_stop_signal_done(work->done);
87 spin_unlock_irqrestore(&stopper->lock, flags);
93 * stop_one_cpu - stop a cpu
95 * @fn: function to execute
96 * @arg: argument to @fn
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
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.
113 * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
114 * otherwise, the return value of @fn.
116 int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
118 struct cpu_stop_done done;
119 struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
121 cpu_stop_init_done(&done, 1);
122 if (!cpu_stop_queue_work(cpu, &work))
125 * In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup
126 * cycle by doing a preemption:
129 wait_for_completion(&done.completion);
133 /* This controls the threads on each CPU. */
134 enum multi_stop_state {
135 /* Dummy starting state for thread. */
137 /* Awaiting everyone to be scheduled. */
139 /* Disable interrupts. */
140 MULTI_STOP_DISABLE_IRQ,
141 /* Run the function */
147 struct multi_stop_data {
150 /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
151 unsigned int num_threads;
152 const struct cpumask *active_cpus;
154 enum multi_stop_state state;
158 static void set_state(struct multi_stop_data *msdata,
159 enum multi_stop_state newstate)
161 /* Reset ack counter. */
162 atomic_set(&msdata->thread_ack, msdata->num_threads);
164 msdata->state = newstate;
167 /* Last one to ack a state moves to the next state. */
168 static void ack_state(struct multi_stop_data *msdata)
170 if (atomic_dec_and_test(&msdata->thread_ack))
171 set_state(msdata, msdata->state + 1);
174 /* This is the cpu_stop function which stops the CPU. */
175 static int multi_cpu_stop(void *data)
177 struct multi_stop_data *msdata = data;
178 enum multi_stop_state curstate = MULTI_STOP_NONE;
179 int cpu = smp_processor_id(), err = 0;
184 * When called from stop_machine_from_inactive_cpu(), irq might
185 * already be disabled. Save the state and restore it on exit.
187 local_save_flags(flags);
189 if (!msdata->active_cpus)
190 is_active = cpu == cpumask_first(cpu_online_mask);
192 is_active = cpumask_test_cpu(cpu, msdata->active_cpus);
194 /* Simple state machine */
196 /* Chill out and ensure we re-read multi_stop_state. */
198 if (msdata->state != curstate) {
199 curstate = msdata->state;
201 case MULTI_STOP_DISABLE_IRQ:
207 err = msdata->fn(msdata->data);
213 } else if (curstate > MULTI_STOP_PREPARE) {
215 * At this stage all other CPUs we depend on must spin
216 * in the same loop. Any reason for hard-lockup should
217 * be detected and reported on their side.
219 touch_nmi_watchdog();
221 } while (curstate != MULTI_STOP_EXIT);
223 local_irq_restore(flags);
227 static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
228 int cpu2, struct cpu_stop_work *work2)
230 struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
231 struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
234 spin_lock_irq(&stopper1->lock);
235 spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
238 if (!stopper1->enabled || !stopper2->enabled)
241 * Ensure that if we race with __stop_cpus() the stoppers won't get
242 * queued up in reverse order leading to system deadlock.
244 * We can't miss stop_cpus_in_progress if queue_stop_cpus_work() has
245 * queued a work on cpu1 but not on cpu2, we hold both locks.
247 * It can be falsely true but it is safe to spin until it is cleared,
248 * queue_stop_cpus_work() does everything under preempt_disable().
251 if (unlikely(stop_cpus_in_progress))
255 __cpu_stop_queue_work(stopper1, work1);
256 __cpu_stop_queue_work(stopper2, work2);
258 spin_unlock(&stopper2->lock);
259 spin_unlock_irq(&stopper1->lock);
261 if (unlikely(err == -EDEADLK)) {
262 while (stop_cpus_in_progress)
269 * stop_two_cpus - stops two cpus
270 * @cpu1: the cpu to stop
271 * @cpu2: the other cpu to stop
272 * @fn: function to execute
273 * @arg: argument to @fn
275 * Stops both the current and specified CPU and runs @fn on one of them.
277 * returns when both are completed.
279 int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
281 struct cpu_stop_done done;
282 struct cpu_stop_work work1, work2;
283 struct multi_stop_data msdata;
285 msdata = (struct multi_stop_data){
289 .active_cpus = cpumask_of(cpu1),
292 work1 = work2 = (struct cpu_stop_work){
293 .fn = multi_cpu_stop,
298 cpu_stop_init_done(&done, 2);
299 set_state(&msdata, MULTI_STOP_PREPARE);
303 if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
306 wait_for_completion(&done.completion);
311 * stop_one_cpu_nowait - stop a cpu but don't wait for completion
313 * @fn: function to execute
314 * @arg: argument to @fn
315 * @work_buf: pointer to cpu_stop_work structure
317 * Similar to stop_one_cpu() but doesn't wait for completion. The
318 * caller is responsible for ensuring @work_buf is currently unused
319 * and will remain untouched until stopper starts executing @fn.
325 * true if cpu_stop_work was queued successfully and @fn will be called,
328 bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
329 struct cpu_stop_work *work_buf)
331 *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
332 return cpu_stop_queue_work(cpu, work_buf);
335 static bool queue_stop_cpus_work(const struct cpumask *cpumask,
336 cpu_stop_fn_t fn, void *arg,
337 struct cpu_stop_done *done)
339 struct cpu_stop_work *work;
344 * Disable preemption while queueing to avoid getting
345 * preempted by a stopper which might wait for other stoppers
346 * to enter @fn which can lead to deadlock.
349 stop_cpus_in_progress = true;
350 for_each_cpu(cpu, cpumask) {
351 work = &per_cpu(cpu_stopper.stop_work, cpu);
355 if (cpu_stop_queue_work(cpu, work))
358 stop_cpus_in_progress = false;
364 static int __stop_cpus(const struct cpumask *cpumask,
365 cpu_stop_fn_t fn, void *arg)
367 struct cpu_stop_done done;
369 cpu_stop_init_done(&done, cpumask_weight(cpumask));
370 if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
372 wait_for_completion(&done.completion);
377 * stop_cpus - stop multiple cpus
378 * @cpumask: cpus to stop
379 * @fn: function to execute
380 * @arg: argument to @fn
382 * Execute @fn(@arg) on online cpus in @cpumask. On each target cpu,
383 * @fn is run in a process context with the highest priority
384 * preempting any task on the cpu and monopolizing it. This function
385 * returns after all executions are complete.
387 * This function doesn't guarantee the cpus in @cpumask stay online
388 * till @fn completes. If some cpus go down in the middle, execution
389 * on the cpu may happen partially or fully on different cpus. @fn
390 * should either be ready for that or the caller should ensure that
391 * the cpus stay online until this function completes.
393 * All stop_cpus() calls are serialized making it safe for @fn to wait
394 * for all cpus to start executing it.
400 * -ENOENT if @fn(@arg) was not executed at all because all cpus in
401 * @cpumask were offline; otherwise, 0 if all executions of @fn
402 * returned 0, any non zero return value if any returned non zero.
404 int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
408 /* static works are used, process one request at a time */
409 mutex_lock(&stop_cpus_mutex);
410 ret = __stop_cpus(cpumask, fn, arg);
411 mutex_unlock(&stop_cpus_mutex);
416 * try_stop_cpus - try to stop multiple cpus
417 * @cpumask: cpus to stop
418 * @fn: function to execute
419 * @arg: argument to @fn
421 * Identical to stop_cpus() except that it fails with -EAGAIN if
422 * someone else is already using the facility.
428 * -EAGAIN if someone else is already stopping cpus, -ENOENT if
429 * @fn(@arg) was not executed at all because all cpus in @cpumask were
430 * offline; otherwise, 0 if all executions of @fn returned 0, any non
431 * zero return value if any returned non zero.
433 int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
437 /* static works are used, process one request at a time */
438 if (!mutex_trylock(&stop_cpus_mutex))
440 ret = __stop_cpus(cpumask, fn, arg);
441 mutex_unlock(&stop_cpus_mutex);
445 static int cpu_stop_should_run(unsigned int cpu)
447 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
451 spin_lock_irqsave(&stopper->lock, flags);
452 run = !list_empty(&stopper->works);
453 spin_unlock_irqrestore(&stopper->lock, flags);
457 static void cpu_stopper_thread(unsigned int cpu)
459 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
460 struct cpu_stop_work *work;
464 spin_lock_irq(&stopper->lock);
465 if (!list_empty(&stopper->works)) {
466 work = list_first_entry(&stopper->works,
467 struct cpu_stop_work, list);
468 list_del_init(&work->list);
470 spin_unlock_irq(&stopper->lock);
473 cpu_stop_fn_t fn = work->fn;
474 void *arg = work->arg;
475 struct cpu_stop_done *done = work->done;
478 /* cpu stop callbacks must not sleep, make in_atomic() == T */
484 cpu_stop_signal_done(done);
487 WARN_ONCE(preempt_count(),
488 "cpu_stop: %pf(%p) leaked preempt count\n", fn, arg);
493 void stop_machine_park(int cpu)
495 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
497 * Lockless. cpu_stopper_thread() will take stopper->lock and flush
498 * the pending works before it parks, until then it is fine to queue
501 stopper->enabled = false;
502 kthread_park(stopper->thread);
505 extern void sched_set_stop_task(int cpu, struct task_struct *stop);
507 static void cpu_stop_create(unsigned int cpu)
509 sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
512 static void cpu_stop_park(unsigned int cpu)
514 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
516 WARN_ON(!list_empty(&stopper->works));
519 void stop_machine_unpark(int cpu)
521 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
523 stopper->enabled = true;
524 kthread_unpark(stopper->thread);
527 static struct smp_hotplug_thread cpu_stop_threads = {
528 .store = &cpu_stopper.thread,
529 .thread_should_run = cpu_stop_should_run,
530 .thread_fn = cpu_stopper_thread,
531 .thread_comm = "migration/%u",
532 .create = cpu_stop_create,
533 .park = cpu_stop_park,
537 static int __init cpu_stop_init(void)
541 for_each_possible_cpu(cpu) {
542 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
544 spin_lock_init(&stopper->lock);
545 INIT_LIST_HEAD(&stopper->works);
548 BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
549 stop_machine_unpark(raw_smp_processor_id());
550 stop_machine_initialized = true;
553 early_initcall(cpu_stop_init);
555 int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data,
556 const struct cpumask *cpus)
558 struct multi_stop_data msdata = {
561 .num_threads = num_online_cpus(),
565 lockdep_assert_cpus_held();
567 if (!stop_machine_initialized) {
569 * Handle the case where stop_machine() is called
570 * early in boot before stop_machine() has been
576 WARN_ON_ONCE(msdata.num_threads != 1);
578 local_irq_save(flags);
581 local_irq_restore(flags);
586 /* Set the initial state and stop all online cpus. */
587 set_state(&msdata, MULTI_STOP_PREPARE);
588 return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
591 int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
595 /* No CPUs can come up or down during this. */
597 ret = stop_machine_cpuslocked(fn, data, cpus);
601 EXPORT_SYMBOL_GPL(stop_machine);
604 * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
605 * @fn: the function to run
606 * @data: the data ptr for the @fn()
607 * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
609 * This is identical to stop_machine() but can be called from a CPU which
610 * is not active. The local CPU is in the process of hotplug (so no other
611 * CPU hotplug can start) and not marked active and doesn't have enough
614 * This function provides stop_machine() functionality for such state by
615 * using busy-wait for synchronization and executing @fn directly for local
619 * Local CPU is inactive. Temporarily stops all active CPUs.
622 * 0 if all executions of @fn returned 0, any non zero return value if any
625 int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
626 const struct cpumask *cpus)
628 struct multi_stop_data msdata = { .fn = fn, .data = data,
629 .active_cpus = cpus };
630 struct cpu_stop_done done;
633 /* Local CPU must be inactive and CPU hotplug in progress. */
634 BUG_ON(cpu_active(raw_smp_processor_id()));
635 msdata.num_threads = num_active_cpus() + 1; /* +1 for local */
637 /* No proper task established and can't sleep - busy wait for lock. */
638 while (!mutex_trylock(&stop_cpus_mutex))
641 /* Schedule work on other CPUs and execute directly for local CPU */
642 set_state(&msdata, MULTI_STOP_PREPARE);
643 cpu_stop_init_done(&done, num_active_cpus());
644 queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
646 ret = multi_cpu_stop(&msdata);
648 /* Busy wait for completion. */
649 while (!completion_done(&done.completion))
652 mutex_unlock(&stop_cpus_mutex);
653 return ret ?: done.ret;