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/lglock.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 bool executed
; /* actually executed? */
32 int ret
; /* collected return value */
33 struct completion completion
; /* fired if nr_todo reaches 0 */
36 /* the actual stopper, one per every possible cpu, enabled on online cpus */
38 struct task_struct
*thread
;
41 bool enabled
; /* is this stopper enabled? */
42 struct list_head works
; /* list of pending works */
44 struct cpu_stop_work stop_work
; /* for stop_cpus */
47 static DEFINE_PER_CPU(struct cpu_stopper
, cpu_stopper
);
48 static bool stop_machine_initialized
= false;
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
56 DEFINE_STATIC_LGLOCK(stop_cpus_lock
);
58 static void cpu_stop_init_done(struct cpu_stop_done
*done
, unsigned int nr_todo
)
60 memset(done
, 0, sizeof(*done
));
61 atomic_set(&done
->nr_todo
, nr_todo
);
62 init_completion(&done
->completion
);
65 /* signal completion unless @done is NULL */
66 static void cpu_stop_signal_done(struct cpu_stop_done
*done
, bool executed
)
70 done
->executed
= true;
71 if (atomic_dec_and_test(&done
->nr_todo
))
72 complete(&done
->completion
);
76 static void __cpu_stop_queue_work(struct cpu_stopper
*stopper
,
77 struct cpu_stop_work
*work
)
79 list_add_tail(&work
->list
, &stopper
->works
);
80 wake_up_process(stopper
->thread
);
83 /* queue @work to @stopper. if offline, @work is completed immediately */
84 static bool cpu_stop_queue_work(unsigned int cpu
, struct cpu_stop_work
*work
)
86 struct cpu_stopper
*stopper
= &per_cpu(cpu_stopper
, cpu
);
90 spin_lock_irqsave(&stopper
->lock
, flags
);
91 enabled
= stopper
->enabled
;
93 __cpu_stop_queue_work(stopper
, work
);
95 cpu_stop_signal_done(work
->done
, false);
96 spin_unlock_irqrestore(&stopper
->lock
, flags
);
102 * stop_one_cpu - stop a cpu
104 * @fn: function to execute
105 * @arg: argument to @fn
107 * Execute @fn(@arg) on @cpu. @fn is run in a process context with
108 * the highest priority preempting any task on the cpu and
109 * monopolizing it. This function returns after the execution is
112 * This function doesn't guarantee @cpu stays online till @fn
113 * completes. If @cpu goes down in the middle, execution may happen
114 * partially or fully on different cpus. @fn should either be ready
115 * for that or the caller should ensure that @cpu stays online until
116 * this function completes.
122 * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
123 * otherwise, the return value of @fn.
125 int stop_one_cpu(unsigned int cpu
, cpu_stop_fn_t fn
, void *arg
)
127 struct cpu_stop_done done
;
128 struct cpu_stop_work work
= { .fn
= fn
, .arg
= arg
, .done
= &done
};
130 cpu_stop_init_done(&done
, 1);
131 if (!cpu_stop_queue_work(cpu
, &work
))
133 wait_for_completion(&done
.completion
);
134 WARN_ON(!done
.executed
);
138 /* This controls the threads on each CPU. */
139 enum multi_stop_state
{
140 /* Dummy starting state for thread. */
142 /* Awaiting everyone to be scheduled. */
144 /* Disable interrupts. */
145 MULTI_STOP_DISABLE_IRQ
,
146 /* Run the function */
152 struct multi_stop_data
{
155 /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
156 unsigned int num_threads
;
157 const struct cpumask
*active_cpus
;
159 enum multi_stop_state state
;
163 static void set_state(struct multi_stop_data
*msdata
,
164 enum multi_stop_state newstate
)
166 /* Reset ack counter. */
167 atomic_set(&msdata
->thread_ack
, msdata
->num_threads
);
169 msdata
->state
= newstate
;
172 /* Last one to ack a state moves to the next state. */
173 static void ack_state(struct multi_stop_data
*msdata
)
175 if (atomic_dec_and_test(&msdata
->thread_ack
))
176 set_state(msdata
, msdata
->state
+ 1);
179 /* This is the cpu_stop function which stops the CPU. */
180 static int multi_cpu_stop(void *data
)
182 struct multi_stop_data
*msdata
= data
;
183 enum multi_stop_state curstate
= MULTI_STOP_NONE
;
184 int cpu
= smp_processor_id(), err
= 0;
189 * When called from stop_machine_from_inactive_cpu(), irq might
190 * already be disabled. Save the state and restore it on exit.
192 local_save_flags(flags
);
194 if (!msdata
->active_cpus
)
195 is_active
= cpu
== cpumask_first(cpu_online_mask
);
197 is_active
= cpumask_test_cpu(cpu
, msdata
->active_cpus
);
199 /* Simple state machine */
201 /* Chill out and ensure we re-read multi_stop_state. */
203 if (msdata
->state
!= curstate
) {
204 curstate
= msdata
->state
;
206 case MULTI_STOP_DISABLE_IRQ
:
212 err
= msdata
->fn(msdata
->data
);
219 } while (curstate
!= MULTI_STOP_EXIT
);
221 local_irq_restore(flags
);
225 static int cpu_stop_queue_two_works(int cpu1
, struct cpu_stop_work
*work1
,
226 int cpu2
, struct cpu_stop_work
*work2
)
228 struct cpu_stopper
*stopper1
= per_cpu_ptr(&cpu_stopper
, cpu1
);
229 struct cpu_stopper
*stopper2
= per_cpu_ptr(&cpu_stopper
, cpu2
);
232 lg_double_lock(&stop_cpus_lock
, cpu1
, cpu2
);
233 spin_lock_irq(&stopper1
->lock
);
234 spin_lock_nested(&stopper2
->lock
, SINGLE_DEPTH_NESTING
);
237 if (!stopper1
->enabled
|| !stopper2
->enabled
)
241 __cpu_stop_queue_work(stopper1
, work1
);
242 __cpu_stop_queue_work(stopper2
, work2
);
244 spin_unlock(&stopper2
->lock
);
245 spin_unlock_irq(&stopper1
->lock
);
246 lg_double_unlock(&stop_cpus_lock
, cpu1
, cpu2
);
251 * stop_two_cpus - stops two cpus
252 * @cpu1: the cpu to stop
253 * @cpu2: the other cpu to stop
254 * @fn: function to execute
255 * @arg: argument to @fn
257 * Stops both the current and specified CPU and runs @fn on one of them.
259 * returns when both are completed.
261 int stop_two_cpus(unsigned int cpu1
, unsigned int cpu2
, cpu_stop_fn_t fn
, void *arg
)
263 struct cpu_stop_done done
;
264 struct cpu_stop_work work1
, work2
;
265 struct multi_stop_data msdata
;
267 msdata
= (struct multi_stop_data
){
271 .active_cpus
= cpumask_of(cpu1
),
274 work1
= work2
= (struct cpu_stop_work
){
275 .fn
= multi_cpu_stop
,
280 cpu_stop_init_done(&done
, 2);
281 set_state(&msdata
, MULTI_STOP_PREPARE
);
285 if (cpu_stop_queue_two_works(cpu1
, &work1
, cpu2
, &work2
))
288 wait_for_completion(&done
.completion
);
289 WARN_ON(!done
.executed
);
294 * stop_one_cpu_nowait - stop a cpu but don't wait for completion
296 * @fn: function to execute
297 * @arg: argument to @fn
298 * @work_buf: pointer to cpu_stop_work structure
300 * Similar to stop_one_cpu() but doesn't wait for completion. The
301 * caller is responsible for ensuring @work_buf is currently unused
302 * and will remain untouched until stopper starts executing @fn.
308 * true if cpu_stop_work was queued successfully and @fn will be called,
311 bool stop_one_cpu_nowait(unsigned int cpu
, cpu_stop_fn_t fn
, void *arg
,
312 struct cpu_stop_work
*work_buf
)
314 *work_buf
= (struct cpu_stop_work
){ .fn
= fn
, .arg
= arg
, };
315 return cpu_stop_queue_work(cpu
, work_buf
);
318 /* static data for stop_cpus */
319 static DEFINE_MUTEX(stop_cpus_mutex
);
321 static void queue_stop_cpus_work(const struct cpumask
*cpumask
,
322 cpu_stop_fn_t fn
, void *arg
,
323 struct cpu_stop_done
*done
)
325 struct cpu_stop_work
*work
;
329 * Disable preemption while queueing to avoid getting
330 * preempted by a stopper which might wait for other stoppers
331 * to enter @fn which can lead to deadlock.
333 lg_global_lock(&stop_cpus_lock
);
334 for_each_cpu(cpu
, cpumask
) {
335 work
= &per_cpu(cpu_stopper
.stop_work
, cpu
);
339 cpu_stop_queue_work(cpu
, work
);
341 lg_global_unlock(&stop_cpus_lock
);
344 static int __stop_cpus(const struct cpumask
*cpumask
,
345 cpu_stop_fn_t fn
, void *arg
)
347 struct cpu_stop_done done
;
349 cpu_stop_init_done(&done
, cpumask_weight(cpumask
));
350 queue_stop_cpus_work(cpumask
, fn
, arg
, &done
);
351 wait_for_completion(&done
.completion
);
352 return done
.executed
? done
.ret
: -ENOENT
;
356 * stop_cpus - stop multiple cpus
357 * @cpumask: cpus to stop
358 * @fn: function to execute
359 * @arg: argument to @fn
361 * Execute @fn(@arg) on online cpus in @cpumask. On each target cpu,
362 * @fn is run in a process context with the highest priority
363 * preempting any task on the cpu and monopolizing it. This function
364 * returns after all executions are complete.
366 * This function doesn't guarantee the cpus in @cpumask stay online
367 * till @fn completes. If some cpus go down in the middle, execution
368 * on the cpu may happen partially or fully on different cpus. @fn
369 * should either be ready for that or the caller should ensure that
370 * the cpus stay online until this function completes.
372 * All stop_cpus() calls are serialized making it safe for @fn to wait
373 * for all cpus to start executing it.
379 * -ENOENT if @fn(@arg) was not executed at all because all cpus in
380 * @cpumask were offline; otherwise, 0 if all executions of @fn
381 * returned 0, any non zero return value if any returned non zero.
383 int stop_cpus(const struct cpumask
*cpumask
, cpu_stop_fn_t fn
, void *arg
)
387 /* static works are used, process one request at a time */
388 mutex_lock(&stop_cpus_mutex
);
389 ret
= __stop_cpus(cpumask
, fn
, arg
);
390 mutex_unlock(&stop_cpus_mutex
);
395 * try_stop_cpus - try to stop multiple cpus
396 * @cpumask: cpus to stop
397 * @fn: function to execute
398 * @arg: argument to @fn
400 * Identical to stop_cpus() except that it fails with -EAGAIN if
401 * someone else is already using the facility.
407 * -EAGAIN if someone else is already stopping cpus, -ENOENT if
408 * @fn(@arg) was not executed at all because all cpus in @cpumask were
409 * offline; otherwise, 0 if all executions of @fn returned 0, any non
410 * zero return value if any returned non zero.
412 int try_stop_cpus(const struct cpumask
*cpumask
, cpu_stop_fn_t fn
, void *arg
)
416 /* static works are used, process one request at a time */
417 if (!mutex_trylock(&stop_cpus_mutex
))
419 ret
= __stop_cpus(cpumask
, fn
, arg
);
420 mutex_unlock(&stop_cpus_mutex
);
424 static int cpu_stop_should_run(unsigned int cpu
)
426 struct cpu_stopper
*stopper
= &per_cpu(cpu_stopper
, cpu
);
430 spin_lock_irqsave(&stopper
->lock
, flags
);
431 run
= !list_empty(&stopper
->works
);
432 spin_unlock_irqrestore(&stopper
->lock
, flags
);
436 static void cpu_stopper_thread(unsigned int cpu
)
438 struct cpu_stopper
*stopper
= &per_cpu(cpu_stopper
, cpu
);
439 struct cpu_stop_work
*work
;
444 spin_lock_irq(&stopper
->lock
);
445 if (!list_empty(&stopper
->works
)) {
446 work
= list_first_entry(&stopper
->works
,
447 struct cpu_stop_work
, list
);
448 list_del_init(&work
->list
);
450 spin_unlock_irq(&stopper
->lock
);
453 cpu_stop_fn_t fn
= work
->fn
;
454 void *arg
= work
->arg
;
455 struct cpu_stop_done
*done
= work
->done
;
456 char ksym_buf
[KSYM_NAME_LEN
] __maybe_unused
;
458 /* cpu stop callbacks are not allowed to sleep */
465 /* restore preemption and check it's still balanced */
467 WARN_ONCE(preempt_count(),
468 "cpu_stop: %s(%p) leaked preempt count\n",
469 kallsyms_lookup((unsigned long)fn
, NULL
, NULL
, NULL
,
472 cpu_stop_signal_done(done
, true);
477 void stop_machine_park(int cpu
)
479 struct cpu_stopper
*stopper
= &per_cpu(cpu_stopper
, cpu
);
481 * Lockless. cpu_stopper_thread() will take stopper->lock and flush
482 * the pending works before it parks, until then it is fine to queue
485 stopper
->enabled
= false;
486 kthread_park(stopper
->thread
);
489 extern void sched_set_stop_task(int cpu
, struct task_struct
*stop
);
491 static void cpu_stop_create(unsigned int cpu
)
493 sched_set_stop_task(cpu
, per_cpu(cpu_stopper
.thread
, cpu
));
496 static void cpu_stop_park(unsigned int cpu
)
498 struct cpu_stopper
*stopper
= &per_cpu(cpu_stopper
, cpu
);
500 WARN_ON(!list_empty(&stopper
->works
));
503 void stop_machine_unpark(int cpu
)
505 struct cpu_stopper
*stopper
= &per_cpu(cpu_stopper
, cpu
);
507 stopper
->enabled
= true;
508 kthread_unpark(stopper
->thread
);
511 static struct smp_hotplug_thread cpu_stop_threads
= {
512 .store
= &cpu_stopper
.thread
,
513 .thread_should_run
= cpu_stop_should_run
,
514 .thread_fn
= cpu_stopper_thread
,
515 .thread_comm
= "migration/%u",
516 .create
= cpu_stop_create
,
517 .park
= cpu_stop_park
,
521 static int __init
cpu_stop_init(void)
525 for_each_possible_cpu(cpu
) {
526 struct cpu_stopper
*stopper
= &per_cpu(cpu_stopper
, cpu
);
528 spin_lock_init(&stopper
->lock
);
529 INIT_LIST_HEAD(&stopper
->works
);
532 BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads
));
533 stop_machine_unpark(raw_smp_processor_id());
534 stop_machine_initialized
= true;
537 early_initcall(cpu_stop_init
);
539 #ifdef CONFIG_STOP_MACHINE
541 static int __stop_machine(cpu_stop_fn_t fn
, void *data
, const struct cpumask
*cpus
)
543 struct multi_stop_data msdata
= {
546 .num_threads
= num_online_cpus(),
550 if (!stop_machine_initialized
) {
552 * Handle the case where stop_machine() is called
553 * early in boot before stop_machine() has been
559 WARN_ON_ONCE(msdata
.num_threads
!= 1);
561 local_irq_save(flags
);
564 local_irq_restore(flags
);
569 /* Set the initial state and stop all online cpus. */
570 set_state(&msdata
, MULTI_STOP_PREPARE
);
571 return stop_cpus(cpu_online_mask
, multi_cpu_stop
, &msdata
);
574 int stop_machine(cpu_stop_fn_t fn
, void *data
, const struct cpumask
*cpus
)
578 /* No CPUs can come up or down during this. */
580 ret
= __stop_machine(fn
, data
, cpus
);
584 EXPORT_SYMBOL_GPL(stop_machine
);
587 * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
588 * @fn: the function to run
589 * @data: the data ptr for the @fn()
590 * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
592 * This is identical to stop_machine() but can be called from a CPU which
593 * is not active. The local CPU is in the process of hotplug (so no other
594 * CPU hotplug can start) and not marked active and doesn't have enough
597 * This function provides stop_machine() functionality for such state by
598 * using busy-wait for synchronization and executing @fn directly for local
602 * Local CPU is inactive. Temporarily stops all active CPUs.
605 * 0 if all executions of @fn returned 0, any non zero return value if any
608 int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn
, void *data
,
609 const struct cpumask
*cpus
)
611 struct multi_stop_data msdata
= { .fn
= fn
, .data
= data
,
612 .active_cpus
= cpus
};
613 struct cpu_stop_done done
;
616 /* Local CPU must be inactive and CPU hotplug in progress. */
617 BUG_ON(cpu_active(raw_smp_processor_id()));
618 msdata
.num_threads
= num_active_cpus() + 1; /* +1 for local */
620 /* No proper task established and can't sleep - busy wait for lock. */
621 while (!mutex_trylock(&stop_cpus_mutex
))
624 /* Schedule work on other CPUs and execute directly for local CPU */
625 set_state(&msdata
, MULTI_STOP_PREPARE
);
626 cpu_stop_init_done(&done
, num_active_cpus());
627 queue_stop_cpus_work(cpu_active_mask
, multi_cpu_stop
, &msdata
,
629 ret
= multi_cpu_stop(&msdata
);
631 /* Busy wait for completion. */
632 while (!completion_done(&done
.completion
))
635 mutex_unlock(&stop_cpus_mutex
);
636 return ret
?: done
.ret
;
639 #endif /* CONFIG_STOP_MACHINE */