1 // SPDX-License-Identifier: GPL-2.0-or-later
3 * kernel/stop_machine.c
5 * Copyright (C) 2008, 2005 IBM Corporation.
6 * Copyright (C) 2008, 2005 Rusty Russell rusty@rustcorp.com.au
7 * Copyright (C) 2010 SUSE Linux Products GmbH
8 * Copyright (C) 2010 Tejun Heo <tj@kernel.org>
10 #include <linux/completion.h>
11 #include <linux/cpu.h>
12 #include <linux/init.h>
13 #include <linux/kthread.h>
14 #include <linux/export.h>
15 #include <linux/percpu.h>
16 #include <linux/sched.h>
17 #include <linux/stop_machine.h>
18 #include <linux/interrupt.h>
19 #include <linux/kallsyms.h>
20 #include <linux/smpboot.h>
21 #include <linux/atomic.h>
22 #include <linux/nmi.h>
23 #include <linux/sched/wake_q.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
,
69 struct wake_q_head
*wakeq
)
71 list_add_tail(&work
->list
, &stopper
->works
);
72 wake_q_add(wakeq
, stopper
->thread
);
75 /* queue @work to @stopper. if offline, @work is completed immediately */
76 static bool cpu_stop_queue_work(unsigned int cpu
, struct cpu_stop_work
*work
)
78 struct cpu_stopper
*stopper
= &per_cpu(cpu_stopper
, cpu
);
84 raw_spin_lock_irqsave(&stopper
->lock
, flags
);
85 enabled
= stopper
->enabled
;
87 __cpu_stop_queue_work(stopper
, work
, &wakeq
);
89 cpu_stop_signal_done(work
->done
);
90 raw_spin_unlock_irqrestore(&stopper
->lock
, flags
);
99 * stop_one_cpu - stop a cpu
101 * @fn: function to execute
102 * @arg: argument to @fn
104 * Execute @fn(@arg) on @cpu. @fn is run in a process context with
105 * the highest priority preempting any task on the cpu and
106 * monopolizing it. This function returns after the execution is
109 * This function doesn't guarantee @cpu stays online till @fn
110 * completes. If @cpu goes down in the middle, execution may happen
111 * partially or fully on different cpus. @fn should either be ready
112 * for that or the caller should ensure that @cpu stays online until
113 * this function completes.
119 * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
120 * otherwise, the return value of @fn.
122 int stop_one_cpu(unsigned int cpu
, cpu_stop_fn_t fn
, void *arg
)
124 struct cpu_stop_done done
;
125 struct cpu_stop_work work
= { .fn
= fn
, .arg
= arg
, .done
= &done
};
127 cpu_stop_init_done(&done
, 1);
128 if (!cpu_stop_queue_work(cpu
, &work
))
131 * In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup
132 * cycle by doing a preemption:
135 wait_for_completion(&done
.completion
);
139 /* This controls the threads on each CPU. */
140 enum multi_stop_state
{
141 /* Dummy starting state for thread. */
143 /* Awaiting everyone to be scheduled. */
145 /* Disable interrupts. */
146 MULTI_STOP_DISABLE_IRQ
,
147 /* Run the function */
153 struct multi_stop_data
{
156 /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
157 unsigned int num_threads
;
158 const struct cpumask
*active_cpus
;
160 enum multi_stop_state state
;
164 static void set_state(struct multi_stop_data
*msdata
,
165 enum multi_stop_state newstate
)
167 /* Reset ack counter. */
168 atomic_set(&msdata
->thread_ack
, msdata
->num_threads
);
170 msdata
->state
= newstate
;
173 /* Last one to ack a state moves to the next state. */
174 static void ack_state(struct multi_stop_data
*msdata
)
176 if (atomic_dec_and_test(&msdata
->thread_ack
))
177 set_state(msdata
, msdata
->state
+ 1);
180 void __weak
stop_machine_yield(const struct cpumask
*cpumask
)
185 /* This is the cpu_stop function which stops the CPU. */
186 static int multi_cpu_stop(void *data
)
188 struct multi_stop_data
*msdata
= data
;
189 enum multi_stop_state curstate
= MULTI_STOP_NONE
;
190 int cpu
= smp_processor_id(), err
= 0;
191 const struct cpumask
*cpumask
;
196 * When called from stop_machine_from_inactive_cpu(), irq might
197 * already be disabled. Save the state and restore it on exit.
199 local_save_flags(flags
);
201 if (!msdata
->active_cpus
) {
202 cpumask
= cpu_online_mask
;
203 is_active
= cpu
== cpumask_first(cpumask
);
205 cpumask
= msdata
->active_cpus
;
206 is_active
= cpumask_test_cpu(cpu
, cpumask
);
209 /* Simple state machine */
211 /* Chill out and ensure we re-read multi_stop_state. */
212 stop_machine_yield(cpumask
);
213 if (msdata
->state
!= curstate
) {
214 curstate
= msdata
->state
;
216 case MULTI_STOP_DISABLE_IRQ
:
222 err
= msdata
->fn(msdata
->data
);
228 } else if (curstate
> MULTI_STOP_PREPARE
) {
230 * At this stage all other CPUs we depend on must spin
231 * in the same loop. Any reason for hard-lockup should
232 * be detected and reported on their side.
234 touch_nmi_watchdog();
236 } while (curstate
!= MULTI_STOP_EXIT
);
238 local_irq_restore(flags
);
242 static int cpu_stop_queue_two_works(int cpu1
, struct cpu_stop_work
*work1
,
243 int cpu2
, struct cpu_stop_work
*work2
)
245 struct cpu_stopper
*stopper1
= per_cpu_ptr(&cpu_stopper
, cpu1
);
246 struct cpu_stopper
*stopper2
= per_cpu_ptr(&cpu_stopper
, cpu2
);
247 DEFINE_WAKE_Q(wakeq
);
252 * The waking up of stopper threads has to happen in the same
253 * scheduling context as the queueing. Otherwise, there is a
254 * possibility of one of the above stoppers being woken up by another
255 * CPU, and preempting us. This will cause us to not wake up the other
259 raw_spin_lock_irq(&stopper1
->lock
);
260 raw_spin_lock_nested(&stopper2
->lock
, SINGLE_DEPTH_NESTING
);
262 if (!stopper1
->enabled
|| !stopper2
->enabled
) {
268 * Ensure that if we race with __stop_cpus() the stoppers won't get
269 * queued up in reverse order leading to system deadlock.
271 * We can't miss stop_cpus_in_progress if queue_stop_cpus_work() has
272 * queued a work on cpu1 but not on cpu2, we hold both locks.
274 * It can be falsely true but it is safe to spin until it is cleared,
275 * queue_stop_cpus_work() does everything under preempt_disable().
277 if (unlikely(stop_cpus_in_progress
)) {
283 __cpu_stop_queue_work(stopper1
, work1
, &wakeq
);
284 __cpu_stop_queue_work(stopper2
, work2
, &wakeq
);
287 raw_spin_unlock(&stopper2
->lock
);
288 raw_spin_unlock_irq(&stopper1
->lock
);
290 if (unlikely(err
== -EDEADLK
)) {
293 while (stop_cpus_in_progress
)
305 * stop_two_cpus - stops two cpus
306 * @cpu1: the cpu to stop
307 * @cpu2: the other cpu to stop
308 * @fn: function to execute
309 * @arg: argument to @fn
311 * Stops both the current and specified CPU and runs @fn on one of them.
313 * returns when both are completed.
315 int stop_two_cpus(unsigned int cpu1
, unsigned int cpu2
, cpu_stop_fn_t fn
, void *arg
)
317 struct cpu_stop_done done
;
318 struct cpu_stop_work work1
, work2
;
319 struct multi_stop_data msdata
;
321 msdata
= (struct multi_stop_data
){
325 .active_cpus
= cpumask_of(cpu1
),
328 work1
= work2
= (struct cpu_stop_work
){
329 .fn
= multi_cpu_stop
,
334 cpu_stop_init_done(&done
, 2);
335 set_state(&msdata
, MULTI_STOP_PREPARE
);
339 if (cpu_stop_queue_two_works(cpu1
, &work1
, cpu2
, &work2
))
342 wait_for_completion(&done
.completion
);
347 * stop_one_cpu_nowait - stop a cpu but don't wait for completion
349 * @fn: function to execute
350 * @arg: argument to @fn
351 * @work_buf: pointer to cpu_stop_work structure
353 * Similar to stop_one_cpu() but doesn't wait for completion. The
354 * caller is responsible for ensuring @work_buf is currently unused
355 * and will remain untouched until stopper starts executing @fn.
361 * true if cpu_stop_work was queued successfully and @fn will be called,
364 bool stop_one_cpu_nowait(unsigned int cpu
, cpu_stop_fn_t fn
, void *arg
,
365 struct cpu_stop_work
*work_buf
)
367 *work_buf
= (struct cpu_stop_work
){ .fn
= fn
, .arg
= arg
, };
368 return cpu_stop_queue_work(cpu
, work_buf
);
371 static bool queue_stop_cpus_work(const struct cpumask
*cpumask
,
372 cpu_stop_fn_t fn
, void *arg
,
373 struct cpu_stop_done
*done
)
375 struct cpu_stop_work
*work
;
380 * Disable preemption while queueing to avoid getting
381 * preempted by a stopper which might wait for other stoppers
382 * to enter @fn which can lead to deadlock.
385 stop_cpus_in_progress
= true;
386 for_each_cpu(cpu
, cpumask
) {
387 work
= &per_cpu(cpu_stopper
.stop_work
, cpu
);
391 if (cpu_stop_queue_work(cpu
, work
))
394 stop_cpus_in_progress
= false;
400 static int __stop_cpus(const struct cpumask
*cpumask
,
401 cpu_stop_fn_t fn
, void *arg
)
403 struct cpu_stop_done done
;
405 cpu_stop_init_done(&done
, cpumask_weight(cpumask
));
406 if (!queue_stop_cpus_work(cpumask
, fn
, arg
, &done
))
408 wait_for_completion(&done
.completion
);
413 * stop_cpus - stop multiple cpus
414 * @cpumask: cpus to stop
415 * @fn: function to execute
416 * @arg: argument to @fn
418 * Execute @fn(@arg) on online cpus in @cpumask. On each target cpu,
419 * @fn is run in a process context with the highest priority
420 * preempting any task on the cpu and monopolizing it. This function
421 * returns after all executions are complete.
423 * This function doesn't guarantee the cpus in @cpumask stay online
424 * till @fn completes. If some cpus go down in the middle, execution
425 * on the cpu may happen partially or fully on different cpus. @fn
426 * should either be ready for that or the caller should ensure that
427 * the cpus stay online until this function completes.
429 * All stop_cpus() calls are serialized making it safe for @fn to wait
430 * for all cpus to start executing it.
436 * -ENOENT if @fn(@arg) was not executed at all because all cpus in
437 * @cpumask were offline; otherwise, 0 if all executions of @fn
438 * returned 0, any non zero return value if any returned non zero.
440 int stop_cpus(const struct cpumask
*cpumask
, cpu_stop_fn_t fn
, void *arg
)
444 /* static works are used, process one request at a time */
445 mutex_lock(&stop_cpus_mutex
);
446 ret
= __stop_cpus(cpumask
, fn
, arg
);
447 mutex_unlock(&stop_cpus_mutex
);
452 * try_stop_cpus - try to stop multiple cpus
453 * @cpumask: cpus to stop
454 * @fn: function to execute
455 * @arg: argument to @fn
457 * Identical to stop_cpus() except that it fails with -EAGAIN if
458 * someone else is already using the facility.
464 * -EAGAIN if someone else is already stopping cpus, -ENOENT if
465 * @fn(@arg) was not executed at all because all cpus in @cpumask were
466 * offline; otherwise, 0 if all executions of @fn returned 0, any non
467 * zero return value if any returned non zero.
469 int try_stop_cpus(const struct cpumask
*cpumask
, cpu_stop_fn_t fn
, void *arg
)
473 /* static works are used, process one request at a time */
474 if (!mutex_trylock(&stop_cpus_mutex
))
476 ret
= __stop_cpus(cpumask
, fn
, arg
);
477 mutex_unlock(&stop_cpus_mutex
);
481 static int cpu_stop_should_run(unsigned int cpu
)
483 struct cpu_stopper
*stopper
= &per_cpu(cpu_stopper
, cpu
);
487 raw_spin_lock_irqsave(&stopper
->lock
, flags
);
488 run
= !list_empty(&stopper
->works
);
489 raw_spin_unlock_irqrestore(&stopper
->lock
, flags
);
493 static void cpu_stopper_thread(unsigned int cpu
)
495 struct cpu_stopper
*stopper
= &per_cpu(cpu_stopper
, cpu
);
496 struct cpu_stop_work
*work
;
500 raw_spin_lock_irq(&stopper
->lock
);
501 if (!list_empty(&stopper
->works
)) {
502 work
= list_first_entry(&stopper
->works
,
503 struct cpu_stop_work
, list
);
504 list_del_init(&work
->list
);
506 raw_spin_unlock_irq(&stopper
->lock
);
509 cpu_stop_fn_t fn
= work
->fn
;
510 void *arg
= work
->arg
;
511 struct cpu_stop_done
*done
= work
->done
;
514 /* cpu stop callbacks must not sleep, make in_atomic() == T */
520 cpu_stop_signal_done(done
);
523 WARN_ONCE(preempt_count(),
524 "cpu_stop: %ps(%p) leaked preempt count\n", fn
, arg
);
529 void stop_machine_park(int cpu
)
531 struct cpu_stopper
*stopper
= &per_cpu(cpu_stopper
, cpu
);
533 * Lockless. cpu_stopper_thread() will take stopper->lock and flush
534 * the pending works before it parks, until then it is fine to queue
537 stopper
->enabled
= false;
538 kthread_park(stopper
->thread
);
541 extern void sched_set_stop_task(int cpu
, struct task_struct
*stop
);
543 static void cpu_stop_create(unsigned int cpu
)
545 sched_set_stop_task(cpu
, per_cpu(cpu_stopper
.thread
, cpu
));
548 static void cpu_stop_park(unsigned int cpu
)
550 struct cpu_stopper
*stopper
= &per_cpu(cpu_stopper
, cpu
);
552 WARN_ON(!list_empty(&stopper
->works
));
555 void stop_machine_unpark(int cpu
)
557 struct cpu_stopper
*stopper
= &per_cpu(cpu_stopper
, cpu
);
559 stopper
->enabled
= true;
560 kthread_unpark(stopper
->thread
);
563 static struct smp_hotplug_thread cpu_stop_threads
= {
564 .store
= &cpu_stopper
.thread
,
565 .thread_should_run
= cpu_stop_should_run
,
566 .thread_fn
= cpu_stopper_thread
,
567 .thread_comm
= "migration/%u",
568 .create
= cpu_stop_create
,
569 .park
= cpu_stop_park
,
573 static int __init
cpu_stop_init(void)
577 for_each_possible_cpu(cpu
) {
578 struct cpu_stopper
*stopper
= &per_cpu(cpu_stopper
, cpu
);
580 raw_spin_lock_init(&stopper
->lock
);
581 INIT_LIST_HEAD(&stopper
->works
);
584 BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads
));
585 stop_machine_unpark(raw_smp_processor_id());
586 stop_machine_initialized
= true;
589 early_initcall(cpu_stop_init
);
591 int stop_machine_cpuslocked(cpu_stop_fn_t fn
, void *data
,
592 const struct cpumask
*cpus
)
594 struct multi_stop_data msdata
= {
597 .num_threads
= num_online_cpus(),
601 lockdep_assert_cpus_held();
603 if (!stop_machine_initialized
) {
605 * Handle the case where stop_machine() is called
606 * early in boot before stop_machine() has been
612 WARN_ON_ONCE(msdata
.num_threads
!= 1);
614 local_irq_save(flags
);
617 local_irq_restore(flags
);
622 /* Set the initial state and stop all online cpus. */
623 set_state(&msdata
, MULTI_STOP_PREPARE
);
624 return stop_cpus(cpu_online_mask
, multi_cpu_stop
, &msdata
);
627 int stop_machine(cpu_stop_fn_t fn
, void *data
, const struct cpumask
*cpus
)
631 /* No CPUs can come up or down during this. */
633 ret
= stop_machine_cpuslocked(fn
, data
, cpus
);
637 EXPORT_SYMBOL_GPL(stop_machine
);
640 * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
641 * @fn: the function to run
642 * @data: the data ptr for the @fn()
643 * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
645 * This is identical to stop_machine() but can be called from a CPU which
646 * is not active. The local CPU is in the process of hotplug (so no other
647 * CPU hotplug can start) and not marked active and doesn't have enough
650 * This function provides stop_machine() functionality for such state by
651 * using busy-wait for synchronization and executing @fn directly for local
655 * Local CPU is inactive. Temporarily stops all active CPUs.
658 * 0 if all executions of @fn returned 0, any non zero return value if any
661 int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn
, void *data
,
662 const struct cpumask
*cpus
)
664 struct multi_stop_data msdata
= { .fn
= fn
, .data
= data
,
665 .active_cpus
= cpus
};
666 struct cpu_stop_done done
;
669 /* Local CPU must be inactive and CPU hotplug in progress. */
670 BUG_ON(cpu_active(raw_smp_processor_id()));
671 msdata
.num_threads
= num_active_cpus() + 1; /* +1 for local */
673 /* No proper task established and can't sleep - busy wait for lock. */
674 while (!mutex_trylock(&stop_cpus_mutex
))
677 /* Schedule work on other CPUs and execute directly for local CPU */
678 set_state(&msdata
, MULTI_STOP_PREPARE
);
679 cpu_stop_init_done(&done
, num_active_cpus());
680 queue_stop_cpus_work(cpu_active_mask
, multi_cpu_stop
, &msdata
,
682 ret
= multi_cpu_stop(&msdata
);
684 /* Busy wait for completion. */
685 while (!completion_done(&done
.completion
))
688 mutex_unlock(&stop_cpus_mutex
);
689 return ret
?: done
.ret
;