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Linux/kernel/stop_machine.c

  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/nmi.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         int                     ret;            /* collected return value */
 32         struct completion       completion;     /* fired if nr_todo reaches 0 */
 33 };
 34 
 35 /* the actual stopper, one per every possible cpu, enabled on online cpus */
 36 struct cpu_stopper {
 37         struct task_struct      *thread;
 38 
 39         spinlock_t              lock;
 40         bool                    enabled;        /* is this stopper enabled? */
 41         struct list_head        works;          /* list of pending works */
 42 
 43         struct cpu_stop_work    stop_work;      /* for stop_cpus */
 44 };
 45 
 46 static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
 47 static bool stop_machine_initialized = false;
 48 
 49 /* static data for stop_cpus */
 50 static DEFINE_MUTEX(stop_cpus_mutex);
 51 static bool stop_cpus_in_progress;
 52 
 53 static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
 54 {
 55         memset(done, 0, sizeof(*done));
 56         atomic_set(&done->nr_todo, nr_todo);
 57         init_completion(&done->completion);
 58 }
 59 
 60 /* signal completion unless @done is NULL */
 61 static void cpu_stop_signal_done(struct cpu_stop_done *done)
 62 {
 63         if (atomic_dec_and_test(&done->nr_todo))
 64                 complete(&done->completion);
 65 }
 66 
 67 static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
 68                                         struct cpu_stop_work *work)
 69 {
 70         list_add_tail(&work->list, &stopper->works);
 71         wake_up_process(stopper->thread);
 72 }
 73 
 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)
 76 {
 77         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 78         unsigned long flags;
 79         bool enabled;
 80 
 81         spin_lock_irqsave(&stopper->lock, flags);
 82         enabled = stopper->enabled;
 83         if (enabled)
 84                 __cpu_stop_queue_work(stopper, work);
 85         else if (work->done)
 86                 cpu_stop_signal_done(work->done);
 87         spin_unlock_irqrestore(&stopper->lock, flags);
 88 
 89         return enabled;
 90 }
 91 
 92 /**
 93  * stop_one_cpu - stop a cpu
 94  * @cpu: cpu to stop
 95  * @fn: function to execute
 96  * @arg: argument to @fn
 97  *
 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
101  * complete.
102  *
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.
108  *
109  * CONTEXT:
110  * Might sleep.
111  *
112  * RETURNS:
113  * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
114  * otherwise, the return value of @fn.
115  */
116 int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
117 {
118         struct cpu_stop_done done;
119         struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
120 
121         cpu_stop_init_done(&done, 1);
122         if (!cpu_stop_queue_work(cpu, &work))
123                 return -ENOENT;
124         /*
125          * In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup
126          * cycle by doing a preemption:
127          */
128         cond_resched();
129         wait_for_completion(&done.completion);
130         return done.ret;
131 }
132 
133 /* This controls the threads on each CPU. */
134 enum multi_stop_state {
135         /* Dummy starting state for thread. */
136         MULTI_STOP_NONE,
137         /* Awaiting everyone to be scheduled. */
138         MULTI_STOP_PREPARE,
139         /* Disable interrupts. */
140         MULTI_STOP_DISABLE_IRQ,
141         /* Run the function */
142         MULTI_STOP_RUN,
143         /* Exit */
144         MULTI_STOP_EXIT,
145 };
146 
147 struct multi_stop_data {
148         cpu_stop_fn_t           fn;
149         void                    *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;
153 
154         enum multi_stop_state   state;
155         atomic_t                thread_ack;
156 };
157 
158 static void set_state(struct multi_stop_data *msdata,
159                       enum multi_stop_state newstate)
160 {
161         /* Reset ack counter. */
162         atomic_set(&msdata->thread_ack, msdata->num_threads);
163         smp_wmb();
164         msdata->state = newstate;
165 }
166 
167 /* Last one to ack a state moves to the next state. */
168 static void ack_state(struct multi_stop_data *msdata)
169 {
170         if (atomic_dec_and_test(&msdata->thread_ack))
171                 set_state(msdata, msdata->state + 1);
172 }
173 
174 /* This is the cpu_stop function which stops the CPU. */
175 static int multi_cpu_stop(void *data)
176 {
177         struct multi_stop_data *msdata = data;
178         enum multi_stop_state curstate = MULTI_STOP_NONE;
179         int cpu = smp_processor_id(), err = 0;
180         unsigned long flags;
181         bool is_active;
182 
183         /*
184          * When called from stop_machine_from_inactive_cpu(), irq might
185          * already be disabled.  Save the state and restore it on exit.
186          */
187         local_save_flags(flags);
188 
189         if (!msdata->active_cpus)
190                 is_active = cpu == cpumask_first(cpu_online_mask);
191         else
192                 is_active = cpumask_test_cpu(cpu, msdata->active_cpus);
193 
194         /* Simple state machine */
195         do {
196                 /* Chill out and ensure we re-read multi_stop_state. */
197                 cpu_relax_yield();
198                 if (msdata->state != curstate) {
199                         curstate = msdata->state;
200                         switch (curstate) {
201                         case MULTI_STOP_DISABLE_IRQ:
202                                 local_irq_disable();
203                                 hard_irq_disable();
204                                 break;
205                         case MULTI_STOP_RUN:
206                                 if (is_active)
207                                         err = msdata->fn(msdata->data);
208                                 break;
209                         default:
210                                 break;
211                         }
212                         ack_state(msdata);
213                 } else if (curstate > MULTI_STOP_PREPARE) {
214                         /*
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.
218                          */
219                         touch_nmi_watchdog();
220                 }
221         } while (curstate != MULTI_STOP_EXIT);
222 
223         local_irq_restore(flags);
224         return err;
225 }
226 
227 static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
228                                     int cpu2, struct cpu_stop_work *work2)
229 {
230         struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
231         struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
232         int err;
233 retry:
234         spin_lock_irq(&stopper1->lock);
235         spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
236 
237         err = -ENOENT;
238         if (!stopper1->enabled || !stopper2->enabled)
239                 goto unlock;
240         /*
241          * Ensure that if we race with __stop_cpus() the stoppers won't get
242          * queued up in reverse order leading to system deadlock.
243          *
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.
246          *
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().
249          */
250         err = -EDEADLK;
251         if (unlikely(stop_cpus_in_progress))
252                         goto unlock;
253 
254         err = 0;
255         __cpu_stop_queue_work(stopper1, work1);
256         __cpu_stop_queue_work(stopper2, work2);
257 unlock:
258         spin_unlock(&stopper2->lock);
259         spin_unlock_irq(&stopper1->lock);
260 
261         if (unlikely(err == -EDEADLK)) {
262                 while (stop_cpus_in_progress)
263                         cpu_relax();
264                 goto retry;
265         }
266         return err;
267 }
268 /**
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
274  *
275  * Stops both the current and specified CPU and runs @fn on one of them.
276  *
277  * returns when both are completed.
278  */
279 int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
280 {
281         struct cpu_stop_done done;
282         struct cpu_stop_work work1, work2;
283         struct multi_stop_data msdata;
284 
285         msdata = (struct multi_stop_data){
286                 .fn = fn,
287                 .data = arg,
288                 .num_threads = 2,
289                 .active_cpus = cpumask_of(cpu1),
290         };
291 
292         work1 = work2 = (struct cpu_stop_work){
293                 .fn = multi_cpu_stop,
294                 .arg = &msdata,
295                 .done = &done
296         };
297 
298         cpu_stop_init_done(&done, 2);
299         set_state(&msdata, MULTI_STOP_PREPARE);
300 
301         if (cpu1 > cpu2)
302                 swap(cpu1, cpu2);
303         if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
304                 return -ENOENT;
305 
306         wait_for_completion(&done.completion);
307         return done.ret;
308 }
309 
310 /**
311  * stop_one_cpu_nowait - stop a cpu but don't wait for completion
312  * @cpu: cpu to stop
313  * @fn: function to execute
314  * @arg: argument to @fn
315  * @work_buf: pointer to cpu_stop_work structure
316  *
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.
320  *
321  * CONTEXT:
322  * Don't care.
323  *
324  * RETURNS:
325  * true if cpu_stop_work was queued successfully and @fn will be called,
326  * false otherwise.
327  */
328 bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
329                         struct cpu_stop_work *work_buf)
330 {
331         *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
332         return cpu_stop_queue_work(cpu, work_buf);
333 }
334 
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)
338 {
339         struct cpu_stop_work *work;
340         unsigned int cpu;
341         bool queued = false;
342 
343         /*
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.
347          */
348         preempt_disable();
349         stop_cpus_in_progress = true;
350         for_each_cpu(cpu, cpumask) {
351                 work = &per_cpu(cpu_stopper.stop_work, cpu);
352                 work->fn = fn;
353                 work->arg = arg;
354                 work->done = done;
355                 if (cpu_stop_queue_work(cpu, work))
356                         queued = true;
357         }
358         stop_cpus_in_progress = false;
359         preempt_enable();
360 
361         return queued;
362 }
363 
364 static int __stop_cpus(const struct cpumask *cpumask,
365                        cpu_stop_fn_t fn, void *arg)
366 {
367         struct cpu_stop_done done;
368 
369         cpu_stop_init_done(&done, cpumask_weight(cpumask));
370         if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
371                 return -ENOENT;
372         wait_for_completion(&done.completion);
373         return done.ret;
374 }
375 
376 /**
377  * stop_cpus - stop multiple cpus
378  * @cpumask: cpus to stop
379  * @fn: function to execute
380  * @arg: argument to @fn
381  *
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.
386  *
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.
392  *
393  * All stop_cpus() calls are serialized making it safe for @fn to wait
394  * for all cpus to start executing it.
395  *
396  * CONTEXT:
397  * Might sleep.
398  *
399  * RETURNS:
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.
403  */
404 int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
405 {
406         int ret;
407 
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);
412         return ret;
413 }
414 
415 /**
416  * try_stop_cpus - try to stop multiple cpus
417  * @cpumask: cpus to stop
418  * @fn: function to execute
419  * @arg: argument to @fn
420  *
421  * Identical to stop_cpus() except that it fails with -EAGAIN if
422  * someone else is already using the facility.
423  *
424  * CONTEXT:
425  * Might sleep.
426  *
427  * RETURNS:
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.
432  */
433 int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
434 {
435         int ret;
436 
437         /* static works are used, process one request at a time */
438         if (!mutex_trylock(&stop_cpus_mutex))
439                 return -EAGAIN;
440         ret = __stop_cpus(cpumask, fn, arg);
441         mutex_unlock(&stop_cpus_mutex);
442         return ret;
443 }
444 
445 static int cpu_stop_should_run(unsigned int cpu)
446 {
447         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
448         unsigned long flags;
449         int run;
450 
451         spin_lock_irqsave(&stopper->lock, flags);
452         run = !list_empty(&stopper->works);
453         spin_unlock_irqrestore(&stopper->lock, flags);
454         return run;
455 }
456 
457 static void cpu_stopper_thread(unsigned int cpu)
458 {
459         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
460         struct cpu_stop_work *work;
461 
462 repeat:
463         work = NULL;
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);
469         }
470         spin_unlock_irq(&stopper->lock);
471 
472         if (work) {
473                 cpu_stop_fn_t fn = work->fn;
474                 void *arg = work->arg;
475                 struct cpu_stop_done *done = work->done;
476                 int ret;
477 
478                 /* cpu stop callbacks must not sleep, make in_atomic() == T */
479                 preempt_count_inc();
480                 ret = fn(arg);
481                 if (done) {
482                         if (ret)
483                                 done->ret = ret;
484                         cpu_stop_signal_done(done);
485                 }
486                 preempt_count_dec();
487                 WARN_ONCE(preempt_count(),
488                           "cpu_stop: %pf(%p) leaked preempt count\n", fn, arg);
489                 goto repeat;
490         }
491 }
492 
493 void stop_machine_park(int cpu)
494 {
495         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
496         /*
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
499          * the new works.
500          */
501         stopper->enabled = false;
502         kthread_park(stopper->thread);
503 }
504 
505 extern void sched_set_stop_task(int cpu, struct task_struct *stop);
506 
507 static void cpu_stop_create(unsigned int cpu)
508 {
509         sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
510 }
511 
512 static void cpu_stop_park(unsigned int cpu)
513 {
514         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
515 
516         WARN_ON(!list_empty(&stopper->works));
517 }
518 
519 void stop_machine_unpark(int cpu)
520 {
521         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
522 
523         stopper->enabled = true;
524         kthread_unpark(stopper->thread);
525 }
526 
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,
534         .selfparking            = true,
535 };
536 
537 static int __init cpu_stop_init(void)
538 {
539         unsigned int cpu;
540 
541         for_each_possible_cpu(cpu) {
542                 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
543 
544                 spin_lock_init(&stopper->lock);
545                 INIT_LIST_HEAD(&stopper->works);
546         }
547 
548         BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
549         stop_machine_unpark(raw_smp_processor_id());
550         stop_machine_initialized = true;
551         return 0;
552 }
553 early_initcall(cpu_stop_init);
554 
555 static int __stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
556 {
557         struct multi_stop_data msdata = {
558                 .fn = fn,
559                 .data = data,
560                 .num_threads = num_online_cpus(),
561                 .active_cpus = cpus,
562         };
563 
564         if (!stop_machine_initialized) {
565                 /*
566                  * Handle the case where stop_machine() is called
567                  * early in boot before stop_machine() has been
568                  * initialized.
569                  */
570                 unsigned long flags;
571                 int ret;
572 
573                 WARN_ON_ONCE(msdata.num_threads != 1);
574 
575                 local_irq_save(flags);
576                 hard_irq_disable();
577                 ret = (*fn)(data);
578                 local_irq_restore(flags);
579 
580                 return ret;
581         }
582 
583         /* Set the initial state and stop all online cpus. */
584         set_state(&msdata, MULTI_STOP_PREPARE);
585         return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
586 }
587 
588 int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
589 {
590         int ret;
591 
592         /* No CPUs can come up or down during this. */
593         get_online_cpus();
594         ret = __stop_machine(fn, data, cpus);
595         put_online_cpus();
596         return ret;
597 }
598 EXPORT_SYMBOL_GPL(stop_machine);
599 
600 /**
601  * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
602  * @fn: the function to run
603  * @data: the data ptr for the @fn()
604  * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
605  *
606  * This is identical to stop_machine() but can be called from a CPU which
607  * is not active.  The local CPU is in the process of hotplug (so no other
608  * CPU hotplug can start) and not marked active and doesn't have enough
609  * context to sleep.
610  *
611  * This function provides stop_machine() functionality for such state by
612  * using busy-wait for synchronization and executing @fn directly for local
613  * CPU.
614  *
615  * CONTEXT:
616  * Local CPU is inactive.  Temporarily stops all active CPUs.
617  *
618  * RETURNS:
619  * 0 if all executions of @fn returned 0, any non zero return value if any
620  * returned non zero.
621  */
622 int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
623                                   const struct cpumask *cpus)
624 {
625         struct multi_stop_data msdata = { .fn = fn, .data = data,
626                                             .active_cpus = cpus };
627         struct cpu_stop_done done;
628         int ret;
629 
630         /* Local CPU must be inactive and CPU hotplug in progress. */
631         BUG_ON(cpu_active(raw_smp_processor_id()));
632         msdata.num_threads = num_active_cpus() + 1;     /* +1 for local */
633 
634         /* No proper task established and can't sleep - busy wait for lock. */
635         while (!mutex_trylock(&stop_cpus_mutex))
636                 cpu_relax();
637 
638         /* Schedule work on other CPUs and execute directly for local CPU */
639         set_state(&msdata, MULTI_STOP_PREPARE);
640         cpu_stop_init_done(&done, num_active_cpus());
641         queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
642                              &done);
643         ret = multi_cpu_stop(&msdata);
644 
645         /* Busy wait for completion. */
646         while (!completion_done(&done.completion))
647                 cpu_relax();
648 
649         mutex_unlock(&stop_cpus_mutex);
650         return ret ?: done.ret;
651 }
652 

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