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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/lglock.h>
 24 #include <linux/nmi.h>
 25 
 26 /*
 27  * Structure to determine completion condition and record errors.  May
 28  * be shared by works on different cpus.
 29  */
 30 struct cpu_stop_done {
 31         atomic_t                nr_todo;        /* nr left to execute */
 32         int                     ret;            /* collected return value */
 33         struct completion       completion;     /* fired if nr_todo reaches 0 */
 34 };
 35 
 36 /* the actual stopper, one per every possible cpu, enabled on online cpus */
 37 struct cpu_stopper {
 38         struct task_struct      *thread;
 39 
 40         spinlock_t              lock;
 41         bool                    enabled;        /* is this stopper enabled? */
 42         struct list_head        works;          /* list of pending works */
 43 
 44         struct cpu_stop_work    stop_work;      /* for stop_cpus */
 45 };
 46 
 47 static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
 48 static bool stop_machine_initialized = false;
 49 
 50 /*
 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
 54  * relatively cheap.
 55  */
 56 DEFINE_STATIC_LGLOCK(stop_cpus_lock);
 57 
 58 static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
 59 {
 60         memset(done, 0, sizeof(*done));
 61         atomic_set(&done->nr_todo, nr_todo);
 62         init_completion(&done->completion);
 63 }
 64 
 65 /* signal completion unless @done is NULL */
 66 static void cpu_stop_signal_done(struct cpu_stop_done *done)
 67 {
 68         if (atomic_dec_and_test(&done->nr_todo))
 69                 complete(&done->completion);
 70 }
 71 
 72 static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
 73                                         struct cpu_stop_work *work)
 74 {
 75         list_add_tail(&work->list, &stopper->works);
 76         wake_up_process(stopper->thread);
 77 }
 78 
 79 /* queue @work to @stopper.  if offline, @work is completed immediately */
 80 static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
 81 {
 82         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 83         unsigned long flags;
 84         bool enabled;
 85 
 86         spin_lock_irqsave(&stopper->lock, flags);
 87         enabled = stopper->enabled;
 88         if (enabled)
 89                 __cpu_stop_queue_work(stopper, work);
 90         else if (work->done)
 91                 cpu_stop_signal_done(work->done);
 92         spin_unlock_irqrestore(&stopper->lock, flags);
 93 
 94         return enabled;
 95 }
 96 
 97 /**
 98  * stop_one_cpu - stop a cpu
 99  * @cpu: cpu to stop
100  * @fn: function to execute
101  * @arg: argument to @fn
102  *
103  * Execute @fn(@arg) on @cpu.  @fn is run in a process context with
104  * the highest priority preempting any task on the cpu and
105  * monopolizing it.  This function returns after the execution is
106  * complete.
107  *
108  * This function doesn't guarantee @cpu stays online till @fn
109  * completes.  If @cpu goes down in the middle, execution may happen
110  * partially or fully on different cpus.  @fn should either be ready
111  * for that or the caller should ensure that @cpu stays online until
112  * this function completes.
113  *
114  * CONTEXT:
115  * Might sleep.
116  *
117  * RETURNS:
118  * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
119  * otherwise, the return value of @fn.
120  */
121 int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
122 {
123         struct cpu_stop_done done;
124         struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
125 
126         cpu_stop_init_done(&done, 1);
127         if (!cpu_stop_queue_work(cpu, &work))
128                 return -ENOENT;
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();
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 
234         lg_double_lock(&stop_cpus_lock, cpu1, cpu2);
235         spin_lock_irq(&stopper1->lock);
236         spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
237 
238         err = -ENOENT;
239         if (!stopper1->enabled || !stopper2->enabled)
240                 goto unlock;
241 
242         err = 0;
243         __cpu_stop_queue_work(stopper1, work1);
244         __cpu_stop_queue_work(stopper2, work2);
245 unlock:
246         spin_unlock(&stopper2->lock);
247         spin_unlock_irq(&stopper1->lock);
248         lg_double_unlock(&stop_cpus_lock, cpu1, cpu2);
249 
250         return err;
251 }
252 /**
253  * stop_two_cpus - stops two cpus
254  * @cpu1: the cpu to stop
255  * @cpu2: the other cpu to stop
256  * @fn: function to execute
257  * @arg: argument to @fn
258  *
259  * Stops both the current and specified CPU and runs @fn on one of them.
260  *
261  * returns when both are completed.
262  */
263 int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
264 {
265         struct cpu_stop_done done;
266         struct cpu_stop_work work1, work2;
267         struct multi_stop_data msdata;
268 
269         msdata = (struct multi_stop_data){
270                 .fn = fn,
271                 .data = arg,
272                 .num_threads = 2,
273                 .active_cpus = cpumask_of(cpu1),
274         };
275 
276         work1 = work2 = (struct cpu_stop_work){
277                 .fn = multi_cpu_stop,
278                 .arg = &msdata,
279                 .done = &done
280         };
281 
282         cpu_stop_init_done(&done, 2);
283         set_state(&msdata, MULTI_STOP_PREPARE);
284 
285         if (cpu1 > cpu2)
286                 swap(cpu1, cpu2);
287         if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
288                 return -ENOENT;
289 
290         wait_for_completion(&done.completion);
291         return done.ret;
292 }
293 
294 /**
295  * stop_one_cpu_nowait - stop a cpu but don't wait for completion
296  * @cpu: cpu to stop
297  * @fn: function to execute
298  * @arg: argument to @fn
299  * @work_buf: pointer to cpu_stop_work structure
300  *
301  * Similar to stop_one_cpu() but doesn't wait for completion.  The
302  * caller is responsible for ensuring @work_buf is currently unused
303  * and will remain untouched until stopper starts executing @fn.
304  *
305  * CONTEXT:
306  * Don't care.
307  *
308  * RETURNS:
309  * true if cpu_stop_work was queued successfully and @fn will be called,
310  * false otherwise.
311  */
312 bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
313                         struct cpu_stop_work *work_buf)
314 {
315         *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
316         return cpu_stop_queue_work(cpu, work_buf);
317 }
318 
319 /* static data for stop_cpus */
320 static DEFINE_MUTEX(stop_cpus_mutex);
321 
322 static bool queue_stop_cpus_work(const struct cpumask *cpumask,
323                                  cpu_stop_fn_t fn, void *arg,
324                                  struct cpu_stop_done *done)
325 {
326         struct cpu_stop_work *work;
327         unsigned int cpu;
328         bool queued = false;
329 
330         /*
331          * Disable preemption while queueing to avoid getting
332          * preempted by a stopper which might wait for other stoppers
333          * to enter @fn which can lead to deadlock.
334          */
335         lg_global_lock(&stop_cpus_lock);
336         for_each_cpu(cpu, cpumask) {
337                 work = &per_cpu(cpu_stopper.stop_work, cpu);
338                 work->fn = fn;
339                 work->arg = arg;
340                 work->done = done;
341                 if (cpu_stop_queue_work(cpu, work))
342                         queued = true;
343         }
344         lg_global_unlock(&stop_cpus_lock);
345 
346         return queued;
347 }
348 
349 static int __stop_cpus(const struct cpumask *cpumask,
350                        cpu_stop_fn_t fn, void *arg)
351 {
352         struct cpu_stop_done done;
353 
354         cpu_stop_init_done(&done, cpumask_weight(cpumask));
355         if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
356                 return -ENOENT;
357         wait_for_completion(&done.completion);
358         return done.ret;
359 }
360 
361 /**
362  * stop_cpus - stop multiple cpus
363  * @cpumask: cpus to stop
364  * @fn: function to execute
365  * @arg: argument to @fn
366  *
367  * Execute @fn(@arg) on online cpus in @cpumask.  On each target cpu,
368  * @fn is run in a process context with the highest priority
369  * preempting any task on the cpu and monopolizing it.  This function
370  * returns after all executions are complete.
371  *
372  * This function doesn't guarantee the cpus in @cpumask stay online
373  * till @fn completes.  If some cpus go down in the middle, execution
374  * on the cpu may happen partially or fully on different cpus.  @fn
375  * should either be ready for that or the caller should ensure that
376  * the cpus stay online until this function completes.
377  *
378  * All stop_cpus() calls are serialized making it safe for @fn to wait
379  * for all cpus to start executing it.
380  *
381  * CONTEXT:
382  * Might sleep.
383  *
384  * RETURNS:
385  * -ENOENT if @fn(@arg) was not executed at all because all cpus in
386  * @cpumask were offline; otherwise, 0 if all executions of @fn
387  * returned 0, any non zero return value if any returned non zero.
388  */
389 int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
390 {
391         int ret;
392 
393         /* static works are used, process one request at a time */
394         mutex_lock(&stop_cpus_mutex);
395         ret = __stop_cpus(cpumask, fn, arg);
396         mutex_unlock(&stop_cpus_mutex);
397         return ret;
398 }
399 
400 /**
401  * try_stop_cpus - try to stop multiple cpus
402  * @cpumask: cpus to stop
403  * @fn: function to execute
404  * @arg: argument to @fn
405  *
406  * Identical to stop_cpus() except that it fails with -EAGAIN if
407  * someone else is already using the facility.
408  *
409  * CONTEXT:
410  * Might sleep.
411  *
412  * RETURNS:
413  * -EAGAIN if someone else is already stopping cpus, -ENOENT if
414  * @fn(@arg) was not executed at all because all cpus in @cpumask were
415  * offline; otherwise, 0 if all executions of @fn returned 0, any non
416  * zero return value if any returned non zero.
417  */
418 int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
419 {
420         int ret;
421 
422         /* static works are used, process one request at a time */
423         if (!mutex_trylock(&stop_cpus_mutex))
424                 return -EAGAIN;
425         ret = __stop_cpus(cpumask, fn, arg);
426         mutex_unlock(&stop_cpus_mutex);
427         return ret;
428 }
429 
430 static int cpu_stop_should_run(unsigned int cpu)
431 {
432         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
433         unsigned long flags;
434         int run;
435 
436         spin_lock_irqsave(&stopper->lock, flags);
437         run = !list_empty(&stopper->works);
438         spin_unlock_irqrestore(&stopper->lock, flags);
439         return run;
440 }
441 
442 static void cpu_stopper_thread(unsigned int cpu)
443 {
444         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
445         struct cpu_stop_work *work;
446 
447 repeat:
448         work = NULL;
449         spin_lock_irq(&stopper->lock);
450         if (!list_empty(&stopper->works)) {
451                 work = list_first_entry(&stopper->works,
452                                         struct cpu_stop_work, list);
453                 list_del_init(&work->list);
454         }
455         spin_unlock_irq(&stopper->lock);
456 
457         if (work) {
458                 cpu_stop_fn_t fn = work->fn;
459                 void *arg = work->arg;
460                 struct cpu_stop_done *done = work->done;
461                 int ret;
462 
463                 /* cpu stop callbacks must not sleep, make in_atomic() == T */
464                 preempt_count_inc();
465                 ret = fn(arg);
466                 if (done) {
467                         if (ret)
468                                 done->ret = ret;
469                         cpu_stop_signal_done(done);
470                 }
471                 preempt_count_dec();
472                 WARN_ONCE(preempt_count(),
473                           "cpu_stop: %pf(%p) leaked preempt count\n", fn, arg);
474                 goto repeat;
475         }
476 }
477 
478 void stop_machine_park(int cpu)
479 {
480         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
481         /*
482          * Lockless. cpu_stopper_thread() will take stopper->lock and flush
483          * the pending works before it parks, until then it is fine to queue
484          * the new works.
485          */
486         stopper->enabled = false;
487         kthread_park(stopper->thread);
488 }
489 
490 extern void sched_set_stop_task(int cpu, struct task_struct *stop);
491 
492 static void cpu_stop_create(unsigned int cpu)
493 {
494         sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
495 }
496 
497 static void cpu_stop_park(unsigned int cpu)
498 {
499         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
500 
501         WARN_ON(!list_empty(&stopper->works));
502 }
503 
504 void stop_machine_unpark(int cpu)
505 {
506         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
507 
508         stopper->enabled = true;
509         kthread_unpark(stopper->thread);
510 }
511 
512 static struct smp_hotplug_thread cpu_stop_threads = {
513         .store                  = &cpu_stopper.thread,
514         .thread_should_run      = cpu_stop_should_run,
515         .thread_fn              = cpu_stopper_thread,
516         .thread_comm            = "migration/%u",
517         .create                 = cpu_stop_create,
518         .park                   = cpu_stop_park,
519         .selfparking            = true,
520 };
521 
522 static int __init cpu_stop_init(void)
523 {
524         unsigned int cpu;
525 
526         for_each_possible_cpu(cpu) {
527                 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
528 
529                 spin_lock_init(&stopper->lock);
530                 INIT_LIST_HEAD(&stopper->works);
531         }
532 
533         BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
534         stop_machine_unpark(raw_smp_processor_id());
535         stop_machine_initialized = true;
536         return 0;
537 }
538 early_initcall(cpu_stop_init);
539 
540 static int __stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
541 {
542         struct multi_stop_data msdata = {
543                 .fn = fn,
544                 .data = data,
545                 .num_threads = num_online_cpus(),
546                 .active_cpus = cpus,
547         };
548 
549         if (!stop_machine_initialized) {
550                 /*
551                  * Handle the case where stop_machine() is called
552                  * early in boot before stop_machine() has been
553                  * initialized.
554                  */
555                 unsigned long flags;
556                 int ret;
557 
558                 WARN_ON_ONCE(msdata.num_threads != 1);
559 
560                 local_irq_save(flags);
561                 hard_irq_disable();
562                 ret = (*fn)(data);
563                 local_irq_restore(flags);
564 
565                 return ret;
566         }
567 
568         /* Set the initial state and stop all online cpus. */
569         set_state(&msdata, MULTI_STOP_PREPARE);
570         return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
571 }
572 
573 int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
574 {
575         int ret;
576 
577         /* No CPUs can come up or down during this. */
578         get_online_cpus();
579         ret = __stop_machine(fn, data, cpus);
580         put_online_cpus();
581         return ret;
582 }
583 EXPORT_SYMBOL_GPL(stop_machine);
584 
585 /**
586  * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
587  * @fn: the function to run
588  * @data: the data ptr for the @fn()
589  * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
590  *
591  * This is identical to stop_machine() but can be called from a CPU which
592  * is not active.  The local CPU is in the process of hotplug (so no other
593  * CPU hotplug can start) and not marked active and doesn't have enough
594  * context to sleep.
595  *
596  * This function provides stop_machine() functionality for such state by
597  * using busy-wait for synchronization and executing @fn directly for local
598  * CPU.
599  *
600  * CONTEXT:
601  * Local CPU is inactive.  Temporarily stops all active CPUs.
602  *
603  * RETURNS:
604  * 0 if all executions of @fn returned 0, any non zero return value if any
605  * returned non zero.
606  */
607 int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
608                                   const struct cpumask *cpus)
609 {
610         struct multi_stop_data msdata = { .fn = fn, .data = data,
611                                             .active_cpus = cpus };
612         struct cpu_stop_done done;
613         int ret;
614 
615         /* Local CPU must be inactive and CPU hotplug in progress. */
616         BUG_ON(cpu_active(raw_smp_processor_id()));
617         msdata.num_threads = num_active_cpus() + 1;     /* +1 for local */
618 
619         /* No proper task established and can't sleep - busy wait for lock. */
620         while (!mutex_trylock(&stop_cpus_mutex))
621                 cpu_relax();
622 
623         /* Schedule work on other CPUs and execute directly for local CPU */
624         set_state(&msdata, MULTI_STOP_PREPARE);
625         cpu_stop_init_done(&done, num_active_cpus());
626         queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
627                              &done);
628         ret = multi_cpu_stop(&msdata);
629 
630         /* Busy wait for completion. */
631         while (!completion_done(&done.completion))
632                 cpu_relax();
633 
634         mutex_unlock(&stop_cpus_mutex);
635         return ret ?: done.ret;
636 }
637 

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