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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 
 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         bool                    executed;       /* actually executed? */
 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         spinlock_t              lock;
 39         bool                    enabled;        /* is this stopper enabled? */
 40         struct list_head        works;          /* list of pending works */
 41 };
 42 
 43 static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
 44 static DEFINE_PER_CPU(struct task_struct *, cpu_stopper_task);
 45 static bool stop_machine_initialized = false;
 46 
 47 /*
 48  * Avoids a race between stop_two_cpus and global stop_cpus, where
 49  * the stoppers could get queued up in reverse order, leading to
 50  * system deadlock. Using an lglock means stop_two_cpus remains
 51  * relatively cheap.
 52  */
 53 DEFINE_STATIC_LGLOCK(stop_cpus_lock);
 54 
 55 static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
 56 {
 57         memset(done, 0, sizeof(*done));
 58         atomic_set(&done->nr_todo, nr_todo);
 59         init_completion(&done->completion);
 60 }
 61 
 62 /* signal completion unless @done is NULL */
 63 static void cpu_stop_signal_done(struct cpu_stop_done *done, bool executed)
 64 {
 65         if (done) {
 66                 if (executed)
 67                         done->executed = true;
 68                 if (atomic_dec_and_test(&done->nr_todo))
 69                         complete(&done->completion);
 70         }
 71 }
 72 
 73 /* queue @work to @stopper.  if offline, @work is completed immediately */
 74 static void cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
 75 {
 76         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 77         struct task_struct *p = per_cpu(cpu_stopper_task, cpu);
 78 
 79         unsigned long flags;
 80 
 81         spin_lock_irqsave(&stopper->lock, flags);
 82 
 83         if (stopper->enabled) {
 84                 list_add_tail(&work->list, &stopper->works);
 85                 wake_up_process(p);
 86         } else
 87                 cpu_stop_signal_done(work->done, false);
 88 
 89         spin_unlock_irqrestore(&stopper->lock, flags);
 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         cpu_stop_queue_work(cpu, &work);
123         wait_for_completion(&done.completion);
124         return done.executed ? done.ret : -ENOENT;
125 }
126 
127 /* This controls the threads on each CPU. */
128 enum multi_stop_state {
129         /* Dummy starting state for thread. */
130         MULTI_STOP_NONE,
131         /* Awaiting everyone to be scheduled. */
132         MULTI_STOP_PREPARE,
133         /* Disable interrupts. */
134         MULTI_STOP_DISABLE_IRQ,
135         /* Run the function */
136         MULTI_STOP_RUN,
137         /* Exit */
138         MULTI_STOP_EXIT,
139 };
140 
141 struct multi_stop_data {
142         int                     (*fn)(void *);
143         void                    *data;
144         /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
145         unsigned int            num_threads;
146         const struct cpumask    *active_cpus;
147 
148         enum multi_stop_state   state;
149         atomic_t                thread_ack;
150 };
151 
152 static void set_state(struct multi_stop_data *msdata,
153                       enum multi_stop_state newstate)
154 {
155         /* Reset ack counter. */
156         atomic_set(&msdata->thread_ack, msdata->num_threads);
157         smp_wmb();
158         msdata->state = newstate;
159 }
160 
161 /* Last one to ack a state moves to the next state. */
162 static void ack_state(struct multi_stop_data *msdata)
163 {
164         if (atomic_dec_and_test(&msdata->thread_ack))
165                 set_state(msdata, msdata->state + 1);
166 }
167 
168 /* This is the cpu_stop function which stops the CPU. */
169 static int multi_cpu_stop(void *data)
170 {
171         struct multi_stop_data *msdata = data;
172         enum multi_stop_state curstate = MULTI_STOP_NONE;
173         int cpu = smp_processor_id(), err = 0;
174         unsigned long flags;
175         bool is_active;
176 
177         /*
178          * When called from stop_machine_from_inactive_cpu(), irq might
179          * already be disabled.  Save the state and restore it on exit.
180          */
181         local_save_flags(flags);
182 
183         if (!msdata->active_cpus)
184                 is_active = cpu == cpumask_first(cpu_online_mask);
185         else
186                 is_active = cpumask_test_cpu(cpu, msdata->active_cpus);
187 
188         /* Simple state machine */
189         do {
190                 /* Chill out and ensure we re-read multi_stop_state. */
191                 cpu_relax();
192                 if (msdata->state != curstate) {
193                         curstate = msdata->state;
194                         switch (curstate) {
195                         case MULTI_STOP_DISABLE_IRQ:
196                                 local_irq_disable();
197                                 hard_irq_disable();
198                                 break;
199                         case MULTI_STOP_RUN:
200                                 if (is_active)
201                                         err = msdata->fn(msdata->data);
202                                 break;
203                         default:
204                                 break;
205                         }
206                         ack_state(msdata);
207                 }
208         } while (curstate != MULTI_STOP_EXIT);
209 
210         local_irq_restore(flags);
211         return err;
212 }
213 
214 struct irq_cpu_stop_queue_work_info {
215         int cpu1;
216         int cpu2;
217         struct cpu_stop_work *work1;
218         struct cpu_stop_work *work2;
219 };
220 
221 /*
222  * This function is always run with irqs and preemption disabled.
223  * This guarantees that both work1 and work2 get queued, before
224  * our local migrate thread gets the chance to preempt us.
225  */
226 static void irq_cpu_stop_queue_work(void *arg)
227 {
228         struct irq_cpu_stop_queue_work_info *info = arg;
229         cpu_stop_queue_work(info->cpu1, info->work1);
230         cpu_stop_queue_work(info->cpu2, info->work2);
231 }
232 
233 /**
234  * stop_two_cpus - stops two cpus
235  * @cpu1: the cpu to stop
236  * @cpu2: the other cpu to stop
237  * @fn: function to execute
238  * @arg: argument to @fn
239  *
240  * Stops both the current and specified CPU and runs @fn on one of them.
241  *
242  * returns when both are completed.
243  */
244 int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
245 {
246         struct cpu_stop_done done;
247         struct cpu_stop_work work1, work2;
248         struct irq_cpu_stop_queue_work_info call_args;
249         struct multi_stop_data msdata;
250 
251         preempt_disable();
252         msdata = (struct multi_stop_data){
253                 .fn = fn,
254                 .data = arg,
255                 .num_threads = 2,
256                 .active_cpus = cpumask_of(cpu1),
257         };
258 
259         work1 = work2 = (struct cpu_stop_work){
260                 .fn = multi_cpu_stop,
261                 .arg = &msdata,
262                 .done = &done
263         };
264 
265         call_args = (struct irq_cpu_stop_queue_work_info){
266                 .cpu1 = cpu1,
267                 .cpu2 = cpu2,
268                 .work1 = &work1,
269                 .work2 = &work2,
270         };
271 
272         cpu_stop_init_done(&done, 2);
273         set_state(&msdata, MULTI_STOP_PREPARE);
274 
275         /*
276          * If we observe both CPUs active we know _cpu_down() cannot yet have
277          * queued its stop_machine works and therefore ours will get executed
278          * first. Or its not either one of our CPUs that's getting unplugged,
279          * in which case we don't care.
280          *
281          * This relies on the stopper workqueues to be FIFO.
282          */
283         if (!cpu_active(cpu1) || !cpu_active(cpu2)) {
284                 preempt_enable();
285                 return -ENOENT;
286         }
287 
288         lg_local_lock(&stop_cpus_lock);
289         /*
290          * Queuing needs to be done by the lowest numbered CPU, to ensure
291          * that works are always queued in the same order on every CPU.
292          * This prevents deadlocks.
293          */
294         smp_call_function_single(min(cpu1, cpu2),
295                                  &irq_cpu_stop_queue_work,
296                                  &call_args, 1);
297         lg_local_unlock(&stop_cpus_lock);
298         preempt_enable();
299 
300         wait_for_completion(&done.completion);
301 
302         return done.executed ? done.ret : -ENOENT;
303 }
304 
305 /**
306  * stop_one_cpu_nowait - stop a cpu but don't wait for completion
307  * @cpu: cpu to stop
308  * @fn: function to execute
309  * @arg: argument to @fn
310  * @work_buf: pointer to cpu_stop_work structure
311  *
312  * Similar to stop_one_cpu() but doesn't wait for completion.  The
313  * caller is responsible for ensuring @work_buf is currently unused
314  * and will remain untouched until stopper starts executing @fn.
315  *
316  * CONTEXT:
317  * Don't care.
318  */
319 void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
320                         struct cpu_stop_work *work_buf)
321 {
322         *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
323         cpu_stop_queue_work(cpu, work_buf);
324 }
325 
326 /* static data for stop_cpus */
327 static DEFINE_MUTEX(stop_cpus_mutex);
328 static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work);
329 
330 static void queue_stop_cpus_work(const struct cpumask *cpumask,
331                                  cpu_stop_fn_t fn, void *arg,
332                                  struct cpu_stop_done *done)
333 {
334         struct cpu_stop_work *work;
335         unsigned int cpu;
336 
337         /* initialize works and done */
338         for_each_cpu(cpu, cpumask) {
339                 work = &per_cpu(stop_cpus_work, cpu);
340                 work->fn = fn;
341                 work->arg = arg;
342                 work->done = done;
343         }
344 
345         /*
346          * Disable preemption while queueing to avoid getting
347          * preempted by a stopper which might wait for other stoppers
348          * to enter @fn which can lead to deadlock.
349          */
350         lg_global_lock(&stop_cpus_lock);
351         for_each_cpu(cpu, cpumask)
352                 cpu_stop_queue_work(cpu, &per_cpu(stop_cpus_work, cpu));
353         lg_global_unlock(&stop_cpus_lock);
354 }
355 
356 static int __stop_cpus(const struct cpumask *cpumask,
357                        cpu_stop_fn_t fn, void *arg)
358 {
359         struct cpu_stop_done done;
360 
361         cpu_stop_init_done(&done, cpumask_weight(cpumask));
362         queue_stop_cpus_work(cpumask, fn, arg, &done);
363         wait_for_completion(&done.completion);
364         return done.executed ? done.ret : -ENOENT;
365 }
366 
367 /**
368  * stop_cpus - stop multiple cpus
369  * @cpumask: cpus to stop
370  * @fn: function to execute
371  * @arg: argument to @fn
372  *
373  * Execute @fn(@arg) on online cpus in @cpumask.  On each target cpu,
374  * @fn is run in a process context with the highest priority
375  * preempting any task on the cpu and monopolizing it.  This function
376  * returns after all executions are complete.
377  *
378  * This function doesn't guarantee the cpus in @cpumask stay online
379  * till @fn completes.  If some cpus go down in the middle, execution
380  * on the cpu may happen partially or fully on different cpus.  @fn
381  * should either be ready for that or the caller should ensure that
382  * the cpus stay online until this function completes.
383  *
384  * All stop_cpus() calls are serialized making it safe for @fn to wait
385  * for all cpus to start executing it.
386  *
387  * CONTEXT:
388  * Might sleep.
389  *
390  * RETURNS:
391  * -ENOENT if @fn(@arg) was not executed at all because all cpus in
392  * @cpumask were offline; otherwise, 0 if all executions of @fn
393  * returned 0, any non zero return value if any returned non zero.
394  */
395 int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
396 {
397         int ret;
398 
399         /* static works are used, process one request at a time */
400         mutex_lock(&stop_cpus_mutex);
401         ret = __stop_cpus(cpumask, fn, arg);
402         mutex_unlock(&stop_cpus_mutex);
403         return ret;
404 }
405 
406 /**
407  * try_stop_cpus - try to stop multiple cpus
408  * @cpumask: cpus to stop
409  * @fn: function to execute
410  * @arg: argument to @fn
411  *
412  * Identical to stop_cpus() except that it fails with -EAGAIN if
413  * someone else is already using the facility.
414  *
415  * CONTEXT:
416  * Might sleep.
417  *
418  * RETURNS:
419  * -EAGAIN if someone else is already stopping cpus, -ENOENT if
420  * @fn(@arg) was not executed at all because all cpus in @cpumask were
421  * offline; otherwise, 0 if all executions of @fn returned 0, any non
422  * zero return value if any returned non zero.
423  */
424 int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
425 {
426         int ret;
427 
428         /* static works are used, process one request at a time */
429         if (!mutex_trylock(&stop_cpus_mutex))
430                 return -EAGAIN;
431         ret = __stop_cpus(cpumask, fn, arg);
432         mutex_unlock(&stop_cpus_mutex);
433         return ret;
434 }
435 
436 static int cpu_stop_should_run(unsigned int cpu)
437 {
438         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
439         unsigned long flags;
440         int run;
441 
442         spin_lock_irqsave(&stopper->lock, flags);
443         run = !list_empty(&stopper->works);
444         spin_unlock_irqrestore(&stopper->lock, flags);
445         return run;
446 }
447 
448 static void cpu_stopper_thread(unsigned int cpu)
449 {
450         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
451         struct cpu_stop_work *work;
452         int ret;
453 
454 repeat:
455         work = NULL;
456         spin_lock_irq(&stopper->lock);
457         if (!list_empty(&stopper->works)) {
458                 work = list_first_entry(&stopper->works,
459                                         struct cpu_stop_work, list);
460                 list_del_init(&work->list);
461         }
462         spin_unlock_irq(&stopper->lock);
463 
464         if (work) {
465                 cpu_stop_fn_t fn = work->fn;
466                 void *arg = work->arg;
467                 struct cpu_stop_done *done = work->done;
468                 char ksym_buf[KSYM_NAME_LEN] __maybe_unused;
469 
470                 /* cpu stop callbacks are not allowed to sleep */
471                 preempt_disable();
472 
473                 ret = fn(arg);
474                 if (ret)
475                         done->ret = ret;
476 
477                 /* restore preemption and check it's still balanced */
478                 preempt_enable();
479                 WARN_ONCE(preempt_count(),
480                           "cpu_stop: %s(%p) leaked preempt count\n",
481                           kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
482                                           ksym_buf), arg);
483 
484                 cpu_stop_signal_done(done, true);
485                 goto repeat;
486         }
487 }
488 
489 extern void sched_set_stop_task(int cpu, struct task_struct *stop);
490 
491 static void cpu_stop_create(unsigned int cpu)
492 {
493         sched_set_stop_task(cpu, per_cpu(cpu_stopper_task, cpu));
494 }
495 
496 static void cpu_stop_park(unsigned int cpu)
497 {
498         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
499         struct cpu_stop_work *work;
500         unsigned long flags;
501 
502         /* drain remaining works */
503         spin_lock_irqsave(&stopper->lock, flags);
504         list_for_each_entry(work, &stopper->works, list)
505                 cpu_stop_signal_done(work->done, false);
506         stopper->enabled = false;
507         spin_unlock_irqrestore(&stopper->lock, flags);
508 }
509 
510 static void cpu_stop_unpark(unsigned int cpu)
511 {
512         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
513 
514         spin_lock_irq(&stopper->lock);
515         stopper->enabled = true;
516         spin_unlock_irq(&stopper->lock);
517 }
518 
519 static struct smp_hotplug_thread cpu_stop_threads = {
520         .store                  = &cpu_stopper_task,
521         .thread_should_run      = cpu_stop_should_run,
522         .thread_fn              = cpu_stopper_thread,
523         .thread_comm            = "migration/%u",
524         .create                 = cpu_stop_create,
525         .setup                  = cpu_stop_unpark,
526         .park                   = cpu_stop_park,
527         .pre_unpark             = cpu_stop_unpark,
528         .selfparking            = true,
529 };
530 
531 static int __init cpu_stop_init(void)
532 {
533         unsigned int cpu;
534 
535         for_each_possible_cpu(cpu) {
536                 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
537 
538                 spin_lock_init(&stopper->lock);
539                 INIT_LIST_HEAD(&stopper->works);
540         }
541 
542         BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
543         stop_machine_initialized = true;
544         return 0;
545 }
546 early_initcall(cpu_stop_init);
547 
548 #ifdef CONFIG_STOP_MACHINE
549 
550 int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
551 {
552         struct multi_stop_data msdata = {
553                 .fn = fn,
554                 .data = data,
555                 .num_threads = num_online_cpus(),
556                 .active_cpus = cpus,
557         };
558 
559         if (!stop_machine_initialized) {
560                 /*
561                  * Handle the case where stop_machine() is called
562                  * early in boot before stop_machine() has been
563                  * initialized.
564                  */
565                 unsigned long flags;
566                 int ret;
567 
568                 WARN_ON_ONCE(msdata.num_threads != 1);
569 
570                 local_irq_save(flags);
571                 hard_irq_disable();
572                 ret = (*fn)(data);
573                 local_irq_restore(flags);
574 
575                 return ret;
576         }
577 
578         /* Set the initial state and stop all online cpus. */
579         set_state(&msdata, MULTI_STOP_PREPARE);
580         return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
581 }
582 
583 int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
584 {
585         int ret;
586 
587         /* No CPUs can come up or down during this. */
588         get_online_cpus();
589         ret = __stop_machine(fn, data, cpus);
590         put_online_cpus();
591         return ret;
592 }
593 EXPORT_SYMBOL_GPL(stop_machine);
594 
595 /**
596  * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
597  * @fn: the function to run
598  * @data: the data ptr for the @fn()
599  * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
600  *
601  * This is identical to stop_machine() but can be called from a CPU which
602  * is not active.  The local CPU is in the process of hotplug (so no other
603  * CPU hotplug can start) and not marked active and doesn't have enough
604  * context to sleep.
605  *
606  * This function provides stop_machine() functionality for such state by
607  * using busy-wait for synchronization and executing @fn directly for local
608  * CPU.
609  *
610  * CONTEXT:
611  * Local CPU is inactive.  Temporarily stops all active CPUs.
612  *
613  * RETURNS:
614  * 0 if all executions of @fn returned 0, any non zero return value if any
615  * returned non zero.
616  */
617 int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
618                                   const struct cpumask *cpus)
619 {
620         struct multi_stop_data msdata = { .fn = fn, .data = data,
621                                             .active_cpus = cpus };
622         struct cpu_stop_done done;
623         int ret;
624 
625         /* Local CPU must be inactive and CPU hotplug in progress. */
626         BUG_ON(cpu_active(raw_smp_processor_id()));
627         msdata.num_threads = num_active_cpus() + 1;     /* +1 for local */
628 
629         /* No proper task established and can't sleep - busy wait for lock. */
630         while (!mutex_trylock(&stop_cpus_mutex))
631                 cpu_relax();
632 
633         /* Schedule work on other CPUs and execute directly for local CPU */
634         set_state(&msdata, MULTI_STOP_PREPARE);
635         cpu_stop_init_done(&done, num_active_cpus());
636         queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
637                              &done);
638         ret = multi_cpu_stop(&msdata);
639 
640         /* Busy wait for completion. */
641         while (!completion_done(&done.completion))
642                 cpu_relax();
643 
644         mutex_unlock(&stop_cpus_mutex);
645         return ret ?: done.ret;
646 }
647 
648 #endif  /* CONFIG_STOP_MACHINE */
649 

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