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TOMOYO Linux Cross Reference
Linux/kernel/stop_machine.c

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  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 #include <linux/sched/wake_q.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 /* static data for stop_cpus */
 51 static DEFINE_MUTEX(stop_cpus_mutex);
 52 static bool stop_cpus_in_progress;
 53 
 54 static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
 55 {
 56         memset(done, 0, sizeof(*done));
 57         atomic_set(&done->nr_todo, nr_todo);
 58         init_completion(&done->completion);
 59 }
 60 
 61 /* signal completion unless @done is NULL */
 62 static void cpu_stop_signal_done(struct cpu_stop_done *done)
 63 {
 64         if (atomic_dec_and_test(&done->nr_todo))
 65                 complete(&done->completion);
 66 }
 67 
 68 static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
 69                                         struct cpu_stop_work *work,
 70                                         struct wake_q_head *wakeq)
 71 {
 72         list_add_tail(&work->list, &stopper->works);
 73         wake_q_add(wakeq, stopper->thread);
 74 }
 75 
 76 /* queue @work to @stopper.  if offline, @work is completed immediately */
 77 static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
 78 {
 79         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 80         DEFINE_WAKE_Q(wakeq);
 81         unsigned long flags;
 82         bool enabled;
 83 
 84         spin_lock_irqsave(&stopper->lock, flags);
 85         enabled = stopper->enabled;
 86         if (enabled)
 87                 __cpu_stop_queue_work(stopper, work, &wakeq);
 88         else if (work->done)
 89                 cpu_stop_signal_done(work->done);
 90         spin_unlock_irqrestore(&stopper->lock, flags);
 91 
 92         wake_up_q(&wakeq);
 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         /*
130          * In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup
131          * cycle by doing a preemption:
132          */
133         cond_resched();
134         wait_for_completion(&done.completion);
135         return done.ret;
136 }
137 
138 /* This controls the threads on each CPU. */
139 enum multi_stop_state {
140         /* Dummy starting state for thread. */
141         MULTI_STOP_NONE,
142         /* Awaiting everyone to be scheduled. */
143         MULTI_STOP_PREPARE,
144         /* Disable interrupts. */
145         MULTI_STOP_DISABLE_IRQ,
146         /* Run the function */
147         MULTI_STOP_RUN,
148         /* Exit */
149         MULTI_STOP_EXIT,
150 };
151 
152 struct multi_stop_data {
153         cpu_stop_fn_t           fn;
154         void                    *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;
158 
159         enum multi_stop_state   state;
160         atomic_t                thread_ack;
161 };
162 
163 static void set_state(struct multi_stop_data *msdata,
164                       enum multi_stop_state newstate)
165 {
166         /* Reset ack counter. */
167         atomic_set(&msdata->thread_ack, msdata->num_threads);
168         smp_wmb();
169         msdata->state = newstate;
170 }
171 
172 /* Last one to ack a state moves to the next state. */
173 static void ack_state(struct multi_stop_data *msdata)
174 {
175         if (atomic_dec_and_test(&msdata->thread_ack))
176                 set_state(msdata, msdata->state + 1);
177 }
178 
179 /* This is the cpu_stop function which stops the CPU. */
180 static int multi_cpu_stop(void *data)
181 {
182         struct multi_stop_data *msdata = data;
183         enum multi_stop_state curstate = MULTI_STOP_NONE;
184         int cpu = smp_processor_id(), err = 0;
185         unsigned long flags;
186         bool is_active;
187 
188         /*
189          * When called from stop_machine_from_inactive_cpu(), irq might
190          * already be disabled.  Save the state and restore it on exit.
191          */
192         local_save_flags(flags);
193 
194         if (!msdata->active_cpus)
195                 is_active = cpu == cpumask_first(cpu_online_mask);
196         else
197                 is_active = cpumask_test_cpu(cpu, msdata->active_cpus);
198 
199         /* Simple state machine */
200         do {
201                 /* Chill out and ensure we re-read multi_stop_state. */
202                 cpu_relax_yield();
203                 if (msdata->state != curstate) {
204                         curstate = msdata->state;
205                         switch (curstate) {
206                         case MULTI_STOP_DISABLE_IRQ:
207                                 local_irq_disable();
208                                 hard_irq_disable();
209                                 break;
210                         case MULTI_STOP_RUN:
211                                 if (is_active)
212                                         err = msdata->fn(msdata->data);
213                                 break;
214                         default:
215                                 break;
216                         }
217                         ack_state(msdata);
218                 } else if (curstate > MULTI_STOP_PREPARE) {
219                         /*
220                          * At this stage all other CPUs we depend on must spin
221                          * in the same loop. Any reason for hard-lockup should
222                          * be detected and reported on their side.
223                          */
224                         touch_nmi_watchdog();
225                 }
226         } while (curstate != MULTI_STOP_EXIT);
227 
228         local_irq_restore(flags);
229         return err;
230 }
231 
232 static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
233                                     int cpu2, struct cpu_stop_work *work2)
234 {
235         struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
236         struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
237         DEFINE_WAKE_Q(wakeq);
238         int err;
239 retry:
240         spin_lock_irq(&stopper1->lock);
241         spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
242 
243         err = -ENOENT;
244         if (!stopper1->enabled || !stopper2->enabled)
245                 goto unlock;
246         /*
247          * Ensure that if we race with __stop_cpus() the stoppers won't get
248          * queued up in reverse order leading to system deadlock.
249          *
250          * We can't miss stop_cpus_in_progress if queue_stop_cpus_work() has
251          * queued a work on cpu1 but not on cpu2, we hold both locks.
252          *
253          * It can be falsely true but it is safe to spin until it is cleared,
254          * queue_stop_cpus_work() does everything under preempt_disable().
255          */
256         err = -EDEADLK;
257         if (unlikely(stop_cpus_in_progress))
258                         goto unlock;
259 
260         err = 0;
261         __cpu_stop_queue_work(stopper1, work1, &wakeq);
262         __cpu_stop_queue_work(stopper2, work2, &wakeq);
263 unlock:
264         spin_unlock(&stopper2->lock);
265         spin_unlock_irq(&stopper1->lock);
266 
267         if (unlikely(err == -EDEADLK)) {
268                 while (stop_cpus_in_progress)
269                         cpu_relax();
270                 goto retry;
271         }
272 
273         wake_up_q(&wakeq);
274 
275         return err;
276 }
277 /**
278  * stop_two_cpus - stops two cpus
279  * @cpu1: the cpu to stop
280  * @cpu2: the other cpu to stop
281  * @fn: function to execute
282  * @arg: argument to @fn
283  *
284  * Stops both the current and specified CPU and runs @fn on one of them.
285  *
286  * returns when both are completed.
287  */
288 int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
289 {
290         struct cpu_stop_done done;
291         struct cpu_stop_work work1, work2;
292         struct multi_stop_data msdata;
293 
294         msdata = (struct multi_stop_data){
295                 .fn = fn,
296                 .data = arg,
297                 .num_threads = 2,
298                 .active_cpus = cpumask_of(cpu1),
299         };
300 
301         work1 = work2 = (struct cpu_stop_work){
302                 .fn = multi_cpu_stop,
303                 .arg = &msdata,
304                 .done = &done
305         };
306 
307         cpu_stop_init_done(&done, 2);
308         set_state(&msdata, MULTI_STOP_PREPARE);
309 
310         if (cpu1 > cpu2)
311                 swap(cpu1, cpu2);
312         if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))
313                 return -ENOENT;
314 
315         wait_for_completion(&done.completion);
316         return done.ret;
317 }
318 
319 /**
320  * stop_one_cpu_nowait - stop a cpu but don't wait for completion
321  * @cpu: cpu to stop
322  * @fn: function to execute
323  * @arg: argument to @fn
324  * @work_buf: pointer to cpu_stop_work structure
325  *
326  * Similar to stop_one_cpu() but doesn't wait for completion.  The
327  * caller is responsible for ensuring @work_buf is currently unused
328  * and will remain untouched until stopper starts executing @fn.
329  *
330  * CONTEXT:
331  * Don't care.
332  *
333  * RETURNS:
334  * true if cpu_stop_work was queued successfully and @fn will be called,
335  * false otherwise.
336  */
337 bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
338                         struct cpu_stop_work *work_buf)
339 {
340         *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
341         return cpu_stop_queue_work(cpu, work_buf);
342 }
343 
344 static bool queue_stop_cpus_work(const struct cpumask *cpumask,
345                                  cpu_stop_fn_t fn, void *arg,
346                                  struct cpu_stop_done *done)
347 {
348         struct cpu_stop_work *work;
349         unsigned int cpu;
350         bool queued = false;
351 
352         /*
353          * Disable preemption while queueing to avoid getting
354          * preempted by a stopper which might wait for other stoppers
355          * to enter @fn which can lead to deadlock.
356          */
357         preempt_disable();
358         stop_cpus_in_progress = true;
359         for_each_cpu(cpu, cpumask) {
360                 work = &per_cpu(cpu_stopper.stop_work, cpu);
361                 work->fn = fn;
362                 work->arg = arg;
363                 work->done = done;
364                 if (cpu_stop_queue_work(cpu, work))
365                         queued = true;
366         }
367         stop_cpus_in_progress = false;
368         preempt_enable();
369 
370         return queued;
371 }
372 
373 static int __stop_cpus(const struct cpumask *cpumask,
374                        cpu_stop_fn_t fn, void *arg)
375 {
376         struct cpu_stop_done done;
377 
378         cpu_stop_init_done(&done, cpumask_weight(cpumask));
379         if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
380                 return -ENOENT;
381         wait_for_completion(&done.completion);
382         return done.ret;
383 }
384 
385 /**
386  * stop_cpus - stop multiple cpus
387  * @cpumask: cpus to stop
388  * @fn: function to execute
389  * @arg: argument to @fn
390  *
391  * Execute @fn(@arg) on online cpus in @cpumask.  On each target cpu,
392  * @fn is run in a process context with the highest priority
393  * preempting any task on the cpu and monopolizing it.  This function
394  * returns after all executions are complete.
395  *
396  * This function doesn't guarantee the cpus in @cpumask stay online
397  * till @fn completes.  If some cpus go down in the middle, execution
398  * on the cpu may happen partially or fully on different cpus.  @fn
399  * should either be ready for that or the caller should ensure that
400  * the cpus stay online until this function completes.
401  *
402  * All stop_cpus() calls are serialized making it safe for @fn to wait
403  * for all cpus to start executing it.
404  *
405  * CONTEXT:
406  * Might sleep.
407  *
408  * RETURNS:
409  * -ENOENT if @fn(@arg) was not executed at all because all cpus in
410  * @cpumask were offline; otherwise, 0 if all executions of @fn
411  * returned 0, any non zero return value if any returned non zero.
412  */
413 int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
414 {
415         int ret;
416 
417         /* static works are used, process one request at a time */
418         mutex_lock(&stop_cpus_mutex);
419         ret = __stop_cpus(cpumask, fn, arg);
420         mutex_unlock(&stop_cpus_mutex);
421         return ret;
422 }
423 
424 /**
425  * try_stop_cpus - try to stop multiple cpus
426  * @cpumask: cpus to stop
427  * @fn: function to execute
428  * @arg: argument to @fn
429  *
430  * Identical to stop_cpus() except that it fails with -EAGAIN if
431  * someone else is already using the facility.
432  *
433  * CONTEXT:
434  * Might sleep.
435  *
436  * RETURNS:
437  * -EAGAIN if someone else is already stopping cpus, -ENOENT if
438  * @fn(@arg) was not executed at all because all cpus in @cpumask were
439  * offline; otherwise, 0 if all executions of @fn returned 0, any non
440  * zero return value if any returned non zero.
441  */
442 int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
443 {
444         int ret;
445 
446         /* static works are used, process one request at a time */
447         if (!mutex_trylock(&stop_cpus_mutex))
448                 return -EAGAIN;
449         ret = __stop_cpus(cpumask, fn, arg);
450         mutex_unlock(&stop_cpus_mutex);
451         return ret;
452 }
453 
454 static int cpu_stop_should_run(unsigned int cpu)
455 {
456         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
457         unsigned long flags;
458         int run;
459 
460         spin_lock_irqsave(&stopper->lock, flags);
461         run = !list_empty(&stopper->works);
462         spin_unlock_irqrestore(&stopper->lock, flags);
463         return run;
464 }
465 
466 static void cpu_stopper_thread(unsigned int cpu)
467 {
468         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
469         struct cpu_stop_work *work;
470 
471 repeat:
472         work = NULL;
473         spin_lock_irq(&stopper->lock);
474         if (!list_empty(&stopper->works)) {
475                 work = list_first_entry(&stopper->works,
476                                         struct cpu_stop_work, list);
477                 list_del_init(&work->list);
478         }
479         spin_unlock_irq(&stopper->lock);
480 
481         if (work) {
482                 cpu_stop_fn_t fn = work->fn;
483                 void *arg = work->arg;
484                 struct cpu_stop_done *done = work->done;
485                 int ret;
486 
487                 /* cpu stop callbacks must not sleep, make in_atomic() == T */
488                 preempt_count_inc();
489                 ret = fn(arg);
490                 if (done) {
491                         if (ret)
492                                 done->ret = ret;
493                         cpu_stop_signal_done(done);
494                 }
495                 preempt_count_dec();
496                 WARN_ONCE(preempt_count(),
497                           "cpu_stop: %pf(%p) leaked preempt count\n", fn, arg);
498                 goto repeat;
499         }
500 }
501 
502 void stop_machine_park(int cpu)
503 {
504         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
505         /*
506          * Lockless. cpu_stopper_thread() will take stopper->lock and flush
507          * the pending works before it parks, until then it is fine to queue
508          * the new works.
509          */
510         stopper->enabled = false;
511         kthread_park(stopper->thread);
512 }
513 
514 extern void sched_set_stop_task(int cpu, struct task_struct *stop);
515 
516 static void cpu_stop_create(unsigned int cpu)
517 {
518         sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
519 }
520 
521 static void cpu_stop_park(unsigned int cpu)
522 {
523         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
524 
525         WARN_ON(!list_empty(&stopper->works));
526 }
527 
528 void stop_machine_unpark(int cpu)
529 {
530         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
531 
532         stopper->enabled = true;
533         kthread_unpark(stopper->thread);
534 }
535 
536 static struct smp_hotplug_thread cpu_stop_threads = {
537         .store                  = &cpu_stopper.thread,
538         .thread_should_run      = cpu_stop_should_run,
539         .thread_fn              = cpu_stopper_thread,
540         .thread_comm            = "migration/%u",
541         .create                 = cpu_stop_create,
542         .park                   = cpu_stop_park,
543         .selfparking            = true,
544 };
545 
546 static int __init cpu_stop_init(void)
547 {
548         unsigned int cpu;
549 
550         for_each_possible_cpu(cpu) {
551                 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
552 
553                 spin_lock_init(&stopper->lock);
554                 INIT_LIST_HEAD(&stopper->works);
555         }
556 
557         BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
558         stop_machine_unpark(raw_smp_processor_id());
559         stop_machine_initialized = true;
560         return 0;
561 }
562 early_initcall(cpu_stop_init);
563 
564 int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data,
565                             const struct cpumask *cpus)
566 {
567         struct multi_stop_data msdata = {
568                 .fn = fn,
569                 .data = data,
570                 .num_threads = num_online_cpus(),
571                 .active_cpus = cpus,
572         };
573 
574         lockdep_assert_cpus_held();
575 
576         if (!stop_machine_initialized) {
577                 /*
578                  * Handle the case where stop_machine() is called
579                  * early in boot before stop_machine() has been
580                  * initialized.
581                  */
582                 unsigned long flags;
583                 int ret;
584 
585                 WARN_ON_ONCE(msdata.num_threads != 1);
586 
587                 local_irq_save(flags);
588                 hard_irq_disable();
589                 ret = (*fn)(data);
590                 local_irq_restore(flags);
591 
592                 return ret;
593         }
594 
595         /* Set the initial state and stop all online cpus. */
596         set_state(&msdata, MULTI_STOP_PREPARE);
597         return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
598 }
599 
600 int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
601 {
602         int ret;
603 
604         /* No CPUs can come up or down during this. */
605         cpus_read_lock();
606         ret = stop_machine_cpuslocked(fn, data, cpus);
607         cpus_read_unlock();
608         return ret;
609 }
610 EXPORT_SYMBOL_GPL(stop_machine);
611 
612 /**
613  * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
614  * @fn: the function to run
615  * @data: the data ptr for the @fn()
616  * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
617  *
618  * This is identical to stop_machine() but can be called from a CPU which
619  * is not active.  The local CPU is in the process of hotplug (so no other
620  * CPU hotplug can start) and not marked active and doesn't have enough
621  * context to sleep.
622  *
623  * This function provides stop_machine() functionality for such state by
624  * using busy-wait for synchronization and executing @fn directly for local
625  * CPU.
626  *
627  * CONTEXT:
628  * Local CPU is inactive.  Temporarily stops all active CPUs.
629  *
630  * RETURNS:
631  * 0 if all executions of @fn returned 0, any non zero return value if any
632  * returned non zero.
633  */
634 int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
635                                   const struct cpumask *cpus)
636 {
637         struct multi_stop_data msdata = { .fn = fn, .data = data,
638                                             .active_cpus = cpus };
639         struct cpu_stop_done done;
640         int ret;
641 
642         /* Local CPU must be inactive and CPU hotplug in progress. */
643         BUG_ON(cpu_active(raw_smp_processor_id()));
644         msdata.num_threads = num_active_cpus() + 1;     /* +1 for local */
645 
646         /* No proper task established and can't sleep - busy wait for lock. */
647         while (!mutex_trylock(&stop_cpus_mutex))
648                 cpu_relax();
649 
650         /* Schedule work on other CPUs and execute directly for local CPU */
651         set_state(&msdata, MULTI_STOP_PREPARE);
652         cpu_stop_init_done(&done, num_active_cpus());
653         queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
654                              &done);
655         ret = multi_cpu_stop(&msdata);
656 
657         /* Busy wait for completion. */
658         while (!completion_done(&done.completion))
659                 cpu_relax();
660 
661         mutex_unlock(&stop_cpus_mutex);
662         return ret ?: done.ret;
663 }
664 

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