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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         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, bool executed)
 67 {
 68         if (done) {
 69                 if (executed)
 70                         done->executed = true;
 71                 if (atomic_dec_and_test(&done->nr_todo))
 72                         complete(&done->completion);
 73         }
 74 }
 75 
 76 static void __cpu_stop_queue_work(struct cpu_stopper *stopper,
 77                                         struct cpu_stop_work *work)
 78 {
 79         list_add_tail(&work->list, &stopper->works);
 80         wake_up_process(stopper->thread);
 81 }
 82 
 83 /* queue @work to @stopper.  if offline, @work is completed immediately */
 84 static void cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
 85 {
 86         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 87         unsigned long flags;
 88 
 89         spin_lock_irqsave(&stopper->lock, flags);
 90         if (stopper->enabled)
 91                 __cpu_stop_queue_work(stopper, work);
 92         else
 93                 cpu_stop_signal_done(work->done, false);
 94         spin_unlock_irqrestore(&stopper->lock, flags);
 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         cpu_stop_queue_work(cpu, &work);
128         wait_for_completion(&done.completion);
129         return done.executed ? done.ret : -ENOENT;
130 }
131 
132 /* This controls the threads on each CPU. */
133 enum multi_stop_state {
134         /* Dummy starting state for thread. */
135         MULTI_STOP_NONE,
136         /* Awaiting everyone to be scheduled. */
137         MULTI_STOP_PREPARE,
138         /* Disable interrupts. */
139         MULTI_STOP_DISABLE_IRQ,
140         /* Run the function */
141         MULTI_STOP_RUN,
142         /* Exit */
143         MULTI_STOP_EXIT,
144 };
145 
146 struct multi_stop_data {
147         cpu_stop_fn_t           fn;
148         void                    *data;
149         /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
150         unsigned int            num_threads;
151         const struct cpumask    *active_cpus;
152 
153         enum multi_stop_state   state;
154         atomic_t                thread_ack;
155 };
156 
157 static void set_state(struct multi_stop_data *msdata,
158                       enum multi_stop_state newstate)
159 {
160         /* Reset ack counter. */
161         atomic_set(&msdata->thread_ack, msdata->num_threads);
162         smp_wmb();
163         msdata->state = newstate;
164 }
165 
166 /* Last one to ack a state moves to the next state. */
167 static void ack_state(struct multi_stop_data *msdata)
168 {
169         if (atomic_dec_and_test(&msdata->thread_ack))
170                 set_state(msdata, msdata->state + 1);
171 }
172 
173 /* This is the cpu_stop function which stops the CPU. */
174 static int multi_cpu_stop(void *data)
175 {
176         struct multi_stop_data *msdata = data;
177         enum multi_stop_state curstate = MULTI_STOP_NONE;
178         int cpu = smp_processor_id(), err = 0;
179         unsigned long flags;
180         bool is_active;
181 
182         /*
183          * When called from stop_machine_from_inactive_cpu(), irq might
184          * already be disabled.  Save the state and restore it on exit.
185          */
186         local_save_flags(flags);
187 
188         if (!msdata->active_cpus)
189                 is_active = cpu == cpumask_first(cpu_online_mask);
190         else
191                 is_active = cpumask_test_cpu(cpu, msdata->active_cpus);
192 
193         /* Simple state machine */
194         do {
195                 /* Chill out and ensure we re-read multi_stop_state. */
196                 cpu_relax();
197                 if (msdata->state != curstate) {
198                         curstate = msdata->state;
199                         switch (curstate) {
200                         case MULTI_STOP_DISABLE_IRQ:
201                                 local_irq_disable();
202                                 hard_irq_disable();
203                                 break;
204                         case MULTI_STOP_RUN:
205                                 if (is_active)
206                                         err = msdata->fn(msdata->data);
207                                 break;
208                         default:
209                                 break;
210                         }
211                         ack_state(msdata);
212                 }
213         } while (curstate != MULTI_STOP_EXIT);
214 
215         local_irq_restore(flags);
216         return err;
217 }
218 
219 static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
220                                     int cpu2, struct cpu_stop_work *work2)
221 {
222         struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
223         struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);
224         int err;
225 
226         lg_double_lock(&stop_cpus_lock, cpu1, cpu2);
227         spin_lock_irq(&stopper1->lock);
228         spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);
229 
230         err = -ENOENT;
231         if (!stopper1->enabled || !stopper2->enabled)
232                 goto unlock;
233 
234         err = 0;
235         __cpu_stop_queue_work(stopper1, work1);
236         __cpu_stop_queue_work(stopper2, work2);
237 unlock:
238         spin_unlock(&stopper2->lock);
239         spin_unlock_irq(&stopper1->lock);
240         lg_double_unlock(&stop_cpus_lock, cpu1, cpu2);
241 
242         return err;
243 }
244 /**
245  * stop_two_cpus - stops two cpus
246  * @cpu1: the cpu to stop
247  * @cpu2: the other cpu to stop
248  * @fn: function to execute
249  * @arg: argument to @fn
250  *
251  * Stops both the current and specified CPU and runs @fn on one of them.
252  *
253  * returns when both are completed.
254  */
255 int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
256 {
257         struct cpu_stop_done done;
258         struct cpu_stop_work work1, work2;
259         struct multi_stop_data msdata;
260 
261         preempt_disable();
262         msdata = (struct multi_stop_data){
263                 .fn = fn,
264                 .data = arg,
265                 .num_threads = 2,
266                 .active_cpus = cpumask_of(cpu1),
267         };
268 
269         work1 = work2 = (struct cpu_stop_work){
270                 .fn = multi_cpu_stop,
271                 .arg = &msdata,
272                 .done = &done
273         };
274 
275         cpu_stop_init_done(&done, 2);
276         set_state(&msdata, MULTI_STOP_PREPARE);
277 
278         if (cpu1 > cpu2)
279                 swap(cpu1, cpu2);
280         if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2)) {
281                 preempt_enable();
282                 return -ENOENT;
283         }
284 
285         preempt_enable();
286 
287         wait_for_completion(&done.completion);
288 
289         return done.executed ? done.ret : -ENOENT;
290 }
291 
292 /**
293  * stop_one_cpu_nowait - stop a cpu but don't wait for completion
294  * @cpu: cpu to stop
295  * @fn: function to execute
296  * @arg: argument to @fn
297  * @work_buf: pointer to cpu_stop_work structure
298  *
299  * Similar to stop_one_cpu() but doesn't wait for completion.  The
300  * caller is responsible for ensuring @work_buf is currently unused
301  * and will remain untouched until stopper starts executing @fn.
302  *
303  * CONTEXT:
304  * Don't care.
305  */
306 void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
307                         struct cpu_stop_work *work_buf)
308 {
309         *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
310         cpu_stop_queue_work(cpu, work_buf);
311 }
312 
313 /* static data for stop_cpus */
314 static DEFINE_MUTEX(stop_cpus_mutex);
315 
316 static void queue_stop_cpus_work(const struct cpumask *cpumask,
317                                  cpu_stop_fn_t fn, void *arg,
318                                  struct cpu_stop_done *done)
319 {
320         struct cpu_stop_work *work;
321         unsigned int cpu;
322 
323         /*
324          * Disable preemption while queueing to avoid getting
325          * preempted by a stopper which might wait for other stoppers
326          * to enter @fn which can lead to deadlock.
327          */
328         lg_global_lock(&stop_cpus_lock);
329         for_each_cpu(cpu, cpumask) {
330                 work = &per_cpu(cpu_stopper.stop_work, cpu);
331                 work->fn = fn;
332                 work->arg = arg;
333                 work->done = done;
334                 cpu_stop_queue_work(cpu, work);
335         }
336         lg_global_unlock(&stop_cpus_lock);
337 }
338 
339 static int __stop_cpus(const struct cpumask *cpumask,
340                        cpu_stop_fn_t fn, void *arg)
341 {
342         struct cpu_stop_done done;
343 
344         cpu_stop_init_done(&done, cpumask_weight(cpumask));
345         queue_stop_cpus_work(cpumask, fn, arg, &done);
346         wait_for_completion(&done.completion);
347         return done.executed ? done.ret : -ENOENT;
348 }
349 
350 /**
351  * stop_cpus - stop multiple cpus
352  * @cpumask: cpus to stop
353  * @fn: function to execute
354  * @arg: argument to @fn
355  *
356  * Execute @fn(@arg) on online cpus in @cpumask.  On each target cpu,
357  * @fn is run in a process context with the highest priority
358  * preempting any task on the cpu and monopolizing it.  This function
359  * returns after all executions are complete.
360  *
361  * This function doesn't guarantee the cpus in @cpumask stay online
362  * till @fn completes.  If some cpus go down in the middle, execution
363  * on the cpu may happen partially or fully on different cpus.  @fn
364  * should either be ready for that or the caller should ensure that
365  * the cpus stay online until this function completes.
366  *
367  * All stop_cpus() calls are serialized making it safe for @fn to wait
368  * for all cpus to start executing it.
369  *
370  * CONTEXT:
371  * Might sleep.
372  *
373  * RETURNS:
374  * -ENOENT if @fn(@arg) was not executed at all because all cpus in
375  * @cpumask were offline; otherwise, 0 if all executions of @fn
376  * returned 0, any non zero return value if any returned non zero.
377  */
378 int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
379 {
380         int ret;
381 
382         /* static works are used, process one request at a time */
383         mutex_lock(&stop_cpus_mutex);
384         ret = __stop_cpus(cpumask, fn, arg);
385         mutex_unlock(&stop_cpus_mutex);
386         return ret;
387 }
388 
389 /**
390  * try_stop_cpus - try to stop multiple cpus
391  * @cpumask: cpus to stop
392  * @fn: function to execute
393  * @arg: argument to @fn
394  *
395  * Identical to stop_cpus() except that it fails with -EAGAIN if
396  * someone else is already using the facility.
397  *
398  * CONTEXT:
399  * Might sleep.
400  *
401  * RETURNS:
402  * -EAGAIN if someone else is already stopping cpus, -ENOENT if
403  * @fn(@arg) was not executed at all because all cpus in @cpumask were
404  * offline; otherwise, 0 if all executions of @fn returned 0, any non
405  * zero return value if any returned non zero.
406  */
407 int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
408 {
409         int ret;
410 
411         /* static works are used, process one request at a time */
412         if (!mutex_trylock(&stop_cpus_mutex))
413                 return -EAGAIN;
414         ret = __stop_cpus(cpumask, fn, arg);
415         mutex_unlock(&stop_cpus_mutex);
416         return ret;
417 }
418 
419 static int cpu_stop_should_run(unsigned int cpu)
420 {
421         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
422         unsigned long flags;
423         int run;
424 
425         spin_lock_irqsave(&stopper->lock, flags);
426         run = !list_empty(&stopper->works);
427         spin_unlock_irqrestore(&stopper->lock, flags);
428         return run;
429 }
430 
431 static void cpu_stopper_thread(unsigned int cpu)
432 {
433         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
434         struct cpu_stop_work *work;
435         int ret;
436 
437 repeat:
438         work = NULL;
439         spin_lock_irq(&stopper->lock);
440         if (!list_empty(&stopper->works)) {
441                 work = list_first_entry(&stopper->works,
442                                         struct cpu_stop_work, list);
443                 list_del_init(&work->list);
444         }
445         spin_unlock_irq(&stopper->lock);
446 
447         if (work) {
448                 cpu_stop_fn_t fn = work->fn;
449                 void *arg = work->arg;
450                 struct cpu_stop_done *done = work->done;
451                 char ksym_buf[KSYM_NAME_LEN] __maybe_unused;
452 
453                 /* cpu stop callbacks are not allowed to sleep */
454                 preempt_disable();
455 
456                 ret = fn(arg);
457                 if (ret)
458                         done->ret = ret;
459 
460                 /* restore preemption and check it's still balanced */
461                 preempt_enable();
462                 WARN_ONCE(preempt_count(),
463                           "cpu_stop: %s(%p) leaked preempt count\n",
464                           kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
465                                           ksym_buf), arg);
466 
467                 cpu_stop_signal_done(done, true);
468                 goto repeat;
469         }
470 }
471 
472 void stop_machine_park(int cpu)
473 {
474         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
475         /*
476          * Lockless. cpu_stopper_thread() will take stopper->lock and flush
477          * the pending works before it parks, until then it is fine to queue
478          * the new works.
479          */
480         stopper->enabled = false;
481         kthread_park(stopper->thread);
482 }
483 
484 extern void sched_set_stop_task(int cpu, struct task_struct *stop);
485 
486 static void cpu_stop_create(unsigned int cpu)
487 {
488         sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));
489 }
490 
491 static void cpu_stop_park(unsigned int cpu)
492 {
493         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
494 
495         WARN_ON(!list_empty(&stopper->works));
496 }
497 
498 void stop_machine_unpark(int cpu)
499 {
500         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
501 
502         stopper->enabled = true;
503         kthread_unpark(stopper->thread);
504 }
505 
506 static struct smp_hotplug_thread cpu_stop_threads = {
507         .store                  = &cpu_stopper.thread,
508         .thread_should_run      = cpu_stop_should_run,
509         .thread_fn              = cpu_stopper_thread,
510         .thread_comm            = "migration/%u",
511         .create                 = cpu_stop_create,
512         .park                   = cpu_stop_park,
513         .selfparking            = true,
514 };
515 
516 static int __init cpu_stop_init(void)
517 {
518         unsigned int cpu;
519 
520         for_each_possible_cpu(cpu) {
521                 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
522 
523                 spin_lock_init(&stopper->lock);
524                 INIT_LIST_HEAD(&stopper->works);
525         }
526 
527         BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
528         stop_machine_unpark(raw_smp_processor_id());
529         stop_machine_initialized = true;
530         return 0;
531 }
532 early_initcall(cpu_stop_init);
533 
534 #if defined(CONFIG_SMP) || defined(CONFIG_HOTPLUG_CPU)
535 
536 static int __stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
537 {
538         struct multi_stop_data msdata = {
539                 .fn = fn,
540                 .data = data,
541                 .num_threads = num_online_cpus(),
542                 .active_cpus = cpus,
543         };
544 
545         if (!stop_machine_initialized) {
546                 /*
547                  * Handle the case where stop_machine() is called
548                  * early in boot before stop_machine() has been
549                  * initialized.
550                  */
551                 unsigned long flags;
552                 int ret;
553 
554                 WARN_ON_ONCE(msdata.num_threads != 1);
555 
556                 local_irq_save(flags);
557                 hard_irq_disable();
558                 ret = (*fn)(data);
559                 local_irq_restore(flags);
560 
561                 return ret;
562         }
563 
564         /* Set the initial state and stop all online cpus. */
565         set_state(&msdata, MULTI_STOP_PREPARE);
566         return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
567 }
568 
569 int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
570 {
571         int ret;
572 
573         /* No CPUs can come up or down during this. */
574         get_online_cpus();
575         ret = __stop_machine(fn, data, cpus);
576         put_online_cpus();
577         return ret;
578 }
579 EXPORT_SYMBOL_GPL(stop_machine);
580 
581 /**
582  * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
583  * @fn: the function to run
584  * @data: the data ptr for the @fn()
585  * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
586  *
587  * This is identical to stop_machine() but can be called from a CPU which
588  * is not active.  The local CPU is in the process of hotplug (so no other
589  * CPU hotplug can start) and not marked active and doesn't have enough
590  * context to sleep.
591  *
592  * This function provides stop_machine() functionality for such state by
593  * using busy-wait for synchronization and executing @fn directly for local
594  * CPU.
595  *
596  * CONTEXT:
597  * Local CPU is inactive.  Temporarily stops all active CPUs.
598  *
599  * RETURNS:
600  * 0 if all executions of @fn returned 0, any non zero return value if any
601  * returned non zero.
602  */
603 int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,
604                                   const struct cpumask *cpus)
605 {
606         struct multi_stop_data msdata = { .fn = fn, .data = data,
607                                             .active_cpus = cpus };
608         struct cpu_stop_done done;
609         int ret;
610 
611         /* Local CPU must be inactive and CPU hotplug in progress. */
612         BUG_ON(cpu_active(raw_smp_processor_id()));
613         msdata.num_threads = num_active_cpus() + 1;     /* +1 for local */
614 
615         /* No proper task established and can't sleep - busy wait for lock. */
616         while (!mutex_trylock(&stop_cpus_mutex))
617                 cpu_relax();
618 
619         /* Schedule work on other CPUs and execute directly for local CPU */
620         set_state(&msdata, MULTI_STOP_PREPARE);
621         cpu_stop_init_done(&done, num_active_cpus());
622         queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
623                              &done);
624         ret = multi_cpu_stop(&msdata);
625 
626         /* Busy wait for completion. */
627         while (!completion_done(&done.completion))
628                 cpu_relax();
629 
630         mutex_unlock(&stop_cpus_mutex);
631         return ret ?: done.ret;
632 }
633 
634 #endif  /* CONFIG_SMP || CONFIG_HOTPLUG_CPU */
635 

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