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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 /**
215  * stop_two_cpus - stops two cpus
216  * @cpu1: the cpu to stop
217  * @cpu2: the other cpu to stop
218  * @fn: function to execute
219  * @arg: argument to @fn
220  *
221  * Stops both the current and specified CPU and runs @fn on one of them.
222  *
223  * returns when both are completed.
224  */
225 int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
226 {
227         struct cpu_stop_done done;
228         struct cpu_stop_work work1, work2;
229         struct multi_stop_data msdata;
230 
231         preempt_disable();
232         msdata = (struct multi_stop_data){
233                 .fn = fn,
234                 .data = arg,
235                 .num_threads = 2,
236                 .active_cpus = cpumask_of(cpu1),
237         };
238 
239         work1 = work2 = (struct cpu_stop_work){
240                 .fn = multi_cpu_stop,
241                 .arg = &msdata,
242                 .done = &done
243         };
244 
245         cpu_stop_init_done(&done, 2);
246         set_state(&msdata, MULTI_STOP_PREPARE);
247 
248         /*
249          * If we observe both CPUs active we know _cpu_down() cannot yet have
250          * queued its stop_machine works and therefore ours will get executed
251          * first. Or its not either one of our CPUs that's getting unplugged,
252          * in which case we don't care.
253          *
254          * This relies on the stopper workqueues to be FIFO.
255          */
256         if (!cpu_active(cpu1) || !cpu_active(cpu2)) {
257                 preempt_enable();
258                 return -ENOENT;
259         }
260 
261         lg_double_lock(&stop_cpus_lock, cpu1, cpu2);
262         cpu_stop_queue_work(cpu1, &work1);
263         cpu_stop_queue_work(cpu2, &work2);
264         lg_double_unlock(&stop_cpus_lock, cpu1, cpu2);
265 
266         preempt_enable();
267 
268         wait_for_completion(&done.completion);
269 
270         return done.executed ? done.ret : -ENOENT;
271 }
272 
273 /**
274  * stop_one_cpu_nowait - stop a cpu but don't wait for completion
275  * @cpu: cpu to stop
276  * @fn: function to execute
277  * @arg: argument to @fn
278  * @work_buf: pointer to cpu_stop_work structure
279  *
280  * Similar to stop_one_cpu() but doesn't wait for completion.  The
281  * caller is responsible for ensuring @work_buf is currently unused
282  * and will remain untouched until stopper starts executing @fn.
283  *
284  * CONTEXT:
285  * Don't care.
286  */
287 void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
288                         struct cpu_stop_work *work_buf)
289 {
290         *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
291         cpu_stop_queue_work(cpu, work_buf);
292 }
293 
294 /* static data for stop_cpus */
295 static DEFINE_MUTEX(stop_cpus_mutex);
296 static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work);
297 
298 static void queue_stop_cpus_work(const struct cpumask *cpumask,
299                                  cpu_stop_fn_t fn, void *arg,
300                                  struct cpu_stop_done *done)
301 {
302         struct cpu_stop_work *work;
303         unsigned int cpu;
304 
305         /* initialize works and done */
306         for_each_cpu(cpu, cpumask) {
307                 work = &per_cpu(stop_cpus_work, cpu);
308                 work->fn = fn;
309                 work->arg = arg;
310                 work->done = done;
311         }
312 
313         /*
314          * Disable preemption while queueing to avoid getting
315          * preempted by a stopper which might wait for other stoppers
316          * to enter @fn which can lead to deadlock.
317          */
318         lg_global_lock(&stop_cpus_lock);
319         for_each_cpu(cpu, cpumask)
320                 cpu_stop_queue_work(cpu, &per_cpu(stop_cpus_work, cpu));
321         lg_global_unlock(&stop_cpus_lock);
322 }
323 
324 static int __stop_cpus(const struct cpumask *cpumask,
325                        cpu_stop_fn_t fn, void *arg)
326 {
327         struct cpu_stop_done done;
328 
329         cpu_stop_init_done(&done, cpumask_weight(cpumask));
330         queue_stop_cpus_work(cpumask, fn, arg, &done);
331         wait_for_completion(&done.completion);
332         return done.executed ? done.ret : -ENOENT;
333 }
334 
335 /**
336  * stop_cpus - stop multiple cpus
337  * @cpumask: cpus to stop
338  * @fn: function to execute
339  * @arg: argument to @fn
340  *
341  * Execute @fn(@arg) on online cpus in @cpumask.  On each target cpu,
342  * @fn is run in a process context with the highest priority
343  * preempting any task on the cpu and monopolizing it.  This function
344  * returns after all executions are complete.
345  *
346  * This function doesn't guarantee the cpus in @cpumask stay online
347  * till @fn completes.  If some cpus go down in the middle, execution
348  * on the cpu may happen partially or fully on different cpus.  @fn
349  * should either be ready for that or the caller should ensure that
350  * the cpus stay online until this function completes.
351  *
352  * All stop_cpus() calls are serialized making it safe for @fn to wait
353  * for all cpus to start executing it.
354  *
355  * CONTEXT:
356  * Might sleep.
357  *
358  * RETURNS:
359  * -ENOENT if @fn(@arg) was not executed at all because all cpus in
360  * @cpumask were offline; otherwise, 0 if all executions of @fn
361  * returned 0, any non zero return value if any returned non zero.
362  */
363 int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
364 {
365         int ret;
366 
367         /* static works are used, process one request at a time */
368         mutex_lock(&stop_cpus_mutex);
369         ret = __stop_cpus(cpumask, fn, arg);
370         mutex_unlock(&stop_cpus_mutex);
371         return ret;
372 }
373 
374 /**
375  * try_stop_cpus - try to stop multiple cpus
376  * @cpumask: cpus to stop
377  * @fn: function to execute
378  * @arg: argument to @fn
379  *
380  * Identical to stop_cpus() except that it fails with -EAGAIN if
381  * someone else is already using the facility.
382  *
383  * CONTEXT:
384  * Might sleep.
385  *
386  * RETURNS:
387  * -EAGAIN if someone else is already stopping cpus, -ENOENT if
388  * @fn(@arg) was not executed at all because all cpus in @cpumask were
389  * offline; otherwise, 0 if all executions of @fn returned 0, any non
390  * zero return value if any returned non zero.
391  */
392 int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
393 {
394         int ret;
395 
396         /* static works are used, process one request at a time */
397         if (!mutex_trylock(&stop_cpus_mutex))
398                 return -EAGAIN;
399         ret = __stop_cpus(cpumask, fn, arg);
400         mutex_unlock(&stop_cpus_mutex);
401         return ret;
402 }
403 
404 static int cpu_stop_should_run(unsigned int cpu)
405 {
406         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
407         unsigned long flags;
408         int run;
409 
410         spin_lock_irqsave(&stopper->lock, flags);
411         run = !list_empty(&stopper->works);
412         spin_unlock_irqrestore(&stopper->lock, flags);
413         return run;
414 }
415 
416 static void cpu_stopper_thread(unsigned int cpu)
417 {
418         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
419         struct cpu_stop_work *work;
420         int ret;
421 
422 repeat:
423         work = NULL;
424         spin_lock_irq(&stopper->lock);
425         if (!list_empty(&stopper->works)) {
426                 work = list_first_entry(&stopper->works,
427                                         struct cpu_stop_work, list);
428                 list_del_init(&work->list);
429         }
430         spin_unlock_irq(&stopper->lock);
431 
432         if (work) {
433                 cpu_stop_fn_t fn = work->fn;
434                 void *arg = work->arg;
435                 struct cpu_stop_done *done = work->done;
436                 char ksym_buf[KSYM_NAME_LEN] __maybe_unused;
437 
438                 /* cpu stop callbacks are not allowed to sleep */
439                 preempt_disable();
440 
441                 ret = fn(arg);
442                 if (ret)
443                         done->ret = ret;
444 
445                 /* restore preemption and check it's still balanced */
446                 preempt_enable();
447                 WARN_ONCE(preempt_count(),
448                           "cpu_stop: %s(%p) leaked preempt count\n",
449                           kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
450                                           ksym_buf), arg);
451 
452                 cpu_stop_signal_done(done, true);
453                 goto repeat;
454         }
455 }
456 
457 extern void sched_set_stop_task(int cpu, struct task_struct *stop);
458 
459 static void cpu_stop_create(unsigned int cpu)
460 {
461         sched_set_stop_task(cpu, per_cpu(cpu_stopper_task, cpu));
462 }
463 
464 static void cpu_stop_park(unsigned int cpu)
465 {
466         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
467         struct cpu_stop_work *work;
468         unsigned long flags;
469 
470         /* drain remaining works */
471         spin_lock_irqsave(&stopper->lock, flags);
472         list_for_each_entry(work, &stopper->works, list)
473                 cpu_stop_signal_done(work->done, false);
474         stopper->enabled = false;
475         spin_unlock_irqrestore(&stopper->lock, flags);
476 }
477 
478 static void cpu_stop_unpark(unsigned int cpu)
479 {
480         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
481 
482         spin_lock_irq(&stopper->lock);
483         stopper->enabled = true;
484         spin_unlock_irq(&stopper->lock);
485 }
486 
487 static struct smp_hotplug_thread cpu_stop_threads = {
488         .store                  = &cpu_stopper_task,
489         .thread_should_run      = cpu_stop_should_run,
490         .thread_fn              = cpu_stopper_thread,
491         .thread_comm            = "migration/%u",
492         .create                 = cpu_stop_create,
493         .setup                  = cpu_stop_unpark,
494         .park                   = cpu_stop_park,
495         .pre_unpark             = cpu_stop_unpark,
496         .selfparking            = true,
497 };
498 
499 static int __init cpu_stop_init(void)
500 {
501         unsigned int cpu;
502 
503         for_each_possible_cpu(cpu) {
504                 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
505 
506                 spin_lock_init(&stopper->lock);
507                 INIT_LIST_HEAD(&stopper->works);
508         }
509 
510         BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
511         stop_machine_initialized = true;
512         return 0;
513 }
514 early_initcall(cpu_stop_init);
515 
516 #ifdef CONFIG_STOP_MACHINE
517 
518 int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
519 {
520         struct multi_stop_data msdata = {
521                 .fn = fn,
522                 .data = data,
523                 .num_threads = num_online_cpus(),
524                 .active_cpus = cpus,
525         };
526 
527         if (!stop_machine_initialized) {
528                 /*
529                  * Handle the case where stop_machine() is called
530                  * early in boot before stop_machine() has been
531                  * initialized.
532                  */
533                 unsigned long flags;
534                 int ret;
535 
536                 WARN_ON_ONCE(msdata.num_threads != 1);
537 
538                 local_irq_save(flags);
539                 hard_irq_disable();
540                 ret = (*fn)(data);
541                 local_irq_restore(flags);
542 
543                 return ret;
544         }
545 
546         /* Set the initial state and stop all online cpus. */
547         set_state(&msdata, MULTI_STOP_PREPARE);
548         return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
549 }
550 
551 int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
552 {
553         int ret;
554 
555         /* No CPUs can come up or down during this. */
556         get_online_cpus();
557         ret = __stop_machine(fn, data, cpus);
558         put_online_cpus();
559         return ret;
560 }
561 EXPORT_SYMBOL_GPL(stop_machine);
562 
563 /**
564  * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
565  * @fn: the function to run
566  * @data: the data ptr for the @fn()
567  * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
568  *
569  * This is identical to stop_machine() but can be called from a CPU which
570  * is not active.  The local CPU is in the process of hotplug (so no other
571  * CPU hotplug can start) and not marked active and doesn't have enough
572  * context to sleep.
573  *
574  * This function provides stop_machine() functionality for such state by
575  * using busy-wait for synchronization and executing @fn directly for local
576  * CPU.
577  *
578  * CONTEXT:
579  * Local CPU is inactive.  Temporarily stops all active CPUs.
580  *
581  * RETURNS:
582  * 0 if all executions of @fn returned 0, any non zero return value if any
583  * returned non zero.
584  */
585 int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
586                                   const struct cpumask *cpus)
587 {
588         struct multi_stop_data msdata = { .fn = fn, .data = data,
589                                             .active_cpus = cpus };
590         struct cpu_stop_done done;
591         int ret;
592 
593         /* Local CPU must be inactive and CPU hotplug in progress. */
594         BUG_ON(cpu_active(raw_smp_processor_id()));
595         msdata.num_threads = num_active_cpus() + 1;     /* +1 for local */
596 
597         /* No proper task established and can't sleep - busy wait for lock. */
598         while (!mutex_trylock(&stop_cpus_mutex))
599                 cpu_relax();
600 
601         /* Schedule work on other CPUs and execute directly for local CPU */
602         set_state(&msdata, MULTI_STOP_PREPARE);
603         cpu_stop_init_done(&done, num_active_cpus());
604         queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
605                              &done);
606         ret = multi_cpu_stop(&msdata);
607 
608         /* Busy wait for completion. */
609         while (!completion_done(&done.completion))
610                 cpu_relax();
611 
612         mutex_unlock(&stop_cpus_mutex);
613         return ret ?: done.ret;
614 }
615 
616 #endif  /* CONFIG_STOP_MACHINE */
617 

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