Root/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
22#include <linux/atomic.h>
23
24/*
25 * Structure to determine completion condition and record errors. May
26 * be shared by works on different cpus.
27 */
28struct cpu_stop_done {
29    atomic_t nr_todo; /* nr left to execute */
30    bool executed; /* actually executed? */
31    int ret; /* collected return value */
32    struct completion completion; /* fired if nr_todo reaches 0 */
33};
34
35/* the actual stopper, one per every possible cpu, enabled on online cpus */
36struct cpu_stopper {
37    spinlock_t lock;
38    bool enabled; /* is this stopper enabled? */
39    struct list_head works; /* list of pending works */
40    struct task_struct *thread; /* stopper thread */
41};
42
43static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
44static bool stop_machine_initialized = false;
45
46static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
47{
48    memset(done, 0, sizeof(*done));
49    atomic_set(&done->nr_todo, nr_todo);
50    init_completion(&done->completion);
51}
52
53/* signal completion unless @done is NULL */
54static void cpu_stop_signal_done(struct cpu_stop_done *done, bool executed)
55{
56    if (done) {
57        if (executed)
58            done->executed = true;
59        if (atomic_dec_and_test(&done->nr_todo))
60            complete(&done->completion);
61    }
62}
63
64/* queue @work to @stopper. if offline, @work is completed immediately */
65static void cpu_stop_queue_work(struct cpu_stopper *stopper,
66                struct cpu_stop_work *work)
67{
68    unsigned long flags;
69
70    spin_lock_irqsave(&stopper->lock, flags);
71
72    if (stopper->enabled) {
73        list_add_tail(&work->list, &stopper->works);
74        wake_up_process(stopper->thread);
75    } else
76        cpu_stop_signal_done(work->done, false);
77
78    spin_unlock_irqrestore(&stopper->lock, flags);
79}
80
81/**
82 * stop_one_cpu - stop a cpu
83 * @cpu: cpu to stop
84 * @fn: function to execute
85 * @arg: argument to @fn
86 *
87 * Execute @fn(@arg) on @cpu. @fn is run in a process context with
88 * the highest priority preempting any task on the cpu and
89 * monopolizing it. This function returns after the execution is
90 * complete.
91 *
92 * This function doesn't guarantee @cpu stays online till @fn
93 * completes. If @cpu goes down in the middle, execution may happen
94 * partially or fully on different cpus. @fn should either be ready
95 * for that or the caller should ensure that @cpu stays online until
96 * this function completes.
97 *
98 * CONTEXT:
99 * Might sleep.
100 *
101 * RETURNS:
102 * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
103 * otherwise, the return value of @fn.
104 */
105int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
106{
107    struct cpu_stop_done done;
108    struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
109
110    cpu_stop_init_done(&done, 1);
111    cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), &work);
112    wait_for_completion(&done.completion);
113    return done.executed ? done.ret : -ENOENT;
114}
115
116/**
117 * stop_one_cpu_nowait - stop a cpu but don't wait for completion
118 * @cpu: cpu to stop
119 * @fn: function to execute
120 * @arg: argument to @fn
121 *
122 * Similar to stop_one_cpu() but doesn't wait for completion. The
123 * caller is responsible for ensuring @work_buf is currently unused
124 * and will remain untouched until stopper starts executing @fn.
125 *
126 * CONTEXT:
127 * Don't care.
128 */
129void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
130            struct cpu_stop_work *work_buf)
131{
132    *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
133    cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), work_buf);
134}
135
136/* static data for stop_cpus */
137static DEFINE_MUTEX(stop_cpus_mutex);
138static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work);
139
140static void queue_stop_cpus_work(const struct cpumask *cpumask,
141                 cpu_stop_fn_t fn, void *arg,
142                 struct cpu_stop_done *done)
143{
144    struct cpu_stop_work *work;
145    unsigned int cpu;
146
147    /* initialize works and done */
148    for_each_cpu(cpu, cpumask) {
149        work = &per_cpu(stop_cpus_work, cpu);
150        work->fn = fn;
151        work->arg = arg;
152        work->done = done;
153    }
154
155    /*
156     * Disable preemption while queueing to avoid getting
157     * preempted by a stopper which might wait for other stoppers
158     * to enter @fn which can lead to deadlock.
159     */
160    preempt_disable();
161    for_each_cpu(cpu, cpumask)
162        cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu),
163                    &per_cpu(stop_cpus_work, cpu));
164    preempt_enable();
165}
166
167static int __stop_cpus(const struct cpumask *cpumask,
168               cpu_stop_fn_t fn, void *arg)
169{
170    struct cpu_stop_done done;
171
172    cpu_stop_init_done(&done, cpumask_weight(cpumask));
173    queue_stop_cpus_work(cpumask, fn, arg, &done);
174    wait_for_completion(&done.completion);
175    return done.executed ? done.ret : -ENOENT;
176}
177
178/**
179 * stop_cpus - stop multiple cpus
180 * @cpumask: cpus to stop
181 * @fn: function to execute
182 * @arg: argument to @fn
183 *
184 * Execute @fn(@arg) on online cpus in @cpumask. On each target cpu,
185 * @fn is run in a process context with the highest priority
186 * preempting any task on the cpu and monopolizing it. This function
187 * returns after all executions are complete.
188 *
189 * This function doesn't guarantee the cpus in @cpumask stay online
190 * till @fn completes. If some cpus go down in the middle, execution
191 * on the cpu may happen partially or fully on different cpus. @fn
192 * should either be ready for that or the caller should ensure that
193 * the cpus stay online until this function completes.
194 *
195 * All stop_cpus() calls are serialized making it safe for @fn to wait
196 * for all cpus to start executing it.
197 *
198 * CONTEXT:
199 * Might sleep.
200 *
201 * RETURNS:
202 * -ENOENT if @fn(@arg) was not executed at all because all cpus in
203 * @cpumask were offline; otherwise, 0 if all executions of @fn
204 * returned 0, any non zero return value if any returned non zero.
205 */
206int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
207{
208    int ret;
209
210    /* static works are used, process one request at a time */
211    mutex_lock(&stop_cpus_mutex);
212    ret = __stop_cpus(cpumask, fn, arg);
213    mutex_unlock(&stop_cpus_mutex);
214    return ret;
215}
216
217/**
218 * try_stop_cpus - try to stop multiple cpus
219 * @cpumask: cpus to stop
220 * @fn: function to execute
221 * @arg: argument to @fn
222 *
223 * Identical to stop_cpus() except that it fails with -EAGAIN if
224 * someone else is already using the facility.
225 *
226 * CONTEXT:
227 * Might sleep.
228 *
229 * RETURNS:
230 * -EAGAIN if someone else is already stopping cpus, -ENOENT if
231 * @fn(@arg) was not executed at all because all cpus in @cpumask were
232 * offline; otherwise, 0 if all executions of @fn returned 0, any non
233 * zero return value if any returned non zero.
234 */
235int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
236{
237    int ret;
238
239    /* static works are used, process one request at a time */
240    if (!mutex_trylock(&stop_cpus_mutex))
241        return -EAGAIN;
242    ret = __stop_cpus(cpumask, fn, arg);
243    mutex_unlock(&stop_cpus_mutex);
244    return ret;
245}
246
247static int cpu_stopper_thread(void *data)
248{
249    struct cpu_stopper *stopper = data;
250    struct cpu_stop_work *work;
251    int ret;
252
253repeat:
254    set_current_state(TASK_INTERRUPTIBLE); /* mb paired w/ kthread_stop */
255
256    if (kthread_should_stop()) {
257        __set_current_state(TASK_RUNNING);
258        return 0;
259    }
260
261    work = NULL;
262    spin_lock_irq(&stopper->lock);
263    if (!list_empty(&stopper->works)) {
264        work = list_first_entry(&stopper->works,
265                    struct cpu_stop_work, list);
266        list_del_init(&work->list);
267    }
268    spin_unlock_irq(&stopper->lock);
269
270    if (work) {
271        cpu_stop_fn_t fn = work->fn;
272        void *arg = work->arg;
273        struct cpu_stop_done *done = work->done;
274        char ksym_buf[KSYM_NAME_LEN] __maybe_unused;
275
276        __set_current_state(TASK_RUNNING);
277
278        /* cpu stop callbacks are not allowed to sleep */
279        preempt_disable();
280
281        ret = fn(arg);
282        if (ret)
283            done->ret = ret;
284
285        /* restore preemption and check it's still balanced */
286        preempt_enable();
287        WARN_ONCE(preempt_count(),
288              "cpu_stop: %s(%p) leaked preempt count\n",
289              kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
290                      ksym_buf), arg);
291
292        cpu_stop_signal_done(done, true);
293    } else
294        schedule();
295
296    goto repeat;
297}
298
299extern void sched_set_stop_task(int cpu, struct task_struct *stop);
300
301/* manage stopper for a cpu, mostly lifted from sched migration thread mgmt */
302static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
303                       unsigned long action, void *hcpu)
304{
305    unsigned int cpu = (unsigned long)hcpu;
306    struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
307    struct task_struct *p;
308
309    switch (action & ~CPU_TASKS_FROZEN) {
310    case CPU_UP_PREPARE:
311        BUG_ON(stopper->thread || stopper->enabled ||
312               !list_empty(&stopper->works));
313        p = kthread_create_on_node(cpu_stopper_thread,
314                       stopper,
315                       cpu_to_node(cpu),
316                       "migration/%d", cpu);
317        if (IS_ERR(p))
318            return notifier_from_errno(PTR_ERR(p));
319        get_task_struct(p);
320        kthread_bind(p, cpu);
321        sched_set_stop_task(cpu, p);
322        stopper->thread = p;
323        break;
324
325    case CPU_ONLINE:
326        /* strictly unnecessary, as first user will wake it */
327        wake_up_process(stopper->thread);
328        /* mark enabled */
329        spin_lock_irq(&stopper->lock);
330        stopper->enabled = true;
331        spin_unlock_irq(&stopper->lock);
332        break;
333
334#ifdef CONFIG_HOTPLUG_CPU
335    case CPU_UP_CANCELED:
336    case CPU_POST_DEAD:
337    {
338        struct cpu_stop_work *work;
339
340        sched_set_stop_task(cpu, NULL);
341        /* kill the stopper */
342        kthread_stop(stopper->thread);
343        /* drain remaining works */
344        spin_lock_irq(&stopper->lock);
345        list_for_each_entry(work, &stopper->works, list)
346            cpu_stop_signal_done(work->done, false);
347        stopper->enabled = false;
348        spin_unlock_irq(&stopper->lock);
349        /* release the stopper */
350        put_task_struct(stopper->thread);
351        stopper->thread = NULL;
352        break;
353    }
354#endif
355    }
356
357    return NOTIFY_OK;
358}
359
360/*
361 * Give it a higher priority so that cpu stopper is available to other
362 * cpu notifiers. It currently shares the same priority as sched
363 * migration_notifier.
364 */
365static struct notifier_block __cpuinitdata cpu_stop_cpu_notifier = {
366    .notifier_call = cpu_stop_cpu_callback,
367    .priority = 10,
368};
369
370static int __init cpu_stop_init(void)
371{
372    void *bcpu = (void *)(long)smp_processor_id();
373    unsigned int cpu;
374    int err;
375
376    for_each_possible_cpu(cpu) {
377        struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
378
379        spin_lock_init(&stopper->lock);
380        INIT_LIST_HEAD(&stopper->works);
381    }
382
383    /* start one for the boot cpu */
384    err = cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_UP_PREPARE,
385                    bcpu);
386    BUG_ON(err != NOTIFY_OK);
387    cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);
388    register_cpu_notifier(&cpu_stop_cpu_notifier);
389
390    stop_machine_initialized = true;
391
392    return 0;
393}
394early_initcall(cpu_stop_init);
395
396#ifdef CONFIG_STOP_MACHINE
397
398/* This controls the threads on each CPU. */
399enum stopmachine_state {
400    /* Dummy starting state for thread. */
401    STOPMACHINE_NONE,
402    /* Awaiting everyone to be scheduled. */
403    STOPMACHINE_PREPARE,
404    /* Disable interrupts. */
405    STOPMACHINE_DISABLE_IRQ,
406    /* Run the function */
407    STOPMACHINE_RUN,
408    /* Exit */
409    STOPMACHINE_EXIT,
410};
411
412struct stop_machine_data {
413    int (*fn)(void *);
414    void *data;
415    /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
416    unsigned int num_threads;
417    const struct cpumask *active_cpus;
418
419    enum stopmachine_state state;
420    atomic_t thread_ack;
421};
422
423static void set_state(struct stop_machine_data *smdata,
424              enum stopmachine_state newstate)
425{
426    /* Reset ack counter. */
427    atomic_set(&smdata->thread_ack, smdata->num_threads);
428    smp_wmb();
429    smdata->state = newstate;
430}
431
432/* Last one to ack a state moves to the next state. */
433static void ack_state(struct stop_machine_data *smdata)
434{
435    if (atomic_dec_and_test(&smdata->thread_ack))
436        set_state(smdata, smdata->state + 1);
437}
438
439/* This is the cpu_stop function which stops the CPU. */
440static int stop_machine_cpu_stop(void *data)
441{
442    struct stop_machine_data *smdata = data;
443    enum stopmachine_state curstate = STOPMACHINE_NONE;
444    int cpu = smp_processor_id(), err = 0;
445    unsigned long flags;
446    bool is_active;
447
448    /*
449     * When called from stop_machine_from_inactive_cpu(), irq might
450     * already be disabled. Save the state and restore it on exit.
451     */
452    local_save_flags(flags);
453
454    if (!smdata->active_cpus)
455        is_active = cpu == cpumask_first(cpu_online_mask);
456    else
457        is_active = cpumask_test_cpu(cpu, smdata->active_cpus);
458
459    /* Simple state machine */
460    do {
461        /* Chill out and ensure we re-read stopmachine_state. */
462        cpu_relax();
463        if (smdata->state != curstate) {
464            curstate = smdata->state;
465            switch (curstate) {
466            case STOPMACHINE_DISABLE_IRQ:
467                local_irq_disable();
468                hard_irq_disable();
469                break;
470            case STOPMACHINE_RUN:
471                if (is_active)
472                    err = smdata->fn(smdata->data);
473                break;
474            default:
475                break;
476            }
477            ack_state(smdata);
478        }
479    } while (curstate != STOPMACHINE_EXIT);
480
481    local_irq_restore(flags);
482    return err;
483}
484
485int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
486{
487    struct stop_machine_data smdata = { .fn = fn, .data = data,
488                        .num_threads = num_online_cpus(),
489                        .active_cpus = cpus };
490
491    if (!stop_machine_initialized) {
492        /*
493         * Handle the case where stop_machine() is called
494         * early in boot before stop_machine() has been
495         * initialized.
496         */
497        unsigned long flags;
498        int ret;
499
500        WARN_ON_ONCE(smdata.num_threads != 1);
501
502        local_irq_save(flags);
503        hard_irq_disable();
504        ret = (*fn)(data);
505        local_irq_restore(flags);
506
507        return ret;
508    }
509
510    /* Set the initial state and stop all online cpus. */
511    set_state(&smdata, STOPMACHINE_PREPARE);
512    return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata);
513}
514
515int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
516{
517    int ret;
518
519    /* No CPUs can come up or down during this. */
520    get_online_cpus();
521    ret = __stop_machine(fn, data, cpus);
522    put_online_cpus();
523    return ret;
524}
525EXPORT_SYMBOL_GPL(stop_machine);
526
527/**
528 * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
529 * @fn: the function to run
530 * @data: the data ptr for the @fn()
531 * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
532 *
533 * This is identical to stop_machine() but can be called from a CPU which
534 * is not active. The local CPU is in the process of hotplug (so no other
535 * CPU hotplug can start) and not marked active and doesn't have enough
536 * context to sleep.
537 *
538 * This function provides stop_machine() functionality for such state by
539 * using busy-wait for synchronization and executing @fn directly for local
540 * CPU.
541 *
542 * CONTEXT:
543 * Local CPU is inactive. Temporarily stops all active CPUs.
544 *
545 * RETURNS:
546 * 0 if all executions of @fn returned 0, any non zero return value if any
547 * returned non zero.
548 */
549int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
550                  const struct cpumask *cpus)
551{
552    struct stop_machine_data smdata = { .fn = fn, .data = data,
553                        .active_cpus = cpus };
554    struct cpu_stop_done done;
555    int ret;
556
557    /* Local CPU must be inactive and CPU hotplug in progress. */
558    BUG_ON(cpu_active(raw_smp_processor_id()));
559    smdata.num_threads = num_active_cpus() + 1; /* +1 for local */
560
561    /* No proper task established and can't sleep - busy wait for lock. */
562    while (!mutex_trylock(&stop_cpus_mutex))
563        cpu_relax();
564
565    /* Schedule work on other CPUs and execute directly for local CPU */
566    set_state(&smdata, STOPMACHINE_PREPARE);
567    cpu_stop_init_done(&done, num_active_cpus());
568    queue_stop_cpus_work(cpu_active_mask, stop_machine_cpu_stop, &smdata,
569                 &done);
570    ret = stop_machine_cpu_stop(&smdata);
571
572    /* Busy wait for completion. */
573    while (!completion_done(&done.completion))
574        cpu_relax();
575
576    mutex_unlock(&stop_cpus_mutex);
577    return ret ?: done.ret;
578}
579
580#endif /* CONFIG_STOP_MACHINE */
581

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