linux/kernel/freezer.c
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   1/*
   2 * kernel/freezer.c - Function to freeze a process
   3 *
   4 * Originally from kernel/power/process.c
   5 */
   6
   7#include <linux/interrupt.h>
   8#include <linux/suspend.h>
   9#include <linux/module.h>
  10#include <linux/syscalls.h>
  11#include <linux/freezer.h>
  12
  13/*
  14 * freezing is complete, mark current process as frozen
  15 */
  16static inline void frozen_process(void)
  17{
  18        if (!unlikely(current->flags & PF_NOFREEZE)) {
  19                current->flags |= PF_FROZEN;
  20                smp_wmb();
  21        }
  22        clear_freeze_flag(current);
  23}
  24
  25/* Refrigerator is place where frozen processes are stored :-). */
  26void refrigerator(void)
  27{
  28        /* Hmm, should we be allowed to suspend when there are realtime
  29           processes around? */
  30        long save;
  31
  32        task_lock(current);
  33        if (freezing(current)) {
  34                frozen_process();
  35                task_unlock(current);
  36        } else {
  37                task_unlock(current);
  38                return;
  39        }
  40        save = current->state;
  41        pr_debug("%s entered refrigerator\n", current->comm);
  42
  43        spin_lock_irq(&current->sighand->siglock);
  44        recalc_sigpending(); /* We sent fake signal, clean it up */
  45        spin_unlock_irq(&current->sighand->siglock);
  46
  47        /* prevent accounting of that task to load */
  48        current->flags |= PF_FREEZING;
  49
  50        for (;;) {
  51                set_current_state(TASK_UNINTERRUPTIBLE);
  52                if (!frozen(current))
  53                        break;
  54                schedule();
  55        }
  56
  57        /* Remove the accounting blocker */
  58        current->flags &= ~PF_FREEZING;
  59
  60        pr_debug("%s left refrigerator\n", current->comm);
  61        __set_current_state(save);
  62}
  63EXPORT_SYMBOL(refrigerator);
  64
  65static void fake_signal_wake_up(struct task_struct *p)
  66{
  67        unsigned long flags;
  68
  69        spin_lock_irqsave(&p->sighand->siglock, flags);
  70        signal_wake_up(p, 0);
  71        spin_unlock_irqrestore(&p->sighand->siglock, flags);
  72}
  73
  74/**
  75 *      freeze_task - send a freeze request to given task
  76 *      @p: task to send the request to
  77 *      @sig_only: if set, the request will only be sent if the task has the
  78 *              PF_FREEZER_NOSIG flag unset
  79 *      Return value: 'false', if @sig_only is set and the task has
  80 *              PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
  81 *
  82 *      The freeze request is sent by setting the tasks's TIF_FREEZE flag and
  83 *      either sending a fake signal to it or waking it up, depending on whether
  84 *      or not it has PF_FREEZER_NOSIG set.  If @sig_only is set and the task
  85 *      has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
  86 *      TIF_FREEZE flag will not be set.
  87 */
  88bool freeze_task(struct task_struct *p, bool sig_only)
  89{
  90        /*
  91         * We first check if the task is freezing and next if it has already
  92         * been frozen to avoid the race with frozen_process() which first marks
  93         * the task as frozen and next clears its TIF_FREEZE.
  94         */
  95        if (!freezing(p)) {
  96                smp_rmb();
  97                if (frozen(p))
  98                        return false;
  99
 100                if (!sig_only || should_send_signal(p))
 101                        set_freeze_flag(p);
 102                else
 103                        return false;
 104        }
 105
 106        if (should_send_signal(p)) {
 107                fake_signal_wake_up(p);
 108                /*
 109                 * fake_signal_wake_up() goes through p's scheduler
 110                 * lock and guarantees that TASK_STOPPED/TRACED ->
 111                 * TASK_RUNNING transition can't race with task state
 112                 * testing in try_to_freeze_tasks().
 113                 */
 114        } else if (sig_only) {
 115                return false;
 116        } else {
 117                wake_up_state(p, TASK_INTERRUPTIBLE);
 118        }
 119
 120        return true;
 121}
 122
 123void cancel_freezing(struct task_struct *p)
 124{
 125        unsigned long flags;
 126
 127        if (freezing(p)) {
 128                pr_debug("  clean up: %s\n", p->comm);
 129                clear_freeze_flag(p);
 130                spin_lock_irqsave(&p->sighand->siglock, flags);
 131                recalc_sigpending_and_wake(p);
 132                spin_unlock_irqrestore(&p->sighand->siglock, flags);
 133        }
 134}
 135
 136static int __thaw_process(struct task_struct *p)
 137{
 138        if (frozen(p)) {
 139                p->flags &= ~PF_FROZEN;
 140                return 1;
 141        }
 142        clear_freeze_flag(p);
 143        return 0;
 144}
 145
 146/*
 147 * Wake up a frozen process
 148 *
 149 * task_lock() is needed to prevent the race with refrigerator() which may
 150 * occur if the freezing of tasks fails.  Namely, without the lock, if the
 151 * freezing of tasks failed, thaw_tasks() might have run before a task in
 152 * refrigerator() could call frozen_process(), in which case the task would be
 153 * frozen and no one would thaw it.
 154 */
 155int thaw_process(struct task_struct *p)
 156{
 157        task_lock(p);
 158        if (__thaw_process(p) == 1) {
 159                task_unlock(p);
 160                wake_up_process(p);
 161                return 1;
 162        }
 163        task_unlock(p);
 164        return 0;
 165}
 166EXPORT_SYMBOL(thaw_process);
 167
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