LXR linux/kernel/freezer.c

   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                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        for (;;) {
  48                set_current_state(TASK_UNINTERRUPTIBLE);
  49                if (!frozen(current))
  50                        break;
  51                schedule();
  52        }
  53        pr_debug("%s left refrigerator\n", current->comm);
  54        __set_current_state(save);
  55}
  56EXPORT_SYMBOL(refrigerator);
  57
  58static void fake_signal_wake_up(struct task_struct *p)
  59{
  60        unsigned long flags;
  61
  62        spin_lock_irqsave(&p->sighand->siglock, flags);
  63        signal_wake_up(p, 0);
  64        spin_unlock_irqrestore(&p->sighand->siglock, flags);
  65}
  66
  67/**
  68 *      freeze_task - send a freeze request to given task
  69 *      @p: task to send the request to
  70 *      @sig_only: if set, the request will only be sent if the task has the
  71 *              PF_FREEZER_NOSIG flag unset
  72 *      Return value: 'false', if @sig_only is set and the task has
  73 *              PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
  74 *
  75 *      The freeze request is sent by setting the tasks's TIF_FREEZE flag and
  76 *      either sending a fake signal to it or waking it up, depending on whether
  77 *      or not it has PF_FREEZER_NOSIG set.  If @sig_only is set and the task
  78 *      has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
  79 *      TIF_FREEZE flag will not be set.
  80 */
  81bool freeze_task(struct task_struct *p, bool sig_only)
  82{
  83        /*
  84         * We first check if the task is freezing and next if it has already
  85         * been frozen to avoid the race with frozen_process() which first marks
  86         * the task as frozen and next clears its TIF_FREEZE.
  87         */
  88        if (!freezing(p)) {
  89                rmb();
  90                if (frozen(p))
  91                        return false;
  92
  93                if (!sig_only || should_send_signal(p))
  94                        set_freeze_flag(p);
  95                else
  96                        return false;
  97        }
  98
  99        if (should_send_signal(p)) {
 100                if (!signal_pending(p))
 101                        fake_signal_wake_up(p);
 102        } else if (sig_only) {
 103                return false;
 104        } else {
 105                wake_up_state(p, TASK_INTERRUPTIBLE);
 106        }
 107
 108        return true;
 109}
 110
 111void cancel_freezing(struct task_struct *p)
 112{
 113        unsigned long flags;
 114
 115        if (freezing(p)) {
 116                pr_debug("  clean up: %s\n", p->comm);
 117                clear_freeze_flag(p);
 118                spin_lock_irqsave(&p->sighand->siglock, flags);
 119                recalc_sigpending_and_wake(p);
 120                spin_unlock_irqrestore(&p->sighand->siglock, flags);
 121        }
 122}
 123
 124static int __thaw_process(struct task_struct *p)
 125{
 126        if (frozen(p)) {
 127                p->flags &= ~PF_FROZEN;
 128                return 1;
 129        }
 130        clear_freeze_flag(p);
 131        return 0;
 132}
 133
 134/*
 135 * Wake up a frozen process
 136 *
 137 * task_lock() is needed to prevent the race with refrigerator() which may
 138 * occur if the freezing of tasks fails.  Namely, without the lock, if the
 139 * freezing of tasks failed, thaw_tasks() might have run before a task in
 140 * refrigerator() could call frozen_process(), in which case the task would be
 141 * frozen and no one would thaw it.
 142 */
 143int thaw_process(struct task_struct *p)
 144{
 145        task_lock(p);
 146        if (__thaw_process(p) == 1) {
 147                task_unlock(p);
 148                wake_up_process(p);
 149                return 1;
 150        }
 151        task_unlock(p);
 152        return 0;
 153}
 154EXPORT_SYMBOL(thaw_process);
 155