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        /* 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                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                if (!signal_pending(p))
 108                        fake_signal_wake_up(p);
 109        } else if (sig_only) {
 110                return false;
 111        } else {
 112                wake_up_state(p, TASK_INTERRUPTIBLE);
 113        }
 114
 115        return true;
 116}
 117
 118void cancel_freezing(struct task_struct *p)
 119{
 120        unsigned long flags;
 121
 122        if (freezing(p)) {
 123                pr_debug("  clean up: %s\n", p->comm);
 124                clear_freeze_flag(p);
 125                spin_lock_irqsave(&p->sighand->siglock, flags);
 126                recalc_sigpending_and_wake(p);
 127                spin_unlock_irqrestore(&p->sighand->siglock, flags);
 128        }
 129}
 130
 131static int __thaw_process(struct task_struct *p)
 132{
 133        if (frozen(p)) {
 134                p->flags &= ~PF_FROZEN;
 135                return 1;
 136        }
 137        clear_freeze_flag(p);
 138        return 0;
 139}
 140
 141/*
 142 * Wake up a frozen process
 143 *
 144 * task_lock() is needed to prevent the race with refrigerator() which may
 145 * occur if the freezing of tasks fails.  Namely, without the lock, if the
 146 * freezing of tasks failed, thaw_tasks() might have run before a task in
 147 * refrigerator() could call frozen_process(), in which case the task would be
 148 * frozen and no one would thaw it.
 149 */
 150int thaw_process(struct task_struct *p)
 151{
 152        task_lock(p);
 153        if (__thaw_process(p) == 1) {
 154                task_unlock(p);
 155                wake_up_process(p);
 156                return 1;
 157        }
 158        task_unlock(p);
 159        return 0;
 160}
 161EXPORT_SYMBOL(thaw_process);
 162