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/export.h>
  10#include <linux/syscalls.h>
  11#include <linux/freezer.h>
  12#include <linux/kthread.h>
  13
  14/* total number of freezing conditions in effect */
  15atomic_t system_freezing_cnt = ATOMIC_INIT(0);
  16EXPORT_SYMBOL(system_freezing_cnt);
  17
  18/* indicate whether PM freezing is in effect, protected by pm_mutex */
  19bool pm_freezing;
  20bool pm_nosig_freezing;
  21
  22/* protects freezing and frozen transitions */
  23static DEFINE_SPINLOCK(freezer_lock);
  24
  25/**
  26 * freezing_slow_path - slow path for testing whether a task needs to be frozen
  27 * @p: task to be tested
  28 *
  29 * This function is called by freezing() if system_freezing_cnt isn't zero
  30 * and tests whether @p needs to enter and stay in frozen state.  Can be
  31 * called under any context.  The freezers are responsible for ensuring the
  32 * target tasks see the updated state.
  33 */
  34bool freezing_slow_path(struct task_struct *p)
  35{
  36        if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))
  37                return false;
  38
  39        if (pm_nosig_freezing || cgroup_freezing(p))
  40                return true;
  41
  42        if (pm_freezing && !(p->flags & PF_KTHREAD))
  43                return true;
  44
  45        return false;
  46}
  47EXPORT_SYMBOL(freezing_slow_path);
  48
  49/* Refrigerator is place where frozen processes are stored :-). */
  50bool __refrigerator(bool check_kthr_stop)
  51{
  52        /* Hmm, should we be allowed to suspend when there are realtime
  53           processes around? */
  54        bool was_frozen = false;
  55        long save = current->state;
  56
  57        pr_debug("%s entered refrigerator\n", current->comm);
  58
  59        for (;;) {
  60                set_current_state(TASK_UNINTERRUPTIBLE);
  61
  62                spin_lock_irq(&freezer_lock);
  63                current->flags |= PF_FROZEN;
  64                if (!freezing(current) ||
  65                    (check_kthr_stop && kthread_should_stop()))
  66                        current->flags &= ~PF_FROZEN;
  67                spin_unlock_irq(&freezer_lock);
  68
  69                if (!(current->flags & PF_FROZEN))
  70                        break;
  71                was_frozen = true;
  72                schedule();
  73        }
  74
  75        pr_debug("%s left refrigerator\n", current->comm);
  76
  77        /*
  78         * Restore saved task state before returning.  The mb'd version
  79         * needs to be used; otherwise, it might silently break
  80         * synchronization which depends on ordered task state change.
  81         */
  82        set_current_state(save);
  83
  84        return was_frozen;
  85}
  86EXPORT_SYMBOL(__refrigerator);
  87
  88static void fake_signal_wake_up(struct task_struct *p)
  89{
  90        unsigned long flags;
  91
  92        if (lock_task_sighand(p, &flags)) {
  93                signal_wake_up(p, 0);
  94                unlock_task_sighand(p, &flags);
  95        }
  96}
  97
  98/**
  99 * freeze_task - send a freeze request to given task
 100 * @p: task to send the request to
 101 *
 102 * If @p is freezing, the freeze request is sent either by sending a fake
 103 * signal (if it's not a kernel thread) or waking it up (if it's a kernel
 104 * thread).
 105 *
 106 * RETURNS:
 107 * %false, if @p is not freezing or already frozen; %true, otherwise
 108 */
 109bool freeze_task(struct task_struct *p)
 110{
 111        unsigned long flags;
 112
 113        /*
 114         * This check can race with freezer_do_not_count, but worst case that
 115         * will result in an extra wakeup being sent to the task.  It does not
 116         * race with freezer_count(), the barriers in freezer_count() and
 117         * freezer_should_skip() ensure that either freezer_count() sees
 118         * freezing == true in try_to_freeze() and freezes, or
 119         * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task
 120         * normally.
 121         */
 122        if (freezer_should_skip(p))
 123                return false;
 124
 125        spin_lock_irqsave(&freezer_lock, flags);
 126        if (!freezing(p) || frozen(p)) {
 127                spin_unlock_irqrestore(&freezer_lock, flags);
 128                return false;
 129        }
 130
 131        if (!(p->flags & PF_KTHREAD))
 132                fake_signal_wake_up(p);
 133        else
 134                wake_up_state(p, TASK_INTERRUPTIBLE);
 135
 136        spin_unlock_irqrestore(&freezer_lock, flags);
 137        return true;
 138}
 139
 140void __thaw_task(struct task_struct *p)
 141{
 142        unsigned long flags;
 143
 144        /*
 145         * Clear freezing and kick @p if FROZEN.  Clearing is guaranteed to
 146         * be visible to @p as waking up implies wmb.  Waking up inside
 147         * freezer_lock also prevents wakeups from leaking outside
 148         * refrigerator.
 149         */
 150        spin_lock_irqsave(&freezer_lock, flags);
 151        if (frozen(p))
 152                wake_up_process(p);
 153        spin_unlock_irqrestore(&freezer_lock, flags);
 154}
 155
 156/**
 157 * set_freezable - make %current freezable
 158 *
 159 * Mark %current freezable and enter refrigerator if necessary.
 160 */
 161bool set_freezable(void)
 162{
 163        might_sleep();
 164
 165        /*
 166         * Modify flags while holding freezer_lock.  This ensures the
 167         * freezer notices that we aren't frozen yet or the freezing
 168         * condition is visible to try_to_freeze() below.
 169         */
 170        spin_lock_irq(&freezer_lock);
 171        current->flags &= ~PF_NOFREEZE;
 172        spin_unlock_irq(&freezer_lock);
 173
 174        return try_to_freeze();
 175}
 176EXPORT_SYMBOL(set_freezable);
 177
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