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/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/*
  23 * Temporary export for the deadlock workaround in ata_scsi_hotplug().
  24 * Remove once the hack becomes unnecessary.
  25 */
  26EXPORT_SYMBOL_GPL(pm_freezing);
  27
  28/* protects freezing and frozen transitions */
  29static DEFINE_SPINLOCK(freezer_lock);
  30
  31/**
  32 * freezing_slow_path - slow path for testing whether a task needs to be frozen
  33 * @p: task to be tested
  34 *
  35 * This function is called by freezing() if system_freezing_cnt isn't zero
  36 * and tests whether @p needs to enter and stay in frozen state.  Can be
  37 * called under any context.  The freezers are responsible for ensuring the
  38 * target tasks see the updated state.
  39 */
  40bool freezing_slow_path(struct task_struct *p)
  41{
  42        if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))
  43                return false;
  44
  45        if (test_tsk_thread_flag(p, TIF_MEMDIE))
  46                return false;
  47
  48        if (pm_nosig_freezing || cgroup_freezing(p))
  49                return true;
  50
  51        if (pm_freezing && !(p->flags & PF_KTHREAD))
  52                return true;
  53
  54        return false;
  55}
  56EXPORT_SYMBOL(freezing_slow_path);
  57
  58/* Refrigerator is place where frozen processes are stored :-). */
  59bool __refrigerator(bool check_kthr_stop)
  60{
  61        /* Hmm, should we be allowed to suspend when there are realtime
  62           processes around? */
  63        bool was_frozen = false;
  64        long save = current->state;
  65
  66        pr_debug("%s entered refrigerator\n", current->comm);
  67
  68        for (;;) {
  69                set_current_state(TASK_UNINTERRUPTIBLE);
  70
  71                spin_lock_irq(&freezer_lock);
  72                current->flags |= PF_FROZEN;
  73                if (!freezing(current) ||
  74                    (check_kthr_stop && kthread_should_stop()))
  75                        current->flags &= ~PF_FROZEN;
  76                spin_unlock_irq(&freezer_lock);
  77
  78                if (!(current->flags & PF_FROZEN))
  79                        break;
  80                was_frozen = true;
  81                schedule();
  82        }
  83
  84        pr_debug("%s left refrigerator\n", current->comm);
  85
  86        /*
  87         * Restore saved task state before returning.  The mb'd version
  88         * needs to be used; otherwise, it might silently break
  89         * synchronization which depends on ordered task state change.
  90         */
  91        set_current_state(save);
  92
  93        return was_frozen;
  94}
  95EXPORT_SYMBOL(__refrigerator);
  96
  97static void fake_signal_wake_up(struct task_struct *p)
  98{
  99        unsigned long flags;
 100
 101        if (lock_task_sighand(p, &flags)) {
 102                signal_wake_up(p, 0);
 103                unlock_task_sighand(p, &flags);
 104        }
 105}
 106
 107/**
 108 * freeze_task - send a freeze request to given task
 109 * @p: task to send the request to
 110 *
 111 * If @p is freezing, the freeze request is sent either by sending a fake
 112 * signal (if it's not a kernel thread) or waking it up (if it's a kernel
 113 * thread).
 114 *
 115 * RETURNS:
 116 * %false, if @p is not freezing or already frozen; %true, otherwise
 117 */
 118bool freeze_task(struct task_struct *p)
 119{
 120        unsigned long flags;
 121
 122        /*
 123         * This check can race with freezer_do_not_count, but worst case that
 124         * will result in an extra wakeup being sent to the task.  It does not
 125         * race with freezer_count(), the barriers in freezer_count() and
 126         * freezer_should_skip() ensure that either freezer_count() sees
 127         * freezing == true in try_to_freeze() and freezes, or
 128         * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task
 129         * normally.
 130         */
 131        if (freezer_should_skip(p))
 132                return false;
 133
 134        spin_lock_irqsave(&freezer_lock, flags);
 135        if (!freezing(p) || frozen(p)) {
 136                spin_unlock_irqrestore(&freezer_lock, flags);
 137                return false;
 138        }
 139
 140        if (!(p->flags & PF_KTHREAD))
 141                fake_signal_wake_up(p);
 142        else
 143                wake_up_state(p, TASK_INTERRUPTIBLE);
 144
 145        spin_unlock_irqrestore(&freezer_lock, flags);
 146        return true;
 147}
 148
 149void __thaw_task(struct task_struct *p)
 150{
 151        unsigned long flags;
 152
 153        spin_lock_irqsave(&freezer_lock, flags);
 154        if (frozen(p))
 155                wake_up_process(p);
 156        spin_unlock_irqrestore(&freezer_lock, flags);
 157}
 158
 159/**
 160 * set_freezable - make %current freezable
 161 *
 162 * Mark %current freezable and enter refrigerator if necessary.
 163 */
 164bool set_freezable(void)
 165{
 166        might_sleep();
 167
 168        /*
 169         * Modify flags while holding freezer_lock.  This ensures the
 170         * freezer notices that we aren't frozen yet or the freezing
 171         * condition is visible to try_to_freeze() below.
 172         */
 173        spin_lock_irq(&freezer_lock);
 174        current->flags &= ~PF_NOFREEZE;
 175        spin_unlock_irq(&freezer_lock);
 176
 177        return try_to_freeze();
 178}
 179EXPORT_SYMBOL(set_freezable);
 180