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 */
  15 atomic_t system_freezing_cnt = ATOMIC_INIT(0);
  16 EXPORT_SYMBOL(system_freezing_cnt);
  17
  18 /* indicate whether PM freezing is in effect, protected by pm_mutex */
  19 bool pm_freezing;
  20 bool pm_nosig_freezing;
  21
  22 /*
  23  * Temporary export for the deadlock workaround in ata_scsi_hotplug().
  24  * Remove once the hack becomes unnecessary.
  25  */
  26 EXPORT_SYMBOL_GPL(pm_freezing);
  27
  28 /* protects freezing and frozen transitions */
  29 static 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  */
  40 bool freezing_slow_path(struct task_struct *p)
  41 {
  42         if (p->flags & PF_NOFREEZE)
  43                 return false;
  44
  45         if (pm_nosig_freezing || cgroup_freezing(p))
  46                 return true;
  47
  48         if (pm_freezing && !(p->flags & PF_KTHREAD))
  49                 return true;
  50
  51         return false;
  52 }
  53 EXPORT_SYMBOL(freezing_slow_path);
  54
  55 /* Refrigerator is place where frozen processes are stored :-). */
  56 bool __refrigerator(bool check_kthr_stop)
  57 {
  58         /* Hmm, should we be allowed to suspend when there are realtime
  59            processes around? */
  60         bool was_frozen = false;
  61         long save = current->state;
  62
  63         pr_debug("%s entered refrigerator\n", current->comm);
  64
  65         for (;;) {
  66                 set_current_state(TASK_UNINTERRUPTIBLE);
  67
  68                 spin_lock_irq(&freezer_lock);
  69                 current->flags |= PF_FROZEN;
  70                 if (!freezing(current) ||
  71                     (check_kthr_stop && kthread_should_stop()))
  72                         current->flags &= ~PF_FROZEN;
  73                 spin_unlock_irq(&freezer_lock);
  74
  75                 if (!(current->flags & PF_FROZEN))
  76                         break;
  77                 was_frozen = true;
  78                 schedule();
  79         }
  80
  81         pr_debug("%s left refrigerator\n", current->comm);
  82
  83         /*
  84          * Restore saved task state before returning.  The mb'd version
  85          * needs to be used; otherwise, it might silently break
  86          * synchronization which depends on ordered task state change.
  87          */
  88         set_current_state(save);
  89
  90         return was_frozen;
  91 }
  92 EXPORT_SYMBOL(__refrigerator);
  93
  94 static void fake_signal_wake_up(struct task_struct *p)
  95 {
  96         unsigned long flags;
  97
  98         if (lock_task_sighand(p, &flags)) {
  99                 signal_wake_up(p, 0);
 100                 unlock_task_sighand(p, &flags);
 101         }
 102 }
 103
 104 /**
 105  * freeze_task - send a freeze request to given task
 106  * @p: task to send the request to
 107  *
 108  * If @p is freezing, the freeze request is sent either by sending a fake
 109  * signal (if it's not a kernel thread) or waking it up (if it's a kernel
 110  * thread).
 111  *
 112  * RETURNS:
 113  * %false, if @p is not freezing or already frozen; %true, otherwise
 114  */
 115 bool freeze_task(struct task_struct *p)
 116 {
 117         unsigned long flags;
 118
 119         /*
 120          * This check can race with freezer_do_not_count, but worst case that
 121          * will result in an extra wakeup being sent to the task.  It does not
 122          * race with freezer_count(), the barriers in freezer_count() and
 123          * freezer_should_skip() ensure that either freezer_count() sees
 124          * freezing == true in try_to_freeze() and freezes, or
 125          * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task
 126          * normally.
 127          */
 128         if (freezer_should_skip(p))
 129                 return false;
 130
 131         spin_lock_irqsave(&freezer_lock, flags);
 132         if (!freezing(p) || frozen(p)) {
 133                 spin_unlock_irqrestore(&freezer_lock, flags);
 134                 return false;
 135         }
 136
 137         if (!(p->flags & PF_KTHREAD))
 138                 fake_signal_wake_up(p);
 139         else
 140                 wake_up_state(p, TASK_INTERRUPTIBLE);
 141
 142         spin_unlock_irqrestore(&freezer_lock, flags);
 143         return true;
 144 }
 145
 146 void __thaw_task(struct task_struct *p)
 147 {
 148         unsigned long flags;
 149
 150         /*
 151          * Clear freezing and kick @p if FROZEN.  Clearing is guaranteed to
 152          * be visible to @p as waking up implies wmb.  Waking up inside
 153          * freezer_lock also prevents wakeups from leaking outside
 154          * refrigerator.
 155          */
 156         spin_lock_irqsave(&freezer_lock, flags);
 157         if (frozen(p))
 158                 wake_up_process(p);
 159         spin_unlock_irqrestore(&freezer_lock, flags);
 160 }
 161
 162 /**
 163  * set_freezable - make %current freezable
 164  *
 165  * Mark %current freezable and enter refrigerator if necessary.
 166  */
 167 bool set_freezable(void)
 168 {
 169         might_sleep();
 170
 171         /*
 172          * Modify flags while holding freezer_lock.  This ensures the
 173          * freezer notices that we aren't frozen yet or the freezing
 174          * condition is visible to try_to_freeze() below.
 175          */
 176         spin_lock_irq(&freezer_lock);
 177         current->flags &= ~PF_NOFREEZE;
 178         spin_unlock_irq(&freezer_lock);
 179
 180         return try_to_freeze();
 181 }
 182 EXPORT_SYMBOL(set_freezable);