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 /* protects freezing and frozen transitions */
  23 static 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  */
  34 bool freezing_slow_path(struct task_struct *p)
  35 {
  36         if (p->flags & PF_NOFREEZE)
  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 }
  47 EXPORT_SYMBOL(freezing_slow_path);
  48
  49 /* Refrigerator is place where frozen processes are stored :-). */
  50 bool __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 }
  86 EXPORT_SYMBOL(__refrigerator);
  87
  88 static 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  */
 109 bool freeze_task(struct task_struct *p)
 110 {
 111         unsigned long flags;
 112
 113         spin_lock_irqsave(&freezer_lock, flags);
 114         if (!freezing(p) || frozen(p)) {
 115                 spin_unlock_irqrestore(&freezer_lock, flags);
 116                 return false;
 117         }
 118
 119         if (!(p->flags & PF_KTHREAD)) {
 120                 fake_signal_wake_up(p);
 121                 /*
 122                  * fake_signal_wake_up() goes through p's scheduler
 123                  * lock and guarantees that TASK_STOPPED/TRACED ->
 124                  * TASK_RUNNING transition can't race with task state
 125                  * testing in try_to_freeze_tasks().
 126                  */
 127         } else {
 128                 wake_up_state(p, TASK_INTERRUPTIBLE);
 129         }
 130
 131         spin_unlock_irqrestore(&freezer_lock, flags);
 132         return true;
 133 }
 134
 135 void __thaw_task(struct task_struct *p)
 136 {
 137         unsigned long flags;
 138
 139         /*
 140          * Clear freezing and kick @p if FROZEN.  Clearing is guaranteed to
 141          * be visible to @p as waking up implies wmb.  Waking up inside
 142          * freezer_lock also prevents wakeups from leaking outside
 143          * refrigerator.
 144          */
 145         spin_lock_irqsave(&freezer_lock, flags);
 146         if (frozen(p))
 147                 wake_up_process(p);
 148         spin_unlock_irqrestore(&freezer_lock, flags);
 149 }
 150
 151 /**
 152  * set_freezable - make %current freezable
 153  *
 154  * Mark %current freezable and enter refrigerator if necessary.
 155  */
 156 bool set_freezable(void)
 157 {
 158         might_sleep();
 159
 160         /*
 161          * Modify flags while holding freezer_lock.  This ensures the
 162          * freezer notices that we aren't frozen yet or the freezing
 163          * condition is visible to try_to_freeze() below.
 164          */
 165         spin_lock_irq(&freezer_lock);
 166         current->flags &= ~PF_NOFREEZE;
 167         spin_unlock_irq(&freezer_lock);
 168
 169         return try_to_freeze();
 170 }
 171 EXPORT_SYMBOL(set_freezable);