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_FREEZER_NOSIG))
  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         spin_lock_irq(&current->sighand->siglock);
  76         recalc_sigpending(); /* We sent fake signal, clean it up */
  77         spin_unlock_irq(&current->sighand->siglock);
  78
  79         pr_debug("%s left refrigerator\n", current->comm);
  80
  81         /*
  82          * Restore saved task state before returning.  The mb'd version
  83          * needs to be used; otherwise, it might silently break
  84          * synchronization which depends on ordered task state change.
  85          */
  86         set_current_state(save);
  87
  88         return was_frozen;
  89 }
  90 EXPORT_SYMBOL(__refrigerator);
  91
  92 static void fake_signal_wake_up(struct task_struct *p)
  93 {
  94         unsigned long flags;
  95
  96         if (lock_task_sighand(p, &flags)) {
  97                 signal_wake_up(p, 0);
  98                 unlock_task_sighand(p, &flags);
  99         }
 100 }
 101
 102 /**
 103  * freeze_task - send a freeze request to given task
 104  * @p: task to send the request to
 105  *
 106  * If @p is freezing, the freeze request is sent by setting %TIF_FREEZE
 107  * flag and either sending a fake signal to it or waking it up, depending
 108  * on whether it has %PF_FREEZER_NOSIG set.
 109  *
 110  * RETURNS:
 111  * %false, if @p is not freezing or already frozen; %true, otherwise
 112  */
 113 bool freeze_task(struct task_struct *p)
 114 {
 115         unsigned long flags;
 116
 117         spin_lock_irqsave(&freezer_lock, flags);
 118         if (!freezing(p) || frozen(p)) {
 119                 spin_unlock_irqrestore(&freezer_lock, flags);
 120                 return false;
 121         }
 122
 123         if (!(p->flags & PF_FREEZER_NOSIG)) {
 124                 fake_signal_wake_up(p);
 125                 /*
 126                  * fake_signal_wake_up() goes through p's scheduler
 127                  * lock and guarantees that TASK_STOPPED/TRACED ->
 128                  * TASK_RUNNING transition can't race with task state
 129                  * testing in try_to_freeze_tasks().
 130                  */
 131         } else {
 132                 wake_up_state(p, TASK_INTERRUPTIBLE);
 133         }
 134
 135         spin_unlock_irqrestore(&freezer_lock, flags);
 136         return true;
 137 }
 138
 139 void __thaw_task(struct task_struct *p)
 140 {
 141         unsigned long flags;
 142
 143         /*
 144          * Clear freezing and kick @p if FROZEN.  Clearing is guaranteed to
 145          * be visible to @p as waking up implies wmb.  Waking up inside
 146          * freezer_lock also prevents wakeups from leaking outside
 147          * refrigerator.
 148          *
 149          * If !FROZEN, @p hasn't reached refrigerator, recalc sigpending to
 150          * avoid leaving dangling TIF_SIGPENDING behind.
 151          */
 152         spin_lock_irqsave(&freezer_lock, flags);
 153         if (frozen(p)) {
 154                 wake_up_process(p);
 155         } else {
 156                 spin_lock(&p->sighand->siglock);
 157                 recalc_sigpending_and_wake(p);
 158                 spin_unlock(&p->sighand->siglock);
 159         }
 160         spin_unlock_irqrestore(&freezer_lock, flags);
 161 }
 162
 163 /**
 164  * __set_freezable - make %current freezable
 165  * @with_signal: do we want %TIF_SIGPENDING for notification too?
 166  *
 167  * Mark %current freezable and enter refrigerator if necessary.
 168  */
 169 bool __set_freezable(bool with_signal)
 170 {
 171         might_sleep();
 172
 173         /*
 174          * Modify flags while holding freezer_lock.  This ensures the
 175          * freezer notices that we aren't frozen yet or the freezing
 176          * condition is visible to try_to_freeze() below.
 177          */
 178         spin_lock_irq(&freezer_lock);
 179         current->flags &= ~PF_NOFREEZE;
 180         if (with_signal)
 181                 current->flags &= ~PF_FREEZER_NOSIG;
 182         spin_unlock_irq(&freezer_lock);
 183
 184         return try_to_freeze();
 185 }
 186 EXPORT_SYMBOL(__set_freezable);