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 | PF_SUSPEND_TASK))
  43                 return false;
  44
  45         if (test_thread_flag(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 }
  56 EXPORT_SYMBOL(freezing_slow_path);
  57
  58 /* Refrigerator is place where frozen processes are stored :-). */
  59 bool __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 }
  95 EXPORT_SYMBOL(__refrigerator);
  96
  97 static 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  */
 118 bool 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
 149 void __thaw_task(struct task_struct *p)
 150 {
 151         unsigned long flags;
 152
 153         /*
 154          * Clear freezing and kick @p if FROZEN.  Clearing is guaranteed to
 155          * be visible to @p as waking up implies wmb.  Waking up inside
 156          * freezer_lock also prevents wakeups from leaking outside
 157          * refrigerator.
 158          */
 159         spin_lock_irqsave(&freezer_lock, flags);
 160         if (frozen(p))
 161                 wake_up_process(p);
 162         spin_unlock_irqrestore(&freezer_lock, flags);
 163 }
 164
 165 /**
 166  * set_freezable - make %current freezable
 167  *
 168  * Mark %current freezable and enter refrigerator if necessary.
 169  */
 170 bool set_freezable(void)
 171 {
 172         might_sleep();
 173
 174         /*
 175          * Modify flags while holding freezer_lock.  This ensures the
 176          * freezer notices that we aren't frozen yet or the freezing
 177          * condition is visible to try_to_freeze() below.
 178          */
 179         spin_lock_irq(&freezer_lock);
 180         current->flags &= ~PF_NOFREEZE;
 181         spin_unlock_irq(&freezer_lock);
 182
 183         return try_to_freeze();
 184 }
 185 EXPORT_SYMBOL(set_freezable);