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
  19  * system_transition_mutex
  20  */
  21 bool pm_freezing;
  22 bool pm_nosig_freezing;
  23
  24 /*
  25  * Temporary export for the deadlock workaround in ata_scsi_hotplug().
  26  * Remove once the hack becomes unnecessary.
  27  */
  28 EXPORT_SYMBOL_GPL(pm_freezing);
  29
  30 /* protects freezing and frozen transitions */
  31 static DEFINE_SPINLOCK(freezer_lock);
  32
  33 /**
  34  * freezing_slow_path - slow path for testing whether a task needs to be frozen
  35  * @p: task to be tested
  36  *
  37  * This function is called by freezing() if system_freezing_cnt isn't zero
  38  * and tests whether @p needs to enter and stay in frozen state.  Can be
  39  * called under any context.  The freezers are responsible for ensuring the
  40  * target tasks see the updated state.
  41  */
  42 bool freezing_slow_path(struct task_struct *p)
  43 {
  44         if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))
  45                 return false;
  46
  47         if (test_tsk_thread_flag(p, TIF_MEMDIE))
  48                 return false;
  49
  50         if (pm_nosig_freezing || cgroup_freezing(p))
  51                 return true;
  52
  53         if (pm_freezing && !(p->flags & PF_KTHREAD))
  54                 return true;
  55
  56         return false;
  57 }
  58 EXPORT_SYMBOL(freezing_slow_path);
  59
  60 /* Refrigerator is place where frozen processes are stored :-). */
  61 bool __refrigerator(bool check_kthr_stop)
  62 {
  63         /* Hmm, should we be allowed to suspend when there are realtime
  64            processes around? */
  65         bool was_frozen = false;
  66         long save = current->state;
  67
  68         pr_debug("%s entered refrigerator\n", current->comm);
  69
  70         for (;;) {
  71                 set_current_state(TASK_UNINTERRUPTIBLE);
  72
  73                 spin_lock_irq(&freezer_lock);
  74                 current->flags |= PF_FROZEN;
  75                 if (!freezing(current) ||
  76                     (check_kthr_stop && kthread_should_stop()))
  77                         current->flags &= ~PF_FROZEN;
  78                 spin_unlock_irq(&freezer_lock);
  79
  80                 if (!(current->flags & PF_FROZEN))
  81                         break;
  82                 was_frozen = true;
  83                 schedule();
  84         }
  85
  86         pr_debug("%s left refrigerator\n", current->comm);
  87
  88         /*
  89          * Restore saved task state before returning.  The mb'd version
  90          * needs to be used; otherwise, it might silently break
  91          * synchronization which depends on ordered task state change.
  92          */
  93         set_current_state(save);
  94
  95         return was_frozen;
  96 }
  97 EXPORT_SYMBOL(__refrigerator);
  98
  99 static void fake_signal_wake_up(struct task_struct *p)
 100 {
 101         unsigned long flags;
 102
 103         if (lock_task_sighand(p, &flags)) {
 104                 signal_wake_up(p, 0);
 105                 unlock_task_sighand(p, &flags);
 106         }
 107 }
 108
 109 /**
 110  * freeze_task - send a freeze request to given task
 111  * @p: task to send the request to
 112  *
 113  * If @p is freezing, the freeze request is sent either by sending a fake
 114  * signal (if it's not a kernel thread) or waking it up (if it's a kernel
 115  * thread).
 116  *
 117  * RETURNS:
 118  * %false, if @p is not freezing or already frozen; %true, otherwise
 119  */
 120 bool freeze_task(struct task_struct *p)
 121 {
 122         unsigned long flags;
 123
 124         /*
 125          * This check can race with freezer_do_not_count, but worst case that
 126          * will result in an extra wakeup being sent to the task.  It does not
 127          * race with freezer_count(), the barriers in freezer_count() and
 128          * freezer_should_skip() ensure that either freezer_count() sees
 129          * freezing == true in try_to_freeze() and freezes, or
 130          * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task
 131          * normally.
 132          */
 133         if (freezer_should_skip(p))
 134                 return false;
 135
 136         spin_lock_irqsave(&freezer_lock, flags);
 137         if (!freezing(p) || frozen(p)) {
 138                 spin_unlock_irqrestore(&freezer_lock, flags);
 139                 return false;
 140         }
 141
 142         if (!(p->flags & PF_KTHREAD))
 143                 fake_signal_wake_up(p);
 144         else
 145                 wake_up_state(p, TASK_INTERRUPTIBLE);
 146
 147         spin_unlock_irqrestore(&freezer_lock, flags);
 148         return true;
 149 }
 150
 151 void __thaw_task(struct task_struct *p)
 152 {
 153         unsigned long flags;
 154
 155         spin_lock_irqsave(&freezer_lock, flags);
 156         if (frozen(p))
 157                 wake_up_process(p);
 158         spin_unlock_irqrestore(&freezer_lock, flags);
 159 }
 160
 161 /**
 162  * set_freezable - make %current freezable
 163  *
 164  * Mark %current freezable and enter refrigerator if necessary.
 165  */
 166 bool set_freezable(void)
 167 {
 168         might_sleep();
 169
 170         /*
 171          * Modify flags while holding freezer_lock.  This ensures the
 172          * freezer notices that we aren't frozen yet or the freezing
 173          * condition is visible to try_to_freeze() below.
 174          */
 175         spin_lock_irq(&freezer_lock);
 176         current->flags &= ~PF_NOFREEZE;
 177         spin_unlock_irq(&freezer_lock);
 178
 179         return try_to_freeze();
 180 }
 181 EXPORT_SYMBOL(set_freezable);