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 /* protects freezing and frozen transitions */
  15 static DEFINE_SPINLOCK(freezer_lock);
  16
  17 /* Refrigerator is place where frozen processes are stored :-). */
  18 bool __refrigerator(bool check_kthr_stop)
  19 {
  20         /* Hmm, should we be allowed to suspend when there are realtime
  21            processes around? */
  22         bool was_frozen = false;
  23         long save;
  24
  25         spin_lock_irq(&freezer_lock);
  26         if (!freezing(current)) {
  27                 spin_unlock_irq(&freezer_lock);
  28                 return was_frozen;
  29         }
  30         if (!(current->flags & PF_NOFREEZE))
  31                 current->flags |= PF_FROZEN;
  32         clear_freeze_flag(current);
  33         spin_unlock_irq(&freezer_lock);
  34
  35         save = current->state;
  36         pr_debug("%s entered refrigerator\n", current->comm);
  37
  38         spin_lock_irq(&current->sighand->siglock);
  39         recalc_sigpending(); /* We sent fake signal, clean it up */
  40         spin_unlock_irq(&current->sighand->siglock);
  41
  42         /* prevent accounting of that task to load */
  43         current->flags |= PF_FREEZING;
  44
  45         for (;;) {
  46                 set_current_state(TASK_UNINTERRUPTIBLE);
  47                 if (!frozen(current) ||
  48                     (check_kthr_stop && kthread_should_stop()))
  49                         break;
  50                 was_frozen = true;
  51                 schedule();
  52         }
  53
  54         /* Remove the accounting blocker */
  55         current->flags &= ~PF_FREEZING;
  56
  57         pr_debug("%s left refrigerator\n", current->comm);
  58
  59         /*
  60          * Restore saved task state before returning.  The mb'd version
  61          * needs to be used; otherwise, it might silently break
  62          * synchronization which depends on ordered task state change.
  63          */
  64         set_current_state(save);
  65
  66         return was_frozen;
  67 }
  68 EXPORT_SYMBOL(__refrigerator);
  69
  70 static void fake_signal_wake_up(struct task_struct *p)
  71 {
  72         unsigned long flags;
  73
  74         spin_lock_irqsave(&p->sighand->siglock, flags);
  75         signal_wake_up(p, 0);
  76         spin_unlock_irqrestore(&p->sighand->siglock, flags);
  77 }
  78
  79 /**
  80  *      freeze_task - send a freeze request to given task
  81  *      @p: task to send the request to
  82  *      @sig_only: if set, the request will only be sent if the task has the
  83  *              PF_FREEZER_NOSIG flag unset
  84  *      Return value: 'false', if @sig_only is set and the task has
  85  *              PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
  86  *
  87  *      The freeze request is sent by setting the tasks's TIF_FREEZE flag and
  88  *      either sending a fake signal to it or waking it up, depending on whether
  89  *      or not it has PF_FREEZER_NOSIG set.  If @sig_only is set and the task
  90  *      has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
  91  *      TIF_FREEZE flag will not be set.
  92  */
  93 bool freeze_task(struct task_struct *p, bool sig_only)
  94 {
  95         unsigned long flags;
  96         bool ret = false;
  97
  98         spin_lock_irqsave(&freezer_lock, flags);
  99
 100         if (sig_only && !should_send_signal(p))
 101                 goto out_unlock;
 102
 103         if (frozen(p))
 104                 goto out_unlock;
 105
 106         set_freeze_flag(p);
 107
 108         if (should_send_signal(p)) {
 109                 fake_signal_wake_up(p);
 110                 /*
 111                  * fake_signal_wake_up() goes through p's scheduler
 112                  * lock and guarantees that TASK_STOPPED/TRACED ->
 113                  * TASK_RUNNING transition can't race with task state
 114                  * testing in try_to_freeze_tasks().
 115                  */
 116         } else {
 117                 wake_up_state(p, TASK_INTERRUPTIBLE);
 118         }
 119         ret = true;
 120 out_unlock:
 121         spin_unlock_irqrestore(&freezer_lock, flags);
 122         return ret;
 123 }
 124
 125 void cancel_freezing(struct task_struct *p)
 126 {
 127         unsigned long flags;
 128
 129         spin_lock_irqsave(&freezer_lock, flags);
 130         if (freezing(p)) {
 131                 pr_debug("  clean up: %s\n", p->comm);
 132                 clear_freeze_flag(p);
 133                 spin_lock(&p->sighand->siglock);
 134                 recalc_sigpending_and_wake(p);
 135                 spin_unlock(&p->sighand->siglock);
 136         }
 137         spin_unlock_irqrestore(&freezer_lock, flags);
 138 }
 139
 140 /*
 141  * Wake up a frozen task
 142  *
 143  * task_lock() is needed to prevent the race with refrigerator() which may
 144  * occur if the freezing of tasks fails.  Namely, without the lock, if the
 145  * freezing of tasks failed, thaw_tasks() might have run before a task in
 146  * refrigerator() could call frozen_process(), in which case the task would be
 147  * frozen and no one would thaw it.
 148  */
 149 void __thaw_task(struct task_struct *p)
 150 {
 151         unsigned long flags;
 152
 153         spin_lock_irqsave(&freezer_lock, flags);
 154         if (frozen(p)) {
 155                 p->flags &= ~PF_FROZEN;
 156                 wake_up_process(p);
 157         } else {
 158                 clear_freeze_flag(p);
 159         }
 160         spin_unlock_irqrestore(&freezer_lock, flags);
 161 }