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/module.h>
  10 #include <linux/syscalls.h>
  11 #include <linux/freezer.h>
  12
  13 /*
  14  * freezing is complete, mark current process as frozen
  15  */
  16 static inline void frozen_process(void)
  17 {
  18         if (!unlikely(current->flags & PF_NOFREEZE)) {
  19                 current->flags |= PF_FROZEN;
  20                 wmb();
  21         }
  22         clear_freeze_flag(current);
  23 }
  24
  25 /* Refrigerator is place where frozen processes are stored :-). */
  26 void refrigerator(void)
  27 {
  28         /* Hmm, should we be allowed to suspend when there are realtime
  29            processes around? */
  30         long save;
  31
  32         task_lock(current);
  33         if (freezing(current)) {
  34                 frozen_process();
  35                 task_unlock(current);
  36         } else {
  37                 task_unlock(current);
  38                 return;
  39         }
  40         save = current->state;
  41         pr_debug("%s entered refrigerator\n", current->comm);
  42
  43         spin_lock_irq(&current->sighand->siglock);
  44         recalc_sigpending(); /* We sent fake signal, clean it up */
  45         spin_unlock_irq(&current->sighand->siglock);
  46
  47         for (;;) {
  48                 set_current_state(TASK_UNINTERRUPTIBLE);
  49                 if (!frozen(current))
  50                         break;
  51                 schedule();
  52         }
  53         pr_debug("%s left refrigerator\n", current->comm);
  54         __set_current_state(save);
  55 }
  56 EXPORT_SYMBOL(refrigerator);
  57
  58 static void fake_signal_wake_up(struct task_struct *p)
  59 {
  60         unsigned long flags;
  61
  62         spin_lock_irqsave(&p->sighand->siglock, flags);
  63         signal_wake_up(p, 0);
  64         spin_unlock_irqrestore(&p->sighand->siglock, flags);
  65 }
  66
  67 /**
  68  *      freeze_task - send a freeze request to given task
  69  *      @p: task to send the request to
  70  *      @sig_only: if set, the request will only be sent if the task has the
  71  *              PF_FREEZER_NOSIG flag unset
  72  *      Return value: 'false', if @sig_only is set and the task has
  73  *              PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
  74  *
  75  *      The freeze request is sent by setting the tasks's TIF_FREEZE flag and
  76  *      either sending a fake signal to it or waking it up, depending on whether
  77  *      or not it has PF_FREEZER_NOSIG set.  If @sig_only is set and the task
  78  *      has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
  79  *      TIF_FREEZE flag will not be set.
  80  */
  81 bool freeze_task(struct task_struct *p, bool sig_only)
  82 {
  83         /*
  84          * We first check if the task is freezing and next if it has already
  85          * been frozen to avoid the race with frozen_process() which first marks
  86          * the task as frozen and next clears its TIF_FREEZE.
  87          */
  88         if (!freezing(p)) {
  89                 rmb();
  90                 if (frozen(p))
  91                         return false;
  92
  93                 if (!sig_only || should_send_signal(p))
  94                         set_freeze_flag(p);
  95                 else
  96                         return false;
  97         }
  98
  99         if (should_send_signal(p)) {
 100                 if (!signal_pending(p))
 101                         fake_signal_wake_up(p);
 102         } else if (sig_only) {
 103                 return false;
 104         } else {
 105                 wake_up_state(p, TASK_INTERRUPTIBLE);
 106         }
 107
 108         return true;
 109 }
 110
 111 void cancel_freezing(struct task_struct *p)
 112 {
 113         unsigned long flags;
 114
 115         if (freezing(p)) {
 116                 pr_debug("  clean up: %s\n", p->comm);
 117                 clear_freeze_flag(p);
 118                 spin_lock_irqsave(&p->sighand->siglock, flags);
 119                 recalc_sigpending_and_wake(p);
 120                 spin_unlock_irqrestore(&p->sighand->siglock, flags);
 121         }
 122 }
 123
 124 static int __thaw_process(struct task_struct *p)
 125 {
 126         if (frozen(p)) {
 127                 p->flags &= ~PF_FROZEN;
 128                 return 1;
 129         }
 130         clear_freeze_flag(p);
 131         return 0;
 132 }
 133
 134 /*
 135  * Wake up a frozen process
 136  *
 137  * task_lock() is needed to prevent the race with refrigerator() which may
 138  * occur if the freezing of tasks fails.  Namely, without the lock, if the
 139  * freezing of tasks failed, thaw_tasks() might have run before a task in
 140  * refrigerator() could call frozen_process(), in which case the task would be
 141  * frozen and no one would thaw it.
 142  */
 143 int thaw_process(struct task_struct *p)
 144 {
 145         task_lock(p);
 146         if (__thaw_process(p) == 1) {
 147                 task_unlock(p);
 148                 wake_up_process(p);
 149                 return 1;
 150         }
 151         task_unlock(p);
 152         return 0;
 153 }
 154 EXPORT_SYMBOL(thaw_process);