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
  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                 smp_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         /* prevent accounting of that task to load */
  48         current->flags |= PF_FREEZING;
  49
  50         for (;;) {
  51                 set_current_state(TASK_UNINTERRUPTIBLE);
  52                 if (!frozen(current))
  53                         break;
  54                 schedule();
  55         }
  56
  57         /* Remove the accounting blocker */
  58         current->flags &= ~PF_FREEZING;
  59
  60         pr_debug("%s left refrigerator\n", current->comm);
  61         __set_current_state(save);
  62 }
  63 EXPORT_SYMBOL(refrigerator);
  64
  65 static void fake_signal_wake_up(struct task_struct *p)
  66 {
  67         unsigned long flags;
  68
  69         spin_lock_irqsave(&p->sighand->siglock, flags);
  70         signal_wake_up(p, 0);
  71         spin_unlock_irqrestore(&p->sighand->siglock, flags);
  72 }
  73
  74 /**
  75  *      freeze_task - send a freeze request to given task
  76  *      @p: task to send the request to
  77  *      @sig_only: if set, the request will only be sent if the task has the
  78  *              PF_FREEZER_NOSIG flag unset
  79  *      Return value: 'false', if @sig_only is set and the task has
  80  *              PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
  81  *
  82  *      The freeze request is sent by setting the tasks's TIF_FREEZE flag and
  83  *      either sending a fake signal to it or waking it up, depending on whether
  84  *      or not it has PF_FREEZER_NOSIG set.  If @sig_only is set and the task
  85  *      has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
  86  *      TIF_FREEZE flag will not be set.
  87  */
  88 bool freeze_task(struct task_struct *p, bool sig_only)
  89 {
  90         /*
  91          * We first check if the task is freezing and next if it has already
  92          * been frozen to avoid the race with frozen_process() which first marks
  93          * the task as frozen and next clears its TIF_FREEZE.
  94          */
  95         if (!freezing(p)) {
  96                 smp_rmb();
  97                 if (frozen(p))
  98                         return false;
  99
 100                 if (!sig_only || should_send_signal(p))
 101                         set_freeze_flag(p);
 102                 else
 103                         return false;
 104         }
 105
 106         if (should_send_signal(p)) {
 107                 fake_signal_wake_up(p);
 108                 /*
 109                  * fake_signal_wake_up() goes through p's scheduler
 110                  * lock and guarantees that TASK_STOPPED/TRACED ->
 111                  * TASK_RUNNING transition can't race with task state
 112                  * testing in try_to_freeze_tasks().
 113                  */
 114         } else if (sig_only) {
 115                 return false;
 116         } else {
 117                 wake_up_state(p, TASK_INTERRUPTIBLE);
 118         }
 119
 120         return true;
 121 }
 122
 123 void cancel_freezing(struct task_struct *p)
 124 {
 125         unsigned long flags;
 126
 127         if (freezing(p)) {
 128                 pr_debug("  clean up: %s\n", p->comm);
 129                 clear_freeze_flag(p);
 130                 spin_lock_irqsave(&p->sighand->siglock, flags);
 131                 recalc_sigpending_and_wake(p);
 132                 spin_unlock_irqrestore(&p->sighand->siglock, flags);
 133         }
 134 }
 135
 136 static int __thaw_process(struct task_struct *p)
 137 {
 138         if (frozen(p)) {
 139                 p->flags &= ~PF_FROZEN;
 140                 return 1;
 141         }
 142         clear_freeze_flag(p);
 143         return 0;
 144 }
 145
 146 /*
 147  * Wake up a frozen process
 148  *
 149  * task_lock() is needed to prevent the race with refrigerator() which may
 150  * occur if the freezing of tasks fails.  Namely, without the lock, if the
 151  * freezing of tasks failed, thaw_tasks() might have run before a task in
 152  * refrigerator() could call frozen_process(), in which case the task would be
 153  * frozen and no one would thaw it.
 154  */
 155 int thaw_process(struct task_struct *p)
 156 {
 157         task_lock(p);
 158         if (__thaw_process(p) == 1) {
 159                 task_unlock(p);
 160                 wake_up_process(p);
 161                 return 1;
 162         }
 163         task_unlock(p);
 164         return 0;
 165 }
 166 EXPORT_SYMBOL(thaw_process);