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 bool __refrigerator(void)
  27 {
  28         /* Hmm, should we be allowed to suspend when there are realtime
  29            processes around? */
  30         bool was_frozen = false;
  31         long save;
  32
  33         task_lock(current);
  34         if (freezing(current)) {
  35                 frozen_process();
  36                 task_unlock(current);
  37         } else {
  38                 task_unlock(current);
  39                 return was_frozen;
  40         }
  41         save = current->state;
  42         pr_debug("%s entered refrigerator\n", current->comm);
  43
  44         spin_lock_irq(&current->sighand->siglock);
  45         recalc_sigpending(); /* We sent fake signal, clean it up */
  46         spin_unlock_irq(&current->sighand->siglock);
  47
  48         /* prevent accounting of that task to load */
  49         current->flags |= PF_FREEZING;
  50
  51         for (;;) {
  52                 set_current_state(TASK_UNINTERRUPTIBLE);
  53                 if (!frozen(current))
  54                         break;
  55                 was_frozen = true;
  56                 schedule();
  57         }
  58
  59         /* Remove the accounting blocker */
  60         current->flags &= ~PF_FREEZING;
  61
  62         pr_debug("%s left refrigerator\n", current->comm);
  63
  64         /*
  65          * Restore saved task state before returning.  The mb'd version
  66          * needs to be used; otherwise, it might silently break
  67          * synchronization which depends on ordered task state change.
  68          */
  69         set_current_state(save);
  70
  71         return was_frozen;
  72 }
  73 EXPORT_SYMBOL(__refrigerator);
  74
  75 static void fake_signal_wake_up(struct task_struct *p)
  76 {
  77         unsigned long flags;
  78
  79         spin_lock_irqsave(&p->sighand->siglock, flags);
  80         signal_wake_up(p, 0);
  81         spin_unlock_irqrestore(&p->sighand->siglock, flags);
  82 }
  83
  84 /**
  85  *      freeze_task - send a freeze request to given task
  86  *      @p: task to send the request to
  87  *      @sig_only: if set, the request will only be sent if the task has the
  88  *              PF_FREEZER_NOSIG flag unset
  89  *      Return value: 'false', if @sig_only is set and the task has
  90  *              PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
  91  *
  92  *      The freeze request is sent by setting the tasks's TIF_FREEZE flag and
  93  *      either sending a fake signal to it or waking it up, depending on whether
  94  *      or not it has PF_FREEZER_NOSIG set.  If @sig_only is set and the task
  95  *      has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
  96  *      TIF_FREEZE flag will not be set.
  97  */
  98 bool freeze_task(struct task_struct *p, bool sig_only)
  99 {
 100         /*
 101          * We first check if the task is freezing and next if it has already
 102          * been frozen to avoid the race with frozen_process() which first marks
 103          * the task as frozen and next clears its TIF_FREEZE.
 104          */
 105         if (!freezing(p)) {
 106                 smp_rmb();
 107                 if (frozen(p))
 108                         return false;
 109
 110                 if (!sig_only || should_send_signal(p))
 111                         set_freeze_flag(p);
 112                 else
 113                         return false;
 114         }
 115
 116         if (should_send_signal(p)) {
 117                 fake_signal_wake_up(p);
 118                 /*
 119                  * fake_signal_wake_up() goes through p's scheduler
 120                  * lock and guarantees that TASK_STOPPED/TRACED ->
 121                  * TASK_RUNNING transition can't race with task state
 122                  * testing in try_to_freeze_tasks().
 123                  */
 124         } else if (sig_only) {
 125                 return false;
 126         } else {
 127                 wake_up_state(p, TASK_INTERRUPTIBLE);
 128         }
 129
 130         return true;
 131 }
 132
 133 void cancel_freezing(struct task_struct *p)
 134 {
 135         unsigned long flags;
 136
 137         if (freezing(p)) {
 138                 pr_debug("  clean up: %s\n", p->comm);
 139                 clear_freeze_flag(p);
 140                 spin_lock_irqsave(&p->sighand->siglock, flags);
 141                 recalc_sigpending_and_wake(p);
 142                 spin_unlock_irqrestore(&p->sighand->siglock, flags);
 143         }
 144 }
 145
 146 static int __thaw_process(struct task_struct *p)
 147 {
 148         if (frozen(p)) {
 149                 p->flags &= ~PF_FROZEN;
 150                 return 1;
 151         }
 152         clear_freeze_flag(p);
 153         return 0;
 154 }
 155
 156 /*
 157  * Wake up a frozen process
 158  *
 159  * task_lock() is needed to prevent the race with refrigerator() which may
 160  * occur if the freezing of tasks fails.  Namely, without the lock, if the
 161  * freezing of tasks failed, thaw_tasks() might have run before a task in
 162  * refrigerator() could call frozen_process(), in which case the task would be
 163  * frozen and no one would thaw it.
 164  */
 165 int thaw_process(struct task_struct *p)
 166 {
 167         task_lock(p);
 168         if (__thaw_process(p) == 1) {
 169                 task_unlock(p);
 170                 wake_up_process(p);
 171                 return 1;
 172         }
 173         task_unlock(p);
 174         return 0;
 175 }
 176 EXPORT_SYMBOL(thaw_process);