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 /*
  15  * freezing is complete, mark current process as frozen
  16  */
  17 static inline void frozen_process(void)
  18 {
  19         if (!unlikely(current->flags & PF_NOFREEZE)) {
  20                 current->flags |= PF_FROZEN;
  21                 smp_wmb();
  22         }
  23         clear_freeze_flag(current);
  24 }
  25
  26 /* Refrigerator is place where frozen processes are stored :-). */
  27 bool __refrigerator(bool check_kthr_stop)
  28 {
  29         /* Hmm, should we be allowed to suspend when there are realtime
  30            processes around? */
  31         bool was_frozen = false;
  32         long save;
  33
  34         task_lock(current);
  35         if (freezing(current)) {
  36                 frozen_process();
  37                 task_unlock(current);
  38         } else {
  39                 task_unlock(current);
  40                 return was_frozen;
  41         }
  42         save = current->state;
  43         pr_debug("%s entered refrigerator\n", current->comm);
  44
  45         spin_lock_irq(&current->sighand->siglock);
  46         recalc_sigpending(); /* We sent fake signal, clean it up */
  47         spin_unlock_irq(&current->sighand->siglock);
  48
  49         /* prevent accounting of that task to load */
  50         current->flags |= PF_FREEZING;
  51
  52         for (;;) {
  53                 set_current_state(TASK_UNINTERRUPTIBLE);
  54                 if (!frozen(current) ||
  55                     (check_kthr_stop && kthread_should_stop()))
  56                         break;
  57                 was_frozen = true;
  58                 schedule();
  59         }
  60
  61         /* Remove the accounting blocker */
  62         current->flags &= ~PF_FREEZING;
  63
  64         pr_debug("%s left refrigerator\n", current->comm);
  65
  66         /*
  67          * Restore saved task state before returning.  The mb'd version
  68          * needs to be used; otherwise, it might silently break
  69          * synchronization which depends on ordered task state change.
  70          */
  71         set_current_state(save);
  72
  73         return was_frozen;
  74 }
  75 EXPORT_SYMBOL(__refrigerator);
  76
  77 static void fake_signal_wake_up(struct task_struct *p)
  78 {
  79         unsigned long flags;
  80
  81         spin_lock_irqsave(&p->sighand->siglock, flags);
  82         signal_wake_up(p, 0);
  83         spin_unlock_irqrestore(&p->sighand->siglock, flags);
  84 }
  85
  86 /**
  87  *      freeze_task - send a freeze request to given task
  88  *      @p: task to send the request to
  89  *      @sig_only: if set, the request will only be sent if the task has the
  90  *              PF_FREEZER_NOSIG flag unset
  91  *      Return value: 'false', if @sig_only is set and the task has
  92  *              PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
  93  *
  94  *      The freeze request is sent by setting the tasks's TIF_FREEZE flag and
  95  *      either sending a fake signal to it or waking it up, depending on whether
  96  *      or not it has PF_FREEZER_NOSIG set.  If @sig_only is set and the task
  97  *      has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
  98  *      TIF_FREEZE flag will not be set.
  99  */
 100 bool freeze_task(struct task_struct *p, bool sig_only)
 101 {
 102         /*
 103          * We first check if the task is freezing and next if it has already
 104          * been frozen to avoid the race with frozen_process() which first marks
 105          * the task as frozen and next clears its TIF_FREEZE.
 106          */
 107         if (!freezing(p)) {
 108                 smp_rmb();
 109                 if (frozen(p))
 110                         return false;
 111
 112                 if (!sig_only || should_send_signal(p))
 113                         set_freeze_flag(p);
 114                 else
 115                         return false;
 116         }
 117
 118         if (should_send_signal(p)) {
 119                 fake_signal_wake_up(p);
 120                 /*
 121                  * fake_signal_wake_up() goes through p's scheduler
 122                  * lock and guarantees that TASK_STOPPED/TRACED ->
 123                  * TASK_RUNNING transition can't race with task state
 124                  * testing in try_to_freeze_tasks().
 125                  */
 126         } else if (sig_only) {
 127                 return false;
 128         } else {
 129                 wake_up_state(p, TASK_INTERRUPTIBLE);
 130         }
 131
 132         return true;
 133 }
 134
 135 void cancel_freezing(struct task_struct *p)
 136 {
 137         unsigned long flags;
 138
 139         if (freezing(p)) {
 140                 pr_debug("  clean up: %s\n", p->comm);
 141                 clear_freeze_flag(p);
 142                 spin_lock_irqsave(&p->sighand->siglock, flags);
 143                 recalc_sigpending_and_wake(p);
 144                 spin_unlock_irqrestore(&p->sighand->siglock, flags);
 145         }
 146 }
 147
 148 /*
 149  * Wake up a frozen task
 150  *
 151  * task_lock() is needed to prevent the race with refrigerator() which may
 152  * occur if the freezing of tasks fails.  Namely, without the lock, if the
 153  * freezing of tasks failed, thaw_tasks() might have run before a task in
 154  * refrigerator() could call frozen_process(), in which case the task would be
 155  * frozen and no one would thaw it.
 156  */
 157 void __thaw_task(struct task_struct *p)
 158 {
 159         bool was_frozen;
 160
 161         task_lock(p);
 162         was_frozen = frozen(p);
 163         if (was_frozen)
 164                 p->flags &= ~PF_FROZEN;
 165         else
 166                 clear_freeze_flag(p);
 167         task_unlock(p);
 168
 169         if (was_frozen)
 170                 wake_up_process(p);
 171 }