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 /* total number of freezing conditions in effect */
  15 atomic_t system_freezing_cnt = ATOMIC_INIT(0);
  16 EXPORT_SYMBOL(system_freezing_cnt);
  17
  18 /* indicate whether PM freezing is in effect, protected by pm_mutex */
  19 bool pm_freezing;
  20 bool pm_nosig_freezing;
  21
  22 /* protects freezing and frozen transitions */
  23 static DEFINE_SPINLOCK(freezer_lock);
  24
  25 /**
  26  * freezing_slow_path - slow path for testing whether a task needs to be frozen
  27  * @p: task to be tested
  28  *
  29  * This function is called by freezing() if system_freezing_cnt isn't zero
  30  * and tests whether @p needs to enter and stay in frozen state.  Can be
  31  * called under any context.  The freezers are responsible for ensuring the
  32  * target tasks see the updated state.
  33  */
  34 bool freezing_slow_path(struct task_struct *p)
  35 {
  36         if (p->flags & PF_NOFREEZE)
  37                 return false;
  38
  39         if (pm_nosig_freezing || cgroup_freezing(p))
  40                 return true;
  41
  42         if (pm_freezing && !(p->flags & PF_FREEZER_NOSIG))
  43                 return true;
  44
  45         return false;
  46 }
  47 EXPORT_SYMBOL(freezing_slow_path);
  48
  49 /* Refrigerator is place where frozen processes are stored :-). */
  50 bool __refrigerator(bool check_kthr_stop)
  51 {
  52         /* Hmm, should we be allowed to suspend when there are realtime
  53            processes around? */
  54         bool was_frozen = false;
  55         long save = current->state;
  56
  57         pr_debug("%s entered refrigerator\n", current->comm);
  58
  59         for (;;) {
  60                 set_current_state(TASK_UNINTERRUPTIBLE);
  61
  62                 spin_lock_irq(&freezer_lock);
  63                 current->flags |= PF_FROZEN;
  64                 if (!freezing(current) ||
  65                     (check_kthr_stop && kthread_should_stop()))
  66                         current->flags &= ~PF_FROZEN;
  67                 spin_unlock_irq(&freezer_lock);
  68
  69                 if (!(current->flags & PF_FROZEN))
  70                         break;
  71                 was_frozen = true;
  72                 schedule();
  73         }
  74
  75         spin_lock_irq(&current->sighand->siglock);
  76         recalc_sigpending(); /* We sent fake signal, clean it up */
  77         spin_unlock_irq(&current->sighand->siglock);
  78
  79         pr_debug("%s left refrigerator\n", current->comm);
  80
  81         /*
  82          * Restore saved task state before returning.  The mb'd version
  83          * needs to be used; otherwise, it might silently break
  84          * synchronization which depends on ordered task state change.
  85          */
  86         set_current_state(save);
  87
  88         return was_frozen;
  89 }
  90 EXPORT_SYMBOL(__refrigerator);
  91
  92 static void fake_signal_wake_up(struct task_struct *p)
  93 {
  94         unsigned long flags;
  95
  96         spin_lock_irqsave(&p->sighand->siglock, flags);
  97         signal_wake_up(p, 0);
  98         spin_unlock_irqrestore(&p->sighand->siglock, flags);
  99 }
 100
 101 /**
 102  *      freeze_task - send a freeze request to given task
 103  *      @p: task to send the request to
 104  *      @sig_only: if set, the request will only be sent if the task has the
 105  *              PF_FREEZER_NOSIG flag unset
 106  *      Return value: 'false', if @sig_only is set and the task has
 107  *              PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
 108  *
 109  *      The freeze request is sent by setting the tasks's TIF_FREEZE flag and
 110  *      either sending a fake signal to it or waking it up, depending on whether
 111  *      or not it has PF_FREEZER_NOSIG set.  If @sig_only is set and the task
 112  *      has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
 113  *      TIF_FREEZE flag will not be set.
 114  */
 115 bool freeze_task(struct task_struct *p, bool sig_only)
 116 {
 117         unsigned long flags;
 118
 119         spin_lock_irqsave(&freezer_lock, flags);
 120         if (!freezing(p) || frozen(p)) {
 121                 spin_unlock_irqrestore(&freezer_lock, flags);
 122                 return false;
 123         }
 124
 125         if (!(p->flags & PF_FREEZER_NOSIG)) {
 126                 fake_signal_wake_up(p);
 127                 /*
 128                  * fake_signal_wake_up() goes through p's scheduler
 129                  * lock and guarantees that TASK_STOPPED/TRACED ->
 130                  * TASK_RUNNING transition can't race with task state
 131                  * testing in try_to_freeze_tasks().
 132                  */
 133         } else {
 134                 wake_up_state(p, TASK_INTERRUPTIBLE);
 135         }
 136
 137         spin_unlock_irqrestore(&freezer_lock, flags);
 138         return true;
 139 }
 140
 141 void __thaw_task(struct task_struct *p)
 142 {
 143         unsigned long flags;
 144
 145         /*
 146          * Clear freezing and kick @p if FROZEN.  Clearing is guaranteed to
 147          * be visible to @p as waking up implies wmb.  Waking up inside
 148          * freezer_lock also prevents wakeups from leaking outside
 149          * refrigerator.
 150          *
 151          * If !FROZEN, @p hasn't reached refrigerator, recalc sigpending to
 152          * avoid leaving dangling TIF_SIGPENDING behind.
 153          */
 154         spin_lock_irqsave(&freezer_lock, flags);
 155         if (frozen(p)) {
 156                 wake_up_process(p);
 157         } else {
 158                 spin_lock(&p->sighand->siglock);
 159                 recalc_sigpending_and_wake(p);
 160                 spin_unlock(&p->sighand->siglock);
 161         }
 162         spin_unlock_irqrestore(&freezer_lock, flags);
 163 }
 164
 165 /**
 166  * __set_freezable - make %current freezable
 167  * @with_signal: do we want %TIF_SIGPENDING for notification too?
 168  *
 169  * Mark %current freezable and enter refrigerator if necessary.
 170  */
 171 bool __set_freezable(bool with_signal)
 172 {
 173         might_sleep();
 174
 175         /*
 176          * Modify flags while holding freezer_lock.  This ensures the
 177          * freezer notices that we aren't frozen yet or the freezing
 178          * condition is visible to try_to_freeze() below.
 179          */
 180         spin_lock_irq(&freezer_lock);
 181         current->flags &= ~PF_NOFREEZE;
 182         if (with_signal)
 183                 current->flags &= ~PF_FREEZER_NOSIG;
 184         spin_unlock_irq(&freezer_lock);
 185
 186         return try_to_freeze();
 187 }
 188 EXPORT_SYMBOL(__set_freezable);