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;
  56
  57         /*
  58          * No point in checking freezing() again - the caller already did.
  59          * Proceed to enter FROZEN.
  60          */
  61         spin_lock_irq(&freezer_lock);
  62         current->flags |= PF_FROZEN;
  63         spin_unlock_irq(&freezer_lock);
  64
  65         save = current->state;
  66         pr_debug("%s entered refrigerator\n", current->comm);
  67
  68         spin_lock_irq(&current->sighand->siglock);
  69         recalc_sigpending(); /* We sent fake signal, clean it up */
  70         spin_unlock_irq(&current->sighand->siglock);
  71
  72         for (;;) {
  73                 set_current_state(TASK_UNINTERRUPTIBLE);
  74                 if (!freezing(current) ||
  75                     (check_kthr_stop && kthread_should_stop()))
  76                         break;
  77                 was_frozen = true;
  78                 schedule();
  79         }
  80
  81         /* leave FROZEN */
  82         spin_lock_irq(&freezer_lock);
  83         current->flags &= ~PF_FROZEN;
  84         spin_unlock_irq(&freezer_lock);
  85
  86         pr_debug("%s left refrigerator\n", current->comm);
  87
  88         /*
  89          * Restore saved task state before returning.  The mb'd version
  90          * needs to be used; otherwise, it might silently break
  91          * synchronization which depends on ordered task state change.
  92          */
  93         set_current_state(save);
  94
  95         return was_frozen;
  96 }
  97 EXPORT_SYMBOL(__refrigerator);
  98
  99 static void fake_signal_wake_up(struct task_struct *p)
 100 {
 101         unsigned long flags;
 102
 103         spin_lock_irqsave(&p->sighand->siglock, flags);
 104         signal_wake_up(p, 0);
 105         spin_unlock_irqrestore(&p->sighand->siglock, flags);
 106 }
 107
 108 /**
 109  *      freeze_task - send a freeze request to given task
 110  *      @p: task to send the request to
 111  *      @sig_only: if set, the request will only be sent if the task has the
 112  *              PF_FREEZER_NOSIG flag unset
 113  *      Return value: 'false', if @sig_only is set and the task has
 114  *              PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
 115  *
 116  *      The freeze request is sent by setting the tasks's TIF_FREEZE flag and
 117  *      either sending a fake signal to it or waking it up, depending on whether
 118  *      or not it has PF_FREEZER_NOSIG set.  If @sig_only is set and the task
 119  *      has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
 120  *      TIF_FREEZE flag will not be set.
 121  */
 122 bool freeze_task(struct task_struct *p, bool sig_only)
 123 {
 124         unsigned long flags;
 125
 126         spin_lock_irqsave(&freezer_lock, flags);
 127         if (!freezing(p) || frozen(p)) {
 128                 spin_unlock_irqrestore(&freezer_lock, flags);
 129                 return false;
 130         }
 131
 132         if (!(p->flags & PF_FREEZER_NOSIG)) {
 133                 fake_signal_wake_up(p);
 134                 /*
 135                  * fake_signal_wake_up() goes through p's scheduler
 136                  * lock and guarantees that TASK_STOPPED/TRACED ->
 137                  * TASK_RUNNING transition can't race with task state
 138                  * testing in try_to_freeze_tasks().
 139                  */
 140         } else {
 141                 wake_up_state(p, TASK_INTERRUPTIBLE);
 142         }
 143
 144         spin_unlock_irqrestore(&freezer_lock, flags);
 145         return true;
 146 }
 147
 148 void __thaw_task(struct task_struct *p)
 149 {
 150         unsigned long flags;
 151
 152         /*
 153          * Clear freezing and kick @p if FROZEN.  Clearing is guaranteed to
 154          * be visible to @p as waking up implies wmb.  Waking up inside
 155          * freezer_lock also prevents wakeups from leaking outside
 156          * refrigerator.
 157          *
 158          * If !FROZEN, @p hasn't reached refrigerator, recalc sigpending to
 159          * avoid leaving dangling TIF_SIGPENDING behind.
 160          */
 161         spin_lock_irqsave(&freezer_lock, flags);
 162         if (frozen(p)) {
 163                 wake_up_process(p);
 164         } else {
 165                 spin_lock(&p->sighand->siglock);
 166                 recalc_sigpending_and_wake(p);
 167                 spin_unlock(&p->sighand->siglock);
 168         }
 169         spin_unlock_irqrestore(&freezer_lock, flags);
 170 }
 171
 172 /**
 173  * __set_freezable - make %current freezable
 174  * @with_signal: do we want %TIF_SIGPENDING for notification too?
 175  *
 176  * Mark %current freezable and enter refrigerator if necessary.
 177  */
 178 bool __set_freezable(bool with_signal)
 179 {
 180         might_sleep();
 181
 182         /*
 183          * Modify flags while holding freezer_lock.  This ensures the
 184          * freezer notices that we aren't frozen yet or the freezing
 185          * condition is visible to try_to_freeze() below.
 186          */
 187         spin_lock_irq(&freezer_lock);
 188         current->flags &= ~PF_NOFREEZE;
 189         if (with_signal)
 190                 current->flags &= ~PF_FREEZER_NOSIG;
 191         spin_unlock_irq(&freezer_lock);
 192
 193         return try_to_freeze();
 194 }
 195 EXPORT_SYMBOL(__set_freezable);