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Linux/kernel/freezer.c

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  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 /*
 23  * Temporary export for the deadlock workaround in ata_scsi_hotplug().
 24  * Remove once the hack becomes unnecessary.
 25  */
 26 EXPORT_SYMBOL_GPL(pm_freezing);
 27 
 28 /* protects freezing and frozen transitions */
 29 static DEFINE_SPINLOCK(freezer_lock);
 30 
 31 /**
 32  * freezing_slow_path - slow path for testing whether a task needs to be frozen
 33  * @p: task to be tested
 34  *
 35  * This function is called by freezing() if system_freezing_cnt isn't zero
 36  * and tests whether @p needs to enter and stay in frozen state.  Can be
 37  * called under any context.  The freezers are responsible for ensuring the
 38  * target tasks see the updated state.
 39  */
 40 bool freezing_slow_path(struct task_struct *p)
 41 {
 42         if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))
 43                 return false;
 44 
 45         if (test_thread_flag(TIF_MEMDIE))
 46                 return false;
 47 
 48         if (pm_nosig_freezing || cgroup_freezing(p))
 49                 return true;
 50 
 51         if (pm_freezing && !(p->flags & PF_KTHREAD))
 52                 return true;
 53 
 54         return false;
 55 }
 56 EXPORT_SYMBOL(freezing_slow_path);
 57 
 58 /* Refrigerator is place where frozen processes are stored :-). */
 59 bool __refrigerator(bool check_kthr_stop)
 60 {
 61         /* Hmm, should we be allowed to suspend when there are realtime
 62            processes around? */
 63         bool was_frozen = false;
 64         long save = current->state;
 65 
 66         pr_debug("%s entered refrigerator\n", current->comm);
 67 
 68         for (;;) {
 69                 set_current_state(TASK_UNINTERRUPTIBLE);
 70 
 71                 spin_lock_irq(&freezer_lock);
 72                 current->flags |= PF_FROZEN;
 73                 if (!freezing(current) ||
 74                     (check_kthr_stop && kthread_should_stop()))
 75                         current->flags &= ~PF_FROZEN;
 76                 spin_unlock_irq(&freezer_lock);
 77 
 78                 if (!(current->flags & PF_FROZEN))
 79                         break;
 80                 was_frozen = true;
 81                 schedule();
 82         }
 83 
 84         pr_debug("%s left refrigerator\n", current->comm);
 85 
 86         /*
 87          * Restore saved task state before returning.  The mb'd version
 88          * needs to be used; otherwise, it might silently break
 89          * synchronization which depends on ordered task state change.
 90          */
 91         set_current_state(save);
 92 
 93         return was_frozen;
 94 }
 95 EXPORT_SYMBOL(__refrigerator);
 96 
 97 static void fake_signal_wake_up(struct task_struct *p)
 98 {
 99         unsigned long flags;
100 
101         if (lock_task_sighand(p, &flags)) {
102                 signal_wake_up(p, 0);
103                 unlock_task_sighand(p, &flags);
104         }
105 }
106 
107 /**
108  * freeze_task - send a freeze request to given task
109  * @p: task to send the request to
110  *
111  * If @p is freezing, the freeze request is sent either by sending a fake
112  * signal (if it's not a kernel thread) or waking it up (if it's a kernel
113  * thread).
114  *
115  * RETURNS:
116  * %false, if @p is not freezing or already frozen; %true, otherwise
117  */
118 bool freeze_task(struct task_struct *p)
119 {
120         unsigned long flags;
121 
122         /*
123          * This check can race with freezer_do_not_count, but worst case that
124          * will result in an extra wakeup being sent to the task.  It does not
125          * race with freezer_count(), the barriers in freezer_count() and
126          * freezer_should_skip() ensure that either freezer_count() sees
127          * freezing == true in try_to_freeze() and freezes, or
128          * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task
129          * normally.
130          */
131         if (freezer_should_skip(p))
132                 return false;
133 
134         spin_lock_irqsave(&freezer_lock, flags);
135         if (!freezing(p) || frozen(p)) {
136                 spin_unlock_irqrestore(&freezer_lock, flags);
137                 return false;
138         }
139 
140         if (!(p->flags & PF_KTHREAD))
141                 fake_signal_wake_up(p);
142         else
143                 wake_up_state(p, TASK_INTERRUPTIBLE);
144 
145         spin_unlock_irqrestore(&freezer_lock, flags);
146         return true;
147 }
148 
149 void __thaw_task(struct task_struct *p)
150 {
151         unsigned long flags;
152 
153         /*
154          * Clear freezing and kick @p if FROZEN.  Clearing is guaranteed to
155          * be visible to @p as waking up implies wmb.  Waking up inside
156          * freezer_lock also prevents wakeups from leaking outside
157          * refrigerator.
158          */
159         spin_lock_irqsave(&freezer_lock, flags);
160         if (frozen(p))
161                 wake_up_process(p);
162         spin_unlock_irqrestore(&freezer_lock, flags);
163 }
164 
165 /**
166  * set_freezable - make %current freezable
167  *
168  * Mark %current freezable and enter refrigerator if necessary.
169  */
170 bool set_freezable(void)
171 {
172         might_sleep();
173 
174         /*
175          * Modify flags while holding freezer_lock.  This ensures the
176          * freezer notices that we aren't frozen yet or the freezing
177          * condition is visible to try_to_freeze() below.
178          */
179         spin_lock_irq(&freezer_lock);
180         current->flags &= ~PF_NOFREEZE;
181         spin_unlock_irq(&freezer_lock);
182 
183         return try_to_freeze();
184 }
185 EXPORT_SYMBOL(set_freezable);
186 

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