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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  */
freezing_slow_path(struct task_struct * p)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 :-). */
__refrigerator(bool check_kthr_stop)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 
fake_signal_wake_up(struct task_struct * p)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  */
freeze_task(struct task_struct * p)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 
__thaw_task(struct task_struct * p)149 void __thaw_task(struct task_struct *p)
150 {
151 	unsigned long flags;
152 
153 	spin_lock_irqsave(&freezer_lock, flags);
154 	if (frozen(p))
155 		wake_up_process(p);
156 	spin_unlock_irqrestore(&freezer_lock, flags);
157 }
158 
159 /**
160  * set_freezable - make %current freezable
161  *
162  * Mark %current freezable and enter refrigerator if necessary.
163  */
set_freezable(void)164 bool set_freezable(void)
165 {
166 	might_sleep();
167 
168 	/*
169 	 * Modify flags while holding freezer_lock.  This ensures the
170 	 * freezer notices that we aren't frozen yet or the freezing
171 	 * condition is visible to try_to_freeze() below.
172 	 */
173 	spin_lock_irq(&freezer_lock);
174 	current->flags &= ~PF_NOFREEZE;
175 	spin_unlock_irq(&freezer_lock);
176 
177 	return try_to_freeze();
178 }
179 EXPORT_SYMBOL(set_freezable);
180