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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 | /* 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_KTHREAD)) |
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 | pr_debug("%s left refrigerator\n", current->comm); |
76 | |
77 | /* |
78 | * Restore saved task state before returning. The mb'd version |
79 | * needs to be used; otherwise, it might silently break |
80 | * synchronization which depends on ordered task state change. |
81 | */ |
82 | set_current_state(save); |
83 | |
84 | return was_frozen; |
85 | } |
86 | EXPORT_SYMBOL(__refrigerator); |
87 | |
88 | static void fake_signal_wake_up(struct task_struct *p) |
89 | { |
90 | unsigned long flags; |
91 | |
92 | if (lock_task_sighand(p, &flags)) { |
93 | signal_wake_up(p, 0); |
94 | unlock_task_sighand(p, &flags); |
95 | } |
96 | } |
97 | |
98 | /** |
99 | * freeze_task - send a freeze request to given task |
100 | * @p: task to send the request to |
101 | * |
102 | * If @p is freezing, the freeze request is sent either by sending a fake |
103 | * signal (if it's not a kernel thread) or waking it up (if it's a kernel |
104 | * thread). |
105 | * |
106 | * RETURNS: |
107 | * %false, if @p is not freezing or already frozen; %true, otherwise |
108 | */ |
109 | bool freeze_task(struct task_struct *p) |
110 | { |
111 | unsigned long flags; |
112 | |
113 | spin_lock_irqsave(&freezer_lock, flags); |
114 | if (!freezing(p) || frozen(p)) { |
115 | spin_unlock_irqrestore(&freezer_lock, flags); |
116 | return false; |
117 | } |
118 | |
119 | if (!(p->flags & PF_KTHREAD)) |
120 | fake_signal_wake_up(p); |
121 | else |
122 | wake_up_state(p, TASK_INTERRUPTIBLE); |
123 | |
124 | spin_unlock_irqrestore(&freezer_lock, flags); |
125 | return true; |
126 | } |
127 | |
128 | void __thaw_task(struct task_struct *p) |
129 | { |
130 | unsigned long flags; |
131 | |
132 | /* |
133 | * Clear freezing and kick @p if FROZEN. Clearing is guaranteed to |
134 | * be visible to @p as waking up implies wmb. Waking up inside |
135 | * freezer_lock also prevents wakeups from leaking outside |
136 | * refrigerator. |
137 | */ |
138 | spin_lock_irqsave(&freezer_lock, flags); |
139 | if (frozen(p)) |
140 | wake_up_process(p); |
141 | spin_unlock_irqrestore(&freezer_lock, flags); |
142 | } |
143 | |
144 | /** |
145 | * set_freezable - make %current freezable |
146 | * |
147 | * Mark %current freezable and enter refrigerator if necessary. |
148 | */ |
149 | bool set_freezable(void) |
150 | { |
151 | might_sleep(); |
152 | |
153 | /* |
154 | * Modify flags while holding freezer_lock. This ensures the |
155 | * freezer notices that we aren't frozen yet or the freezing |
156 | * condition is visible to try_to_freeze() below. |
157 | */ |
158 | spin_lock_irq(&freezer_lock); |
159 | current->flags &= ~PF_NOFREEZE; |
160 | spin_unlock_irq(&freezer_lock); |
161 | |
162 | return try_to_freeze(); |
163 | } |
164 | EXPORT_SYMBOL(set_freezable); |
165 |
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