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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/module.h> |
10 | #include <linux/syscalls.h> |
11 | #include <linux/freezer.h> |
12 | |
13 | /* |
14 | * freezing is complete, mark current process as frozen |
15 | */ |
16 | static inline void frozen_process(void) |
17 | { |
18 | if (!unlikely(current->flags & PF_NOFREEZE)) { |
19 | current->flags |= PF_FROZEN; |
20 | wmb(); |
21 | } |
22 | clear_freeze_flag(current); |
23 | } |
24 | |
25 | /* Refrigerator is place where frozen processes are stored :-). */ |
26 | void refrigerator(void) |
27 | { |
28 | /* Hmm, should we be allowed to suspend when there are realtime |
29 | processes around? */ |
30 | long save; |
31 | |
32 | task_lock(current); |
33 | if (freezing(current)) { |
34 | frozen_process(); |
35 | task_unlock(current); |
36 | } else { |
37 | task_unlock(current); |
38 | return; |
39 | } |
40 | save = current->state; |
41 | pr_debug("%s entered refrigerator\n", current->comm); |
42 | |
43 | spin_lock_irq(¤t->sighand->siglock); |
44 | recalc_sigpending(); /* We sent fake signal, clean it up */ |
45 | spin_unlock_irq(¤t->sighand->siglock); |
46 | |
47 | /* prevent accounting of that task to load */ |
48 | current->flags |= PF_FREEZING; |
49 | |
50 | for (;;) { |
51 | set_current_state(TASK_UNINTERRUPTIBLE); |
52 | if (!frozen(current)) |
53 | break; |
54 | schedule(); |
55 | } |
56 | |
57 | /* Remove the accounting blocker */ |
58 | current->flags &= ~PF_FREEZING; |
59 | |
60 | pr_debug("%s left refrigerator\n", current->comm); |
61 | __set_current_state(save); |
62 | } |
63 | EXPORT_SYMBOL(refrigerator); |
64 | |
65 | static void fake_signal_wake_up(struct task_struct *p) |
66 | { |
67 | unsigned long flags; |
68 | |
69 | spin_lock_irqsave(&p->sighand->siglock, flags); |
70 | signal_wake_up(p, 0); |
71 | spin_unlock_irqrestore(&p->sighand->siglock, flags); |
72 | } |
73 | |
74 | /** |
75 | * freeze_task - send a freeze request to given task |
76 | * @p: task to send the request to |
77 | * @sig_only: if set, the request will only be sent if the task has the |
78 | * PF_FREEZER_NOSIG flag unset |
79 | * Return value: 'false', if @sig_only is set and the task has |
80 | * PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise |
81 | * |
82 | * The freeze request is sent by setting the tasks's TIF_FREEZE flag and |
83 | * either sending a fake signal to it or waking it up, depending on whether |
84 | * or not it has PF_FREEZER_NOSIG set. If @sig_only is set and the task |
85 | * has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its |
86 | * TIF_FREEZE flag will not be set. |
87 | */ |
88 | bool freeze_task(struct task_struct *p, bool sig_only) |
89 | { |
90 | /* |
91 | * We first check if the task is freezing and next if it has already |
92 | * been frozen to avoid the race with frozen_process() which first marks |
93 | * the task as frozen and next clears its TIF_FREEZE. |
94 | */ |
95 | if (!freezing(p)) { |
96 | rmb(); |
97 | if (frozen(p)) |
98 | return false; |
99 | |
100 | if (!sig_only || should_send_signal(p)) |
101 | set_freeze_flag(p); |
102 | else |
103 | return false; |
104 | } |
105 | |
106 | if (should_send_signal(p)) { |
107 | fake_signal_wake_up(p); |
108 | /* |
109 | * fake_signal_wake_up() goes through p's scheduler |
110 | * lock and guarantees that TASK_STOPPED/TRACED -> |
111 | * TASK_RUNNING transition can't race with task state |
112 | * testing in try_to_freeze_tasks(). |
113 | */ |
114 | } else if (sig_only) { |
115 | return false; |
116 | } else { |
117 | wake_up_state(p, TASK_INTERRUPTIBLE); |
118 | } |
119 | |
120 | return true; |
121 | } |
122 | |
123 | void cancel_freezing(struct task_struct *p) |
124 | { |
125 | unsigned long flags; |
126 | |
127 | if (freezing(p)) { |
128 | pr_debug(" clean up: %s\n", p->comm); |
129 | clear_freeze_flag(p); |
130 | spin_lock_irqsave(&p->sighand->siglock, flags); |
131 | recalc_sigpending_and_wake(p); |
132 | spin_unlock_irqrestore(&p->sighand->siglock, flags); |
133 | } |
134 | } |
135 | |
136 | static int __thaw_process(struct task_struct *p) |
137 | { |
138 | if (frozen(p)) { |
139 | p->flags &= ~PF_FROZEN; |
140 | return 1; |
141 | } |
142 | clear_freeze_flag(p); |
143 | return 0; |
144 | } |
145 | |
146 | /* |
147 | * Wake up a frozen process |
148 | * |
149 | * task_lock() is needed to prevent the race with refrigerator() which may |
150 | * occur if the freezing of tasks fails. Namely, without the lock, if the |
151 | * freezing of tasks failed, thaw_tasks() might have run before a task in |
152 | * refrigerator() could call frozen_process(), in which case the task would be |
153 | * frozen and no one would thaw it. |
154 | */ |
155 | int thaw_process(struct task_struct *p) |
156 | { |
157 | task_lock(p); |
158 | if (__thaw_process(p) == 1) { |
159 | task_unlock(p); |
160 | wake_up_process(p); |
161 | return 1; |
162 | } |
163 | task_unlock(p); |
164 | return 0; |
165 | } |
166 | EXPORT_SYMBOL(thaw_process); |
167 |
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