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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_tsk_thread_flag(p, 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 | 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 | */ | |
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); |