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