projects/linux·blob v3.13 · refs

182 lines · 4.6 KiB

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 */
15atomic_t system_freezing_cnt = ATOMIC_INIT(0);
16EXPORT_SYMBOL(system_freezing_cnt);
17
18/* indicate whether PM freezing is in effect, protected by pm_mutex */
19bool pm_freezing;
20bool pm_nosig_freezing;
21
22/*
23 * Temporary export for the deadlock workaround in ata_scsi_hotplug().
24 * Remove once the hack becomes unnecessary.
25 */
26EXPORT_SYMBOL_GPL(pm_freezing);
27
28/* protects freezing and frozen transitions */
29static 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 */
40bool 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}
53EXPORT_SYMBOL(freezing_slow_path);
54
55/* Refrigerator is place where frozen processes are stored :-). */
56bool __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}
92EXPORT_SYMBOL(__refrigerator);
93
94static 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 */
115bool 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
146void __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 */
167bool 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}
182EXPORT_SYMBOL(set_freezable);