Root/kernel/freezer.c

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);
183

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