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/module.h>
10#include <linux/syscalls.h>
11#include <linux/freezer.h>
12
13/*
14 * freezing is complete, mark current process as frozen
15 */
16static inline void frozen_process(void)
17{
18    if (!unlikely(current->flags & PF_NOFREEZE)) {
19        current->flags |= PF_FROZEN;
20        smp_wmb();
21    }
22    clear_freeze_flag(current);
23}
24
25/* Refrigerator is place where frozen processes are stored :-). */
26void 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(&current->sighand->siglock);
44    recalc_sigpending(); /* We sent fake signal, clean it up */
45    spin_unlock_irq(&current->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}
63EXPORT_SYMBOL(refrigerator);
64
65static 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 */
88bool 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        smp_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
123void 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
136static 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 */
155int 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}
166EXPORT_SYMBOL(thaw_process);
167

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