aboutsummaryrefslogtreecommitdiff
path: root/kernel/freezer.c
blob: 66ecd2ead215a9cb88ca8ae9f674e1c82766a066 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
/*
 * kernel/freezer.c - Function to freeze a process
 *
 * Originally from kernel/power/process.c
 */

#include <linux/interrupt.h>
#include <linux/suspend.h>
#include <linux/module.h>
#include <linux/syscalls.h>
#include <linux/freezer.h>

/*
 * freezing is complete, mark current process as frozen
 */
static inline void frozen_process(void)
{
	if (!unlikely(current->flags & PF_NOFREEZE)) {
		current->flags |= PF_FROZEN;
		wmb();
	}
	clear_freeze_flag(current);
}

/* Refrigerator is place where frozen processes are stored :-). */
void refrigerator(void)
{
	/* Hmm, should we be allowed to suspend when there are realtime
	   processes around? */
	long save;

	task_lock(current);
	if (freezing(current)) {
		frozen_process();
		task_unlock(current);
	} else {
		task_unlock(current);
		return;
	}
	save = current->state;
	pr_debug("%s entered refrigerator\n", current->comm);

	spin_lock_irq(&current->sighand->siglock);
	recalc_sigpending(); /* We sent fake signal, clean it up */
	spin_unlock_irq(&current->sighand->siglock);

	/* prevent accounting of that task to load */
	current->flags |= PF_FREEZING;

	for (;;) {
		set_current_state(TASK_UNINTERRUPTIBLE);
		if (!frozen(current))
			break;
		schedule();
	}

	/* Remove the accounting blocker */
	current->flags &= ~PF_FREEZING;

	pr_debug("%s left refrigerator\n", current->comm);
	__set_current_state(save);
}
EXPORT_SYMBOL(refrigerator);

static void fake_signal_wake_up(struct task_struct *p)
{
	unsigned long flags;

	spin_lock_irqsave(&p->sighand->siglock, flags);
	signal_wake_up(p, 0);
	spin_unlock_irqrestore(&p->sighand->siglock, flags);
}

/**
 *	freeze_task - send a freeze request to given task
 *	@p: task to send the request to
 *	@sig_only: if set, the request will only be sent if the task has the
 *		PF_FREEZER_NOSIG flag unset
 *	Return value: 'false', if @sig_only is set and the task has
 *		PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
 *
 *	The freeze request is sent by setting the tasks's TIF_FREEZE flag and
 *	either sending a fake signal to it or waking it up, depending on whether
 *	or not it has PF_FREEZER_NOSIG set.  If @sig_only is set and the task
 *	has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
 *	TIF_FREEZE flag will not be set.
 */
bool freeze_task(struct task_struct *p, bool sig_only)
{
	/*
	 * We first check if the task is freezing and next if it has already
	 * been frozen to avoid the race with frozen_process() which first marks
	 * the task as frozen and next clears its TIF_FREEZE.
	 */
	if (!freezing(p)) {
		rmb();
		if (frozen(p))
			return false;

		if (!sig_only || should_send_signal(p))
			set_freeze_flag(p);
		else
			return false;
	}

	if (should_send_signal(p)) {
		fake_signal_wake_up(p);
		/*
		 * fake_signal_wake_up() goes through p's scheduler
		 * lock and guarantees that TASK_STOPPED/TRACED ->
		 * TASK_RUNNING transition can't race with task state
		 * testing in try_to_freeze_tasks().
		 */
	} else if (sig_only) {
		return false;
	} else {
		wake_up_state(p, TASK_INTERRUPTIBLE);
	}

	return true;
}

void cancel_freezing(struct task_struct *p)
{
	unsigned long flags;

	if (freezing(p)) {
		pr_debug("  clean up: %s\n", p->comm);
		clear_freeze_flag(p);
		spin_lock_irqsave(&p->sighand->siglock, flags);
		recalc_sigpending_and_wake(p);
		spin_unlock_irqrestore(&p->sighand->siglock, flags);
	}
}

static int __thaw_process(struct task_struct *p)
{
	if (frozen(p)) {
		p->flags &= ~PF_FROZEN;
		return 1;
	}
	clear_freeze_flag(p);
	return 0;
}

/*
 * Wake up a frozen process
 *
 * task_lock() is needed to prevent the race with refrigerator() which may
 * occur if the freezing of tasks fails.  Namely, without the lock, if the
 * freezing of tasks failed, thaw_tasks() might have run before a task in
 * refrigerator() could call frozen_process(), in which case the task would be
 * frozen and no one would thaw it.
 */
int thaw_process(struct task_struct *p)
{
	task_lock(p);
	if (__thaw_process(p) == 1) {
		task_unlock(p);
		wake_up_process(p);
		return 1;
	}
	task_unlock(p);
	return 0;
}
EXPORT_SYMBOL(thaw_process);