summaryrefslogtreecommitdiffstats
path: root/kernel/freezer.c
blob: c450fa8b8b5ef4472cac53a70d99975ccca82c01 (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
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
// SPDX-License-Identifier: GPL-2.0-only
/*
 * kernel/freezer.c - Function to freeze a process
 *
 * Originally from kernel/power/process.c
 */

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

/* total number of freezing conditions in effect */
DEFINE_STATIC_KEY_FALSE(freezer_active);
EXPORT_SYMBOL(freezer_active);

/*
 * indicate whether PM freezing is in effect, protected by
 * system_transition_mutex
 */
bool pm_freezing;
bool pm_nosig_freezing;

/* protects freezing and frozen transitions */
static DEFINE_SPINLOCK(freezer_lock);

/**
 * freezing_slow_path - slow path for testing whether a task needs to be frozen
 * @p: task to be tested
 *
 * This function is called by freezing() if freezer_active isn't zero
 * and tests whether @p needs to enter and stay in frozen state.  Can be
 * called under any context.  The freezers are responsible for ensuring the
 * target tasks see the updated state.
 */
bool freezing_slow_path(struct task_struct *p)
{
	if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))
		return false;

	if (test_tsk_thread_flag(p, TIF_MEMDIE))
		return false;

	if (pm_nosig_freezing || cgroup_freezing(p))
		return true;

	if (pm_freezing && !(p->flags & PF_KTHREAD))
		return true;

	return false;
}
EXPORT_SYMBOL(freezing_slow_path);

bool frozen(struct task_struct *p)
{
	return READ_ONCE(p->__state) & TASK_FROZEN;
}

/* Refrigerator is place where frozen processes are stored :-). */
bool __refrigerator(bool check_kthr_stop)
{
	unsigned int state = get_current_state();
	bool was_frozen = false;

	pr_debug("%s entered refrigerator\n", current->comm);

	WARN_ON_ONCE(state && !(state & TASK_NORMAL));

	for (;;) {
		bool freeze;

		raw_spin_lock_irq(&current->pi_lock);
		set_current_state(TASK_FROZEN);
		/* unstale saved_state so that __thaw_task() will wake us up */
		current->saved_state = TASK_RUNNING;
		raw_spin_unlock_irq(&current->pi_lock);

		spin_lock_irq(&freezer_lock);
		freeze = freezing(current) && !(check_kthr_stop && kthread_should_stop());
		spin_unlock_irq(&freezer_lock);

		if (!freeze)
			break;

		was_frozen = true;
		schedule();
	}
	__set_current_state(TASK_RUNNING);

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

	return was_frozen;
}
EXPORT_SYMBOL(__refrigerator);

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

	if (lock_task_sighand(p, &flags)) {
		signal_wake_up(p, 0);
		unlock_task_sighand(p, &flags);
	}
}

static int __set_task_frozen(struct task_struct *p, void *arg)
{
	unsigned int state = READ_ONCE(p->__state);

	if (p->on_rq)
		return 0;

	if (p != current && task_curr(p))
		return 0;

	if (!(state & (TASK_FREEZABLE | __TASK_STOPPED | __TASK_TRACED)))
		return 0;

	/*
	 * Only TASK_NORMAL can be augmented with TASK_FREEZABLE, since they
	 * can suffer spurious wakeups.
	 */
	if (state & TASK_FREEZABLE)
		WARN_ON_ONCE(!(state & TASK_NORMAL));

#ifdef CONFIG_LOCKDEP
	/*
	 * It's dangerous to freeze with locks held; there be dragons there.
	 */
	if (!(state & __TASK_FREEZABLE_UNSAFE))
		WARN_ON_ONCE(debug_locks && p->lockdep_depth);
#endif

	p->saved_state = p->__state;
	WRITE_ONCE(p->__state, TASK_FROZEN);
	return TASK_FROZEN;
}

static bool __freeze_task(struct task_struct *p)
{
	/* TASK_FREEZABLE|TASK_STOPPED|TASK_TRACED -> TASK_FROZEN */
	return task_call_func(p, __set_task_frozen, NULL);
}

/**
 * freeze_task - send a freeze request to given task
 * @p: task to send the request to
 *
 * If @p is freezing, the freeze request is sent either by sending a fake
 * signal (if it's not a kernel thread) or waking it up (if it's a kernel
 * thread).
 *
 * RETURNS:
 * %false, if @p is not freezing or already frozen; %true, otherwise
 */
bool freeze_task(struct task_struct *p)
{
	unsigned long flags;

	spin_lock_irqsave(&freezer_lock, flags);
	if (!freezing(p) || frozen(p) || __freeze_task(p)) {
		spin_unlock_irqrestore(&freezer_lock, flags);
		return false;
	}

	if (!(p->flags & PF_KTHREAD))
		fake_signal_wake_up(p);
	else
		wake_up_state(p, TASK_NORMAL);

	spin_unlock_irqrestore(&freezer_lock, flags);
	return true;
}

/*
 * Restore the saved_state before the task entered freezer. For typical task
 * in the __refrigerator(), saved_state == TASK_RUNNING so nothing happens
 * here. For tasks which were TASK_NORMAL | TASK_FREEZABLE, their initial state
 * is restored unless they got an expected wakeup (see ttwu_state_match()).
 * Returns 1 if the task state was restored.
 */
static int __restore_freezer_state(struct task_struct *p, void *arg)
{
	unsigned int state = p->saved_state;

	if (state != TASK_RUNNING) {
		WRITE_ONCE(p->__state, state);
		return 1;
	}

	return 0;
}

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

	spin_lock_irqsave(&freezer_lock, flags);
	if (WARN_ON_ONCE(freezing(p)))
		goto unlock;

	if (task_call_func(p, __restore_freezer_state, NULL))
		goto unlock;

	wake_up_state(p, TASK_FROZEN);
unlock:
	spin_unlock_irqrestore(&freezer_lock, flags);
}

/**
 * set_freezable - make %current freezable
 *
 * Mark %current freezable and enter refrigerator if necessary.
 */
bool set_freezable(void)
{
	might_sleep();

	/*
	 * Modify flags while holding freezer_lock.  This ensures the
	 * freezer notices that we aren't frozen yet or the freezing
	 * condition is visible to try_to_freeze() below.
	 */
	spin_lock_irq(&freezer_lock);
	current->flags &= ~PF_NOFREEZE;
	spin_unlock_irq(&freezer_lock);

	return try_to_freeze();
}
EXPORT_SYMBOL(set_freezable);