1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * kernel/freezer.c - Function to freeze a process
4 *
5 * Originally from kernel/power/process.c
6 */
7
8#include <linux/interrupt.h>
9#include <linux/suspend.h>
10#include <linux/export.h>
11#include <linux/syscalls.h>
12#include <linux/freezer.h>
13#include <linux/kthread.h>
14
15/* total number of freezing conditions in effect */
16DEFINE_STATIC_KEY_FALSE(freezer_active);
17EXPORT_SYMBOL(freezer_active);
18
19/*
20 * indicate whether PM freezing is in effect, protected by
21 * system_transition_mutex
22 */
23bool pm_freezing;
24bool pm_nosig_freezing;
25
26/* protects freezing and frozen transitions */
27static DEFINE_SPINLOCK(freezer_lock);
28
29/**
30 * freezing_slow_path - slow path for testing whether a task needs to be frozen
31 * @p: task to be tested
32 *
33 * This function is called by freezing() if freezer_active isn't zero
34 * and tests whether @p needs to enter and stay in frozen state.  Can be
35 * called under any context.  The freezers are responsible for ensuring the
36 * target tasks see the updated state.
37 */
38bool freezing_slow_path(struct task_struct *p)
39{
40	if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))
41		return false;
42
43	if (test_tsk_thread_flag(p, TIF_MEMDIE))
44		return false;
45
46	if (pm_nosig_freezing || cgroup_freezing(p))
47		return true;
48
49	if (pm_freezing && !(p->flags & PF_KTHREAD))
50		return true;
51
52	return false;
53}
54EXPORT_SYMBOL(freezing_slow_path);
55
56bool frozen(struct task_struct *p)
57{
58	return READ_ONCE(p->__state) & TASK_FROZEN;
59}
60
61/* Refrigerator is place where frozen processes are stored :-). */
62bool __refrigerator(bool check_kthr_stop)
63{
64	unsigned int state = get_current_state();
65	bool was_frozen = false;
66
67	pr_debug("%s entered refrigerator\n", current->comm);
68
69	WARN_ON_ONCE(state && !(state & TASK_NORMAL));
70
71	for (;;) {
72		bool freeze;
73
74		raw_spin_lock_irq(&current->pi_lock);
75		set_current_state(TASK_FROZEN);
76		/* unstale saved_state so that __thaw_task() will wake us up */
77		current->saved_state = TASK_RUNNING;
78		raw_spin_unlock_irq(&current->pi_lock);
79
80		spin_lock_irq(&freezer_lock);
81		freeze = freezing(current) && !(check_kthr_stop && kthread_should_stop());
82		spin_unlock_irq(&freezer_lock);
83
84		if (!freeze)
85			break;
86
87		was_frozen = true;
88		schedule();
89	}
90	__set_current_state(TASK_RUNNING);
91
92	pr_debug("%s left refrigerator\n", current->comm);
93
94	return was_frozen;
95}
96EXPORT_SYMBOL(__refrigerator);
97
98static void fake_signal_wake_up(struct task_struct *p)
99{
100	unsigned long flags;
101
102	if (lock_task_sighand(p, &flags)) {
103		signal_wake_up(p, 0);
104		unlock_task_sighand(p, &flags);
105	}
106}
107
108static int __set_task_frozen(struct task_struct *p, void *arg)
109{
110	unsigned int state = READ_ONCE(p->__state);
111
112	if (p->on_rq)
113		return 0;
114
115	if (p != current && task_curr(p))
116		return 0;
117
118	if (!(state & (TASK_FREEZABLE | __TASK_STOPPED | __TASK_TRACED)))
119		return 0;
120
121	/*
122	 * Only TASK_NORMAL can be augmented with TASK_FREEZABLE, since they
123	 * can suffer spurious wakeups.
124	 */
125	if (state & TASK_FREEZABLE)
126		WARN_ON_ONCE(!(state & TASK_NORMAL));
127
128#ifdef CONFIG_LOCKDEP
129	/*
130	 * It's dangerous to freeze with locks held; there be dragons there.
131	 */
132	if (!(state & __TASK_FREEZABLE_UNSAFE))
133		WARN_ON_ONCE(debug_locks && p->lockdep_depth);
134#endif
135
136	p->saved_state = p->__state;
137	WRITE_ONCE(p->__state, TASK_FROZEN);
138	return TASK_FROZEN;
139}
140
141static bool __freeze_task(struct task_struct *p)
142{
143	/* TASK_FREEZABLE|TASK_STOPPED|TASK_TRACED -> TASK_FROZEN */
144	return task_call_func(p, __set_task_frozen, NULL);
145}
146
147/**
148 * freeze_task - send a freeze request to given task
149 * @p: task to send the request to
150 *
151 * If @p is freezing, the freeze request is sent either by sending a fake
152 * signal (if it's not a kernel thread) or waking it up (if it's a kernel
153 * thread).
154 *
155 * RETURNS:
156 * %false, if @p is not freezing or already frozen; %true, otherwise
157 */
158bool freeze_task(struct task_struct *p)
159{
160	unsigned long flags;
161
162	spin_lock_irqsave(&freezer_lock, flags);
163	if (!freezing(p) || frozen(p) || __freeze_task(p)) {
164		spin_unlock_irqrestore(&freezer_lock, flags);
165		return false;
166	}
167
168	if (!(p->flags & PF_KTHREAD))
169		fake_signal_wake_up(p);
170	else
171		wake_up_state(p, TASK_NORMAL);
172
173	spin_unlock_irqrestore(&freezer_lock, flags);
174	return true;
175}
176
177/*
178 * Restore the saved_state before the task entered freezer. For typical task
179 * in the __refrigerator(), saved_state == TASK_RUNNING so nothing happens
180 * here. For tasks which were TASK_NORMAL | TASK_FREEZABLE, their initial state
181 * is restored unless they got an expected wakeup (see ttwu_state_match()).
182 * Returns 1 if the task state was restored.
183 */
184static int __restore_freezer_state(struct task_struct *p, void *arg)
185{
186	unsigned int state = p->saved_state;
187
188	if (state != TASK_RUNNING) {
189		WRITE_ONCE(p->__state, state);
190		p->saved_state = TASK_RUNNING;
191		return 1;
192	}
193
194	return 0;
195}
196
197void __thaw_task(struct task_struct *p)
198{
199	unsigned long flags;
200
201	spin_lock_irqsave(&freezer_lock, flags);
202	if (WARN_ON_ONCE(freezing(p)))
203		goto unlock;
204
205	if (!frozen(p) || task_call_func(p, __restore_freezer_state, NULL))
206		goto unlock;
207
208	wake_up_state(p, TASK_FROZEN);
209unlock:
210	spin_unlock_irqrestore(&freezer_lock, flags);
211}
212
213/**
214 * set_freezable - make %current freezable
215 *
216 * Mark %current freezable and enter refrigerator if necessary.
217 */
218bool set_freezable(void)
219{
220	might_sleep();
221
222	/*
223	 * Modify flags while holding freezer_lock.  This ensures the
224	 * freezer notices that we aren't frozen yet or the freezing
225	 * condition is visible to try_to_freeze() below.
226	 */
227	spin_lock_irq(&freezer_lock);
228	current->flags &= ~PF_NOFREEZE;
229	spin_unlock_irq(&freezer_lock);
230
231	return try_to_freeze();
232}
233EXPORT_SYMBOL(set_freezable);
234