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(tsk: p, TIF_MEMDIE))
44 return false;
45
46 if (pm_nosig_freezing || cgroup_freezing(task: 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 WRITE_ONCE(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(lock: &freezer_lock);
81 freeze = freezing(current) && !(check_kthr_stop && kthread_should_stop());
82 spin_unlock_irq(lock: &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(task: p, flags: &flags)) {
103 signal_wake_up(t: p, fatal: 0);
104 unlock_task_sighand(task: p, flags: &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 /*
113 * Allow freezing the sched_delayed tasks; they will not execute until
114 * ttwu() fixes them up, so it is safe to swap their state now, instead
115 * of waiting for them to get fully dequeued.
116 */
117 if (task_is_runnable(p))
118 return 0;
119
120 if (p != current && task_curr(p))
121 return 0;
122
123 if (!(state & (TASK_FREEZABLE | __TASK_STOPPED | __TASK_TRACED)))
124 return 0;
125
126 /*
127 * Only TASK_NORMAL can be augmented with TASK_FREEZABLE, since they
128 * can suffer spurious wakeups.
129 */
130 if (state & TASK_FREEZABLE)
131 WARN_ON_ONCE(!(state & TASK_NORMAL));
132
133#ifdef CONFIG_LOCKDEP
134 /*
135 * It's dangerous to freeze with locks held; there be dragons there.
136 */
137 if (!(state & __TASK_FREEZABLE_UNSAFE))
138 WARN_ON_ONCE(debug_locks && p->lockdep_depth);
139#endif
140
141 p->saved_state = p->__state;
142 WRITE_ONCE(p->__state, TASK_FROZEN);
143 return TASK_FROZEN;
144}
145
146static bool __freeze_task(struct task_struct *p)
147{
148 /* TASK_FREEZABLE|TASK_STOPPED|TASK_TRACED -> TASK_FROZEN */
149 return task_call_func(p, func: __set_task_frozen, NULL);
150}
151
152/**
153 * freeze_task - send a freeze request to given task
154 * @p: task to send the request to
155 *
156 * If @p is freezing, the freeze request is sent either by sending a fake
157 * signal (if it's not a kernel thread) or waking it up (if it's a kernel
158 * thread).
159 *
160 * RETURNS:
161 * %false, if @p is not freezing or already frozen; %true, otherwise
162 */
163bool freeze_task(struct task_struct *p)
164{
165 unsigned long flags;
166
167 spin_lock_irqsave(&freezer_lock, flags);
168 if (!freezing(p) || frozen(p) || __freeze_task(p)) {
169 spin_unlock_irqrestore(lock: &freezer_lock, flags);
170 return false;
171 }
172
173 if (!(p->flags & PF_KTHREAD))
174 fake_signal_wake_up(p);
175 else
176 wake_up_state(tsk: p, TASK_NORMAL);
177
178 spin_unlock_irqrestore(lock: &freezer_lock, flags);
179 return true;
180}
181
182/*
183 * Restore the saved_state before the task entered freezer. For typical task
184 * in the __refrigerator(), saved_state == TASK_RUNNING so nothing happens
185 * here. For tasks which were TASK_NORMAL | TASK_FREEZABLE, their initial state
186 * is restored unless they got an expected wakeup (see ttwu_state_match()).
187 * Returns 1 if the task state was restored.
188 */
189static int __restore_freezer_state(struct task_struct *p, void *arg)
190{
191 unsigned int state = p->saved_state;
192
193 if (state != TASK_RUNNING) {
194 WRITE_ONCE(p->__state, state);
195 p->saved_state = TASK_RUNNING;
196 return 1;
197 }
198
199 return 0;
200}
201
202void __thaw_task(struct task_struct *p)
203{
204 unsigned long flags;
205
206 spin_lock_irqsave(&freezer_lock, flags);
207 if (WARN_ON_ONCE(freezing(p)))
208 goto unlock;
209
210 if (!frozen(p) || task_call_func(p, func: __restore_freezer_state, NULL))
211 goto unlock;
212
213 wake_up_state(tsk: p, TASK_FROZEN);
214unlock:
215 spin_unlock_irqrestore(lock: &freezer_lock, flags);
216}
217
218/**
219 * set_freezable - make %current freezable
220 *
221 * Mark %current freezable and enter refrigerator if necessary.
222 */
223bool set_freezable(void)
224{
225 might_sleep();
226
227 /*
228 * Modify flags while holding freezer_lock. This ensures the
229 * freezer notices that we aren't frozen yet or the freezing
230 * condition is visible to try_to_freeze() below.
231 */
232 spin_lock_irq(lock: &freezer_lock);
233 current->flags &= ~PF_NOFREEZE;
234 spin_unlock_irq(lock: &freezer_lock);
235
236 return try_to_freeze();
237}
238EXPORT_SYMBOL(set_freezable);
239

source code of linux/kernel/freezer.c