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247 lines · 5.9 KiB

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/oom.h>
14#include <linux/kthread.h>
15
16/* total number of freezing conditions in effect */
17DEFINE_STATIC_KEY_FALSE(freezer_active);
18EXPORT_SYMBOL(freezer_active);
19
20/*
21 * indicate whether PM freezing is in effect, protected by
22 * system_transition_mutex
23 */
24bool pm_freezing;
25bool pm_nosig_freezing;
26
27/* protects freezing and frozen transitions */
28static DEFINE_SPINLOCK(freezer_lock);
29
30/**
31 * freezing_slow_path - slow path for testing whether a task needs to be frozen
32 * @p: task to be tested
33 *
34 * This function is called by freezing() if freezer_active isn't zero
35 * and tests whether @p needs to enter and stay in frozen state. Can be
36 * called under any context. The freezers are responsible for ensuring the
37 * target tasks see the updated state.
38 */
39bool freezing_slow_path(struct task_struct *p)
40{
41 if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))
42 return false;
43
44 if (tsk_is_oom_victim(p))
45 return false;
46
47 if (pm_nosig_freezing || cgroup1_freezing(p))
48 return true;
49
50 if (pm_freezing && !(p->flags & PF_KTHREAD))
51 return true;
52
53 return false;
54}
55EXPORT_SYMBOL(freezing_slow_path);
56
57bool frozen(struct task_struct *p)
58{
59 return READ_ONCE(p->__state) & TASK_FROZEN;
60}
61
62/* Refrigerator is place where frozen processes are stored :-). */
63bool __refrigerator(bool check_kthr_stop)
64{
65 unsigned int state = get_current_state();
66 bool was_frozen = false;
67
68 pr_debug("%s entered refrigerator\n", current->comm);
69
70 WARN_ON_ONCE(state && !(state & TASK_NORMAL));
71
72 for (;;) {
73 bool freeze;
74
75 raw_spin_lock_irq(&current->pi_lock);
76 WRITE_ONCE(current->__state, TASK_FROZEN);
77 /* unstale saved_state so that __thaw_task() will wake us up */
78 current->saved_state = TASK_RUNNING;
79 raw_spin_unlock_irq(&current->pi_lock);
80
81 spin_lock_irq(&freezer_lock);
82 freeze = freezing(current) && !(check_kthr_stop && kthread_should_stop());
83 spin_unlock_irq(&freezer_lock);
84
85 if (!freeze)
86 break;
87
88 was_frozen = true;
89 schedule();
90 }
91 __set_current_state(TASK_RUNNING);
92
93 pr_debug("%s left refrigerator\n", current->comm);
94
95 return was_frozen;
96}
97EXPORT_SYMBOL(__refrigerator);
98
99static void fake_signal_wake_up(struct task_struct *p)
100{
101 unsigned long flags;
102
103 if (lock_task_sighand(p, &flags)) {
104 signal_wake_up(p, 0);
105 unlock_task_sighand(p, &flags);
106 }
107}
108
109static int __set_task_frozen(struct task_struct *p, void *arg)
110{
111 unsigned int state = READ_ONCE(p->__state);
112
113 /*
114 * Allow freezing the sched_delayed tasks; they will not execute until
115 * ttwu() fixes them up, so it is safe to swap their state now, instead
116 * of waiting for them to get fully dequeued.
117 */
118 if (task_is_runnable(p))
119 return 0;
120
121 if (p != current && task_curr(p))
122 return 0;
123
124 if (!(state & (TASK_FREEZABLE | __TASK_STOPPED | __TASK_TRACED)))
125 return 0;
126
127 /*
128 * Only TASK_NORMAL can be augmented with TASK_FREEZABLE, since they
129 * can suffer spurious wakeups.
130 */
131 if (state & TASK_FREEZABLE)
132 WARN_ON_ONCE(!(state & TASK_NORMAL));
133
134#ifdef CONFIG_LOCKDEP
135 /*
136 * It's dangerous to freeze with locks held; there be dragons there.
137 */
138 if (!(state & __TASK_FREEZABLE_UNSAFE))
139 WARN_ON_ONCE(debug_locks && p->lockdep_depth);
140#endif
141
142 p->saved_state = p->__state;
143 WRITE_ONCE(p->__state, TASK_FROZEN);
144 return TASK_FROZEN;
145}
146
147static bool __freeze_task(struct task_struct *p)
148{
149 /* TASK_FREEZABLE|TASK_STOPPED|TASK_TRACED -> TASK_FROZEN */
150 return task_call_func(p, __set_task_frozen, NULL);
151}
152
153/**
154 * freeze_task - send a freeze request to given task
155 * @p: task to send the request to
156 *
157 * If @p is freezing, the freeze request is sent either by sending a fake
158 * signal (if it's not a kernel thread) or waking it up (if it's a kernel
159 * thread).
160 *
161 * RETURNS:
162 * %false, if @p is not freezing or already frozen; %true, otherwise
163 */
164bool freeze_task(struct task_struct *p)
165{
166 unsigned long flags;
167
168 spin_lock_irqsave(&freezer_lock, flags);
169 if (!freezing(p) || frozen(p) || __freeze_task(p)) {
170 spin_unlock_irqrestore(&freezer_lock, flags);
171 return false;
172 }
173
174 if (!(p->flags & PF_KTHREAD))
175 fake_signal_wake_up(p);
176 else
177 wake_up_state(p, TASK_NORMAL);
178
179 spin_unlock_irqrestore(&freezer_lock, flags);
180 return true;
181}
182
183/*
184 * Restore the saved_state before the task entered freezer. For typical task
185 * in the __refrigerator(), saved_state == TASK_RUNNING so nothing happens
186 * here. For tasks which were TASK_NORMAL | TASK_FREEZABLE, their initial state
187 * is restored unless they got an expected wakeup (see ttwu_state_match()).
188 * Returns 1 if the task state was restored.
189 */
190static int __restore_freezer_state(struct task_struct *p, void *arg)
191{
192 unsigned int state = p->saved_state;
193
194 if (state != TASK_RUNNING) {
195 WRITE_ONCE(p->__state, state);
196 p->saved_state = TASK_RUNNING;
197 return 1;
198 }
199
200 return 0;
201}
202
203void __thaw_task(struct task_struct *p)
204{
205 guard(spinlock_irqsave)(&freezer_lock);
206 if (frozen(p) && !task_call_func(p, __restore_freezer_state, NULL))
207 wake_up_state(p, TASK_FROZEN);
208}
209
210/*
211 * thaw_process - Thaw a frozen process
212 * @p: the process to be thawed
213 *
214 * Iterate over all threads of @p and call __thaw_task() on each.
215 */
216void thaw_process(struct task_struct *p)
217{
218 struct task_struct *t;
219
220 rcu_read_lock();
221 for_each_thread(p, t) {
222 __thaw_task(t);
223 }
224 rcu_read_unlock();
225}
226
227/**
228 * set_freezable - make %current freezable
229 *
230 * Mark %current freezable and enter refrigerator if necessary.
231 */
232bool set_freezable(void)
233{
234 might_sleep();
235
236 /*
237 * Modify flags while holding freezer_lock. This ensures the
238 * freezer notices that we aren't frozen yet or the freezing
239 * condition is visible to try_to_freeze() below.
240 */
241 spin_lock_irq(&freezer_lock);
242 current->flags &= ~PF_NOFREEZE;
243 spin_unlock_irq(&freezer_lock);
244
245 return try_to_freeze();
246}
247EXPORT_SYMBOL(set_freezable);