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 */
16 DEFINE_STATIC_KEY_FALSE(freezer_active);
17 EXPORT_SYMBOL(freezer_active);
18
19 /*
20 * indicate whether PM freezing is in effect, protected by
21 * system_transition_mutex
22 */
23 bool pm_freezing;
24 bool pm_nosig_freezing;
25
26 /* protects freezing and frozen transitions */
27 static 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 */
freezing_slow_path(struct task_struct * p)38 bool 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 }
54 EXPORT_SYMBOL(freezing_slow_path);
55
frozen(struct task_struct * p)56 bool 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 :-). */
__refrigerator(bool check_kthr_stop)62 bool __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 set_current_state(TASK_FROZEN);
75
76 spin_lock_irq(&freezer_lock);
77 freeze = freezing(current) && !(check_kthr_stop && kthread_should_stop());
78 spin_unlock_irq(&freezer_lock);
79
80 if (!freeze)
81 break;
82
83 was_frozen = true;
84 schedule();
85 }
86 __set_current_state(TASK_RUNNING);
87
88 pr_debug("%s left refrigerator\n", current->comm);
89
90 return was_frozen;
91 }
92 EXPORT_SYMBOL(__refrigerator);
93
fake_signal_wake_up(struct task_struct * p)94 static void fake_signal_wake_up(struct task_struct *p)
95 {
96 unsigned long flags;
97
98 if (lock_task_sighand(p, &flags)) {
99 signal_wake_up(p, 0);
100 unlock_task_sighand(p, &flags);
101 }
102 }
103
__set_task_frozen(struct task_struct * p,void * arg)104 static int __set_task_frozen(struct task_struct *p, void *arg)
105 {
106 unsigned int state = READ_ONCE(p->__state);
107
108 if (p->on_rq)
109 return 0;
110
111 if (p != current && task_curr(p))
112 return 0;
113
114 if (!(state & (TASK_FREEZABLE | __TASK_STOPPED | __TASK_TRACED)))
115 return 0;
116
117 /*
118 * Only TASK_NORMAL can be augmented with TASK_FREEZABLE, since they
119 * can suffer spurious wakeups.
120 */
121 if (state & TASK_FREEZABLE)
122 WARN_ON_ONCE(!(state & TASK_NORMAL));
123
124 #ifdef CONFIG_LOCKDEP
125 /*
126 * It's dangerous to freeze with locks held; there be dragons there.
127 */
128 if (!(state & __TASK_FREEZABLE_UNSAFE))
129 WARN_ON_ONCE(debug_locks && p->lockdep_depth);
130 #endif
131
132 WRITE_ONCE(p->__state, TASK_FROZEN);
133 return TASK_FROZEN;
134 }
135
__freeze_task(struct task_struct * p)136 static bool __freeze_task(struct task_struct *p)
137 {
138 /* TASK_FREEZABLE|TASK_STOPPED|TASK_TRACED -> TASK_FROZEN */
139 return task_call_func(p, __set_task_frozen, NULL);
140 }
141
142 /**
143 * freeze_task - send a freeze request to given task
144 * @p: task to send the request to
145 *
146 * If @p is freezing, the freeze request is sent either by sending a fake
147 * signal (if it's not a kernel thread) or waking it up (if it's a kernel
148 * thread).
149 *
150 * RETURNS:
151 * %false, if @p is not freezing or already frozen; %true, otherwise
152 */
freeze_task(struct task_struct * p)153 bool freeze_task(struct task_struct *p)
154 {
155 unsigned long flags;
156
157 spin_lock_irqsave(&freezer_lock, flags);
158 if (!freezing(p) || frozen(p) || __freeze_task(p)) {
159 spin_unlock_irqrestore(&freezer_lock, flags);
160 return false;
161 }
162
163 if (!(p->flags & PF_KTHREAD))
164 fake_signal_wake_up(p);
165 else
166 wake_up_state(p, TASK_NORMAL);
167
168 spin_unlock_irqrestore(&freezer_lock, flags);
169 return true;
170 }
171
172 /*
173 * The special task states (TASK_STOPPED, TASK_TRACED) keep their canonical
174 * state in p->jobctl. If either of them got a wakeup that was missed because
175 * TASK_FROZEN, then their canonical state reflects that and the below will
176 * refuse to restore the special state and instead issue the wakeup.
177 */
__set_task_special(struct task_struct * p,void * arg)178 static int __set_task_special(struct task_struct *p, void *arg)
179 {
180 unsigned int state = 0;
181
182 if (p->jobctl & JOBCTL_TRACED)
183 state = TASK_TRACED;
184
185 else if (p->jobctl & JOBCTL_STOPPED)
186 state = TASK_STOPPED;
187
188 if (state)
189 WRITE_ONCE(p->__state, state);
190
191 return state;
192 }
193
__thaw_task(struct task_struct * p)194 void __thaw_task(struct task_struct *p)
195 {
196 unsigned long flags, flags2;
197
198 spin_lock_irqsave(&freezer_lock, flags);
199 if (WARN_ON_ONCE(freezing(p)))
200 goto unlock;
201
202 if (lock_task_sighand(p, &flags2)) {
203 /* TASK_FROZEN -> TASK_{STOPPED,TRACED} */
204 bool ret = task_call_func(p, __set_task_special, NULL);
205 unlock_task_sighand(p, &flags2);
206 if (ret)
207 goto unlock;
208 }
209
210 wake_up_state(p, TASK_FROZEN);
211 unlock:
212 spin_unlock_irqrestore(&freezer_lock, flags);
213 }
214
215 /**
216 * set_freezable - make %current freezable
217 *
218 * Mark %current freezable and enter refrigerator if necessary.
219 */
set_freezable(void)220 bool set_freezable(void)
221 {
222 might_sleep();
223
224 /*
225 * Modify flags while holding freezer_lock. This ensures the
226 * freezer notices that we aren't frozen yet or the freezing
227 * condition is visible to try_to_freeze() below.
228 */
229 spin_lock_irq(&freezer_lock);
230 current->flags &= ~PF_NOFREEZE;
231 spin_unlock_irq(&freezer_lock);
232
233 return try_to_freeze();
234 }
235 EXPORT_SYMBOL(set_freezable);
236
