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 atomic_t system_freezing_cnt = ATOMIC_INIT(0);
17 EXPORT_SYMBOL(system_freezing_cnt);
18 
19 /* indicate whether PM freezing is in effect, protected by
20  * system_transition_mutex
21  */
22 bool pm_freezing;
23 bool pm_nosig_freezing;
24 
25 /* protects freezing and frozen transitions */
26 static DEFINE_SPINLOCK(freezer_lock);
27 
28 /**
29  * freezing_slow_path - slow path for testing whether a task needs to be frozen
30  * @p: task to be tested
31  *
32  * This function is called by freezing() if system_freezing_cnt isn't zero
33  * and tests whether @p needs to enter and stay in frozen state.  Can be
34  * called under any context.  The freezers are responsible for ensuring the
35  * target tasks see the updated state.
36  */
freezing_slow_path(struct task_struct * p)37 bool freezing_slow_path(struct task_struct *p)
38 {
39 	if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))
40 		return false;
41 
42 	if (test_tsk_thread_flag(p, TIF_MEMDIE))
43 		return false;
44 
45 	if (pm_nosig_freezing || cgroup_freezing(p))
46 		return true;
47 
48 	if (pm_freezing && !(p->flags & PF_KTHREAD))
49 		return true;
50 
51 	return false;
52 }
53 EXPORT_SYMBOL(freezing_slow_path);
54 
55 /* Refrigerator is place where frozen processes are stored :-). */
__refrigerator(bool check_kthr_stop)56 bool __refrigerator(bool check_kthr_stop)
57 {
58 	/* Hmm, should we be allowed to suspend when there are realtime
59 	   processes around? */
60 	bool was_frozen = false;
61 	unsigned int save = get_current_state();
62 
63 	pr_debug("%s entered refrigerator\n", current->comm);
64 
65 	for (;;) {
66 		set_current_state(TASK_UNINTERRUPTIBLE);
67 
68 		spin_lock_irq(&freezer_lock);
69 		current->flags |= PF_FROZEN;
70 		if (!freezing(current) ||
71 		    (check_kthr_stop && kthread_should_stop()))
72 			current->flags &= ~PF_FROZEN;
73 		spin_unlock_irq(&freezer_lock);
74 
75 		if (!(current->flags & PF_FROZEN))
76 			break;
77 		was_frozen = true;
78 		schedule();
79 	}
80 
81 	pr_debug("%s left refrigerator\n", current->comm);
82 
83 	/*
84 	 * Restore saved task state before returning.  The mb'd version
85 	 * needs to be used; otherwise, it might silently break
86 	 * synchronization which depends on ordered task state change.
87 	 */
88 	set_current_state(save);
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 
104 /**
105  * freeze_task - send a freeze request to given task
106  * @p: task to send the request to
107  *
108  * If @p is freezing, the freeze request is sent either by sending a fake
109  * signal (if it's not a kernel thread) or waking it up (if it's a kernel
110  * thread).
111  *
112  * RETURNS:
113  * %false, if @p is not freezing or already frozen; %true, otherwise
114  */
freeze_task(struct task_struct * p)115 bool freeze_task(struct task_struct *p)
116 {
117 	unsigned long flags;
118 
119 	/*
120 	 * This check can race with freezer_do_not_count, but worst case that
121 	 * will result in an extra wakeup being sent to the task.  It does not
122 	 * race with freezer_count(), the barriers in freezer_count() and
123 	 * freezer_should_skip() ensure that either freezer_count() sees
124 	 * freezing == true in try_to_freeze() and freezes, or
125 	 * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task
126 	 * normally.
127 	 */
128 	if (freezer_should_skip(p))
129 		return false;
130 
131 	spin_lock_irqsave(&freezer_lock, flags);
132 	if (!freezing(p) || frozen(p)) {
133 		spin_unlock_irqrestore(&freezer_lock, flags);
134 		return false;
135 	}
136 
137 	if (!(p->flags & PF_KTHREAD))
138 		fake_signal_wake_up(p);
139 	else
140 		wake_up_state(p, TASK_INTERRUPTIBLE);
141 
142 	spin_unlock_irqrestore(&freezer_lock, flags);
143 	return true;
144 }
145 
__thaw_task(struct task_struct * p)146 void __thaw_task(struct task_struct *p)
147 {
148 	unsigned long flags;
149 
150 	spin_lock_irqsave(&freezer_lock, flags);
151 	if (frozen(p))
152 		wake_up_process(p);
153 	spin_unlock_irqrestore(&freezer_lock, flags);
154 }
155 
156 /**
157  * set_freezable - make %current freezable
158  *
159  * Mark %current freezable and enter refrigerator if necessary.
160  */
set_freezable(void)161 bool set_freezable(void)
162 {
163 	might_sleep();
164 
165 	/*
166 	 * Modify flags while holding freezer_lock.  This ensures the
167 	 * freezer notices that we aren't frozen yet or the freezing
168 	 * condition is visible to try_to_freeze() below.
169 	 */
170 	spin_lock_irq(&freezer_lock);
171 	current->flags &= ~PF_NOFREEZE;
172 	spin_unlock_irq(&freezer_lock);
173 
174 	return try_to_freeze();
175 }
176 EXPORT_SYMBOL(set_freezable);
177