1/*
2 * kernel/freezer.c - Function to freeze a process
3 *
4 * Originally from kernel/power/process.c
5 */
6
7#include <linux/interrupt.h>
8#include <linux/suspend.h>
9#include <linux/export.h>
10#include <linux/syscalls.h>
11#include <linux/freezer.h>
12#include <linux/kthread.h>
13
14/* total number of freezing conditions in effect */
15atomic_t system_freezing_cnt = ATOMIC_INIT(0);
16EXPORT_SYMBOL(system_freezing_cnt);
17
18/* indicate whether PM freezing is in effect, protected by pm_mutex */
19bool pm_freezing;
20bool pm_nosig_freezing;
21
22/*
23 * Temporary export for the deadlock workaround in ata_scsi_hotplug().
24 * Remove once the hack becomes unnecessary.
25 */
26EXPORT_SYMBOL_GPL(pm_freezing);
27
28/* protects freezing and frozen transitions */
29static DEFINE_SPINLOCK(freezer_lock);
30
31/**
32 * freezing_slow_path - slow path for testing whether a task needs to be frozen
33 * @p: task to be tested
34 *
35 * This function is called by freezing() if system_freezing_cnt isn't zero
36 * and tests whether @p needs to enter and stay in frozen state.  Can be
37 * called under any context.  The freezers are responsible for ensuring the
38 * target tasks see the updated state.
39 */
40bool freezing_slow_path(struct task_struct *p)
41{
42	if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))
43		return false;
44
45	if (test_thread_flag(TIF_MEMDIE))
46		return false;
47
48	if (pm_nosig_freezing || cgroup_freezing(p))
49		return true;
50
51	if (pm_freezing && !(p->flags & PF_KTHREAD))
52		return true;
53
54	return false;
55}
56EXPORT_SYMBOL(freezing_slow_path);
57
58/* Refrigerator is place where frozen processes are stored :-). */
59bool __refrigerator(bool check_kthr_stop)
60{
61	/* Hmm, should we be allowed to suspend when there are realtime
62	   processes around? */
63	bool was_frozen = false;
64	long save = current->state;
65
66	pr_debug("%s entered refrigerator\n", current->comm);
67
68	for (;;) {
69		set_current_state(TASK_UNINTERRUPTIBLE);
70
71		spin_lock_irq(&freezer_lock);
72		current->flags |= PF_FROZEN;
73		if (!freezing(current) ||
74		    (check_kthr_stop && kthread_should_stop()))
75			current->flags &= ~PF_FROZEN;
76		spin_unlock_irq(&freezer_lock);
77
78		if (!(current->flags & PF_FROZEN))
79			break;
80		was_frozen = true;
81		schedule();
82	}
83
84	pr_debug("%s left refrigerator\n", current->comm);
85
86	/*
87	 * Restore saved task state before returning.  The mb'd version
88	 * needs to be used; otherwise, it might silently break
89	 * synchronization which depends on ordered task state change.
90	 */
91	set_current_state(save);
92
93	return was_frozen;
94}
95EXPORT_SYMBOL(__refrigerator);
96
97static void fake_signal_wake_up(struct task_struct *p)
98{
99	unsigned long flags;
100
101	if (lock_task_sighand(p, &flags)) {
102		signal_wake_up(p, 0);
103		unlock_task_sighand(p, &flags);
104	}
105}
106
107/**
108 * freeze_task - send a freeze request to given task
109 * @p: task to send the request to
110 *
111 * If @p is freezing, the freeze request is sent either by sending a fake
112 * signal (if it's not a kernel thread) or waking it up (if it's a kernel
113 * thread).
114 *
115 * RETURNS:
116 * %false, if @p is not freezing or already frozen; %true, otherwise
117 */
118bool freeze_task(struct task_struct *p)
119{
120	unsigned long flags;
121
122	/*
123	 * This check can race with freezer_do_not_count, but worst case that
124	 * will result in an extra wakeup being sent to the task.  It does not
125	 * race with freezer_count(), the barriers in freezer_count() and
126	 * freezer_should_skip() ensure that either freezer_count() sees
127	 * freezing == true in try_to_freeze() and freezes, or
128	 * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task
129	 * normally.
130	 */
131	if (freezer_should_skip(p))
132		return false;
133
134	spin_lock_irqsave(&freezer_lock, flags);
135	if (!freezing(p) || frozen(p)) {
136		spin_unlock_irqrestore(&freezer_lock, flags);
137		return false;
138	}
139
140	if (!(p->flags & PF_KTHREAD))
141		fake_signal_wake_up(p);
142	else
143		wake_up_state(p, TASK_INTERRUPTIBLE);
144
145	spin_unlock_irqrestore(&freezer_lock, flags);
146	return true;
147}
148
149void __thaw_task(struct task_struct *p)
150{
151	unsigned long flags;
152
153	spin_lock_irqsave(&freezer_lock, flags);
154	if (frozen(p))
155		wake_up_process(p);
156	spin_unlock_irqrestore(&freezer_lock, flags);
157}
158
159/**
160 * set_freezable - make %current freezable
161 *
162 * Mark %current freezable and enter refrigerator if necessary.
163 */
164bool set_freezable(void)
165{
166	might_sleep();
167
168	/*
169	 * Modify flags while holding freezer_lock.  This ensures the
170	 * freezer notices that we aren't frozen yet or the freezing
171	 * condition is visible to try_to_freeze() below.
172	 */
173	spin_lock_irq(&freezer_lock);
174	current->flags &= ~PF_NOFREEZE;
175	spin_unlock_irq(&freezer_lock);
176
177	return try_to_freeze();
178}
179EXPORT_SYMBOL(set_freezable);
180