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
19 * system_transition_mutex
20 */
21bool pm_freezing;
22bool pm_nosig_freezing;
23
24/*
25 * Temporary export for the deadlock workaround in ata_scsi_hotplug().
26 * Remove once the hack becomes unnecessary.
27 */
28EXPORT_SYMBOL_GPL(pm_freezing);
29
30/* protects freezing and frozen transitions */
31static DEFINE_SPINLOCK(freezer_lock);
32
33/**
34 * freezing_slow_path - slow path for testing whether a task needs to be frozen
35 * @p: task to be tested
36 *
37 * This function is called by freezing() if system_freezing_cnt isn't zero
38 * and tests whether @p needs to enter and stay in frozen state. Can be
39 * called under any context. The freezers are responsible for ensuring the
40 * target tasks see the updated state.
41 */
42bool freezing_slow_path(struct task_struct *p)
43{
44 if (p->flags & (PF_NOFREEZE | PF_SUSPEND_TASK))
45 return false;
46
47 if (test_tsk_thread_flag(p, TIF_MEMDIE))
48 return false;
49
50 if (pm_nosig_freezing || cgroup_freezing(p))
51 return true;
52
53 if (pm_freezing && !(p->flags & PF_KTHREAD))
54 return true;
55
56 return false;
57}
58EXPORT_SYMBOL(freezing_slow_path);
59
60/* Refrigerator is place where frozen processes are stored :-). */
61bool __refrigerator(bool check_kthr_stop)
62{
63 /* Hmm, should we be allowed to suspend when there are realtime
64 processes around? */
65 bool was_frozen = false;
66 long save = current->state;
67
68 pr_debug("%s entered refrigerator\n", current->comm);
69
70 for (;;) {
71 set_current_state(TASK_UNINTERRUPTIBLE);
72
73 spin_lock_irq(&freezer_lock);
74 current->flags |= PF_FROZEN;
75 if (!freezing(current) ||
76 (check_kthr_stop && kthread_should_stop()))
77 current->flags &= ~PF_FROZEN;
78 spin_unlock_irq(&freezer_lock);
79
80 if (!(current->flags & PF_FROZEN))
81 break;
82 was_frozen = true;
83 schedule();
84 }
85
86 pr_debug("%s left refrigerator\n", current->comm);
87
88 /*
89 * Restore saved task state before returning. The mb'd version
90 * needs to be used; otherwise, it might silently break
91 * synchronization which depends on ordered task state change.
92 */
93 set_current_state(save);
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
109/**
110 * freeze_task - send a freeze request to given task
111 * @p: task to send the request to
112 *
113 * If @p is freezing, the freeze request is sent either by sending a fake
114 * signal (if it's not a kernel thread) or waking it up (if it's a kernel
115 * thread).
116 *
117 * RETURNS:
118 * %false, if @p is not freezing or already frozen; %true, otherwise
119 */
120bool freeze_task(struct task_struct *p)
121{
122 unsigned long flags;
123
124 /*
125 * This check can race with freezer_do_not_count, but worst case that
126 * will result in an extra wakeup being sent to the task. It does not
127 * race with freezer_count(), the barriers in freezer_count() and
128 * freezer_should_skip() ensure that either freezer_count() sees
129 * freezing == true in try_to_freeze() and freezes, or
130 * freezer_should_skip() sees !PF_FREEZE_SKIP and freezes the task
131 * normally.
132 */
133 if (freezer_should_skip(p))
134 return false;
135
136 spin_lock_irqsave(&freezer_lock, flags);
137 if (!freezing(p) || frozen(p)) {
138 spin_unlock_irqrestore(&freezer_lock, flags);
139 return false;
140 }
141
142 if (!(p->flags & PF_KTHREAD))
143 fake_signal_wake_up(p);
144 else
145 wake_up_state(p, TASK_INTERRUPTIBLE);
146
147 spin_unlock_irqrestore(&freezer_lock, flags);
148 return true;
149}
150
151void __thaw_task(struct task_struct *p)
152{
153 unsigned long flags;
154
155 spin_lock_irqsave(&freezer_lock, flags);
156 if (frozen(p))
157 wake_up_process(p);
158 spin_unlock_irqrestore(&freezer_lock, flags);
159}
160
161/**
162 * set_freezable - make %current freezable
163 *
164 * Mark %current freezable and enter refrigerator if necessary.
165 */
166bool set_freezable(void)
167{
168 might_sleep();
169
170 /*
171 * Modify flags while holding freezer_lock. This ensures the
172 * freezer notices that we aren't frozen yet or the freezing
173 * condition is visible to try_to_freeze() below.
174 */
175 spin_lock_irq(&freezer_lock);
176 current->flags &= ~PF_NOFREEZE;
177 spin_unlock_irq(&freezer_lock);
178
179 return try_to_freeze();
180}
181EXPORT_SYMBOL(set_freezable);
182