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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 (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}
53EXPORT_SYMBOL(freezing_slow_path);
54
55/* Refrigerator is place where frozen processes are stored :-). */
56bool __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 long save = 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}
92EXPORT_SYMBOL(__refrigerator);
93
94static 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 */
115bool 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
146void __thaw_task(struct task_struct *p)
147{
148 unsigned long flags;
149
150 /*
151 * Clear freezing and kick @p if FROZEN. Clearing is guaranteed to
152 * be visible to @p as waking up implies wmb. Waking up inside
153 * freezer_lock also prevents wakeups from leaking outside
154 * refrigerator.
155 */
156 spin_lock_irqsave(&freezer_lock, flags);
157 if (frozen(p))
158 wake_up_process(p);
159 spin_unlock_irqrestore(&freezer_lock, flags);
160}
161
162/**
163 * set_freezable - make %current freezable
164 *
165 * Mark %current freezable and enter refrigerator if necessary.
166 */
167bool set_freezable(void)
168{
169 might_sleep();
170
171 /*
172 * Modify flags while holding freezer_lock. This ensures the
173 * freezer notices that we aren't frozen yet or the freezing
174 * condition is visible to try_to_freeze() below.
175 */
176 spin_lock_irq(&freezer_lock);
177 current->flags &= ~PF_NOFREEZE;
178 spin_unlock_irq(&freezer_lock);
179
180 return try_to_freeze();
181}
182EXPORT_SYMBOL(set_freezable);
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/module.h>
10#include <linux/syscalls.h>
11#include <linux/freezer.h>
12
13/*
14 * freezing is complete, mark current process as frozen
15 */
16static inline void frozen_process(void)
17{
18 if (!unlikely(current->flags & PF_NOFREEZE)) {
19 current->flags |= PF_FROZEN;
20 smp_wmb();
21 }
22 clear_freeze_flag(current);
23}
24
25/* Refrigerator is place where frozen processes are stored :-). */
26void refrigerator(void)
27{
28 /* Hmm, should we be allowed to suspend when there are realtime
29 processes around? */
30 long save;
31
32 task_lock(current);
33 if (freezing(current)) {
34 frozen_process();
35 task_unlock(current);
36 } else {
37 task_unlock(current);
38 return;
39 }
40 save = current->state;
41 pr_debug("%s entered refrigerator\n", current->comm);
42
43 spin_lock_irq(¤t->sighand->siglock);
44 recalc_sigpending(); /* We sent fake signal, clean it up */
45 spin_unlock_irq(¤t->sighand->siglock);
46
47 /* prevent accounting of that task to load */
48 current->flags |= PF_FREEZING;
49
50 for (;;) {
51 set_current_state(TASK_UNINTERRUPTIBLE);
52 if (!frozen(current))
53 break;
54 schedule();
55 }
56
57 /* Remove the accounting blocker */
58 current->flags &= ~PF_FREEZING;
59
60 pr_debug("%s left refrigerator\n", current->comm);
61 __set_current_state(save);
62}
63EXPORT_SYMBOL(refrigerator);
64
65static void fake_signal_wake_up(struct task_struct *p)
66{
67 unsigned long flags;
68
69 spin_lock_irqsave(&p->sighand->siglock, flags);
70 signal_wake_up(p, 0);
71 spin_unlock_irqrestore(&p->sighand->siglock, flags);
72}
73
74/**
75 * freeze_task - send a freeze request to given task
76 * @p: task to send the request to
77 * @sig_only: if set, the request will only be sent if the task has the
78 * PF_FREEZER_NOSIG flag unset
79 * Return value: 'false', if @sig_only is set and the task has
80 * PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
81 *
82 * The freeze request is sent by setting the tasks's TIF_FREEZE flag and
83 * either sending a fake signal to it or waking it up, depending on whether
84 * or not it has PF_FREEZER_NOSIG set. If @sig_only is set and the task
85 * has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
86 * TIF_FREEZE flag will not be set.
87 */
88bool freeze_task(struct task_struct *p, bool sig_only)
89{
90 /*
91 * We first check if the task is freezing and next if it has already
92 * been frozen to avoid the race with frozen_process() which first marks
93 * the task as frozen and next clears its TIF_FREEZE.
94 */
95 if (!freezing(p)) {
96 smp_rmb();
97 if (frozen(p))
98 return false;
99
100 if (!sig_only || should_send_signal(p))
101 set_freeze_flag(p);
102 else
103 return false;
104 }
105
106 if (should_send_signal(p)) {
107 fake_signal_wake_up(p);
108 /*
109 * fake_signal_wake_up() goes through p's scheduler
110 * lock and guarantees that TASK_STOPPED/TRACED ->
111 * TASK_RUNNING transition can't race with task state
112 * testing in try_to_freeze_tasks().
113 */
114 } else if (sig_only) {
115 return false;
116 } else {
117 wake_up_state(p, TASK_INTERRUPTIBLE);
118 }
119
120 return true;
121}
122
123void cancel_freezing(struct task_struct *p)
124{
125 unsigned long flags;
126
127 if (freezing(p)) {
128 pr_debug(" clean up: %s\n", p->comm);
129 clear_freeze_flag(p);
130 spin_lock_irqsave(&p->sighand->siglock, flags);
131 recalc_sigpending_and_wake(p);
132 spin_unlock_irqrestore(&p->sighand->siglock, flags);
133 }
134}
135
136static int __thaw_process(struct task_struct *p)
137{
138 if (frozen(p)) {
139 p->flags &= ~PF_FROZEN;
140 return 1;
141 }
142 clear_freeze_flag(p);
143 return 0;
144}
145
146/*
147 * Wake up a frozen process
148 *
149 * task_lock() is needed to prevent the race with refrigerator() which may
150 * occur if the freezing of tasks fails. Namely, without the lock, if the
151 * freezing of tasks failed, thaw_tasks() might have run before a task in
152 * refrigerator() could call frozen_process(), in which case the task would be
153 * frozen and no one would thaw it.
154 */
155int thaw_process(struct task_struct *p)
156{
157 task_lock(p);
158 if (__thaw_process(p) == 1) {
159 task_unlock(p);
160 wake_up_process(p);
161 return 1;
162 }
163 task_unlock(p);
164 return 0;
165}
166EXPORT_SYMBOL(thaw_process);