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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/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);
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/* protects freezing and frozen transitions */
23static DEFINE_SPINLOCK(freezer_lock);
24
25/**
26 * freezing_slow_path - slow path for testing whether a task needs to be frozen
27 * @p: task to be tested
28 *
29 * This function is called by freezing() if system_freezing_cnt isn't zero
30 * and tests whether @p needs to enter and stay in frozen state. Can be
31 * called under any context. The freezers are responsible for ensuring the
32 * target tasks see the updated state.
33 */
34bool freezing_slow_path(struct task_struct *p)
35{
36 if (p->flags & PF_NOFREEZE)
37 return false;
38
39 if (pm_nosig_freezing || cgroup_freezing(p))
40 return true;
41
42 if (pm_freezing && !(p->flags & PF_KTHREAD))
43 return true;
44
45 return false;
46}
47EXPORT_SYMBOL(freezing_slow_path);
48
49/* Refrigerator is place where frozen processes are stored :-). */
50bool __refrigerator(bool check_kthr_stop)
51{
52 /* Hmm, should we be allowed to suspend when there are realtime
53 processes around? */
54 bool was_frozen = false;
55 long save = current->state;
56
57 pr_debug("%s entered refrigerator\n", current->comm);
58
59 for (;;) {
60 set_current_state(TASK_UNINTERRUPTIBLE);
61
62 spin_lock_irq(&freezer_lock);
63 current->flags |= PF_FROZEN;
64 if (!freezing(current) ||
65 (check_kthr_stop && kthread_should_stop()))
66 current->flags &= ~PF_FROZEN;
67 spin_unlock_irq(&freezer_lock);
68
69 if (!(current->flags & PF_FROZEN))
70 break;
71 was_frozen = true;
72 schedule();
73 }
74
75 pr_debug("%s left refrigerator\n", current->comm);
76
77 /*
78 * Restore saved task state before returning. The mb'd version
79 * needs to be used; otherwise, it might silently break
80 * synchronization which depends on ordered task state change.
81 */
82 set_current_state(save);
83
84 return was_frozen;
85}
86EXPORT_SYMBOL(__refrigerator);
87
88static void fake_signal_wake_up(struct task_struct *p)
89{
90 unsigned long flags;
91
92 if (lock_task_sighand(p, &flags)) {
93 signal_wake_up(p, 0);
94 unlock_task_sighand(p, &flags);
95 }
96}
97
98/**
99 * freeze_task - send a freeze request to given task
100 * @p: task to send the request to
101 *
102 * If @p is freezing, the freeze request is sent either by sending a fake
103 * signal (if it's not a kernel thread) or waking it up (if it's a kernel
104 * thread).
105 *
106 * RETURNS:
107 * %false, if @p is not freezing or already frozen; %true, otherwise
108 */
109bool freeze_task(struct task_struct *p)
110{
111 unsigned long flags;
112
113 spin_lock_irqsave(&freezer_lock, flags);
114 if (!freezing(p) || frozen(p)) {
115 spin_unlock_irqrestore(&freezer_lock, flags);
116 return false;
117 }
118
119 if (!(p->flags & PF_KTHREAD)) {
120 fake_signal_wake_up(p);
121 /*
122 * fake_signal_wake_up() goes through p's scheduler
123 * lock and guarantees that TASK_STOPPED/TRACED ->
124 * TASK_RUNNING transition can't race with task state
125 * testing in try_to_freeze_tasks().
126 */
127 } else {
128 wake_up_state(p, TASK_INTERRUPTIBLE);
129 }
130
131 spin_unlock_irqrestore(&freezer_lock, flags);
132 return true;
133}
134
135void __thaw_task(struct task_struct *p)
136{
137 unsigned long flags;
138
139 /*
140 * Clear freezing and kick @p if FROZEN. Clearing is guaranteed to
141 * be visible to @p as waking up implies wmb. Waking up inside
142 * freezer_lock also prevents wakeups from leaking outside
143 * refrigerator.
144 */
145 spin_lock_irqsave(&freezer_lock, flags);
146 if (frozen(p))
147 wake_up_process(p);
148 spin_unlock_irqrestore(&freezer_lock, flags);
149}
150
151/**
152 * set_freezable - make %current freezable
153 *
154 * Mark %current freezable and enter refrigerator if necessary.
155 */
156bool set_freezable(void)
157{
158 might_sleep();
159
160 /*
161 * Modify flags while holding freezer_lock. This ensures the
162 * freezer notices that we aren't frozen yet or the freezing
163 * condition is visible to try_to_freeze() below.
164 */
165 spin_lock_irq(&freezer_lock);
166 current->flags &= ~PF_NOFREEZE;
167 spin_unlock_irq(&freezer_lock);
168
169 return try_to_freeze();
170}
171EXPORT_SYMBOL(set_freezable);