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 */
frozen_process(void)16 static inline void frozen_process(void)
17 {
18 if (!unlikely(current->flags & PF_NOFREEZE)) {
19 current->flags |= PF_FROZEN;
20 wmb();
21 }
22 clear_freeze_flag(current);
23 }
24
25 /* Refrigerator is place where frozen processes are stored :-). */
refrigerator(void)26 void 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 for (;;) {
48 set_current_state(TASK_UNINTERRUPTIBLE);
49 if (!frozen(current))
50 break;
51 schedule();
52 }
53 pr_debug("%s left refrigerator\n", current->comm);
54 __set_current_state(save);
55 }
56 EXPORT_SYMBOL(refrigerator);
57
fake_signal_wake_up(struct task_struct * p)58 static void fake_signal_wake_up(struct task_struct *p)
59 {
60 unsigned long flags;
61
62 spin_lock_irqsave(&p->sighand->siglock, flags);
63 signal_wake_up(p, 0);
64 spin_unlock_irqrestore(&p->sighand->siglock, flags);
65 }
66
67 /**
68 * freeze_task - send a freeze request to given task
69 * @p: task to send the request to
70 * @sig_only: if set, the request will only be sent if the task has the
71 * PF_FREEZER_NOSIG flag unset
72 * Return value: 'false', if @sig_only is set and the task has
73 * PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
74 *
75 * The freeze request is sent by setting the tasks's TIF_FREEZE flag and
76 * either sending a fake signal to it or waking it up, depending on whether
77 * or not it has PF_FREEZER_NOSIG set. If @sig_only is set and the task
78 * has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
79 * TIF_FREEZE flag will not be set.
80 */
freeze_task(struct task_struct * p,bool sig_only)81 bool freeze_task(struct task_struct *p, bool sig_only)
82 {
83 /*
84 * We first check if the task is freezing and next if it has already
85 * been frozen to avoid the race with frozen_process() which first marks
86 * the task as frozen and next clears its TIF_FREEZE.
87 */
88 if (!freezing(p)) {
89 rmb();
90 if (frozen(p))
91 return false;
92
93 if (!sig_only || should_send_signal(p))
94 set_freeze_flag(p);
95 else
96 return false;
97 }
98
99 if (should_send_signal(p)) {
100 if (!signal_pending(p))
101 fake_signal_wake_up(p);
102 } else if (sig_only) {
103 return false;
104 } else {
105 wake_up_state(p, TASK_INTERRUPTIBLE);
106 }
107
108 return true;
109 }
110
cancel_freezing(struct task_struct * p)111 void cancel_freezing(struct task_struct *p)
112 {
113 unsigned long flags;
114
115 if (freezing(p)) {
116 pr_debug(" clean up: %s\n", p->comm);
117 clear_freeze_flag(p);
118 spin_lock_irqsave(&p->sighand->siglock, flags);
119 recalc_sigpending_and_wake(p);
120 spin_unlock_irqrestore(&p->sighand->siglock, flags);
121 }
122 }
123
__thaw_process(struct task_struct * p)124 static int __thaw_process(struct task_struct *p)
125 {
126 if (frozen(p)) {
127 p->flags &= ~PF_FROZEN;
128 return 1;
129 }
130 clear_freeze_flag(p);
131 return 0;
132 }
133
134 /*
135 * Wake up a frozen process
136 *
137 * task_lock() is needed to prevent the race with refrigerator() which may
138 * occur if the freezing of tasks fails. Namely, without the lock, if the
139 * freezing of tasks failed, thaw_tasks() might have run before a task in
140 * refrigerator() could call frozen_process(), in which case the task would be
141 * frozen and no one would thaw it.
142 */
thaw_process(struct task_struct * p)143 int thaw_process(struct task_struct *p)
144 {
145 task_lock(p);
146 if (__thaw_process(p) == 1) {
147 task_unlock(p);
148 wake_up_process(p);
149 return 1;
150 }
151 task_unlock(p);
152 return 0;
153 }
154 EXPORT_SYMBOL(thaw_process);
155