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 */
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 :-). */
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 /* 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 }
63 EXPORT_SYMBOL(refrigerator);
64
65 static 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 */
88 bool 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 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 if (!signal_pending(p))
108 fake_signal_wake_up(p);
109 } else if (sig_only) {
110 return false;
111 } else {
112 wake_up_state(p, TASK_INTERRUPTIBLE);
113 }
114
115 return true;
116 }
117
118 void cancel_freezing(struct task_struct *p)
119 {
120 unsigned long flags;
121
122 if (freezing(p)) {
123 pr_debug(" clean up: %s\n", p->comm);
124 clear_freeze_flag(p);
125 spin_lock_irqsave(&p->sighand->siglock, flags);
126 recalc_sigpending_and_wake(p);
127 spin_unlock_irqrestore(&p->sighand->siglock, flags);
128 }
129 }
130
131 static int __thaw_process(struct task_struct *p)
132 {
133 if (frozen(p)) {
134 p->flags &= ~PF_FROZEN;
135 return 1;
136 }
137 clear_freeze_flag(p);
138 return 0;
139 }
140
141 /*
142 * Wake up a frozen process
143 *
144 * task_lock() is needed to prevent the race with refrigerator() which may
145 * occur if the freezing of tasks fails. Namely, without the lock, if the
146 * freezing of tasks failed, thaw_tasks() might have run before a task in
147 * refrigerator() could call frozen_process(), in which case the task would be
148 * frozen and no one would thaw it.
149 */
150 int thaw_process(struct task_struct *p)
151 {
152 task_lock(p);
153 if (__thaw_process(p) == 1) {
154 task_unlock(p);
155 wake_up_process(p);
156 return 1;
157 }
158 task_unlock(p);
159 return 0;
160 }
161 EXPORT_SYMBOL(thaw_process);
162
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