Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...
[linux-2.6.git] / kernel / freezer.c
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                 smp_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(&current->sighand->siglock);
44         recalc_sigpending(); /* We sent fake signal, clean it up */
45         spin_unlock_irq(&current->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                 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
123 void 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
136 static 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  */
155 int 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 }
166 EXPORT_SYMBOL(thaw_process);