Merge git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb-2.6
[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                 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                 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);