freezer: use dedicated lock instead of task_lock() + memory barrier
[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/export.h>
10 #include <linux/syscalls.h>
11 #include <linux/freezer.h>
12 #include <linux/kthread.h>
13
14 /* protects freezing and frozen transitions */
15 static DEFINE_SPINLOCK(freezer_lock);
16
17 /* Refrigerator is place where frozen processes are stored :-). */
18 bool __refrigerator(bool check_kthr_stop)
19 {
20         /* Hmm, should we be allowed to suspend when there are realtime
21            processes around? */
22         bool was_frozen = false;
23         long save;
24
25         spin_lock_irq(&freezer_lock);
26         if (!freezing(current)) {
27                 spin_unlock_irq(&freezer_lock);
28                 return was_frozen;
29         }
30         if (!(current->flags & PF_NOFREEZE))
31                 current->flags |= PF_FROZEN;
32         clear_freeze_flag(current);
33         spin_unlock_irq(&freezer_lock);
34
35         save = current->state;
36         pr_debug("%s entered refrigerator\n", current->comm);
37
38         spin_lock_irq(&current->sighand->siglock);
39         recalc_sigpending(); /* We sent fake signal, clean it up */
40         spin_unlock_irq(&current->sighand->siglock);
41
42         /* prevent accounting of that task to load */
43         current->flags |= PF_FREEZING;
44
45         for (;;) {
46                 set_current_state(TASK_UNINTERRUPTIBLE);
47                 if (!frozen(current) ||
48                     (check_kthr_stop && kthread_should_stop()))
49                         break;
50                 was_frozen = true;
51                 schedule();
52         }
53
54         /* Remove the accounting blocker */
55         current->flags &= ~PF_FREEZING;
56
57         pr_debug("%s left refrigerator\n", current->comm);
58
59         /*
60          * Restore saved task state before returning.  The mb'd version
61          * needs to be used; otherwise, it might silently break
62          * synchronization which depends on ordered task state change.
63          */
64         set_current_state(save);
65
66         return was_frozen;
67 }
68 EXPORT_SYMBOL(__refrigerator);
69
70 static void fake_signal_wake_up(struct task_struct *p)
71 {
72         unsigned long flags;
73
74         spin_lock_irqsave(&p->sighand->siglock, flags);
75         signal_wake_up(p, 0);
76         spin_unlock_irqrestore(&p->sighand->siglock, flags);
77 }
78
79 /**
80  *      freeze_task - send a freeze request to given task
81  *      @p: task to send the request to
82  *      @sig_only: if set, the request will only be sent if the task has the
83  *              PF_FREEZER_NOSIG flag unset
84  *      Return value: 'false', if @sig_only is set and the task has
85  *              PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
86  *
87  *      The freeze request is sent by setting the tasks's TIF_FREEZE flag and
88  *      either sending a fake signal to it or waking it up, depending on whether
89  *      or not it has PF_FREEZER_NOSIG set.  If @sig_only is set and the task
90  *      has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
91  *      TIF_FREEZE flag will not be set.
92  */
93 bool freeze_task(struct task_struct *p, bool sig_only)
94 {
95         unsigned long flags;
96         bool ret = false;
97
98         spin_lock_irqsave(&freezer_lock, flags);
99
100         if (sig_only && !should_send_signal(p))
101                 goto out_unlock;
102
103         if (frozen(p))
104                 goto out_unlock;
105
106         set_freeze_flag(p);
107
108         if (should_send_signal(p)) {
109                 fake_signal_wake_up(p);
110                 /*
111                  * fake_signal_wake_up() goes through p's scheduler
112                  * lock and guarantees that TASK_STOPPED/TRACED ->
113                  * TASK_RUNNING transition can't race with task state
114                  * testing in try_to_freeze_tasks().
115                  */
116         } else {
117                 wake_up_state(p, TASK_INTERRUPTIBLE);
118         }
119         ret = true;
120 out_unlock:
121         spin_unlock_irqrestore(&freezer_lock, flags);
122         return ret;
123 }
124
125 void cancel_freezing(struct task_struct *p)
126 {
127         unsigned long flags;
128
129         spin_lock_irqsave(&freezer_lock, flags);
130         if (freezing(p)) {
131                 pr_debug("  clean up: %s\n", p->comm);
132                 clear_freeze_flag(p);
133                 spin_lock(&p->sighand->siglock);
134                 recalc_sigpending_and_wake(p);
135                 spin_unlock(&p->sighand->siglock);
136         }
137         spin_unlock_irqrestore(&freezer_lock, flags);
138 }
139
140 /*
141  * Wake up a frozen task
142  *
143  * task_lock() is needed to prevent the race with refrigerator() which may
144  * occur if the freezing of tasks fails.  Namely, without the lock, if the
145  * freezing of tasks failed, thaw_tasks() might have run before a task in
146  * refrigerator() could call frozen_process(), in which case the task would be
147  * frozen and no one would thaw it.
148  */
149 void __thaw_task(struct task_struct *p)
150 {
151         unsigned long flags;
152
153         spin_lock_irqsave(&freezer_lock, flags);
154         if (frozen(p)) {
155                 p->flags &= ~PF_FROZEN;
156                 wake_up_process(p);
157         } else {
158                 clear_freeze_flag(p);
159         }
160         spin_unlock_irqrestore(&freezer_lock, flags);
161 }