freezer: make freezing() test freeze conditions in effect instead of TIF_FREEZE
[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 /* total number of freezing conditions in effect */
15 atomic_t system_freezing_cnt = ATOMIC_INIT(0);
16 EXPORT_SYMBOL(system_freezing_cnt);
17
18 /* indicate whether PM freezing is in effect, protected by pm_mutex */
19 bool pm_freezing;
20 bool pm_nosig_freezing;
21
22 /* protects freezing and frozen transitions */
23 static DEFINE_SPINLOCK(freezer_lock);
24
25 /**
26  * freezing_slow_path - slow path for testing whether a task needs to be frozen
27  * @p: task to be tested
28  *
29  * This function is called by freezing() if system_freezing_cnt isn't zero
30  * and tests whether @p needs to enter and stay in frozen state.  Can be
31  * called under any context.  The freezers are responsible for ensuring the
32  * target tasks see the updated state.
33  */
34 bool freezing_slow_path(struct task_struct *p)
35 {
36         if (p->flags & PF_NOFREEZE)
37                 return false;
38
39         if (pm_nosig_freezing || cgroup_freezing(p))
40                 return true;
41
42         if (pm_freezing && !(p->flags & PF_FREEZER_NOSIG))
43                 return true;
44
45         return false;
46 }
47 EXPORT_SYMBOL(freezing_slow_path);
48
49 /* Refrigerator is place where frozen processes are stored :-). */
50 bool __refrigerator(bool check_kthr_stop)
51 {
52         /* Hmm, should we be allowed to suspend when there are realtime
53            processes around? */
54         bool was_frozen = false;
55         long save;
56
57         /*
58          * No point in checking freezing() again - the caller already did.
59          * Proceed to enter FROZEN.
60          */
61         spin_lock_irq(&freezer_lock);
62 repeat:
63         current->flags |= PF_FROZEN;
64         spin_unlock_irq(&freezer_lock);
65
66         save = current->state;
67         pr_debug("%s entered refrigerator\n", current->comm);
68
69         spin_lock_irq(&current->sighand->siglock);
70         recalc_sigpending(); /* We sent fake signal, clean it up */
71         spin_unlock_irq(&current->sighand->siglock);
72
73         for (;;) {
74                 set_current_state(TASK_UNINTERRUPTIBLE);
75                 if (!freezing(current) ||
76                     (check_kthr_stop && kthread_should_stop()))
77                         break;
78                 was_frozen = true;
79                 schedule();
80         }
81
82         /* leave FROZEN */
83         spin_lock_irq(&freezer_lock);
84         if (freezing(current))
85                 goto repeat;
86         current->flags &= ~PF_FROZEN;
87         spin_unlock_irq(&freezer_lock);
88
89         pr_debug("%s left refrigerator\n", current->comm);
90
91         /*
92          * Restore saved task state before returning.  The mb'd version
93          * needs to be used; otherwise, it might silently break
94          * synchronization which depends on ordered task state change.
95          */
96         set_current_state(save);
97
98         return was_frozen;
99 }
100 EXPORT_SYMBOL(__refrigerator);
101
102 static void fake_signal_wake_up(struct task_struct *p)
103 {
104         unsigned long flags;
105
106         spin_lock_irqsave(&p->sighand->siglock, flags);
107         signal_wake_up(p, 0);
108         spin_unlock_irqrestore(&p->sighand->siglock, flags);
109 }
110
111 /**
112  *      freeze_task - send a freeze request to given task
113  *      @p: task to send the request to
114  *      @sig_only: if set, the request will only be sent if the task has the
115  *              PF_FREEZER_NOSIG flag unset
116  *      Return value: 'false', if @sig_only is set and the task has
117  *              PF_FREEZER_NOSIG set or the task is frozen, 'true', otherwise
118  *
119  *      The freeze request is sent by setting the tasks's TIF_FREEZE flag and
120  *      either sending a fake signal to it or waking it up, depending on whether
121  *      or not it has PF_FREEZER_NOSIG set.  If @sig_only is set and the task
122  *      has PF_FREEZER_NOSIG set (ie. it is a typical kernel thread), its
123  *      TIF_FREEZE flag will not be set.
124  */
125 bool freeze_task(struct task_struct *p, bool sig_only)
126 {
127         unsigned long flags;
128
129         spin_lock_irqsave(&freezer_lock, flags);
130         if (!freezing(p) || frozen(p)) {
131                 spin_unlock_irqrestore(&freezer_lock, flags);
132                 return false;
133         }
134
135         if (should_send_signal(p)) {
136                 fake_signal_wake_up(p);
137                 /*
138                  * fake_signal_wake_up() goes through p's scheduler
139                  * lock and guarantees that TASK_STOPPED/TRACED ->
140                  * TASK_RUNNING transition can't race with task state
141                  * testing in try_to_freeze_tasks().
142                  */
143         } else {
144                 wake_up_state(p, TASK_INTERRUPTIBLE);
145         }
146
147         spin_unlock_irqrestore(&freezer_lock, flags);
148         return true;
149 }
150
151 void __thaw_task(struct task_struct *p)
152 {
153         unsigned long flags;
154
155         /*
156          * Clear freezing and kick @p if FROZEN.  Clearing is guaranteed to
157          * be visible to @p as waking up implies wmb.  Waking up inside
158          * freezer_lock also prevents wakeups from leaking outside
159          * refrigerator.
160          *
161          * If !FROZEN, @p hasn't reached refrigerator, recalc sigpending to
162          * avoid leaving dangling TIF_SIGPENDING behind.
163          */
164         spin_lock_irqsave(&freezer_lock, flags);
165         if (frozen(p)) {
166                 wake_up_process(p);
167         } else {
168                 spin_lock(&p->sighand->siglock);
169                 recalc_sigpending_and_wake(p);
170                 spin_unlock(&p->sighand->siglock);
171         }
172         spin_unlock_irqrestore(&freezer_lock, flags);
173 }