cgroup: Add generic cgroup subsystem permission checks.
[linux-2.6.git] / kernel / irq_work.c
1 /*
2  * Copyright (C) 2010 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
3  *
4  * Provides a framework for enqueueing and running callbacks from hardirq
5  * context. The enqueueing is NMI-safe.
6  */
7
8 #include <linux/kernel.h>
9 #include <linux/module.h>
10 #include <linux/irq_work.h>
11 #include <linux/hardirq.h>
12
13 /*
14  * An entry can be in one of four states:
15  *
16  * free      NULL, 0 -> {claimed}       : free to be used
17  * claimed   NULL, 3 -> {pending}       : claimed to be enqueued
18  * pending   next, 3 -> {busy}          : queued, pending callback
19  * busy      NULL, 2 -> {free, claimed} : callback in progress, can be claimed
20  *
21  * We use the lower two bits of the next pointer to keep PENDING and BUSY
22  * flags.
23  */
24
25 #define IRQ_WORK_PENDING        1UL
26 #define IRQ_WORK_BUSY           2UL
27 #define IRQ_WORK_FLAGS          3UL
28
29 static inline bool irq_work_is_set(struct irq_work *entry, int flags)
30 {
31         return (unsigned long)entry->next & flags;
32 }
33
34 static inline struct irq_work *irq_work_next(struct irq_work *entry)
35 {
36         unsigned long next = (unsigned long)entry->next;
37         next &= ~IRQ_WORK_FLAGS;
38         return (struct irq_work *)next;
39 }
40
41 static inline struct irq_work *next_flags(struct irq_work *entry, int flags)
42 {
43         unsigned long next = (unsigned long)entry;
44         next |= flags;
45         return (struct irq_work *)next;
46 }
47
48 static DEFINE_PER_CPU(struct irq_work *, irq_work_list);
49
50 /*
51  * Claim the entry so that no one else will poke at it.
52  */
53 static bool irq_work_claim(struct irq_work *entry)
54 {
55         struct irq_work *next, *nflags;
56
57         do {
58                 next = entry->next;
59                 if ((unsigned long)next & IRQ_WORK_PENDING)
60                         return false;
61                 nflags = next_flags(next, IRQ_WORK_FLAGS);
62         } while (cmpxchg(&entry->next, next, nflags) != next);
63
64         return true;
65 }
66
67
68 void __weak arch_irq_work_raise(void)
69 {
70         /*
71          * Lame architectures will get the timer tick callback
72          */
73 }
74
75 /*
76  * Queue the entry and raise the IPI if needed.
77  */
78 static void __irq_work_queue(struct irq_work *entry)
79 {
80         struct irq_work *next;
81
82         preempt_disable();
83
84         do {
85                 next = __this_cpu_read(irq_work_list);
86                 /* Can assign non-atomic because we keep the flags set. */
87                 entry->next = next_flags(next, IRQ_WORK_FLAGS);
88         } while (this_cpu_cmpxchg(irq_work_list, next, entry) != next);
89
90         /* The list was empty, raise self-interrupt to start processing. */
91         if (!irq_work_next(entry))
92                 arch_irq_work_raise();
93
94         preempt_enable();
95 }
96
97 /*
98  * Enqueue the irq_work @entry, returns true on success, failure when the
99  * @entry was already enqueued by someone else.
100  *
101  * Can be re-enqueued while the callback is still in progress.
102  */
103 bool irq_work_queue(struct irq_work *entry)
104 {
105         if (!irq_work_claim(entry)) {
106                 /*
107                  * Already enqueued, can't do!
108                  */
109                 return false;
110         }
111
112         __irq_work_queue(entry);
113         return true;
114 }
115 EXPORT_SYMBOL_GPL(irq_work_queue);
116
117 /*
118  * Run the irq_work entries on this cpu. Requires to be ran from hardirq
119  * context with local IRQs disabled.
120  */
121 void irq_work_run(void)
122 {
123         struct irq_work *list;
124
125         if (this_cpu_read(irq_work_list) == NULL)
126                 return;
127
128         BUG_ON(!in_irq());
129         BUG_ON(!irqs_disabled());
130
131         list = this_cpu_xchg(irq_work_list, NULL);
132
133         while (list != NULL) {
134                 struct irq_work *entry = list;
135
136                 list = irq_work_next(list);
137
138                 /*
139                  * Clear the PENDING bit, after this point the @entry
140                  * can be re-used.
141                  */
142                 entry->next = next_flags(NULL, IRQ_WORK_BUSY);
143                 entry->func(entry);
144                 /*
145                  * Clear the BUSY bit and return to the free state if
146                  * no-one else claimed it meanwhile.
147                  */
148                 (void)cmpxchg(&entry->next,
149                               next_flags(NULL, IRQ_WORK_BUSY),
150                               NULL);
151         }
152 }
153 EXPORT_SYMBOL_GPL(irq_work_run);
154
155 /*
156  * Synchronize against the irq_work @entry, ensures the entry is not
157  * currently in use.
158  */
159 void irq_work_sync(struct irq_work *entry)
160 {
161         WARN_ON_ONCE(irqs_disabled());
162
163         while (irq_work_is_set(entry, IRQ_WORK_BUSY))
164                 cpu_relax();
165 }
166 EXPORT_SYMBOL_GPL(irq_work_sync);