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authorMatthew Wilcox <matthew@wil.cx>2008-03-07 21:55:58 -0500
committerMatthew Wilcox <willy@linux.intel.com>2008-04-17 10:42:34 -0400
commit64ac24e738823161693bf791f87adc802cf529ff (patch)
tree19c0b0cf314d4394ca580c05b86cdf874ce0a167 /include/asm-alpha
parente48b3deee475134585eed03e7afebe4bf9e0dba9 (diff)
Generic semaphore implementation
Semaphores are no longer performance-critical, so a generic C implementation is better for maintainability, debuggability and extensibility. Thanks to Peter Zijlstra for fixing the lockdep warning. Thanks to Harvey Harrison for pointing out that the unlikely() was unnecessary. Signed-off-by: Matthew Wilcox <willy@linux.intel.com> Acked-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'include/asm-alpha')
-rw-r--r--include/asm-alpha/semaphore.h150
1 files changed, 1 insertions, 149 deletions
diff --git a/include/asm-alpha/semaphore.h b/include/asm-alpha/semaphore.h
index f1e9278a9fe..d9b2034ed1d 100644
--- a/include/asm-alpha/semaphore.h
+++ b/include/asm-alpha/semaphore.h
@@ -1,149 +1 @@
1#ifndef _ALPHA_SEMAPHORE_H #include <linux/semaphore.h>
2#define _ALPHA_SEMAPHORE_H
3
4/*
5 * SMP- and interrupt-safe semaphores..
6 *
7 * (C) Copyright 1996 Linus Torvalds
8 * (C) Copyright 1996, 2000 Richard Henderson
9 */
10
11#include <asm/current.h>
12#include <asm/system.h>
13#include <asm/atomic.h>
14#include <linux/compiler.h>
15#include <linux/wait.h>
16#include <linux/rwsem.h>
17
18struct semaphore {
19 atomic_t count;
20 wait_queue_head_t wait;
21};
22
23#define __SEMAPHORE_INITIALIZER(name, n) \
24{ \
25 .count = ATOMIC_INIT(n), \
26 .wait = __WAIT_QUEUE_HEAD_INITIALIZER((name).wait), \
27}
28
29#define __DECLARE_SEMAPHORE_GENERIC(name,count) \
30 struct semaphore name = __SEMAPHORE_INITIALIZER(name,count)
31
32#define DECLARE_MUTEX(name) __DECLARE_SEMAPHORE_GENERIC(name,1)
33
34static inline void sema_init(struct semaphore *sem, int val)
35{
36 /*
37 * Logically,
38 * *sem = (struct semaphore)__SEMAPHORE_INITIALIZER((*sem),val);
39 * except that gcc produces better initializing by parts yet.
40 */
41
42 atomic_set(&sem->count, val);
43 init_waitqueue_head(&sem->wait);
44}
45
46static inline void init_MUTEX (struct semaphore *sem)
47{
48 sema_init(sem, 1);
49}
50
51static inline void init_MUTEX_LOCKED (struct semaphore *sem)
52{
53 sema_init(sem, 0);
54}
55
56extern void down(struct semaphore *);
57extern void __down_failed(struct semaphore *);
58extern int down_interruptible(struct semaphore *);
59extern int __down_failed_interruptible(struct semaphore *);
60extern int down_trylock(struct semaphore *);
61extern void up(struct semaphore *);
62extern void __up_wakeup(struct semaphore *);
63
64/*
65 * Hidden out of line code is fun, but extremely messy. Rely on newer
66 * compilers to do a respectable job with this. The contention cases
67 * are handled out of line in arch/alpha/kernel/semaphore.c.
68 */
69
70static inline void __down(struct semaphore *sem)
71{
72 long count;
73 might_sleep();
74 count = atomic_dec_return(&sem->count);
75 if (unlikely(count < 0))
76 __down_failed(sem);
77}
78
79static inline int __down_interruptible(struct semaphore *sem)
80{
81 long count;
82 might_sleep();
83 count = atomic_dec_return(&sem->count);
84 if (unlikely(count < 0))
85 return __down_failed_interruptible(sem);
86 return 0;
87}
88
89/*
90 * down_trylock returns 0 on success, 1 if we failed to get the lock.
91 */
92
93static inline int __down_trylock(struct semaphore *sem)
94{
95 long ret;
96
97 /* "Equivalent" C:
98
99 do {
100 ret = ldl_l;
101 --ret;
102 if (ret < 0)
103 break;
104 ret = stl_c = ret;
105 } while (ret == 0);
106 */
107 __asm__ __volatile__(
108 "1: ldl_l %0,%1\n"
109 " subl %0,1,%0\n"
110 " blt %0,2f\n"
111 " stl_c %0,%1\n"
112 " beq %0,3f\n"
113 " mb\n"
114 "2:\n"
115 ".subsection 2\n"
116 "3: br 1b\n"
117 ".previous"
118 : "=&r" (ret), "=m" (sem->count)
119 : "m" (sem->count));
120
121 return ret < 0;
122}
123
124static inline void __up(struct semaphore *sem)
125{
126 if (unlikely(atomic_inc_return(&sem->count) <= 0))
127 __up_wakeup(sem);
128}
129
130#if !defined(CONFIG_DEBUG_SEMAPHORE)
131extern inline void down(struct semaphore *sem)
132{
133 __down(sem);
134}
135extern inline int down_interruptible(struct semaphore *sem)
136{
137 return __down_interruptible(sem);
138}
139extern inline int down_trylock(struct semaphore *sem)
140{
141 return __down_trylock(sem);
142}
143extern inline void up(struct semaphore *sem)
144{
145 __up(sem);
146}
147#endif
148
149#endif
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