]>
Commit | Line | Data |
---|---|---|
1da177e4 LT |
1 | /* |
2 | * linux/arch/m32r/semaphore.c | |
3 | * orig : i386 2.6.4 | |
4 | * | |
5 | * M32R semaphore implementation. | |
6 | * | |
7 | * Copyright (c) 2002 - 2004 Hitoshi Yamamoto | |
8 | */ | |
9 | ||
10 | /* | |
11 | * i386 semaphore implementation. | |
12 | * | |
13 | * (C) Copyright 1999 Linus Torvalds | |
14 | * | |
15 | * Portions Copyright 1999 Red Hat, Inc. | |
16 | * | |
17 | * This program is free software; you can redistribute it and/or | |
18 | * modify it under the terms of the GNU General Public License | |
19 | * as published by the Free Software Foundation; either version | |
20 | * 2 of the License, or (at your option) any later version. | |
21 | * | |
22 | * rw semaphores implemented November 1999 by Benjamin LaHaise <bcrl@kvack.org> | |
23 | */ | |
24 | #include <linux/config.h> | |
25 | #include <linux/sched.h> | |
26 | #include <linux/err.h> | |
27 | #include <linux/init.h> | |
28 | #include <asm/semaphore.h> | |
29 | ||
30 | /* | |
31 | * Semaphores are implemented using a two-way counter: | |
32 | * The "count" variable is decremented for each process | |
33 | * that tries to acquire the semaphore, while the "sleeping" | |
34 | * variable is a count of such acquires. | |
35 | * | |
36 | * Notably, the inline "up()" and "down()" functions can | |
37 | * efficiently test if they need to do any extra work (up | |
38 | * needs to do something only if count was negative before | |
39 | * the increment operation. | |
40 | * | |
41 | * "sleeping" and the contention routine ordering is protected | |
42 | * by the spinlock in the semaphore's waitqueue head. | |
43 | * | |
44 | * Note that these functions are only called when there is | |
45 | * contention on the lock, and as such all this is the | |
46 | * "non-critical" part of the whole semaphore business. The | |
47 | * critical part is the inline stuff in <asm/semaphore.h> | |
48 | * where we want to avoid any extra jumps and calls. | |
49 | */ | |
50 | ||
51 | /* | |
52 | * Logic: | |
53 | * - only on a boundary condition do we need to care. When we go | |
54 | * from a negative count to a non-negative, we wake people up. | |
55 | * - when we go from a non-negative count to a negative do we | |
56 | * (a) synchronize with the "sleeper" count and (b) make sure | |
57 | * that we're on the wakeup list before we synchronize so that | |
58 | * we cannot lose wakeup events. | |
59 | */ | |
60 | ||
61 | asmlinkage void __up(struct semaphore *sem) | |
62 | { | |
63 | wake_up(&sem->wait); | |
64 | } | |
65 | ||
66 | asmlinkage void __sched __down(struct semaphore * sem) | |
67 | { | |
68 | struct task_struct *tsk = current; | |
69 | DECLARE_WAITQUEUE(wait, tsk); | |
70 | unsigned long flags; | |
71 | ||
72 | tsk->state = TASK_UNINTERRUPTIBLE; | |
73 | spin_lock_irqsave(&sem->wait.lock, flags); | |
74 | add_wait_queue_exclusive_locked(&sem->wait, &wait); | |
75 | ||
76 | sem->sleepers++; | |
77 | for (;;) { | |
78 | int sleepers = sem->sleepers; | |
79 | ||
80 | /* | |
81 | * Add "everybody else" into it. They aren't | |
82 | * playing, because we own the spinlock in | |
83 | * the wait_queue_head. | |
84 | */ | |
85 | if (!atomic_add_negative(sleepers - 1, &sem->count)) { | |
86 | sem->sleepers = 0; | |
87 | break; | |
88 | } | |
89 | sem->sleepers = 1; /* us - see -1 above */ | |
90 | spin_unlock_irqrestore(&sem->wait.lock, flags); | |
91 | ||
92 | schedule(); | |
93 | ||
94 | spin_lock_irqsave(&sem->wait.lock, flags); | |
95 | tsk->state = TASK_UNINTERRUPTIBLE; | |
96 | } | |
97 | remove_wait_queue_locked(&sem->wait, &wait); | |
98 | wake_up_locked(&sem->wait); | |
99 | spin_unlock_irqrestore(&sem->wait.lock, flags); | |
100 | tsk->state = TASK_RUNNING; | |
101 | } | |
102 | ||
103 | asmlinkage int __sched __down_interruptible(struct semaphore * sem) | |
104 | { | |
105 | int retval = 0; | |
106 | struct task_struct *tsk = current; | |
107 | DECLARE_WAITQUEUE(wait, tsk); | |
108 | unsigned long flags; | |
109 | ||
110 | tsk->state = TASK_INTERRUPTIBLE; | |
111 | spin_lock_irqsave(&sem->wait.lock, flags); | |
112 | add_wait_queue_exclusive_locked(&sem->wait, &wait); | |
113 | ||
114 | sem->sleepers++; | |
115 | for (;;) { | |
116 | int sleepers = sem->sleepers; | |
117 | ||
118 | /* | |
119 | * With signals pending, this turns into | |
120 | * the trylock failure case - we won't be | |
121 | * sleeping, and we* can't get the lock as | |
122 | * it has contention. Just correct the count | |
123 | * and exit. | |
124 | */ | |
125 | if (signal_pending(current)) { | |
126 | retval = -EINTR; | |
127 | sem->sleepers = 0; | |
128 | atomic_add(sleepers, &sem->count); | |
129 | break; | |
130 | } | |
131 | ||
132 | /* | |
133 | * Add "everybody else" into it. They aren't | |
134 | * playing, because we own the spinlock in | |
135 | * wait_queue_head. The "-1" is because we're | |
136 | * still hoping to get the semaphore. | |
137 | */ | |
138 | if (!atomic_add_negative(sleepers - 1, &sem->count)) { | |
139 | sem->sleepers = 0; | |
140 | break; | |
141 | } | |
142 | sem->sleepers = 1; /* us - see -1 above */ | |
143 | spin_unlock_irqrestore(&sem->wait.lock, flags); | |
144 | ||
145 | schedule(); | |
146 | ||
147 | spin_lock_irqsave(&sem->wait.lock, flags); | |
148 | tsk->state = TASK_INTERRUPTIBLE; | |
149 | } | |
150 | remove_wait_queue_locked(&sem->wait, &wait); | |
151 | wake_up_locked(&sem->wait); | |
152 | spin_unlock_irqrestore(&sem->wait.lock, flags); | |
153 | ||
154 | tsk->state = TASK_RUNNING; | |
155 | return retval; | |
156 | } | |
157 | ||
158 | /* | |
159 | * Trylock failed - make sure we correct for | |
160 | * having decremented the count. | |
161 | * | |
162 | * We could have done the trylock with a | |
163 | * single "cmpxchg" without failure cases, | |
164 | * but then it wouldn't work on a 386. | |
165 | */ | |
166 | asmlinkage int __down_trylock(struct semaphore * sem) | |
167 | { | |
168 | int sleepers; | |
169 | unsigned long flags; | |
170 | ||
171 | spin_lock_irqsave(&sem->wait.lock, flags); | |
172 | sleepers = sem->sleepers + 1; | |
173 | sem->sleepers = 0; | |
174 | ||
175 | /* | |
176 | * Add "everybody else" and us into it. They aren't | |
177 | * playing, because we own the spinlock in the | |
178 | * wait_queue_head. | |
179 | */ | |
180 | if (!atomic_add_negative(sleepers, &sem->count)) { | |
181 | wake_up_locked(&sem->wait); | |
182 | } | |
183 | ||
184 | spin_unlock_irqrestore(&sem->wait.lock, flags); | |
185 | return 1; | |
186 | } |