ia64/linux-2.6.18-xen.hg

view arch/xtensa/kernel/semaphore.c @ 647:a5bb490065f6

Fix the build after public header sync.
Signed-off-by: Keir Fraser <keir.fraser@citrix.com>
author Keir Fraser <keir.fraser@citrix.com>
date Wed Aug 13 14:01:49 2008 +0100 (2008-08-13)
parents 831230e53067
children
line source
1 /*
2 * arch/xtensa/kernel/semaphore.c
3 *
4 * Generic semaphore code. Buyer beware. Do your own specific changes
5 * in <asm/semaphore-helper.h>
6 *
7 * This file is subject to the terms and conditions of the GNU General Public
8 * License. See the file "COPYING" in the main directory of this archive
9 * for more details.
10 *
11 * Copyright (C) 2001 - 2005 Tensilica Inc.
12 *
13 * Joe Taylor <joe@tensilica.com, joetylr@yahoo.com>
14 * Chris Zankel <chris@zankel.net>
15 * Marc Gauthier<marc@tensilica.com, marc@alumni.uwaterloo.ca>
16 * Kevin Chea
17 */
19 #include <linux/sched.h>
20 #include <linux/wait.h>
21 #include <linux/init.h>
22 #include <asm/semaphore.h>
23 #include <asm/errno.h>
25 /*
26 * These two _must_ execute atomically wrt each other.
27 */
29 static __inline__ void wake_one_more(struct semaphore * sem)
30 {
31 atomic_inc((atomic_t *)&sem->sleepers);
32 }
34 static __inline__ int waking_non_zero(struct semaphore *sem)
35 {
36 unsigned long flags;
37 int ret = 0;
39 spin_lock_irqsave(&semaphore_wake_lock, flags);
40 if (sem->sleepers > 0) {
41 sem->sleepers--;
42 ret = 1;
43 }
44 spin_unlock_irqrestore(&semaphore_wake_lock, flags);
45 return ret;
46 }
48 /*
49 * waking_non_zero_interruptible:
50 * 1 got the lock
51 * 0 go to sleep
52 * -EINTR interrupted
53 *
54 * We must undo the sem->count down_interruptible() increment while we are
55 * protected by the spinlock in order to make atomic this atomic_inc() with the
56 * atomic_read() in wake_one_more(), otherwise we can race. -arca
57 */
59 static __inline__ int waking_non_zero_interruptible(struct semaphore *sem,
60 struct task_struct *tsk)
61 {
62 unsigned long flags;
63 int ret = 0;
65 spin_lock_irqsave(&semaphore_wake_lock, flags);
66 if (sem->sleepers > 0) {
67 sem->sleepers--;
68 ret = 1;
69 } else if (signal_pending(tsk)) {
70 atomic_inc(&sem->count);
71 ret = -EINTR;
72 }
73 spin_unlock_irqrestore(&semaphore_wake_lock, flags);
74 return ret;
75 }
77 /*
78 * waking_non_zero_trylock:
79 * 1 failed to lock
80 * 0 got the lock
81 *
82 * We must undo the sem->count down_trylock() increment while we are
83 * protected by the spinlock in order to make atomic this atomic_inc() with the
84 * atomic_read() in wake_one_more(), otherwise we can race. -arca
85 */
87 static __inline__ int waking_non_zero_trylock(struct semaphore *sem)
88 {
89 unsigned long flags;
90 int ret = 1;
92 spin_lock_irqsave(&semaphore_wake_lock, flags);
93 if (sem->sleepers <= 0)
94 atomic_inc(&sem->count);
95 else {
96 sem->sleepers--;
97 ret = 0;
98 }
99 spin_unlock_irqrestore(&semaphore_wake_lock, flags);
100 return ret;
101 }
103 spinlock_t semaphore_wake_lock;
105 /*
106 * Semaphores are implemented using a two-way counter:
107 * The "count" variable is decremented for each process
108 * that tries to sleep, while the "waking" variable is
109 * incremented when the "up()" code goes to wake up waiting
110 * processes.
111 *
112 * Notably, the inline "up()" and "down()" functions can
113 * efficiently test if they need to do any extra work (up
114 * needs to do something only if count was negative before
115 * the increment operation.
116 *
117 * waking_non_zero() (from asm/semaphore.h) must execute
118 * atomically.
119 *
120 * When __up() is called, the count was negative before
121 * incrementing it, and we need to wake up somebody.
122 *
123 * This routine adds one to the count of processes that need to
124 * wake up and exit. ALL waiting processes actually wake up but
125 * only the one that gets to the "waking" field first will gate
126 * through and acquire the semaphore. The others will go back
127 * to sleep.
128 *
129 * Note that these functions are only called when there is
130 * contention on the lock, and as such all this is the
131 * "non-critical" part of the whole semaphore business. The
132 * critical part is the inline stuff in <asm/semaphore.h>
133 * where we want to avoid any extra jumps and calls.
134 */
136 void __up(struct semaphore *sem)
137 {
138 wake_one_more(sem);
139 wake_up(&sem->wait);
140 }
142 /*
143 * Perform the "down" function. Return zero for semaphore acquired,
144 * return negative for signalled out of the function.
145 *
146 * If called from __down, the return is ignored and the wait loop is
147 * not interruptible. This means that a task waiting on a semaphore
148 * using "down()" cannot be killed until someone does an "up()" on
149 * the semaphore.
150 *
151 * If called from __down_interruptible, the return value gets checked
152 * upon return. If the return value is negative then the task continues
153 * with the negative value in the return register (it can be tested by
154 * the caller).
155 *
156 * Either form may be used in conjunction with "up()".
157 *
158 */
160 #define DOWN_VAR \
161 struct task_struct *tsk = current; \
162 wait_queue_t wait; \
163 init_waitqueue_entry(&wait, tsk);
165 #define DOWN_HEAD(task_state) \
166 \
167 \
168 tsk->state = (task_state); \
169 add_wait_queue(&sem->wait, &wait); \
170 \
171 /* \
172 * Ok, we're set up. sem->count is known to be less than zero \
173 * so we must wait. \
174 * \
175 * We can let go the lock for purposes of waiting. \
176 * We re-acquire it after awaking so as to protect \
177 * all semaphore operations. \
178 * \
179 * If "up()" is called before we call waking_non_zero() then \
180 * we will catch it right away. If it is called later then \
181 * we will have to go through a wakeup cycle to catch it. \
182 * \
183 * Multiple waiters contend for the semaphore lock to see \
184 * who gets to gate through and who has to wait some more. \
185 */ \
186 for (;;) {
188 #define DOWN_TAIL(task_state) \
189 tsk->state = (task_state); \
190 } \
191 tsk->state = TASK_RUNNING; \
192 remove_wait_queue(&sem->wait, &wait);
194 void __sched __down(struct semaphore * sem)
195 {
196 DOWN_VAR
197 DOWN_HEAD(TASK_UNINTERRUPTIBLE)
198 if (waking_non_zero(sem))
199 break;
200 schedule();
201 DOWN_TAIL(TASK_UNINTERRUPTIBLE)
202 }
204 int __sched __down_interruptible(struct semaphore * sem)
205 {
206 int ret = 0;
207 DOWN_VAR
208 DOWN_HEAD(TASK_INTERRUPTIBLE)
210 ret = waking_non_zero_interruptible(sem, tsk);
211 if (ret)
212 {
213 if (ret == 1)
214 /* ret != 0 only if we get interrupted -arca */
215 ret = 0;
216 break;
217 }
218 schedule();
219 DOWN_TAIL(TASK_INTERRUPTIBLE)
220 return ret;
221 }
223 int __down_trylock(struct semaphore * sem)
224 {
225 return waking_non_zero_trylock(sem);
226 }