ia64/linux-2.6.18-xen.hg

view arch/v850/kernel/semaphore.c @ 0:831230e53067

Import 2.6.18 from kernel.org tarball.
author Ian Campbell <ian.campbell@xensource.com>
date Wed Apr 11 14:15:44 2007 +0100 (2007-04-11)
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1 /*
2 * arch/v850/kernel/semaphore.c -- Semaphore support
3 *
4 * Copyright (C) 1998-2000 IBM Corporation
5 * Copyright (C) 1999 Linus Torvalds
6 *
7 * This file is subject to the terms and conditions of the GNU General
8 * Public License. See the file COPYING in the main directory of this
9 * archive for more details.
10 *
11 * This file is a copy of the s390 version, arch/s390/kernel/semaphore.c
12 * Author(s): Martin Schwidefsky
13 * which was derived from the i386 version, linux/arch/i386/kernel/semaphore.c
14 */
16 #include <linux/errno.h>
17 #include <linux/sched.h>
18 #include <linux/init.h>
20 #include <asm/semaphore.h>
22 /*
23 * Semaphores are implemented using a two-way counter:
24 * The "count" variable is decremented for each process
25 * that tries to acquire the semaphore, while the "sleeping"
26 * variable is a count of such acquires.
27 *
28 * Notably, the inline "up()" and "down()" functions can
29 * efficiently test if they need to do any extra work (up
30 * needs to do something only if count was negative before
31 * the increment operation.
32 *
33 * "sleeping" and the contention routine ordering is
34 * protected by the semaphore spinlock.
35 *
36 * Note that these functions are only called when there is
37 * contention on the lock, and as such all this is the
38 * "non-critical" part of the whole semaphore business. The
39 * critical part is the inline stuff in <asm/semaphore.h>
40 * where we want to avoid any extra jumps and calls.
41 */
43 /*
44 * Logic:
45 * - only on a boundary condition do we need to care. When we go
46 * from a negative count to a non-negative, we wake people up.
47 * - when we go from a non-negative count to a negative do we
48 * (a) synchronize with the "sleeper" count and (b) make sure
49 * that we're on the wakeup list before we synchronize so that
50 * we cannot lose wakeup events.
51 */
53 void __up(struct semaphore *sem)
54 {
55 wake_up(&sem->wait);
56 }
58 static DEFINE_SPINLOCK(semaphore_lock);
60 void __sched __down(struct semaphore * sem)
61 {
62 struct task_struct *tsk = current;
63 DECLARE_WAITQUEUE(wait, tsk);
64 tsk->state = TASK_UNINTERRUPTIBLE;
65 add_wait_queue_exclusive(&sem->wait, &wait);
67 spin_lock_irq(&semaphore_lock);
68 sem->sleepers++;
69 for (;;) {
70 int sleepers = sem->sleepers;
72 /*
73 * Add "everybody else" into it. They aren't
74 * playing, because we own the spinlock.
75 */
76 if (!atomic_add_negative(sleepers - 1, &sem->count)) {
77 sem->sleepers = 0;
78 break;
79 }
80 sem->sleepers = 1; /* us - see -1 above */
81 spin_unlock_irq(&semaphore_lock);
83 schedule();
84 tsk->state = TASK_UNINTERRUPTIBLE;
85 spin_lock_irq(&semaphore_lock);
86 }
87 spin_unlock_irq(&semaphore_lock);
88 remove_wait_queue(&sem->wait, &wait);
89 tsk->state = TASK_RUNNING;
90 wake_up(&sem->wait);
91 }
93 int __sched __down_interruptible(struct semaphore * sem)
94 {
95 int retval = 0;
96 struct task_struct *tsk = current;
97 DECLARE_WAITQUEUE(wait, tsk);
98 tsk->state = TASK_INTERRUPTIBLE;
99 add_wait_queue_exclusive(&sem->wait, &wait);
101 spin_lock_irq(&semaphore_lock);
102 sem->sleepers ++;
103 for (;;) {
104 int sleepers = sem->sleepers;
106 /*
107 * With signals pending, this turns into
108 * the trylock failure case - we won't be
109 * sleeping, and we* can't get the lock as
110 * it has contention. Just correct the count
111 * and exit.
112 */
113 if (signal_pending(current)) {
114 retval = -EINTR;
115 sem->sleepers = 0;
116 atomic_add(sleepers, &sem->count);
117 break;
118 }
120 /*
121 * Add "everybody else" into it. They aren't
122 * playing, because we own the spinlock. The
123 * "-1" is because we're still hoping to get
124 * the lock.
125 */
126 if (!atomic_add_negative(sleepers - 1, &sem->count)) {
127 sem->sleepers = 0;
128 break;
129 }
130 sem->sleepers = 1; /* us - see -1 above */
131 spin_unlock_irq(&semaphore_lock);
133 schedule();
134 tsk->state = TASK_INTERRUPTIBLE;
135 spin_lock_irq(&semaphore_lock);
136 }
137 spin_unlock_irq(&semaphore_lock);
138 tsk->state = TASK_RUNNING;
139 remove_wait_queue(&sem->wait, &wait);
140 wake_up(&sem->wait);
141 return retval;
142 }
144 /*
145 * Trylock failed - make sure we correct for
146 * having decremented the count.
147 */
148 int __down_trylock(struct semaphore * sem)
149 {
150 unsigned long flags;
151 int sleepers;
153 spin_lock_irqsave(&semaphore_lock, flags);
154 sleepers = sem->sleepers + 1;
155 sem->sleepers = 0;
157 /*
158 * Add "everybody else" and us into it. They aren't
159 * playing, because we own the spinlock.
160 */
161 if (!atomic_add_negative(sleepers, &sem->count))
162 wake_up(&sem->wait);
164 spin_unlock_irqrestore(&semaphore_lock, flags);
165 return 1;
166 }