Merge master.kernel.org:/pub/scm/linux/kernel/git/jejb/scsi-misc-2.6
[linux-2.6] / arch / v850 / kernel / semaphore.c
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  */
15
16 #include <linux/errno.h>
17 #include <linux/sched.h>
18 #include <linux/init.h>
19
20 #include <asm/semaphore.h>
21
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  */
42
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  */
52
53 void __up(struct semaphore *sem)
54 {
55         wake_up(&sem->wait);
56 }
57
58 static DEFINE_SPINLOCK(semaphore_lock);
59
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);
66
67         spin_lock_irq(&semaphore_lock);
68         sem->sleepers++;
69         for (;;) {
70                 int sleepers = sem->sleepers;
71
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);
82
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 }
92
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);
100
101         spin_lock_irq(&semaphore_lock);
102         sem->sleepers ++;
103         for (;;) {
104                 int sleepers = sem->sleepers;
105
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                 }
119
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);
132
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 }
143
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;
152
153         spin_lock_irqsave(&semaphore_lock, flags);
154         sleepers = sem->sleepers + 1;
155         sem->sleepers = 0;
156
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);
163
164         spin_unlock_irqrestore(&semaphore_lock, flags);
165         return 1;
166 }