4 * PowerPC-specific semaphore code.
6 * Copyright (C) 1999 Cort Dougan <cort@cs.nmt.edu>
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License
10 * as published by the Free Software Foundation; either version
11 * 2 of the License, or (at your option) any later version.
13 * April 2001 - Reworked by Paul Mackerras <paulus@samba.org>
14 * to eliminate the SMP races in the old version between the updates
15 * of `count' and `waking'. Now we use negative `count' values to
16 * indicate that some process(es) are waiting for the semaphore.
19 #include <linux/sched.h>
20 #include <linux/init.h>
21 #include <linux/module.h>
23 #include <asm/atomic.h>
24 #include <asm/semaphore.h>
25 #include <asm/errno.h>
28 * Atomically update sem->count.
29 * This does the equivalent of the following:
31 * old_count = sem->count;
32 * tmp = MAX(old_count, 0) + incr;
36 static inline int __sem_update_count(struct semaphore *sem, int incr)
40 __asm__ __volatile__("\n"
47 : "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)
48 : "r" (&sem->count), "r" (incr), "m" (sem->count)
54 void __up(struct semaphore *sem)
57 * Note that we incremented count in up() before we came here,
58 * but that was ineffective since the result was <= 0, and
59 * any negative value of count is equivalent to 0.
60 * This ends up setting count to 1, unless count is now > 0
61 * (i.e. because some other cpu has called up() in the meantime),
62 * in which case we just increment count.
64 __sem_update_count(sem, 1);
70 * Note that when we come in to __down or __down_interruptible,
71 * we have already decremented count, but that decrement was
72 * ineffective since the result was < 0, and any negative value
73 * of count is equivalent to 0.
74 * Thus it is only when we decrement count from some value > 0
75 * that we have actually got the semaphore.
77 void __sched __down(struct semaphore *sem)
79 struct task_struct *tsk = current;
80 DECLARE_WAITQUEUE(wait, tsk);
82 __set_task_state(tsk, TASK_UNINTERRUPTIBLE);
83 add_wait_queue_exclusive(&sem->wait, &wait);
86 * Try to get the semaphore. If the count is > 0, then we've
87 * got the semaphore; we decrement count and exit the loop.
88 * If the count is 0 or negative, we set it to -1, indicating
89 * that we are asleep, and then sleep.
91 while (__sem_update_count(sem, -1) <= 0) {
93 set_task_state(tsk, TASK_UNINTERRUPTIBLE);
95 remove_wait_queue(&sem->wait, &wait);
96 __set_task_state(tsk, TASK_RUNNING);
99 * If there are any more sleepers, wake one of them up so
100 * that it can either get the semaphore, or set count to -1
101 * indicating that there are still processes sleeping.
105 EXPORT_SYMBOL(__down);
107 int __sched __down_interruptible(struct semaphore * sem)
110 struct task_struct *tsk = current;
111 DECLARE_WAITQUEUE(wait, tsk);
113 __set_task_state(tsk, TASK_INTERRUPTIBLE);
114 add_wait_queue_exclusive(&sem->wait, &wait);
116 while (__sem_update_count(sem, -1) <= 0) {
117 if (signal_pending(current)) {
119 * A signal is pending - give up trying.
120 * Set sem->count to 0 if it is negative,
121 * since we are no longer sleeping.
123 __sem_update_count(sem, 0);
128 set_task_state(tsk, TASK_INTERRUPTIBLE);
130 remove_wait_queue(&sem->wait, &wait);
131 __set_task_state(tsk, TASK_RUNNING);
136 EXPORT_SYMBOL(__down_interruptible);