136 строки
3.7 KiB
C
136 строки
3.7 KiB
C
/*
|
|
* PowerPC-specific semaphore code.
|
|
*
|
|
* Copyright (C) 1999 Cort Dougan <cort@cs.nmt.edu>
|
|
*
|
|
* This program is free software; you can redistribute it and/or
|
|
* modify it under the terms of the GNU General Public License
|
|
* as published by the Free Software Foundation; either version
|
|
* 2 of the License, or (at your option) any later version.
|
|
*
|
|
* April 2001 - Reworked by Paul Mackerras <paulus@samba.org>
|
|
* to eliminate the SMP races in the old version between the updates
|
|
* of `count' and `waking'. Now we use negative `count' values to
|
|
* indicate that some process(es) are waiting for the semaphore.
|
|
*/
|
|
|
|
#include <linux/sched.h>
|
|
#include <linux/init.h>
|
|
#include <linux/module.h>
|
|
|
|
#include <asm/atomic.h>
|
|
#include <asm/semaphore.h>
|
|
#include <asm/errno.h>
|
|
|
|
/*
|
|
* Atomically update sem->count.
|
|
* This does the equivalent of the following:
|
|
*
|
|
* old_count = sem->count;
|
|
* tmp = MAX(old_count, 0) + incr;
|
|
* sem->count = tmp;
|
|
* return old_count;
|
|
*/
|
|
static inline int __sem_update_count(struct semaphore *sem, int incr)
|
|
{
|
|
int old_count, tmp;
|
|
|
|
__asm__ __volatile__("\n"
|
|
"1: lwarx %0,0,%3\n"
|
|
" srawi %1,%0,31\n"
|
|
" andc %1,%0,%1\n"
|
|
" add %1,%1,%4\n"
|
|
PPC405_ERR77(0,%3)
|
|
" stwcx. %1,0,%3\n"
|
|
" bne 1b"
|
|
: "=&r" (old_count), "=&r" (tmp), "=m" (sem->count)
|
|
: "r" (&sem->count), "r" (incr), "m" (sem->count)
|
|
: "cc");
|
|
|
|
return old_count;
|
|
}
|
|
|
|
void __up(struct semaphore *sem)
|
|
{
|
|
/*
|
|
* Note that we incremented count in up() before we came here,
|
|
* but that was ineffective since the result was <= 0, and
|
|
* any negative value of count is equivalent to 0.
|
|
* This ends up setting count to 1, unless count is now > 0
|
|
* (i.e. because some other cpu has called up() in the meantime),
|
|
* in which case we just increment count.
|
|
*/
|
|
__sem_update_count(sem, 1);
|
|
wake_up(&sem->wait);
|
|
}
|
|
EXPORT_SYMBOL(__up);
|
|
|
|
/*
|
|
* Note that when we come in to __down or __down_interruptible,
|
|
* we have already decremented count, but that decrement was
|
|
* ineffective since the result was < 0, and any negative value
|
|
* of count is equivalent to 0.
|
|
* Thus it is only when we decrement count from some value > 0
|
|
* that we have actually got the semaphore.
|
|
*/
|
|
void __sched __down(struct semaphore *sem)
|
|
{
|
|
struct task_struct *tsk = current;
|
|
DECLARE_WAITQUEUE(wait, tsk);
|
|
|
|
__set_task_state(tsk, TASK_UNINTERRUPTIBLE);
|
|
add_wait_queue_exclusive(&sem->wait, &wait);
|
|
|
|
/*
|
|
* Try to get the semaphore. If the count is > 0, then we've
|
|
* got the semaphore; we decrement count and exit the loop.
|
|
* If the count is 0 or negative, we set it to -1, indicating
|
|
* that we are asleep, and then sleep.
|
|
*/
|
|
while (__sem_update_count(sem, -1) <= 0) {
|
|
schedule();
|
|
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
|
|
}
|
|
remove_wait_queue(&sem->wait, &wait);
|
|
__set_task_state(tsk, TASK_RUNNING);
|
|
|
|
/*
|
|
* If there are any more sleepers, wake one of them up so
|
|
* that it can either get the semaphore, or set count to -1
|
|
* indicating that there are still processes sleeping.
|
|
*/
|
|
wake_up(&sem->wait);
|
|
}
|
|
EXPORT_SYMBOL(__down);
|
|
|
|
int __sched __down_interruptible(struct semaphore * sem)
|
|
{
|
|
int retval = 0;
|
|
struct task_struct *tsk = current;
|
|
DECLARE_WAITQUEUE(wait, tsk);
|
|
|
|
__set_task_state(tsk, TASK_INTERRUPTIBLE);
|
|
add_wait_queue_exclusive(&sem->wait, &wait);
|
|
|
|
while (__sem_update_count(sem, -1) <= 0) {
|
|
if (signal_pending(current)) {
|
|
/*
|
|
* A signal is pending - give up trying.
|
|
* Set sem->count to 0 if it is negative,
|
|
* since we are no longer sleeping.
|
|
*/
|
|
__sem_update_count(sem, 0);
|
|
retval = -EINTR;
|
|
break;
|
|
}
|
|
schedule();
|
|
set_task_state(tsk, TASK_INTERRUPTIBLE);
|
|
}
|
|
remove_wait_queue(&sem->wait, &wait);
|
|
__set_task_state(tsk, TASK_RUNNING);
|
|
|
|
wake_up(&sem->wait);
|
|
return retval;
|
|
}
|
|
EXPORT_SYMBOL(__down_interruptible);
|