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/*
* linux/arch/s390/kernel/semaphore.c
*
* S390 version
* Copyright (C) 1998-2000 IBM Corporation
* Author(s): Martin Schwidefsky
*
* Derived from "linux/arch/i386/kernel/semaphore.c
* Copyright (C) 1999, Linus Torvalds
*
*/
#include <linux/sched.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <asm/semaphore.h>
/*
* Atomically update sem->count. Equivalent to:
* old_val = sem->count.counter;
* new_val = ((old_val >= 0) ? old_val : 0) + incr;
* sem->count.counter = new_val;
* return old_val;
*/
static inline int __sem_update_count(struct semaphore *sem, int incr)
{
int old_val, new_val;
asm volatile(
" l %0,0(%3)\n"
"0: ltr %1,%0\n"
" jhe 1f\n"
" lhi %1,0\n"
"1: ar %1,%4\n"
" cs %0,%1,0(%3)\n"
" jl 0b\n"
: "=&d" (old_val), "=&d" (new_val), "=m" (sem->count)
: "a" (&sem->count), "d" (incr), "m" (sem->count)
: "cc");
return old_val;
}
/*
* The inline function up() incremented count but the result
* was <= 0. This indicates that some process is waiting on
* the semaphore. The semaphore is free and we'll wake the
* first sleeping process, so we set count to 1 unless some
* other cpu has called up in the meantime in which case
* we just increment count by 1.
*/
void __up(struct semaphore *sem)
{
__sem_update_count(sem, 1);
wake_up(&sem->wait);
}
/*
* The inline function down() decremented count and the result
* was < 0. The wait loop will atomically test and update the
* semaphore counter following the rules:
* count > 0: decrement count, wake up queue and exit.
* count <= 0: set count to -1, go to sleep.
*/
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);
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);
wake_up(&sem->wait);
}
/*
* Same as __down() with an additional test for signals.
* If a signal is pending the count is updated as follows:
* count > 0: wake up queue and exit.
* count <= 0: set count to 0, wake up queue and exit.
*/
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)) {
__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;
}
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