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/* MN10300 Semaphore implementation
*
* Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/
#include <linux/sched.h>
#include <linux/module.h>
#include <asm/semaphore.h>
struct sem_waiter {
struct list_head list;
struct task_struct *task;
};
#if SEMAPHORE_DEBUG
void semtrace(struct semaphore *sem, const char *str)
{
if (sem->debug)
printk(KERN_DEBUG "[%d] %s({%d,%d})\n",
current->pid,
str,
atomic_read(&sem->count),
list_empty(&sem->wait_list) ? 0 : 1);
}
#else
#define semtrace(SEM, STR) do { } while (0)
#endif
/*
* wait for a token to be granted from a semaphore
* - entered with lock held and interrupts disabled
*/
void __down(struct semaphore *sem, unsigned long flags)
{
struct task_struct *tsk = current;
struct sem_waiter waiter;
semtrace(sem, "Entering __down");
/* set up my own style of waitqueue */
waiter.task = tsk;
get_task_struct(tsk);
list_add_tail(&waiter.list, &sem->wait_list);
/* we don't need to touch the semaphore struct anymore */
spin_unlock_irqrestore(&sem->wait_lock, flags);
/* wait to be given the semaphore */
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
for (;;) {
if (!waiter.task)
break;
schedule();
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
}
tsk->state = TASK_RUNNING;
semtrace(sem, "Leaving __down");
}
EXPORT_SYMBOL(__down);
/*
* interruptibly wait for a token to be granted from a semaphore
* - entered with lock held and interrupts disabled
*/
int __down_interruptible(struct semaphore *sem, unsigned long flags)
{
struct task_struct *tsk = current;
struct sem_waiter waiter;
int ret;
semtrace(sem, "Entering __down_interruptible");
/* set up my own style of waitqueue */
waiter.task = tsk;
get_task_struct(tsk);
list_add_tail(&waiter.list, &sem->wait_list);
/* we don't need to touch the semaphore struct anymore */
set_task_state(tsk, TASK_INTERRUPTIBLE);
spin_unlock_irqrestore(&sem->wait_lock, flags);
/* wait to be given the semaphore */
ret = 0;
for (;;) {
if (!waiter.task)
break;
if (unlikely(signal_pending(current)))
goto interrupted;
schedule();
set_task_state(tsk, TASK_INTERRUPTIBLE);
}
out:
tsk->state = TASK_RUNNING;
semtrace(sem, "Leaving __down_interruptible");
return ret;
interrupted:
spin_lock_irqsave(&sem->wait_lock, flags);
list_del(&waiter.list);
spin_unlock_irqrestore(&sem->wait_lock, flags);
ret = 0;
if (!waiter.task) {
put_task_struct(current);
ret = -EINTR;
}
goto out;
}
EXPORT_SYMBOL(__down_interruptible);
/*
* release a single token back to a semaphore
* - entered with lock held and interrupts disabled
*/
void __up(struct semaphore *sem)
{
struct task_struct *tsk;
struct sem_waiter *waiter;
semtrace(sem, "Entering __up");
/* grant the token to the process at the front of the queue */
waiter = list_entry(sem->wait_list.next, struct sem_waiter, list);
/* We must be careful not to touch 'waiter' after we set ->task = NULL.
* It is an allocated on the waiter's stack and may become invalid at
* any time after that point (due to a wakeup from another source).
*/
list_del_init(&waiter->list);
tsk = waiter->task;
smp_mb();
waiter->task = NULL;
wake_up_process(tsk);
put_task_struct(tsk);
semtrace(sem, "Leaving __up");
}
EXPORT_SYMBOL(__up);
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