/*
* 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");
}
/*
* 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 (list_empty(&waiter.list))
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);
if (!list_empty(&waiter.list)) {
list_del(&waiter.list);
ret = -EINTR;
}
spin_unlock_irqrestore(&sem->wait_lock, flags);
if (ret == -EINTR)
put_task_struct(current);
goto out;
}
/*
* 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");
}
