[AIO] add cancellation support to i386 aio_down()



diff -purN 40_lock_kiocb/arch/i386/kernel/semaphore.c 50_aio_down_cancel/arch/i386/kernel/semaphore.c
--- 40_lock_kiocb/arch/i386/kernel/semaphore.c	2005-06-20 15:55:07.044745688 -0400
+++ 50_aio_down_cancel/arch/i386/kernel/semaphore.c	2005-06-20 15:48:41.534352176 -0400
@@ -104,6 +104,7 @@ static int aio_down_wait(wait_queue_t *w
 	 * the wait_queue_head.
 	 */
 	if (!atomic_add_negative(sleepers - 1, &sem->count)) {
+		iocb->ki_cancel = NULL;
 		sem->sleepers = 0;
 		sem->aio_owner = iocb;
 		list_del_init(&wait->task_list);
@@ -116,6 +117,28 @@ static int aio_down_wait(wait_queue_t *w
 	return 1;
 }
 
+static void fixup_down_trylock_locked(struct semaphore *sem);
+static int cancel_aio_down(struct kiocb *iocb, struct io_event *res)
+{
+	/* At this point, the kiocb is locked and even if we have kicked 
+	 * it, the pointer to the semaphore is still valid.
+	 */
+	struct semaphore *sem = iocb->ki_wait.private;
+	unsigned long flags;
+	int ret = 0;
+
+	spin_lock_irqsave(&sem->wait.lock, flags);
+	if (!list_empty(&iocb->ki_wait.task_list)) {
+		/* Ensure aio_down_wait() can no longer be called. */
+		list_del_init(&iocb->ki_wait.task_list);
+		fixup_down_trylock_locked(sem);
+	} else
+		ret = -EAGAIN;	/* we lost the race with aio_down_wait(). */
+	spin_unlock_irqrestore(&sem->wait.lock, flags);
+
+	return ret;
+}
+
 static fastcall int __attribute_used__ __sched __aio_down(struct kiocb *iocb, struct semaphore * sem)
 {
 	unsigned long flags;
@@ -132,6 +155,8 @@ static fastcall int __attribute_used__ _
 
 	sem->sleepers++;
 
+	iocb->ki_cancel = cancel_aio_down;
+
 	aio_down_wait(&iocb->ki_wait, 0, 0, NULL);
 	spin_unlock_irqrestore(&sem->wait.lock, flags);
 	return -EIOCBRETRY;
@@ -200,12 +225,9 @@ static fastcall int __attribute_used__ _
  * single "cmpxchg" without failure cases,
  * but then it wouldn't work on a 386.
  */
-static fastcall int __attribute_used__ __down_trylock(struct semaphore * sem)
+static void fixup_down_trylock_locked(struct semaphore *sem)
 {
 	int sleepers;
-	unsigned long flags;
-
-	spin_lock_irqsave(&sem->wait.lock, flags);
 	sleepers = sem->sleepers + 1;
 	sem->sleepers = 0;
 
@@ -214,15 +236,20 @@ static fastcall int __attribute_used__ _
 	 * playing, because we own the spinlock in the
 	 * wait_queue_head.
 	 */
-	if (!atomic_add_negative(sleepers, &sem->count)) {
+	if (!atomic_add_negative(sleepers, &sem->count))
 		wake_up_locked(&sem->wait);
-	}
+}
 
+static fastcall int __attribute_used__ __down_trylock(struct semaphore * sem)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&sem->wait.lock, flags);
+	fixup_down_trylock_locked(sem);
 	spin_unlock_irqrestore(&sem->wait.lock, flags);
 	return 1;
 }
 
-
 /*
  * The semaphore operations have a special calling sequence that
  * allow us to do a simpler in-line version of them. These routines