[PATCH] autofs4: post expire race fix

At the tail end of an expire it's possible for a process to enter
autofs4_wait, with a waitq type of NFY_NONE but find that the expire is
finished.  In this cause autofs4_wait will try to create a new wait but not
notify the daemon leading to a hang.  As the wait type is meant to delay mount
requests from revalidate or lookup during an expire and the expire is done all
we need to do is check if the dentry is a mountpoint.  If it's not then we're
done.
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/autofs4/waitq.c

@@ -191,6 +191,13 @@ int autofs4_wait(struct autofs_sb_info *sbi, struct dentry *dentry,
 	}
 
 	if ( !wq ) {
+		/* Can't wait for an expire if there's no mount */
+		if (notify == NFY_NONE && !d_mountpoint(dentry)) {
+			kfree(name);
+			up(&sbi->wq_sem);
+			return -ENOENT;
+		}
+
 		/* Create a new wait queue */
 		wq = kmalloc(sizeof(struct autofs_wait_queue),GFP_KERNEL);
 		if ( !wq ) {