autofs4 - fix lockdep splat in autofs

When recursing down the locks when traversing a tree/list in
get_next_positive_dentry() or get_next_positive_subdir() a lock can
change from being nested to being a parent which breaks lockdep. This
patch tells lockdep about what we did.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Ian Kent <raven@themaw.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/autofs4/expire.c

@@ -124,6 +124,7 @@ start:
 	/* Negative dentry - try next */
 	if (!simple_positive(q)) {
 		spin_unlock(&p->d_lock);
+		lock_set_subclass(&q->d_lock.dep_map, 0, _RET_IP_);
 		p = q;
 		goto again;
 	}
@@ -186,6 +187,7 @@ again:
 	/* Negative dentry - try next */
 	if (!simple_positive(ret)) {
 		spin_unlock(&p->d_lock);
+		lock_set_subclass(&ret->d_lock.dep_map, 0, _RET_IP_);
 		p = ret;
 		goto again;
 	}