kernfs: fix a subdir count leak

Currently kernfs_link_sibling() increates parent->dir.subdirs before
adding the node into parent's chidren rb tree.

Because it is possible that kernfs_link_sibling() couldn't find
a suitable slot and bail out, this leads to a mismatch between
elevated subdir count with actual children node numbers.

This patches fix this problem, by moving the subdir accouting
after the actual addtion happening.
Signed-off-by: Jianyu Zhan <nasa4836@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/kernfs/dir.c

@@ -232,9 +232,6 @@ static int kernfs_link_sibling(struct kernfs_node *kn)
 	struct rb_node **node = &kn->parent->dir.children.rb_node;
 	struct rb_node *parent = NULL;
 
-	if (kernfs_type(kn) == KERNFS_DIR)
-		kn->parent->dir.subdirs++;
-
 	while (*node) {
 		struct kernfs_node *pos;
 		int result;
@@ -249,9 +246,15 @@ static int kernfs_link_sibling(struct kernfs_node *kn)
 		else
 			return -EEXIST;
 	}
+
 	/* add new node and rebalance the tree */
 	rb_link_node(&kn->rb, parent, node);
 	rb_insert_color(&kn->rb, &kn->parent->dir.children);
+
+	/* successfully added, account subdir number */
+	if (kernfs_type(kn) == KERNFS_DIR)
+		kn->parent->dir.subdirs++;
+
 	return 0;
 }