Btrfs: reorder tree mod log operations in deleting a pointer

Since we don't use MOD_LOG_KEY_REMOVE_WHILE_MOVING to add nritems
during rewinding, we should insert a MOD_LOG_KEY_REMOVE operation first.
Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

fs/btrfs/ctree.c

@@ -4609,6 +4609,12 @@ static void del_ptr(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 	u32 nritems;
 	int ret;
 
+	if (tree_mod_log && level) {
+		ret = tree_mod_log_insert_key(root->fs_info, parent, slot,
+					      MOD_LOG_KEY_REMOVE);
+		BUG_ON(ret < 0);
+	}
+
 	nritems = btrfs_header_nritems(parent);
 	if (slot != nritems - 1) {
 		if (tree_mod_log && level)
@@ -4619,10 +4625,6 @@ static void del_ptr(struct btrfs_trans_handle *trans, struct btrfs_root *root,
 			      btrfs_node_key_ptr_offset(slot + 1),
 			      sizeof(struct btrfs_key_ptr) *
 			      (nritems - slot - 1));
-	} else if (tree_mod_log && level) {
-		ret = tree_mod_log_insert_key(root->fs_info, parent, slot,
-					      MOD_LOG_KEY_REMOVE);
-		BUG_ON(ret < 0);
 	}
 
 	nritems--;