Btrfs: return immediately if tree log mod is not necessary

In ctree.c:tree_mod_log_set_node_key() we were calling
__tree_mod_log_insert_key() even when the modification doesn't need
to be logged. This would allocate a tree_mod_elem structure, fill it
and pass it to  __tree_mod_log_insert(), which would just acquire
the tree mod log write lock and then free the tree_mod_elem structure
and return (that is, a no-op).

Therefore call tree_mod_log_insert() instead of __tree_mod_log_insert()
which just returns immediately if the modification doesn't need to be
logged (without allocating the structure, fill it, acquire write lock,
free structure).
Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/ctree.c

@@ -771,7 +771,7 @@ tree_mod_log_set_node_key(struct btrfs_fs_info *fs_info,
 {
 	int ret;
 
-	ret = __tree_mod_log_insert_key(fs_info, eb, slot,
+	ret = tree_mod_log_insert_key(fs_info, eb, slot,
 					MOD_LOG_KEY_REPLACE,
 					atomic ? GFP_ATOMIC : GFP_NOFS);
 	BUG_ON(ret < 0);