Function btrfs_uuid_tree_iterate() is defined in file fs/btrfs/uuid-tree.c. When the call to btrfs_alloc_path() fails, it assigns "-ENOMEM" to variable ret and jumps to label "out". However, 0 rather than ret is returned at the end. As a result, the callers will not be able to detect errors during the execution of btrfs_uuid_tree_iterate(). Maybe it is better to use "return ret;" instead of "return 0;" at line 356. Codes related to this bug are summarised as follows.

btrfs_uuid_tree_iterate @@ fs/btrfs/uuid-tree.c
260 int btrfs_uuid_tree_iterate(struct btrfs_fs_info *fs_info,
261                 int (*check_func)(struct btrfs_fs_info *, u8 *, u8,
262                           u64))
263 {
264     struct btrfs_root *root = fs_info->uuid_root;
265     struct btrfs_key key;
266     struct btrfs_path *path;
267     int ret = 0;
268     struct extent_buffer *leaf;
269     int slot;
270     u32 item_size;
271     unsigned long offset;
272 
273     path = btrfs_alloc_path();
274     if (!path) {
275         ret = -ENOMEM;
276         goto out;
277     }
        ...
352 out:
353     btrfs_free_path(path);
354     if (ret)
355         btrfs_warn(fs_info, "btrfs_uuid_tree_iterate failed %d", ret);
356     return 0;   // return ret?
357 }

Thanks very much!