The patch in above branch is different from:
https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git/commit/?h=for-next&id=72d04bdcf3f7d7e07d82f9757946f68802a7270a
return (READ_ONCE(map->word) & word_mask) == word_mask;
should be
return (READ_ONCE(map->word) & word_mask) != word_mask;