reproduce (this is a W=1 build):
        # https://github.com/norov/linux/commit/a879cc36a6d1a8b9a7084b24110b0046ed110626
        git remote add norov https://github.com/norov/linux
        git fetch --no-tags norov find_and-v4.1
        git checkout a879cc36a6d1a8b9a7084b24110b0046ed110626
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 olddefconfig
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash drivers/block/null_blk/