reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/snitzer/linux.git/commit/?id=27f81c6a85b36d6948b768cc1ec584b92fe7ee30
        git remote add snitzer https://git.kernel.org/pub/scm/linux/kernel/git/snitzer/linux.git
        git fetch --no-tags snitzer nfs-localio-for-next
        git checkout 27f81c6a85b36d6948b768cc1ec584b92fe7ee30
        # 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 fs/nfsd/