reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/snitzer/linux.git/commit/?id=987bb33e11a334f6b224f92ab1f1f6c694eb96ee
        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 987bb33e11a334f6b224f92ab1f1f6c694eb96ee
        # 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/