reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/snitzer/linux.git/commit/?id=3a235de0be361b80d2689bfb42e3da7b71840e5b
        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 3a235de0be361b80d2689bfb42e3da7b71840e5b
        # 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/