reproduce:
        # apt-get install sparse
        # sparse version: v0.6.4-66-g0196afe1
        # https://git.kernel.org/pub/scm/linux/kernel/git/melver/linux.git/commit/?id=7550ab865bc73e6365cbcf09e09d0a6a58d9afcd
        git remote add melver https://git.kernel.org/pub/scm/linux/kernel/git/melver/linux.git
        git fetch --no-tags melver cap-analysis/dev
        git checkout 7550ab865bc73e6365cbcf09e09d0a6a58d9afcd
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=x86_64 olddefconfig
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__ -fmax-errors=unlimited -fmax-warnings=unlimited' O=build_dir ARCH=x86_64 SHELL=/bin/bash fs/nfsd/ net/ipv4/