reproduce (this is a W=1 build):
        git remote add brauner-vfs https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
        git fetch brauner-vfs vfs.all
        git checkout brauner-vfs/vfs.all
        b4 shazam https://lore.kernel.org/r/adKJMRkQJXEwHs-j@redhat.com
        # apt-get install sparse
        # sparse: v0.6.5-rc1

        # 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/