reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/sj/linux.git/commit/?id=b40ae505a5ff6123396b42b79f42ad45df461634
        git remote add sj https://git.kernel.org/pub/scm/linux/kernel/git/sj/linux.git
        git fetch --no-tags sj damon/next
        git checkout b40ae505a5ff6123396b42b79f42ad45df461634
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash mm/