reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/sj/linux.git/commit/?id=c9e6712790c0d20de3914c44e8a22d9df00cb28a
        git remote add sj https://git.kernel.org/pub/scm/linux/kernel/git/sj/linux.git
        git fetch --no-tags sj mm-new
        git checkout c9e6712790c0d20de3914c44e8a22d9df00cb28a
        # 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