reproduce (this is a W=1 build):
        git clone https://github.com/intel/lkp-tests.git ~/lkp-tests
        # https://github.com/alexshi/linux/commit/8b464a88364f8c7a51ee0baf4a79c6a22f1ae9ef
        git remote add alexshi https://github.com/alexshi/linux.git
        git fetch --no-tags alexshi mmunstable
        git checkout 8b464a88364f8c7a51ee0baf4a79c6a22f1ae9ef
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=powerpc olddefconfig
        ~/lkp-tests/kbuild/make.cross W=1 O=build_dir ARCH=powerpc SHELL=/bin/bash mm/