reproduce (this is a W=1 build):
        git checkout 643ec9dfcfa248b19ed1a1acce12f05d6dda6de4
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 olddefconfig
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash mm/ net/