reproduce (this is a W=1 build):
        # https://github.com/jonhunter/linux/commit/ae173249d9028ef159fba040bdab260d80dda43f
        git remote add jonhunter https://github.com/jonhunter/linux
        git fetch --no-tags jonhunter tegra/next-fixes
        git checkout ae173249d9028ef159fba040bdab260d80dda43f

        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=um olddefconfig
        make W=1 O=build_dir ARCH=um SHELL=/bin/bash kernel/