reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git/commit/?id=a4841d91a7f57d38d3a63c18b4ce68ee5e06829b
        git remote add tytso-ext4 https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git
        git fetch --no-tags tytso-ext4 dev
        git checkout a4841d91a7f57d38d3a63c18b4ce68ee5e06829b

        # 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