reproduce (this is a W=1 build):
        git remote add tytso-ext4 https://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4.git
        git fetch tytso-ext4 dev
        git checkout tytso-ext4/dev
        b4 shazam https://lore.kernel.org/r/tencent_E4CFC65D09852ECE2EF28C83A7C3C6E41206@qq.com
        # 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 fs/ext4/