reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/chao/linux.git/commit/?id=c85deae607667bb160a277e75324a45879161285
        git remote add chao https://git.kernel.org/pub/scm/linux/kernel/git/chao/linux.git
        git fetch --no-tags chao bugfix/common
        git checkout c85deae607667bb160a277e75324a45879161285

        # 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/f2fs/