reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/chao/linux.git/commit/?id=d98bac3cd94b6c0375a7b6e7728b8cf17cc080d0
        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 d98bac3cd94b6c0375a7b6e7728b8cf17cc080d0
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 olddefconfig
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash fs/f2fs/