reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git/commit/?id=728f5c019e921428fac77ee4fd48a03b2d435c19
        git remote add jaegeuk-f2fs https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git
        git fetch --no-tags jaegeuk-f2fs dev-test
        git checkout 728f5c019e921428fac77ee4fd48a03b2d435c19
        # 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