reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/commit/?id=3d64521d183c25ed63ae122087ec6919b3b2b609
        git remote add djwong-xfs https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git
        git fetch --no-tags djwong-xfs hch-wtf
        git checkout 3d64521d183c25ed63ae122087ec6919b3b2b609
        # 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/xfs/