reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/jlayton/linux.git/commit/?id=b6232347709692f6d08fa8f15ace5ceb06a803e9
        git remote add jlayton https://git.kernel.org/pub/scm/linux/kernel/git/jlayton/linux.git
        git fetch --no-tags jlayton dir-deleg
        git checkout b6232347709692f6d08fa8f15ace5ceb06a803e9
        # 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/