reproduce (this is a W=1 build):
        # https://git.kernel.org/pub/scm/linux/kernel/git/rdma/rdma.git/commit/?id=95a89ec304c38f7447cdbf271f2d1cbad4c3bf81
        git remote add rdma-rdma https://git.kernel.org/pub/scm/linux/kernel/git/rdma/rdma.git
        git fetch --no-tags rdma-rdma wip/leon-for-next
        git checkout 95a89ec304c38f7447cdbf271f2d1cbad4c3bf81
        # 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