From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,UNPARSEABLE_RELAY, URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 106EBC10F03 for ; Tue, 23 Apr 2019 19:15:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D92EE217D9 for ; Tue, 23 Apr 2019 19:15:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726915AbfDWTPr (ORCPT ); Tue, 23 Apr 2019 15:15:47 -0400 Received: from mail-il-dmz.mellanox.com ([193.47.165.129]:36138 "EHLO mellanox.co.il" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726599AbfDWTPq (ORCPT ); Tue, 23 Apr 2019 15:15:46 -0400 Received: from Internal Mail-Server by MTLPINE1 (envelope-from saeedm@mellanox.com) with ESMTPS (AES256-SHA encrypted); 23 Apr 2019 22:15:41 +0300 Received: from sx1.mtl.com ([172.16.5.39]) by labmailer.mlnx (8.13.8/8.13.8) with ESMTP id x3NJFD0L010291; Tue, 23 Apr 2019 22:15:39 +0300 From: Saeed Mahameed To: "David S. Miller" Cc: netdev@vger.kernel.org, Jesper Dangaard Brouer , Jonathan Lemon , Maxim Mikityanskiy , Tariq Toukan , Saeed Mahameed Subject: [net-next V2 09/13] net/mlx5e: Add an underflow warning comment Date: Tue, 23 Apr 2019 12:14:56 -0700 Message-Id: <20190423191500.16632-10-saeedm@mellanox.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190423191500.16632-1-saeedm@mellanox.com> References: <20190423191500.16632-1-saeedm@mellanox.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Maxim Mikityanskiy mlx5e_mpwqe_get_log_rq_size calculates the number of WQEs (N) based on the requested number of frames in the RQ (F) and the number of packets per WQE (P). It ensures that N is not less than the minimum number of WQEs in an RQ (N_min). Arithmetically, it means that F / P >= N_min should be true. This function deals with logarithms, so it should check that log(F) - log(P) >= log(N_min). However, if F < P, this expression will cause an unsigned underflow. Check log(F) >= log(P) + log(N_min) instead. Signed-off-by: Maxim Mikityanskiy Reviewed-by: Tariq Toukan Signed-off-by: Saeed Mahameed --- drivers/net/ethernet/mellanox/mlx5/core/en/params.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c index 658337c3bba1..fa6661ea6310 100644 --- a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c @@ -62,11 +62,14 @@ bool mlx5e_rx_mpwqe_is_linear_skb(struct mlx5_core_dev *mdev, u8 mlx5e_mpwqe_get_log_rq_size(struct mlx5e_params *params) { + u8 log_pkts_per_wqe = mlx5e_mpwqe_log_pkts_per_wqe(params); + + /* Numbers are unsigned, don't subtract to avoid underflow. */ if (params->log_rq_mtu_frames < - mlx5e_mpwqe_log_pkts_per_wqe(params) + MLX5E_PARAMS_MINIMUM_LOG_RQ_SIZE_MPW) + log_pkts_per_wqe + MLX5E_PARAMS_MINIMUM_LOG_RQ_SIZE_MPW) return MLX5E_PARAMS_MINIMUM_LOG_RQ_SIZE_MPW; - return params->log_rq_mtu_frames - mlx5e_mpwqe_log_pkts_per_wqe(params); + return params->log_rq_mtu_frames - log_pkts_per_wqe; } u8 mlx5e_mpwqe_get_log_stride_size(struct mlx5_core_dev *mdev, -- 2.20.1