From: Maxim Mikityanskiy Date: Wed, 27 Mar 2019 11:39:21 +0000 (+0200) Subject: net/mlx5e: Add an underflow warning comment X-Git-Tag: v5.15~6431^2~121^2~4 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=b1b187e1029a374e83942e6c591ee5bf8b60f070;p=platform%2Fkernel%2Flinux-starfive.git net/mlx5e: Add an underflow warning comment 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 --- diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/params.c b/drivers/net/ethernet/mellanox/mlx5/core/en/params.c index 658337c..fa6661e 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,