linux-kernel - Re: [PATCH] net/mlx4_en: ensure rx_desc updating reaches HW before prod db updating

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Date:   Fri, 12 Jan 2018 09:32:47 -0700
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Jianchao Wang <jianchao.w.wang@...cle.com>
Cc:     tariqt@...lanox.com, junxiao.bi@...cle.com, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        Saeed Mahameed <saeedm@...lanox.com>
Subject: Re: [PATCH] net/mlx4_en: ensure rx_desc updating reaches HW before
 prod db updating

On Fri, Jan 12, 2018 at 11:42:22AM +0800, Jianchao Wang wrote:
> Customer reported memory corruption issue on previous mlx4_en driver
> version where the order-3 pages and multiple page reference counting
> were still used.
> 
> Finally, find out one of the root causes is that the HW may see stale
> rx_descs due to prod db updating reaches HW before rx_desc. Especially
> when cross order-3 pages boundary and update a new one, HW may write
> on the pages which may has been freed and allocated again by others.
> 
> To fix it, add a wmb between rx_desc and prod db updating to ensure
> the order. Even thougth order-0 and page recycling has been introduced,
> the disorder between rx_desc and prod db still could lead to corruption
> on different inbound packages.
> 
> Signed-off-by: Jianchao Wang <jianchao.w.wang@...cle.com>
>  drivers/net/ethernet/mellanox/mlx4/en_rx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> index 85e28ef..eefa82c 100644
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
> @@ -555,7 +555,7 @@ static void mlx4_en_refill_rx_buffers(struct mlx4_en_priv *priv,
>  			break;
>  		ring->prod++;
>  	} while (likely(--missing));
> -
> +	wmb(); /* ensure rx_desc updating reaches HW before prod db updating */
>  	mlx4_en_update_rx_prod_db(ring);
>  }
>  

Does this need to be dma_wmb(), and should it be in
mlx4_en_update_rx_prod_db ?

Jason