Subject: Re: [PATCH net] net: mellanox: mlxbf_gige: Fix skb_panic splat under memory pressure

From: Jakub Kicinski <[email-masked]>
Date: Tue, 23 May 2023 20:42:57 -0700

On Mon, 22 May 2023 21:07:13 +0200 Thomas Bogendoerfer wrote:
> Do skp_put() after a new skb has been successfully allocated otherwise
> the reused skb leads to skp_panics or incorrect packet sizes.

s/skp/skb/

Please add a Fixes tag pointing at the patch which introduced 
the problem (could be the first commit adding this driver).

> Signed-off-by: Thomas Bogendoerfer <[email-masked]>
> ---
>  .../ethernet/mellanox/mlxbf_gige/mlxbf_gige_rx.c    | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlxbf_gige/mlxbf_gige_rx.c b/drivers/net/ethernet/mellanox/mlxbf_gige/mlxbf_gige_rx.c
> index afa3b92a6905..2c132849a76d 100644
> --- a/drivers/net/ethernet/mellanox/mlxbf_gige/mlxbf_gige_rx.c
> +++ b/drivers/net/ethernet/mellanox/mlxbf_gige/mlxbf_gige_rx.c
> @@ -245,18 +245,19 @@ static bool mlxbf_gige_rx_packet(struct mlxbf_gige *priv, int *rx_pkts)
>  
>  		skb = priv->rx_skb[rx_pi_rem];
>  
> -		skb_put(skb, datalen);
> -
> -		skb->ip_summed = CHECKSUM_NONE; /* device did not checksum packet */
> -
> -		skb->protocol = eth_type_trans(skb, netdev);
> -
>  		/* Alloc another RX SKB for this same index */
>  		rx_skb = mlxbf_gige_alloc_skb(priv, MLXBF_GIGE_DEFAULT_BUF_SZ,
>  					      &rx_buf_dma, DMA_FROM_DEVICE);
>  		if (!rx_skb)
>  			return false;
>  		priv->rx_skb[rx_pi_rem] = rx_skb;
> +
> +		skb_put(skb, datalen);
> +
> +		skb->ip_summed = CHECKSUM_NONE; /* device did not checksum packet */
> +
> +		skb->protocol = eth_type_trans(skb, netdev);
>
>  		dma_unmap_single(priv->dev, *rx_wqe_addr,
>  				 MLXBF_GIGE_DEFAULT_BUF_SZ, DMA_FROM_DEVICE);

You should move the code here, after the dma_unmap().
eth_type_trans() will access the payload and until dma_unmap
the data should not be accessed by the CPU.

>  		*rx_wqe_addr = rx_buf_dma;

-- 
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