linux-kernel - Re: [PATCH] net: ethernet: mtk-star-emac: fix wrong unmap in RX handling

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Date:   Tue, 2 Mar 2021 09:42:26 +0100
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     Biao Huang <biao.huang@...iatek.com>
Cc:     Felix Fietkau <nbd@....name>, John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        netdev <netdev@...r.kernel.org>,
        arm-soc <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC..." 
        <linux-mediatek@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        srv_heupstream <srv_heupstream@...iatek.com>
Subject: Re: [PATCH] net: ethernet: mtk-star-emac: fix wrong unmap in RX handling

On Tue, Mar 2, 2021 at 4:33 AM Biao Huang <biao.huang@...iatek.com> wrote:
>
> mtk_star_dma_unmap_rx() should unmap the dma_addr of old skb rather than
> that of new skb.
> Assign new_dma_addr to desc_data.dma_addr after all handling of old skb
> ends to avoid unexpected receive side error.
>
> Fixes: f96e9641e92b ("net: ethernet: mtk-star-emac: fix error path in RX handling")
> Signed-off-by: Biao Huang <biao.huang@...iatek.com>
> ---
>  drivers/net/ethernet/mediatek/mtk_star_emac.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/ethernet/mediatek/mtk_star_emac.c b/drivers/net/ethernet/mediatek/mtk_star_emac.c
> index a8641a407c06..96d2891f1675 100644
> --- a/drivers/net/ethernet/mediatek/mtk_star_emac.c
> +++ b/drivers/net/ethernet/mediatek/mtk_star_emac.c
> @@ -1225,8 +1225,6 @@ static int mtk_star_receive_packet(struct mtk_star_priv *priv)
>                 goto push_new_skb;
>         }
>
> -       desc_data.dma_addr = new_dma_addr;
> -
>         /* We can't fail anymore at this point: it's safe to unmap the skb. */
>         mtk_star_dma_unmap_rx(priv, &desc_data);
>
> @@ -1236,6 +1234,9 @@ static int mtk_star_receive_packet(struct mtk_star_priv *priv)
>         desc_data.skb->dev = ndev;
>         netif_receive_skb(desc_data.skb);
>
> +       /* update dma_addr for new skb */
> +       desc_data.dma_addr = new_dma_addr;
> +
>  push_new_skb:
>         desc_data.len = skb_tailroom(new_skb);
>         desc_data.skb = new_skb;
> --
> 2.18.0
>

Thanks for spotting that. Maybe also update the commit so that it
says: "it's safe to unmap the old skb"? Would make the thing clearer
IMO.

In any case:

Acked-by: Bartosz Golaszewski <bgolaszewski@...libre.com>

Bartosz