netdev - Re: [PATCH net 1/3] net: bcmgenet: fix off-by-one in incrementing read pointer

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Date:	Thu, 9 Oct 2014 23:01:48 -0700
From:	Petri Gynther <pgynther@...gle.com>
To:	Florian Fainelli <f.fainelli@...il.com>
Cc:	netdev@...r.kernel.org, David Miller <davem@...emloft.net>,
	jaedon.shin@...il.com
Subject: Re: [PATCH net 1/3] net: bcmgenet: fix off-by-one in incrementing
 read pointer

Hi Florian,

On Thu, Oct 9, 2014 at 6:06 PM, Florian Fainelli <f.fainelli@...il.com> wrote:
> Commit b629be5c8399d7c423b92135eb43a86c924d1cbc ("net: bcmgenet: check
> harder for out of memory conditions") moved the increment of the local
> read pointer *before* reading from the hardware descriptor using
> dmadesc_get_length_status(), which creates an off-by-one situation.
>
> Fix this by moving again the read_ptr increment after we have read the
> hardware descriptor to get both the control block and the read pointer
> back in sync.
>
> Fixes: b629be5c8399 ("net: bcmgenet: check harder for out of memory conditions")
> Reported-by: Jaedon Shin <jaedon.shin@...il.com>
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---
>  drivers/net/ethernet/broadcom/genet/bcmgenet.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> index fff2634b6f34..f1bcebcbba80 100644
> --- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> +++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> @@ -1287,9 +1287,6 @@ static unsigned int bcmgenet_desc_rx(struct bcmgenet_priv *priv,
>
>                 rxpktprocessed++;
>
> -               priv->rx_read_ptr++;
> -               priv->rx_read_ptr &= (priv->num_rx_bds - 1);
> -

Wouldn't it be better to move the three lines:
rxpktprocessed++;
priv->rx_read_ptr++;
priv->rx_read_ptr &= (priv->num_rx_bds - 1)

as the last lines of the while-loop, after the CB refill?

-- Petri


>                 /* We do not have a backing SKB, so we do not have a
>                  * corresponding DMA mapping for this incoming packet since
>                  * bcmgenet_rx_refill always either has both skb and mapping or
> @@ -1332,6 +1329,9 @@ static unsigned int bcmgenet_desc_rx(struct bcmgenet_priv *priv,
>                           __func__, p_index, priv->rx_c_index,
>                           priv->rx_read_ptr, dma_length_status);
>
> +               priv->rx_read_ptr++;
> +               priv->rx_read_ptr &= (priv->num_rx_bds - 1);
> +
>                 if (unlikely(!(dma_flag & DMA_EOP) || !(dma_flag & DMA_SOP))) {
>                         netif_err(priv, rx_status, dev,
>                                   "dropping fragmented packet!\n");
> --
> 1.9.1
>
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