netdev - Re: [PATCH] net: macb: Increment rx bd head after allocating skb and buffer

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Message-ID: <4fb95509-97af-bce5-bf2f-3be8962e5e6a@microchip.com>
Date:   Tue, 10 May 2022 10:11:13 +0000
From:   <Claudiu.Beznea@...rochip.com>
To:     <harini.katakam@...inx.com>, <Nicolas.Ferre@...rochip.com>,
        <davem@...emloft.net>, <kuba@...nel.org>, <dumazet@...gle.com>,
        <pabeni@...hat.com>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <michal.simek@...inx.com>, <harinikatakamlinux@...il.com>,
        <radhey.shyam.pandey@...inx.com>
Subject: Re: [PATCH] net: macb: Increment rx bd head after allocating skb and
 buffer

On 09.05.2022 15:19, Harini Katakam wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> In gem_rx_refill rx_prepared_head is incremented at the beginning of
> the while loop preparing the skb and data buffers. If the skb or data
> buffer allocation fails, this BD will be unusable BDs until the head
> loops back to the same BD (and obviously buffer allocation succeeds).
> In the unlikely event that there's a string of allocation failures,
> there will be an equal number of unusable BDs and an inconsistent RX
> BD chain. Hence increment the head at the end of the while loop to be
> clean.
> 
> Signed-off-by: Harini Katakam <harini.katakam@...inx.com>
> Signed-off-by: Michal Simek <michal.simek@...inx.com>
> Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>

Reviewed-by: Claudiu Beznea <claudiu.beznea@...rochip.com>


> ---
>  drivers/net/ethernet/cadence/macb_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index 0b03305ad6a0..9c7d590c0188 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -1215,7 +1215,6 @@ static void gem_rx_refill(struct macb_queue *queue)
>                 /* Make hw descriptor updates visible to CPU */
>                 rmb();
> 
> -               queue->rx_prepared_head++;
>                 desc = macb_rx_desc(queue, entry);
> 
>                 if (!queue->rx_skbuff[entry]) {
> @@ -1254,6 +1253,7 @@ static void gem_rx_refill(struct macb_queue *queue)
>                         dma_wmb();
>                         desc->addr &= ~MACB_BIT(RX_USED);
>                 }
> +               queue->rx_prepared_head++;
>         }
> 
>         /* Make descriptor updates visible to hardware */
> --
> 2.17.1
>