netdev - Re: [PATCH net-next 2/2] net: bcmgenet: add support for xmit

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Date:	Mon, 09 Mar 2015 15:10:20 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Florian Fainelli <f.fainelli@...il.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net, pgynther@...gle.com,
	jaedon.shin@...il.com
Subject: Re: [PATCH net-next 2/2] net: bcmgenet: add support for xmit_more

On Mon, 2015-03-09 at 14:52 -0700, Florian Fainelli wrote:
> Delay the update of the TDMA producer index unless this is the last SKB in a
> batch, or the queue is already stopped.
> 
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---
>  drivers/net/ethernet/broadcom/genet/bcmgenet.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> index 9b3b8a3db59b..8419826da6a7 100644
> --- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> +++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
> @@ -1316,8 +1316,10 @@ static netdev_tx_t bcmgenet_xmit(struct sk_buff *skb, struct net_device *dev)
>  	ring->prod_index += nr_frags + 1;
>  	ring->prod_index &= DMA_P_INDEX_MASK;
>  
> -	bcmgenet_tdma_ring_writel(priv, ring->index,
> -				  ring->prod_index, TDMA_PROD_INDEX);
> +	if (!skb->xmit_more || netif_xmit_stopped(txq))
> +		/* Packets are ready, update producer index */
> +		bcmgenet_tdma_ring_writel(priv, ring->index,
> +					  ring->prod_index, TDMA_PROD_INDEX);
>  
>  	if (ring->free_bds <= (MAX_SKB_FRAGS + 1))
>  		netif_tx_stop_queue(txq);

It seems you have a race here, if you stop the queue right now, while
this skb had skb->xmit_more set.





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