netdev - Re: [PATCH v2] bgmac: add support for Byte Queue Limits

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Date:	Sat, 28 Sep 2013 16:03:20 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hauke Mehrtens <hauke@...ke-m.de>
Cc:	davem@...emloft.net, zajec5@...il.com, netdev@...r.kernel.org
Subject: Re: [PATCH v2] bgmac: add support for Byte Queue Limits

On Sun, 2013-09-29 at 00:35 +0200, Hauke Mehrtens wrote:
> This makes it possible to use some more advanced queuing
> techniques with this driver.
> 
> When multi queue support will be added some changes to Byte Queue
> handling is needed.
> 
> Signed-off-by: Hauke Mehrtens <hauke@...ke-m.de>
> ---
>  drivers/net/ethernet/broadcom/bgmac.c |   10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/net/ethernet/broadcom/bgmac.c b/drivers/net/ethernet/broadcom/bgmac.c
> index 249468f..e5519f1 100644
> --- a/drivers/net/ethernet/broadcom/bgmac.c
> +++ b/drivers/net/ethernet/broadcom/bgmac.c
> @@ -164,6 +164,8 @@ static netdev_tx_t bgmac_dma_tx_add(struct bgmac *bgmac,
>  	if (--free_slots == 1)
>  		netif_stop_queue(net_dev);
>  
> +	netdev_sent_queue(net_dev, skb->len);
> +
>  	return NETDEV_TX_OK;
>  

Unfortunately, skb->len is unsafe : hardware might already sent the
packet and TX completion have freed it.

You must cache skb->len in a variable before allowing hardware to send
the frame.


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