Re: [BUG] 2.6.30-rc4: Kernel BUG under network load with gianfar

[David Miller <davem@davemloft.net>]

From: Lennert Buytenhek <buytenh@wantstofly.org>
Date: Wed, 20 May 2009 23:47:34 +0200

> gianfar puts skbuffs that are in the rx ring back onto the recycle
> list if there was a receive error, but this breaks the following
> invariant: that all skbuffs on the recycle list have skb->data =
> skb->head + NET_SKB_PAD (NET_SKB_PAD being 32 for you).
> 
> In this case, the skb's ->data will be skb->head + RXBUF_ALIGNMENT
> (where RXBUF_ALIGNMENT is 64) when it is put onto the recycle list.
> And when gfar_new_skb() picks this skb off the recycle list again,
> it'll do:
> 
>         alignamount = RXBUF_ALIGNMENT -
>                 (((unsigned long) skb->data) & (RXBUF_ALIGNMENT - 1));
> 
>         /* We need the data buffer to be aligned properly.  We will reserve
>          * as many bytes as needed to align the data properly
>          */
>         skb_reserve(skb, alignamount);
> 
> So now skb->data will be skb->head + 128, and there won't be enough
> space between skb->head and skb->end to hold a full-sized packet.
> 
> Something like the patch below would fix it.

Let me know when a final, tested, version of this patch is available
and please make sure it makes it to netdev@vger.kernel.org

Thanks.