netdev - Re: Gianfar: RX Recycle skb->len error

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Date:	Mon, 22 Mar 2010 20:24:46 +0300
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	David Miller <davem@...emloft.net>
Cc:	ben@...footnetworks.com, netdev@...r.kernel.org,
	Sandeep.Kumar@...escale.com
Subject: Re: Gianfar: RX Recycle skb->len error

On Sun, Mar 21, 2010 at 09:46:42PM -0700, David Miller wrote:
[...]
> > 				 * recycle list.
> >  				 */
> >  				skb->data = skb->head + NET_SKB_PAD;
> > +				skb_reset_tail_pointer(skb);
> > 				__skb_queue_head(&priv->rx_recycle, skb);
> > 			}
> > 		} else {
> 
> This code is essentially trying to undo skb_reserve()
> but as you found it's doing so in a buggy manner.
> 
> skb_reserve() adjusts both the 'data' and 'tail' pointers,
> but this attempt at a reversal is only modifying 'data'.
> 
> Your fix is fine, but really any by-hand modification of
> skb->data is a bug, and we should provide an skb_unreserve()
> or similar to hide such details away, and use it here.
> 
> Anton?

Yes, skb_unreserve() (or skb_reset_reserved() for naming consistency?)
would be great.

Ben, note that ucc_geth.c driver is also affected by that bug,
so I guess it needs a similar fix.

Thanks,

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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