Subject: Re: [3.15-rc3] Bisected: xen-netback mangles packets between two guests on a bridge since merge of "TX grant mapping with SKBTX_DEV_ZEROCOPY instead of copy" series.

From: Zoltan Kiss <[email-masked]>
Date: Wed, 30 Apr 2014 21:40:55 +0100

On 30/04/14 16:24, Eric Dumazet wrote:
> On Wed, 2014-04-30 at 12:45 +0200, Sander Eikelenboom wrote:
>
> This looks like skb->data_len is not properly set
>
> (Small note :
> alloc_page(GFP_ATOMIC|__GFP_COLD) should be a plain
> alloc_page(GFP_ATOMIC) : We prefer a page that has been used recently to
> avoid cache misses if possible.
> )
>
> This probably confuses skb_try_coalesce()
>
> My guess is xenvif_get_requests() forgets to init nskb->len /
> nskb->data_len for the skb that is attached to frag_list
xenvif_get_requests() calls alloc_skb() which inits these values to zero
>
> So the "skb->data_len += nskb->len;" at line 1353 is probably a nop.