netdev - Re: [PATCH 2/2] net: ip, ipv6: handle gso skbs in forwarding path

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Date:	Mon, 10 Feb 2014 13:23:31 +0100
From:	Florian Westphal <fw@...len.de>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Florian Westphal <fw@...len.de>, netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] net: ip, ipv6: handle gso skbs in forwarding path

Herbert Xu <herbert@...dor.apana.org.au> wrote:
> > > static void ip_gso_adjust_seglen(struct sk_buff *skb)
> > > {
> > >         unsigned int mtu;
> > > 
> > >         if (!skb_is_gso(skb))
> > >                 return;
> > > 
> > >         mtu = ip_dst_mtu_maybe_forward(skb_dst(skb), true);
> > >         skb_shinfo(skb)->gso_size = mtu - sizeof(struct iphdr);
> > > }
> > > 
> > > But this yields
> > > 
> > > [   28.644776] kernel BUG at net/net/core/skbuff.c:2984!
> > 
> > Yep, lets CC Herbert Xu, as he 'owns' skb_segment()
> 
> IMHO we should just stop merging ~DF packets altogether, at least
> for TCP.

Eric, you added DF aggregation in db8caf3dbc77599dc90f4ea0a803cd1d97116f30
(gro: should aggregate frames without DF).

I guess you don't want to revert this commit?
Any other ideas?

skb_gso_segment() is already very complex, I don't want to add more code
to it.  And that seems unavoidable if we need to de-couple nr_frags and
gso_size.
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