netdev - Re: [PATCH net-next] tcp: gso: fix truesize tracking

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Message-Id: <20131028.005835.2085407982365928314.davem@davemloft.net>
Date:	Mon, 28 Oct 2013 00:58:35 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	ast@...mgrid.com, edumazet@...gle.com, stephen@...workplumber.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] tcp: gso: fix truesize tracking

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 25 Oct 2013 17:26:17 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> commit 6ff50cd55545 ("tcp: gso: do not generate out of order packets")
> had an heuristic that can trigger a warning in skb_try_coalesce(),
> because skb->truesize of the gso segments were exactly set to mss.
> 
> This breaks the requirement that
> 
> skb->truesize >= skb->len + truesizeof(struct sk_buff);
> 
> It can trivially be reproduced by :
> 
> ifconfig lo mtu 1500
> ethtool -K lo tso off
> netperf
> 
> As the skbs are looped into the TCP networking stack, skb_try_coalesce()
> warns us of these skb under-estimating their truesize.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Alexei Starovoitov <ast@...mgrid.com>
> ---
> Based on net-next but applies as well on net tree with some fuzz.
> 
> David, we might backport this one to 3.12 and stable later, I let you
> decide.

I'm still thinking about what to do with this one.
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