netdev - Re: Suspicious fackets

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Message-Id: <20070531.125929.77054675.davem@davemloft.net>
Date:	Thu, 31 May 2007 12:59:29 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	ilpo.jarvinen@...sinki.fi
Cc:	netdev@...r.kernel.org
Subject: Re: Suspicious fackets_out handling

From: "Ilpo_Järvinen" <ilpo.jarvinen@...sinki.fi>
Date: Mon, 23 Apr 2007 14:28:21 +0300 (EEST)

> There are IMHO two problems in it. First of all, nothing ensures that the 
> skb TCP is fragmenting is actually below the forwardmost sack block (and 
> thus is included to the fackets_out)...

Good catch, I agree with your analysis completely.

> What I'm not sure of though, is how to fix this in net-2.6(.22), it
> is due to the fact that there is no pointer/seq which can be used in
> testing for it like in tcp-2.6 which has the highest_sack.

We can add highest_sack to 2.6.22 in order to fix a bug like this,
if necessary.

> Second problem is even more obvious: if adjustment here is being
> done and the sacktag code then uses fastpath at the arrival of the
> next ACK, the sacktag code will use a stale value from
> fastpath_cnt_hint and fails to notice all that math TCP did here
> unless we start clearing fastpath_skb_hint.

Let's try not to clear fastpath_skb_hint here if possible :-)

Is it possible to update fastpath_cnt_hint properly perhaps?
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