netdev - Re: [PATCHv2] tcp: fix crash in tcp_xmit_retransmit

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Date:	Mon, 19 Jul 2010 19:39:08 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Cc:	Lennart Schulte <lennart.schulte@...s.rwth-aachen.de>,
	David Miller <davem@...emloft.net>, Tejun Heo <tj@...nel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Fehrmann, Henning" <henning.fehrmann@....mpg.de>,
	Carsten Aulbert <carsten.aulbert@....mpg.de>
Subject: Re: [PATCHv2] tcp: fix crash in tcp_xmit_retransmit_queue

Le lundi 19 juillet 2010 à 20:25 +0300, Ilpo Järvinen a écrit :

> This difference is well thought and intentional, I didn't use different 
> one by accident. We want to make sure we won't use NULL from 
> tcp_write_queue_head() while the pre 08ebd1721ab8fd3 kernels was 
> interested mainly whether the first loop should run or not (and of course 
> ends up avoid the null deref too but it's more optimization like 
> thing in there, ie., if there's no lost packets no work to-do). The deref 
> could have been fixed by moving TCP_SKB_CB(skb)->sacked a bit later but 
> that would again make us depend on the side-effect of the send_head check 
> (in the case of packets_out being zero and wq empty) which is something I 
> don't like too much.
> 

Thanks Ilpo.

Do you know in what exact circumstance the bug triggers ?

It's hard to believe thousand of machines on the Internet never hit
it :(

Maybe another problem in congestion control ?


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