netdev - Re: [PATCH v2] tcp: fix MSG

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Message-Id: <20090517.153127.22116458.davem@davemloft.net>
Date:	Sun, 17 May 2009 15:31:27 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	ilpo.jarvinen@...sinki.fi
Cc:	elendil@...net.nl, matthias.andree@....de, netdev@...r.kernel.org
Subject: Re: [PATCH v2] tcp: fix MSG_PEEK race check

From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
Date: Mon, 11 May 2009 17:57:13 +0300 (EEST)

> On Mon, 11 May 2009, Frans Pop wrote:
> 
>> On Monday 11 May 2009, Ilpo Järvinen wrote:
>> OK. I understood that there's always been a corner case with URG that 
>> could cause incorrect messages [1] and I thought the additional change 
>> was to fix that, but if this is related to the same regression then of 
>> course it's fine by me.
>> 
>> [1] http://linux.derkeiler.com/Mailing-Lists/Kernel/2003-09/6009.html
> 
> Ah, so there's some urg race for real... ...I didn't know about that
> which is no wonder since I've very little interest on knowing all
> corner cases of urg madness really :-).
> 
> I guess it is not exactly the same though I have problem in understanding 
> what Dave is exactly meaning there but it could well be that there isn't 
> a sane case where the urg hole thing matters for real. Well, Dave probably 
> knows whether the v2 is necessary or not, I've no clue who is the one 
> advancing the copied_seq (if it's not the gem in tcp_check_urg doing the 
> conditional copied_seq++, but that condition is beyond my current level of 
> concentration really).

The issue being discussed there is exactly the case where a thread
is triggering the copied_seq advance in tcp_check_urg() and using
MSG_PEEK at the same time.

I'm looking more closely into this patch right now, but I might ask
you to split the two fixes up if I can't convince myself %100 of the
URG part.  We've already broken URG enough lately :-)
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