Re: [PATCH v2] tcp: fix MSG_PEEK race check

[David Miller <davem@davemloft.net>]

From: "Ilpo Järvinen" <ilpo.jarvinen@helsinki.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 :-)