netdev - Re: [bug] stuck localhost TCP connections, v2.6.26-rc3+

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Date:	Sat, 31 May 2008 14:46:21 +0300 (EEST)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Ingo Molnar <mingo@...e.hu>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Evgeniy Polyakov <johnpol@....mipt.ru>
Subject: Re: [bug] stuck localhost TCP connections, v2.6.26-rc3+

On Sat, 31 May 2008, Ingo Molnar wrote:

> * Ingo Molnar <mingo@...e.hu> wrote:
> 
> > ah, in retrospect i realized that this test had one flaw: some of the 
> > systems i the build cluster already ran a newer kernel and hence were 
> > targets for this bug.
> > 
> > so i turned off CONFIG_TCP_CONG_CUBIC on all the testboxes and 
> > rebooted the cluster boxes into 2.6.25, and the hung sockets are now 
> > gone. (about 150 successful iterations)
> > 
> > i did another change as well: i removed the localhost distcc 
> > component. I'll reinstate that now to make sure it's really related to 
> > TCP_CONG_CUBIC and not to localhost networking.
> 
> ok, once i added back the localhost distcc component and the hung kernel 
> build + stuck TCP socket bug happened again overnight:
> 
>  Active Internet connections (w/o servers)
>  Proto Recv-Q Send-Q Local Address               Foreign Address             State
>  tcp    72187      0 10.0.1.14:3632              10.0.1.14:47910             ESTABLISHED
>  tcp        0 174464 10.0.1.14:47910             10.0.1.14:3632              ESTABLISHED
> 
> so it seems distcc over localhost was the aspect that made it fail.
> 
> _Perhaps_ what matters is to have the new post-rc3 TCP code on _both_ 
> sides of the connection. But that is just a theory - it could be timing, 
> etc.

Btw, does your distcc perhaps happen enable TCP_DEFER_ACCEPT (there were
some post 2.6.25 changes into it)?

-- 
 i.
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