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

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Message-ID: <20080531060947.GA26441@elte.hu>
Date:	Sat, 31 May 2008 08:09:47 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Ilpo J?rvinen <ilpo.jarvinen@...sinki.fi>
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>
Subject: Re: [bug] stuck localhost TCP connections, v2.6.26-rc3+


* 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.

	Ingo
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