linux-kernel - Re: [fixed] [patch] Re: [bug] stuck localhost TCP connections, v2.6.26-rc3+

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Message-ID: <Pine.LNX.4.64.0806040927410.16057@wrl-59.cs.helsinki.fi>
Date:	Wed, 4 Jun 2008 09:42:58 +0300 (EEST)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Patrick McManus <mcmanus@...ksong.com>
cc:	David Miller <davem@...emloft.net>, mingo@...e.hu,
	peterz@...radead.org, LKML <linux-kernel@...r.kernel.org>,
	Netdev <netdev@...r.kernel.org>, rjw@...k.pl,
	Andrew Morton <akpm@...ux-foundation.org>, johnpol@....mipt.ru
Subject: Re: [fixed] [patch] Re: [bug] stuck localhost TCP connections,
 v2.6.26-rc3+

On Tue, 3 Jun 2008, Patrick McManus wrote:

> On Wed, 2008-06-04 at 02:22 +0300, Ilpo Järvinen wrote:
> ==
> > --
> > [PATCH] tcp DEFER_ACCEPT: fix racy access to listen_sk
> > 
> > It seems that replacement of DA code also moved parts outside
> > of appropriate locking. The Ingo's problem seems to come from
> > the fact that two flows could now race in
> > (inet_csk_)reqsk_queue_add corrupting the queue. ...This can
> > leave dangling socks around which won't resolve themselves
> > without stimuli from outside (e.g., external RST would help
> > I think).

> do_rcv() clearly has the listening socket locked in the non-DA case, and
> in the DA case it is the 'child' ESTABLISHED socket that is locked -
> leaving the accept queue unprotected. So simple.

It also well explains why Ingo finally got the KERNEL: assertion 
(!sk->sk_ack_backlog) which is adjusted in the very same reqsk_queue_add 
making it and the actual queue come out of sync.

...too bad this has no relevance to Håkon's case, so more digging
is necessary... :-)

-- 
 i.