From owner-freebsd-net@FreeBSD.ORG  Fri Dec 14 19:46:12 2007
Return-Path: <owner-freebsd-net@FreeBSD.ORG>
Delivered-To: net@FreeBSD.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 6A35416A419
	for <net@FreeBSD.org>; Fri, 14 Dec 2007 19:46:12 +0000 (UTC)
	(envelope-from julian@elischer.org)
Received: from outP.internet-mail-service.net (outP.internet-mail-service.net
	[216.240.47.239])
	by mx1.freebsd.org (Postfix) with ESMTP id 44E4C13C457
	for <net@FreeBSD.org>; Fri, 14 Dec 2007 19:46:12 +0000 (UTC)
	(envelope-from julian@elischer.org)
Received: from mx0.idiom.com (HELO idiom.com) (216.240.32.160)
	by out.internet-mail-service.net (qpsmtpd/0.40) with ESMTP;
	Fri, 14 Dec 2007 11:46:11 -0800
Received: from julian-mac.elischer.org (localhost [127.0.0.1])
	by idiom.com (Postfix) with ESMTP id 9E050126CD9;
	Fri, 14 Dec 2007 11:46:10 -0800 (PST)
Message-ID: <4762DD82.9070904@elischer.org>
Date: Fri, 14 Dec 2007 11:46:10 -0800
From: Julian Elischer <julian@elischer.org>
User-Agent: Thunderbird 2.0.0.9 (Macintosh/20071031)
MIME-Version: 1.0
To: Gleb Smirnoff <glebius@FreeBSD.org>
References: <20071213133817.GC71713@elvis.mu.org>
	<47617AF5.7070701@elischer.org>
	<20071214092539.GB14339@glebius.int.ru>
In-Reply-To: <20071214092539.GB14339@glebius.int.ru>
Content-Type: text/plain; charset=KOI8-R; format=flowed
Content-Transfer-Encoding: 7bit
Cc: Maxime Henrion <mux@FreeBSD.org>, net@FreeBSD.org
Subject: Re: Deadlock in the routing code
X-BeenThere: freebsd-net@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Networking and TCP/IP with FreeBSD <freebsd-net.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-net>,
	<mailto:freebsd-net-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-net>
List-Post: <mailto:freebsd-net@freebsd.org>
List-Help: <mailto:freebsd-net-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-net>,
	<mailto:freebsd-net-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 14 Dec 2007 19:46:12 -0000

Gleb Smirnoff wrote:
> On Thu, Dec 13, 2007 at 10:33:25AM -0800, Julian Elischer wrote:
> J>  Maxime Henrion wrote:
> J> > Replying to myself on this one, sorry about that.
> J> > I said in my previous mail that I didn't know yet what process was
> J> > holding the lock of the rtentry that the routed process is dealing
> J> > with in rt_setgate(), and I just could verify that it is held by
> J> > the swi1: net thread.
> J> > So, in a nutshell:
> J> > - The routed process does its business on the routing socket, that ends up
> J> >   calling rt_setgate().  While in rt_setgate() it drops the lock on its
> J> >   rtentry in order to call rtalloc1().  At this point, the routed
> J> >   process hold the gateway route (rtalloc1() returns it locked), and it
> J> >   now tries to re-lock the original rtentry.
> J> > - At the same time, the swi net thread calls arpresolve() which ends up
> J> >   calling rt_check().  Then rt_check() locks the rtentry, and tries to
> J> >   lock the gateway route.
> J> > A classical case of deadlock with mutexes because of different locking
> J> > order.  Now, it's not obvious to me how to fix it :-).
> J> 
> J>  On failure to re-lock, the routed call to rt_setgate should completely abort 
> J>  and restart from scratch, releasing all locks it has on the way out.
> 
> Do you suggest mtx_trylock?

I think that would be the cleanest way..

>