From owner-cvs-all@FreeBSD.ORG  Wed Jun  9 09:33:08 2004
Return-Path: <owner-cvs-all@FreeBSD.ORG>
Delivered-To: cvs-all@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP
	id 0769A16A4CE; Wed,  9 Jun 2004 09:33:08 +0000 (GMT)
Received: from critter.freebsd.dk (critter.freebsd.dk [212.242.86.163])
	by mx1.FreeBSD.org (Postfix) with ESMTP
	id 3672C43D1D; Wed,  9 Jun 2004 09:33:07 +0000 (GMT)
	(envelope-from phk@phk.freebsd.dk)
Received: from critter.freebsd.dk (localhost [127.0.0.1])
	by critter.freebsd.dk (8.12.11/8.12.11) with ESMTP id i599X5Jq053419;
	Wed, 9 Jun 2004 11:33:05 +0200 (CEST)
	(envelope-from phk@phk.freebsd.dk)
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Wed, 09 Jun 2004 09:29:08 -0000."
             <200406090929.i599T8h6065944@repoman.freebsd.org> 
Date: Wed, 09 Jun 2004 11:33:05 +0200
Message-ID: <53418.1086773585@critter.freebsd.dk>
cc: cvs-src@FreeBSD.org
cc: src-committers@FreeBSD.org
cc: cvs-all@FreeBSD.org
Subject: Re: cvs commit: src/sys/kern kern_proc.c 
X-BeenThere: cvs-all@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: CVS commit messages for the entire tree <cvs-all.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/cvs-all>,
	<mailto:cvs-all-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/cvs-all>
List-Post: <mailto:cvs-all@freebsd.org>
List-Help: <mailto:cvs-all-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/cvs-all>,
	<mailto:cvs-all-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 09 Jun 2004 09:33:08 -0000

In message <200406090929.i599T8h6065944@repoman.freebsd.org>, Poul-Henning Kamp
 writes:
>
>  Modified files:
>    sys/kern             kern_proc.c 
>  Log:
>  Fix a race in destruction of sessions.

Not to pick on anybody, but this is a perfect example of getting locking
almost right:

BAD:

	LOCK(foo->lock)
	foo->refcount--;
	UNLOCK(foo->lock)
	if (foo->refcount == 0)
		destroy(foo);

GOOD:

	LOCK(foo->lock)
	i = --foo->refcount;
	UNLOCK(foo->lock)
	if (i == 0)
		destroy(foo);


-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.