From owner-freebsd-hackers@FreeBSD.ORG  Mon Dec 27 22:11:05 2004
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Delivered-To: freebsd-hackers@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id 3ADFB16A4CE
	for <freebsd-hackers@FreeBSD.org>;
	Mon, 27 Dec 2004 22:11:05 +0000 (GMT)
Received: from mail3.speakeasy.net (mail3.speakeasy.net [216.254.0.203])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 0B86443D39
	for <freebsd-hackers@FreeBSD.org>;
	Mon, 27 Dec 2004 22:11:05 +0000 (GMT)	(envelope-from jhb@FreeBSD.org)
Received: (qmail 22824 invoked from network); 27 Dec 2004 22:11:04 -0000
Received: from dsl027-160-063.atl1.dsl.speakeasy.net (HELO server.baldwin.cx)
	([216.27.160.63])          (envelope-sender <jhb@FreeBSD.org>)
	encrypted SMTP
	for <jengelh@linux01.gwdg.de>; 27 Dec 2004 22:11:04 -0000
Received: from [10.50.41.243] (gw1.twc.weather.com [216.133.140.1])
	(authenticated bits=0)
	by server.baldwin.cx (8.12.11/8.12.11) with ESMTP id iBRMArTL089244;
	Mon, 27 Dec 2004 17:10:59 -0500 (EST)
	(envelope-from jhb@FreeBSD.org)
From: John Baldwin <jhb@FreeBSD.org>
To: freebsd-hackers@FreeBSD.org
Date: Mon, 27 Dec 2004 15:38:11 -0500
User-Agent: KMail/1.6.2
References: <Pine.GSO.4.43.0412231700480.8053-100000@sea.ntplx.net>
	<Pine.LNX.4.61.0412241311530.19395@yvahk01.tjqt.qr>
In-Reply-To: <Pine.LNX.4.61.0412241311530.19395@yvahk01.tjqt.qr>
MIME-Version: 1.0
Content-Disposition: inline
Content-Type: text/plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Message-Id: <200412271538.11938.jhb@FreeBSD.org>
X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on server.baldwin.cx
Subject: Re: Kernel crash w/o reason
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
	<freebsd-hackers.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Mon, 27 Dec 2004 22:11:05 -0000

On Friday 24 December 2004 07:13 am, Jan Engelhardt wrote:
> >> What should I use instead? A semaphore?
> >
> >You shouldn't have unrelated kernel threads waiting for a user
> >process at all, so this sounds like a design problem, regardless
> >of which mutual exclusion primitive you use.  (Bear in mind that I
> >haven't actually looked into what you're trying to do.)  In any
> >case, you can always use mutexes to implement whatever other
> >synchronization mechanism you need.
>
> I wanted that the device can only be opened once, and holding a mutex while
> it is open seemed like a simple idea. (Since mtx_trylock() will then fail
> -- easy to implement.)

Use a flag in your softc and use a mutex to protect access to the flag.

-- 
John Baldwin <jhb@FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org