From owner-freebsd-current@FreeBSD.ORG  Mon May  9 00:00:41 2005
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Delivered-To: freebsd-current@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP
	id 15FF416A4E6; Mon,  9 May 2005 00:00:41 +0000 (GMT)
Received: from carver.gumbysoft.com (carver.gumbysoft.com [66.220.23.50])
	by mx1.FreeBSD.org (Postfix) with ESMTP
	id E388043D86; Mon,  9 May 2005 00:00:40 +0000 (GMT)
	(envelope-from dwhite@gumbysoft.com)
Received: by carver.gumbysoft.com (Postfix, from userid 1000)
	id D7C4072DDB; Sun,  8 May 2005 17:00:40 -0700 (PDT)
Received: from localhost (localhost [127.0.0.1])
	by carver.gumbysoft.com (Postfix) with ESMTP id D24BD72DCB;
	Sun,  8 May 2005 17:00:40 -0700 (PDT)
Date: Sun, 8 May 2005 17:00:40 -0700 (PDT)
From: Doug White <dwhite@gumbysoft.com>
To: Kris Kennaway <kris@obsecurity.org>
In-Reply-To: <20050508233831.GA33797@xor.obsecurity.org>
Message-ID: <20050508165054.S77229@carver.gumbysoft.com>
References: <20050508231255.GA28688@xor.obsecurity.org>
	<20050508163107.A77229@carver.gumbysoft.com>
	<20050508233831.GA33797@xor.obsecurity.org>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
cc: dwhite@FreeBSD.org
cc: phk@freeBSD.org
cc: current@FreeBSD.org
Subject: Re: ptcwrite panic (with dump)
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Discussions about the use of FreeBSD-current
	<freebsd-current.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
	<mailto:freebsd-current-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current>
List-Post: <mailto:freebsd-current@freebsd.org>
List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
	<mailto:freebsd-current-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Mon, 09 May 2005 00:00:41 -0000

On Sun, 8 May 2005, Kris Kennaway wrote:

> $2 = (struct pgrp *) 0x0

Looks like t_pgrp became NULL between us checking it and us inspecting the
list attached to it. Nice.

Try moving the sx_slock(&proctree_lock); grab above the tp->t_pgrp NULL
check and add a sx_sunlock(&proctree_lock); inside that if() block.

I don't know if proctree_lock or the per-tty mutex protects the t_pgrp
item in struct tty.  In any case we need to pick up some lock to keep it
from going away :-)

I'll bash up a draft patch for discussion.

-- 
Doug White                    |  FreeBSD: The Power to Serve
dwhite@gumbysoft.com          |  www.FreeBSD.org