From owner-freebsd-threads@FreeBSD.ORG  Fri Apr 18 03:49:59 2003
Return-Path: <owner-freebsd-threads@FreeBSD.ORG>
Delivered-To: freebsd-threads@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP
	id BA85A37B401; Fri, 18 Apr 2003 03:49:59 -0700 (PDT)
Received: from fledge.watson.org (fledge.watson.org [204.156.12.50])
	by mx1.FreeBSD.org (Postfix) with ESMTP
	id DC94343F85; Fri, 18 Apr 2003 03:49:58 -0700 (PDT)
	(envelope-from robert@fledge.watson.org)
Received: from fledge.watson.org (fledge.pr.watson.org [192.0.2.3])
	by fledge.watson.org (8.12.9/8.12.9) with SMTP id h3IAoDua039356;
	Fri, 18 Apr 2003 06:50:14 -0400 (EDT)
	(envelope-from robert@fledge.watson.org)
Date: Fri, 18 Apr 2003 06:50:12 -0400 (EDT)
From: Robert Watson <rwatson@freebsd.org>
X-Sender: robert@fledge.watson.org
To: Terry Lambert <tlambert2@mindspring.com>
In-Reply-To: <3E9FAE89.4D656F38@mindspring.com>
Message-ID: <Pine.NEB.3.96L.1030418063854.24445U-100000@fledge.watson.org>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
cc: freebsd-threads@freebsd.org
cc: David Xu <davidxu@freebsd.org>
cc: Daniel Eischen <eischen@pcnet1.pcnet.com>
Subject: Re: libpthread patch
X-BeenThere: freebsd-threads@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Threading on FreeBSD <freebsd-threads.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-threads>,
	<mailto:freebsd-threads-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-threads>
List-Post: <mailto:freebsd-threads@freebsd.org>
List-Help: <mailto:freebsd-threads-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-threads>,
	<mailto:freebsd-threads-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 18 Apr 2003 10:50:00 -0000


On Fri, 18 Apr 2003, Terry Lambert wrote:

> You are allowed to recurse on a mutex in the kernel, because there's
> some depth to code paths that shouldn't be there, but it's easier to
> allow recursion than it is to correct the code. 

By default, mutexes are not permitted to be recursed, and recursing them
will cause a panic.  Recursion is only permitted if the MTX_RECURSE flag
is set at mutex initialization time, which is strongly discouraged.  There
are several mutex in the kernel where the flag is set, but I hope to see
the list remain small (and go down).  A quick grep of of kern shows four
classes of mutexes with MTX_RECURSE set (one is Giant), and 57 without
(approximately).  The IP stack locking, on the other hand, has four mutex
classes, of which two permit recursion (PCB locks).

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert@fledge.watson.org      Network Associates Laboratories