From owner-freebsd-current@FreeBSD.ORG  Mon Sep  1 14:04:06 2003
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 5E19D16A4BF
	for <current@freebsd.org>; Mon,  1 Sep 2003 14:04:06 -0700 (PDT)
Received: from heron.mail.pas.earthlink.net (heron.mail.pas.earthlink.net
	[207.217.120.189])
	by mx1.FreeBSD.org (Postfix) with ESMTP id BDC1B43FDD
	for <current@freebsd.org>; Mon,  1 Sep 2003 14:04:05 -0700 (PDT)
	(envelope-from tlambert2@mindspring.com)
Received: from user-38ldup2.dialup.mindspring.com ([209.86.251.34]
	helo=mindspring.com)
	by heron.mail.pas.earthlink.net with asmtp (SSLv3:RC4-MD5:128)
	(Exim 3.33 #1)	id 19tvpl-0006tV-00; Mon, 01 Sep 2003 14:03:34 -0700
Message-ID: <3F53B3EF.2DC9F755@mindspring.com>
Date: Mon, 01 Sep 2003 14:02:39 -0700
From: Terry Lambert <tlambert2@mindspring.com>
X-Mailer: Mozilla 4.79 [en] (Win98; U)
X-Accept-Language: en
MIME-Version: 1.0
To: Pawel Jakub Dawidek <nick@garage.freebsd.pl>
References: <20030831070854.GA54748@panzer.kdm.org>
	<20030901064840.GA61253@panzer.kdm.org>
	<20030901103016.GI47959@garage.freebsd.pl>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-ELNK-Trace: b1a02af9316fbb217a47c185c03b154d40683398e744b8a46b5862f011f5f1bac3be32df2f85d759667c3043c0873f7e350badd9bab72f9c350badd9bab72f9c
cc: Poul-Henning Kamp <phk@phk.freebsd.dk>
cc: "Kenneth D. Merry" <ken@kdm.org>
cc: current@FreeBSD.org
Subject: Re: need some debugging help
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, 01 Sep 2003 21:04:06 -0000

Pawel Jakub Dawidek wrote:
> On Mon, Sep 01, 2003 at 12:48:41AM -0600, Kenneth D. Merry wrote:
> +>  - I tried just holding a mutex all the time, but obviously you can't
> +>    malloc while holding a mutex (except Giant), and the sysctl code does a
> +>    number of mallocs.  (The original cause of this problem -- M_WAITOK
> +>    mallocs.)
> 
> I've proposed some time ago changing M_WAITOK to M_NOWAIT, because
> function/macros responsible for sysctl creation could failed from other
> reasons, so I don't see any reason why they couldn't fail because of
> insufficient memory. Caller is obliged to check return value...

M_WAITOK is obliged to wait for fricking ever if it can't allocate
the memory, rather than failing and returning a NULL pointer that
then gets dereferenced because the function returned when the code
expected the traditional M_WAITOK semantics.

In other words, this problem derives from a semantics change, not
from any actual bug.

If you don't like it, then you need to change every instance of a
call to malloc with M_WAITOK to check its return value before using
it.  Doing this does'nt require introducing yet another semantic.

-- Terry