From owner-freebsd-current@FreeBSD.ORG  Mon Dec  8 14:04:39 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 3D1B616A4CE
	for <current@freebsd.org>; Mon,  8 Dec 2003 14:04:39 -0800 (PST)
Received: from dan.emsphone.com (dan.emsphone.com [199.67.51.101])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 2C74B43D33
	for <current@freebsd.org>; Mon,  8 Dec 2003 14:04:26 -0800 (PST)
	(envelope-from dan@dan.emsphone.com)
Received: (from dan@localhost)
	by dan.emsphone.com (8.12.10/8.12.10) id hB8M4JX0049099;
	Mon, 8 Dec 2003 16:04:19 -0600 (CST)
	(envelope-from dan)
Date: Mon, 8 Dec 2003 16:04:19 -0600
From: Dan Nelson <dnelson@allantgroup.com>
To: Kris Kennaway <kris@obsecurity.org>
Message-ID: <20031208220419.GB2435@dan.emsphone.com>
References: <1070918549.702.22.camel@klotz.local>
	<20031208214056.GA52416@xor.obsecurity.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20031208214056.GA52416@xor.obsecurity.org>
X-OS: FreeBSD 5.2-BETA
X-message-flag: Outlook Error
User-Agent: Mutt/1.5.5.1i
cc: current@freebsd.org
cc: Martin <nakal@web.de>
Subject: Re: Is "vm_fault" a kernel bug here?
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, 08 Dec 2003 22:04:39 -0000
X-List-Received-Date: Mon, 08 Dec 2003 22:04:39 -0000

In the last episode (Dec 08), Kris Kennaway said:
> On Mon, Dec 08, 2003 at 10:22:30PM +0100, Martin wrote:
> > Here is the result of a read access on a file, which is obviously
> > unreadable:
> > 
> > acd0: FAILURE - READ BIG status=51<READY,DSC,ERROR> sensekey=MEDIUM
> > ERROR error=4<ABORTED>
> > vm_fault: pager read error, pid 606 (cp)
> > cp: filename: Bad address
> > 
> > I want to report it, because of the "vm_fault", it sounds "scary".
> > Is this a correct behaviour or a bug in the kernel?
> 
> That's just what happens when an error is detected by the disk
> driver. This can be caused by hardware failure or incompatibility, or
> a driver bug.

More specifically, you get a vm_fault if the kernel is trying to page
in a block of memory for a process but can't.  The reason you get this
instead of a regular read error is because cp uses mmap() on files
smaller than 8 MB.

-- 
	Dan Nelson
	dnelson@allantgroup.com