From owner-freebsd-hackers@FreeBSD.ORG Sun Nov 30 20:31:45 2008 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id A7F321065673 for ; Sun, 30 Nov 2008 20:31:45 +0000 (UTC) (envelope-from jhs@berklix.org) Received: from flat.berklix.org (flat.berklix.org [83.236.223.115]) by mx1.freebsd.org (Postfix) with ESMTP id 263C08FC13 for ; Sun, 30 Nov 2008 20:31:44 +0000 (UTC) (envelope-from jhs@berklix.org) Received: from js.berklix.net (p549A55D6.dip.t-dialin.net [84.154.85.214]) (authenticated bits=0) by flat.berklix.org (8.13.8/8.13.8) with ESMTP id mAUKEVii031710; Sun, 30 Nov 2008 21:14:36 +0100 (CET) (envelope-from jhs@berklix.org) Received: from fire.js.berklix.net (fire.js.berklix.net [192.168.91.41]) by js.berklix.net (8.13.8/8.13.8) with ESMTP id mAUKEKaV042230; Sun, 30 Nov 2008 21:14:21 +0100 (CET) (envelope-from jhs@berklix.org) Received: from fire.js.berklix.net (localhost [127.0.0.1]) by fire.js.berklix.net (8.14.3/8.14.3) with ESMTP id mAUKE5YF046736; Sun, 30 Nov 2008 21:14:15 +0100 (CET) (envelope-from jhs@fire.js.berklix.net) Message-Id: <200811302014.mAUKE5YF046736@fire.js.berklix.net> To: Andriy Gapon , freebsd-hackers@freebsd.org From: "Julian Stacey" Organization: http://berklix.com BSD Unix Linux Consultancy, Munich Germany User-agent: EXMH on FreeBSD http://berklix.com/free/ X-URL: http://berklix.com In-reply-to: Your message "Sun, 30 Nov 2008 16:24:37 +0100." <20081130162437.1bae4371@ernst.jennejohn.org> Date: Sun, 30 Nov 2008 21:14:05 +0100 Sender: jhs@berklix.org Cc: Subject: Re: dd if=/dev/mem can hang a machine? X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 30 Nov 2008 20:31:45 -0000 Gary Jennejohn wrote: > On Fri, 28 Nov 2008 15:28:35 +0200 > Andriy Gapon wrote: > > > > > I have a new machine with DG33TL mainboard (ICH9/G33). > > In a course of some hacking I ran dd if=/dev/mem ... to scan all memory, > > this caused the machine to hang. > > I tried to reproduce and this is 100% reproducible. > > > > I am not used to such behavior. In older days I could scan all the > > memory without any issues. > > > > Could this be related to some modern form of memory-mapped IO? Or to > > Intel Management Engine (that seems t bite into DRAM)? > > Or something else? > > > > Just wondering. > > > > That's what I would assume. With some hardware just reading a register > can be harmful. I just crashed 3 normally stable machines trying that. I only tried for casual interest. I acknowledge Gary's comment above :-) dd if=/dev/mem of=/dev/null FreeBSD lapa.js.berklix.net 4.11-RELEASE FreeBSD 4.11-RELEASE #0: Fri Jul 7 17:56:30 CEST 2006 jhs@lapa.jhs.private:/usr/src/sys/compile/LAPA.small i386 FreeBSD laps.js.berklix.net 7.0-RELEASE FreeBSD 7.0-RELEASE #2: Mon Sep 8 15:39:53 CEST 2008 jhs@laps.js.berklix.net:/usr1/ftp/pri/FreeBSD/releases/7.0-RELEASE/src/sys/i386/compile/LAPS.small i386 FreeBSD john.js.berklix.net 7.1-BETA2 FreeBSD 7.1-BETA2 #0: Sun Oct 12 20:59:28 UTC 2008 root@driscoll.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC amd64 Cheers, Julian -- Julian Stacey: BSDUnixLinux C Prog Admin SysEng Consult Munich www.berklix.com Mail plain ASCII text. HTML & Base64 text are spam. www.asciiribbon.org