Date: Sun, 30 Nov 2008 21:14:05 +0100 From: "Julian Stacey" <jhs@berklix.org> To: Andriy Gapon <avg@icyb.net.ua>, freebsd-hackers@freebsd.org Subject: Re: dd if=/dev/mem can hang a machine? Message-ID: <200811302014.mAUKE5YF046736@fire.js.berklix.net> In-Reply-To: Your message "Sun, 30 Nov 2008 16:24:37 %2B0100." <20081130162437.1bae4371@ernst.jennejohn.org>
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Gary Jennejohn wrote: > On Fri, 28 Nov 2008 15:28:35 +0200 > Andriy Gapon <avg@icyb.net.ua> 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
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