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Date:      Fri, 1 Apr 2005 20:26:03 -0800 (PST)
From:      Doug White <dwhite@gumbysoft.com>
To:        Gary Mu1der <gmulder@infotechfl.com>
Cc:        freebsd-amd64@freebsd.org
Subject:   Re: Tyan k8sr lockups
Message-ID:  <20050401201907.U95587@carver.gumbysoft.com>
In-Reply-To: <424DA4B3.3070703@infotechfl.com>
References:  <f0111a98c01333b3c306c81d10294de4@khera.org> <Pine.SOC.4.61.0503300229560.3181@tea.blinkenlights.nl> <424C215E.5080201@infotechfl.com><424C4EED.5070601@infotechfl.com> <424D58F7.1010005@infotechfl.com><424DA4B3.3070703@infotechfl.com>

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On Fri, 1 Apr 2005, Gary Mu1der wrote:

> I have isolated the crash to the following dd command:
>
> 	dd if=/dev/mem of=/dev/null bs=1024k skip=4040 count=1

Reading from random places in /dev/mem will cause unpredicatable behavior.
Memory at that offset is in PCI memory-mapped device space, and reading
from there may disrupt the PCI bridge, enable or disable interrupts, or
worse.

-- 
Doug White                    |  FreeBSD: The Power to Serve
dwhite@gumbysoft.com          |  www.FreeBSD.org



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