linux-kernel - Re: [Patch 1/4][kernel][slimdump] Add new elf-note of type NT

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Message-ID: <20111005071844.GB2235@in.ibm.com>
Date:	Wed, 5 Oct 2011 12:48:44 +0530
From:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-kernel@...r.kernel.org, crash-utility@...hat.com,
	kexec@...ts.infradead.org, Andi Kleen <andi@...stfloor.org>,
	"Luck, Tony" <tony.luck@...el.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>, anderson@...hat.com,
	tachibana@....nes.nec.co.jp, oomichi@....nes.nec.co.jp,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [Patch 1/4][kernel][slimdump] Add new elf-note of type
 NT_NOCOREDUMP to capture slimdump

On Tue, Oct 04, 2011 at 10:04:37AM -0400, Vivek Goyal wrote:
> On Mon, Oct 03, 2011 at 01:02:03PM +0530, K.Prasad wrote:
> > There are certain types of crashes induced by faulty hardware in which
> > capturing crashing kernel's memory (through kdump) makes no sense (or sometimes
> > dangerous).
> > 
> > A case in point, is unrecoverable memory errors (resulting in fatal machine
> > check exceptions) in which reading from the faulty memory location from the
> > kexec'ed kernel will cause double fault and system reset (leaving no
> > information for the user).
> 
> Prasad,
> 
> I am just trying to remember what was wrong with Andi's approach of
> disable MCE while copying the dump?
>

Hi Vivek,
	The behaviour upon a read operation on an UC memory location is
undefined and so we want to avoid it (previously discussed here:
http://article.gmane.org/gmane.linux.kernel/1146799). When we disable
MCE and copy the dump, we will invariably read the faulty memory
location.

Thanks,
K.Prasad
 
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