linux-kernel - Re: [RFC] Kdump and memory error handling

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Message-ID: <20110509172935.GD1963@in.ibm.com>
Date:	Mon, 9 May 2011 22:59:35 +0530
From:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Luck, Tony" <tony.luck@...el.com>,
	Vivek Goyal <vgoyal@...hat.com>, kexec@...ts.infradead.org,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>
Subject: Re: [RFC] Kdump and memory error handling

On Wed, May 04, 2011 at 10:39:14PM +0200, Andi Kleen wrote:
> > Any thoughts/suggestions?
> 
> My old attempts to solve this are
> 
> Don't dump on MCE:
> 
> http://git.kernel.org/?p=linux/kernel/git/ak/linux-mce-2.6.git;a=shortlog;h=refs/heads/mce/xpanic
> 

The problem we seen in avoiding a panic->crash_kexec->[coredump capture] is
that the user may not have a means to know the reason for crash, unless
the serial console is connected to capture and store the panic string.

Alternatively a 'slim' kdump (as described here:
https://lkml.org/lkml/2011/5/4/396) would not contain meaningless data from
the old memory, but inform the user about the cause of the crash. I'm
intending to post some patches with a quick implementation of it soon.

> Handle dumps of corrupted memory regresions:
> 
> http://git.kernel.org/?p=linux/kernel/git/ak/linux-mce-2.6.git;a=shortlog;h=refs/heads/mce/crashdump
> 

> IMHO these patches are still the right solutions for this.
> 

Like Vatsa had raised, the processor's behaviour upon reading (or any I/O
operation) the faulty memory location isn't clearly defined (to the
extent I read through System Programming Guide Part 1, Volume 3A,
Chapter 15). In such a scenario, disabling MCE for the kdump kernel (which can
potentially read the faulty memory) is making things hazy.

Thanks,
K.Prasad

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