linux-kernel - Re: KVM induced panic on 2.6.38[2367] & 2.6.39

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Message-ID: <4DE5853E.8040106@fnarfbargle.com>
Date:	Wed, 01 Jun 2011 08:18:06 +0800
From:	Brad Campbell <lists2009@...rfbargle.com>
To:	Hugh Dickins <hughd@...gle.com>
CC:	Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, linux-mm <linux-mm@...ck.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Izik Eidus <ieidus@...hat.com>
Subject: Re: KVM induced panic on 2.6.38[2367] & 2.6.39

On 01/06/11 06:31, Hugh Dickins wrote:
>
> Brad, my suspicion is that in each case the top 16 bits of RDX have been
> mysteriously corrupted from ffff to 0000, causing the general protection
> faults.  I don't understand what that has to do with KSM.

No, nor do I. The panic I reproduced with KSM off was in a completely 
unrelated code path. To be honest I would not be surprised if it turns 
out I have dodgy RAM, although it has passed multiple memtests and I've 
tried clocking it down. Just a gut feeling.

> But it's only a suspicion, because I can't make sense of the "Code:"
> lines in your traces, they have more than the expected 64 bytes, and
> only one of them has a ">" (with no"<") to mark faulting instruction.

Yeah, with hindsight I must have removed them when I re-formatted the 
code from the oops. Each byte was one line in the syslog so there was a 
lot of deleting to get it to a postable format.

> I did try compiling the 2.6.39 kernel from your config, but of course
> we have different compilers, so although I got close, it wasn't exact.
>
> Would you mind mailing me privately (it's about 73MB) the "objdump -trd"
> output for your original vmlinux (with KSM on)?  (Those -trd options are
> the ones I'm used to typing, I bet not they're not all relevant.)
>
> Of course, it's only a tiny fraction of that output that I need,
> might be better to cut it down to remove_rmap_item_from_tree and
> dup_fd and ksm_scan_thread, if you have the time to do so.

Ok, so since my initial posting I've figured out how to get a clean oops 
out of netconsole, so tonight (after 9PM GMT+8) I'll reproduce the oops 
a couple of times. What about I upload the oops, plus the vmlinux, plus 
.config and System.map to a server with a fat pipe and give you a link 
to it?

At least I can reproduce it quickly and easily.

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