linux-kernel - Re: 2.6.{26.2,27-rc} oops on virtualbox

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Date:	Tue, 26 Aug 2008 21:27:34 +0200
From:	Gerhard Brauer <gerhard.brauer@....de>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	"Luiz Fernando N. Capitulino" <lcapitulino@...driva.com.br>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: 2.6.{26.2,27-rc} oops on virtualbox

On Tue, Aug 26, 2008 at 10:53:38AM -0400, Mathieu Desnoyers wrote:
> * Gerhard Brauer (gerhard.brauer@....de) wrote:
> > 
> > Here is also an archive with guest dmesg and messages.log from such an
> > oops when heavy disk io leads to the oops:
> > http://bugs.archlinux.org/task/11141?getfile=2445
> > 
> 
> Hrm, can you try this ?

Sorry for the delay but i need to build a complete distribution kernel
and my machine is not the fastest.

My host:
archlinux 2.6.26 P4 2Ghz
VirtualBox: Sun xVM 1.6.4
gcc 4.4.1-3

My guest:
archlinux 2.6.26

My "tests":
I could sometimes boot the guest with the "tricks" (VT-x enabled, acpi
off,...). But i always get an oops if i compile something bigger on this
guest (ex. virtualbox-modules where the tarball must be untarrt with
bsdtar -> disk io)
If this happens the next reboot leads always to the early oops (Freeing
smp....). Each reboot do this. Then i close virtualbox application,
unload/reload vboxdrv from host and start vbox again. Then i could
mostimes boot the guest again. But next heavy disk IO leads again to the
oops.
If i could boot without oops, and reboot or halt the guest, then the
next boots are clean.

> 1 - Make sure you kernel is not CONFIG_DEBUG_RODATA
Not set.

> 2 - Change the whole text_poke implementation in
> arch/x86/kernel/alternative.c to this :
With this changes i also get the oops, in all above mentioned tests.

> Then, after having tested (2), try this on top of it :
> 
> In arch/x86/kernel/alternative.c, alternatives_smp_switch()
> 
> Add   unsigned long flags;
> Change 
> spin_lock -> spin_lock_irqsave(&smp_alt, flags);
> spin_unlock(&smp_alt); -> spin_unlock_irqrestore(&smp_alt, flags);

With our distribution kernel i could change these spin_lock/unlock in
alternatives.c. Fist thought was that there was a slightly better
behavior (first boot goes on, i could compile something, but next
package i build thee opps (heavy io opps) comes again. And then also
after reboot the early oops (freeing smp...)
Here is a screenie from oops when building something:
http://users.archlinux.de/~gerbra/tmp/2008-08-26-210724_724x456_scrot.png

Sometimes (could not be reproduced) the virtualbox app also traps with
an error dialog (Guru message), which offers a log from the VM and a
scren shot. Maybe this could be helpfull. Log and screenie could be
found here:
http://users.archlinux.de/~gerbra/tmp/vbox-guru/

> 
> This will help testing if there is a problem with interrupts coming
> shortly after the modification. If it fixes the problem, my guess is
> that we should flush the instruction cache (and maybe the data cache ?)
> in text_poke and text_poke early when interrupts are off.

>From my side i would say: both changes would not solve the oops.

> Mathieu

Regards
	Gerhard

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