linux-kernel - Re: [-mm patch] enforce noreplace-smp in alternative

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Message-Id: <1188043649.20041.81.camel@localhost.localdomain>
Date:	Sat, 25 Aug 2007 22:07:29 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Frederik Deweerdt <deweerdt@...e.fr>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Andi Kleen <ak@...e.de>,
	kraxel@...hat.com
Subject: Re: [-mm patch] enforce noreplace-smp in alternative_instructions()

On Fri, 2007-08-24 at 10:22 +0200, Frederik Deweerdt wrote:
> [Added Gerd Hoffman and Rusty Russel to cc]
> On Thu, Aug 23, 2007 at 11:46:52PM -0700, Jeremy Fitzhardinge wrote:
> > Frederik Deweerdt wrote:
> > > That means that even when you specify noreplace_smp, some replacing
> > > takes place anyway. One of the consequences, besides noreplace_smp not
> > > working as expected, is that lguest crashes when you feed it an SMP kernel
> > > (I suspect that you can not replace alternatives for smp _and_ paravirt).
> > >   
> > 
> > No, that should be fine.  Why does lguest crash?
> It dies with:
> [    0.131000] SMP alternatives: switching to UP code
> lguest: bad stack page 0xc057a000

How odd!  This means that the guest set the kernel to a stack which it
hadn't mapped writable (or perhaps not mapped at all).  I always run SMP
kernels, and that seems a very strange side effect of a patching
problem...

Nonetheless, I did have a previous problem with a bug in the patching
code which didn't show up native and did show up under lguest.

Can you send your config?  Do you need noreplace-smp even on 2.6.23-rc3,
or only 2.6.23-rc3-mm1?

Thanks,
Rusty.


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