linux-kernel - Re: BUG: unable to handle kernel NULL pointer dereference at 00000002

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Date:	Tue, 29 Jul 2008 16:53:48 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Andi Kleen <andi@...stfloor.org>, Mike Galbraith <efault@....de>,
	Frederik Deweerdt <deweerdt@...e.fr>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	suresh.b.siddha@...el.com, Ingo Molnar <mingo@...e.hu>
Subject: Re: BUG: unable to handle kernel NULL pointer dereference at 00000002

On Tue, Jul 29, 2008 at 06:56:35AM -0700, Arjan van de Ven wrote:
> On Tue, 29 Jul 2008 14:09:11 +0200
> Andi Kleen <andi@...stfloor.org> wrote:
> 
> > On Tue, Jul 29, 2008 at 06:22:15AM +0200, Mike Galbraith wrote:
> > > On Tue, 2008-07-29 at 00:26 +0200, Frederik Deweerdt wrote:
> > > > Hello  Aneesh,
> > > > 
> > > > On Fri, Jul 25, 2008 at 03:23:17PM +0530, Aneesh Kumar K.V wrote:
> > > > > [  163.378265] BUG: unable to handle kernel NULL pointer
> > > > > dereference at 00000002 [  163.378276] IP: [<c0124933>]
> > > > > sched_power_savings_store+0x13/0x70
> > > > 
> > > > Does the attached patch solve the problem?
> > > 
> > > Patch seems to have missed the boat for rc1 too.
> > 
> > Hmm.  I'll resend. 
> > 
> > BTW i think it's clearly a  bug that distributions are even accessing
> > that file. It doesn't make any sense in the context they are using
> > it (like at every boot). 
> 
> it's a power saving feature that they very likely turn on by default...

A power saving feature that has a significant trade off between power
and performance. 

This means performance will go down. Perhaps it would be ok on  battery,
but it's a feature that only makes sense on servers which don't have batteries.
So enabling it by default in a standard installation seems quite wrong 
to me.

BTW opensuse seems to even set it to 2 which doesn't even exist. This means
there was a BOF at OLS discussing adding more modes, but right now there is 
only 0 or 1.

-Andi
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