From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1757962Ab1ANQeQ (ORCPT <rfc822;w@1wt.eu>);
	Fri, 14 Jan 2011 11:34:16 -0500
Received: from e39.co.us.ibm.com ([32.97.110.160]:60918 "EHLO
	e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1757650Ab1ANQeE (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Fri, 14 Jan 2011 11:34:04 -0500
Subject: Re: [PATCH] acpi/pm: If failed at validating ACPI PM timer,
 inhibit future reads.
From: john stultz <johnstul@us.ibm.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Jeremy Fitzhardinge <jeremy@goop.org>,
        Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
        Ian Campbell <Ian.Campbell@eu.citrix.com>, mingo@redhat.com,
        hpa@zytor.com, linux-kernel@vger.kernel.org, andi@firstfloor.org,
        williams@redhat.com, schwidefsky@de.ibm.com, mingo@elte.hu,
        linux-tip-commits@vger.kernel.org
In-Reply-To: <alpine.LFD.2.00.1101141701360.2678@localhost6.localdomain6>
References: <tip-08ec0c58fb8a05d3191d5cb6f5d6f81adb419798@git.kernel.org>
	 <20110111081352.GA22867@shutemov.name>
	 <alpine.LFD.2.00.1101110926040.12146@localhost6.localdomain6>
	 <20110111083054.GB22867@shutemov.name>
	 <alpine.LFD.2.00.1101110936291.12146@localhost6.localdomain6>
	 <20110111095640.GC22867@shutemov.name>
	 <20110113174909.GA28738@dumpdata.com> <1294941698.5617.12.camel@work-vm>
	 <20110113214022.GA12097@dumpdata.com>
	 <alpine.LFD.2.00.1101132301300.2678@localhost6.localdomain6>
	 <20110114140941.GA3062@dumpdata.com>  <1295019849.2655.8.camel@work-vm>
	 <1295020487.2655.17.camel@work-vm>
	 <alpine.LFD.2.00.1101141701360.2678@localhost6.localdomain6>
Content-Type: text/plain; charset="UTF-8"
Date: Fri, 14 Jan 2011 08:33:49 -0800
Message-ID: <1295022829.2655.18.camel@work-vm>
Mime-Version: 1.0
X-Mailer: Evolution 2.30.3 
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, 2011-01-14 at 17:02 +0100, Thomas Gleixner wrote:
> On Fri, 14 Jan 2011, john stultz wrote:
> 
> > On Fri, 2011-01-14 at 07:44 -0800, john stultz wrote:
> > > I'm actually looking at a different fix, as I'm worried by Thomas'
> > > comment about hitting the same issue on real hardware if we catch the
> > > same pmtrm value both times.
> > 
> > Konrad: Mind trying the following?
> > 
> > 
> > The conditional (!hpet && !ref_start && !ref_stop) doesn't really make
> > sense. If the refs are null, but hpet is on, we still want to break out.
> > 
> > So checking if both the ref values are the same should handle if we
> > don't have hardware (both null) or if they are the same value (either by
> > invalid hardware, or by chance), which can cause a divzero issue.
> > 
> > NOT FOR INCLUSION, I haven't had my coffee yet.
> > Signed-off-by: John Stultz <johnstul@us.ibm.com>
> > 
> > diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> > index 823f79a..fa2cb5e 100644
> > --- a/arch/x86/kernel/tsc.c
> > +++ b/arch/x86/kernel/tsc.c
> > @@ -935,7 +935,7 @@ static void tsc_refine_calibration_work(struct work_struct *work)
> >  	tsc_stop = tsc_read_refs(&ref_stop, hpet);
> >  
> >  	/* hpet or pmtimer available ? */
> > -	if (!hpet && !ref_start && !ref_stop)
> > +	if (ref_start == ref_stop)
> >  		goto out;
> >  
> >  	/* Check, whether the sampling was disturbed by an SMI */
> 
> That makes sense, though we really should kill pmtimer when we detect
> that it's crappy.

Agreed. 

thanks
-john