linux-kernel - Re: [Bug #12155] Regression in 2.6.28-rc and 2.6.27-stable

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Date:	Tue, 16 Dec 2008 20:07:07 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Fabio Comolli <fabio.comolli@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Chuck Ebbert <cebbert@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [Bug #12155] Regression in 2.6.28-rc and 2.6.27-stable -
	hibernate related


* Rafael J. Wysocki <rjw@...k.pl> wrote:

> On Saturday, 13 of December 2008, Fabio Comolli wrote:
> > Hi.
> 
> Hi,
> 
> > On Sat, Dec 13, 2008 at 5:33 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > > This message has been generated automatically as a part of a report
> > > of recent regressions.
> > >
> > > The following bug entry is on the current list of known regressions
> > > from 2.6.27.  Please verify if it still should be listed and let me know
> > > (either way).
> > >
> > >
> > > Bug-Entry       : http://bugzilla.kernel.org/show_bug.cgi?id=12155
> > > Subject         : Regression in 2.6.28-rc and 2.6.27-stable - hibernate related
> > > Submitter       : Fabio Comolli <fabio.comolli@...il.com>
> > > Date            : 2008-11-23 16:17 (21 days old)
> > > References      : http://marc.info/?l=linux-kernel&m=122745709926361&w=4
> > 
> > Still present. It has been bisected to:
> > 
> > ---------------------------------------------------------------------------------------------------------------
> > commit 5e55aa8db085dad1aabb4574c73c23c7ae571e7b
> > Author: Dave Kleikamp <shaggy@...ux.vnet.ibm.com>
> > Date:   Sun Oct 26 18:20:14 2008 -0400
> > 
> >     sched_clock: prevent scd->clock from moving backwards
> > 
> >     commit 5b7dba4ff834259a5623e03a565748704a8fe449 upstream
> > 
> >     sched_clock: prevent scd->clock from moving backwards
> > 
> >     When sched_clock_cpu() couples the clocks between two cpus, it may
> >     increment scd->clock beyond the GTOD tick window that __update_sched_clock()
> >     uses to clamp the clock.  A later call to __update_sched_clock() may move
> >     the clock back to scd->tick_gtod + TICK_NSEC, violating the clock's
> >     monotonic property.
> > 
> >     This patch ensures that scd->clock will not be set backward.
> > 
> >     Signed-off-by: Dave Kleikamp <shaggy@...ux.vnet.ibm.com>
> >     Acked-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> >     Signed-off-by: Ingo Molnar <mingo@...e.hu>
> >     Cc: Chuck Ebbert <cebbert@...hat.com>
> >     Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
> > ------------------------------------------------------------------------------------------------------------
> > 
> > Both 2.6.27.8 and 2.6.28-rc8 with that commit reverted work fine
> > (well, at least they failed to show the bug so far).
> 
> Thanks for the update, I have put this information into the Bugzilla entry.
> 
> Would everyone involved agree with reverting the above commit for now 
> and revisiting the issue in the 2.6.29 time frame?

yeah - i think it's too late to do anything but a revert here.

	Ingo
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