Re: [Bug #12155] Regression in 2.6.28-rc and 2.6.27-stable - hibernate related

[Rafael J. Wysocki]

On Saturday, 13 of December 2008, Fabio Comolli wrote:
> Hi.

Hi,

> On Sat, Dec 13, 2008 at 5:33 PM, Rafael J. Wysocki <rjw@xxxxxxx> 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@xxxxxxxxx>
> > 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@xxxxxxxxxxxxxxxxxx>
> 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@xxxxxxxxxxxxxxxxxx>
>     Acked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
>     Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
>     Cc: Chuck Ebbert <cebbert@xxxxxxxxxx>
>     Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>
> ------------------------------------------------------------------------------------------------------------
> 
> 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?

Rafael


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