linux-kernel - Re: [Regression 3.4] tick_broadcast_mask is not restored after a CPU has been offline/onlined

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Date:	Mon, 30 Jul 2012 21:09:56 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Feng Tang <feng.tang@...el.com>
Cc:	"Paul E. McKenney" <paul.mckenney@...aro.org>,
	Len Brown <len.brown@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mail List <linux-kernel@...r.kernel.org>
Subject: Re: [Regression 3.4] tick_broadcast_mask is not restored after a CPU
 has been offline/onlined

On Tue, Jul 31, 2012 at 11:18:32AM +0800, Feng Tang wrote:
> Hi Paul,
> 
> On Mon, 30 Jul 2012 10:42:18 -0700
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > On Mon, Jul 30, 2012 at 10:08:47AM -0700, Paul E. McKenney wrote:
> > > On Mon, Jul 30, 2012 at 11:07:47PM +0800, Feng Tang wrote:
> > > > Hi Paul,
> > > > 
> > > > On Mon, 30 Jul 2012 06:39:13 -0700
> > > > "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> > > > 
> > > > > On Mon, Jul 30, 2012 at 03:15:59PM +0800, Feng Tang wrote:
> > > > > > Hi All,
> > > > > > 
> > > > > > When I debugged a suspend/resume bug, I found that
> > > > > > tick_broadcast_mask is not restored for a CPU after it is
> > > > > > offline/onlined since kernel 3.4, while it's fine for 3.3.
> > > > > 
> > > > > Could you please try 3.5?
> > > > 
> > > > Yes, it's the same for 3.5
> > > 
> > > Thank you for checking, Feng.
> > > 
> > > Len, the comment above the change says:
> > > 
> > > 	/*
> > > 	 * FIXME:  Design the ACPI notification to make it once per
> > > 	 * system instead of once per-cpu.  This condition is a hack
> > > 	 * to make the code that updates C-States be called once.
> > > 	 */
> > > 
> > > Is it time for this design-level change?  Or is there something obvious
> > > that I missed when fixing the smp_processor_id() splat?
> > > 
> > > I could revert back, but use raw_smp_processor_id() rather than
> > > smp_processor_id(), but that feels like papering over a problem rather
> > > than fixing it.
> > 
> > But should papering be appropriate, here is the patch.
> > 
> > 							Thanx, Paul
> 
> Just found and have a patch to fix a typo in acpi processor_driver.c, which
> could also fix  this tick_broadcast_mask issue.
> 	
> Patch is in https://lkml.org/lkml/2012/7/30/483 
> 
> So I think we don't need this "papering over" patch :)

Very good, I have dropped it.

							Thanx, Paul

> Thanks,
> Feng
> 
> > 
> > ------------------------------------------------------------------------
> > 
> > ACPI: Repair fix to unprotected smp_processor_id()
> > 
> > Commit 9505626d (ACPI: Fix unprotected smp_processor_id() in
> > acpi_processor_cst_has_changed()) introduced a suspend/resume bug.
> > This commit therefore introduces a bug-for-bug compatible fix for the
> > original problem.
> > 
> > Reported-by: Feng Tang <feng.tang@...el.com>
> > Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>
> > 
> > diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> > index 47a8caa..19c151a 100644
> > --- a/drivers/acpi/processor_idle.c
> > +++ b/drivers/acpi/processor_idle.c
> > @@ -1218,7 +1218,8 @@ int acpi_processor_cst_has_changed(struct
> > acpi_processor *pr)
> >  	 * to make the code that updates C-States be called once.
> >  	 */
> >  
> > -	if (pr->id == 0 && cpuidle_get_driver() == &acpi_idle_driver) {
> > +	if (raw_smp_processor_id() == 0 &&
> > +	    cpuidle_get_driver() == &acpi_idle_driver) {
> >  
> >  		cpuidle_pause_and_lock();
> >  		/* Protect against cpu-hotplug */
> > 
> 

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