linux-kernel - Re: perf,arm -- oops in validate

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Message-ID: <20130807135437.GD28558@e106331-lin.cambridge.arm.com>
Date:	Wed, 7 Aug 2013 14:54:37 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Will Deacon <will.deacon@....com>
Cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"trinity@...r.kernel.org" <trinity@...r.kernel.org>
Subject: Re: perf,arm -- oops in validate_event

On Wed, Aug 07, 2013 at 02:00:27PM +0100, Will Deacon wrote:
> On Tue, Aug 06, 2013 at 02:08:15PM +0100, Mark Rutland wrote:
> > On Tue, Aug 06, 2013 at 12:59:21PM +0100, Will Deacon wrote:
> > > But we already check `event->pmu != leader_pmu' in validate_event, so we
> > > shouldn't get anywhere nearer calling get_event_idx in the case you
> > > describe. It sounds more like we have an inconsistency with one of the
> > > events.
> > 
> > Note in my example that the software event was the group leader (so in
> > fact we'd *only* be checking those events which we can't actually
> > handle...).
> > 
> > I was also under the impression that in the case of mixed hardware and
> > software events, a hardware event must be the group leader. That
> > doesn't seem to be the case. If a hardware event is added to a software
> > group, the group is moved to hardware context but the original software
> > event stays as the group leader.
> 
> Ok, so the following quick hack below should solve the issue (can you confirm
> it please, since I don't have access to any hardware atm?)

It works for me when running Vince's test case.

Tested-by: Mark Rutland <mark.rutland@....com>

> 
> We should revisit this for 3.12 though, because I'm not sure that our
> validation code even does the right thing when there are multiple PMUs
> involved.

Certainly. I suspect we're not alone there.

Thanks,
Mark.

> 
> Will
> 
> --->8
> 
> diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
> index d9f5cd4..0500f10b 100644
> --- a/arch/arm/kernel/perf_event.c
> +++ b/arch/arm/kernel/perf_event.c
> @@ -253,6 +253,9 @@ validate_event(struct pmu_hw_events *hw_events,
>         struct arm_pmu *armpmu = to_arm_pmu(event->pmu);
>         struct pmu *leader_pmu = event->group_leader->pmu;
>  
> +       if (is_software_event(event))
> +               return 1;
> +
>         if (event->pmu != leader_pmu || event->state < PERF_EVENT_STATE_OFF)
>                 return 1;
--
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