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

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Message-ID: <alpine.DEB.2.10.1308071129000.8139@vincent-weaver-1.um.maine.edu>
Date:	Wed, 7 Aug 2013 11:30:33 -0400 (EDT)
From:	Vince Weaver <vincent.weaver@...ne.edu>
To:	Vince Weaver <vincent.weaver@...ne.edu>
cc:	Will Deacon <will.deacon@....com>,
	Mark Rutland <mark.rutland@....com>,
	"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, 7 Aug 2013, Vince Weaver wrote:

> On Wed, 7 Aug 2013, Will Deacon wrote:
> 
> > 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?)
> > 
> > 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.
> > 
> > --->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;
> 
> this isn't enough.  You can also trigger the oops by using
> tracepoint or breakpoint events as group leaders in addition to software
> events.

I take that back, it turns out tracepoint and breakpoint both
have task_ctx_nr set to perf_sw_context (althouth breakpoint has
a comment saying this may change in the future).

Let me compile and verify the fix.  It may take some time for the compile 
to finish as it's not a very fast machine.

Vince
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