linux-kernel - Re: [PATCH] perf/x86/uncore: Allow single pmu/box within events group

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Date:   Fri, 18 Nov 2016 15:45:09 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     "Liang, Kan" <kan.liang@...el.com>,
        Andi Kleen <andi@...stfloor.org>,
        Vince Weaver <vince@...ter.net>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] perf/x86/uncore: Allow single pmu/box within events group

On Fri, Nov 18, 2016 at 03:30:48PM +0100, Jiri Olsa wrote:
> > > > +static bool is_box_event(struct intel_uncore_box *box, struct perf_event *event)
> > > >  {
> > > > -	return event->pmu->event_init == uncore_pmu_event_init;
> > > > +	return box->pmu == event->pmu;
> > > 
> > > this one needs to be:
> > > 
> > > +       return box->pmu == uncore_event_to_pmu(event);
> > > 
> > > and it works.. ;-)
> > 
> > Will that not explode if we fudge a software event in there?
> > 
> > Wouldn't:
> > 
> > 	return box->pmu.pmu == event->pmu;
> > 
> > be the safer option?
> 
> hum right.. but for some reason I can't crash it nor even fuzzer complains

Its because pmu is the first member, so the pointer is the exact same,
just the type changes. But that is a 'happy' accident of implementation.