linux-kernel - Re: BUG: using smp_processor_id() in preemptible [00000000] code: asm/8267

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Date:	Wed, 27 Mar 2013 10:49:32 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Namhyung Kim <namhyung.kim@....com>,
	Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: BUG: using smp_processor_id() in preemptible [00000000] code:
 asm/8267

On Wed, Mar 27, 2013 at 03:02:10PM +0900, Namhyung Kim wrote:
> > --
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index 7b4a55d41efc..f3bb3384a106 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -4455,8 +4455,11 @@ static void perf_event_task_event(struct perf_task_event *task_event)
> >  next:
> >  		put_cpu_ptr(pmu->pmu_cpu_context);
> >  	}
> > +
> > +	preempt_disable();
> >  	if (task_event->task_ctx)
> >  		perf_event_task_ctx(task_event->task_ctx, task_event);
> > +	preempt_enable();

Ok, just for my own understanding: how do the events on the
->task_ctx->event_list relate to the current cpu in this path? I mean,
we're on the task exit path here so is it possible to be rescheduled
somewhere else and the check in event_filter_match to become
meaningless?

Because with this fix, we have a small window between enabling
preemption after the last pmu context and disabling it again to get
moved somewhere else.

Hmm.

Thanks.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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