linux-kernel - Re: [PATCH -tip] x86,perf: P4 PMU -- protect sensible procedures from preemption

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Date:	Wed, 5 May 2010 21:42:34 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH -tip] x86,perf: P4 PMU -- protect sensible procedures
	from preemption

On Wed, May 05, 2010 at 06:57:34PM +0200, Frederic Weisbecker wrote:
...
> > @@ -741,7 +743,7 @@ static int p4_pmu_schedule_events(struct
> >  {
> >  	unsigned long used_mask[BITS_TO_LONGS(X86_PMC_IDX_MAX)];
> >  	unsigned long escr_mask[BITS_TO_LONGS(ARCH_P4_TOTAL_ESCR)];
> > -	int cpu = raw_smp_processor_id();
> > +	int cpu = get_cpu();
> >  	struct hw_perf_event *hwc;
> >  	struct p4_event_bind *bind;
> >  	unsigned int i, thread, num;
> > @@ -777,6 +779,7 @@ reserve:
> >  	}
> >  
> >  done:
> > +	put_cpu();
> >  	return num ? -ENOSPC : 0;
> >  }
> 
> That's no big deal. But I think the schedule_events() is called on
> pmu::enable() time, when preemption is already disabled.
> 

We'll be on a safe side using get/put_cpu here (ie in case
if something get changed one day).

	-- Cyrill
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