linux-kernel - Re: [PATCH] perf_events: fix validate

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Date:	Mon, 23 Nov 2009 14:34:04 +0100
From:	stephane eranian <eranian@...glemail.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, paulus@...ba.org,
	perfmon2-devel@...ts.sf.net, eranian@...gle.com
Subject: Re: [PATCH] perf_events: fix validate_event bug

Hi,

Sorry for the delay,

On Wed, Nov 18, 2009 at 5:46 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Thu, 2009-10-22 at 16:51 +0200, Stephane Eranian wrote:
>>       The validate_event() was failing on valid event
>>       combinations. The function was assuming that if
>>       x86_schedule_event() returned 0, it meant error.
>>       But x86_schedule_event() returns the counter index
>>       and 0 is a perfectly valid value. An error is returned
>>       if the function returns a negative value.
>
> Good point.
>
>>       Furthermore, validate_event() was also failing for
>>       event groups because the event->pmu was not set until
>>       after hw_perf_pmu_init().
>
> (hw_perf_event_init, right?)
>
Yes.

> Won't this give very funny results for mixed pmu groups?
>

What do you mean by 'mixed pmu groups'?

> How about something like:
>
>  if (event->pmu && event->pmu != &pmu)
>        return 0;
>
> That should deal with new events, who do not yet have their pmu set and
> for those we know they're for us, but exclude events for other PMUs.
>
>>       Signed-off-by: Stephane Eranian <eranian@...il.com>
>> --
>>  arch/x86/kernel/cpu/perf_event.c |    5 +----
>>  1 file changed, 1 insertion(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
>> index 2e20bca..d321ff7 100644
>> --- a/arch/x86/kernel/cpu/perf_event.c
>> +++ b/arch/x86/kernel/cpu/perf_event.c
>> @@ -2229,10 +2229,7 @@ validate_event(struct cpu_hw_events *cpuc, struct perf_event *event)
>>  {
>>       struct hw_perf_event fake_event = event->hw;
>>
>> -     if (event->pmu != &pmu)
>> -             return 0;
>> -
>> -     return x86_schedule_event(cpuc, &fake_event);
>> +     return x86_schedule_event(cpuc, &fake_event) >= 0;
>>  }
>>
>>  static int validate_group(struct perf_event *event)
>
>
>
--
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