linux-kernel - Re: [PATCH] perf: Do not check PERF_EVENT_STATE

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Message-ID: <CABPqkBTp2Sh788hmgC-w74MzTJZ-ySzEM-Su2M4oMO4OgDMsJA@mail.gmail.com>
Date:	Wed, 10 Sep 2014 15:49:32 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jiri Olsa <jolsa@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	David Ahern <dsahern@...il.com>
Subject: Re: [PATCH] perf: Do not check PERF_EVENT_STATE_EXIT on syscall read path

Peter,



On Mon, Sep 8, 2014 at 5:22 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, Sep 08, 2014 at 04:31:07PM +0200, Jiri Olsa wrote:
>> Revert PERF_EVENT_STATE_EXIT check on read syscall path.
>> It breaks standard way to read counter, which is to open
>> the counter, wait for the monitored process to die and
>> read the counter.
>>
>> Reported-by: Stephane Eranian <eranian@...gle.com>
>> Acked-by: Stephane Eranian <eranian@...gle.com>
>> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
>> Cc: Frederic Weisbecker <fweisbec@...il.com>
>> Cc: Ingo Molnar <mingo@...nel.org>
>> Cc: Paul Mackerras <paulus@...ba.org>
>> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
>> Cc: Stephane Eranian <eranian@...gle.com>
>> Signed-off-by: Jiri Olsa <jolsa@...nel.org>
>
> Thanks!
Still don't see this fix in tip.git.

>> ---
>>  kernel/events/core.c | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index d8cb4d21a346..6d1c9ce1643e 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -3600,8 +3600,7 @@ perf_read_hw(struct perf_event *event, char __user *buf, size_t count)
>>        * error state (i.e. because it was pinned but it couldn't be
>>        * scheduled on to the CPU at some point).
>>        */
>> -     if ((event->state == PERF_EVENT_STATE_ERROR) ||
>> -         (event->state == PERF_EVENT_STATE_EXIT))
>> +     if (event->state == PERF_EVENT_STATE_ERROR)
>>               return 0;
>>
>>       if (count < event->read_size)
>> --
>> 1.8.3.1
>>
--
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