linux-kernel - Re: [RFC PATCH] perf session: fixing uninitialised cpumode

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Date:	Mon, 16 May 2016 10:37:22 -0600
From:	Mathieu Poirier <mathieu.poirier@...aro.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	jolsa@...nel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] perf session: fixing uninitialised cpumode

On 16 May 2016 at 00:01, Jiri Olsa <jolsa@...hat.com> wrote:
> On Fri, May 13, 2016 at 05:36:16PM -0600, Mathieu Poirier wrote:
>> The following patch[1] adds a new "cpumode" to the perf_sample
>> structure that gets initialised as events are read from the data
>> event file.
>>
>> With the advent of HW tracers and more specifically the decoding of
>> the traces they generate, function perf_session__deliver_synth_event()
>> gets called directly from the infrastructure that decodes the traces,
>> for example[2].
>
> hum, but this one ends up calling perf_session__deliver_synth_event
> with sample == NULL right?

Wrong example - this highlights the problem [1].  Here "sample" is
created from scratch and "->cpumode" isn't initialised.  Looking at
things with a rested head this morning it is apparent to me that
adding something like:

sample.cpumode = event->header.misc;

to line 1048 is probably a better solution.

Thanks,
Mathieu

[1]. http://lxr.free-electrons.com/source/tools/perf/util/intel-pt.c#L1070


>
> I checked callers of perf_session__deliver_synth_event and it seems
> all either init sample->cpumode or pass sample as NULL.. what do I miss?
>
> thanks,
> jirka
>
>>
>> As such initialisation of perf_sample::cpumode doesn't get done, which
>> prevents the shared object name from being printed in the perf report
>> output.
>>
>> Before this patch:
>>
>>      4.13%     4.13%  uname    [unknown]         [H] 0x0000007fae8b4758
>>      3.74%     3.74%  uname    [unknown]         [H] 0x0000007fae8b4e50
>>      2.06%     2.06%  uname    [unknown]         [H] 0x0000007fae938af4
>>      1.65%     1.65%  uname    [unknown]         [H] 0x0000007fae938ae4
>>      1.59%     1.59%  uname    [unknown]         [H] 0x0000007fae98f7f4
>>      1.50%     1.50%  uname    [unknown]         [H] 0x0000007fae8b4e40
>>      1.43%     1.43%  uname    [unknown]         [H] 0x0000007fae938ac4
>>      1.31%     1.31%  uname    [unknown]         [H] 0x0000007fae86b0c0
>>      1.26%     1.26%  uname    [unknown]         [H] 0x0000007fae99b888
>>
>> And after this patch:
>>
>>      4.13%     4.13%  uname    libc-2.21.so      [.] 0x0000000000078758
>>      3.74%     3.74%  uname    libc-2.21.so      [.] 0x0000000000078e50
>>      2.06%     2.06%  uname    libc-2.21.so      [.] 0x00000000000fcaf4
>>      1.65%     1.65%  uname    libc-2.21.so      [.] 0x00000000000fcae4
>>      1.59%     1.59%  uname    ld-2.21.so        [.] 0x000000000000a7f4
>>      1.50%     1.50%  uname    libc-2.21.so      [.] 0x0000000000078e40
>>      1.43%     1.43%  uname    libc-2.21.so      [.] 0x00000000000fcac4
>>      1.31%     1.31%  uname    libc-2.21.so      [.] 0x000000000002f0c0
>>      1.26%     1.26%  uname    ld-2.21.so        [.] 0x0000000000016888
>>
>> This was tested using CoreSight but the same is very likely to happen on
>> IntelPT.  I'm pretty sure this isn't the right solution but we can start
>> building from that.
>>
>> Comments welcomed.
>>
>> [1]. commit 473398a21d28 ("perf tools: Add cpumode to struct perf_sample")
>> [2]. http://lxr.free-electrons.com/source/tools/perf/util/intel-pt.c#L1806
>>
>> Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
>> ---
>>  tools/perf/util/session.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
>> index 4abd85c6346d..28cc405e7245 100644
>> --- a/tools/perf/util/session.c
>> +++ b/tools/perf/util/session.c
>> @@ -1352,6 +1352,10 @@ int perf_session__deliver_synth_event(struct perf_session *session,
>>  {
>>       struct perf_evlist *evlist = session->evlist;
>>       struct perf_tool *tool = session->tool;
>> +     u8 mode = event->header.misc & PERF_RECORD_MISC_CPUMODE_MASK;
>> +
>> +     if (sample)
>> +             sample->cpumode = mode;
>>
>>       events_stats__inc(&evlist->stats, event->header.type);
>>
>> --
>> 2.5.0
>>