Re: [PATCH 2/2] perf tools: Fix record failure when mixed with ARM SPE event

[liwei (GF)]

Hi Mathieu,

On 2020/7/3 7:03, Mathieu Poirier wrote:
> Hi Li,
> 
> On Tue, Jun 23, 2020 at 08:31:41PM +0800, Wei Li wrote:
>> When recording with cache-misses and arm_spe_x event, i found that
>> it will just fail without showing any error info if i put cache-misses
>> after arm_spe_x event.
>>
>> [root@localhost 0620]# perf record -e cache-misses -e \
>> arm_spe_0/ts_enable=1,pct_enable=1,pa_enable=1,load_filter=1,\
>> jitter=1,store_filter=1,min_latency=0/ sleep 1
>> [ perf record: Woken up 1 times to write data ]
>> [ perf record: Captured and wrote 0.067 MB perf.data ]
>> [root@localhost 0620]# perf record -e \
>> arm_spe_0/ts_enable=1,pct_enable=1,pa_enable=1,load_filter=1,jitter=1,\
>> store_filter=1,min_latency=0/ -e cache-misses sleep 1
>> [root@localhost 0620]#
>>
>> Finally, i found the reason is that the parameter 'arm_spe_pmu' passed to
>> arm_spe_recording_init() in auxtrace_record__init() is wrong. When the
>> arm_spe_x event is not the last event, 'arm_spe_pmus[i]' will be out of
>> bounds.
> 
> Yes, this indeed broken.  
> 
> The current code can only work if the only event to be
> traced is an arm_spe_X, or if it is the last event to be specified.
> Otherwise the last event type will be checked against all the
> arm_spe_pmus[i]->types, none will match and an out of bound i index will be
> used in arm_spc_recording_init().
> 
> Since this problem is not easy to figure out please include the above
> explanation in the changelog.

OK.
>>
>> It seems that the code can't support concurrent multiple different
>> arm_spe_x events currently. So add the code to check and record the
>> found 'arm_spe_pmu' to fix this issue.
>>
>> In fact, we don't support concurrent multiple same arm_spe_x events either,
>> that is checked in arm_spe_recording_options(), and it will show the
>> relevant info.
>>
>> Fixes: ffd3d18c20b8d ("perf tools: Add ARM Statistical Profiling Extensions (SPE) support")
>> Signed-off-by: Wei Li <liwei391@xxxxxxxxxx>
>> ---
>>  tools/perf/arch/arm/util/auxtrace.c | 10 +++++++++-
>>  1 file changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/tools/perf/arch/arm/util/auxtrace.c b/tools/perf/arch/arm/util/auxtrace.c
>> index 62b7b03d691a..7bb6f29e766c 100644
>> --- a/tools/perf/arch/arm/util/auxtrace.c
>> +++ b/tools/perf/arch/arm/util/auxtrace.c
>> @@ -58,6 +58,7 @@ struct auxtrace_record
>>  	bool found_etm = false;
>>  	bool found_spe = false;
>>  	static struct perf_pmu **arm_spe_pmus;
>> +	static struct perf_pmu *arm_spe_pmu;
> 
> As far as I can tell the "static" doesn't do anything.
> 
I will remove that in v2.
>>  	static int nr_spes = 0;
>>  	int i = 0;
>>  
>> @@ -77,6 +78,13 @@ struct auxtrace_record
>>  
>>  		for (i = 0; i < nr_spes; i++) {
>>  			if (evsel->core.attr.type == arm_spe_pmus[i]->type) {
>> +				if (found_spe && (arm_spe_pmu != arm_spe_pmus[i])) {
>> +					pr_err("Concurrent multiple SPE operation not currently supported\n");
>> +					*err = -EOPNOTSUPP;
>> +					return NULL;
>> +				}
> 
> Instead of the above, which as you rightly pointed out, is also done in
> arm_spe_recording_options() it might be best to just fix the "if (!nr_spes)"
> condition:
>                 if (!nr_spes || arm_spe_pmu)
>                         continue

This is more brief, i will use 'found_spe' as 'arm_spe_pmu' is not initialized.
> Furthermore, instead of having a new arm_spe_pmu variable you could simply make
> found_spe a struct perf_pmu.  That would be one less variable to take care of.
> 
>> +
>> +				arm_spe_pmu = arm_spe_pmus[i];
>>  				found_spe = true;
> 
> Last but not least do you know where the memory allocated for array arm_spe_pmus
> is released?  If you can't find it either then we have a memory leak and it
> would be nice to have that fixed.
Yes, we have a memory leak here indeed, i forgot to free it in this function.
As 'arm_spe_pmus' is defined as static, i think the author meant to assign it only at the first call,
but this function is only called once when we executing 'record', should i go on fixing it
or just drop the patch 1?

> Regards
> Mathieu
> 
> PS: Leo Yan has spent a fair amount of time in the SPE code - please CC him on
> your next revision.
> 
Thanks,
Wei