Re: [PATCH v16 4/4] perf tools: Merge deferred user callchains

[Jens Remus <jremus@linux.ibm.com>]

Hello Namhyung,

could you please adapt your patches from this series to Peter's latest
changes to unwind user and related perf support, especially his new
version c69993ecdd4d ("perf: Support deferred user unwind") available
at:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git perf/core

On 10/24/2025 3:02 PM, Peter Zijlstra wrote:
> On Thu, Oct 02, 2025 at 01:49:38PM -0400, Steven Rostedt wrote:
>> On Mon, 08 Sep 2025 13:53:23 -0400
>> Steven Rostedt <rostedt@kernel.org> wrote:
>>
>>> +static int evlist__deliver_deferred_samples(struct evlist *evlist,
>>> +					    const struct perf_tool *tool,
>>> +					    union  perf_event *event,
>>> +					    struct perf_sample *sample,
>>> +					    struct machine *machine)
>>> +{
>>> +	struct deferred_event *de, *tmp;
>>> +	struct evsel *evsel;
>>> +	int ret = 0;
>>> +
>>> +	if (!tool->merge_deferred_callchains) {
>>> +		evsel = evlist__id2evsel(evlist, sample->id);
>>> +		return tool->callchain_deferred(tool, event, sample,
>>> +						evsel, machine);
>>> +	}
>>> +
>>> +	list_for_each_entry_safe(de, tmp, &evlist->deferred_samples, list) {
>>> +		struct perf_sample orig_sample;
>>
>> orig_sample is not initialized and can then contain junk.
>>
>>> +
>>> +		ret = evlist__parse_sample(evlist, de->event, &orig_sample);
>>> +		if (ret < 0) {
>>> +			pr_err("failed to parse original sample\n");
>>> +			break;
>>> +		}
>>> +
>>> +		if (sample->tid != orig_sample.tid)
>>> +			continue;
>>> +
>>> +		if (event->callchain_deferred.cookie == orig_sample.deferred_cookie)
>>> +			sample__merge_deferred_callchain(&orig_sample, sample);
>>
>> The sample__merge_deferred_callchain() initializes both
>> orig_sample.deferred_callchain and the callchain. But now that it's not
>> being called, it can cause the below free to happen with junk as the
>> callchain. This needs:
>>
>> 		else
>> 			orig_sample.deferred_callchain = false;
> 
> Ah, so I saw crashes from here and just deleted both free()s and got on
> with things ;-)

This needs to be properly resolved.  In the meantime I am using Steven's
suggestion above to continue my work on unwind user sframe (s390).

> 
>>> +
>>> +		evsel = evlist__id2evsel(evlist, orig_sample.id);
>>> +		ret = evlist__deliver_sample(evlist, tool, de->event,
>>> +					     &orig_sample, evsel,> machine); +
>>> +		if (orig_sample.deferred_callchain)
>>> +			free(orig_sample.callchain);
>>> +
>>> +		list_del(&de->list);
>>> +		free(de);
>>> +
>>> +		if (ret)
>>> +			break;
>>> +	}
>>> +	return ret;
>>> +}
>>
>> -- Steve

Thanks and regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
+49-7031-16-1128 Office
jremus@de.ibm.com

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