linux-kernel - Re: [PATCH 2/2] perf report: Don't add to histogram when there is no thread found

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Message-ID: <3a0fff38-b364-a6b4-1d10-41311e2073b4@arm.com>
Date:   Mon, 3 Jul 2023 09:18:50 +0100
From:   James Clark <james.clark@....com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Ian Rogers <irogers@...gle.com>, linux-perf-users@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        John Garry <john.g.garry@...cle.com>,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] perf report: Don't add to histogram when there is no
 thread found



On 30/06/2023 22:02, Namhyung Kim wrote:
> On Wed, Jun 28, 2023 at 1:06 PM Namhyung Kim <namhyung@...nel.org> wrote:
>>
>> On Wed, Jun 28, 2023 at 3:34 AM James Clark <james.clark@....com> wrote:
>>>
>>>
>>>
>>> On 27/06/2023 18:19, Ian Rogers wrote:
>>>> On Tue, Jun 27, 2023 at 9:58 AM Namhyung Kim <namhyung@...nel.org> wrote:
>>>>>
>>>>> On Tue, Jun 27, 2023 at 9:43 AM Ian Rogers <irogers@...gle.com> wrote:
>>>>>>
>>>>>> On Mon, Jun 26, 2023 at 5:02 PM Namhyung Kim <namhyung@...nel.org> wrote:
>>>>>>>
>>>>>>> On Mon, Jun 26, 2023 at 05:10:58PM +0100, James Clark wrote:
>>>>>>>> thread__find_map() chooses to exit without assigning a thread to the
>>>>>>>> addr_location in some scenarios, for example when there are samples from
>>>>>>>> a guest and perf_guest == false. This results in a segfault when adding
>>>>>>>> to the histogram because it uses unguarded accesses to the thread member
>>>>>>>> of the addr_location.
>>>>>>>
>>>>>>> Looking at the commit 0dd5041c9a0ea ("perf addr_location: Add
>>>>>>> init/exit/copy functions") that introduced the change, I'm not sure if
>>>>>>> it's the intend behavior.
>>>>>>>
>>>>>>> It might change maps and map, but not thread.  Then I think no reason
>>>>>>> to not set the al->thread at the beginning.
>>>>>>>
>>>>>>> How about this?  Ian?
>>>>>>> (I guess we can get rid of the duplicate 'al->map = NULL' part)
>>>>>>
>>>>>> It seemed strange that we were failing to find a map (the function's
>>>>>> purpose) but then populating the address_location. The change below
>>>>>> brings back that somewhat odd behavior. I'm okay with reverting to the
>>>>>> old behavior, clearly there were users relying on it. We should
>>>>>> probably also copy maps and not just thread, as that was the previous
>>>>>> behavior.
>>>>>
>>>>> Probably.  But it used to support samples without maps and I think
>>>>> that's why it ignores the return value of thread__find_map().  So
>>>>> we can expect al.map is NULL and maybe fine to leave it for now.
>>>>>
>>>>> As machine__resolve() returns -1 if it gets no thread, we should set
>>>>> al.thread when it returns 0.
>>>>>
>>>>> Can I get your Acked-by?
>>>>
>>>> Yep:
>>>> Acked-by: Ian Rogers <irogers@...gle.com>
>>>
>>> Looks good to me too. Should I resend the set with this change instead
>>> of my one?
>>
>> No, I can take care of that.  I'll take this as your Acked-by. :)
> 
> This part is applied to perf-tools-next, thanks!

Thanks Namhyung