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: <CAM9d7chKj4pnhtuuA6wN6TBLUYq_9bTxvr6dRT7CKW3CfQ1Avg@mail.gmail.com>
Date:   Fri, 30 Jun 2023 14:02:38 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     James Clark <james.clark@....com>
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 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!