linux-kernel - Re: [PATCH 2/2] perf metricgroup: Return error code from metricgroup__add_metric_sys_event

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Date:   Tue, 15 Jun 2021 10:51:04 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     John Garry <john.garry@...wei.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        kajoljain <kjain@...ux.ibm.com>,
        linux-perf-users <linux-perf-users@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] perf metricgroup: Return error code from metricgroup__add_metric_sys_event_iter()

On Mon, Jun 14, 2021 at 7:56 AM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> Em Thu, Jun 10, 2021 at 11:45:17AM -0700, Ian Rogers escreveu:
> > On Thu, Jun 10, 2021 at 7:37 AM John Garry <john.garry@...wei.com> wrote:
> > >
> > > The error code is not set at all in the sys event iter function.
> > >
> > > This may lead to an uninitialized value of "ret" in
> > > metricgroup__add_metric() when no CPU metric is added.
> > >
> > > Fix by properly setting the error code.
> > >
> > > It is not necessary to init "ret" to 0 in metricgroup__add_metric(), as
> > > if we have no CPU or sys event metric matching, then "has_match" should
> > > be 0 and "ret" is set to -EINVAL.
> > >
> > > However gcc cannot detect that it may not have been set after the
> > > map_for_each_metric() loop for CPU metrics, which is strange.
> > >
> > > Fixes: be335ec28efa8 ("perf metricgroup: Support adding metrics for system PMUs")
> > > Signed-off-by: John Garry <john.garry@...wei.com>
> >
> > Acked-by: Ian Rogers <irogers@...gle.com>
>
> Do your Acked-by applies to both patches? Or just 2/2?  I reproduced the
> problem fixed by 1/2 on a Thinkpad T450S (broadwell) and after applying
> the patch it doesn't segfaults.

IIRC I need to look at what is going on with the names in patch 1/2
and didn't have a repro. I don't mind to ack it given that you've
repro-ed the problem and confirmed the fix. In general this logic
isn't working well (especially for --metric-no-group) so I plan to
take a stab at reorganizing it.

Thanks,
Ian

> Please clarify,
>
> - Arnaldo
>
>
> > Thanks,
> > Ian
> >
> > > ---
> > >  tools/perf/util/metricgroup.c | 8 +++++---
> > >  1 file changed, 5 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/tools/perf/util/metricgroup.c b/tools/perf/util/metricgroup.c
> > > index c456fdeae06a..d3cf2dee36c8 100644
> > > --- a/tools/perf/util/metricgroup.c
> > > +++ b/tools/perf/util/metricgroup.c
> > > @@ -1073,16 +1073,18 @@ static int metricgroup__add_metric_sys_event_iter(struct pmu_event *pe,
> > >
> > >         ret = add_metric(d->metric_list, pe, d->metric_no_group, &m, NULL, d->ids);
> > >         if (ret)
> > > -               return ret;
> > > +               goto out;
> > >
> > >         ret = resolve_metric(d->metric_no_group,
> > >                                      d->metric_list, NULL, d->ids);
> > >         if (ret)
> > > -               return ret;
> > > +               goto out;
> > >
> > >         *(d->has_match) = true;
> > >
> > > -       return *d->ret;
> > > +out:
> > > +       *(d->ret) = ret;
> > > +       return ret;
> > >  }
> > >
> > >  static int metricgroup__add_metric(const char *metric, bool metric_no_group,
> > > --
> > > 2.26.2
> > >
>
> --
>
> - Arnaldo