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

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Date:   Thu, 10 Jun 2021 11:45:17 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     John Garry <john.garry@...wei.com>
Cc:     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@...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 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>

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
>