linux-kernel - Re: [PATCH 04/11] perf parse-event: Fix cpu map leaks

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Date:   Tue, 15 Sep 2020 23:39:56 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>
Subject: Re: [PATCH 04/11] perf parse-event: Fix cpu map leaks

Hi Arnaldo,

On Tue, Sep 15, 2020 at 9:18 PM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> Em Tue, Sep 15, 2020 at 12:18:12PM +0900, Namhyung Kim escreveu:
> > Like evlist cpu map, evsel's cpu map should have proper refcount by
> > releasing the original count after creation.
>
> "releasing original count after creation"?
>
> There are two fixes here, one its legit, i.e. when failing to create
> the new evsel, if you created the perf_cpu_map, drop the refcount,
> which, in this case, will free it since perf_cpu_map__new() sets it to
> 1.
>
> But what about the other? Humm, I see, since a new refcount is being
> obtained, then we need to drop the first.
>
> This all got complicated, perhaps the following patch is simpler?
>
> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
> index c4d2394e2b2dc60f..3dceeacf8669bc5d 100644
> --- a/tools/perf/util/parse-events.c
> +++ b/tools/perf/util/parse-events.c
> @@ -353,18 +353,20 @@ __add_event(struct list_head *list, int *idx,
>             const char *cpu_list)
>  {
>         struct evsel *evsel;
> -       struct perf_cpu_map *cpus = pmu ? pmu->cpus :
> +       struct perf_cpu_map *cpus = pmu ? perf_cpu_map__get(pmu->cpus) :
>                                cpu_list ? perf_cpu_map__new(cpu_list) : NULL;
>
>         if (init_attr)
>                 event_attr_init(attr);
>
>         evsel = evsel__new_idx(attr, *idx);
> -       if (!evsel)
> +       if (!evsel) {
> +               perf_cpu_map__put(cpus);
>                 return NULL;
> +       }
>
>         (*idx)++;
> -       evsel->core.cpus   = perf_cpu_map__get(cpus);
> +       evsel->core.cpus     = cpus;
>         evsel->core.own_cpus = perf_cpu_map__get(cpus);
>         evsel->core.system_wide = pmu ? pmu->is_uncore : false;
>         evsel->auto_merge_stats = auto_merge_stats;
>
>
> ---
>
> I.e. if we're going to share pmu->cpus, grab the necessary refcount at
> that point, if we're going to create one (pmu == NULL), then
> perf_cpu_map__new() will have the refcount we need (will set it to 1).
>
> Then, if we fail to create the new evsel, we just drop the refcount we
> got either from perf_cpu_map__get(pmu->cpus) or from
> perf_cpu_map__new(cpu_list) (NULL is ok for __put() operations, that
> covers that last ': NULL').
>
> And then, when we go make evsel->core.cpus share that cpu_map, we know
> we have the necessary refcount already, right?

Indeed! This looks a lot better.  Do you want me to resend?

Thanks
Namhyung


>
> No need to later on drop the one obtained previously via:
>
>   evsel->core.cpus   = perf_cpu_map__get(cpus);
>
> And we don't need to drop it later when we want to drop the extra
> refcount it gets when pmu == NULL.
>
> - Arnaldo