linux-kernel - Re: [PATCH v1] perf evsel: Avoid segv if delete is called on NULL

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Date:   Mon, 10 Apr 2023 16:20:57 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Ian Rogers <irogers@...gle.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@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Florian Fischer <florian.fischer@...q.space>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] perf evsel: Avoid segv if delete is called on NULL

Hi Ian,

On Mon, Apr 10, 2023 at 1:57 PM Ian Rogers <irogers@...gle.com> wrote:
>
> Seen in "perf stat --bpf-counters --for-each-cgroup test" running in a
> container:
>
> libbpf: Failed to bump RLIMIT_MEMLOCK (err = -1), you might need to do it explicitly!
> libbpf: Error in bpf_object__probe_loading():Operation not permitted(1). Couldn't load trivial BPF program. Make sure your kernel supports BPF (CONFIG_BPF_SYSCALL=y) and/or that RLIMIT_MEMLOCK is set to big enough value.
> libbpf: failed to load object 'bperf_cgroup_bpf'
> libbpf: failed to load BPF skeleton 'bperf_cgroup_bpf': -1
> Failed to load cgroup skeleton
>
>     #0 0x55f28a650981 in list_empty tools/include/linux/list.h:189
>     #1 0x55f28a6593b4 in evsel__exit util/evsel.c:1518
>     #2 0x55f28a6596af in evsel__delete util/evsel.c:1544
>     #3 0x55f28a89d166 in bperf_cgrp__destroy util/bpf_counter_cgroup.c:283
>     #4 0x55f28a899e9a in bpf_counter__destroy util/bpf_counter.c:816
>     #5 0x55f28a659455 in evsel__exit util/evsel.c:1520
>     #6 0x55f28a6596af in evsel__delete util/evsel.c:1544
>     #7 0x55f28a640d4d in evlist__purge util/evlist.c:148
>     #8 0x55f28a640ea6 in evlist__delete util/evlist.c:169
>     #9 0x55f28a4efbf2 in cmd_stat tools/perf/builtin-stat.c:2598
>     #10 0x55f28a6050c2 in run_builtin tools/perf/perf.c:330
>     #11 0x55f28a605633 in handle_internal_command tools/perf/perf.c:384
>     #12 0x55f28a6059fb in run_argv tools/perf/perf.c:428
>     #13 0x55f28a6061d3 in main tools/perf/perf.c:562
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>

Acked-by: Namhyung Kim <namhyung@...nel.org>

In addition to this, I think bperf code should clear the evsel->bpf_skel
at the end of the bpf_counter__destroy() to avoid confusion with the
bpf_filter as they share the fields in a union.

Thanks,
Namhyung


> ---
>  tools/perf/util/evsel.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index dc3faf005c3b..fe3ce765a4f3 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1541,6 +1541,9 @@ void evsel__exit(struct evsel *evsel)
>
>  void evsel__delete(struct evsel *evsel)
>  {
> +       if (!evsel)
> +               return;
> +
>         evsel__exit(evsel);
>         free(evsel);
>  }
> --
> 2.40.0.577.gac1e443424-goog
>