linux-kernel - Re: [PATCH] Fix perf stat repeat segfault

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Date:   Sun, 14 Jul 2019 14:36:42 -0700
From:   Stephane Eranian <eranian@...gle.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Numfor Mbiziwo-Tiapo <nums@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Song Liu <songliubraving@...com>, mbd@...com,
        LKML <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.com>
Subject: Re: [PATCH] Fix perf stat repeat segfault

On Sun, Jul 14, 2019 at 1:55 PM Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Sun, Jul 14, 2019 at 10:44:36PM +0200, Jiri Olsa wrote:
> > On Wed, Jul 10, 2019 at 01:45:40PM -0700, Numfor Mbiziwo-Tiapo wrote:
> > > When perf stat is called with event groups and the repeat option,
> > > a segfault occurs because the cpu ids are stored on each iteration
> > > of the repeat, when they should only be stored on the first iteration,
> > > which causes a buffer overflow.
> > >
> > > This can be replicated by running (from the tip directory):
> > >
> > > make -C tools/perf
> > >
> > > then running:
> > >
> > > tools/perf/perf stat -e '{cycles,instructions}' -r 10 ls
> > >
> > > Since run_idx keeps track of the current iteration of the repeat,
> > > only storing the cpu ids on the first iteration (when run_idx < 1)
> > > fixes this issue.
> > >
> > > Signed-off-by: Numfor Mbiziwo-Tiapo <nums@...gle.com>
> > > ---
> > >  tools/perf/builtin-stat.c | 7 ++++---
> > >  1 file changed, 4 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> > > index 63a3afc7f32b..92d6694367e4 100644
> > > --- a/tools/perf/builtin-stat.c
> > > +++ b/tools/perf/builtin-stat.c
> > > @@ -378,9 +378,10 @@ static void workload_exec_failed_signal(int signo __maybe_unused, siginfo_t *inf
> > >     workload_exec_errno = info->si_value.sival_int;
> > >  }
> > >
> > > -static bool perf_evsel__should_store_id(struct perf_evsel *counter)
> > > +static bool perf_evsel__should_store_id(struct perf_evsel *counter, int run_idx)
> > >  {
> > > -   return STAT_RECORD || counter->attr.read_format & PERF_FORMAT_ID;
> > > +   return STAT_RECORD || counter->attr.read_format & PERF_FORMAT_ID
> > > +           && run_idx < 1;
> >
> > we create counters for every iteration, so this can't be
> > based on iteration
> >
> > I think that's just a workaround for memory corruption,
> > that's happening for repeating groupped events stats,
> > I'll check on this
>
> how about something like this? we did not cleanup
> ids on evlist close, so it kept on raising and
> causing corruption in next iterations
>
not sure, that would realloc on each iteration of the repeats.

>
> jirka
>
>
> ---
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index ebb46da4dfe5..52459dd5ad0c 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1291,6 +1291,7 @@ static void perf_evsel__free_id(struct perf_evsel *evsel)
>         xyarray__delete(evsel->sample_id);
>         evsel->sample_id = NULL;
>         zfree(&evsel->id);
> +       evsel->ids = 0;
>  }
>
>  static void perf_evsel__free_config_terms(struct perf_evsel *evsel)
> @@ -2077,6 +2078,7 @@ void perf_evsel__close(struct perf_evsel *evsel)
>
>         perf_evsel__close_fd(evsel);
>         perf_evsel__free_fd(evsel);
> +       perf_evsel__free_id(evsel);
>  }
>
>  int perf_evsel__open_per_cpu(struct perf_evsel *evsel,