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

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Date:   Mon, 15 Jul 2019 01:14:59 -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 Mon, Jul 15, 2019 at 12:59 AM Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Sun, Jul 14, 2019 at 02:36:42PM -0700, Stephane Eranian wrote:
> > 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.
>
> well, we need new ids, because we create new events every iteration
>
If you recreate them, then agreed.
It is not clear to me why you need ids when not running is STAT_RECORD mode.

> jirka
>
> >
> > >
> > > 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,