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

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Date:   Sun, 14 Jul 2019 22:55:05 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Numfor Mbiziwo-Tiapo <nums@...gle.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, namhyung@...nel.org,
        songliubraving@...com, mbd@...com, linux-kernel@...r.kernel.org,
        irogers@...gle.com, eranian@...gle.com
Subject: Re: [PATCH] Fix perf stat repeat segfault

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

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,