[PATCH] perf stat: Fix segfault for event group in repeat mode

[Jiri Olsa <jolsa@redhat.com>]

Numfor Mbiziwo-Tiapo reported segfault on stat of event
group in repeat mode:

  # perf stat -e '{cycles,instructions}' -r 10 ls

It's caused by memory corruption due to not cleaned
evsel's id array and index, which needs to be rebuilt
in every stat iteration. Currently the ids index grows,
while the array (which is also not freed) has the same
size.

Fixing this by releasing id array and zeroing ids index
in perf_evsel__close function.

We also need to keep the evsel_list alive for stat
record (which is disabled in repeat mode).

Reported-by: Numfor Mbiziwo-Tiapo <nums@google.com>
Link: http://lkml.kernel.org/n/tip-07t75chgdhcr00uerh51hb6j@git.kernel.org
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/perf/builtin-stat.c | 9 ++++++++-
 tools/perf/util/evsel.c   | 2 ++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
index b55a534b4de0..352cf39d7c2f 100644
--- a/tools/perf/builtin-stat.c
+++ b/tools/perf/builtin-stat.c
@@ -607,7 +607,13 @@ static int __run_perf_stat(int argc, const char **argv, int run_idx)
 	 * group leaders.
 	 */
 	read_counters(&(struct timespec) { .tv_nsec = t1-t0 });
-	perf_evlist__close(evsel_list);
+
+	/*
+	 * We need to keep evsel_list alive, because it's processed
+	 * later the evsel_list will be closed after.
+	 */
+	if (!STAT_RECORD)
+		perf_evlist__close(evsel_list);
 
 	return WEXITSTATUS(status);
 }
@@ -1997,6 +2003,7 @@ int cmd_stat(int argc, const char **argv)
 			perf_session__write_header(perf_stat.session, evsel_list, fd, true);
 		}
 
+		perf_evlist__close(evsel_list);
 		perf_session__delete(perf_stat.session);
 	}
 
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,
-- 
2.21.0