linux-kernel - [PATCH v1] perf test: Fix maps use after put

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Date:   Wed, 19 Apr 2023 20:04:30 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     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>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v1] perf test: Fix maps use after put

Fix a use after put reference count issue. maps is copied from leader,
but the leader is put on line 79 and then maps is used to read the
reference count below - so a use after put, with the put of maps
happening within thread__put. Fix by reversing the order of puts so
that the leader is put last.

To explain the reference count checker, I wrote this up as a little
example here:
https://perf.wiki.kernel.org/index.php/Reference_Count_Checking

Note, the bug was introduced by the committer and wasn't present in
the original reference count patch set.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/tests/thread-maps-share.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/perf/tests/thread-maps-share.c b/tools/perf/tests/thread-maps-share.c
index 75ce8aedfc78..858e725318a9 100644
--- a/tools/perf/tests/thread-maps-share.c
+++ b/tools/perf/tests/thread-maps-share.c
@@ -76,16 +76,16 @@ static int test__thread_maps_share(struct test_suite *test __maybe_unused, int s
 	TEST_ASSERT_VAL("maps don't match", RC_CHK_ACCESS(other_maps) == RC_CHK_ACCESS(other_leader->maps));
 
 	/* release thread group */
-	thread__put(leader);
+	thread__put(t3);
 	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(maps__refcnt(maps)), 3);
 
-	thread__put(t1);
+	thread__put(t2);
 	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(maps__refcnt(maps)), 2);
 
-	thread__put(t2);
+	thread__put(t1);
 	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(maps__refcnt(maps)), 1);
 
-	thread__put(t3);
+	thread__put(leader);
 
 	/* release other group  */
 	thread__put(other_leader);
-- 
2.40.0.634.g4ca3ef3211-goog