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Sender: Namhyung Kim <namhyung@gmail.com>
From:   Namhyung Kim <namhyung@kernel.org>
To:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Jiri Olsa <jolsa@kernel.org>
Cc:     Ian Rogers <irogers@google.com>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-perf-users@vger.kernel.org
Subject: [PATCH] perf lock contention: Fix msan issue in lock_contention_read()
Date:   Thu, 23 Mar 2023 17:19:22 -0700
Message-Id: <20230324001922.937634-1-namhyung@kernel.org>
MIME-Version: 1.0
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Precedence: bulk

I got a report of a msan failure like below:

  $ sudo perf lock con -ab -- sleep 1
  ...
  ==224416==WARNING: MemorySanitizer: use-of-uninitialized-value
      #0 0x5651160d6c96 in lock_contention_read  util/bpf_lock_contention.c:290:8
      #1 0x565115f90870 in __cmd_contention  builtin-lock.c:1919:3
      #2 0x565115f90870 in cmd_lock  builtin-lock.c:2385:8
      #3 0x565115f03a83 in run_builtin  perf.c:330:11
      #4 0x565115f03756 in handle_internal_command  perf.c:384:8
      #5 0x565115f02d53 in run_argv  perf.c:428:2
      #6 0x565115f02d53 in main  perf.c:562:3
      #7 0x7f43553bc632 in __libc_start_main
      #8 0x565115e865a9 in _start

It was because the 'key' variable is not initialized.  Actually it'd be set
by bpf_map_get_next_key() but msan didn't seem to understand it.  Let's make
msan happy by initializing the variable.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/util/bpf_lock_contention.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
index 235fc7150545..5927bf0bd92b 100644
--- a/tools/perf/util/bpf_lock_contention.c
+++ b/tools/perf/util/bpf_lock_contention.c
@@ -249,7 +249,7 @@ static const char *lock_contention_get_name(struct lock_contention *con,
 int lock_contention_read(struct lock_contention *con)
 {
 	int fd, stack, err = 0;
-	struct contention_key *prev_key, key;
+	struct contention_key *prev_key, key = {};
 	struct contention_data data = {};
 	struct lock_stat *st = NULL;
 	struct machine *machine = con->machine;
-- 
2.40.0.348.gf938b09366-goog