linux-kernel - Re: [PATCH] perf lock contention: Fix msan issue in lock_contention

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Date:   Thu, 23 Mar 2023 23:50:57 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH] perf lock contention: Fix msan issue in lock_contention_read()

On Thu, Mar 23, 2023 at 5:19 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> 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@...nel.org>

Acked-by: Ian Rogers <irogers@...gle.com>

Thanks,
Ian

> ---
>  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
>