Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230324001922.937634-1-namhyung@kernel.org>
In-Reply-To: <20230324001922.937634-1-namhyung@kernel.org>
From:   Ian Rogers <irogers@google.com>
Date:   Thu, 23 Mar 2023 23:50:57 -0700
Message-ID: <CAP-5=fWPDSy31BLtxvJAsRq2pwnhKHN8T-CYckv=tELGCO9p0w@mail.gmail.com>
Subject: Re: [PATCH] perf lock contention: Fix msan issue in lock_contention_read()
To:     Namhyung Kim <namhyung@kernel.org>
Cc:     Arnaldo Carvalho de Melo <acme@kernel.org>,
        Jiri Olsa <jolsa@kernel.org>,
        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
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Thu, Mar 23, 2023 at 5:19=E2=80=AFPM Namhyung Kim <namhyung@kernel.org> =
wrote:
>
> I got a report of a msan failure like below:
>
>   $ sudo perf lock con -ab -- sleep 1
>   ...
>   =3D=3D224416=3D=3DWARNING: 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 s=
et
> by bpf_map_get_next_key() but msan didn't seem to understand it.  Let's m=
ake
> msan happy by initializing the variable.
>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>

Acked-by: Ian Rogers <irogers@google.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 lo=
ck_contention *con,
>  int lock_contention_read(struct lock_contention *con)
>  {
>         int fd, stack, err =3D 0;
> -       struct contention_key *prev_key, key;
> +       struct contention_key *prev_key, key =3D {};
>         struct contention_data data =3D {};
>         struct lock_stat *st =3D NULL;
>         struct machine *machine =3D con->machine;
> --
> 2.40.0.348.gf938b09366-goog
>