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

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Message-ID: <ZB3/52fEm7/5w72q@kernel.org>
Date:   Fri, 24 Mar 2023 16:54:15 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Namhyung Kim <namhyung@...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()

Em Thu, Mar 23, 2023 at 11:50:57PM -0700, Ian Rogers escreveu:
> 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, applied.

- Arnaldo

 
> 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
> >

-- 

- Arnaldo