2023-03-24 00:20:28

by Namhyung Kim

Subject: [PATCH] perf lock contention: Fix msan issue in lock_contention_read()

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 <[email protected]>
---
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

2023-03-24 07:01:21

by Ian Rogers

Subject: Re: [PATCH] perf lock contention: Fix msan issue in lock_contention_read()

On Thu, Mar 23, 2023 at 5:19 PM Namhyung Kim <[email protected]> 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 <[email protected]>

Acked-by: Ian Rogers <[email protected]>

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
>

2023-03-24 19:57:20

by Arnaldo Carvalho de Melo

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 <[email protected]> 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 <[email protected]>
>
> Acked-by: Ian Rogers <[email protected]>

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