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SubjectRe: [PATCH] Fix perf test data race for tsan build
On Wed, Jul 10, 2019 at 03:16:20PM -0700, Numfor Mbiziwo-Tiapo wrote:
> The tsan build of perf gives a data race warning in

hi,
what's 'tsan build of perf' ?

thanks,
jirka


> mmap-thread-lookup.c when perf test is run on our local machines.
> This is because there is no lock around the "go_away" variable in
> "mmap-thread-lookup.c".
>
> The warning is difficult to reproduce from the tip branch and we
> suspect it has something to do with tsan working differently
> depending on the clang version.
>
> The warning can be silenced by adding locks around the variable
> but it is better practice to make the variable atomic and use
> the atomic_set and atomic_read functions. This does not actually
> silence the warning because tsan doesn't recognize the atomic
> functions as thread safe, but in actuality it should prevent a
> data race.
>
> Signed-off-by: Numfor Mbiziwo-Tiapo <nums@google.com>
> ---
> tools/perf/tests/mmap-thread-lookup.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/tests/mmap-thread-lookup.c b/tools/perf/tests/mmap-thread-lookup.c
> index 5ede9b561d32..f4cbb3d92a46 100644
> --- a/tools/perf/tests/mmap-thread-lookup.c
> +++ b/tools/perf/tests/mmap-thread-lookup.c
> @@ -17,7 +17,7 @@
>
> #define THREADS 4
>
> -static int go_away;
> +static atomic_t go_away;
>
> struct thread_data {
> pthread_t pt;
> @@ -64,7 +64,7 @@ static void *thread_fn(void *arg)
> return NULL;
> }
>
> - while (!go_away) {
> + while (!atomic_read(&go_away)) {
> /* Waiting for main thread to kill us. */
> usleep(100);
> }
> @@ -98,7 +98,7 @@ static int threads_create(void)
> struct thread_data *td0 = &threads[0];
> int i, err = 0;
>
> - go_away = 0;
> + atomic_set(&go_away, 0);
>
> /* 0 is main thread */
> if (thread_init(td0))
> @@ -118,7 +118,7 @@ static int threads_destroy(void)
> /* cleanup the main thread */
> munmap(td0->map, page_size);
>
> - go_away = 1;
> + atomic_set(&go_away, 1);
>
> for (i = 1; !err && i < THREADS; i++)
> err = pthread_join(threads[i].pt, NULL);
> --
> 2.22.0.410.gd8fdbe21b5-goog
>

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