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 <[email protected]> > --- > 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 >
