Messages in this thread | | | Date | Tue, 16 Jul 2019 14:34:11 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] Fix perf test data race for tsan build |
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On Tue, Jul 16, 2019 at 11:10:39AM +0200, Jiri Olsa wrote: > 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' ?
Thread Sanitizer, from the group that brought us KASAN and UBSAN.
I'd much rather see the below use READ_ONCE() and WRITE_ONCE(). Using atomic_t without RmW ops is confusing.
> > 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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