| Message ID | 20200602050349.215037-1-andriin@fb.com |
|---|---|
| State | Accepted |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | [bpf-next] selftests/bpf: fix sample_cnt shared between two threads | expand |
On Mon, Jun 1, 2020 at 10:04 PM Andrii Nakryiko <andriin@fb.com> wrote: > > Make sample_cnt volatile to fix possible selftests failure due to compiler > optimization preventing latest sample_cnt value to be visible to main thread. > sample_cnt is incremented in background thread, which is then joined into main > thread. So in terms of visibility sample_cnt update is ok. But because it's > not volatile, compiler might make optimizations that would prevent main thread > to see latest updated value. Fix this by marking global variable volatile. > > Fixes: cb1c9ddd5525 ("selftests/bpf: Add BPF ringbuf selftests") > Signed-off-by: Andrii Nakryiko <andriin@fb.com> Acked-by: Song Liu <songliubraving@fb.com>
On Tue, Jun 2, 2020 at 9:22 AM Song Liu <song@kernel.org> wrote: > > On Mon, Jun 1, 2020 at 10:04 PM Andrii Nakryiko <andriin@fb.com> wrote: > > > > Make sample_cnt volatile to fix possible selftests failure due to compiler > > optimization preventing latest sample_cnt value to be visible to main thread. > > sample_cnt is incremented in background thread, which is then joined into main > > thread. So in terms of visibility sample_cnt update is ok. But because it's > > not volatile, compiler might make optimizations that would prevent main thread > > to see latest updated value. Fix this by marking global variable volatile. > > > > Fixes: cb1c9ddd5525 ("selftests/bpf: Add BPF ringbuf selftests") > > Signed-off-by: Andrii Nakryiko <andriin@fb.com> > > Acked-by: Song Liu <songliubraving@fb.com> Applied. Thanks. I also pushed trivial commit to fix test_verifier.
diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c index bb8541f240e2..2bba908dfa63 100644 --- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c +++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c @@ -25,7 +25,7 @@ struct sample { char comm[16]; }; -static int sample_cnt; +static volatile int sample_cnt; static int process_sample(void *ctx, void *data, size_t len) {
Make sample_cnt volatile to fix possible selftests failure due to compiler optimization preventing latest sample_cnt value to be visible to main thread. sample_cnt is incremented in background thread, which is then joined into main thread. So in terms of visibility sample_cnt update is ok. But because it's not volatile, compiler might make optimizations that would prevent main thread to see latest updated value. Fix this by marking global variable volatile. Fixes: cb1c9ddd5525 ("selftests/bpf: Add BPF ringbuf selftests") Signed-off-by: Andrii Nakryiko <andriin@fb.com> --- tools/testing/selftests/bpf/prog_tests/ringbuf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)