[PATCH bpf 2/2] selftests/bpf: drain ringbuf samples at the end of test

[Andrii Nakryiko <andrii@kernel.org>]

Avoid occasional test failures due to the last sample being delayed to
another ring_buffer__poll() call. Instead, drain samples completely with
ring_buffer__consume(). This is supposed to fix a rare and non-deterministic
test failure in libbpf CI.

Fixes: cb1c9ddd5525 ("selftests/bpf: Add BPF ringbuf selftests")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 tools/testing/selftests/bpf/prog_tests/ringbuf.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
index 1a48c6f7f54e..fddbc5db5d6a 100644
--- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c
+++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
@@ -220,6 +220,12 @@ void test_ringbuf(void)
 	if (CHECK(bg_ret <= 0, "bg_ret", "epoll_wait result: %ld", bg_ret))
 		goto cleanup;
 
+	/* due to timing variations, there could still be non-notified
+	 * samples, so consume them here to collect all the samples
+	 */
+	err = ring_buffer__consume(ringbuf);
+	CHECK(err < 0, "rb_consume", "failed: %d\b", err);
+
 	/* 3 rounds, 2 samples each */
 	cnt = atomic_xchg(&sample_cnt, 0);
 	CHECK(cnt != 6, "cnt", "exp %d samples, got %d\n", 6, cnt);
-- 
2.24.1