[PATCH bpf] selftests/bpf: de-flake test_tcpbpf

* [PATCH bpf] selftests/bpf: de-flake test_tcpbpf
@ 2019-12-04 19:09 Stanislav Fomichev
  2019-12-05  2:01 ` Alexei Starovoitov
  0 siblings, 1 reply; 2+ messages in thread
From: Stanislav Fomichev @ 2019-12-04 19:09 UTC (permalink / raw)
  To: netdev, bpf; +Cc: davem, ast, daniel, Stanislav Fomichev, Lawrence Brakmo

It looks like BPF program that handles BPF_SOCK_OPS_STATE_CB state
can race with the bpf_map_lookup_elem("global_map"); I sometimes
see the failures in this test and re-running helps.

Since we know that we expect the callback to be called 3 times (one
time for listener socket, two times for both ends of the connection),
let's export this number and add simple retry logic around that.

Also, let's make EXPECT_EQ() not return on failure, but continue
evaluating all conditions; that should make potential debugging
easier.

With this fix in place I don't observe the flakiness anymore.

Cc: Lawrence Brakmo <brakmo@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
---
 .../selftests/bpf/progs/test_tcpbpf_kern.c    |  1 +
 tools/testing/selftests/bpf/test_tcpbpf.h     |  1 +
 .../testing/selftests/bpf/test_tcpbpf_user.c  | 25 +++++++++++++------
 3 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/test_tcpbpf_kern.c b/tools/testing/selftests/bpf/progs/test_tcpbpf_kern.c
index 2e233613d1fc..7fa4595d2b66 100644
--- a/tools/testing/selftests/bpf/progs/test_tcpbpf_kern.c
+++ b/tools/testing/selftests/bpf/progs/test_tcpbpf_kern.c
@@ -131,6 +131,7 @@ int bpf_testcb(struct bpf_sock_ops *skops)
 				g.bytes_received = skops->bytes_received;
 				g.bytes_acked = skops->bytes_acked;
 			}
+			g.num_close_events++;
 			bpf_map_update_elem(&global_map, &key, &g,
 					    BPF_ANY);
 		}
diff --git a/tools/testing/selftests/bpf/test_tcpbpf.h b/tools/testing/selftests/bpf/test_tcpbpf.h
index 7bcfa6207005..6220b95cbd02 100644
--- a/tools/testing/selftests/bpf/test_tcpbpf.h
+++ b/tools/testing/selftests/bpf/test_tcpbpf.h
@@ -13,5 +13,6 @@ struct tcpbpf_globals {
 	__u64 bytes_received;
 	__u64 bytes_acked;
 	__u32 num_listen;
+	__u32 num_close_events;
 };
 #endif
diff --git a/tools/testing/selftests/bpf/test_tcpbpf_user.c b/tools/testing/selftests/bpf/test_tcpbpf_user.c
index 716b4e3be581..3ae127620463 100644
--- a/tools/testing/selftests/bpf/test_tcpbpf_user.c
+++ b/tools/testing/selftests/bpf/test_tcpbpf_user.c
@@ -16,6 +16,9 @@
 
 #include "test_tcpbpf.h"
 
+/* 3 comes from one listening socket + both ends of the connection */
+#define EXPECTED_CLOSE_EVENTS		3
+
 #define EXPECT_EQ(expected, actual, fmt)			\
 	do {							\
 		if ((expected) != (actual)) {			\
@@ -23,13 +26,14 @@
 			       "    Actual: %" fmt "\n"		\
 			       "  Expected: %" fmt "\n",	\
 			       (actual), (expected));		\
-			goto err;				\
+			ret--;					\
 		}						\
 	} while (0)
 
 int verify_result(const struct tcpbpf_globals *result)
 {
 	__u32 expected_events;
+	int ret = 0;
 
 	expected_events = ((1 << BPF_SOCK_OPS_TIMEOUT_INIT) |
 			   (1 << BPF_SOCK_OPS_RWND_INIT) |
@@ -48,15 +52,15 @@ int verify_result(const struct tcpbpf_globals *result)
 	EXPECT_EQ(0x80, result->bad_cb_test_rv, PRIu32);
 	EXPECT_EQ(0, result->good_cb_test_rv, PRIu32);
 	EXPECT_EQ(1, result->num_listen, PRIu32);
+	EXPECT_EQ(EXPECTED_CLOSE_EVENTS, result->num_close_events, PRIu32);
 
-	return 0;
-err:
-	return -1;
+	return ret;
 }
 
 int verify_sockopt_result(int sock_map_fd)
 {
 	__u32 key = 0;
+	int ret = 0;
 	int res;
 	int rv;
 
@@ -69,9 +73,7 @@ int verify_sockopt_result(int sock_map_fd)
 	rv = bpf_map_lookup_elem(sock_map_fd, &key, &res);
 	EXPECT_EQ(0, rv, "d");
 	EXPECT_EQ(1, res, "d");
-	return 0;
-err:
-	return -1;
+	return ret;
 }
 
 static int bpf_find_map(const char *test, struct bpf_object *obj,
@@ -96,6 +98,7 @@ int main(int argc, char **argv)
 	int error = EXIT_FAILURE;
 	struct bpf_object *obj;
 	int cg_fd = -1;
+	int retry = 10;
 	__u32 key = 0;
 	int rv;
 
@@ -134,12 +137,20 @@ int main(int argc, char **argv)
 	if (sock_map_fd < 0)
 		goto err;
 
+retry_lookup:
 	rv = bpf_map_lookup_elem(map_fd, &key, &g);
 	if (rv != 0) {
 		printf("FAILED: bpf_map_lookup_elem returns %d\n", rv);
 		goto err;
 	}
 
+	if (g.num_close_events != EXPECTED_CLOSE_EVENTS && retry--) {
+		printf("Unexpected number of close events (%d), retrying!\n",
+		       g.num_close_events);
+		usleep(100);
+		goto retry_lookup;
+	}
+
 	if (verify_result(&g)) {
 		printf("FAILED: Wrong stats\n");
 		goto err;
-- 
2.24.0.393.g34dc348eaf-goog


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