selftests/xsk: add timeout for Tx thread

Add a timeout for the transmission thread. If packets are not
completed properly, for some reason, the test harness would previously
get stuck forever in a while loop. But with this patch, this timeout
will trigger, flag the test as a failure, and continue with the next
test.

Signed-off-by: Magnus Karlsson <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/testing/selftests/bpf/xskxceiver.c

···
 	return TEST_CONTINUE;
 }
 
-static void wait_for_tx_completion(struct xsk_socket_info *xsk)
+static int wait_for_tx_completion(struct xsk_socket_info *xsk)
 {
-	while (xsk->outstanding_tx)
+	struct timeval tv_end, tv_now, tv_timeout = {THREAD_TMOUT, 0};
+	int ret;
+
+	ret = gettimeofday(&tv_now, NULL);
+	if (ret)
+		exit_with_error(errno);
+	timeradd(&tv_now, &tv_timeout, &tv_end);
+
+	while (xsk->outstanding_tx) {
+		ret = gettimeofday(&tv_now, NULL);
+		if (ret)
+			exit_with_error(errno);
+		if (timercmp(&tv_now, &tv_end, >)) {
+			ksft_print_msg("ERROR: [%s] Transmission loop timed out\n", __func__);
+			return TEST_FAILURE;
+		}
+
 		complete_pkts(xsk, BATCH_SIZE);
+	}
+
+	return TEST_PASS;
 }
 
 static int send_pkts(struct test_spec *test, struct ifobject *ifobject)
···
 			return ret;
 	}
 
-	wait_for_tx_completion(ifobject->xsk);
-	return TEST_PASS;
+	return wait_for_tx_completion(ifobject->xsk);
 }
 
 static int get_xsk_stats(struct xsk_socket *xsk, struct xdp_statistics *stats)