zdtm: fix a race in socket_udp and socket_udplite

If we have two sockets and send an upd message from one to another,
we can't be sure that it will be delivered immediately,
there is a change to get from recv(..., MSG_DONTWAIT) EGAIN.

This message is handled asynchronously in a kernel space, so
there may be a small timeout before we get it from another socket.

v2: fix socket6_udp too

Reported-by: Mr Travis
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

test/zdtm/static/socket6_udp.c

@@ -85,7 +85,7 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
-	ret = recvfrom(sk1, buf, sizeof(buf), MSG_DONTWAIT,
+	ret = recvfrom(sk1, buf, sizeof(buf), 0,
 			(struct sockaddr *)&addr, &len);
 	if (ret <= 0) {
 		fail("Can't recv C");
@@ -102,7 +102,7 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
-	ret = recvfrom(sk2, buf, sizeof(buf), MSG_DONTWAIT,
+	ret = recvfrom(sk2, buf, sizeof(buf), 0,
 			(struct sockaddr *)&addr, &len);
 	if (ret <= 0) {
 		fail("Can't recv");

test/zdtm/static/socket_udp.c

@@ -90,7 +90,7 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
-	ret = recvfrom(sk1, buf, sizeof(buf), MSG_DONTWAIT,
+	ret = recvfrom(sk1, buf, sizeof(buf), 0,
 			(struct sockaddr *)&addr, &len);
 	if (ret <= 0) {
 		fail("Can't recv C");
@@ -107,7 +107,7 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
-	ret = recvfrom(sk2, buf, sizeof(buf), MSG_DONTWAIT,
+	ret = recvfrom(sk2, buf, sizeof(buf), 0,
 			(struct sockaddr *)&addr, &len);
 	if (ret <= 0) {
 		fail("Can't recv");

test/zdtm/static/socket_udplite.c

@@ -90,7 +90,7 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
-	ret = recvfrom(sk1, buf, sizeof(buf), MSG_DONTWAIT,
+	ret = recvfrom(sk1, buf, sizeof(buf), 0,
 			(struct sockaddr *)&addr, &len);
 	if (ret <= 0) {
 		fail("Can't recv C");
@@ -107,7 +107,7 @@ int main(int argc, char **argv)
 		return 1;
 	}
 
-	ret = recvfrom(sk2, buf, sizeof(buf), MSG_DONTWAIT,
+	ret = recvfrom(sk2, buf, sizeof(buf), 0,
 			(struct sockaddr *)&addr, &len);
 	if (ret <= 0) {
 		fail("Can't recv");