drbd: when receive times out on meta socket, also check last receive time on data socket

If we have an asymetrically congested network, we may send P_PING,
but due to congestion, the corresponding P_PING_ACK would time out,
and we would drop a (congested, but otherwise) healthy connection
("PingAck did not arrive in time.")
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_receiver.c

@@ -4602,6 +4602,11 @@ int drbd_asender(struct drbd_thread *thi)
 			dev_err(DEV, "meta connection shut down by peer.\n");
 			goto reconnect;
 		} else if (rv == -EAGAIN) {
+			/* If the data socket received something meanwhile,
+			 * that is good enough: peer is still alive. */
+			if (time_after(mdev->last_received,
+				jiffies - mdev->meta.socket->sk->sk_rcvtimeo))
+				continue;
 			if (ping_timeout_active) {
 				dev_err(DEV, "PingAck did not arrive in time.\n");
 				goto reconnect;
@@ -4637,6 +4642,7 @@ int drbd_asender(struct drbd_thread *thi)
 				goto reconnect;
 		}
 		if (received == expect) {
+			mdev->last_received = jiffies;
 			D_ASSERT(cmd != NULL);
 			if (!cmd->process(mdev, h))
 				goto reconnect;