drbd: fix disconnect/reconnect loop, if ping-timeout == ping-int

If there is no replication traffic within the idle timeout
(ping-int seconds), DRBD will send a P_PING,
and adjust the timeout to ping-timeout.

If there is no P_PING_ACK received within this ping-timeout,
DRBD finally drops the connection, and tries to re-establish it.

To decide which timeout was active, we compared the current timeout
with the ping-timeout, and dropped the connection, if that was the case.

By default, ping-int is 10 seconds, ping-timeout is 500 ms.

Unfortunately, if you configure ping-timeout to be the same as ping-int,
expiry of the idle-timeout had been mistaken for a missing ping ack,
and caused an immediate reconnection attempt.

Fix:
Allow both timeouts to be equal, use a local variable
to store which timeout is active.
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_receiver.c

@@ -4554,6 +4554,7 @@ int drbd_asender(struct drbd_thread *thi)
 	int received = 0;
 	int expect   = sizeof(struct p_header80);
 	int empty;
+	int ping_timeout_active = 0;
 
 	sprintf(current->comm, "drbd%d_asender", mdev_to_minor(mdev));
 
@@ -4566,6 +4567,7 @@ int drbd_asender(struct drbd_thread *thi)
 			ERR_IF(!drbd_send_ping(mdev)) goto reconnect;
 			mdev->meta.socket->sk->sk_rcvtimeo =
 				mdev->net_conf->ping_timeo*HZ/10;
+			ping_timeout_active = 1;
 		}
 
 		/* conditionally cork;
@@ -4620,8 +4622,7 @@ int drbd_asender(struct drbd_thread *thi)
 			dev_err(DEV, "meta connection shut down by peer.\n");
 			goto reconnect;
 		} else if (rv == -EAGAIN) {
-			if (mdev->meta.socket->sk->sk_rcvtimeo ==
-			    mdev->net_conf->ping_timeo*HZ/10) {
+			if (ping_timeout_active) {
 				dev_err(DEV, "PingAck did not arrive in time.\n");
 				goto reconnect;
 			}
@@ -4660,6 +4661,11 @@ int drbd_asender(struct drbd_thread *thi)
 			if (!cmd->process(mdev, h))
 				goto reconnect;
 
+			/* the idle_timeout (ping-int)
+			 * has been restored in got_PingAck() */
+			if (cmd == get_asender_cmd(P_PING_ACK))
+				ping_timeout_active = 0;
+
 			buf	 = h;
 			received = 0;
 			expect	 = sizeof(struct p_header80);