drbd: Fixed compat issue with disconnecting 8.4 from a primary 8.3

For compatibility reasons 8.4 has to send P_STATE_CHG_REQ (instead
of P_CONN_ST_CHG_REQ) when disconnecting.

In the receiving code path we missed to convert the old
answer (P_STATE_CHG_REPLY) back to 8.4 logic. Therefore
the CL_ST_CHG_SUCCESS or CL_ST_CHG_FAIL bit in the flags word
of mdev got set, while the state code was waiting for
the CONN_WD_ST_CHG_OKAY or CONN_WD_ST_CHG_FAIL bits in tconn.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_int.h

@@ -811,6 +811,7 @@ enum {
 	SEND_PING,		/* whether asender should send a ping asap */
 	SIGNAL_ASENDER,		/* whether asender wants to be interrupted */
 	GOT_PING_ACK,		/* set when we receive a ping_ack packet, ping_wait gets woken */
+	CONN_WD_ST_CHG_REQ,	/* A cluster wide state change on the connection is active */
 	CONN_WD_ST_CHG_OKAY,
 	CONN_WD_ST_CHG_FAIL,
 	CONN_DRY_RUN,		/* Expect disconnect after resync handshake. */

drivers/block/drbd/drbd_receiver.c

@@ -4827,6 +4827,11 @@ static int got_RqSReply(struct drbd_tconn *tconn, struct packet_info *pi)
 	if (!mdev)
 		return -EIO;
 
+	if (test_bit(CONN_WD_ST_CHG_REQ, &tconn->flags)) {
+		D_ASSERT(tconn->agreed_pro_version < 100);
+		return got_conn_RqSReply(tconn, pi);
+	}
+
 	if (retcode >= SS_SUCCESS) {
 		set_bit(CL_ST_CHG_SUCCESS, &mdev->flags);
 	} else {

drivers/block/drbd/drbd_state.c

@@ -1671,14 +1671,17 @@ conn_cl_wide(struct drbd_tconn *tconn, union drbd_state mask, union drbd_state v
 	spin_unlock_irq(&tconn->req_lock);
 	mutex_lock(&tconn->cstate_mutex);
 
+	set_bit(CONN_WD_ST_CHG_REQ, &tconn->flags);
 	if (conn_send_state_req(tconn, mask, val)) {
+		clear_bit(CONN_WD_ST_CHG_REQ, &tconn->flags);
 		rv = SS_CW_FAILED_BY_PEER;
 		/* if (f & CS_VERBOSE)
 		   print_st_err(mdev, os, ns, rv); */
 		goto abort;
 	}
 
 	wait_event(tconn->ping_wait, (rv = _conn_rq_cond(tconn, mask, val)));
+	clear_bit(CONN_WD_ST_CHG_REQ, &tconn->flags);
 
 abort:
 	mutex_unlock(&tconn->cstate_mutex);