drbd: Finish requests that completed while IO was frozen

Requests of an acked epoch are stored on the barrier_acked_requests list. In
case the private bio of such a request completes while IO on the drbd device
is suspended [req_mod(completed_ok)] then the request stays there.

When thawing IO because the fence_peer handler returned, then we use
tl_clear() to apply the connection_lost_while_pending event to all requests
on the transfer-log and the barrier_acked_requests list.

Up to now the connection_lost_while_pending event was not applied
on requests on the barrier_acked_requests list. Fixed that.

I.e. now the connection_lost_while_pending and resend events are
applied to requests on the barrier_acked_requests list. For that
it is necessary that the resend event finishes (local only)
READS correctly.

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

drivers/block/drbd/drbd_req.c

@@ -683,6 +683,12 @@ int __req_mod(struct drbd_request *req, enum drbd_req_event what,
 		break;
 
 	case RESEND:
+		/* Simply complete (local only) READs. */
+		if (!(req->rq_state & RQ_WRITE) && !req->w.cb) {
+			mod_rq_state(req, m, RQ_COMPLETION_SUSP, 0);
+			break;
+		}
+
 		/* If RQ_NET_OK is already set, we got a P_WRITE_ACK or P_RECV_ACK
 		   before the connection loss (B&C only); only P_BARRIER_ACK
 		   (or the local completion?) was missing when we suspended.

drivers/block/drbd/drbd_state.c

@@ -1503,7 +1503,6 @@ static int w_after_conn_state_ch(struct drbd_work *w, int unused)
 	if (ns_max.susp_fen) {
 		/* case1: The outdate peer handler is successful: */
 		if (ns_max.pdsk <= D_OUTDATED) {
-			tl_clear(tconn);
 			rcu_read_lock();
 			idr_for_each_entry(&tconn->volumes, mdev, vnr) {
 				if (test_bit(NEW_CUR_UUID, &mdev->flags)) {
@@ -1512,10 +1511,13 @@ static int w_after_conn_state_ch(struct drbd_work *w, int unused)
 				}
 			}
 			rcu_read_unlock();
-			conn_request_state(tconn,
-					   (union drbd_state) { { .susp_fen = 1 } },
-					   (union drbd_state) { { .susp_fen = 0 } },
-					   CS_VERBOSE);
+			spin_lock_irq(&tconn->req_lock);
+			_tl_restart(tconn, CONNECTION_LOST_WHILE_PENDING);
+			_conn_request_state(tconn,
+					    (union drbd_state) { { .susp_fen = 1 } },
+					    (union drbd_state) { { .susp_fen = 0 } },
+					    CS_VERBOSE);
+			spin_unlock_irq(&tconn->req_lock);
 		}
 		/* case2: The connection was established again: */
 		if (ns_min.conn >= C_CONNECTED) {