drbd: fix hang on local read errors while disconnected

"canceled" w_read_retry_remote never completed, if they have been
canceled after drbd_disconnect connection teardown cleanup has already
run (or we are currently not connected anyways).

Fixed by not queueing a remote retry if we already know it won't work
(pdsk not uptodate), and cleanup ourselves on "cancel", in case we hit a
race with drbd_disconnect.

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

drivers/block/drbd/drbd_req.c

@@ -452,20 +452,21 @@ void __req_mod(struct drbd_request *req, enum drbd_req_event what,
 
 		dev_alert(DEV, "Local READ failed sec=%llus size=%u\n",
 		      (unsigned long long)req->sector, req->size);
-		/* _req_mod(req,to_be_send); oops, recursion... */
 		D_ASSERT(!(req->rq_state & RQ_NET_MASK));
-		req->rq_state |= RQ_NET_PENDING;
-		inc_ap_pending(mdev);
 
 		__drbd_chk_io_error(mdev, FALSE);
 		put_ldev(mdev);
-		/* NOTE: if we have no connection,
-		 * or know the peer has no good data either,
-		 * then we don't actually need to "queue_for_net_read",
-		 * but we do so anyways, since the drbd_io_error()
-		 * and the potential state change to "Diskless"
-		 * needs to be done from process context */
 
+		/* no point in retrying if there is no good remote data,
+		 * or we have no connection. */
+		if (mdev->state.pdsk != D_UP_TO_DATE) {
+			_req_may_be_done(req, m);
+			break;
+		}
+
+		/* _req_mod(req,to_be_send); oops, recursion... */
+		req->rq_state |= RQ_NET_PENDING;
+		inc_ap_pending(mdev);
 		/* fall through: _req_mod(req,queue_for_net_read); */
 
 	case queue_for_net_read:
@@ -575,6 +576,9 @@ void __req_mod(struct drbd_request *req, enum drbd_req_event what,
 		_req_may_be_done(req, m);
 		break;
 
+	case read_retry_remote_canceled:
+		req->rq_state &= ~RQ_NET_QUEUED;
+		/* fall through, in case we raced with drbd_disconnect */
 	case connection_lost_while_pending:
 		/* transfer log cleanup after connection loss */
 		/* assert something? */

drivers/block/drbd/drbd_req.h

@@ -91,6 +91,7 @@ enum drbd_req_event {
 	send_failed,
 	handed_over_to_network,
 	connection_lost_while_pending,
+	read_retry_remote_canceled,
 	recv_acked_by_peer,
 	write_acked_by_peer,
 	write_acked_by_peer_and_sis, /* and set_in_sync */

drivers/block/drbd/drbd_worker.c

@@ -266,10 +266,8 @@ int w_read_retry_remote(struct drbd_conf *mdev, struct drbd_work *w, int cancel)
 	 * to give the disk the chance to relocate that block */
 
 	spin_lock_irq(&mdev->req_lock);
-	if (cancel ||
-	    mdev->state.conn < C_CONNECTED ||
-	    mdev->state.pdsk <= D_INCONSISTENT) {
-		_req_mod(req, send_canceled);
+	if (cancel || mdev->state.pdsk != D_UP_TO_DATE) {
+		_req_mod(req, read_retry_remote_canceled);
 		spin_unlock_irq(&mdev->req_lock);
 		dev_alert(DEV, "WE ARE LOST. Local IO failure, no peer.\n");
 		return 1;