drbd: fix potential imbalance of ap_in_flight

When we receive a barrier ack, we walk the ring list of drbd requests
in the transfer log of the respective epoch, do some housekeeping,
and free those objects.

We tried to keep epochs of mirrored and unmirrored drbd requests
separate, and assert that no local-only requests are present in a
barrier_acked epoch.

It turns out that this has quite a number of corner cases and would
add bloated code without functional benefit.

We now revert the (insufficient) commits
 drbd: Fixed an issue with AHEAD -> SYNC_SOURCE transitions
 drbd: Ensure that an epoch contains only requests of one kind
and instead fix the processing of barrier acks to cope with
a mix of local-only and mirrored requests.
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

drivers/block/drbd/drbd_main.c

@@ -337,23 +337,6 @@ void tl_release(struct drbd_conf *mdev, unsigned int barrier_nr,
 }
 
 
-/* In C_AHEAD mode only out_of_sync packets are sent for requests. Detach
- * those requests from the newsest barrier when changing to an other cstate.
- *
- * That headless list vanishes when the last request finished its write or
- * send out_of_sync packet.  */
-static void tl_forget(struct drbd_conf *mdev)
-{
-	struct drbd_tl_epoch *b;
-
-	if (test_bit(CREATE_BARRIER, &mdev->flags))
-		return;
-
-	b = mdev->newest_tle;
-	list_del(&b->requests);
-	_tl_add_barrier(mdev, b);
-}
-
 /**
  * _tl_restart() - Walks the transfer log, and applies an action to all requests
  * @mdev:	DRBD device.
@@ -1265,14 +1248,6 @@ __drbd_set_state(struct drbd_conf *mdev, union drbd_state ns,
 	if (os.conn < C_CONNECTED && ns.conn >= C_CONNECTED)
 		drbd_resume_al(mdev);
 
-	/* Start a new epoch in case we start to mirror write requests */
-	if (!drbd_should_do_remote(os) && drbd_should_do_remote(ns))
-		tl_forget(mdev);
-
-	/* Do not add local-only requests to an epoch with mirrored requests */
-	if (drbd_should_do_remote(os) && !drbd_should_do_remote(ns))
-		set_bit(CREATE_BARRIER, &mdev->flags);
-
 	ascw = kmalloc(sizeof(*ascw), GFP_ATOMIC);
 	if (ascw) {
 		ascw->os = os;

drivers/block/drbd/drbd_req.c

@@ -712,10 +712,11 @@ int __req_mod(struct drbd_request *req, enum drbd_req_event what,
 			dev_err(DEV, "FIXME (barrier_acked but pending)\n");
 			list_move(&req->tl_requests, &mdev->out_of_sequence_requests);
 		}
-		D_ASSERT(req->rq_state & RQ_NET_SENT);
-		req->rq_state |= RQ_NET_DONE;
-		if (mdev->net_conf->wire_protocol == DRBD_PROT_A)
-			atomic_sub(req->size>>9, &mdev->ap_in_flight);
+		if ((req->rq_state & RQ_NET_MASK) != 0) {
+			req->rq_state |= RQ_NET_DONE;
+			if (mdev->net_conf->wire_protocol == DRBD_PROT_A)
+				atomic_sub(req->size>>9, &mdev->ap_in_flight);
+		}
 		_req_may_be_done(req, m); /* Allowed while state.susp */
 		break;