nvmet-rdma: drain the queue-pair just before freeing it

draining the qp right after disconnect might not suffice because
the nvmet sq is not fully drained (in nvmet_sq_destroy) and we might
see completions after the drain. Instead, drain right before the
qp destroy which comes after the sq destruction and we can be sure
that no posts come after the drain.
Tested-by: NSteve Wise <swise@opengridcomputing.com>
Signed-off-by: NSagi Grimberg <sagi@grimberg.me>

drivers/nvme/target/rdma.c

@@ -951,6 +951,7 @@ static int nvmet_rdma_create_queue_ib(struct nvmet_rdma_queue *queue)
 
 static void nvmet_rdma_destroy_queue_ib(struct nvmet_rdma_queue *queue)
 {
+	ib_drain_qp(queue->cm_id->qp);
 	rdma_destroy_qp(queue->cm_id);
 	ib_free_cq(queue->cq);
 }
@@ -1245,7 +1246,6 @@ static void __nvmet_rdma_queue_disconnect(struct nvmet_rdma_queue *queue)
 
 	if (disconnect) {
 		rdma_disconnect(queue->cm_id);
-		ib_drain_qp(queue->cm_id->qp);
 		schedule_work(&queue->release_work);
 	}
 }