nvmet-rdma: avoid circular locking dependency on install_queue()

nvmet_rdma_install_queue() is driven from the ->io_work workqueue
function, but will call flush_workqueue() which might trigger
->release_work() which in itself calls flush_work on ->io_work.

To avoid that check for pending queue in disconnecting status,
and return 'controller busy' when we reached a certain threshold.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Keith Busch <kbusch@kernel.org>

Author: hreinecke

drivers/nvme/target/rdma.c

@@ -37,6 +37,8 @@
 #define NVMET_RDMA_MAX_MDTS			8
 #define NVMET_RDMA_MAX_METADATA_MDTS		5
 
+#define NVMET_RDMA_BACKLOG 128
+
 struct nvmet_rdma_srq;
 
 struct nvmet_rdma_cmd {
@@ -1583,8 +1585,19 @@ static int nvmet_rdma_queue_connect(struct rdma_cm_id *cm_id,
 	}
 
 	if (queue->host_qid == 0) {
-		/* Let inflight controller teardown complete */
-		flush_workqueue(nvmet_wq);
+		struct nvmet_rdma_queue *q;
+		int pending = 0;
+
+		/* Check for pending controller teardown */
+		mutex_lock(&nvmet_rdma_queue_mutex);
+		list_for_each_entry(q, &nvmet_rdma_queue_list, queue_list) {
+			if (q->nvme_sq.ctrl == queue->nvme_sq.ctrl &&
+			    q->state == NVMET_RDMA_Q_DISCONNECTING)
+				pending++;
+		}
+		mutex_unlock(&nvmet_rdma_queue_mutex);
+		if (pending > NVMET_RDMA_BACKLOG)
+			return NVME_SC_CONNECT_CTRL_BUSY;
 	}
 
 	ret = nvmet_rdma_cm_accept(cm_id, queue, &event->param.conn);
@@ -1880,7 +1893,7 @@ static int nvmet_rdma_enable_port(struct nvmet_rdma_port *port)
 		goto out_destroy_id;
 	}
 
-	ret = rdma_listen(cm_id, 128);
+	ret = rdma_listen(cm_id, NVMET_RDMA_BACKLOG);
 	if (ret) {
 		pr_err("listening to %pISpcs failed (%d)\n", addr, ret);
 		goto out_destroy_id;