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

nvmet_tcp_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/tcp.c

@@ -25,6 +25,7 @@
 
 #define NVMET_TCP_DEF_INLINE_DATA_SIZE	(4 * PAGE_SIZE)
 #define NVMET_TCP_MAXH2CDATA		0x400000 /* 16M arbitrary limit */
+#define NVMET_TCP_BACKLOG 128
 
 static int param_store_val(const char *str, int *val, int min, int max)
 {
@@ -2067,7 +2068,7 @@ static int nvmet_tcp_add_port(struct nvmet_port *nport)
 		goto err_sock;
 	}
 
-	ret = kernel_listen(port->sock, 128);
+	ret = kernel_listen(port->sock, NVMET_TCP_BACKLOG);
 	if (ret) {
 		pr_err("failed to listen %d on port sock\n", ret);
 		goto err_sock;
@@ -2133,8 +2134,19 @@ static u16 nvmet_tcp_install_queue(struct nvmet_sq *sq)
 		container_of(sq, struct nvmet_tcp_queue, nvme_sq);
 
 	if (sq->qid == 0) {
-		/* Let inflight controller teardown complete */
-		flush_workqueue(nvmet_wq);
+		struct nvmet_tcp_queue *q;
+		int pending = 0;
+
+		/* Check for pending controller teardown */
+		mutex_lock(&nvmet_tcp_queue_mutex);
+		list_for_each_entry(q, &nvmet_tcp_queue_list, queue_list) {
+			if (q->nvme_sq.ctrl == sq->ctrl &&
+			    q->state == NVMET_TCP_Q_DISCONNECTING)
+				pending++;
+		}
+		mutex_unlock(&nvmet_tcp_queue_mutex);
+		if (pending > NVMET_TCP_BACKLOG)
+			return NVME_SC_CONNECT_CTRL_BUSY;
 	}
 
 	queue->nr_cmds = sq->size * 2;