nvme-tcp: fix possible null deref on a timed out io queue connect

If I/O queue connect times out, we might have freed the queue socket
already, so check for that on the error path in nvme_tcp_start_queue.
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/tcp.c

@@ -1423,7 +1423,8 @@ static int nvme_tcp_start_queue(struct nvme_ctrl *nctrl, int idx)
 	if (!ret) {
 		set_bit(NVME_TCP_Q_LIVE, &ctrl->queues[idx].flags);
 	} else {
-		__nvme_tcp_stop_queue(&ctrl->queues[idx]);
+		if (test_bit(NVME_TCP_Q_ALLOCATED, &ctrl->queues[idx].flags))
+			__nvme_tcp_stop_queue(&ctrl->queues[idx]);
 		dev_err(nctrl->device,
 			"failed to connect queue: %d ret=%d\n", idx, ret);
 	}