cxgb4: avoid enabling napi twice to the same queue

BugLink: http://bugs.launchpad.net/bugs/1698799

[ Upstream commit e7519f99 ]

Take uld mutex to avoid race between cxgb_up() and
cxgb4_register_uld() to enable napi for the same uld
queue.
Signed-off-by: Ganesh Goudar <ganeshgr@chelsio.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c

@@ -2714,10 +2714,14 @@ static int cxgb_up(struct adapter *adap)
 		if (err)
 			goto irq_err;
 	}
+
+	mutex_lock(&uld_mutex);
 	enable_rx(adap);
 	t4_sge_start(adap);
 	t4_intr_enable(adap);
 	adap->flags |= FULL_INIT_DONE;
+	mutex_unlock(&uld_mutex);
+
 	notify_ulds(adap, CXGB4_STATE_UP);
 #if IS_ENABLED(CONFIG_IPV6)
 	update_clip(adap);