diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 6960715..e8c564a 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -539,7 +539,6 @@
 {
 	int i;
 
-	mutex_lock(&open_mutex);
 	if (acm->dev) {
 		usb_autopm_get_interface(acm->control);
 		acm_set_control(acm, acm->ctrlout = 0);
@@ -551,14 +550,15 @@
 		acm->control->needs_remote_wakeup = 0;
 		usb_autopm_put_interface(acm->control);
 	}
-	mutex_unlock(&open_mutex);
 }
 
 static void acm_tty_hangup(struct tty_struct *tty)
 {
 	struct acm *acm = tty->driver_data;
 	tty_port_hangup(&acm->port);
+	mutex_lock(&open_mutex);
 	acm_port_down(acm);
+	mutex_unlock(&open_mutex);
 }
 
 static void acm_tty_close(struct tty_struct *tty, struct file *filp)
@@ -569,8 +569,9 @@
 	   shutdown */
 	if (!acm)
 		return;
+
+	mutex_lock(&open_mutex);
 	if (tty_port_close_start(&acm->port, tty, filp) == 0) {
-		mutex_lock(&open_mutex);
 		if (!acm->dev) {
 			tty_port_tty_set(&acm->port, NULL);
 			acm_tty_unregister(acm);
@@ -582,6 +583,7 @@
 	acm_port_down(acm);
 	tty_port_close_end(&acm->port, tty);
 	tty_port_tty_set(&acm->port, NULL);
+	mutex_unlock(&open_mutex);
 }
 
 static int acm_tty_write(struct tty_struct *tty,