diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 90ceef1776c34197c65fb58988e0fc5771184a35..d07fccf3bab5caa431dd5d77d3d552913a89ac9c 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -1886,24 +1886,22 @@ static void ftdi_dtr_rts(struct usb_serial_port *port, int on)
 {
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
 
-	mutex_lock(&port->serial->disc_mutex);
-	if (!port->serial->disconnected) {
-		/* Disable flow control */
-		if (!on && usb_control_msg(port->serial->dev,
+	/* Disable flow control */
+	if (!on) {
+		if (usb_control_msg(port->serial->dev,
 			    usb_sndctrlpipe(port->serial->dev, 0),
 			    FTDI_SIO_SET_FLOW_CTRL_REQUEST,
 			    FTDI_SIO_SET_FLOW_CTRL_REQUEST_TYPE,
 			    0, priv->interface, NULL, 0,
 			    WDR_TIMEOUT) < 0) {
-			    dev_err(&port->dev, "error from flowcontrol urb\n");
+			dev_err(&port->dev, "error from flowcontrol urb\n");
 		}
-		/* drop RTS and DTR */
-		if (on)
-			set_mctrl(port, TIOCM_DTR | TIOCM_RTS);
-		else
-			clear_mctrl(port, TIOCM_DTR | TIOCM_RTS);
 	}
-	mutex_unlock(&port->serial->disc_mutex);
+	/* drop RTS and DTR */
+	if (on)
+		set_mctrl(port, TIOCM_DTR | TIOCM_RTS);
+	else
+		clear_mctrl(port, TIOCM_DTR | TIOCM_RTS);
 }
 
 /*
diff --git a/drivers/usb/serial/mct_u232.c b/drivers/usb/serial/mct_u232.c
index b6911757c855b6802d82c126ce60f778d5b0f8db..d9c86516fed434fb80cc4a40613f9fc3f5a80eb5 100644
--- a/drivers/usb/serial/mct_u232.c
+++ b/drivers/usb/serial/mct_u232.c
@@ -499,19 +499,15 @@ static void mct_u232_dtr_rts(struct usb_serial_port *port, int on)
 	unsigned int control_state;
 	struct mct_u232_private *priv = usb_get_serial_port_data(port);
 
-	mutex_lock(&port->serial->disc_mutex);
-	if (!port->serial->disconnected) {
-		/* drop DTR and RTS */
-		spin_lock_irq(&priv->lock);
-		if (on)
-			priv->control_state |= TIOCM_DTR | TIOCM_RTS;
-		else
-			priv->control_state &= ~(TIOCM_DTR | TIOCM_RTS);
-		control_state = priv->control_state;
-		spin_unlock_irq(&priv->lock);
-		mct_u232_set_modem_ctrl(port, control_state);
-	}
-	mutex_unlock(&port->serial->disc_mutex);
+	spin_lock_irq(&priv->lock);
+	if (on)
+		priv->control_state |= TIOCM_DTR | TIOCM_RTS;
+	else
+		priv->control_state &= ~(TIOCM_DTR | TIOCM_RTS);
+	control_state = priv->control_state;
+	spin_unlock_irq(&priv->lock);
+
+	mct_u232_set_modem_ctrl(port, control_state);
 }
 
 static void mct_u232_close(struct usb_serial_port *port)
diff --git a/drivers/usb/serial/quatech2.c b/drivers/usb/serial/quatech2.c
index d152be97d041b61727df4648fa8918e5eff10a23..a8d5110d4cc566369ebc6f47a2d99c023ef5e5a2 100644
--- a/drivers/usb/serial/quatech2.c
+++ b/drivers/usb/serial/quatech2.c
@@ -945,19 +945,17 @@ static void qt2_dtr_rts(struct usb_serial_port *port, int on)
 	struct usb_device *dev = port->serial->dev;
 	struct qt2_port_private *port_priv = usb_get_serial_port_data(port);
 
-	mutex_lock(&port->serial->disc_mutex);
-	if (!port->serial->disconnected) {
-		/* Disable flow control */
-		if (!on && qt2_setregister(dev, port_priv->device_port,
+	/* Disable flow control */
+	if (!on) {
+		if (qt2_setregister(dev, port_priv->device_port,
 					   UART_MCR, 0) < 0)
 			dev_warn(&port->dev, "error from flowcontrol urb\n");
-		/* drop RTS and DTR */
-		if (on)
-			update_mctrl(port_priv, TIOCM_DTR | TIOCM_RTS, 0);
-		else
-			update_mctrl(port_priv, 0, TIOCM_DTR | TIOCM_RTS);
 	}
-	mutex_unlock(&port->serial->disc_mutex);
+	/* drop RTS and DTR */
+	if (on)
+		update_mctrl(port_priv, TIOCM_DTR | TIOCM_RTS, 0);
+	else
+		update_mctrl(port_priv, 0, TIOCM_DTR | TIOCM_RTS);
 }
 
 static void qt2_update_msr(struct usb_serial_port *port, unsigned char *ch)
diff --git a/drivers/usb/serial/sierra.c b/drivers/usb/serial/sierra.c
index af06f2f5f38b36f1b11976429cec35cd92ddb9b5..d4426c038c325933d8f26afeed550f0918e3892f 100644
--- a/drivers/usb/serial/sierra.c
+++ b/drivers/usb/serial/sierra.c
@@ -861,19 +861,13 @@ static int sierra_open(struct tty_struct *tty, struct usb_serial_port *port)
 
 static void sierra_dtr_rts(struct usb_serial_port *port, int on)
 {
-	struct usb_serial *serial = port->serial;
 	struct sierra_port_private *portdata;
 
 	portdata = usb_get_serial_port_data(port);
 	portdata->rts_state = on;
 	portdata->dtr_state = on;
 
-	if (serial->dev) {
-		mutex_lock(&serial->disc_mutex);
-		if (!serial->disconnected)
-			sierra_send_setup(port);
-		mutex_unlock(&serial->disc_mutex);
-	}
+	sierra_send_setup(port);
 }
 
 static int sierra_startup(struct usb_serial *serial)
diff --git a/drivers/usb/serial/ssu100.c b/drivers/usb/serial/ssu100.c
index 4543ea35022939976886dc576b7e6c1f2d37584c..d938396171e87f22dd4f1f685dc3d33cccf751a9 100644
--- a/drivers/usb/serial/ssu100.c
+++ b/drivers/usb/serial/ssu100.c
@@ -506,19 +506,16 @@ static void ssu100_dtr_rts(struct usb_serial_port *port, int on)
 {
 	struct usb_device *dev = port->serial->dev;
 
-	mutex_lock(&port->serial->disc_mutex);
-	if (!port->serial->disconnected) {
-		/* Disable flow control */
-		if (!on &&
-		    ssu100_setregister(dev, 0, UART_MCR, 0) < 0)
+	/* Disable flow control */
+	if (!on) {
+		if (ssu100_setregister(dev, 0, UART_MCR, 0) < 0)
 			dev_err(&port->dev, "error from flowcontrol urb\n");
-		/* drop RTS and DTR */
-		if (on)
-			set_mctrl(dev, TIOCM_DTR | TIOCM_RTS);
-		else
-			clear_mctrl(dev, TIOCM_DTR | TIOCM_RTS);
 	}
-	mutex_unlock(&port->serial->disc_mutex);
+	/* drop RTS and DTR */
+	if (on)
+		set_mctrl(dev, TIOCM_DTR | TIOCM_RTS);
+	else
+		clear_mctrl(dev, TIOCM_DTR | TIOCM_RTS);
 }
 
 static void ssu100_update_msr(struct usb_serial_port *port, u8 msr)
diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index 0a17f5942552a92d1addeb4248fc5e9c6b93501c..a19ed74d770d73b016e69070cb27e282bbc21fad 100644
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -694,10 +694,20 @@ static int serial_carrier_raised(struct tty_port *port)
 static void serial_dtr_rts(struct tty_port *port, int on)
 {
 	struct usb_serial_port *p = container_of(port, struct usb_serial_port, port);
-	struct usb_serial_driver *drv = p->serial->type;
+	struct usb_serial *serial = p->serial;
+	struct usb_serial_driver *drv = serial->type;
 
-	if (drv->dtr_rts)
+	if (!drv->dtr_rts)
+		return;
+	/*
+	 * Work-around bug in the tty-layer which can result in dtr_rts
+	 * being called after a disconnect (and tty_unregister_device
+	 * has returned). Remove once bug has been squashed.
+	 */
+	mutex_lock(&serial->disc_mutex);
+	if (!serial->disconnected)
 		drv->dtr_rts(p, on);
+	mutex_unlock(&serial->disc_mutex);
 }
 
 static const struct tty_port_operations serial_port_ops = {
diff --git a/drivers/usb/serial/usb_wwan.c b/drivers/usb/serial/usb_wwan.c
index 01c94aada56cc2fbb97e1ad083b054143535706d..1355a6cd45089832ee73520e9e9b1c6343bf7a23 100644
--- a/drivers/usb/serial/usb_wwan.c
+++ b/drivers/usb/serial/usb_wwan.c
@@ -38,7 +38,6 @@
 
 void usb_wwan_dtr_rts(struct usb_serial_port *port, int on)
 {
-	struct usb_serial *serial = port->serial;
 	struct usb_wwan_port_private *portdata;
 	struct usb_wwan_intf_private *intfdata;
 
@@ -48,12 +47,11 @@ void usb_wwan_dtr_rts(struct usb_serial_port *port, int on)
 		return;
 
 	portdata = usb_get_serial_port_data(port);
-	mutex_lock(&serial->disc_mutex);
+	/* FIXME: locking */
 	portdata->rts_state = on;
 	portdata->dtr_state = on;
-	if (serial->dev)
-		intfdata->send_setup(port);
-	mutex_unlock(&serial->disc_mutex);
+
+	intfdata->send_setup(port);
 }
 EXPORT_SYMBOL(usb_wwan_dtr_rts);