[PATCH] USB: serial: keyspan_pda: fix data loss on receive throttling

[Johan Hovold <johan@kernel.org>]

Killing the interrupt-in urb when the line disciple requests throttling
may lead to data loss if an ongoing transfer is cancelled.

Instead set a flag to prevent the completion handler from resubmitting
the urb until the port is unthrottled.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/usb/serial/keyspan_pda.c | 44 +++++++++++++++++++++++++-------
 1 file changed, 35 insertions(+), 9 deletions(-)

diff --git a/drivers/usb/serial/keyspan_pda.c b/drivers/usb/serial/keyspan_pda.c
index f05bcce60600..dd4cfd17f7ad 100644
--- a/drivers/usb/serial/keyspan_pda.c
+++ b/drivers/usb/serial/keyspan_pda.c
@@ -33,6 +33,8 @@ struct keyspan_pda_private {
 	struct work_struct	unthrottle_work;
 	struct usb_serial	*serial;
 	struct usb_serial_port	*port;
+	bool			throttled;
+	bool			throttle_req;
 };
 
 static int keyspan_pda_write_start(struct usb_serial_port *port);
@@ -148,6 +150,7 @@ static void keyspan_pda_rx_interrupt(struct urb *urb)
 	int retval;
 	int status = urb->status;
 	struct keyspan_pda_private *priv;
+	bool throttled = false;
 	unsigned long flags;
 
 	priv = usb_get_serial_port_data(port);
@@ -209,16 +212,24 @@ static void keyspan_pda_rx_interrupt(struct urb *urb)
 	}
 
 exit:
-	retval = usb_submit_urb(urb, GFP_ATOMIC);
-	if (retval)
-		dev_err(&port->dev,
-			"%s - usb_submit_urb failed with result %d\n",
-			__func__, retval);
+	spin_lock_irqsave(&port->lock, flags);
+	if (priv->throttle_req) {
+		priv->throttled = true;
+		throttled = true;
+	}
+	spin_unlock_irqrestore(&port->lock, flags);
+
+	if (!throttled) {
+		retval = usb_submit_urb(urb, GFP_ATOMIC);
+		if (retval)
+			dev_err(&port->dev, "failed to resubmit in urb: %d\n", retval);
+	}
 }
 
 static void keyspan_pda_rx_throttle(struct tty_struct *tty)
 {
 	struct usb_serial_port *port = tty->driver_data;
+	struct keyspan_pda_private *priv = usb_get_serial_port_data(port);
 
 	/*
 	 * Stop receiving characters. We just turn off the URB request, and
@@ -228,16 +239,29 @@ static void keyspan_pda_rx_throttle(struct tty_struct *tty)
 	 * send an XOFF, although it might make sense to foist that off upon
 	 * the device too.
 	 */
-	usb_kill_urb(port->interrupt_in_urb);
+	spin_lock_irq(&port->lock);
+	priv->throttle_req = true;
+	spin_unlock_irq(&port->lock);
 }
 
 static void keyspan_pda_rx_unthrottle(struct tty_struct *tty)
 {
 	struct usb_serial_port *port = tty->driver_data;
+	struct keyspan_pda_private *priv = usb_get_serial_port_data(port);
+	bool throttled;
+	int ret;
 
-	/* just restart the receive interrupt URB */
-	if (usb_submit_urb(port->interrupt_in_urb, GFP_KERNEL))
-		dev_dbg(&port->dev, "usb_submit_urb(read urb) failed\n");
+	spin_lock_irq(&port->lock);
+	throttled = priv->throttled;
+	priv->throttled = false;
+	priv->throttle_req = false;
+	spin_unlock_irq(&port->lock);
+
+	if (throttled) {
+		ret = usb_submit_urb(port->interrupt_in_urb, GFP_KERNEL);
+		if (ret)
+			dev_err(&port->dev, "failed to submit in urb: %d\n", ret);
+	}
 }
 
 static speed_t keyspan_pda_setbaud(struct usb_serial *serial, speed_t baud)
@@ -577,6 +601,8 @@ static int keyspan_pda_open(struct tty_struct *tty,
 
 	spin_lock_irq(&port->lock);
 	priv->tx_room = rc;
+	priv->throttled = false;
+	priv->throttle_req = false;
 	spin_unlock_irq(&port->lock);
 
 	rc = usb_submit_urb(port->interrupt_in_urb, GFP_KERNEL);
-- 
2.54.0