USB: usbserial - fix potential deadlock between write() and IRQ

patch acd2a847 in mainline.

USB: usbserial - fix potential deadlock between write() and IRQ

usb_serial_generic_write() doesn't disable interrupts when taking port->lock,
and could therefore deadlock with usb_serial_generic_read_bulk_callback()
being called from interrupt, taking the same lock. Fix it.
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Acked-by: Larry Finger <larry.finger@lwfinger.net>
Cc: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/generic.c

@@ -190,14 +190,15 @@ int usb_serial_generic_write(struct usb_serial_port *port, const unsigned char *
 
 	/* only do something if we have a bulk out endpoint */
 	if (serial->num_bulk_out) {
-		spin_lock_bh(&port->lock);
+		unsigned long flags;
+		spin_lock_irqsave(&port->lock, flags);
 		if (port->write_urb_busy) {
-			spin_unlock_bh(&port->lock);
+			spin_unlock_irqrestore(&port->lock, flags);
 			dbg("%s - already writing", __FUNCTION__);
 			return 0;
 		}
 		port->write_urb_busy = 1;
-		spin_unlock_bh(&port->lock);
+		spin_unlock_irqrestore(&port->lock, flags);
 
 		count = (count > port->bulk_out_size) ? port->bulk_out_size : count;