USB: usblcd: drop redundant disconnect mutex

Drop the redundant disconnect mutex which was introduced after the
open-disconnect race had been addressed generally in USB core by commit
d4ead16f ("USB: prevent char device open/deregister race").

Specifically, the rw-semaphore in core guarantees that all calls to
open() will have completed and that no new calls to open() will occur
after usb_deregister_dev() returns. Hence there is no need use the
driver data as an inverted disconnected flag.
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20190926091228.24634-8-johan@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/misc/usblcd.c

@@ -37,9 +37,6 @@ static const struct usb_device_id id_table[] = {
 };
 MODULE_DEVICE_TABLE(usb, id_table);
 
-static DEFINE_MUTEX(open_disc_mutex);
-
-
 struct usb_lcd {
 	struct usb_device	*udev;			/* init: probe_lcd */
 	struct usb_interface	*interface;		/* the interface for
@@ -95,17 +92,10 @@ static int lcd_open(struct inode *inode, struct file *file)
 		return -ENODEV;
 	}
 
-	mutex_lock(&open_disc_mutex);
 	dev = usb_get_intfdata(interface);
-	if (!dev) {
-		mutex_unlock(&open_disc_mutex);
-		mutex_unlock(&lcd_mutex);
-		return -ENODEV;
-	}
 
 	/* increment our usage count for the device */
 	kref_get(&dev->kref);
-	mutex_unlock(&open_disc_mutex);
 
 	/* grab a power reference */
 	r = usb_autopm_get_interface(interface);
@@ -388,7 +378,6 @@ static int lcd_probe(struct usb_interface *interface,
 		/* something prevented us from registering this driver */
 		dev_err(&interface->dev,
 			"Not able to get a minor for this device.\n");
-		usb_set_intfdata(interface, NULL);
 		goto error;
 	}
 
@@ -434,14 +423,9 @@ static int lcd_resume(struct usb_interface *intf)
 
 static void lcd_disconnect(struct usb_interface *interface)
 {
-	struct usb_lcd *dev;
+	struct usb_lcd *dev = usb_get_intfdata(interface);
 	int minor = interface->minor;
 
-	mutex_lock(&open_disc_mutex);
-	dev = usb_get_intfdata(interface);
-	usb_set_intfdata(interface, NULL);
-	mutex_unlock(&open_disc_mutex);
-
 	/* give back our minor */
 	usb_deregister_dev(interface, &lcd_class);