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
d4ead16f50f9 ("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.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/misc/usblcd.c b/drivers/usb/misc/usblcd.c
index aa982d3..b898650 100644 (file)
--- a/drivers/usb/misc/usblcd.c
+++ b/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);