[media] em28xx: fix race on disconnect

This patch closes the race on the device and extension lists at USB disconnect
time. Previously, the device was removed from the device list during
em28xx_release_resources(), and then passed to the em28xx_close_extension()
function so that all extensions could run their fini() operations. However, this
left a (brief, theoretical, highly unlikely ;-)) window between these two calls
during which a new module could call em28xx_register_extension(). The result
would have been that the em28xx_usb_disconnect() function would also have passed
the device to the new extension's fini() function, despite never having called
the extension's init() function.

This patch also restores em28xx_close_extension()'s symmetry with
em28xx_init_extension(), and establishes the property that every device in the
device list must have been initialised for every extension in the extension list.
Signed-off-by: Chris Rankin <rankincj@yahoo.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/em28xx/em28xx-cards.c

@@ -2800,9 +2800,9 @@ static void flush_request_modules(struct em28xx *dev)
 #endif /* CONFIG_MODULES */
 
 /*
- * em28xx_realease_resources()
+ * em28xx_release_resources()
  * unregisters the v4l2,i2c and usb devices
- * called when the device gets disconected or at module unload
+ * called when the device gets disconnected or at module unload
 */
 void em28xx_release_resources(struct em28xx *dev)
 {
@@ -2816,8 +2816,6 @@ void em28xx_release_resources(struct em28xx *dev)
 
 	em28xx_release_analog_resources(dev);
 
-	em28xx_remove_from_devlist(dev);
-
 	em28xx_i2c_unregister(dev);
 
 	v4l2_device_unregister(&dev->v4l2_dev);
@@ -3255,7 +3253,7 @@ static int em28xx_usb_probe(struct usb_interface *interface,
 
 /*
  * em28xx_usb_disconnect()
- * called when the device gets diconencted
+ * called when the device gets disconnected
  * video device will be unregistered on v4l2_close in case it is still open
  */
 static void em28xx_usb_disconnect(struct usb_interface *interface)

drivers/media/video/em28xx/em28xx-core.c

@@ -1183,18 +1183,6 @@ void em28xx_wake_i2c(struct em28xx *dev)
 static LIST_HEAD(em28xx_devlist);
 static DEFINE_MUTEX(em28xx_devlist_mutex);
 
-/*
- * em28xx_realease_resources()
- * unregisters the v4l2,i2c and usb devices
- * called when the device gets disconected or at module unload
-*/
-void em28xx_remove_from_devlist(struct em28xx *dev)
-{
-	mutex_lock(&em28xx_devlist_mutex);
-	list_del(&dev->devlist);
-	mutex_unlock(&em28xx_devlist_mutex);
-};
-
 /*
  * Extension interface
  */
@@ -1245,14 +1233,13 @@ void em28xx_init_extension(struct em28xx *dev)
 
 void em28xx_close_extension(struct em28xx *dev)
 {
-	struct em28xx_ops *ops = NULL;
+	const struct em28xx_ops *ops = NULL;
 
 	mutex_lock(&em28xx_devlist_mutex);
-	if (!list_empty(&em28xx_extension_devlist)) {
-		list_for_each_entry(ops, &em28xx_extension_devlist, next) {
-			if (ops->fini)
-				ops->fini(dev);
-		}
+	list_for_each_entry(ops, &em28xx_extension_devlist, next) {
+		if (ops->fini)
+			ops->fini(dev);
 	}
+	list_del(&dev->devlist);
 	mutex_unlock(&em28xx_devlist_mutex);
 }