[PATCH] rtc_cmos oops fix

Fix an oops on the rtc_device_unregister() path by waiting until the last
moment before nulling the rtc->ops vector.  Fix some potential oopses by
having the rtc_class_open()/rtc_class_close() interface increase the RTC's
reference count while an RTC handle is available outside the RTC framework.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/class.c

@@ -113,10 +113,16 @@ EXPORT_SYMBOL_GPL(rtc_device_register);
  */
 void rtc_device_unregister(struct rtc_device *rtc)
 {
-	mutex_lock(&rtc->ops_lock);
-	rtc->ops = NULL;
-	mutex_unlock(&rtc->ops_lock);
-	class_device_unregister(&rtc->class_dev);
+	if (class_device_get(&rtc->class_dev) != NULL) {
+		mutex_lock(&rtc->ops_lock);
+		/* remove innards of this RTC, then disable it, before
+		 * letting any rtc_class_open() users access it again
+		 */
+		class_device_unregister(&rtc->class_dev);
+		rtc->ops = NULL;
+		mutex_unlock(&rtc->ops_lock);
+		class_device_put(&rtc->class_dev);
+	}
 }
 EXPORT_SYMBOL_GPL(rtc_device_unregister);
 

drivers/rtc/interface.c

@@ -179,7 +179,7 @@ struct class_device *rtc_class_open(char *name)
 	down(&rtc_class->sem);
 	list_for_each_entry(class_dev_tmp, &rtc_class->children, node) {
 		if (strncmp(class_dev_tmp->class_id, name, BUS_ID_SIZE) == 0) {
-			class_dev = class_dev_tmp;
+			class_dev = class_device_get(class_dev_tmp);
 			break;
 		}
 	}
@@ -197,6 +197,7 @@ EXPORT_SYMBOL_GPL(rtc_class_open);
 void rtc_class_close(struct class_device *class_dev)
 {
 	module_put(to_rtc_device(class_dev)->owner);
+	class_device_put(class_dev);
 }
 EXPORT_SYMBOL_GPL(rtc_class_close);