[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>

1 files changed, 10 insertions, 4 deletions

diff --git a/drivers/rtc/class.c b/drivers/rtc/class.c
index 7a0d8ee2de9c..04aaa6347234 100644
--- a/drivers/rtc/class.c
+++ b/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);