drm: delete unconsumed pending event list in drm_events_release

When there are unconsumed pending events, the events are
destroyed by calling destroy callback, but the events list
are remained, because there is no list_del().

It is possible that the page flip request is handled after
drm_events_release() is called and before drm_fb_release().
In this case a drm_pending_event is remained not freed.
So exynos driver checks again to remove it in its post
close routine. But the file_priv->event_list contains
undeleted ones, this can make oops for accessing invalid
memory.
Signed-off-by: YoungJun Cho <yj44.cho@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_fops.c

@@ -378,8 +378,10 @@ static void drm_events_release(struct drm_file *file_priv)
 		}
 
 	/* Remove unconsumed events */
-	list_for_each_entry_safe(e, et, &file_priv->event_list, link)
+	list_for_each_entry_safe(e, et, &file_priv->event_list, link) {
+		list_del(&e->link);
 		e->destroy(e);
+	}
 
 	spin_unlock_irqrestore(&dev->event_lock, flags);
 }