diff --git a/include/asm-s390/ccwgroup.h b/include/asm-s390/ccwgroup.h
index d2f9c0d..925b3dd 100644
--- a/include/asm-s390/ccwgroup.h
+++ b/include/asm-s390/ccwgroup.h
@@ -11,6 +11,7 @@
 		CCWGROUP_ONLINE,
 	} state;
 	atomic_t onoff;
+	struct mutex reg_mutex;
 	unsigned int count;		/* number of attached slave devices */
 	struct device	dev;		/* master device		    */
 	struct ccw_device *cdev[0];	/* variable number, allocate as needed */