Index: kernel/generic/include/synch/mutex.h
===================================================================
--- kernel/generic/include/synch/mutex.h	(revision 597fa246c9481b40ae4d512256c4ceea4506b215)
+++ kernel/generic/include/synch/mutex.h	(revision 28c39f381d8c28d1a927bdfd8bbf498df7f1b90c)
@@ -44,5 +44,4 @@
 	MUTEX_PASSIVE,
 	MUTEX_RECURSIVE,
-	MUTEX_ACTIVE
 } mutex_type_t;
 
@@ -51,14 +50,14 @@
 typedef struct {
 	mutex_type_t type;
+	int nesting;
 	semaphore_t sem;
-	struct thread *owner;
-	unsigned nesting;
+	_Atomic(struct thread *) owner;
 } mutex_t;
 
 #define MUTEX_INITIALIZER(name, mtype) (mutex_t) { \
 	.type = (mtype), \
+	.nesting = 0, \
 	.sem = SEMAPHORE_INITIALIZER((name).sem, 1), \
 	.owner = NULL, \
-	.nesting = 0, \
 }