re #13613 rb4516 Tunables needs volatile keyword

@@ -18,10 +18,11 @@
  *
  * CDDL HEADER END
  */
 /*
  * Copyright (c) 1990, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright 2013 Nexenta Systems, Inc.  All rights reserved.
  */
 
 #ifndef _SYS_MODCTL_H
 #define _SYS_MODCTL_H
 

@@ -545,11 +546,11 @@
  */
 extern kmutex_t mod_lock;
 
 extern char *systemfile;
 extern char **syscallnames;
-extern int moddebug;
+extern volatile int moddebug;
 
 /*
  * this is the head of a doubly linked list.  Only the next and prev
  * pointers are used
  */