re #13613 rb4516 Tunables needs volatile keyword

@@ -18,10 +18,11 @@
  *
  * CDDL HEADER END
  */
 /*
  * Copyright (c) 1983, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright 2013 Nexenta Systems, Inc.  All rights reserved.
  * Copyright (c) 2016, 2017 by Delphix. All rights reserved.
  */
 
 /*      Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T     */
 /*        All Rights Reserved   */

@@ -133,12 +134,12 @@
  * These are validated in ufs_iinit() since improper settings
  * can lead to filesystem hangs.
  */
 #define UFS_HW_DEFAULT  (16 * 1024 * 1024)
 #define UFS_LW_DEFAULT  (8 * 1024 * 1024)
-int     ufs_HW = UFS_HW_DEFAULT;
-int     ufs_LW = UFS_LW_DEFAULT;
+volatile int    ufs_HW = UFS_HW_DEFAULT;
+volatile int    ufs_LW = UFS_LW_DEFAULT;
 
 static void ihinit(void);
 extern int hash2ints(int, int);
 
 static int ufs_iget_internal(struct vfs *, ino_t, struct inode **,