Illumos #3464

3464 zfs synctask code needs restructuring
Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Approved by: Garrett D'Amore <garrett@damore.org>

References:
  https://www.illumos.org/issues/3464
  illumos/illumos-gate@3b2aab1880

Ported-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1495

include/sys/zfs_znode.h

@@ -20,6 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012 by Delphix. All rights reserved.
  */
 
 #ifndef	_SYS_FS_ZFS_ZNODE_H
@@ -254,7 +255,7 @@ typedef struct znode {
  */
 #define	ZFS_ENTER(zsb) \
 	{ \
-		rrw_enter(&(zsb)->z_teardown_lock, RW_READER, FTAG); \
+		rrw_enter_read(&(zsb)->z_teardown_lock, FTAG); \
 		if ((zsb)->z_unmounted) { \
 			ZFS_EXIT(zsb); \
 			return (EIO); \