--- releng_7_ref/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_zfetch.c	2009-05-20 16:39:36.677203795 -0700
+++ releng_7_2_fcs/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_zfetch.c	2009-08-17 14:50:55.332013723 -0700
@@ -305,7 +305,9 @@
 	 * modified in a number of different ways.
 	 */
 
-	rw_enter(&zf->zf_rwlock, RW_READER);
+	if (rw_tryenter(&zf->zf_rwlock, RW_READER) == 0) 
+		return (1);
+
 top:
 
 	for (zs = list_head(&zf->zf_stream); zs;
@@ -339,8 +341,10 @@
 
 			reset = !prefetched && zs->zst_len > 1;
 
-			mutex_enter(&zs->zst_lock);
-
+			if (mutex_tryenter(&zs->zst_lock) == 0) {
+				rc = 1;
+				goto out;
+			}
 			if (zh->zst_offset != zs->zst_offset + zs->zst_len) {
 				mutex_exit(&zs->zst_lock);
 				goto top;
@@ -364,8 +368,10 @@
 
 			reset = !prefetched && zs->zst_len > 1;
 
-			mutex_enter(&zs->zst_lock);
-
+			if (mutex_tryenter(&zs->zst_lock) == 0) {
+				rc = 1;
+				goto out;
+			}
 			if (zh->zst_offset != zs->zst_offset - zh->zst_len) {
 				mutex_exit(&zs->zst_lock);
 				goto top;
@@ -392,8 +398,10 @@
 		    zs->zst_len) && (zs->zst_len != zs->zst_stride)) {
 			/* strided forward access */
 
-			mutex_enter(&zs->zst_lock);
-
+			if (mutex_tryenter(&zs->zst_lock) == 0) {
+				rc = 1;
+				goto out;
+			}
 			if ((zh->zst_offset - zs->zst_offset - zs->zst_stride >=
 			    zs->zst_len) || (zs->zst_len == zs->zst_stride)) {
 				mutex_exit(&zs->zst_lock);
@@ -409,8 +417,10 @@
 		    zs->zst_len) && (zs->zst_len != zs->zst_stride)) {
 			/* strided reverse access */
 
-			mutex_enter(&zs->zst_lock);
-
+			if (mutex_tryenter(&zs->zst_lock) == 0) {
+				rc = 1;
+				goto out;
+			}
 			if ((zh->zst_offset - zs->zst_offset + zs->zst_stride >=
 			    zs->zst_len) || (zs->zst_len == zs->zst_stride)) {
 				mutex_exit(&zs->zst_lock);