MFV r260834:

Fix memory leak of compressed buffers in l2arc_write_done (Illumos
#3995).

sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c

@@ -21,7 +21,7 @@
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2013 by Delphix. All rights reserved.
- * Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
+ * Copyright (c) 2014 by Saso Kiselkov. All rights reserved.
  * Copyright 2013 Nexenta Systems, Inc.  All rights reserved.
  */
 
@@ -4597,6 +4597,13 @@ l2arc_write_done(zio_t *zio)
 	 */
 	for (ab = list_prev(buflist, head); ab; ab = ab_prev) {
 		ab_prev = list_prev(buflist, ab);
+		abl2 = ab->b_l2hdr;
+
+		/*
+		 * Release the temporary compressed buffer as soon as possible.
+		 */
+		if (abl2->b_compress != ZIO_COMPRESS_OFF)
+			l2arc_release_cdata_buf(ab);
 
 		hash_lock = HDR_LOCK(ab);
 		if (!mutex_tryenter(hash_lock)) {
@@ -4609,14 +4616,6 @@ l2arc_write_done(zio_t *zio)
 			continue;
 		}
 
-		abl2 = ab->b_l2hdr;
-
-		/*
-		 * Release the temporary compressed buffer as soon as possible.
-		 */
-		if (abl2->b_compress != ZIO_COMPRESS_OFF)
-			l2arc_release_cdata_buf(ab);
-
 		if (zio->io_error != 0) {
 			/*
 			 * Error - drop L2ARC entry.