OpenZFS 7254 - ztest failed assertion in ztest_dataset_dirobj_verify: dirobjs + 1 == usedobjs

Authored by: Paul Dagnelie <pcd@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Steve Gonczi <steve.gonczi@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Ported-by: George Melikov <mail@gmelikov.ru>

OpenZFS-issue: https://www.illumos.org/issues/7254
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/c166b69
Closes #5670

include/sys/dmu_objset.h

@@ -20,8 +20,8 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2015 by Delphix. All rights reserved.
  * Copyright (c) 2013 by Saso Kiselkov. All rights reserved.
- * Copyright (c) 2012, 2014 by Delphix. All rights reserved.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
  */
 
@@ -104,9 +104,14 @@ struct objset {
 	zfs_redundant_metadata_type_t os_redundant_metadata;
 	int os_recordsize;
 
+	/*
+	 * Pointer is constant; the blkptr it points to is protected by
+	 * os_dsl_dataset->ds_bp_rwlock
+	 */
+	blkptr_t *os_rootbp;
+
 	/* no lock needed: */
 	struct dmu_tx *os_synctx; /* XXX sketchy */
-	blkptr_t *os_rootbp;
 	zil_header_t os_zil_header;
 	list_t os_synced_dnodes;
 	uint64_t os_flags;

include/sys/dsl_dataset.h

@@ -38,6 +38,7 @@
 #include <sys/zfs_context.h>
 #include <sys/dsl_deadlist.h>
 #include <sys/refcount.h>
+#include <sys/rrwlock.h>
 #include <zfeature_common.h>
 
 #ifdef	__cplusplus
@@ -149,6 +150,7 @@ typedef struct dsl_dataset_phys {
 
 typedef struct dsl_dataset {
 	dmu_buf_user_t ds_dbu;
+	rrwlock_t ds_bp_rwlock; /* Protects ds_phys->ds_bp */
 
 	/* Immutable: */
 	struct dsl_dir *ds_dir;