1 files changed, 30 insertions, 5 deletions

diff --git a/module/zfs/dsl_dataset.c b/module/zfs/dsl_dataset.c
index ddab3eddb..fb6feeec9 100644
--- a/module/zfs/dsl_dataset.c
+++ b/module/zfs/dsl_dataset.c
@@ -20,7 +20,7 @@
  */
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
- * Copyright (c) 2011, 2015 by Delphix. All rights reserved.
+ * Copyright (c) 2011, 2016 by Delphix. All rights reserved.
  * Copyright (c) 2014, Joyent, Inc. All rights reserved.
  * Copyright (c) 2014 RackTop Systems.
  * Copyright (c) 2014 Spectra Logic Corporation, All rights reserved.
@@ -273,16 +273,30 @@ dsl_dataset_block_freeable(dsl_dataset_t *ds, const blkptr_t *bp,
 	return (B_TRUE);
 }
 
+/*
+ * We have to release the fsid syncronously or we risk that a subsequent
+ * mount of the same dataset will fail to unique_insert the fsid.  This
+ * failure would manifest itself as the fsid of this dataset changing
+ * between mounts which makes NFS clients quite unhappy.
+ */
 static void
-dsl_dataset_evict(void *dbu)
+dsl_dataset_evict_sync(void *dbu)
 {
 	dsl_dataset_t *ds = dbu;
 
 	ASSERT(ds->ds_owner == NULL);
 
-	ds->ds_dbuf = NULL;
-
 	unique_remove(ds->ds_fsid_guid);
+}
+
+static void
+dsl_dataset_evict_async(void *dbu)
+{
+	dsl_dataset_t *ds = dbu;
+
+	ASSERT(ds->ds_owner == NULL);
+
+	ds->ds_dbuf = NULL;
 
 	if (ds->ds_objset != NULL)
 		dmu_objset_evict(ds->ds_objset);
@@ -525,7 +539,8 @@ dsl_dataset_hold_obj(dsl_pool_t *dp, uint64_t dsobj, void *tag,
 			ds->ds_reserved = ds->ds_quota = 0;
 		}
 
-		dmu_buf_init_user(&ds->ds_dbu, dsl_dataset_evict, &ds->ds_dbuf);
+		dmu_buf_init_user(&ds->ds_dbu, dsl_dataset_evict_sync,
+		    dsl_dataset_evict_async, &ds->ds_dbuf);
 		if (err == 0)
 			winner = dmu_buf_set_user_ie(dbuf, &ds->ds_dbu);
 
@@ -548,6 +563,16 @@ dsl_dataset_hold_obj(dsl_pool_t *dp, uint64_t dsobj, void *tag,
 		} else {
 			ds->ds_fsid_guid =
 			    unique_insert(dsl_dataset_phys(ds)->ds_fsid_guid);
+			if (ds->ds_fsid_guid !=
+			    dsl_dataset_phys(ds)->ds_fsid_guid) {
+				zfs_dbgmsg("ds_fsid_guid changed from "
+				    "%llx to %llx for pool %s dataset id %llu",
+				    (long long)
+				    dsl_dataset_phys(ds)->ds_fsid_guid,
+				    (long long)ds->ds_fsid_guid,
+				    spa_name(dp->dp_spa),
+				    dsobj);
+			}
 		}
 	}
 	ASSERT3P(ds->ds_dbuf, ==, dbuf);