Illumos 5047 - don't use atomic_*_nv if you discard the return value

5047 don't use atomic_*_nv if you discard the return value
Author: Josef 'Jeff' Sipek <josef.sipek@nexenta.com>
Reviewed by: Garrett D'Amore <garrett@damore.org>
Reviewed by: Jason King <jason.brian.king@gmail.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>

References:
  https://www.illumos.org/issues/5047
  illumos/illumos-gate@640c167

Porting Notes:

Several hunks from the original patch where not specific to ZFS
and thus were dropped.

Ported-by: Chris Dunlop <chris@onthe.net.au>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Richard Yao <ryao@gentoo.org>
Issue #3172

Author: Josef 'Jeff' Sipek

module/zfs/dbuf.c

@@ -1647,7 +1647,7 @@ dbuf_clear(dmu_buf_impl_t *db)
 	dndb = dn->dn_dbuf;
 	if (db->db_blkid != DMU_BONUS_BLKID && MUTEX_HELD(&dn->dn_dbufs_mtx)) {
 		list_remove(&dn->dn_dbufs, db);
-		(void) atomic_dec_32_nv(&dn->dn_dbufs_count);
+		atomic_dec_32(&dn->dn_dbufs_count);
 		membar_producer();
 		DB_DNODE_EXIT(db);
 		/*
@@ -1832,7 +1832,7 @@ dbuf_create(dnode_t *dn, uint8_t level, uint64_t blkid,
 	ASSERT(dn->dn_object == DMU_META_DNODE_OBJECT ||
 	    refcount_count(&dn->dn_holds) > 0);
 	(void) refcount_add(&dn->dn_holds, db);
-	(void) atomic_inc_32_nv(&dn->dn_dbufs_count);
+	atomic_inc_32(&dn->dn_dbufs_count);
 
 	dprintf_dbuf(db, "db=%p\n", db);
 
@@ -1878,7 +1878,7 @@ dbuf_destroy(dmu_buf_impl_t *db)
 			dn = DB_DNODE(db);
 			mutex_enter(&dn->dn_dbufs_mtx);
 			list_remove(&dn->dn_dbufs, db);
-			(void) atomic_dec_32_nv(&dn->dn_dbufs_count);
+			atomic_dec_32(&dn->dn_dbufs_count);
 			mutex_exit(&dn->dn_dbufs_mtx);
 			DB_DNODE_EXIT(db);
 			/*
@@ -2207,7 +2207,7 @@ dbuf_rele_and_unlock(dmu_buf_impl_t *db, void *tag)
 			 * until the move completes.
 			 */
 			DB_DNODE_ENTER(db);
-			(void) atomic_dec_32_nv(&DB_DNODE(db)->dn_dbufs_count);
+			atomic_dec_32(&DB_DNODE(db)->dn_dbufs_count);
 			DB_DNODE_EXIT(db);
 			/*
 			 * The bonus buffer's dnode hold is no longer discounted

module/zfs/dmu.c

@@ -283,7 +283,7 @@ dmu_bonus_hold(objset_t *os, uint64_t object, void *tag, dmu_buf_t **dbp)
 	/* as long as the bonus buf is held, the dnode will be held */
 	if (refcount_add(&db->db_holds, tag) == 1) {
 		VERIFY(dnode_add_ref(dn, db));
-		(void) atomic_inc_32_nv(&dn->dn_dbufs_count);
+		atomic_inc_32(&dn->dn_dbufs_count);
 	}
 
 	/*