Illumos 5117 - spacemap reallocation can cause corruption

5117 space map reallocation can cause corruption
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Sebastien Roy <sebastien.roy@delphix.com>
Reviewed by: Richard Elling <richard.elling@gmail.com>
Approved by: Richard Lowe <richlowe@richlowe.net>

References:
  https://www.illumos.org/projects/illumos-gate/issues/5117
  illumos/illumos-gate@e503a68

Ported by: Turbo Fredriksson <turbo@bayour.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2662

Author: grwilson

module/zfs/dnode_sync.c

@@ -695,6 +695,11 @@ dnode_sync(dnode_t *dn, dmu_tx_t *tx)
 		return;
 	}
 
+	if (dn->dn_next_nlevels[txgoff]) {
+		dnode_increase_indirection(dn, tx);
+		dn->dn_next_nlevels[txgoff] = 0;
+	}
+
 	if (dn->dn_next_nblkptr[txgoff]) {
 		/* this should only happen on a realloc */
 		ASSERT(dn->dn_allocated_txg == tx->tx_txg);
@@ -720,11 +725,6 @@ dnode_sync(dnode_t *dn, dmu_tx_t *tx)
 		mutex_exit(&dn->dn_mtx);
 	}
 
-	if (dn->dn_next_nlevels[txgoff]) {
-		dnode_increase_indirection(dn, tx);
-		dn->dn_next_nlevels[txgoff] = 0;
-	}
-
 	dbuf_sync_list(list, tx);
 
 	if (!DMU_OBJECT_IS_SPECIAL(dn->dn_object)) {