ITS#9342 delta-sync ignore add of already existing entry

if the entryCSN is older. Previous patch breaks if writes are
received out of order, e.g. during a refresh.

servers/slapd/syncrepl.c

@@ -2603,29 +2603,20 @@ syncrepl_message_to_op(
 				"mods2entry (%s)\n",
 					si->si_ridtxt, text, 0 );
 			} else {
-				rc = CV_CSN_OK;
-				if ( do_lock ) {
-					/* do_lock is only true because we didn't get a cookieCSN and
-					 * therefore didn't already lock the pending list. See if the
-					 * entryCSN is fresh enough. Ignore this op if too old.
-					 */
+				rc = op->o_bd->be_add( op, &rs );
+				Debug( LDAP_DEBUG_SYNC,
+					"syncrepl_message_to_op: %s be_add %s (%d)\n",
+					si->si_ridtxt, op->o_req_dn.bv_val, rc );
+				do_graduate = 0;
+				if ( rc == LDAP_ALREADY_EXISTS ) {
 					Attribute *a = attr_find( e->e_attrs, slap_schema.si_ad_entryCSN );
-					if ( a ) {
-						int sid = slap_parse_csn_sid( &a->a_nvals[0] );
-						ldap_pvt_thread_mutex_lock( &si->si_cookieState->cs_mutex );
-						rc = check_csn_age( si, &op->o_req_dn, &a->a_nvals[0],
-							sid, (cookie_vals *)&si->si_cookieState->cs_vals, NULL );
-						ldap_pvt_thread_mutex_unlock( &si->si_cookieState->cs_mutex );
-					}
-				}
-				if ( rc == CV_CSN_OLD ) {
-					rc = LDAP_SUCCESS;
-				} else {
-					rc = op->o_bd->be_add( op, &rs );
-					Debug( LDAP_DEBUG_SYNC,
-						"syncrepl_message_to_op: %s be_add %s (%d)\n",
-						si->si_ridtxt, op->o_req_dn.bv_val, rc );
-					do_graduate = 0;
+					struct berval *vals;
+					if ( a && backend_attribute( op, NULL, &op->o_req_ndn,
+						slap_schema.si_ad_entryCSN, &vals, ACL_READ ) == LDAP_SUCCESS ) {
+						if ( ber_bvcmp( &vals[0], &a->a_vals[0] ) >= 0 )
+							rc = LDAP_SUCCESS;
+						ber_bvarray_free_x( vals, op->o_tmpmemctx );
+ 					}
 				}
 			}
 			if ( e == op->ora_e )