MDEV-33952: Fix flaky galera_create_table_as_select test with debug sync

The test that triggers multi-master conflict between two CTAS commands
uses LOCK/UNLOCK TABLES to block local CTAS from progress. It could
result in a race when UNLOCK TABLES command is issued a bit earlier
then needed, causing local CTAS to run further and change wsrep
transaction state, so that a different code path is taken later and
the original error gets overridden, causing the test to fail.
The solution is to replace LOCK/UNLOCK TABLES with debug sync points.
Signed-off-by: Julius Goryavsky <julius.goryavsky@mariadb.com>

mysql-test/suite/galera/disabled.def

@@ -19,4 +19,3 @@ galera_slave_replay : MDEV-32780 galera_as_slave_replay: assertion in the wsrep:
 galera_sst_mysqldump_with_key : MDEV-32782 galera_sst_mysqldump_with_key test failed
 galera_var_ignore_apply_errors : MENT-1997 galera_var_ignore_apply_errors test freezes
 galera_desync_overlapped : MDEV-21538 galera_desync_overlapped MTR failed: Result content mismatch
-galera_create_table_as_select : MDEV-33952 fails sporadically

mysql-test/suite/galera/r/galera_create_table_as_select.result

@@ -76,22 +76,21 @@ EXECUTE stmt;
 DEALLOCATE PREPARE stmt;
 DROP TABLE t1, t2;
 connection node_1;
+SET GLOBAL DEBUG_DBUG = 'd,sync.wsrep_apply_cb';
 CREATE TABLE t2 (f1 INTEGER) ENGINE=InnoDB;
 INSERT INTO t2 VALUES (1),(2),(3),(4),(5);
-connect node_1a, 127.0.0.1, root, , test, $NODE_MYPORT_1;
-LOCK TABLE t2 WRITE;
-connection node_1;
+SET DEBUG_SYNC = 'create_table_select_before_create WAIT_FOR sync.wsrep_apply_cb_reached';
+SET DEBUG_SYNC = 'create_table_select_before_lock SIGNAL signal.wsrep_apply_cb WAIT_FOR bf_abort';
 CREATE TABLE t1 AS SELECT * FROM t2;;
-connection node_1a;
 connection node_2;
 SELECT COUNT(*) = 5 FROM t2;
 COUNT(*) = 5
 1
 CREATE TABLE t1 AS SELECT * FROM t2;
-connection node_1a;
-UNLOCK TABLES;
 connection node_1;
-Got one of the listed errors
+ERROR 70100: Query execution was interrupted
+SET GLOBAL DEBUG_DBUG = '';
+SET DEBUG_SYNC = 'RESET';
 DROP TABLE t1, t2;
 CREATE TABLE t2 (f1 INTEGER) ENGINE=InnoDB;
 INSERT INTO t2 VALUES (1),(2),(3),(4),(5);

mysql-test/suite/galera/t/galera_create_table_as_select.test

@@ -3,6 +3,8 @@
 #
 
 --source include/galera_cluster.inc
+--source include/have_debug_sync.inc
+--source include/have_debug.inc
 
 --connection node_1
 SET SESSION default_storage_engine=InnoDB;
@@ -103,31 +105,27 @@ DROP TABLE t1, t2;
 #
 
 --connection node_1
+# Pause applying CTAS command from the other node
+SET GLOBAL DEBUG_DBUG = 'd,sync.wsrep_apply_cb';
 
 CREATE TABLE t2 (f1 INTEGER) ENGINE=InnoDB;
 INSERT INTO t2 VALUES (1),(2),(3),(4),(5);
 
---connect node_1a, 127.0.0.1, root, , test, $NODE_MYPORT_1
-LOCK TABLE t2 WRITE;
-
---connection node_1
+# Wait until local CTAS grabs MDL lock and let applied CTAS BF-abort it
+SET DEBUG_SYNC = 'create_table_select_before_create WAIT_FOR sync.wsrep_apply_cb_reached';
+SET DEBUG_SYNC = 'create_table_select_before_lock SIGNAL signal.wsrep_apply_cb WAIT_FOR bf_abort';
 --send CREATE TABLE t1 AS SELECT * FROM t2;
 
---connection node_1a
---let $wait_condition = SELECT COUNT(*) = 1 FROM information_schema.processlist WHERE STATE LIKE 'Waiting for table metadata lock%'
---source include/wait_condition.inc
-
 --connection node_2
 SELECT COUNT(*) = 5 FROM t2;
 CREATE TABLE t1 AS SELECT * FROM t2;
 
---connection node_1a
-UNLOCK TABLES;
-
 --connection node_1
---error ER_TABLE_EXISTS_ERROR,ER_QUERY_INTERRUPTED
+--error ER_QUERY_INTERRUPTED
 --reap
 
+SET GLOBAL DEBUG_DBUG = '';
+SET DEBUG_SYNC = 'RESET';
 DROP TABLE t1, t2;
 
 #