MDEV-22055: Assertion `active() == false' failed in...

MDEV-22055: Assertion `active() == false' failed in wsrep::transaction::start_transaction upon ROLLBACK AND CHAIN

The optional AND CHAIN clause is a convenience for initiating a new
transaction as soon as the old transaction terminates. Therefore,
do not start new transaction if it is already started
at wsrep_start_transaction.

mysql-test/suite/galera/r/MDEV-22055.result

+connection node_2;
+connection node_1;
+ROLLBACK AND CHAIN;
+CREATE TABLE t1(a int not null primary key) engine=innodb;
+INSERT INTO t1 values (1);
+BEGIN;
+INSERT INTO t1 values (2);
+ROLLBACK AND CHAIN;
+SELECT * FROM t1;
+a
+1
+connection node_2;
+SET SESSION wsrep_sync_wait=15;
+SELECT * FROM t1;
+a
+1
+connection node_1;
+DROP TABLE t1;

mysql-test/suite/galera/t/MDEV-22055.test

+--source include/galera_cluster.inc
+
+ROLLBACK AND CHAIN;
+
+CREATE TABLE t1(a int not null primary key) engine=innodb;
+INSERT INTO t1 values (1);
+
+BEGIN;
+INSERT INTO t1 values (2);
+ROLLBACK AND CHAIN;
+
+SELECT * FROM t1;
+
+--connection node_2
+SET SESSION wsrep_sync_wait=15;
+SELECT * FROM t1;
+
+--connection node_1
+DROP TABLE t1;

sql/wsrep_trans_observer.h

@@ -133,9 +133,11 @@ static inline size_t wsrep_fragments_certified_for_stmt(THD* thd)
 
 static inline int wsrep_start_transaction(THD* thd, wsrep_trx_id_t trx_id)
 {
-  return (thd->wsrep_cs().state() != wsrep::client_state::s_none  ?
-          thd->wsrep_cs().start_transaction(wsrep::transaction_id(trx_id)) :
-          0);
+  if (thd->wsrep_cs().state() != wsrep::client_state::s_none) {
+    if (wsrep_is_active(thd) == false)
+      return thd->wsrep_cs().start_transaction(wsrep::transaction_id(trx_id));
+  }
+  return 0;
 }
 
 /**/