MW-286 Avoid spurious deadlock errors when wsrep_on is disabled

If a conflict happens under wsrep_on, the THD's wsrep_conflict_state
is typically set to MUST_ABORT and cleared later, when transaction is
aborted. However, when wsrep_on is disabled, no check is performed to
see whether wsrep_conflict_state is set. So this potentially creates
spurious deadlock errors on the subsequent statement that runs with
wsrep_on enabled.
To avoid this problem wsrep_thd_set_conflict_state() sets the conflict
state only if wsrep_on is enabled.

mysql-test/suite/galera/r/MW-286.result

+CREATE TABLE ten (f1 INTEGER);
+INSERT INTO ten VALUES (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+CREATE TABLE t1 (f1 INTEGER) Engine=InnoDB;
+INSERT INTO t1 (f1) SELECT 000000 + (10000 * a1.f1) + (1000 * a2.f1) + (100 * a3.f1) + (10 * a4.f1) + a5.f1 FROM ten AS a1, ten AS a2, ten AS a3, ten AS a4, ten AS a5;
+INSERT INTO t1 (f1) SELECT 100000 + (10000 * a1.f1) + (1000 * a2.f1) + (100 * a3.f1) + (10 * a4.f1) + a5.f1 FROM ten AS a1, ten AS a2, ten AS a3, ten AS a4, ten AS a5;;
+SET GLOBAL wsrep_desync = TRUE;
+SET wsrep_on = FALSE;
+ALTER TABLE t1 ADD PRIMARY KEY (f1);
+ERROR 70100: Query execution was interrupted
+SET wsrep_on = TRUE;
+SET GLOBAL wsrep_desync = FALSE;
+DROP TABLE t1;
+DROP TABLE ten;

mysql-test/suite/galera/t/MW-286.test

+#
+# MW-286 Spurious deadlock error after error with wsrep_desync and wsrep_on
+#
+
+--source include/galera_cluster.inc
+--source include/have_innodb.inc
+--source include/big_test.inc
+
+--connection node_1
+CREATE TABLE ten (f1 INTEGER);
+INSERT INTO ten VALUES (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
+
+CREATE TABLE t1 (f1 INTEGER) Engine=InnoDB;
+
+# Insert some values before the ALTER
+INSERT INTO t1 (f1) SELECT 000000 + (10000 * a1.f1) + (1000 * a2.f1) + (100 * a3.f1) + (10 * a4.f1) + a5.f1 FROM ten AS a1, ten AS a2, ten AS a3, ten AS a4, ten AS a5;
+
+# Insert more values while the ALTER is running
+--send INSERT INTO t1 (f1) SELECT 100000 + (10000 * a1.f1) + (1000 * a2.f1) + (100 * a3.f1) + (10 * a4.f1) + a5.f1 FROM ten AS a1, ten AS a2, ten AS a3, ten AS a4, ten AS a5;
+
+--connection node_2
+SET GLOBAL wsrep_desync = TRUE;
+SET wsrep_on = FALSE;
+
+--error ER_QUERY_INTERRUPTED
+ALTER TABLE t1 ADD PRIMARY KEY (f1);
+
+SET wsrep_on = TRUE;
+SET GLOBAL wsrep_desync = FALSE;
+
+DROP TABLE t1;
+DROP TABLE ten;

sql/sql_class.cc

@@ -846,7 +846,7 @@ extern "C" void wsrep_thd_set_query_state(
 extern "C" void wsrep_thd_set_conflict_state(
 	THD *thd, enum wsrep_conflict_state state)
 {
-  thd->wsrep_conflict_state= state;
+  if (WSREP(thd)) thd->wsrep_conflict_state= state;
 }