MDEV-10812 WSREP causes responses being sent to protocol commands

that must not send a response

Problem:- When using wsrep (w/ galera) and issuing commands that can
cause deadlocks, deadlock exception errors are sent in responses to
commands such as close prepared statement and close connection which,
by spec, must not send a response.

Solution:- In dispatch_command, we will handle COM_QUIT and COM_STMT_CLOSE
commands even in case of error.

Patch Credit:- Jaka Močnik

mysql-test/suite/galera/r/galera_mdev_10812.result

+#
+# MDEV-10812: On COM_STMT_CLOSE/COM_QUIT, when wsrep_conflict_state
+# is ABORTED, it causes wrong response to be sent to the client
+#
+SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
+CREATE TABLE t1(a INT PRIMARY KEY);
+INSERT INTO t1 VALUES(1),(2),(3);
+START TRANSACTION ;
+UPDATE t1 SET a=a+100;
+UPDATE t1 SET a=a+100;
+DROP TABLE t1;

mysql-test/suite/galera/t/galera_mdev_10812.test

+--source include/galera_cluster.inc
+--source include/have_innodb.inc
+
+--echo #
+--echo # MDEV-10812: On COM_STMT_CLOSE/COM_QUIT, when wsrep_conflict_state
+--echo # is ABORTED, it causes wrong response to be sent to the client
+--echo #
+
+#  First create a deadlock
+--connect node_1a, 127.0.0.1, root, , test, $NODE_MYPORT_1
+SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
+CREATE TABLE t1(a INT PRIMARY KEY);
+INSERT INTO t1 VALUES(1),(2),(3);
+START TRANSACTION ;
+UPDATE t1 SET a=a+100;
+
+--sleep 2
+--connection node_2
+UPDATE t1 SET a=a+100;
+
+--sleep 2
+--connection node_1a
+# here we get deadlock error
+--disconnect node_1a
+
+--connection node_2
+DROP TABLE t1;

sql/sql_parse.cc

@@ -1265,7 +1265,9 @@ bool dispatch_command(enum enum_server_command command, THD *thd,
     {
       wsrep_client_rollback(thd);
     }
-    if (thd->wsrep_conflict_state== ABORTED)
+    /* We let COM_QUIT and COM_STMT_CLOSE to execute even if wsrep aborted. */
+    if (thd->wsrep_conflict_state == ABORTED &&
+        command != COM_STMT_CLOSE && command != COM_QUIT)
     {
       my_error(ER_LOCK_DEADLOCK, MYF(0), "wsrep aborted transaction");
       WSREP_DEBUG("Deadlock error for: %s", thd->query());
@@ -1918,6 +1920,12 @@ bool dispatch_command(enum enum_server_command command, THD *thd,
 
   if (WSREP(thd))
   {
+    /*
+      MDEV-10812
+      In the case of COM_QUIT/COM_STMT_CLOSE thread status should be disabled.
+    */
+    DBUG_ASSERT((command != COM_QUIT && command != COM_STMT_CLOSE)
+                  || thd->get_stmt_da()->is_disabled());
     /* wsrep BF abort in query exec phase */
     mysql_mutex_lock(&thd->LOCK_wsrep_thd);
     do_end_of_statement= thd->wsrep_conflict_state != REPLAYING &&