MDEV-6832: ER_LOCK_WAIT_TIMEOUT on SHOW STATUS

Synchronous read view should not be needed for
SHOW commands.

mysql-test/suite/wsrep/r/mdev_6832.result

+#
+# MDEV-6832: ER_LOCK_WAIT_TIMEOUT on SHOW STATUS
+#
+SHOW STATUS LIKE 'wsrep_ready';
+Variable_name	Value
+wsrep_ready	ON
+SHOW STATUS LIKE 'wsrep_ready';
+Variable_name	Value
+wsrep_ready	OFF
+SET @@global.wsrep_cluster_address='gcomm://';
+# End of test.

mysql-test/suite/wsrep/r/variables.result

@@ -141,7 +141,6 @@ SET GLOBAL wsrep_provider=none;
 #
 # MDEV#6206: wsrep_slave_threads subtracts from max_connections
 #
-call mtr.add_suppression("safe_mutex: Found wrong usage of mutex 'LOCK_wsrep_slave_threads' and 'LOCK_global_system_variables'");
 call mtr.add_suppression("WSREP: Failed to get provider options");
 SELECT @@global.wsrep_provider;
 @@global.wsrep_provider

mysql-test/suite/wsrep/t/mdev_6832.opt

+--wsrep-provider=$WSREP_PROVIDER --wsrep-cluster-address=gcomm:// --wsrep_provider_options='base_port=$GALERA_BASE_PORT' --wsrep-on=1 --wsrep_causal_reads=ON

mysql-test/suite/wsrep/t/mdev_6832.test

+--source include/have_wsrep_provider.inc
+--source include/have_binlog_format_row.inc
+
+--echo #
+--echo # MDEV-6832: ER_LOCK_WAIT_TIMEOUT on SHOW STATUS
+--echo #
+
+SHOW STATUS LIKE 'wsrep_ready';
+--disable_query_log
+eval SET @@global.wsrep_provider='$WSREP_PROVIDER';
+--enable_query_log
+SHOW STATUS LIKE 'wsrep_ready';
+SET @@global.wsrep_cluster_address='gcomm://';
+
+--echo # End of test.

mysql-test/suite/wsrep/t/variables.test

@@ -78,7 +78,6 @@ SET GLOBAL wsrep_provider=none;
 --echo #
 --echo # MDEV#6206: wsrep_slave_threads subtracts from max_connections
 --echo #
-call mtr.add_suppression("safe_mutex: Found wrong usage of mutex 'LOCK_wsrep_slave_threads' and 'LOCK_global_system_variables'");
 call mtr.add_suppression("WSREP: Failed to get provider options");
 
 --disable_query_log

sql/sql_parse.cc

@@ -2754,10 +2754,10 @@ mysql_execute_command(THD *thd)
 #endif
   case SQLCOM_SHOW_STATUS:
   {
+    execute_show_status(thd, all_tables);
 #ifdef WITH_WSREP
-    if (WSREP_CLIENT(thd) && wsrep_sync_wait(thd)) goto error;
+    wsrep_free_status(thd);
 #endif /* WITH_WSREP */
-    execute_show_status(thd, all_tables);
     break;
   }
   case SQLCOM_SHOW_EXPLAIN:

sql/wsrep_var.cc

@@ -365,7 +365,14 @@ bool wsrep_cluster_address_update (sys_var *self, THD* thd, enum_var_type type)
   */
   mysql_mutex_unlock(&LOCK_global_system_variables);
   wsrep_stop_replication(thd);
+
+  /*
+    Unlock and lock LOCK_wsrep_slave_threads to maintain lock order & avoid
+    any potential deadlock.
+  */
+  mysql_mutex_unlock(&LOCK_wsrep_slave_threads);
   mysql_mutex_lock(&LOCK_global_system_variables);
+  mysql_mutex_lock(&LOCK_wsrep_slave_threads);
 
   if (wsrep_start_replication())
   {