MW-259 - moved wsrep desync/resync calls from wsrep_desync_update() to...

MW-259 - moved wsrep desync/resync calls from wsrep_desync_update() to wsrep_desync_check() method which does not hold the lock and is arguably a more fitting place to change provider state - before changing the actual variable value.

mysql-test/suite/galera/r/MW-259.result

+CREATE TABLE t1 (f1 INTEGER) Engine=InnoDB;
+SET GLOBAL wsrep_desync=0;
+Warnings:
+Warning	1231	'wsrep_desync' is already OFF.
+SET wsrep_OSU_method=RSU;
+SET DEBUG_SYNC = 'alter_table_before_open_tables WAIT_FOR continue';
+ALTER TABLE t1 ADD COLUMN f2 INTEGER;;
+SET GLOBAL wsrep_desync=1;;
+SET DEBUG_SYNC= 'now SIGNAL continue';
+DROP TABLE t1;
+SET GLOBAL wsrep_desync=0;
+SET DEBUG_SYNC= 'RESET';

mysql-test/suite/galera/t/MW-259.test

+--source include/galera_cluster.inc
+--source include/have_innodb.inc
+--source include/have_debug_sync.inc
+
+--connect node_1a, 127.0.0.1, root, , test, $NODE_MYPORT_1
+--connect node_1b, 127.0.0.1, root, , test, $NODE_MYPORT_1
+
+--connection node_1
+CREATE TABLE t1 (f1 INTEGER) Engine=InnoDB;
+
+SET GLOBAL wsrep_desync=0;
+SET wsrep_OSU_method=RSU;
+
+SET DEBUG_SYNC = 'alter_table_before_open_tables WAIT_FOR continue';
+--send ALTER TABLE t1 ADD COLUMN f2 INTEGER;
+
+--connection node_1a
+
+--let $wait_condition = SELECT COUNT(*) = 1 FROM INFORMATION_SCHEMA.PROCESSLIST WHERE STATE = 'debug sync point: alter_table_before_open_tables'
+--source include/wait_condition.inc
+
+# wsrep_desync=1 will block
+--send SET GLOBAL wsrep_desync=1;
+
+--connection node_1b
+--sleep 2
+--let $wait_condition = SELECT COUNT(*) = 1 FROM INFORMATION_SCHEMA.PROCESSLIST WHERE STATE = 'exit open_tables()' and INFO = 'SET GLOBAL wsrep_desync=1'
+--source include/wait_condition.inc
+
+SET DEBUG_SYNC= 'now SIGNAL continue';
+DROP TABLE t1;
+SET GLOBAL wsrep_desync=0;
+
+--connection node_1
+--reap
+
+--connection node_1a
+--reap
+
+# Cleanup
+SET DEBUG_SYNC= 'RESET';
+

sql/wsrep_var.cc

@@ -529,14 +529,10 @@ bool wsrep_desync_check (sys_var *self, THD* thd, set_var* var)
                    ER_WRONG_VALUE_FOR_VAR,
                    "'wsrep_desync' is already OFF.");
     }
+    return false;
   }
-  return 0;
-}
-
-bool wsrep_desync_update (sys_var *self, THD* thd, enum_var_type type)
-{
   wsrep_status_t ret(WSREP_WARNING);
-  if (wsrep_desync) {
+  if (new_wsrep_desync) {
     ret = wsrep->desync (wsrep);
     if (ret != WSREP_OK) {
       WSREP_WARN ("SET desync failed %d for schema: %s, query: %s", ret,
@@ -558,6 +554,11 @@ bool wsrep_desync_update (sys_var *self, THD* thd, enum_var_type type)
   return false;
 }
 
+bool wsrep_desync_update (sys_var *self, THD* thd, enum_var_type type)
+{
+  return false;
+}
+
 bool wsrep_max_ws_size_update (sys_var *self, THD *thd, enum_var_type)
 {
   char max_ws_size_opt[128];