sql_plugin.cc:

  fixed uninit memory access in SET pluginvar=DEFAULT
innodb_mysql.test, innodb_mysql.result:
  test case for SET pluginvar=DEFAULT

mysql-test/r/innodb_mysql.result

+set global innodb_support_xa=default;
+set session innodb_support_xa=default;
 SET SESSION STORAGE_ENGINE = InnoDB;
 drop table if exists t1,t2,t3,t1m,t1i,t2m,t2i,t4;
 create table t1 (

mysql-test/t/innodb_mysql.test

@@ -10,5 +10,6 @@ let $engine_type= InnoDB;
 let $other_engine_type= MEMORY;
 # InnoDB does support FOREIGN KEYFOREIGN KEYs
 let $test_foreign_keys= 1;
-
+set global innodb_support_xa=default;
+set session innodb_support_xa=default;
 --source include/mix1.inc

sql/sql_plugin.cc

@@ -181,6 +181,7 @@ class sys_var_pluginvar: public sys_var
   TYPELIB* plugin_var_typelib(void);
   uchar* value_ptr(THD *thd, enum_var_type type, LEX_STRING *base);
   bool check(THD *thd, set_var *var);
+  bool check_default(enum_var_type type) { return is_readonly(); }
   void set_default(THD *thd, enum_var_type type);
   bool update(THD *thd, set_var *var);
 };
@@ -2168,9 +2169,11 @@ static st_bookmark *register_var(const char *plugin, const char *name,
     size= sizeof(int);
     break;
   case PLUGIN_VAR_LONG:
+  case PLUGIN_VAR_ENUM:
     size= sizeof(long);
     break;
   case PLUGIN_VAR_LONGLONG:
+  case PLUGIN_VAR_SET:
     size= sizeof(ulonglong);
     break;
   case PLUGIN_VAR_STR:
@@ -2611,6 +2614,7 @@ void sys_var_pluginvar::set_default(THD *thd, enum_var_type type)
   if (is_readonly())
     return;
 
+  pthread_mutex_lock(&LOCK_global_system_variables);
   tgt= real_value_ptr(thd, type);
   src= ((void **) (plugin_var + 1) + 1);
 
@@ -2627,12 +2631,14 @@ void sys_var_pluginvar::set_default(THD *thd, enum_var_type type)
 
   if (!(plugin_var->flags & PLUGIN_VAR_THDLOCAL) || type == OPT_GLOBAL)
   {
-    pthread_mutex_lock(&LOCK_plugin);
     plugin_var->update(thd, plugin_var, tgt, src);
-    pthread_mutex_unlock(&LOCK_plugin);
+    pthread_mutex_unlock(&LOCK_global_system_variables);
   }
   else
+  {
+    pthread_mutex_unlock(&LOCK_global_system_variables);
     plugin_var->update(thd, plugin_var, tgt, src);
+  }
 }