MDEV-26: Global transaction ID.

Fix remaining two sporadic test failures in the full test suite:

 - Remove crash in DBUG_ASSERT() in _db_flush() (bug also exists in main
   tree).

 - Fix locking order violation for LOCK_status by temporarily unlocking it
   while locking LOCK_active_mi (like a similar fix for
   LOCK_global_variables).

include/my_dbug.h

@@ -89,7 +89,7 @@ extern  const char* _db_get_func_(void);
 #define DBUG_END()  _db_end_ ()
 #define DBUG_LOCK_FILE _db_lock_file_()
 #define DBUG_UNLOCK_FILE _db_unlock_file_()
-#define DBUG_ASSERT(A) do { _db_flush_(); assert(A); } while(0)
+#define DBUG_ASSERT(A) assert(A)
 #define DBUG_EXPLAIN(buf,len) _db_explain_(0, (buf),(len))
 #define DBUG_EXPLAIN_INITIAL(buf,len) _db_explain_init_((buf),(len))
 #define DEBUGGER_OFF                    do { _dbug_on_= 0; } while(0)

sql/mysqld.cc

@@ -6681,19 +6681,24 @@ static int show_rpl_status(THD *thd, SHOW_VAR *var, char *buff)
 static int show_slave_running(THD *thd, SHOW_VAR *var, char *buff)
 {
   Master_info *mi;
+  bool tmp;
+
   var->type= SHOW_MY_BOOL;
   var->value= buff;
+  mysql_mutex_unlock(&LOCK_status);
   mysql_mutex_lock(&LOCK_active_mi);
   mi= master_info_index->
     get_master_info(&thd->variables.default_master_connection,
                     MYSQL_ERROR::WARN_LEVEL_NOTE);
   if (mi)
-    *((my_bool *)buff)= (my_bool) (mi->slave_running ==
-                                   MYSQL_SLAVE_RUN_CONNECT &&
-                                   mi->rli.slave_running);
+    tmp= (my_bool) (mi->slave_running == MYSQL_SLAVE_RUN_CONNECT &&
+                    mi->rli.slave_running);
+  mysql_mutex_unlock(&LOCK_active_mi);
+  mysql_mutex_lock(&LOCK_status);
+  if (mi)
+    *((my_bool *)buff)= tmp;
   else
     var->type= SHOW_UNDEF;
-  mysql_mutex_unlock(&LOCK_active_mi);
   return 0;
 }
 
@@ -6701,17 +6706,23 @@ static int show_slave_running(THD *thd, SHOW_VAR *var, char *buff)
 static int show_slave_received_heartbeats(THD *thd, SHOW_VAR *var, char *buff)
 {
   Master_info *mi;
+  longlong tmp;
+
   var->type= SHOW_LONGLONG;
   var->value= buff;
+  mysql_mutex_unlock(&LOCK_status);
   mysql_mutex_lock(&LOCK_active_mi);
   mi= master_info_index->
     get_master_info(&thd->variables.default_master_connection,
                     MYSQL_ERROR::WARN_LEVEL_NOTE);
   if (mi)
-    *((longlong *)buff)= mi->received_heartbeats;
+    tmp= mi->received_heartbeats;
+  mysql_mutex_unlock(&LOCK_active_mi);
+  mysql_mutex_lock(&LOCK_status);
+  if (mi)
+    *((longlong *)buff)= tmp;
   else
     var->type= SHOW_UNDEF;
-  mysql_mutex_unlock(&LOCK_active_mi);
   return 0;
 }
 
@@ -6719,17 +6730,23 @@ static int show_slave_received_heartbeats(THD *thd, SHOW_VAR *var, char *buff)
 static int show_heartbeat_period(THD *thd, SHOW_VAR *var, char *buff)
 {
   Master_info *mi;
+  float heartbeat_period;
+
   var->type= SHOW_CHAR;
   var->value= buff;
+  mysql_mutex_unlock(&LOCK_status);
   mysql_mutex_lock(&LOCK_active_mi);
   mi= master_info_index->
     get_master_info(&thd->variables.default_master_connection,
                     MYSQL_ERROR::WARN_LEVEL_NOTE);
   if (mi)
-    sprintf(buff, "%.3f", mi->heartbeat_period);
+    heartbeat_period= mi->heartbeat_period;
+  mysql_mutex_unlock(&LOCK_active_mi);
+  mysql_mutex_lock(&LOCK_status);
+  if (mi)
+    sprintf(buff, "%.3f", heartbeat_period);
   else
     var->type= SHOW_UNDEF;
-  mysql_mutex_unlock(&LOCK_active_mi);
   return 0;
 }
 

sql/sql_base.cc

@@ -380,6 +380,13 @@ bool table_def_init(void)
 #endif
   mysql_mutex_init(key_LOCK_open, &LOCK_open, MY_MUTEX_INIT_FAST);
   mysql_mutex_record_order(&LOCK_active_mi, &LOCK_open);
+  /*
+    When we delete from the table_def_cache(), the free function
+    table_def_free_entry() is invoked from my_hash_delete(), which calls
+    free_table_share(), which may unload plugins, which can remove status
+    variables and hence takes LOCK_status. Record this locking order here.
+  */
+  mysql_mutex_record_order(&LOCK_open, &LOCK_status);
   oldest_unused_share= &end_of_unused_share;
   end_of_unused_share.prev= &oldest_unused_share;