sql_db.cc:

  Revert Monty's change to the positioning of ha_drop_database(): otherwise a running query on a table to be dropped in DROP DATABASE always causes the server to hang

sql/sql_db.cc

@@ -166,7 +166,6 @@ void mysql_rm_db(THD *thd,char *db,bool if_exists)
 
   if ((deleted=mysql_rm_known_files(thd, dirp, path,0)) >= 0)
   {
-    ha_drop_database(path);
     if (!thd->query)
     {
       thd->query = path;
@@ -190,6 +189,17 @@ void mysql_rm_db(THD *thd,char *db,bool if_exists)
 exit:
   VOID(pthread_mutex_unlock(&LOCK_open));
   VOID(pthread_mutex_unlock(&LOCK_mysql_create_db));
+
+  /* If there are running queries on the tables, MySQL needs to get
+     access to LOCK_open to end them. InnoDB on the other hand waits
+     for the queries to end before dropping the database. That is why we
+     must do the dropping outside of the mutexes above, otherwise the server
+     always hangs if there are running queries. We only drop inside InnoDB
+     if deleted got value >= 0 which means that it was successful. */
+
+  if (deleted >= 0)
+    ha_drop_database(path);
+
   DBUG_VOID_RETURN;
 }