Commit on behalf of Dmitry Lenev.

Merge his patch for Bug#52044 into 5.5, and apply 
review comments.

sql/sql_base.h

@@ -70,6 +70,7 @@ enum enum_tdc_remove_table_type {TDC_RT_REMOVE_ALL, TDC_RT_REMOVE_NOT_OWN,
 #define RTFC_CHECK_KILLED_FLAG      0x0004
 
 bool check_dup(const char *db, const char *name, TABLE_LIST *tables);
+extern mysql_mutex_t LOCK_open;
 bool table_cache_init(void);
 void table_cache_free(void);
 bool table_def_init(void);
@@ -226,7 +227,8 @@ TABLE *open_performance_schema_table(THD *thd, TABLE_LIST *one_table,
                                      Open_tables_state *backup);
 void close_performance_schema_table(THD *thd, Open_tables_state *backup);
 
-bool close_cached_tables(THD *thd, TABLE_LIST *tables, bool wait_for_refresh);
+bool close_cached_tables(THD *thd, TABLE_LIST *tables,
+                         bool wait_for_refresh, ulong timeout);
 bool close_cached_connection_tables(THD *thd, bool wait_for_refresh,
                                     LEX_STRING *connect_string);
 void close_all_tables_for_name(THD *thd, TABLE_SHARE *share,
@@ -426,8 +428,8 @@ public:
   enum enum_open_table_action
   {
     OT_NO_ACTION= 0,
-    OT_MDL_CONFLICT,
-    OT_WAIT_TDC,
+    OT_BACKOFF_AND_RETRY,
+    OT_REOPEN_TABLES,
     OT_DISCOVER,
     OT_REPAIR
   };
@@ -437,9 +439,6 @@ public:
   bool request_backoff_action(enum_open_table_action action_arg,
                               TABLE_LIST *table);
 
-  void add_request(MDL_request *request)
-  { m_mdl_requests.push_front(request); }
-
   bool can_recover_from_failed_open() const
   { return m_action != OT_NO_ACTION; }
 
@@ -461,8 +460,6 @@ public:
 
   uint get_flags() const { return m_flags; }
 private:
-  /** List of requests for all locks taken so far. Used for waiting on locks. */
-  MDL_request_list m_mdl_requests;
   /**
     For OT_DISCOVER and OT_REPAIR actions, the table list element for
     the table which definition should be re-discovered or which