A fix for Bug#41158 "DROP TABLE holds LOCK_open during unlink()".

Remove acquisition of LOCK_open around file system operations,
since such operations are now protected by metadata locks.
Rework table discovery algorithm to not require LOCK_open.

No new tests added since all MDL locking operations are covered
in lock.test and mdl_sync.test, and as long as these tests
pass despite the increased concurrency, consistency must be
unaffected.

1 files changed, 5 insertions, 14 deletions

diff --git a/sql/sql_rename.cc b/sql/sql_rename.cc
index 301b22bd70e..f0b53abcb03 100644
--- a/sql/sql_rename.cc
+++ b/sql/sql_rename.cc
@@ -147,13 +147,15 @@ bool mysql_rename_tables(THD *thd, TABLE_LIST *table_list, bool silent)
                        MYSQL_OPEN_SKIP_TEMPORARY))
     goto err;
 
-  mysql_mutex_lock(&LOCK_open);
-
   for (ren_table= table_list; ren_table; ren_table= ren_table->next_local)
     tdc_remove_table(thd, TDC_RT_REMOVE_ALL, ren_table->db,
-                     ren_table->table_name);
+                     ren_table->table_name, FALSE);
 
   error=0;
+  /*
+    An exclusive lock on table names is satisfactory to ensure
+    no other thread accesses this table.
+  */
   if ((ren_table=rename_tables(thd,table_list,0)))
   {
     /* Rename didn't succeed;  rename back the tables in reverse order */
@@ -175,17 +177,6 @@ bool mysql_rename_tables(THD *thd, TABLE_LIST *table_list, bool silent)
 
     error= 1;
   }
-  /*
-    An exclusive lock on table names is satisfactory to ensure
-    no other thread accesses this table.
-    However, NDB assumes that handler::rename_tables is called under
-    LOCK_open. And it indeed is, from ALTER TABLE.
-    TODO: remove this limitation.
-    We still should unlock LOCK_open as early as possible, to provide
-    higher concurrency - query_cache_invalidate can take minutes to
-    complete.
-  */
-  mysql_mutex_unlock(&LOCK_open);
 
   if (!silent && !error)
   {