MDEV-7894 - ALTER TABLE ... IMPORT/DISCARD TABLESPACE under LOCK TABLES doesn'tbb-mdev7894

            acquire X metadata lock

Due to coding mistake thr_lock.c lock was necessary to isolate ALTER TABLE
IMPORT/DISCARD TABLESPACE under LOCK TABLES from concurrent I_S queries/
open HANDLERs.

Change ALTER TABLE IMPORT/DISCARD TABLESPACE code to acquire X
lock on table being imported/discarded even under lock tables.

1 files changed, 25 insertions, 0 deletions

diff --git a/sql/sql_table.cc b/sql/sql_table.cc
index c4b07ad2035..b4cbc936fa1 100644
--- a/sql/sql_table.cc
+++ b/sql/sql_table.cc
@@ -5561,6 +5561,24 @@ int mysql_discard_or_import_tablespace(THD *thd,
     DBUG_RETURN(-1);
   }
 
+  /*
+    Under LOCK TABLES we need to upgrade SNRW metadata lock to X lock
+    before doing discard or import of tablespace.
+
+    Skip this step for temporary tables as metadata locks are not
+    applicable for them.
+  */
+  if (table_list->table->s->tmp_table == NO_TMP_TABLE &&
+      (thd->locked_tables_mode == LTM_LOCK_TABLES ||
+       thd->locked_tables_mode == LTM_PRELOCKED_UNDER_LOCK_TABLES) &&
+      thd->mdl_context.upgrade_shared_lock(table_list->table->mdl_ticket,
+                                           MDL_EXCLUSIVE,
+                                           thd->variables.lock_wait_timeout))
+  {
+    thd->tablespace_op= FALSE;
+    DBUG_RETURN(-1);
+  }
+
   error= table_list->table->file->ha_discard_or_import_tablespace(discard);
 
   THD_STAGE_INFO(thd, stage_end);
@@ -5583,6 +5601,13 @@ int mysql_discard_or_import_tablespace(THD *thd,
   error= write_bin_log(thd, FALSE, thd->query(), thd->query_length());
 
 err:
+  if (table_list->table->s->tmp_table == NO_TMP_TABLE &&
+      (thd->locked_tables_mode == LTM_LOCK_TABLES ||
+       thd->locked_tables_mode == LTM_PRELOCKED_UNDER_LOCK_TABLES))
+  {
+    table_list->table->mdl_ticket->downgrade_lock(MDL_SHARED_NO_READ_WRITE);
+  }
+
   thd->tablespace_op=FALSE;
 
   if (error == 0)