MDEV-18507 can't update temporary table when joined with table with triggers on read-only

triggers are opened and tables used in triggers are prelocked in
open_tables(). But multi-update can detect what tables will actually
be updated only later, after all main tables are opened.

Meaning, if a table is used in multi-update, but is not actually updated,
its on-update treggers will be opened and tables will be prelocked,
even if it's unnecessary. This can cause more tables to be
write-locked than needed, causing read_only errors, privilege errors
and lock waits.

Fix: don't open/prelock triggers unless table->updating is true.
In multi-update after setting table->updating=true, do a second
open_tables() for newly added tables, if any.

1 files changed, 26 insertions, 5 deletions

diff --git a/sql/sql_update.cc b/sql/sql_update.cc
index b23c295a1af..c6da864c0a1 100644
--- a/sql/sql_update.cc
+++ b/sql/sql_update.cc
@@ -1208,6 +1208,9 @@ int mysql_multi_update_prepare(THD *thd)
   List<Item> *fields= &lex->select_lex.item_list;
   table_map tables_for_update;
   bool update_view= 0;
+  DML_prelocking_strategy prelocking_strategy;
+  bool has_prelocking_list= thd->lex->requires_prelocking();
+
   /*
     if this multi-update was converted from usual update, here is table
     counter else junk will be assigned here, but then replaced with real
@@ -1228,10 +1231,10 @@ int mysql_multi_update_prepare(THD *thd)
     keep prepare of multi-UPDATE compatible with concurrent LOCK TABLES WRITE
     and global read lock.
   */
-  if ((original_multiupdate &&
-       open_tables(thd, &table_list, &table_count,
-                   (thd->stmt_arena->is_stmt_prepare() ?
-                    MYSQL_OPEN_FORCE_SHARED_MDL : 0))) ||
+  if ((original_multiupdate && open_tables(thd, &table_list, &table_count,
+                                           thd->stmt_arena->is_stmt_prepare()
+                                           ? MYSQL_OPEN_FORCE_SHARED_MDL : 0,
+                                           &prelocking_strategy)) ||
       mysql_handle_derived(lex, DT_INIT))
     DBUG_RETURN(TRUE);
   /*
@@ -1278,6 +1281,9 @@ int mysql_multi_update_prepare(THD *thd)
   if (unsafe_key_update(lex->select_lex.leaf_tables, tables_for_update))
     DBUG_RETURN(true);
 
+  TABLE_LIST **new_tables= lex->query_tables_last;
+  DBUG_ASSERT(*new_tables== NULL);
+
   /*
     Setup timestamp handling and locking mode
   */
@@ -1308,6 +1314,8 @@ int mysql_multi_update_prepare(THD *thd)
       tl->updating= 1;
       if (tl->belong_to_view)
         tl->belong_to_view->updating= 1;
+      if (extend_table_list(thd, tl, &prelocking_strategy, has_prelocking_list))
+        DBUG_RETURN(TRUE);
     }
     else
     {
@@ -1328,6 +1336,19 @@ int mysql_multi_update_prepare(THD *thd)
         tl->set_lock_type(thd, read_lock_type_for_table(thd, lex, tl));
     }
   }
+
+  uint addon_table_count= 0;
+  if (*new_tables)
+  {
+    Sroutine_hash_entry **new_routines= thd->lex->sroutines_list.next;
+    DBUG_ASSERT(*new_routines == NULL);
+    if (open_tables(thd, new_tables, &addon_table_count, new_routines,
+                    thd->stmt_arena->is_stmt_prepare()
+                    ? MYSQL_OPEN_FORCE_SHARED_MDL : 0,
+                    &prelocking_strategy))
+      DBUG_RETURN(TRUE);
+  }
+
   for (tl= table_list; tl; tl= tl->next_local)
   {
     /* Check access privileges for table */
@@ -1360,7 +1381,7 @@ int mysql_multi_update_prepare(THD *thd)
 
   /* now lock and fill tables */
   if (!thd->stmt_arena->is_stmt_prepare() &&
-      lock_tables(thd, table_list, table_count, 0))
+      lock_tables(thd, table_list, table_count + addon_table_count, 0))
   {
     DBUG_RETURN(TRUE);
   }