Fixed deadlock with LOCK TABLES and ALTER TABLE

MDEV-21398 Deadlock (server hang) or assertion failure in
Diagnostics_area::set_error_status upon ALTER under lock

This failure could only happen if one locked the same table
multiple times and then did an ALTER TABLE on the table.

Major change is to change all instances of
table->m_needs_reopen= true;
to
table->mark_table_for_reopen();

The main fix for the problem was to ensure that we mark all
instances of the table in the locked_table_list and when we
reopen the tables, we first close all tables before reopening
and locking them.

Other things:
- Don't call thd->locked_tables_list.reopen_tables if there
  are no tables marked for reopen. (performance)

1 files changed, 11 insertions, 0 deletions

diff --git a/sql/table.cc b/sql/table.cc
index 995852651d0..611b8d1296f 100644
--- a/sql/table.cc
+++ b/sql/table.cc
@@ -8647,3 +8647,14 @@ void TABLE::initialize_quick_structures()
   bzero(quick_costs, sizeof(quick_costs));
   bzero(quick_n_ranges, sizeof(quick_n_ranges));
 }
+
+/*
+  Mark table to be reopened after query
+*/
+
+void TABLE::mark_table_for_reopen()
+{
+  THD *thd= in_use;
+  DBUG_ASSERT(thd);
+  thd->locked_tables_list.mark_table_for_reopen(thd, this);
+}