MDEV-16986 Unitialized mutex, SIGSEGV and assorted assertion failures in Aria code

The problem was that when a mysql.proc table was
opened for reading it was added to the current Aria
transaction context but never properly deleted from
it. Normally this isn't a problem, except if the
mysql.proc table is closed before the transaction
ended, which happened in this test case.

Fixed by removing mysql.proc from the transaction
context before closing the table.

mysql-test/suite/maria/system_tables.result

+CREATE TABLE t1 (i INT) ENGINE=Aria;
+LOCK TABLE t1 WRITE;
+connect  con1,localhost,root,,test;
+SET lock_wait_timeout= 2;
+FLUSH TABLES;
+connection default;
+CALL non_existing_sp;
+ERROR 42000: PROCEDURE test.non_existing_sp does not exist
+connection con1;
+ERROR HY000: Lock wait timeout exceeded; try restarting transaction
+disconnect con1;
+connection default;
+DROP TABLE t1;

mysql-test/suite/maria/system_tables.test

+#
+# Test related to Aria system tables
+#
+
+#
+# MDEV-16986 Unitialized mutex, SIGSEGV and assorted assertion failures in
+# Aria code
+#
+
+CREATE TABLE t1 (i INT) ENGINE=Aria;
+LOCK TABLE t1 WRITE;
+
+--connect (con1,localhost,root,,test)
+SET lock_wait_timeout= 2;
+--send
+  FLUSH TABLES;
+--connection default
+--error ER_SP_DOES_NOT_EXIST
+CALL non_existing_sp;
+--connection con1
+--error ER_LOCK_WAIT_TIMEOUT
+--reap
+
+# Cleanup
+--disconnect con1
+--connection default
+DROP TABLE t1;

sql/sql_base.cc

@@ -8772,6 +8772,13 @@ open_system_tables_for_read(THD *thd, TABLE_LIST *table_list,
 void
 close_system_tables(THD *thd, Open_tables_backup *backup)
 {
+  /*
+    Inform the transaction handler that we are closing the
+    system tables and we don't need the read view anymore.
+  */
+  for (TABLE *table= thd->open_tables ; table ; table= table->next)
+    table->file->extra(HA_EXTRA_PREPARE_FOR_FORCED_CLOSE);
+
   close_thread_tables(thd);
   thd->restore_backup_open_tables_state(backup);
 }