MDEV-15551 Server hangs or assertion `strcmp(share->unique_file_name,filename) || share->last_version' fails in test_if_reopen or unexpected ER_LOCK_DEADLOCK

only use HA_EXTRA_PREPARE_FOR_DROP when the table is going to be dropped

Author: vuvova

mysql-test/suite/parts/r/truncate_locked.result

@@ -0,0 +1,7 @@
+create table t1 (i int) engine=myisam partition by hash(i) partitions 2 ;
+lock table t1 write;
+truncate table t1;
+desc t1;
+Field	Type	Null	Key	Default	Extra
+i	int(11)	YES		NULL	
+drop table t1;

mysql-test/suite/parts/t/truncate_locked.test

@@ -0,0 +1,10 @@
+#
+# MDEV-15551 Server hangs or assertion `strcmp(share->unique_file_name,filename) || share->last_version' fails in test_if_reopen or unexpected ER_LOCK_DEADLOCK
+#
+--source include/have_partition.inc
+create table t1 (i int) engine=myisam partition by hash(i) partitions 2 ;
+lock table t1 write;
+truncate table t1;
+desc t1;
+drop table t1;
+

sql/sql_truncate.cc

@@ -400,7 +400,8 @@ bool Sql_cmd_truncate_table::lock_table(THD *thd, TABLE_LIST *table_ref,
   {
     DEBUG_SYNC(thd, "upgrade_lock_for_truncate");
     /* To remove the table from the cache we need an exclusive lock. */
-    if (wait_while_table_is_used(thd, table, HA_EXTRA_PREPARE_FOR_DROP))
+    if (wait_while_table_is_used(thd, table,
+          *hton_can_recreate ? HA_EXTRA_PREPARE_FOR_DROP : HA_EXTRA_NOT_USED))
       DBUG_RETURN(TRUE);
     m_ticket_downgrade= table->mdl_ticket;
     /* Close if table is going to be recreated. */