DDL is blocked when modifies column and creates view concurrently

[wjhuang2016]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

create table t( a int);
alter table t modify column a char(10); then create view v as select * from t; in other session.

2. What did you expect to see? (Required)

These two DDLs finish eventually.

3. What did you see instead (Required)

DDL is blocked.

4. What is your TiDB version? (Required)

master