stuck when query information_schema.columns

[crazycs520]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

from https://asktug.com/t/topic/36253

create user 'u2'@'%' identified by '123456';
use test;
create table t1 (a int, b int, c int, unique index (a));

then connection tidb use user u2;

select count(*) from columns;  -- stuck.

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

3. What did you see instead (Required)

4. Affected version (Required)

• master, v4.0.3

***************************[ 1. row ]***************************
tidb_version() | Release Version: v4.0.0-beta.2-852-g1e7454c81
Edition: Community
Git Commit Hash: 1e7454c81d1f4fae464e835d1a4023a911cfa87b
Git Branch: master
UTC Build Time: 2020-07-29 03:46:26
GoVersion: go1.14.4
Race Enabled: false
TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306
Check Table Before Drop: false

5. Root Cause Analysis