ER_KEY_NOT_FOUND upon concurrent online auto-increment addition and DELETE

--source include/have_debug_sync.inc

--source include/have_innodb.inc

create table t1 (a int) engine=InnoDB;

insert into t1 values (10),(20),(30);

--send

  set debug_sync= 'now wait_for downgraded';

--connect (con_alter,localhost,root,,test)

set debug_sync= 'alter_table_online_downgraded signal downgraded wait_for goforit';

--send

  alter table t1 add pk int auto_increment primary key, algorithm=copy, lock=none;

--connection default

--reap

delete from t1 where a = 20;

set debug_sync= 'now signal goforit';

--connection con_alter

--reap

select * from t1;

show create table t1;

# Cleanup

drop table t1;

set debug_sync= reset;

mysqltest: At line 20: query 'reap' failed: ER_KEY_NOT_FOUND (1032): Can't find record in 't1'

MariaDB [test]> alter table t1 add pk int auto_increment primary key, algorithm=copy, lock=none;

ERROR 1032 (HY000): Can't find record in 't1'e done