Inconsistency in vacuum behavior

Hi.

We've run regress isolation tests on partitioned tables and found 
interesting VACUUM behavior. I'm not sure, if it's intended.

In the following example, partitioned tables and regular tables behave 
differently:

CREATE TABLE vacuum_tab (a int) PARTITION BY HASH (a);
CREATE TABLE vacuum_tab_1 PARTITION OF vacuum_tab FOR VALUES WITH 
(MODULUS 2, REMAINDER 0);
CREATE TABLE vacuum_tab_2 PARTITION OF vacuum_tab FOR VALUES WITH 
(MODULUS 2, REMAINDER 1);
CREATE ROLE regress_vacuum_conflict;

In the first session:

begin;
  LOCK vacuum_tab IN SHARE UPDATE EXCLUSIVE MODE;

In the second:
SET ROLE regress_vacuum_conflict;
  VACUUM vacuum_tab;
  WARNING:  permission denied to vacuum "vacuum_tab", skipping it <---- 
hangs here, trying to lock vacuum_tab_1

In non-partitioned case second session exits after emitting warning. In 
partitioned case, it hangs, trying to get locks.
This is due to the fact that in expand_vacuum_rel() we skip parent table 
if vacuum_is_permitted_for_relation(), but don't perform such check for 
its child.
The check will be performed later in vacuum_rel(), but after 
vacuum_open_relation(), which leads to hang in the second session.

Is it intended? Why don't we perform vacuum_is_permitted_for_relation() 
check for inheritors in expand_vacuum_rel()?

-- 
Best regards,
Alexander Pyhalov,
Postgres Professional