Message-ID: <5315d15a42109297259d1a3264ad09e363eb98df.camel@j-davis.com>
Subject: Re: Avoid orphaned objects dependencies, take 3
From: Jeff Davis <pgsql@j-davis.com>
To: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, Heikki Linnakangas
	 <hlinnaka@iki.fi>
Cc: Robert Haas <robertmhaas@gmail.com>, Roman Eskin <r.eskin@arenadata.io>,
  Michael Paquier <michael@paquier.xyz>, Alexander Lakhin
 <exclusion@gmail.com>, pgsql-hackers@lists.postgresql.org,  Tom Lane
 <tgl@sss.pgh.pa.us>
Date: Wed, 03 Jun 2026 11:08:13 -0700
In-Reply-To: <ah1PIyqtT+427dWb@bdtpg>
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On Mon, 2026-06-01 at 09:21 +0000, Bertrand Drouvot wrote:
> Now that we avoid orphaned objects dependencies, I resumed working on
> Robert's
> concern about the TOCTOU window where a REVOKE could land between the
> original
> permission check and the dependency recording.
>=20
> Based on our discussion during PGConf.dev, PFA a new patch that uses
> the same
> approach as RangeVarGetRelidExtended(): record
> SharedInvalidMessageCounter at the
> time of the original aclcheck, then before locking compare the
> current counter to
> the saved value. If it changed, recheck permission before acquiring
> the lock.
> After the lock wait, if more invalidations arrived, release and
> retry.

RangeVarGetRelidExtended() coordinates three things:

  - name lookup
  - lock
  - ACL check

whereas recheckAclAndLock() only coordinates the latter two. That means
there can still be some strange failures, like:

  -- Session 1
  BEGIN;
  DROP SCHEMA s2;

  -- Session 2
  SET search_path=3Ds2, s1;
  CREATE FUNCTION f() RETURNS INT LANGUAGE plpgsql AS
    $$ BEGIN RETURN 42; END; $$;

  -- Session 1
  COMMIT;

  -- Session 2
  ERROR:  referenced schema was concurrently dropped

even though no schema was actually referenced in the query, and a retry
of the transaction successfully creates the function in s1. Is that
expected?

Regards,
	Jeff Davis