From: Andres Freund <andres@anarazel.de>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: bufmgr: Fix ordering of checks in PinBuffer()
Date: Wed, 01 Apr 2026 00:27:47 +0000
Message-ID: <E1w7jQw-002NfP-0p@gemulon.postgresql.org> (raw)
bufmgr: Fix ordering of checks in PinBuffer()
The check for skip_if_not_valid added in 819dc118c0f6 was put at the start of
the loop. A CAS loop in theory does allow to make that check in a race free
manner. However, just after the check, there's a
old_buf_state = WaitBufHdrUnlocked(buf);
which introduces a race, because it would allow BM_VALID to be cleared, after
the skip_if_not_valid check.
Fix by restarting the loop after WaitBufHdrUnlocked().
Reported-by: Yura Sokolov <y.sokolov@postgrespro.ru>
Discussion: https://postgr.es/m/5bf667f3-5270-4b19-a08f-0facbecdff68@postgrespro.ru
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/c0af4eb4e71ecd4826ae6c9985f1d10ace5e1be6
Modified Files
--------------
src/backend/storage/buffer/bufmgr.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
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To: pgsql-committers@postgresql.org
Cc: andres@anarazel.de, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: bufmgr: Fix ordering of checks in PinBuffer()
In-Reply-To: <E1w7jQw-002NfP-0p@gemulon.postgresql.org>
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