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help / color / mirror / Atom feedFrom: Andres Freund <andres@anarazel.de>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: bufmgr: Fix order of operations in UnlockBufHdrExt
Date: Fri, 10 Jul 2026 17:27:09 +0000
Message-ID: <E1wiF0H-000TfH-0E@gemulon.postgresql.org> (raw)
bufmgr: Fix order of operations in UnlockBufHdrExt
In c75ebc657ffc I (Andres) introduced UnlockBufHdrExt() which can set and
clear bits in the buffer state using CAS. Unfortunately I added bits before
subtracting them, which means that a bit that was both removed and set would
remain unset. Fix the order of operations.
The only known case where that is a problem is that BM_IO_ERROR would not
actually remain set.
It's unfortunately not trivial to add a decent, race-free, test to verify that
BM_IO_ERROR remains set. That's therefore left for the 20 cycle.
Reported-by: Yura Sokolov <y.sokolov@postgrespro.ru>
Discussion: https://postgr.es/m/ab0dcc9e-aba0-44e3-ac23-8d74c48888e6@postgrespro.ru
Backpatch-through: 19, where c75ebc657ffc went in
Branch
------
REL_19_STABLE
Details
-------
https://git.postgresql.org/pg/commitdiff/a1b74b7279c24638c44f9d3d1af2da30cfb7068d
Modified Files
--------------
src/include/storage/buf_internals.h | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)
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To: pgsql-committers@postgresql.org
Cc: andres@anarazel.de, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: bufmgr: Fix order of operations in UnlockBufHdrExt
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