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Switch memory contexts in ReinitializeParallelDSM.

author Robert Haas <rhaas@postgresql.org>

2025年12月16日 15:40:53 +0000 (10:40 -0500)

committer Robert Haas <rhaas@postgresql.org>

2025年12月16日 17:24:55 +0000 (12:24 -0500)

We already do this in CreateParallelContext, InitializeParallelDSM, and
LaunchParallelWorkers. I suspect the reason why the matching logic was
omitted from ReinitializeParallelDSM is that I failed to realize that
any memory allocation was happening here -- but shm_mq_attach does
allocate, which could result in a shm_mq_handle being allocated in a
shorter-lived context than the ParallelContext which points to it.

That could result in a crash if the shorter-lived context is freed
before the parallel context is destroyed. As far as I am currently
aware, there is no way to reach a crash using only code that is
present in core PostgreSQL, but extensions could potentially trip
over this. Fixing this in the back-branches appears low-risk, so
back-patch to all supported versions.

Author: Jakub Wartak <jakub.wartak@enterprisedb.com>
Co-authored-by: Jeevan Chalke <jeevan.chalke@enterprisedb.com>
Backpatch-through: 14
Discussion: http://postgr.es/m/CAKZiRmwfVripa3FGo06=5D1EddpsLu9JY2iJOTgbsxUQ339ogQ@mail.gmail.com

src/backend/access/transam/parallel.c patch | blob | blame | history

diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c

index 956b23816dea6beb34f7efd0564eec8f7876fe67..642c61fc55ce20d3942363e57ded23631a698204 100644 (file)

--- a/src/backend/access/transam/parallel.c

+++ b/src/backend/access/transam/parallel.c

@@ -508,8 +508,12 @@ InitializeParallelDSM(ParallelContext *pcxt)

void

ReinitializeParallelDSM(ParallelContext *pcxt)

{

+ MemoryContext oldcontext;

FixedParallelState *fps;

+ /* We might be running in a very short-lived memory context. */