From: Tom Lane <tgl@sss.pgh.pa.us>
To: pgsql-committers@lists.postgresql.org
Subject: pgsql: Use the same cmd_context throughout a walsender's lifetime.
Date: Mon, 21 Apr 2025 16:09:41 +0000
Message-ID: <E1u6tiH-00182e-0a@gemulon.postgresql.org> (raw)
Use the same cmd_context throughout a walsender's lifetime.
exec_replication_command created a cmd_context to work in and
then deleted it on exit. This is pretty dangerous because
some replication commands start/finish transactions. In the
wake of commit 1afe31f03, that could lead to re-selecting a
CurrentMemoryContext that's already been deleted, leading to
hilarity such as a memory context that is its own parent.
To fix, let's make the cmd_context persist across
exec_replication_command calls; instead of deleting it, we'll just
reset it each time. In this way it retains the same identity and
there's no problem if transaction abort restores it as the working
context. It probably even saves a few microseconds to do this.
This fix also ensures that exec_replication_command returns to the
caller (PostgresMain) with the same context active that had been
when it was called (probably MessageContext). The previous
coding could get that wrong too.
Reported-by: Anthonin Bonnefoy <anthonin.bonnefoy@datadoghq.com>
Author: Anthonin Bonnefoy <anthonin.bonnefoy@datadoghq.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CAO6_XqoJA7-_G6t7Uqe5nWF3nj+QBGn4F6Ptp=rUGDr0zo+KvA@mail.gmail.com
Branch
------
master
Details
-------
https://git.postgresql.org/pg/commitdiff/80b727eb9deab589a8648750bc20f1623d5acd3e
Modified Files
--------------
src/backend/replication/walsender.c | 42 +++++++++++++++++++++++++++++--------
src/test/subscription/t/100_bugs.pl | 18 ++++++++++++++++
2 files changed, 51 insertions(+), 9 deletions(-)
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To: pgsql-committers@postgresql.org
Cc: tgl@sss.pgh.pa.us, pgsql-committers@lists.postgresql.org
Subject: Re: pgsql: Use the same cmd_context throughout a walsender's lifetime.
In-Reply-To: <E1u6tiH-00182e-0a@gemulon.postgresql.org>
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