[Stas Kelvich <s.kelvich@postgrespro.ru>]

Hello.

It seems that during COMMIT PREPARED FinishPreparedTransaction() doesn't
hold interrupts around writing to wal and cleaning up ProcArray and GXact
entries. At least RemoveTwoPhaseFile (which is called in between) can print
a warning with ereport(), which, in turn will check for interrupts and
therefore can cancel backend or throw an error before GXact clean-up.

Other similar places like CommitTransaction and PrepareTransaction have
such hold interrupts sections.

--
Stas Kelvich
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company

Attachments:

0001-Add-HOLD_INTERRUPTS-section-into-FinishPreparedTrans.patch (application/octet-stream, 1.3K) download
From 8760cbda323b6e725db44e8c26d8d6a063d692a5 Mon Sep 17 00:00:00 2001
From: Stas Kelvich <stanconn@gmail.com>
Date: Fri, 27 Apr 2018 23:52:26 +0300
Subject: [PATCH] Add HOLD_INTERRUPTS section into FinishPreparedTransaction.

If an interrupt arrives in the middle of FinishPreparedTransaction
and any callback decide to call CHECK_FOR_INTERRUPTS (e.g.
RemoveTwoPhaseFile can write a warning with ereport, which checks for
interrupts) then it's possible to leave current GXact undeleted.
---
 src/backend/access/transam/twophase.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c
index cdd8156ce4..a68769fb0d 100644
--- a/src/backend/access/transam/twophase.c
+++ b/src/backend/access/transam/twophase.c
@@ -1487,6 +1487,9 @@ FinishPreparedTransaction(const char *gid, bool isCommit)
 	/* compute latestXid among all children */
 	latestXid = TransactionIdLatest(xid, hdr->nsubxacts, children);
 
+	/* Prevent cancel/die interrupt while cleaning up */
+	HOLD_INTERRUPTS();
+
 	/*
 	 * The order of operations here is critical: make the XLOG entry for
 	 * commit or abort, then mark the transaction committed or aborted in
@@ -1579,6 +1582,7 @@ FinishPreparedTransaction(const char *gid, bool isCommit)
 	MyLockedGxact = NULL;
 
 	pfree(buf);
+	RESUME_INTERRUPTS();
 }
 
 /*
-- 
2.16.2

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