From b75c1f6879c542c79959b42661c7f7bbf8e358be Mon Sep 17 00:00:00 2001 From: Amit Kapila Date: Mon, 28 Jun 2021 08:55:47 +0530 Subject: [PATCH] Fix race condition in TransactionGroupUpdateXidStatus(). When we cannot immediately acquire CLogControlLock in exclusive mode at commit time, we add ourselves to a list of processes that need their XIDs status update. We do this if the clog page where we need to update the current transaction status is the same as the group leader's clog page, otherwise, we allow the caller to clear it by itself. Now, when we can't add ourselves to any group, we were not clearing the current proc if it has already become a member of some group which was leading to an assertion failure when the same proc was assigned to another backend after the current backend exits. Reported-by: Alexander Lakhin Bug: 17072 Author: Amit Kapila Tested-By: Alexander Lakhin Backpatch-through: 11, where it was introduced Discussion: https://postgr.es/m/17072-2f8764857ef2c92a@postgresql.org --- src/backend/access/transam/clog.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/src/backend/access/transam/clog.c b/src/backend/access/transam/clog.c index 726ef87e6e..0a473d2661 100644 --- a/src/backend/access/transam/clog.c +++ b/src/backend/access/transam/clog.c @@ -450,7 +450,12 @@ TransactionGroupUpdateXidStatus(TransactionId xid, XidStatus status, if (nextidx != INVALID_PGPROCNO && ProcGlobal->allProcs[nextidx].clogGroupMemberPage != proc->clogGroupMemberPage) { + /* + * Ensure that this proc is not a member of any clog group that + * needs an XID status update. + */ proc->clogGroupMember = false; + pg_atomic_write_u32(&proc->clogGroupNext, INVALID_PGPROCNO); return false; }