From: Tom Lane <tgl@sss.pgh.pa.us>
To: exclusion@gmail.com
cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #16378: Invalid memory access on interrupting CLUSTER after
 CREATE TEMP TABLE
In-reply-to: <16378-7a70ca41b3ec2009@postgresql.org>
References: <16378-7a70ca41b3ec2009@postgresql.org>
Comments: In-reply-to PG Bug reporting form <noreply@postgresql.org>
	message dated "Sun, 19 Apr 2020 07:07:08 -0000"
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Date: Sun, 19 Apr 2020 14:11:37 -0400
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PG Bug reporting form <noreply@postgresql.org> writes:
> The following script:
> ...
> leads to a cassert-enabled server crash with the following messages in the
> log (for the master branch):

Hm, I can get a crash here without valgrind, as long as it's a cassert
build.  We're accessing a list that's been thrown away by memory context
cleanup, so this results:
TRAP: FailedAssertion("IsOidList(list)", File: "list.c", Line: 678)
The timing is a bit finicky, but no more so than you report for the
valgrind case.

The difficulty is that the pendingReindexedIndexes list is kept in
some transaction-local context, so it gets flushed during the transaction
abort that is the first step of proc_exit processing.  But the static
pointer to it is still set, causing big problems if we do any system
catalog accesses later --- like, say, while dropping the session's
temp tables.

One idea would be to keep the list in TopMemoryContext, but that feels
like a band-aid solution.  I think more likely what we ought to do is
stop trying to use a PG_TRY in reindex_relation to drive cleanup,
and instead hook ResetReindexPending into transaction abort processing
honestly.

I wonder how many other uses of PG_TRY have similar issues?  It's
not really obvious that this is an unsafe coding pattern.

			regards, tom lane