From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>
cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Re: check failure with -DRELCACHE_FORCE_RELEASE
 -DCLOBBER_FREED_MEMORY
In-reply-to: <2b2c4bc2-160c-8626-1374-c0da6a638339@2ndQuadrant.com>
References: <7b52f900-0579-cda9-ae2e-de5da17090e6@2ndQuadrant.com>
 <2b2c4bc2-160c-8626-1374-c0da6a638339@2ndQuadrant.com>
Comments: In-reply-to Andrew Dunstan <andrew.dunstan@2ndquadrant.com>
	message dated "Sat, 04 Mar 2017 09:20:23 -0500"
Date: Sat, 04 Mar 2017 15:41:53 -0500
Message-ID: <22846.1488660113@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-hackers-owner@postgresql.org

Andrew Dunstan <andrew.dunstan@2ndquadrant.com> writes:
> On 03/03/2017 02:24 PM, Andrew Dunstan wrote:
>> I have been setting up a buildfarm member with -DRELCACHE_FORCE_RELEASE
>> -DCLOBBER_FREED_MEMORY, settings which Alvaro suggested to me.I got core
>> dumps with these stack traces. The platform is Amazon Linux.

> I have replicated this on a couple of other platforms (Fedora, FreeBSD)
> and back to 9.5. The same failure doesn't happen with buildfarm runs on
> earlier branches, although possibly they don't have the same set of tests.

well, the problem in rebuild_relation() seems pretty blatant:

    /* Close relcache entry, but keep lock until transaction commit */
    heap_close(OldHeap, NoLock);

    /* Create the transient table that will receive the re-ordered data */
    OIDNewHeap = make_new_heap(tableOid, tableSpace,
                               OldHeap->rd_rel->relpersistence,
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                               AccessExclusiveLock);

There are two such references after the heap_close.  I don't know that
those are the only bugs, but this reference is certainly the proximate
cause of the crash I'm seeing.

Will push a fix in a little bit.

			regards, tom lane


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