Horton

Re: pgsql: Avoid improbable PANIC during heap_update.

Peter Geoghegan <pg@bowt.ie>

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From: Peter Geoghegan <pg@bowt.ie>
To: Jeff Davis <pgsql@j-davis.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Jaime Casanova <jcasanov@systemguards.com.ec>, pgsql-committers@lists.postgresql.org
Date: 2022-10-01T16:53:59Z
Lists: pgsql-hackers 
On Sat, Oct 1, 2022 at 9:35 AM Jeff Davis <pgsql@j-davis.com> wrote:
> Doesn't that deal with the case you brought up directly? heap_delete()
> can't get the exclusive lock until VACUUM releases its cleanup lock, at
> which point all-visible will be set. Then heap_delete() should notice
> in line 2509 and then pin the VM buffer. Right?

I now believe that you're right. I don't think that this code was ever
designed to rely on cleanup locks in any way; that was kind of an
accident all along. Even still, I'm not sure how I missed such an
obvious thing. Sorry for the misdirection.

Still, there has to be *some* reason why the bug could repro on 13.

--
Peter Geoghegan

Commits

  1. Avoid improbable PANIC during heap_update, redux.

  2. Fix race condition where heap_delete() fails to pin VM page.

  3. Avoid improbable PANIC during heap_update.