Horton

Re: Postmaster self-deadlock due to PLT linkage resolution

Noah Misch <noah@leadboat.com>

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From: Noah Misch <noah@leadboat.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@lists.postgresql.org
Date: 2022-08-30T02:42:01Z
Lists: pgsql-hackers 
On Mon, Aug 29, 2022 at 03:43:55PM -0400, Tom Lane wrote:
> I'd originally intended to make this code "#ifdef __NetBSD__",
> but on looking into the FreeBSD sources I find much the same locking
> logic in their dynamic loader, and now I'm wondering if such behavior
> isn't pretty standard.

I doubt it's standard.  POSIX specifies select() to be async-signal-safe.
This NetBSD bug makes select() not be async-signal-safe.

> The added calls should have negligible cost,
> so it doesn't seem unreasonable to do them everywhere.

Agreed.  I would make the comment mention the NetBSD version that prompted
this, so we have a better chance of removing the workaround in a few decades.

Commits

  1. Use WaitEventSet API for postmaster's event loop.

  2. On NetBSD, force dynamic symbol resolution at postmaster start.