Re: Race conditions with WAL sender PID lookups

On Thu, May 11, 2017 at 1:48 PM, Michael Paquier
<michael(dot)paquier(at)gmail(dot)com> wrote:
> I had my eyes on the WAL sender code this morning, and I have noticed
> that walsender.c is not completely consistent with the PID lookups it
> does in walsender.c. In two code paths, the PID value is checked
> without holding the WAL sender spin lock (WalSndRqstFileReload and
> pg_stat_get_wal_senders), which looks like a very bad idea contrary to
> what the new WalSndWaitStopping() does and what InitWalSenderSlot() is
> doing for ages.

There is also code that accesses shared walsender state without
spinlocks over in syncrep.c. I think that file could use a few words
of explanation for why it's OK to access pid, state and flush without
synchronisation.

--
Thomas Munro
http://www.enterprisedb.com