Cyrus 2.2.5, problems spawning lmtpd

[Simon Fraser]

Recently a mailserver here got into a bit of trouble.  It's a debian
machine running a 2.4.25 kernel, cyrus 2.2.5 (not the debian package),
with exim 4.34 as the MTA. The symptoms seemed to echo the process
accounting bug from 2.1, as at various intervals there'd be no lmtpd
processes available for deliveries, and the master process would not
spawn any more. Looking at what some debugging information, it seems
that the master process became convinced that there were more
ready_workers than there were nactive processes, and so when the last
of the lmtpd died naturally, it saw no need to spawn any more.  I've a
kludge in place at the moment that will spawn a new service based on
both ready_workers and nactive, instead of just ready_workers, but I'd
like a more stable solution.

It may be related when deliveries were happening, and lmtpd was
running, both deliver and lmtpd were operating slowly, as they were
both blocking on the unix domain socket used to communicate.  Even
with more idle lmtpd processes than deliver processes, deliver was
still blocking trying to access the socket.  This was only fixed by
rebooting the machine.

I'm unsure exactly what's going on, as this is a production mail
system, and I'm unable to do much tinkering with it.  Any advice on
what's happened and what can be done to stop it happening again is
appreciated.

Thanks,
Simon.
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