Hanging at shutdown with mystery "file system full" error

["Ian D. Leroux" <idleroux%fastmail.fm@localhost>]

With sources from Oct. 17th I get a repeatable hang whenever I shutdown
my laptop (NetBSD/amd64 current).  If X is running at shutdown time,
then I can't switch back to the console (Ctrl-Alt-F1 has no effect) and
my only recourse is to kill the power.  If X is not running I can
switch to the console and see that the last messages to the console are
kernel (green) warnings of the form

uid 0, pid 1, command init, on /var: file system full

Besides init, I also see such warnings for login, halt, and/or reboot.
The exact set of processes that generate the warning changes from hang
to hang, and init sometimes generates several copies of the warning.

However, when the system is running, df shows /var only 72% full, with
32M available.  So either something is writing 30M to /var at shutdown
time (and that write is not surviving the reboot and subsequent fsck)
or something is trying to write to /var after it gets unmounted (the
root partition is mounted read-only and is, in fact, nearly full, so an
attempt to write after /var is unmounted might plausibly cause such an
error).  On the other hand, If I kill the power I do see some data
corruption on partitions that were mounted read-write, including /var
(strings of \0s, notably in /var/log/messages), which would seem to
indicate that the hang happens before /var can be cleanly unmounted.

While the system is hanging I can enter DDB, though I'm not sure
what to look for or write down once I do.  I've noted the line:

"stopped in pid 1053.1 (estd) at netbsd:breakpoint+0x5"

I've tried shutting down after stopping the estd daemon by hand, in
which case DDB shows the kernel stopped in the syslogd process, so it's
not being triggered by estd.

Does this sound familiar to anyone?  Any hints on how I might extract
more useful information?

--
IDL