I've just recently started seeing this - I was using pax to copy some files,
specifically /usr/X11R6 (in preparation for an update to X 4.4.0) from one
softdep-enabled partition to another, and the machine froze completely (I
was in X; I assume the pagedaemon messages were scrolling on console, but
I had no way of telling.)

Just a few minutes ago, I had it happen while I was in console using pax to
install a newly-built userland - it started spamming "pagedaemon: deadlock
detected!" every few files, then a few times for every file, then over and
over, until the machine was dead. well, not totally dead - the pagedaemon
messages were coming out just fine.

I did a hard reset and booted the machine single-user, and enough had been
pax'd over before the lockup for me to edit fstab so that softdep was no
longer enabled on any of my partitions - this time, the pax install of
userland went just fine. In case it makes any difference, the syntax I was
using was (in the DESTDIR):
pax -rwvpe rescue libexec lib bin sbin usr var/db/obsolete /

Any ideas? I've disabled softdep for now, but I was under the impression
that softdep was "safe" -- I haven't had a softdep-related problem before
this in years.

If any additional information would help, let me know and I'll be happy to
provide it.

Thanks,
-Sean

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