So I decide to give LFS another whirl.

I put all of /usr/src, /usr/pkgsrc and /usr/xsrc in a LFS, along with
the obj directories for 3 platforms.  I then started a `make -j4' on
the file server (a PC).

At some point, everything hung.  One of the cpp(1) processes was hung
with `lfsino??' (DDB ought to show the rest) and everything appeared
to be backed up from there.

Upon rebooting the machine, it consistently loses with:

panic: lockmgr: draining against myself

The backtrace is:

syscall() -> lfs_bmapv() -> lfs_vget() -> lfs_vcreate() -> getnewvnode() ->
vgonel() -> vclean() -> ufs_lock() -> lockmgr() -> panic()

Also, fsck_lfs(8) reports:

! INO 66722: daddr 0x35e28f is in clean segment 1724
! INO 66722: daddr 0x35e28f is in clean segment 1724

For the moment, I'm going to turn this back into a FFS.