Hi,

For the past half year I have had problems on our server which seem to
indicate a locking problem in NULLFS. I cannot reliably reproduce it,
but now and then a filesystem (that is remounted with NULLFS
elsewhere) completely locks up. And my only solution has been to
reboot the machine when this happens (and now by getting rid of the
NULLFS mounts). Time between manifestations of this problem range
between a few hours to several weeks. We've ruled out hardware as the
problem source, and have seen the problem on various NetBSD kernel
versions (from -current as of end of last year to NetBSD-1.5_ALPHA and
NetBSD-1.5_ALPHA2).

I thought of writing a PR on it, but basically have no clue what to
write in it. Checked Gnats database and AFAIKS all known nullfs locking
problem reports are in closed state. Therefor I just wanted to state 
my suspicions towards NULLFS here. 

Feico.