Gotten this a few times (not sure if apache triggered it both times tho):

panic: ubc_fault: concurrent writes vp 0x46f8d44
Stopped in pid 261 (httpd) at	_cpu_Debugger+0x6:	unlk	a6
db>trace
_cpu_Debugger
_panic
_ubc_alloc
_nfs_write
_VOP_write

_vn_write
_dofilewrite
_sys_write
_syscall(4)
_trap0

Notes:

Q650 24/80
No local UFS partitions
NFS mounted everything (/usr/home/NetBSD/root->/,/usr/ports,/usr/home/alex/cvs/kde-cvs->/mnt/kde-cvs)
Three NFS backed swapfiles (/swap,/swap2,/swap3)
Internal ethernet being used

I think the kernel says 1.5R, but I'm sure I downloaded the most recent
-CURRENT snapshot.  Either way compiling a custom kernel is on my TODO
list (when I wake up, and turn the box back on again).

- alex