I got this running a 19990527 kernel with a 19990423 userland, during
multiuser boot at the point where filesystems are NFS-mounted I assume.

panic: getblk: block size invariant failed
Stopped in mount at _Debugger+0x6: unlk a6
db> trace
_Debugger(2004,0,0,e772a7c,f1d9d20) + 6
_panic(e02fb1d,2000,0,f1b8500,0) + 54
_getblk(f1ae924,0,2000,0,0) + c0
_nfs_getcacheblk(f1ae924,0,2000,f1b8500) + 84
_nfs_bioread(f1ae924,f1d9ef0,0,e16db80,0) + 62a
_nfs_read(f1d9ea0) + 24
_vn_read(f1d4058,f1d4070,f1d9ef0,e16db80,1) + ba
_dofileread(f1b8500,3,f1d4058,3c000,200) + 8c
_sys_read(f1b8500,f1d9f84,f1d9f7c) + 6e
_syscall(3) + 114
_trap0() + e
db> 

The machine is NFS-rooted.  It runs well with a 19990423 kernel.
Debugging suggestions are welcome--i'm building a kernel with -g symbols
now.  Anyone know how to get crash dumps on an NFS-swaped machine?

-- 
Miles Nordin / 1-888-857-2723
555 Bryant Street PMB 182 / Palo Alto, CA 94301-1700