Using 3.0 netbsd sparc on sparcstation 20 w/ dual hypersparc 150s and 
512M RAM
...
GENERIC seemed to run fine (though simply locked up in the middle of a huge
compile sequence once) but GENERIC.MP always panics during startup.

I built a custom MP kernel based on a config that worked fine for me in 2.1
and that had the same problem.  I know other's on this list reported MP
running fine so I looked more closely at the last couple lines 
before/during panic:

isp0 at sbus 0 slot 2 offsaet 0x10000 level 3 (ipl 5) for QLGC, isp
data fault: pc=0xf01cf620 addr=0x1c sfsr=126 <PERR=0,LVL=1,AT=1,FT=1,FAV,0W>
panic: kernel fault

I figured my QLOGIC controller's module must be breaking the kernel in 
MP mode. 

So recompiled the kernel with that module commented out of
the config file, pulled the associated fstab entry, and, ....
I now have a custom MP netbsd kernel running fine on my box
though at the expense of slower disk speed.

IF ... someone wants me to try out a patch on the isp/qlogic
module and see if that fixes something I'll do that.  Or give me a clue
how to back that message up to the original code (?)

Heitzso