> 
> Ok, the obvious question is how can you tell it's concurrent access?

That's easy.. just disable the Big Lock entirely.

Ok, so I had to hack other locking stuff besides just the buf queues; I'll
get back on those later.  Doing all this allows the machine to come up
multi-user and stay up long enough to do some skimpy concurrent file
system access testing.

Note that the kernel lock currently cannot be partially disabled to test
some subsystem or other, since that creates a locking order problem against
about every other spinlock.

-pk