zs3: silo overflow crashes

[smb at arpa.att.com]

Your machine isn't crashing because of a silo overflow, it's getting some
sort of bus error or other internal trap.  While it's printing the panic
and traceback stuff, the input silo -- from the mouse? dunno -- has filled
up and overflowed because interrupts are disabled.  When it finally has
the leisure to look at the i/o ports, while trying to sync the disks, it
notices the async i/o error and reports it.  That's pure cascade, and the
message itself is not relevant.

I don't know, though, why it's talking about zs3.