This is an update of AIO fallback patch and with the bio_count race
fixed by changing bio_list_lock into bio_lock and using that for all
the bio fields.  I changed bio_count and bios_in_flight from atomics
into int.  They are now proctected by the bio_lock.  I fixed the race,
by in finished_one_bio() by leaving the bio_count at 1 until after the
dio_complete() and then do the bio_count decrement and wakeup holding
the bio_lock.

I re-diffed to 2.6.1-rc1-mm1.

I've been stressing this code for several weeks.

Daniel