I found several SMP and UP locking errors in usb-storage, attached is a
patch:

Changes:
* srb->result is a bitfield, several << 1 were missing.
* add scsi_lock calls around midlayer calls, release the lock before
  calling usb functions that might sleep.
* replace the queue semaphore with a queue spinlocks, queuecommand is
  called from bh context.