Fix more locking, do a major rethink on the bh handling (now workqueue)

This is stuff like next: pointers that are not present rather than
anything bigger

The problem was that when the refcount hit 0, it was unconditionally
assuming that it had been added, which is wrong.  The patch below
corrects that, and fixes the Oops when loading the floppy driver.

into home.transmeta.com:/home/torvalds/v2.5/linux