Bill Studenmund <wrstuden@netbsd.org> writes:

> Two file descriptors referencing the upper node, which in turn references
> the lower node. The lower node will have one reference, so the hardware
> close routine will get called when either one of the upper references'
> close routine is called. And then it will get called again when the other
> file descriptor is closed.

The lower vnode has one reference but upper (layer fs) vnode has two
references.  Closing one of those file descriptor just decrease
the reference count of upper vnode.

enami.