This is related to this bug:
http://bugme.osdl.org/show_bug.cgi?id=2995

The kernel currently only checks that the memory is file-backed if
MADV_WILLNEED is set.  It's not entirely clear from the manpage at least
that *all* non-file-backed madvise() calls should fail.  

The attached patch returns -EBADF for all non-file-backed madvise()
calls.  I'm not suggesting that this is the absolutely right behavior,
but it certainly does what the bug submitter wants.

Comments?

-- Dave