"Indefinite wait buffer"

[Tim Kientzle]

On BeagleBone (r246278) I'm seeing the following after letting
buildworld run for a while:

swap_pager: indefinite wait buffer: bufobj: 0, blkno: 5120, size: 49152
swap_pager: indefinite wait buffer: bufobj: 0, blkno: 5120, size: 49152
swap_pager: indefinite wait buffer: bufobj: 0, blkno: 5120, size: 49152
swap_pager: indefinite wait buffer: bufobj: 0, blkno: 6722, size: 8192
swap_pager: indefinite wait buffer: bufobj: 0, blkno: 6724, size: 8192
swap_pager: indefinite wait buffer: bufobj: 0, blkno: 6781, size: 8192
swap_pager: indefinite wait buffer: bufobj: 0, blkno: 6781, size: 8192
swap_pager: indefinite wait buffer: bufobj: 0, blkno: 6781, size: 8192

At first I thought this was related to NFS but I've since seen
it running just purely with local MMCSD.

I've not debugged swap-related issues before; any suggestions
on how to track this down?

(Obviously, my first step will be to go back to a WITNESS+INVARIANTS
kernel…)

Tim