Comment 56 for bug 252977

digging around i've found this:

- it could be hw related.
http://lkml.indiana.edu/hypermail/linux/kernel/0812.3/01426.html
http://www.flickr.com/photos/kernelslacker/251807263/in/set-72157594298237090/

- it could be triggered by a proprietary module (including vbox)
http://bugs.gentoo.org/138366
http://lkml.indiana.edu/hypermail/linux/kernel/0607.0/0136.html

- it seems to be present since 2.6.18
http://lkml.org/lkml/2006/12/12/177

- a patch to get more debugging output is available but it never went upstream (as far as i could check)
http://lkml.org/lkml/2006/12/19/30

Probably testing with Mainline kernel we can rule out the modules

https://wiki.ubuntu.com/KernelMainlineBuilds

(i've marked some dupes including mdz's one, the mm/rmap.c:xxx line is the only one missing)