Investigating the error by building the packages of scanbd and libsane
from source and adding some debugging output turned out that it is not
an issue of scanbd. Thus, this bug can be closed.
This kernel Oops is triggered by the canon_pp backend of libsane.
Disabling it in /etc/scanbd/dll.conf resolves the issue and scanbd works
This Oops can be triggered directly by calling 'sane-find-scanner -p'
which explicitly probes for parallel port scanners. Because the
raspberrypi platform does not have a parallel port, it leads to the
kernel Oops, I assume.
More specifically, the functions from ieee1284.h such as
ieee1284_read_status() trigger this Oops. Therefore, it is also not an
issue of libsane.
At this point, my research stopped and I can't tell if it is a bug of
package libieee1284 or the kernel itself. Presumably, ieee1284 function
should be no-op if there is no parallel port(?).
I hope this helps anyone running into this too.