Comment # 21 on bug 1175908 from Franck Bui

(In reply to Harald Koenig from comment #19)
> native cryptsetup showed the same error.
> 

Ok then it's not specific to systemd-cryptsetup.

> 
> how can I find/provide the missing kernel mod?
> 

You can try to dump the content of 2 initrds, one which fails to boot and the
other one which is ok, and compare the outputs.

You can dump the relevant content of an initrd with the following commnad:

>  $ lsinitrd --kver <kernel-version-ko> | sed -ne 's,.* \(lib/modules/.*.ko\),\1,p'

Please make sure to restore the initrds you modified previously (by adding
cryptsetup and other kern modules).

Thanks.