I had the same problem on my T420s with graphics set to discrete in the BIOS. Comment 40 in bug 776999 solved it for me: disable the VT-d extensions in the BIOS.
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/868208 Title: Changing screen back-light freezes thinkpad t420 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+bug/868208/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
