This issue comes from broken BIOS SMI (like generated when you kick specifica keys etc) hang because it does not aware of OS in x2apic mode. So the workround way is to blacklist issued platform.
Yes. there are other T420 platforms have the issue (https://launchpadlibrarian.net/109393850/dmidecode.txt), so I tend to disable x2apic at all of T420 platforms. Refer to bug reports: https://bugzilla.kernel.org/show_bug.cgi?id=43054 https://bugs.launchpad.net/ubuntu/+source/linux/+bug/776999 Please try the patches if it works on your T420. ** Bug watch added: Linux Kernel Bug Tracker #43054 http://bugzilla.kernel.org/show_bug.cgi?id=43054 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/922037 Title: "reduce brightness" key freezes system To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/922037/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
