RFC: hung_task: taint kernel

There's the hung_task_panic sysctl, but that's a bit an extreme measure.
As a fallback taint at least the machine.

Our CI uses this to decide when a reboot is necessary, plus to figure
out whether the kernel is still happy.

v2: Works much better when I put the else { add_taint() } at the right
place.

References: https://gitlab.freedesktop.org/drm/intel/-/issues/8034


Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: "Liu, Chuansheng" <chuansheng.liu@intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk> (for core-for-CI)
Link: https://patchwork.freedesktop.org/patch/msgid/20190502204648.5537-1-daniel.vetter@ffwll.ch


Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>