Jonathan Woithe [off-list ref] :
[...]

While we can rely on the retry system to paper over this regression, the
behaviour of earlier kernels suggests that there is a real issue at play. 
Is there any chance that this can be looked at ?

Yes.

You'll have to be a bit patient since I still have to spend a pair of non
worked hours on a compromised system. :o/

Take it for what it's worth but I don't test much with PREEMPT, NOHZ or
SLUB and I never tried all those at the same time.

-- 
Ueimor