Add some code to validate assumptions we're making and output
warnings if they are not.

If this trigger we want to know about it.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Alex Shi <lkml.alex@gmail.com>
Link: http://lkml.kernel.org/n/tip-6uc3wk5s9udxtdl9cnku0vtt@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>