- Fix scheduler frequency invariance bug related to overly long tickless periods
  triggering an integer overflow and disabling the feature.

- Fix use-after-free bug in dup_user_cpus_ptr().

- Fix do_set_cpus_allowed() deadlock scenarios related to calling kfree() with
  the pi_lock held. NOTE: the rcu_free() is the 'lazy' solution here - we looked
  at patches to free the structure after the pi_lock got dropped, but that looked
  quite a bit messier - and none of this is truly performance critical. We can
  revisit this if it's too lazy of a solution ...

Signed-off-by: Ingo Molnar <mingo@kernel.org>