On Sun, Aug 03, 2014 at 10:36:16PM -0400, Waiman Long wrote:

For a fully preemptive kernel, a call to preempt_enable() could
potentially trigger a task rescheduling event. In the case of rwsem
optimistic spinning, the task has either gotten the lock or is going
to sleep soon. So there is no point to do rescheduling here.

Uh what? Why shouldn't we preempt if we've gotten the lock? What if a
FIFO task just woke up?