[$] Deferred scheduling for user-space critical sections

User-space developers working with highly threaded applications would oftenlike to be able to use spinlocks to protect shared data structures fromconcurrent access. There is a fundamental problem with user-spacespinlocks, though: there is no way to prevent a thread from beingpreempted. Various ways of working around this problem have been explored,but thispatch from Steven Rostedt questions the premise on which much of thatwork is based: what if it were possible to prevent preemption, for ashort period at least?