- wait_task_inactive() preemption-latency optimization: we should

  enable/disable preemption to not spend too much time with
  preemption disabled. wait_task_inactive() can take quite some
  time occasionally ...

kernel/sched.c

@@ -303,9 +303,15 @@ void wait_task_inactive(task_t * p)
 repeat:
 	preempt_disable();
 	rq = task_rq(p);
-	while (unlikely(rq->curr == p)) {
+	if (unlikely(rq->curr == p)) {
 		cpu_relax();
-		barrier();
+		/*
+		 * enable/disable preemption just to make this
+		 * a preemption point - we are busy-waiting
+		 * anyway.
+		 */
+		preempt_enable();
+		goto repeat;
 	}
 	rq = task_rq_lock(p, &flags);
 	if (unlikely(rq->curr == p)) {