sched: Clarify ordering between task_rq_lock() and move_queued_task()

		raw_spin_lock_irqsave(&p->pi_lock, *flags);

		rq = task_rq(p);

		raw_spin_lock(&rq->lock);

		/*

		 *	move_queued_task()		task_rq_lock()

		 *

		 *	ACQUIRE (rq->lock)

		 *	[S] ->on_rq = MIGRATING		[L] rq = task_rq()

		 *	WMB (__set_task_cpu())		ACQUIRE (rq->lock);

		 *	[S] ->cpu = new_cpu		[L] task_rq()

		 *					[L] ->on_rq

		 *	RELEASE (rq->lock)

		 *

		 * If we observe the old cpu in task_rq_lock, the acquire of

		 * the old rq->lock will fully serialize against the stores.

		 *

		 * If we observe the new cpu in task_rq_lock, the acquire will

		 * pair with the WMB to ensure we must then also see migrating.

		 */

		if (likely(rq == task_rq(p) && !task_on_rq_migrating(p)))

			return rq;

		raw_spin_unlock(&rq->lock);