sched: fix wakeup preemption clock

Impact: sharpen the wakeup-granularity to always be against current scheduler time

It was possible to do the preemption check against an old time stamp.

Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched.c

@@ -2266,6 +2266,7 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync)
 
 	smp_wmb();
 	rq = task_rq_lock(p, &flags);
+	update_rq_clock(rq);
 	old_state = p->state;
 	if (!(old_state & state))
 		goto out;
@@ -2323,7 +2324,6 @@ static int try_to_wake_up(struct task_struct *p, unsigned int state, int sync)
 		schedstat_inc(p, se.nr_wakeups_local);
 	else
 		schedstat_inc(p, se.nr_wakeups_remote);
-	update_rq_clock(rq);
 	activate_task(rq, p, 1);
 	success = 1;
 

kernel/sched_fair.c

@@ -1345,12 +1345,11 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int sync)
 {
 	struct task_struct *curr = rq->curr;
 	struct sched_entity *se = &curr->se, *pse = &p->se;
+	struct cfs_rq *cfs_rq = task_cfs_rq(curr);
 
-	if (unlikely(rt_prio(p->prio))) {
-		struct cfs_rq *cfs_rq = task_cfs_rq(curr);
+	update_curr(cfs_rq);
 
-		update_rq_clock(rq);
-		update_curr(cfs_rq);
+	if (unlikely(rt_prio(p->prio))) {
 		resched_task(curr);
 		return;
 	}