sched: Fix cross-sched-class wakeup preemption

Instead of dealing with sched classes inside each check_preempt_curr()
implementation, pull out this logic into the generic wakeup preemption
path.

Manually applied the partial patch set from
http://www.spinics.net/lists/kvm-commits/msg00039.html and
cross-refernce'd the k39 kernel

Bug 886798

Change-Id: Ib5bb12eec6c276ded9231e9ed2238499d42e31da
Reviewed-on: http://git-master/r/59405
Reviewed-by: Ryan Wong <ryanw@nvidia.com>
Tested-by: Ryan Wong <ryanw@nvidia.com>

2 files changed, 27 insertions, 18 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index a2e90f022cdb..ab209ca2fb90 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -558,18 +558,7 @@ struct rq {
 
 static DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
 
-static inline
-void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
-{
-	rq->curr->sched_class->check_preempt_curr(rq, p, flags);
-
-	/*
-	 * A queue event has occurred, and we're going to schedule.  In
-	 * this case, we can save a useless back to back clock update.
-	 */
-	if (rq->curr->se.on_rq && test_tsk_need_resched(rq->curr))
-		rq->skip_clock_update = 1;
-}
+static void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags);
 
 static inline int cpu_of(struct rq *rq)
 {
@@ -1985,6 +1974,32 @@ static inline void check_class_changed(struct rq *rq, struct task_struct *p,
 		p->sched_class->prio_changed(rq, p, oldprio, running);
 }
 
+static void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
+{
+	const struct sched_class *class;
+
+	if (p->sched_class == rq->curr->sched_class) {
+		rq->curr->sched_class->check_preempt_curr(rq, p, flags);
+	} else {
+		for_each_class(class) {
+			if (class == rq->curr->sched_class)
+				break;
+			if (class == p->sched_class) {
+				resched_task(rq->curr);
+				break;
+			}
+		}
+	}
+
+        /*
+         * A queue event has occurred, and we're going to schedule.  In
+         * this case, we can save a useless back to back clock update.
+         */
+	if (rq->curr->se.on_rq && test_tsk_need_resched(rq->curr))
+		rq->skip_clock_update = 1;
+}
+
+
 #ifdef CONFIG_SMP
 /*
  * Is this task likely cache-hot:
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 1bb879013173..b8ae4e51b46d 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1658,12 +1658,6 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
 	struct cfs_rq *cfs_rq = task_cfs_rq(curr);
 	int scale = cfs_rq->nr_running >= sched_nr_latency;
 
-	if (unlikely(rt_prio(p->prio)))
-		goto preempt;
-
-	if (unlikely(p->sched_class != &fair_sched_class))
-		return;
-
 	if (unlikely(se == pse))
 		return;