Hook into rt scheduling class to protect LITMUS^RT tasks

The rt scheduling class thinks it's the highest-priority scheduling
class around, next to SCHED_DEADLINE. It is not in LITMUS^RT. Don't go
preempting remote cores that run SCHED_LITMUS tasks.

1 files changed, 6 insertions, 3 deletions

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 575da76a3874..613574c71a68 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -8,6 +8,8 @@
 #include <linux/slab.h>
 #include <linux/irq_work.h>
 
+#include <litmus/litmus.h>
+
 int sched_rr_timeslice = RR_TIMESLICE;
 
 static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun);
@@ -487,8 +489,9 @@ static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
                         enqueue_top_rt_rq(rt_rq);
                 else if (!on_rt_rq(rt_se))
                         enqueue_rt_entity(rt_se, false);
-
-                if (rt_rq->highest_prio.curr < curr->prio)
+                if (rt_rq->highest_prio.curr < curr->prio
+                    /* Don't subject LITMUS^RT tasks to remote reschedules. */
+                    && !is_realtime(curr))
                         resched_curr(rq);
         }
 }
@@ -575,7 +578,7 @@ static inline void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
 {
         struct rq *rq = rq_of_rt_rq(rt_rq);
 
-        if (!rt_rq->rt_nr_running)
+        if (!rt_rq->rt_nr_running || is_realtime(rq_of_rt_rq(rt_rq)->curr))
                 return;
 
         enqueue_top_rt_rq(rt_rq);