Hook into rt scheduling class to protect LITMUS^RT tasks

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

1 files changed, 7 insertions, 2 deletions

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 15334e6de832..dbe21ae888f8 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -7,6 +7,8 @@
 
 #include <linux/slab.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);
@@ -436,7 +438,9 @@ static void sched_rt_rq_enqueue(struct rt_rq *rt_rq)
         if (rt_rq->rt_nr_running) {
                 if (rt_se && !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_task(curr);
         }
 }
@@ -530,7 +534,8 @@ static inline struct rt_rq *group_rt_rq(struct sched_rt_entity *rt_se)
 
 static inline void sched_rt_rq_enqueue(struct 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))
                 resched_task(rq_of_rt_rq(rt_rq)->curr);
 }