Make LITMUS^RT scheduling class the highest-priority scheduling class

Needs to be above stop_machine_class for legacy reasons; the main
plugins were developed before stop_machine_class was introduced and
assume that they are the highest-priority scheduling class.

2 files changed, 7 insertions, 2 deletions

diff --git a/kernel/sched/litmus.c b/kernel/sched/litmus.c
index 80e6928d9c55..6c587bdff401 100644
--- a/kernel/sched/litmus.c
+++ b/kernel/sched/litmus.c
@@ -359,7 +359,7 @@ const struct sched_class litmus_sched_class = {
          * cpu-hotplug or cpu throttling. Allows Litmus to use up to 1.0
          * CPU capacity.
          */
-        .next                   = &dl_sched_class,
+        .next                   = &stop_sched_class,
         .enqueue_task           = enqueue_task_litmus,
         .dequeue_task           = dequeue_task_litmus,
         .yield_task             = yield_task_litmus,
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index bce8ff9d43f1..585b193b2442 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1295,10 +1295,15 @@ static inline void set_curr_task(struct rq *rq, struct task_struct *curr)
         curr->sched_class->set_curr_task(rq);
 }
 
-#define sched_class_highest (&stop_sched_class)
+/* Yes, this is conceptually wrong; this should be below the stop-machine class,
+ * but existing plugins (that predate the stop-machine class) depend on the
+ * assumption that LITMUS^RT plugins are the top scheduling class (FIXME).
+ */
+#define sched_class_highest (&litmus_sched_class)
 #define for_each_class(class) \
    for (class = sched_class_highest; class; class = class->next)
 
+extern const struct sched_class litmus_sched_class;
 extern const struct sched_class stop_sched_class;
 extern const struct sched_class dl_sched_class;
 extern const struct sched_class rt_sched_class;