Fix balancing issue, GEDF plugin

 - Fixed a bug where some new balancing code wasn't commented out when
   it needed to be. (It wasn't in the version of Linux that the previous
   version of LITMUS was based on, so I missed it earlier.)

 - The GSN-EDF plugin can now be activated, and runs tasks without
   crashing (though I haven't verified that it schedules stuff in the
   correct order yet).

 - *All remaining plugins probably need to be modified in the same was
   as the GSN-EDF plugin*. Specifically, the "prev" argument to the
   "<plugin>_schedule(...)" function may be NULL, and the plugin must be
   able to handle such a case!

2 files changed, 25 insertions, 22 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 34525bf04f0f..9ab7655edd2d 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3993,20 +3993,20 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
 restart:
         */
 
-#ifdef CONFIG_SMP
-        /*
-         * We must do the balancing pass before put_next_task(), such
-         * that when we release the rq->lock the task is in the same
-         * state as before we took rq->lock.
-         *
-         * We can terminate the balance pass as soon as we know there is
-         * a runnable task of @class priority or higher.
-         */
-        for_class_range(class, prev->sched_class, &idle_sched_class) {
-                if (class->balance(rq, prev, rf))
-                        break;
-        }
-#endif
+//#ifdef CONFIG_SMP
+//      /*
+//       * We must do the balancing pass before put_next_task(), such
+//       * that when we release the rq->lock the task is in the same
+//       * state as before we took rq->lock.
+//       *
+//       * We can terminate the balance pass as soon as we know there is
+//       * a runnable task of @class priority or higher.
+//       */
+//      for_class_range(class, prev->sched_class, &idle_sched_class) {
+//              if (class->balance(rq, prev, rf))
+//                      break;
+//      }
+//#endif
 
         put_prev_task(rq, prev);
 
diff --git a/kernel/sched/litmus.c b/kernel/sched/litmus.c
index 468aa0197d1d..38f638f7eb4f 100644
--- a/kernel/sched/litmus.c
+++ b/kernel/sched/litmus.c
@@ -50,9 +50,14 @@ litmus_schedule(struct rq *rq, struct task_struct *prev)
 
         sched_state_plugin_check();
 
+        if (!next) {
+                update_enforcement_timer(next);
+                return next;
+        }
+
 #ifdef CONFIG_SMP
         /* check if a global plugin pulled a task from a different RQ */
-        if (next && task_rq(next) != rq) {
+        if (task_rq(next) != rq) {
                 /* we need to migrate the task */
                 other_rq = task_rq(next);
                 from_where = other_rq->cpu;
@@ -168,7 +173,7 @@ litmus_schedule(struct rq *rq, struct task_struct *prev)
 #endif
 
         /* check if the task became invalid while we dropped the lock */
-        if (next && (!is_realtime(next) || !tsk_rt(next)->present)) {
+        if (!is_realtime(next) || !tsk_rt(next)->present) {
                 TRACE_TASK(next,
                         "BAD: next (no longer?) valid\n");
                 litmus->next_became_invalid(next);
@@ -176,15 +181,13 @@ litmus_schedule(struct rq *rq, struct task_struct *prev)
                 next = NULL;
         }
 
-        if (next) {
 #ifdef CONFIG_SMP
-                next->rt_param.stack_in_use = rq->cpu;
+        next->rt_param.stack_in_use = rq->cpu;
 #else
-                next->rt_param.stack_in_use = 0;
+        next->rt_param.stack_in_use = 0;
 #endif
-                update_rq_clock(rq);
-                next->se.exec_start = rq->clock;
-        }
+        update_rq_clock(rq);
+        next->se.exec_start = rq->clock;
 
 out:
         update_enforcement_timer(next);