Add P-FP scheduler plugin

1 files changed, 12 insertions, 5 deletions

diff --git a/litmus/fp_common.c b/litmus/fp_common.c
index 964a4729deff..ff0f30a9f536 100644
--- a/litmus/fp_common.c
+++ b/litmus/fp_common.c
@@ -32,7 +32,6 @@ int fp_higher_prio(struct task_struct* first,
                 return 0;
         }
 
-
         /* check for NULL tasks */
         if (!first || !second)
                 return first && !second;
@@ -50,6 +49,15 @@ int fp_higher_prio(struct task_struct* first,
         if (unlikely(second->rt_param.inh_task))
                 second_task = second->rt_param.inh_task;
 
+        /* Comparisons to itself are only possible with
+         * priority inheritance when svc_preempt interrupt just
+         * before scheduling (and everything that could follow in the
+         * ready queue). Always favour the original job, as that one will just
+         * suspend itself to resolve this.
+         */
+        if(first_task == second_task)
+                return first_task == first;
+
         /* Check for priority boosting. Tie-break by start of boosting.
          */
         if (unlikely(is_priority_boosted(first_task))) {
@@ -65,11 +73,10 @@ int fp_higher_prio(struct task_struct* first,
                 /* second_task is boosted, first is not*/
                 return 0;
 
-#endif
-
-        /* Comparisons to itself are not expected; priority inheritance
-         * should also not cause this to happen. */
+#else
+        /* No locks, no priority inheritance, no comparisons to itself */
         BUG_ON(first_task == second_task);
+#endif
 
         if (get_priority(first_task) < get_priority(second_task))
                 return 1;