P-FP: fix BUG_ON releated to priority inheritancearchive/unc-master-3.0

In some cases, the PCP priority inheritance code triggered a
(defensive) BUG_ON() in fp_common.c. This shuffles the order of
operations a bit to be compliant with the restriction that tasks are
never compared against themselves.

1 files changed, 7 insertions, 5 deletions

diff --git a/litmus/sched_pfp.c b/litmus/sched_pfp.c
index 91e52391a173..0e875a3b5cba 100644
--- a/litmus/sched_pfp.c
+++ b/litmus/sched_pfp.c
@@ -182,7 +182,7 @@ static struct task_struct* pfp_schedule(struct task_struct * prev)
         np          = exists && is_np(pfp->scheduled);
         sleep       = exists && is_completed(pfp->scheduled);
         migrate     = exists && get_partition(pfp->scheduled) != pfp->cpu;
-        preempt     = migrate || fp_preemption_needed(&pfp->ready_queue, prev);
+        preempt     = !blocks && (migrate || fp_preemption_needed(&pfp->ready_queue, prev));
 
         /* If we need to preempt do so.
          * The following checks set resched to 1 in case of special
@@ -1089,8 +1089,10 @@ static void pcp_priority_inheritance(void)
                 fp_set_prio_inh(pfp, blocker, blocked);
         }
 
-        /* check if anything changed */
-        if (fp_higher_prio(fp_prio_peek(&pfp->ready_queue), pfp->scheduled))
+        /* Check if anything changed. If the blocked job is current, then it is
+         * just blocking and hence is going to call the scheduler anyway. */
+        if (blocked != current &&
+            fp_higher_prio(fp_prio_peek(&pfp->ready_queue), pfp->scheduled))
                 preempt(pfp);
 
         raw_spin_unlock_irqrestore(&pfp->slock, flags);
@@ -1201,10 +1203,10 @@ static void pcp_lower_ceiling(struct pcp_semaphore* sem)
 
         TRACE_CUR("PCP released sem %p\n", sem);
 
+        pcp_priority_inheritance();
+
         /* Wake up all ceiling-blocked jobs that now pass the ceiling. */
         pcp_resume_unblocked();
-
-        pcp_priority_inheritance();
 }
 
 static void pcp_update_prio_ceiling(struct pcp_semaphore* sem,