Fixed race condition in preemption code.

1 files changed, 10 insertions, 5 deletions

diff --git a/litmus/sched_mc.c b/litmus/sched_mc.c
index f24c89341629..55d604fa07cc 100644
--- a/litmus/sched_mc.c
+++ b/litmus/sched_mc.c
@@ -1287,7 +1287,16 @@ static void process_signals(struct cpu_entry *entry)
                 if (ce->server.state == SS_ACTIVE &&
                     mc_preempt_needed(ce->domain, ce->server.linked)) {
                         preempted = preempt_crit(ce->domain, ce);
-                        raw_spin_unlock(&entry->lock);
+
+                        /* Can't requeue while we hold the entry lock, but
+                         * can't release that lock until state of lower-crit
+                         * servers is updated
+                         */
+                        if (!is_ghost(ce->server.linked)) {
+                                update_crit_levels(entry);
+                        } else {
+                                raw_spin_unlock(&entry->lock);
+                        }
 
                         if (preempted) {
                                 dom->requeue(dom, preempted);
@@ -1295,10 +1304,6 @@ static void process_signals(struct cpu_entry *entry)
 
                         raw_spin_unlock(dom->lock);
                         raw_spin_lock(&entry->lock);
-                        if (!is_ghost(ce->server.linked)) {
-                                update_crit_levels(entry);
-                                raw_spin_lock(&entry->lock);
-                        }
                 } else {
                         raw_spin_unlock(dom->lock);
                 }