Fixed issue where long delay in VM could lose global tasks.

1 files changed, 11 insertions, 3 deletions

diff --git a/litmus/sched_mc.c b/litmus/sched_mc.c
index 9edf038ef164..3d311505f437 100644
--- a/litmus/sched_mc.c
+++ b/litmus/sched_mc.c
@@ -41,6 +41,7 @@
 struct cpu_entry {
         int                     cpu;
         struct task_struct*     scheduled;
+        struct task_struct*     will_schedule;
         struct task_struct*     linked;
         raw_spinlock_t          lock;
         struct crit_entry       crit_entries[NUM_CRIT_LEVELS];
@@ -892,12 +893,18 @@ static struct task_struct* mc_schedule(struct task_struct* prev)
         QT_START;
 
         local_irq_save(flags);
-        raw_spin_lock(&entry->lock);
 
-        if (entry->scheduled && entry->scheduled != prev) {
-                TRACE_TASK(entry->scheduled, " and prev is %d\n", prev->pid);
+        /* Litmus gave up because it couldn't access the stack of the CPU
+         * on which will_schedule was migrating from. Requeue it.
+         * This really only happens in VMs.
+         */
+        if (entry->will_schedule && entry->will_schedule != prev) {
+                entry->will_schedule->rt_param.scheduled_on = NO_CPU;
+                low_prio_arrival(entry->will_schedule);
         }
 
+        raw_spin_lock(&entry->lock);
+
         /* Sanity checking */
         BUG_ON(entry->scheduled && entry->scheduled != prev);
         BUG_ON(entry->scheduled && !is_realtime(prev));
@@ -988,6 +995,7 @@ static struct task_struct* mc_schedule(struct task_struct* prev)
         next = entry->linked;
         if (entry->linked)
                 entry->linked->rt_param.scheduled_on = entry->cpu;
+        entry->will_schedule = entry->linked;
         sched_state_task_picked();
 
         raw_spin_unlock(&entry->lock);