From bc92369ba24f72b916384ed80d4381549c6537a7 Mon Sep 17 00:00:00 2001
From: Jonathan Herman <hermanjl@cs.unc.edu>
Date: Sun, 9 Oct 2011 18:42:07 -0400
Subject: Fixed bug where finish switch could strand level-C tasks in neverland

---
 litmus/rt_domain.c |  4 +++-
 litmus/sched_mc.c  | 17 ++++++++++++-----
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/litmus/rt_domain.c b/litmus/rt_domain.c
index 93f2a35fb29d..f242f33e990e 100644
--- a/litmus/rt_domain.c
+++ b/litmus/rt_domain.c
@@ -20,7 +20,7 @@
 #include <litmus/bheap.h>
 
 /* Uncomment when debugging timer races... */
-#if 1
+#if 0
 #define VTRACE_TASK TRACE_TASK
 #define VTRACE TRACE
 #else
@@ -404,7 +404,9 @@ void __add_release(rt_domain_t* rt, struct task_struct *task)
 static void pd_requeue(domain_t *dom, struct task_struct *task)
 {
 	rt_domain_t *domain = (rt_domain_t*)dom->data;
+
 	BUG_ON(!task || !is_realtime(task));
+	TRACE_TASK(task, "Requeueing");
 	BUG_ON(is_queued(task));
 	BUG_ON(get_task_domain(task) != dom);
 
diff --git a/litmus/sched_mc.c b/litmus/sched_mc.c
index 277762709d3d..61eb961eda23 100644
--- a/litmus/sched_mc.c
+++ b/litmus/sched_mc.c
@@ -63,8 +63,10 @@ static int interrupt_cpu;
 #define is_global_task(t) (is_global(get_task_domain(t)))
 #define can_use(ce) \
 	((ce)->state == CS_ACTIVE || (ce->state == CS_ACTIVATE))
-#define can_requeue(t)					\
-	(!is_global_task(t) || (t)->rt_param.scheduled_on == NO_CPU)
+#define can_requeue(t)							\
+	((t)->rt_param.linked_on == NO_CPU && /* Not linked anywhere */ \
+	 !is_queued(t) &&	              /* Not gonna be linked */ \
+	 (!is_global_task(t) || (t)->rt_param.scheduled_on == NO_CPU))
 #define entry_level(e) \
 	(((e)->linked) ? tsk_mc_crit((e)->linked) : NUM_CRIT_LEVELS - 1)
 #define crit_cpu(ce) \
@@ -288,11 +290,11 @@ static void job_arrival(struct task_struct *task)
 	TRACE_MC_TASK(task, "Job arriving\n");
 	BUG_ON(!task);
 
+	raw_spin_lock(dom->lock);
 	if (can_requeue(task)) {
-		raw_spin_lock(dom->lock);
+		BUG_ON(task->rt_param.linked_on != NO_CPU);
 		dom->requeue(dom, task);
 		check_for_preempt(dom);
-		raw_spin_unlock(dom->lock);
 	} else {
 		/* If a global task is scheduled on one cpu, it CANNOT
 		 * be requeued into a global domain. Another cpu might
@@ -302,6 +304,7 @@ static void job_arrival(struct task_struct *task)
 		 */
 		TRACE_MC_TASK(task, "Delayed arrival of scheduled task\n");
 	}
+	raw_spin_unlock(dom->lock);
 }
 
 /**
@@ -547,11 +550,15 @@ static void remove_from_all(struct task_struct* task)
 				update = 1;
 				link_task_to_cpu(entry, NULL);
 			}
+		} else {
+			TRACE_MC_TASK(task, "Unlinked before we got lock!");
 		}
 		if (update)
 			update_crit_levels(entry);
 		else
 			raw_spin_unlock(&entry->lock);
+	} else {
+		TRACE_MC_TASK(task, "Not linked to anything\n");
 	}
 
 	/* Ensure the task isn't returned by its domain */
@@ -874,7 +881,7 @@ static struct task_struct* mc_schedule(struct task_struct* prev)
 	local_irq_save(flags);
 	raw_spin_lock(&entry->lock);
 
-	if (entry->scheduled) {
+	if (entry->scheduled && entry->scheduled != prev) {
 		TRACE_TASK(entry->scheduled, " and prev is %d\n", prev->pid);
 	}
 
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