From 64f2ca225974f808be23f1e1450e4d490770cae7 Mon Sep 17 00:00:00 2001
From: Ali Mashtizadeh <mashti@cs.stanford.edu>
Date: Thu, 15 Jan 2015 21:24:15 -0800
Subject: [PATCH] Fix a bug in the scheduler

---
 sys/kern/thread.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/sys/kern/thread.c b/sys/kern/thread.c
index 8b70a25..47bc712 100644
--- a/sys/kern/thread.c
+++ b/sys/kern/thread.c
@@ -226,6 +226,14 @@ Thread_Scheduler()
 
     // Select next thread
     next = TAILQ_FIRST(&runnableQueue);
+    if (!next) {
+	/*
+	 * There may be no other runnable processes on this core.  This is a 
+	 * good opportunity to migrate threads.
+	 */
+	Spinlock_Unlock(&threadLock);
+	return;
+    }
     TAILQ_REMOVE(&runnableQueue, next, schedQueue);
 
     prev = curProc;