From: Andrew Morton <akpm@osdl.org>

migration_call() is called during CPU bringup even if CONFIG_HOTPLUG_CPU=n. 
So we need to release that lock, else it deadlocks.

Cc: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/sched.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff -puN kernel/sched.c~eliminate-lock_cpu_hotplug-in-kernel-schedc-fix kernel/sched.c
--- a/kernel/sched.c~eliminate-lock_cpu_hotplug-in-kernel-schedc-fix
+++ a/kernel/sched.c
@@ -5255,11 +5255,10 @@ migration_call(struct notifier_block *nf
 		}
 		spin_unlock_irq(&rq->lock);
 		break;
-
+#endif
 	case CPU_LOCK_RELEASE:
 		mutex_unlock(&sched_hotcpu_mutex);
 		break;
-#endif
 	}
 	return NOTIFY_OK;
 }
_