sched: set_cpus_allowed_ptr(): Don't use rq->migration_thread after unlock

Trivial typo fix. rq->migration_thread can be NULL after
task_rq_unlock(), this is why we have "mt" which should be
 used instead.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20100330165829.GA18284@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched.c

@@ -5387,7 +5387,7 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
 
 		get_task_struct(mt);
 		task_rq_unlock(rq, &flags);
-		wake_up_process(rq->migration_thread);
+		wake_up_process(mt);
 		put_task_struct(mt);
 		wait_for_completion(&req.done);
 		tlb_migrate_finish(p->mm);