[PATCH] sched: Look at another CPU's domain

From: Nick Piggin <nickpiggin@yahoo.com.au>

The SMT wake_idle code really wants to look at a non-local CPU's domain in
order to check for idle siblings.

So change the domain attachment code a little bit so we continue to hold a
runqueue's lock while attaching a new domain.  This means the locking rules
have changed to: you may access your own domain without any lock, you must
hold a remote runqueue's lock in order to view its domain.

kernel/sched.c

@@ -3392,18 +3392,18 @@ static int migration_thread(void * data)
 		req = list_entry(head->next, migration_req_t, list);
 		list_del_init(head->next);
 
-		spin_unlock(&rq->lock);
-
 		if (req->type == REQ_MOVE_TASK) {
+			spin_unlock(&rq->lock);
 			__migrate_task(req->task, req->dest_cpu);
+			local_irq_enable();
 		} else if (req->type == REQ_SET_DOMAIN) {
 			rq->sd = req->sd;
+			spin_unlock_irq(&rq->lock);
 		} else {
+			spin_unlock_irq(&rq->lock);
 			WARN_ON(1);
 		}
 
-		local_irq_enable();
-
 		complete(&req->done);
 	}
 	return 0;