elevator: fix oops on early call to elevator_change()
[linux-2.6.git] / block / elevator.c
index 205b09a..4e11559 100644 (file)
@@ -938,6 +938,7 @@ int elv_register_queue(struct request_queue *q)
                        }
                }
                kobject_uevent(&e->kobj, KOBJ_ADD);
+               e->registered = 1;
        }
        return error;
 }
@@ -947,6 +948,7 @@ static void __elv_unregister_queue(struct elevator_queue *e)
 {
        kobject_uevent(&e->kobj, KOBJ_REMOVE);
        kobject_del(&e->kobj);
+       e->registered = 0;
 }
 
 void elv_unregister_queue(struct request_queue *q)
@@ -1042,11 +1044,13 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 
        spin_unlock_irq(q->queue_lock);
 
-       __elv_unregister_queue(old_elevator);
+       if (old_elevator->registered) {
+               __elv_unregister_queue(old_elevator);
 
-       err = elv_register_queue(q);
-       if (err)
-               goto fail_register;
+               err = elv_register_queue(q);
+               if (err)
+                       goto fail_register;
+       }
 
        /*
         * finally exit old elevator and turn off BYPASS.