2 files changed, 9 insertions, 4 deletions

diff --git a/block/elevator.c b/block/elevator.c
index 205b09a5bd9e..4e11559aa2b0 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -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.
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index 926b50322a46..4fd978e7eb83 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -93,6 +93,7 @@ struct elevator_queue
         struct elevator_type *elevator_type;
         struct mutex sysfs_lock;
         struct hlist_head *hash;
+        unsigned int registered:1;
 };
 
 /*