1 files changed, 45 insertions, 45 deletions

diff --git a/block/elevator.c b/block/elevator.c
index f016855a46b0..f8c08e1bff2b 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -121,11 +121,10 @@ static struct elevator_type *elevator_get(const char *name)
         return e;
 }
 
-static int elevator_init_queue(struct request_queue *q,
-                               struct elevator_queue *eq)
+static int elevator_init_queue(struct request_queue *q)
 {
-        eq->elevator_data = eq->type->ops.elevator_init_fn(q);
-        if (eq->elevator_data)
+        q->elevator->elevator_data = q->elevator->type->ops.elevator_init_fn(q);
+        if (q->elevator->elevator_data)
                 return 0;
         return -ENOMEM;
 }
@@ -188,7 +187,6 @@ static void elevator_release(struct kobject *kobj)
 int elevator_init(struct request_queue *q, char *name)
 {
         struct elevator_type *e = NULL;
-        struct elevator_queue *eq;
         int err;
 
         if (unlikely(q->elevator))
@@ -222,17 +220,16 @@ int elevator_init(struct request_queue *q, char *name)
                 }
         }
 
-        eq = elevator_alloc(q, e);
-        if (!eq)
+        q->elevator = elevator_alloc(q, e);
+        if (!q->elevator)
                 return -ENOMEM;
 
-        err = elevator_init_queue(q, eq);
+        err = elevator_init_queue(q);
         if (err) {
-                kobject_put(&eq->kobj);
+                kobject_put(&q->elevator->kobj);
                 return err;
         }
 
-        q->elevator = eq;
         return 0;
 }
 EXPORT_SYMBOL(elevator_init);
@@ -801,8 +798,9 @@ static struct kobj_type elv_ktype = {
         .release        = elevator_release,
 };
 
-int __elv_register_queue(struct request_queue *q, struct elevator_queue *e)
+int elv_register_queue(struct request_queue *q)
 {
+        struct elevator_queue *e = q->elevator;
         int error;
 
         error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
@@ -820,11 +818,6 @@ int __elv_register_queue(struct request_queue *q, struct elevator_queue *e)
         }
         return error;
 }
-
-int elv_register_queue(struct request_queue *q)
-{
-        return __elv_register_queue(q, q->elevator);
-}
 EXPORT_SYMBOL(elv_register_queue);
 
 void elv_unregister_queue(struct request_queue *q)
@@ -907,51 +900,58 @@ EXPORT_SYMBOL_GPL(elv_unregister);
  */
 static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 {
-        struct elevator_queue *old_elevator, *e;
+        struct elevator_queue *old = q->elevator;
+        bool registered = old->registered;
         int err;
 
-        /* allocate new elevator */
-        e = elevator_alloc(q, new_e);
-        if (!e)
-                return -ENOMEM;
-
-        err = elevator_init_queue(q, e);
-        if (err) {
-                kobject_put(&e->kobj);
-                return err;
-        }
-
-        /* turn on BYPASS and drain all requests w/ elevator private data */
+        /*
+         * Turn on BYPASS and drain all requests w/ elevator private data.
+         * Block layer doesn't call into a quiesced elevator - all requests
+         * are directly put on the dispatch list without elevator data
+         * using INSERT_BACK.  All requests have SOFTBARRIER set and no
+         * merge happens either.
+         */
         elv_quiesce_start(q);
 
-        /* unregister old queue, register new one and kill old elevator */
-        if (q->elevator->registered) {
+        /* unregister and clear all auxiliary data of the old elevator */
+        if (registered)
                 elv_unregister_queue(q);
-                err = __elv_register_queue(q, e);
-                if (err)
-                        goto fail_register;
-        }
 
-        /* done, clear io_cq's, switch elevators and turn off BYPASS */
         spin_lock_irq(q->queue_lock);
         ioc_clear_queue(q);
-        old_elevator = q->elevator;
-        q->elevator = e;
         spin_unlock_irq(q->queue_lock);
 
-        elevator_exit(old_elevator);
+        /* allocate, init and register new elevator */
+        err = -ENOMEM;
+        q->elevator = elevator_alloc(q, new_e);
+        if (!q->elevator)
+                goto fail_init;
+
+        err = elevator_init_queue(q);
+        if (err) {
+                kobject_put(&q->elevator->kobj);
+                goto fail_init;
+        }
+
+        if (registered) {
+                err = elv_register_queue(q);
+                if (err)
+                        goto fail_register;
+        }
+
+        /* done, kill the old one and finish */
+        elevator_exit(old);
         elv_quiesce_end(q);
 
-        blk_add_trace_msg(q, "elv switch: %s", e->type->elevator_name);
+        blk_add_trace_msg(q, "elv switch: %s", new_e->elevator_name);
 
         return 0;
 
 fail_register:
-        /*
-         * switch failed, exit the new io scheduler and reattach the old
-         * one again (along with re-adding the sysfs dir)
-         */
-        elevator_exit(e);
+        elevator_exit(q->elevator);
+fail_init:
+        /* switch failed, restore and re-register old elevator */
+        q->elevator = old;
         elv_register_queue(q);
         elv_quiesce_end(q);