1 files changed, 25 insertions, 21 deletions

diff --git a/block/elevator.c b/block/elevator.c
index fae58b2f906f..72ce7a4a2632 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -833,13 +833,16 @@ static struct kobj_type elv_ktype = {
 	.release	= elevator_release,
 };
 
-int elv_register_queue(struct request_queue *q)
+/*
+ * elv_register_queue is called from either blk_register_queue or
+ * elevator_switch, elevator switch is prevented from being happen
+ * in the two paths, so it is safe to not hold q->sysfs_lock.
+ */
+int elv_register_queue(struct request_queue *q, bool uevent)
 {
 	struct elevator_queue *e = q->elevator;
 	int error;
 
-	lockdep_assert_held(&q->sysfs_lock);
-
 	error = kobject_add(&e->kobj, &q->kobj, "%s", "iosched");
 	if (!error) {
 		struct elv_fs_entry *attr = e->type->elevator_attrs;
@@ -850,7 +853,9 @@ int elv_register_queue(struct request_queue *q)
 				attr++;
 			}
 		}
-		kobject_uevent(&e->kobj, KOBJ_ADD);
+		if (uevent)
+			kobject_uevent(&e->kobj, KOBJ_ADD);
+
 		e->registered = 1;
 		if (!e->uses_mq && e->type->ops.sq.elevator_registered_fn)
 			e->type->ops.sq.elevator_registered_fn(q);
@@ -858,18 +863,20 @@ int elv_register_queue(struct request_queue *q)
 	return error;
 }
 
+/*
+ * elv_unregister_queue is called from either blk_unregister_queue or
+ * elevator_switch, elevator switch is prevented from being happen
+ * in the two paths, so it is safe to not hold q->sysfs_lock.
+ */
 void elv_unregister_queue(struct request_queue *q)
 {
-	lockdep_assert_held(&q->sysfs_lock);
-
 	if (q) {
 		struct elevator_queue *e = q->elevator;
 
 		kobject_uevent(&e->kobj, KOBJ_REMOVE);
 		kobject_del(&e->kobj);
+
 		e->registered = 0;
-		/* Re-enable throttling in case elevator disabled it */
-		wbt_enable_default(q);
 	}
 }
 
@@ -942,6 +949,7 @@ int elevator_switch_mq(struct request_queue *q,
 	if (q->elevator) {
 		if (q->elevator->registered)
 			elv_unregister_queue(q);
+
 		ioc_clear_queue(q);
 		elevator_exit(q, q->elevator);
 	}
@@ -951,7 +959,7 @@ int elevator_switch_mq(struct request_queue *q,
 		goto out;
 
 	if (new_e) {
-		ret = elv_register_queue(q);
+		ret = elv_register_queue(q, true);
 		if (ret) {
 			elevator_exit(q, q->elevator);
 			goto out;
@@ -980,23 +988,19 @@ int elevator_init_mq(struct request_queue *q)
 	if (q->nr_hw_queues != 1)
 		return 0;
 
-	/*
-	 * q->sysfs_lock must be held to provide mutual exclusion between
-	 * elevator_switch() and here.
-	 */
-	mutex_lock(&q->sysfs_lock);
+	WARN_ON_ONCE(test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags));
+
 	if (unlikely(q->elevator))
-		goto out_unlock;
+		goto out;
 
 	e = elevator_get(q, "mq-deadline", false);
 	if (!e)
-		goto out_unlock;
+		goto out;
 
 	err = blk_mq_init_sched(q, e);
 	if (err)
 		elevator_put(e);
-out_unlock:
-	mutex_unlock(&q->sysfs_lock);
+out:
 	return err;
 }
 
@@ -1051,7 +1055,7 @@ static int elevator_switch(struct request_queue *q, struct elevator_type *new_e)
 	if (err)
 		goto fail_init;
 
-	err = elv_register_queue(q);
+	err = elv_register_queue(q, true);
 	if (err)
 		goto fail_register;
 
@@ -1071,7 +1075,7 @@ fail_init:
 	/* switch failed, restore and re-register old elevator */
 	if (old) {
 		q->elevator = old;
-		elv_register_queue(q);
+		elv_register_queue(q, true);
 		blk_queue_bypass_end(q);
 	}
 
@@ -1087,7 +1091,7 @@ static int __elevator_change(struct request_queue *q, const char *name)
 	struct elevator_type *e;
 
 	/* Make sure queue is not in the middle of being removed */
-	if (!test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags))
+	if (!blk_queue_registered(q))
 		return -ENOENT;
 
 	/*