Re: [PATCH] block: don't release queue's sysfs lock during switching elevator

[Bart Van Assche <bvanassche@xxxxxxx>]

On 9/23/19 8:12 AM, Ming Lei wrote:
> @@ -523,11 +521,9 @@ void elv_unregister_queue(struct request_queue *q)
>   		kobject_uevent(&e->kobj, KOBJ_REMOVE);
>   		kobject_del(&e->kobj);
>   
> -		mutex_lock(&q->sysfs_lock);
>   		e->registered = 0;
>   		/* Re-enable throttling in case elevator disabled it */
>   		wbt_enable_default(q);
> -		mutex_unlock(&q->sysfs_lock);
>   	}
>   }

Does this patch cause sysfs_lock to be held around 
kobject_del(&e->kobj)? Since sysfs_lock is locked from inside 
elv_attr_show() and elv_attr_store(), does this mean that this patch 
reintroduces the lock inversion problem that was fixed recently?

Thanks,

Bart.