Re: [PATCH] block: Fix elevator_get_default() to check for null q->tag_set

[Christoph Hellwig]

>  static struct elevator_type *elevator_get_default(struct request_queue *q)
>  {
> -	if (q->tag_set && q->tag_set->flags & BLK_MQ_F_NO_SCHED_BY_DEFAULT)
> -		return NULL;
> +	if (q->tag_set) {

q->tag_set can't be NULL for a blk-mq queue.  So you can just remove
the q->tag_set check here and also in elv_support_iosched.