linux-kernel - Re: [PATCH 03/16] blk-mq: remove useless checkings from blk_mq_update_nr

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Message-ID: <97b63163-a122-48f0-805a-a06cf792903f@linux.ibm.com>
Date: Thu, 14 Aug 2025 17:53:41 +0530
From: Nilay Shroff <nilay@...ux.ibm.com>
To: Yu Kuai <yukuai1@...weicloud.com>, axboe@...nel.dk, yukuai3@...wei.com,
        bvanassche@....org, hare@...e.de, ming.lei@...hat.com
Cc: linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com, yangerkun@...wei.com, johnny.chenyi@...wei.com
Subject: Re: [PATCH 03/16] blk-mq: remove useless checkings from
 blk_mq_update_nr_requests()



On 8/14/25 9:05 AM, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@...wei.com>
> 
> 1) queue_requests_store() is the only caller of
> blk_mq_update_nr_requests(), where queue is already freezed, no need to
> check mq_freeze_depth;
> 2) q->tag_set must be set for request_based device, and queue_is_mq() is
> already checked in blk_mq_queue_attr_visible(), no need to check
> q->tag_set.
> 3) During initialization, hctx->tags in initialized before queue
> kobject, and during del_gendisk, queue kobject is deleted before
> exiting hctx, hence checking hctx->tags is useless.
> 
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> ---
>  block/blk-mq.c | 11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index b67d6c02eceb..3a219b7b3688 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -4921,24 +4921,15 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
>  {
>  	struct blk_mq_tag_set *set = q->tag_set;
>  	struct blk_mq_hw_ctx *hctx;
> -	int ret;
> +	int ret = 0;
>  	unsigned long i;
>  
> -	if (WARN_ON_ONCE(!q->mq_freeze_depth))
> -		return -EINVAL;
> -
> -	if (!set)
> -		return -EINVAL;
> -
>  	if (q->nr_requests == nr)
>  		return 0;
>  
>  	blk_mq_quiesce_queue(q);
>  
> -	ret = 0;
>  	queue_for_each_hw_ctx(q, hctx, i) {
> -		if (!hctx->tags)
> -			continue;
It's possible that hctx->tags is set to NULL in case no software 
queues are mapped to the hardware queue. So it seems that this
check is valid. Please see blk_mq_map_swqueue().

Thanks,
--Nilay