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

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Message-ID: <31a567ac-180a-b2de-2233-e758a9a977d8@huaweicloud.com>
Date: Fri, 15 Aug 2025 09:32:22 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Nilay Shroff <nilay@...ux.ibm.com>, Yu Kuai <yukuai1@...weicloud.com>,
 axboe@...nel.dk, 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,
 "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH 03/16] blk-mq: remove useless checkings from
 blk_mq_update_nr_requests()

Hi,

在 2025/08/14 20:23, Nilay Shroff 写道:
> 
> 
> 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().

Ok, thanks for the reviw.

I didn't notice this, just wonder how can this happen?
nr_hw_queues > NR_CPUS?

Thanks,
Kuai

> 
> Thanks,
> --Nilay
> 
> .
>