linux-kernel - Re: [PATCH 04/10] blk-mq: serialize updating nr_requests with update_nr_hwq

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Message-ID: <9194a254-5cbc-4adc-8710-271d95395b96@kernel.org>
Date: Sat, 16 Aug 2025 08:49:41 +0800
From: Yu Kuai <yukuai@...nel.org>
To: Ming Lei <ming.lei@...hat.com>, Yu Kuai <yukuai1@...weicloud.com>
Cc: axboe@...nel.dk, hare@...e.de, nilay@...ux.ibm.com,
 linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 yukuai3@...wei.com, yi.zhang@...wei.com, yangerkun@...wei.com,
 johnny.chenyi@...wei.com
Subject: Re: [PATCH 04/10] blk-mq: serialize updating nr_requests with
 update_nr_hwq_lock

Hi,

在 2025/8/15 22:47, Ming Lei 写道:
> On Fri, Aug 15, 2025 at 04:02:10PM +0800, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@...wei.com>
>>
>> request_queue->nr_requests can be changed by:
>>
>> a) switching elevator by update nr_hw_queues
>> b) switching elevator by elevator sysfs attribute
>> c) configue queue sysfs attribute nr_requests
>   ->elevator_lock is grabbed for updating ->nr_requests except for queue
> initialization, so what is the real problem you are trying to solve?
>
In order to fix the regression and prevent deadlock, we'll have to 
allocate memory

in the case bitmap tags grow before freezing the queue, also prevent 
nr_requests

to be updated by case a and b concurrently.


Thanks,

Kuai

> Thanks,
> Ming
>
>