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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aJ_rqOrxMsi3nDqq@fedora>
Date: Sat, 16 Aug 2025 10:23:36 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Yu Kuai <yukuai@...nel.org>
Cc: Yu Kuai <yukuai1@...weicloud.com>, 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

On Sat, Aug 16, 2025 at 08:49:41AM +0800, Yu Kuai wrote:
> 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.

Yeah, that is potential deadlock issue in updating nr_request.

I feel the patch title is a bit confusing because q->nr_requests updating
is already serialized.


Thanks,
Ming