linux-kernel - Re: [PATCH 1/1] block: Use RCU in blk_mq_[un]quiesce_tagset() instead of set->tag_list

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: <201a7e9e-4782-4f71-a73b-9d58a51ee8ec@acm.org>
Date: Thu, 4 Dec 2025 13:22:49 -1000
From: Bart Van Assche <bvanassche@....org>
To: Keith Busch <kbusch@...nel.org>
Cc: Mohamed Khalfella <mkhalfella@...estorage.com>,
 Chaitanya Kulkarni <kch@...dia.com>, Christoph Hellwig <hch@....de>,
 Jens Axboe <axboe@...nel.dk>, Sagi Grimberg <sagi@...mberg.me>,
 Casey Chen <cachen@...estorage.com>, Yuanyuan Zhong
 <yzhong@...estorage.com>, Hannes Reinecke <hare@...e.de>,
 Ming Lei <ming.lei@...hat.com>, Waiman Long <llong@...hat.com>,
 Hillf Danton <hdanton@...a.com>, linux-nvme@...ts.infradead.org,
 linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] block: Use RCU in blk_mq_[un]quiesce_tagset() instead
 of set->tag_list_lock


On 12/4/25 11:26 AM, Keith Busch wrote:
> On Thu, Dec 04, 2025 at 10:24:03AM -1000, Bart Van Assche wrote:>> Hence, the deadlock can be
>> solved by removing the blk_mq_quiesce_tagset() call from nvme_timeout()
>> and by failing I/O from inside nvme_timeout(). If nvme_timeout() fails
>> I/O and does not call blk_mq_quiesce_tagset() then the
>> blk_mq_freeze_queue_wait() call will finish instead of triggering a
>> deadlock. However, I do not know whether this proposal seems acceptable
>> to the NVMe maintainers.
> 
> You periodically make this suggestion, but there's never a reason
> offered to introduce yet another work queue for the driver to
> synchronize with at various points. The whole point of making blk-mq
> timeout handler in a work queue (it used to be a timer) was so that we
> could do blocking actions like this.
Hi Keith,

The blk_mq_quiesce_tagset() call from the NVMe timeout handler is
unfortunate because it triggers a deadlock with
blk_mq_update_tag_set_shared().

I proposed to modify the NVMe driver because I think that's a better
approach than introducing a new synchronize_rcu() call in the block
layer core.

However, there may be better approaches for fixing this in the NVMe
driver than what I proposed so far.

Thanks,

Bart.