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

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Message-ID: <6994b9a7-ef2b-42f3-9e72-7489a56f8f8e@acm.org>
Date: Thu, 4 Dec 2025 10:24:03 -1000
From: Bart Van Assche <bvanassche@....org>
To: Mohamed Khalfella <mkhalfella@...estorage.com>
Cc: Chaitanya Kulkarni <kch@...dia.com>, Christoph Hellwig <hch@....de>,
 Jens Axboe <axboe@...nel.dk>, Keith Busch <kbusch@...nel.org>,
 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 9:57 AM, Mohamed Khalfella wrote:
> I do not see how running this code in another thread will solve the
> problem.
blk_mq_freeze_queue_wait() waits forever because nvme_timeout() waits
for blk_mq_freeze_queue_wait() to finish. 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.

Bart.