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: <5450d3fa-3f00-40ae-ac95-1f08886de3b6@acm.org>
Date: Thu, 4 Dec 2025 08:22:23 -1000
From: Bart Van Assche <bvanassche@....org>
To: Mohamed Khalfella <mkhalfella@...estorage.com>,
 Chaitanya Kulkarni <kch@...dia.com>, Christoph Hellwig <hch@....de>,
 Jens Axboe <axboe@...nel.dk>, Keith Busch <kbusch@...nel.org>,
 Sagi Grimberg <sagi@...mberg.me>
Cc: 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 8:11 AM, Mohamed Khalfella wrote:
> @@ -4302,6 +4302,8 @@ static void blk_mq_del_queue_tag_set(struct request_queue *q)
>   		blk_mq_update_tag_set_shared(set, false);
>   	}
>   	mutex_unlock(&set->tag_list_lock);
> +
> +	synchronize_rcu();
>   	INIT_LIST_HEAD(&q->tag_set_list);
>   }
Yikes. This change slows down all blk_mq_del_queue_tag_set() callers.
Please fix the reported deadlock by modifying the NVMe code instead of
slowing down the block layer.

Thanks,

Bart.