From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH v2 -next] blk-cgroup: synchoronize blkg creation against
 policy deactivation
Date: Thu, 14 Oct 2021 13:02:06 -1000
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Sender: Tejun Heo <htejun@gmail.com>
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To: Yu Kuai <yukuai3@huawei.com>
Cc: axboe@kernel.dk, paolo.valente@linaro.org, fchecconi@gmail.com, avanzini.arianna@gmail.com, mkoutny@suse.com, cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, yi.zhang@huawei.com

On Wed, Oct 13, 2021 at 08:44:56PM +0800, Yu Kuai wrote:
> @@ -1401,6 +1406,7 @@ void blkcg_deactivate_policy(struct request_queue *q,
>  	if (queue_is_mq(q))
>  		blk_mq_freeze_queue(q);
>  
> +	mutex_lock(&q->blkg_lock);
>  	spin_lock_irq(&q->queue_lock);

Given that deactivation drains q_usage_counter through
blk_mq_freeze_queue(), can't the blkg_conf_prep() just pin the usage count?

Thanks.

-- 
tejun