linux-kernel - Re: [PATCH v2 -next] blk-cgroup: synchoronize blkg creation against policy deactivation

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Message-ID: <YWi27oAU0v5v86eN@slm.duckdns.org>
Date:   Thu, 14 Oct 2021 13:02:06 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Yu Kuai <yukuai3@...wei.com>
Cc:     axboe@...nel.dk, paolo.valente@...aro.org, fchecconi@...il.com,
        avanzini.arianna@...il.com, mkoutny@...e.com,
        cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com
Subject: Re: [PATCH v2 -next] blk-cgroup: synchoronize blkg creation against
 policy deactivation

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