linux-kernel - Re: [PATCH v4 6/7] blk-mq: fix freeze queue race

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Message-ID: <20150926173256.GA3572@htj.duckdns.org>
Date:	Sat, 26 Sep 2015 13:32:56 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Akinobu Mita <akinobu.mita@...il.com>
Cc:	linux-kernel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
	Ming Lei <tom.leiming@...il.com>,
	Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v4 6/7] blk-mq: fix freeze queue race

Hello,

On Sun, Sep 27, 2015 at 02:09:24AM +0900, Akinobu Mita wrote:
> @@ -420,7 +420,9 @@ static void blk_mq_sysfs_init(struct request_queue *q)
>  /* see blk_register_queue() */
>  void blk_mq_finish_init(struct request_queue *q)
>  {
> +	mutex_lock(&q->mq_freeze_lock);
>  	percpu_ref_switch_to_percpu(&q->mq_usage_counter);
> +	mutex_unlock(&q->mq_freeze_lock);

This looks weird to me.  What can it race against at this point?

> @@ -115,11 +115,15 @@ void blk_mq_freeze_queue_start(struct request_queue *q)
>  {
>  	int freeze_depth;
>  
> +	mutex_lock(&q->mq_freeze_lock);
> +
>  	freeze_depth = atomic_inc_return(&q->mq_freeze_depth);

It doesn't have to be an atomic anymore, right?

Thanks.

-- 
tejun
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