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From: "Jinlong Chen" <nickyc975@zju.edu.cn>
To: "Bart Van Assche" <bvanassche@acm.org>
Cc: axboe@kernel.dk, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me,
	 linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	 linux-nvme@lists.infradead.org
Subject: Re: Re: [PATCH 1/3] blk-mq: remove redundant call to blk_freeze_queue_start in blk_mq_destroy_queue
Date: Sun, 30 Oct 2022 10:27:22 +0800 (GMT+08:00)	[thread overview]
Message-ID: <42681e4e.15223d.18426b71124.Coremail.nickyc975@zju.edu.cn> (raw)
In-Reply-To: <adaea16a-c7cd-5d68-50c8-d56de851061a@acm.org>

Hi, Bart.

> > Calling blk_freeze_queue results in a redundant call to
> > blk_freeze_queue_start as it has been called in blk_queue_start_drain.
> > 
> > Replace blk_freeze_queue with blk_mq_freeze_queue_wait to avoid the
> > redundant call.
> 
> blk_mq_destroy_queue() has more callers than blk_queue_start_drain() so 
> the above description is at least misleading.
> 
> Additionally, the word "cleanup" from the patch series title indicates 
> that no patch in this series changes the behavior of the code. This 
> patch involves a behavior change.

Sorry for my poor description. I'll send a new series with these
description problems resolved.

> I think this patch introduces a hang for every caller of 
> blk_mq_destroy_queue() other than blk_queue_start_drain().
> 
> Bart.

I don't see why the patch introduces a hang. The calling relationship in
blk_mq_destroy_queue is as follows:

blk_mq_destroy_queue()
    ...
    -> blk_queue_start_drain()
        -> blk_freeze_queue_start()  <- called
        ...
    -> blk_freeze_queue()
        -> blk_freeze_queue_start()  <- called again
        -> blk_mq_freeze_queue_wait()
    ...

So I think there is a redundant call to blk_freeze_queue_start(), we
just need to call blk_mq_freeze_queue_wait() after calling
blk_queue_start_drain().

Thanks!
Jinlong Chen


  reply	other threads:[~2022-10-30  2:27 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-29 10:02 [PATCH 0/3] cleanups for queue freezing functions Jinlong Chen
2022-10-29 10:02 ` [PATCH 1/3] blk-mq: remove redundant call to blk_freeze_queue_start in blk_mq_destroy_queue Jinlong Chen
2022-10-30  0:34   ` Bart Van Assche
2022-10-30  2:27     ` Jinlong Chen [this message]
2022-10-30 14:25       ` Bart Van Assche
2022-10-29 10:02 ` [PATCH 2/3] blk-mq: remove blk_freeze_queue Jinlong Chen
2022-10-29 10:02 ` [PATCH 3/3] block: hide back blk_freeze_queue_start and export its blk-mq alias Jinlong Chen

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