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From: Ming Lei <ming.lei@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org
Subject: Re: [PATCH] block: don't protect submit_bio_checks by q_usage_counter
Date: Tue, 11 Jan 2022 09:16:14 +0800	[thread overview]
Message-ID: <YdzaXp4DVyCP6lKS@T590> (raw)
In-Reply-To: <20220110164909.GA7372@lst.de>

On Mon, Jan 10, 2022 at 05:49:09PM +0100, Christoph Hellwig wrote:
> On Tue, Jan 04, 2022 at 09:42:23PM +0800, Ming Lei wrote:
> > Commit cc9c884dd7f4 ("block: call submit_bio_checks under q_usage_counter")
> > uses q_usage_counter to protect submit_bio_checks for avoiding IO after
> > disk is deleted by del_gendisk().
> > 
> > Turns out the protection isn't necessary, because once
> > blk_mq_freeze_queue_wait() in del_gendisk() returns:
> > 
> > 1) all in-flight IO has been done
> 
> Only for blk-mq drivers.

Yes, but the q_usage_counter protection for bio based queue is just for
calling ->submit_bio(), which is added in:

3ef28e83ab15 block: generic request_queue reference counting

Also we never support to drain in-flight IO for bio based queue, and
this patch doesn't make a difference on this area.

> 
> So I don't think this is actually safe.

Draining bio based queue is always driver's responsibility, block
layer never supports that.


Thanks,
Ming


      reply	other threads:[~2022-01-11  1:16 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-04 13:42 [PATCH] block: don't protect submit_bio_checks by q_usage_counter Ming Lei
2022-01-10  0:05 ` Ming Lei
2022-01-10  1:56 ` Jens Axboe
2022-01-10  1:59 ` Jens Axboe
2022-01-10 16:49 ` Christoph Hellwig
2022-01-11  1:16   ` Ming Lei [this message]

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