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From: Ming Lei <ming.lei@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>,
	linux-block@vger.kernel.org
Subject: Re: [PATCH 3/4] block: drain file system I/O on del_gendisk
Date: Thu, 23 Sep 2021 14:39:59 +0800	[thread overview]
Message-ID: <YUwhPy1J8lzHQF77@T590> (raw)
In-Reply-To: <20210923052705.GA5314@lst.de>

On Thu, Sep 23, 2021 at 07:27:05AM +0200, Christoph Hellwig wrote:
> On Thu, Sep 23, 2021 at 09:34:03AM +0800, Ming Lei wrote:
> > > +	set_bit(GD_DEAD, &disk->state);
> > >  	set_capacity(disk, 0);
> > >  
> > > +	/*
> > > +	 * Prevent new I/O from crossing bio_queue_enter().
> > > +	 */
> > > +	blk_queue_start_drain(q);
> > > +	blk_mq_freeze_queue_wait(q);
> > > +
> > > +	rq_qos_exit(q);
> > > +	blk_sync_queue(q);
> > > +	blk_flush_integrity();
> > > +	/*
> > > +	 * Allow using passthrough request again after the queue is torn down.
> > > +	 */
> > > +	blk_mq_unfreeze_queue(q);
> > 
> > After blk_mq_unfreeze_queue() returns, blk_try_enter_queue() will return
> > true, so new FS I/O from opened bdev still won't be blocked, right?
> 
> It won't be blocked by blk_mq_unfreeze_queue, but because the capacity
> is set to 0 it still won't make it to the driver.

One bio could be made & checked before set_capacity(0), then is
submitted after blk_mq_unfreeze_queue() returns.

blk_mq_freeze_queue_wait() doesn't always imply RCU grace period, for
example, the .q_usage_counter may have been in atomic mode before
calling blk_queue_start_drain() & blk_mq_freeze_queue_wait().


Thanks,
Ming


  reply	other threads:[~2021-09-23  6:40 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-22 17:22 tear down file system I/O in del_gendisk v2 Christoph Hellwig
2021-09-22 17:22 ` [PATCH 1/4] block: factor out a blk_try_enter_queue helper Christoph Hellwig
2021-09-22 17:22 ` [PATCH 2/4] block: split bio_queue_enter from blk_queue_enter Christoph Hellwig
2021-09-22 17:22 ` [PATCH 3/4] block: drain file system I/O on del_gendisk Christoph Hellwig
2021-09-23  1:34   ` Ming Lei
2021-09-23  5:27     ` Christoph Hellwig
2021-09-23  6:39       ` Ming Lei [this message]
2021-09-27 12:04         ` Christoph Hellwig
2021-09-27 14:32           ` Ming Lei
2021-09-23  6:21   ` Hannes Reinecke
2021-09-22 17:22 ` [PATCH 4/4] block: keep q_usage_counter in atomic mode after del_gendisk Christoph Hellwig
  -- strict thread matches above, loose matches on Subject: below --
2021-09-20 11:24 tear down file system I/O in del_gendisk Christoph Hellwig
2021-09-20 11:24 ` [PATCH 3/4] block: drain file system I/O on del_gendisk Christoph Hellwig

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