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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: Mon, 27 Sep 2021 22:32:26 +0800	[thread overview]
Message-ID: <YVHV+q5Mwj/mUjU7@T590> (raw)
In-Reply-To: <20210927120441.GA25223@lst.de>

On Mon, Sep 27, 2021 at 02:04:41PM +0200, Christoph Hellwig wrote:
> On Thu, Sep 23, 2021 at 02:39:59PM +0800, Ming Lei wrote:
> > > > 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().
> 
> True, but this isn't really a new issue as we never had proper quiesce
> behavior.  I have a bunch of ideas of how to make this actually solid,
> but none of them looks like 5.15 material.

It is new issue since edb0872f44ec ("block: move the bdi from the
request_queue to the gendisk").

Previously bdi has longer lifetime than request queue, but now it becomes
not, then either queue_to_disk() or queue->disk may cause panic.


Thanks,
Ming


  reply	other threads:[~2021-09-27 14:32 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
2021-09-27 12:04         ` Christoph Hellwig
2021-09-27 14:32           ` Ming Lei [this message]
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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