From mboxrd@z Thu Jan  1 00:00:00 1970
From: bvanassche@acm.org (Bart Van Assche)
Date: Fri, 26 Apr 2019 10:04:23 -0700
Subject: [PATCH V7 9/9] nvme: hold request queue's refcount in ns's
 whole lifetime
In-Reply-To: <20190426151114.GB20438@lst.de>
References: <20190424110221.17435-1-ming.lei@redhat.com>
 <20190424110221.17435-10-ming.lei@redhat.com>
 <20190424162746.GE23854@lst.de> <20190425010030.GD22636@ming.t460p>
 <20190426151114.GB20438@lst.de>
Message-ID: <1556298263.161891.152.camel@acm.org>

On Fri, 2019-04-26@17:11 +0200, Christoph Hellwig wrote:
> On Thu, Apr 25, 2019@09:00:31AM +0800, Ming Lei wrote:
> > The issue is driver(NVMe) specific, the race window is just between
> > between blk_cleanup_queue() and removing the ns from the controller namspace
> > list in nvme_ns_remove()
> 
> And I wouldn't be surprised if others have the same issue.
> 
> > 
> > blk_mq_init_queue() does hold one refcount, and its counter-part is
> > blk_cleanup_queue().
> > 
> > It is simply ugly to ask blk_mq_init_queue() to grab a refcnt for driver,
> > then who is the counter-part for releasing the extra refcount?
> 
> Well, the problem is exactly that blk_cleanup_queue drops the reference.
> If move the blk_put_queue() call from the end of it to the callers the
> callers can keep the reference as long as they need them, and we wouldn't
> need an extra reference.

Hi Christoph,

There are more than hundred callers of blk_cleanup_queue() so that change
would cause a lot of churn. Since blk_get_queue() and blk_put_queue() are
available, how inserting a pair of calls to these functions where necessary?

Thanks,

Bart.