Re: [PATCH V7 9/9] nvme: hold request queue's refcount in ns's whole lifetime

[Bart Van Assche <bvanassche@acm.org>]

On Fri, 2019-04-26 at 17:11 +0200, Christoph Hellwig wrote:
> On Thu, Apr 25, 2019 at 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.