Re: [PATCH 2/2] Revert "ublk_drv: fix request queue leak"

[Ming Lei <ming.lei@redhat.com>]

On Wed, Jul 20, 2022 at 11:00:40AM +0200, Christoph Hellwig wrote:
> On Wed, Jul 20, 2022 at 03:47:27PM +0800, Ming Lei wrote:
> > > What is broken in START_DEV/STOP_DEV?  Please explain the semantics you
> > > want and what doesn't work.  FYI, there is nothing in the test suite the
> > > complains.  And besides the obvious block layer bug that Jens found you
> > > seemed to be perfectly happy with the semantics.
> > 
> > START_DEV calls add_disk(), and STOP_DEV calls del_gendisk(), but if 
> > GD_OWNS_QUEUE is set, blk_mq_exit_queue() will be called in
> > del_gendisk(), then the following START_DEV will stuck.
> 
> Uh, yeah.  alloc_disk and add_disk are supposed to be paired and
> not split over different ioctls.  The lifetime rules here are
> rather broken.

Even though alloc_disk and add_disk is paired here, GD_OWNS_QUEUE still
can't be set because request queue has to be workable for the new alloc/
added disk, just like scsi.

So it is nothing to do with pair of alloc_disk/add_disk().

Not mention I don't see any thing wrong with adding/deleting disk
multiple times.

Thanks,
Ming