RE: [PATCH v2 01/14] vfio: Remove extra put/gets around vfio_device->group

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Wednesday, March 17, 2021 7:08 AM
> 
> On Tue, Mar 16, 2021 at 07:33:55AM +0000, Tian, Kevin wrote:
> 
> > > It is tricky to see, but the get at the start of vfio_del_group_dev() is
> > > actually pairing with the put hidden inside vfio_device_put() a few lines
> > > below.
> >
> > I feel that the put inside vfio_device_put was meant to pair with the get in
> > vfio_group_create_device before this patch is applied. Because
> vfio_device_
> > put may drop the last reference to the group, vfio_del_group_dev then
> > issues its own get to hold the reference until the put at the end of the func.
> 
> Here I am talking about how this patch removes 3 gets and 2 puts -
> which should be a red flag. The reason it is OK is because the 3rd
> extra removed get is paring with the put hidden inside another put.

Fine. We are just looking at it from different angles.

> 
> > > @@ -1008,6 +990,7 @@ void *vfio_del_group_dev(struct device *dev)
> > >  	if (list_empty(&group->device_list))
> > >  		wait_event(group->container_q, !group->container);
> > >
> > > +	/* Matches the get in vfio_group_create_device() */
> >
> > There is no get there now.
> 
> It is refering to this comment:
> 
> /* Our reference on group is moved to the device */
> 
> The get is a move in this case
> 
> Later delete the function and this becomes perfectly clear
> 

Looks above comment is not updated after vfio_group_create_device 
is removed in patch03.

Thanks
Kevin