RE: [PATCH v2 13/15] vfio/ccw: Use the new device life cycle helpers

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

> From: Eric Farman
> Sent: Friday, September 9, 2022 4:51 AM
> 
> On Thu, 2022-09-08 at 07:19 +0000, Tian, Kevin wrote:
> > ping @Eric Farman.
> >
> > ccw is the only tricky player in this series. Please help take a look
> > in case of
> > any oversight here.
> 
> Apologies, I had started looking at v1 before I left on holiday, and
> only returned today.
> 
> >
> > > From: Tian, Kevin <kevin.tian@intel.com>
> > > Sent: Thursday, September 1, 2022 10:38 PM
> > >
> > > ccw is the only exception which cannot use vfio_alloc_device()
> > > because
> > > its private device structure is designed to serve both mdev and
> > > parent.
> > > Life cycle of the parent is managed by css_driver so
> > > vfio_ccw_private
> > > must be allocated/freed in css_driver probe/remove path instead of
> > > conforming to vfio core life cycle for mdev.
> > >
> > > Given that use a wait/completion scheme so the mdev remove path
> > > waits
> > > after vfio_put_device() until receiving a completion notification
> > > from
> > > @release. The completion indicates that all active references on
> > > vfio_device have been released.
> > >
> > > After that point although free of vfio_ccw_private is delayed to
> > > css_driver it's at least guaranteed to have no parallel reference
> > > on
> > > released vfio device part from other code paths.
> > >
> > > memset() in @probe is removed. vfio_device is either already
> > > cleared
> > > when probed for the first time or cleared in @release from last
> > > probe.
> > >
> > > The right fix is to introduce separate structures for mdev and
> > > parent,
> > > but this won't happen in short term per prior discussions.
> 
> I did start looking at the above, while the mdev series is outstanding.
> Will try to get back to that sooner rather than later, but for the
> purposes of this series this patch looks/works fine to me.
> 
> Reviewed-by: Eric Farman <farman@linux.ibm.com>
> 

Thanks!