Re: [PATCH 03/14] iommufd: Replace the hwpt->devices list with iommufd_group

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On Tue, Mar 07, 2023 at 02:38:47AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > Sent: Tuesday, March 7, 2023 4:22 AM
> > 
> > On Thu, Mar 02, 2023 at 08:01:00AM +0000, Tian, Kevin wrote:
> > > > From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > > > Sent: Saturday, February 25, 2023 8:28 AM
> > > >
> > > > +struct iommufd_hw_pagetable *
> > > > +iommufd_hw_pagetable_detach(struct iommufd_device *idev)
> > > >  {
> > > > -	if (!iommufd_hw_pagetable_has_group(hwpt, idev->igroup))
> > > > +	struct iommufd_hw_pagetable *hwpt = idev->igroup->hwpt;
> > > > +
> > > > +	lockdep_assert_held(&idev->igroup->lock);
> > > > +
> > > > +	idev->igroup->devices--;
> > > > +	if (!idev->igroup->devices) {
> > > >  		iommu_detach_group(hwpt->domain, idev->igroup->group);
> > > > +		idev->igroup->hwpt = NULL;
> > >
> > > hwpt->obj.users should be decremented here instead of leaving it
> > > in iommufd_device_detach().
> > 
> > It is like this because eventually we can't call
> > iommufd_object_destroy_user() while holding the locks.
> > 
> > So the lowest function returns the hwpt up the call chain and once
> > everything is unlocked then it calls iommufd_hw_pagetable_put()
> 
> but don't we have unbalanced refcnt poke?

Yes, the refcount should be incremented for every attached device

Jason



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