Re: [PATCH] iommufd/selftest: Simplify iommufd_device_remove_vdev()

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, Jul 14, 2026 at 01:11:09AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@nvidia.com>
> > Sent: Tuesday, July 14, 2026 1:25 AM
> > 
> > Peiyang reports that this function indirectly includes a fault injection
> > point through iommufd_get_object() that was intended to cover the uAPI use
> > of object IDs, not in places like this that cannot fail.
> > 
> > On deeper inspection this can be written using a dedicated helper to
> > obtain a users refcount relying entirely on the xa locking instead of
> > going through the whole get/put scheme. The new helper doesn't need the
> > fault injection point.
> 
> I thought a plain refcount_inc_not_zero() in iommufd_device_remove_vdev()
> could work too, but having the new helper check xarray is more defensive.

It does seem like that would be safe alone

> > + * the object is installed in the xarray, otherwise things are racing with
> > + * a parallel destruction.
> > + */
> > +int iommufd_inc_users(struct iommufd_ctx *ictx, struct iommufd_object
> > *obj)
> 
> iommufd_try_inc_users()?

Sure

Thanks,
Jason