Re: [PATCH 3/3] iommu: Do not attempt to re-lock the iommu device when probing

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, Aug 09, 2023 at 04:01:42AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@nvidia.com>
> > Sent: Wednesday, August 9, 2023 1:27 AM
> > 
> > @@ -1800,11 +1801,18 @@ struct probe_iommu_args {
> >  static int probe_iommu_group(struct device *dev, void *data)
> >  {
> >  	struct probe_iommu_args *args = data;
> > +	bool need_lock;
> >  	int ret;
> > 
> > -	device_lock(dev);
> > +	/* Probing the iommu itself is always done under the device_lock */
> > +	need_lock = !args->iommu || args->iommu->hwdev != dev;
> > +
> 
> is !args->iommu a valid case?

Hmm, not any more, it used to happen in an earlier version
 
> btw probably a dumb question. Why do we continue to probe the
> iommu device itself instead of skipping it? The group is a concept
> for devices which require DMA protection from iommu instead of
> for the iommu device itself...

Yeah, that is how I originally did it, but since the locking appeared
here I thought it would be safer to just continue to invoke probe as
we have always done. I don't know for sure that there isn't some
driver that relies on this for some reason.

eg it might change the group layouts or something.

Thanks,
Jason