Re: [PATCH v3 06/11] iommu: Defer __iommu_group_free_device() to be outside group->mutex

[Nicolin Chen <nicolinc@nvidia.com>]

On Thu, Apr 23, 2026 at 03:55:02PM +0800, Baolu Lu wrote:
> On 4/17/26 07:28, Nicolin Chen wrote:
> > +static void __iommu_group_empty_assert_owner_cnt(struct iommu_group *group)
> > +{
> > +	lockdep_assert_held(&group->mutex);
> > +	/*
> > +	 * If the group has become empty then ownership must have been
> > +	 * released, and the current domain must be set back to NULL or
> > +	 * the default domain.
> > +	 */
> 
> Nit: this comment doesn't quite match the following code. The code
> doesn't check "group->domain != NULL". Or perhaps in that case,
> group->default_domain must be NULL?

This is the original patch from Jason:
https://lore.kernel.org/r/4-v3-328044aa278c+45e49-iommu_probe_jgg@nvidia.com

I kept the comments as-is, though It might be slightly confusing?

I think it means:
If group->default_domain == NULL, it does check "set back to NULL".
If group->default_domain != NULL, it then checks "default domain".

Maybe it could be "must be set back to the default domain (which
itself can be NULL"?

> Furthermore, if a device is currently quarantined, group->domain will be
> the blocking_domain. If that quarantined device is then hot-removed and
> happens to be the last device in the group, will this WARN_ON trigger
> unnecessarily?

If a device is quarantined, its group->domain is retained to the
previously attached domain. Its blocking state is logged in the
gdev->blocked flag. So, I think it can pass the test.

Thanks
Nicolin