Re: [PATCH v2 05/10] iommu: Add iommu_init/deinit_device() paired functions

[Jason Gunthorpe <jgg@nvidia.com>]

On Sun, May 21, 2023 at 07:31:38PM +0800, Baolu Lu wrote:
> I revisited this patch. And I still have some questions.
> 
> On 5/20/23 2:42 AM, Jason Gunthorpe wrote:
> > -/*
> > - * Remove the iommu_group from the struct device. The attached group must be put
> > - * by the caller after releaseing the group->mutex.
> > - */
> > +/* Remove the iommu_group from the struct device. */
> >   static void __iommu_group_remove_device(struct device *dev)
> >   {
> >   	struct iommu_group *group = dev->iommu_group;
> >   	struct group_device *device;
> > +	mutex_lock(&group->mutex);
> >   	lockdep_assert_held(&group->mutex);
> 
> By moving mutex_lock/unlock into this helper, above
> lockdep_assert_held() is unnecessary.

Woops, got it thanks

> The group->devices_kobj was increased on the probe device path twice:
> 
> - iommu_init_device() - allocate the group
> - iommu_group_add_device() - add device to the group
> 
> But, on the release path, it seems that group->devices_kobj is only
> decreased once.
> 
> Did I overlook anything? Otherwise, the group will never be released,
> right?

Your answer was right, when VFIO uses add/remove device it doesn't do
init_device.

Jason