Re: [PATCH v2 10/19] iommufd/viommu: Add vdev_id helpers for IOMMU drivers

On Mon, Oct 07, 2024 at 03:28:16PM -0300, Jason Gunthorpe wrote:

On Mon, Oct 07, 2024 at 10:25:01AM -0700, Nicolin Chen wrote:

...

This is for vdev/dev v.s. hwpt. We need the lock for viommu's vdev xarray.

Yet, giving a 2nd thought, I feel the lock would be useless if a driver tries to refer the returned vdev (with this helper) after the vdev object is destroyed..

We could only note something similar that caller must be aware of the life cycle of vdev itself..

Yes, I imagined you'd use the xa_lock for this an it solves both problems at once.

Ah! We don't even need a rwsem then..

Thanks! Nicolin