Re: [PATCH v7 09/28] iommufd/access: Add internal APIs for HW queue to use

Jason Gunthorpe
2025-07-04T13:30:43Z

On Thu, Jun 26, 2025 at 12:34:40PM -0700, Nicolin Chen wrote:
> The new HW queue object, as an internal iommufd object, wants to reuse the
> struct iommufd_access to pin some iova range in the iopt.
>
> However, an access generally takes the refcount of an ictx. So, in such an
> internal case, a deadlock could happen when the release of the ictx has to
> wait for the release of the access first when releasing a hw_queue object,
> which could wait for the release of the ictx that is refcounted:
> ictx --releases--> hw_queue --releases--> access
> ^ |
> |_________________releases________________v
>
> To address this, add a set of lightweight internal APIs to unlink the ictx
> and the access, i.e. no ictx refcounting by the access:
> ictx --releases--> hw_queue --releases--> access
>
> Then, there's no point in setting the access->ictx. So simply define !ictx
> as an flag for an internal use and add an inline helper.
>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
> drivers/iommu/iommufd/iommufd_private.h | 23 ++++++++++
> drivers/iommu/iommufd/device.c | 59 +++++++++++++++++++++----
> 2 files changed, 73 insertions(+), 9 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason