Re: [PATCH v4 06/23] iommufd/driver: Add iommufd_struct_destroy to revert iommufd_viommu_alloc

[Nicolin Chen <nicolinc@nvidia.com>]

On Wed, May 14, 2025 at 03:26:00PM -0300, Jason Gunthorpe wrote:
> On Thu, May 08, 2025 at 08:02:27PM -0700, Nicolin Chen wrote:
> > An IOMMU driver that allocated a vIOMMU may want to revert the allocation,
> > if it encounters an internal error after the allocation. So, there needs a
> > destroy helper for drivers to use. For instance:
> > 
> > static my_viommu_alloc()
> > {
> > 	...
> > 	my_viommu = iommufd_viommu_alloc(viomm, struct my_viommu, core);
> > 	...
> > 	ret = init_my_viommu();
> > 	if (ret) {
> > 		/* Need to destroy the my_viommu->core */
> > 		return ERR_PTR(ret);
> > 	}
> > 	return &my_viommu->core;
> > }
> > 
> > Move iommufd_object_abort() to the driver.c file and the public header, to
> > introduce common iommufd_struct_destroy() helper that will abort all kinds
> > of driver structures, not confined to iommufd_viommu but also the new ones
> > being added in the future.
> > 
> > Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> > Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
> > Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> > ---
> >  drivers/iommu/iommufd/iommufd_private.h |  1 -
> >  include/linux/iommufd.h                 | 16 ++++++++++++++++
> >  drivers/iommu/iommufd/driver.c          | 14 ++++++++++++++
> >  drivers/iommu/iommufd/main.c            | 13 -------------
> >  4 files changed, 30 insertions(+), 14 deletions(-)
> 
> One idea that struck me when I was looking at this was to copy the
> technique from rdma.
> 
> When an object is allocated we keep track of it in the struct
> iommufd_ucmd.
> 
> Then when the command is over the core code either aborts or finalizes
> the objects in the iommufd_ucmd. This way you don't have to expose
> abort and related to drivers.

I see! Do you want this to apply to the all objects or just driver
allocated ones?

We would need a bigger preparatory series to roll out that to all
the allocators, and need to be careful at the existing abort() that
intertwines with other steps like an unlock().

Thanks
Nicolin