linux-kernel - Re: [PATCH v5 3/8] iommufd: Add a pre

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Message-ID: <20250715131939.GN2067380@nvidia.com>
Date: Tue, 15 Jul 2025 10:19:39 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Xu Yilun <yilun.xu@...ux.intel.com>
Cc: kevin.tian@...el.com, will@...nel.org, aneesh.kumar@...nel.org,
	iommu@...ts.linux.dev, linux-kernel@...r.kernel.org,
	joro@...tes.org, robin.murphy@....com, shuah@...nel.org,
	nicolinc@...dia.com, aik@....com, dan.j.williams@...el.com,
	baolu.lu@...ux.intel.com, yilun.xu@...el.com
Subject: Re: [PATCH v5 3/8] iommufd: Add a pre_destroy() op for objects

On Tue, Jul 15, 2025 at 02:32:40PM +0800, Xu Yilun wrote:
> Add a pre_destroy() op which gives objects a chance to clear their
> short term users references before destruction. This op is intended for
> external driver created objects (e.g. idev) which does deterministic
> destruction.
> 
> In order to manage the lifecycle of interrelated objects as well as the
> deterministic destruction (e.g. vdev can't outlive idev, and idev
> destruction can't fail), short term users references are allowed to
> live out of an ioctl execution. An immediate use case is, vdev holds
> idev's short term user reference until vdev destruction completes, idev
> leverages existing wait_shortterm mechanism to ensure it is destroyed
> after vdev.
> 
> This extended usage makes the referenced object unable to just wait for
> its reference gone. It needs to actively trigger the reference removal,
> as well as prevent new references before wait. Should implement these
> work in pre_destroy().
> 
> Suggested-by: Jason Gunthorpe <jgg@...dia.com>
> Reviewed-by: Kevin Tian <kevin.tian@...el.com>
> Reviewed-by: Nicolin Chen <nicolinc@...dia.com>
> Signed-off-by: Xu Yilun <yilun.xu@...ux.intel.com>
> ---
>  drivers/iommu/iommufd/main.c | 4 ++++
>  1 file changed, 4 insertions(+)

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

>  struct iommufd_object_ops {
> +	void (*pre_destroy)(struct iommufd_object *obj);

I would capture the key points of the commit message in a comment
right here though..

Jason