linux-kernel - Re: [PATCH v4 3/7] iommufd: Add a pre

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Message-ID: <aHGLrJnGUVdkO3SF@Asurada-Nvidia>
Date: Fri, 11 Jul 2025 15:09:48 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Xu Yilun <yilun.xu@...ux.intel.com>
CC: <jgg@...dia.com>, <jgg@...pe.ca>, <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>, <aik@....com>, <dan.j.williams@...el.com>,
	<baolu.lu@...ux.intel.com>, <yilun.xu@...el.com>
Subject: Re: [PATCH v4 3/7] iommufd: Add a pre_destroy() op for objects

On Wed, Jul 09, 2025 at 12:02:30PM +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>
> Signed-off-by: Xu Yilun <yilun.xu@...ux.intel.com>

Reviewed-by: Nicolin Chen <nicolinc@...dia.com>