linux-kernel - Re: [PATCH v2 3/4] iommufd: Destroy vdevice on idevice destroy

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Message-ID: <20250626143657.GK167785@nvidia.com>
Date: Thu, 26 Jun 2025 11:36:57 -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 v2 3/4] iommufd: Destroy vdevice on idevice destroy

On Thu, Jun 26, 2025 at 11:31:06AM +0800, Xu Yilun wrote:
> > The wait_event is a ugly hack though, even in its existing code. The
> > above version is better because it doesn't have any failure mode and
> > doesn't introduce any unlocked use of the idev->vdev which is easier
> > to reason about, no READ_ONCE/WRITE_ONCE/etc
> > 
> > It sounds like you should largely leave the existing other parts the
> > same as this v2, though can you try reorganize it to look a little
> > more like the version I shared?
> 
> Sure. But may I confirm that your only want reentrant
> iommufd_vdevice_abort() but not your iommufd_object_remove_tombstone()
> changes?

I think take a look at how I organized the control flow in the patch I
sent and try to use some of those ideas, it was a bit simpler

> To me, grab a shortterm_users but not a user is a new operation model. I
> hesitate to add it when the existing refcount_inc(&obj->user) works for
> this case.

Yes, I am convinced you should not do this. Just hold the users only
and use the normal destroy with the XA_ZERO_ENTRY change

Along with the locked abort idea.

Jason