linux-kernel - Re: [PATCH v5 10/29] iommufd: Abstract iopt_pin_pages and iopt_unpin

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Message-ID: <20250605194034.GF19710@nvidia.com>
Date: Thu, 5 Jun 2025 16:40:34 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: kevin.tian@...el.com, corbet@....net, will@...nel.org,
	bagasdotme@...il.com, robin.murphy@....com, joro@...tes.org,
	thierry.reding@...il.com, vdumpa@...dia.com, jonathanh@...dia.com,
	shuah@...nel.org, jsnitsel@...hat.com, nathan@...nel.org,
	peterz@...radead.org, yi.l.liu@...el.com, mshavit@...gle.com,
	praan@...gle.com, zhangzekun11@...wei.com, iommu@...ts.linux.dev,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-tegra@...r.kernel.org,
	linux-kselftest@...r.kernel.org, patches@...ts.linux.dev,
	mochs@...dia.com, alok.a.tiwari@...cle.com, vasant.hegde@....com,
	dwmw2@...radead.org, baolu.lu@...ux.intel.com
Subject: Re: [PATCH v5 10/29] iommufd: Abstract iopt_pin_pages and
 iopt_unpin_pages helpers

On Thu, Jun 05, 2025 at 10:04:35AM -0700, Nicolin Chen wrote:
> On Thu, Jun 05, 2025 at 12:16:48PM -0300, Jason Gunthorpe wrote:
> > On Wed, Jun 04, 2025 at 09:11:07PM -0700, Nicolin Chen wrote:
> > 
> > > I found the entire ictx would be locked by iommufd_access_create(),
> > > then the release fop couldn't even get invoked to destroy objects.
> > 
> > Yes, that makes sense..
> > 
> > It looks to me like you can safely leave ictx as NULL instead of
> > adding a flag? That would be nicer than leaving a unrefcounted
> > pointer floating around..
> 
> Hmm, there are a few iommufd_get_object calls using access->ictx
> in iommufd_access_attach() and iommufd_access_destroy().

I counted:

iommufd_access_change_ioas_id
 * Don't call this
iommufd_access_destroy_object
 * Don't put if null
iommufd_access_create
 * Don't set it
iommufd_access_destroy
 * Call iommufd_object_destroy_user directly
iommufd_access_notify_unmap
 * Check for null access->ops->unmap and skip the lock_obj/put_obj

Jason