linux-kernel - Re: [PATCH v5 09/13] iommufd/selftest: Add refcount to mock_iommu

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Message-ID: <ZyEHMr7bQi0fFoUv@Asurada-Nvidia>
Date: Tue, 29 Oct 2024 09:02:58 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: <kevin.tian@...el.com>, <will@...nel.org>, <joro@...tes.org>,
	<suravee.suthikulpanit@....com>, <robin.murphy@....com>,
	<dwmw2@...radead.org>, <baolu.lu@...ux.intel.com>, <shuah@...nel.org>,
	<linux-kernel@...r.kernel.org>, <iommu@...ts.linux.dev>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kselftest@...r.kernel.org>,
	<eric.auger@...hat.com>, <jean-philippe@...aro.org>, <mdf@...nel.org>,
	<mshavit@...gle.com>, <shameerali.kolothum.thodi@...wei.com>,
	<smostafa@...gle.com>, <yi.l.liu@...el.com>, <aik@....com>,
	<zhangfei.gao@...aro.org>, <patches@...ts.linux.dev>
Subject: Re: [PATCH v5 09/13] iommufd/selftest: Add refcount to
 mock_iommu_device

On Tue, Oct 29, 2024 at 12:34:38PM -0300, Jason Gunthorpe wrote:
> On Fri, Oct 25, 2024 at 04:49:49PM -0700, Nicolin Chen wrote:
> > For an iommu_dev that can unplug (so far only this selftest does so), the
> > viommu->iommu_dev pointer has no guarantee of its life cycle after it is
> > copied from the idev->dev->iommu->iommu_dev.
> > 
> > Track the user count of the iommu_dev. Postpone the exit routine using a
> > completion, if refcount is unbalanced. The refcount inc/dec will be added
> > in the following patch.
> > 
> > Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> > ---
> >  drivers/iommu/iommufd/selftest.c | 32 ++++++++++++++++++++++++--------
> >  1 file changed, 24 insertions(+), 8 deletions(-)
> 
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> 
> Since this is built into the iommufd module it can't be unloaded
> without also unloading iommufd, which is impossible as long as any
> iommufd FDs are open. So I expect that the WARN_ON can never happen.

Hmm, I assume we still need this patch then?

Could a faulty "--force" possibly trigger it?

Nicolin