linux-kernel - Re: [PATCH v3 07/11] iommufd/selftest: Add refcount to mock_iommu

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Message-ID: <20241017171326.GL3559746@nvidia.com>
Date: Thu, 17 Oct 2024 14:13:26 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...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, patches@...ts.linux.dev
Subject: Re: [PATCH v3 07/11] iommufd/selftest: Add refcount to
 mock_iommu_device

On Wed, Oct 09, 2024 at 09:38:07AM -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. Delay the exit routine 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 | 33 ++++++++++++++++++++++++--------
>  1 file changed, 25 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/iommu/iommufd/selftest.c b/drivers/iommu/iommufd/selftest.c
> index f4be87b49447..a89a865617db 100644
> --- a/drivers/iommu/iommufd/selftest.c
> +++ b/drivers/iommu/iommufd/selftest.c
> @@ -508,14 +508,17 @@ static bool mock_domain_capable(struct device *dev, enum iommu_cap cap)
>  
>  static struct iopf_queue *mock_iommu_iopf_queue;
>  
> -static struct iommu_device mock_iommu_device = {
> -};
> +static struct mock_iommu_device {
> +	struct iommu_device iommu_dev;
> +	wait_queue_head_t wait;

Just use a completion instead of a wait_queue, a few more bytes but it
is easier to code. This has some subtle issue where the device memory
could be freed while a concurrent thread is going to trigger the wait.

Jason