linux-kernel - Re: [PATCH 3/3] iommu/vt-d: Simplify domain_attach

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Message-ID: <680bd94098249_1d522945b@dwillia2-xfh.jf.intel.com.notmuch>
Date: Fri, 25 Apr 2025 11:49:36 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>, "Will
 Deacon" <will@...nel.org>, Robin Murphy <robin.murphy@....com>, "Jason
 Gunthorpe" <jgg@...pe.ca>, Kevin Tian <kevin.tian@...el.com>
CC: <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>, Lu Baolu
	<baolu.lu@...ux.intel.com>
Subject: Re: [PATCH 3/3] iommu/vt-d: Simplify domain_attach_iommu()

Lu Baolu wrote:
> Use the __free(kfree) attribute with kzalloc() to automatically handle
> the freeing of the allocated struct iommu_domain_info on error or early
> exit paths, eliminating the need for explicit kfree() calls in error
> handling branches.
> 
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  drivers/iommu/intel/iommu.c | 29 ++++++++---------------------
>  1 file changed, 8 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 3a9ea0ad2cd3..12382c85495f 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -1337,13 +1337,14 @@ static bool first_level_by_default(struct intel_iommu *iommu)
>  
>  int domain_attach_iommu(struct dmar_domain *domain, struct intel_iommu *iommu)
>  {
> -	struct iommu_domain_info *info, *curr;
> -	int num, ret = -ENOSPC;
> +	struct iommu_domain_info *curr;
> +	int num;
>  
>  	if (domain->domain.type == IOMMU_DOMAIN_SVA)
>  		return 0;
>  
> -	info = kzalloc(sizeof(*info), GFP_KERNEL);
> +	struct iommu_domain_info *info __free(kfree) =
> +		kzalloc(sizeof(*info), GFP_KERNEL);
>  	if (!info)
>  		return -ENOMEM;
>  
> @@ -1351,34 +1352,20 @@ int domain_attach_iommu(struct dmar_domain *domain, struct intel_iommu *iommu)
[..]
> -err_clear:
> -	ida_free(&iommu->domain_ida, info->did);
> -err_unlock:
> -	kfree(info);
> -	return ret;
> +	return xa_err(xa_store(&domain->iommu_array, iommu->seq_id,
> +			       no_free_ptr(info), GFP_KERNEL));
>  }

This pattern looks like it wants a "xa_store_or_{reset,kfree}()" helper that
handles both canceling a scope based cleanup and taking responsibility for
error-exit-freeing @info in one statement.

I.e. this is similar to a:

	"return devm_add_action_or_reset(..., no_free_ptr(obj), ...)"

...pattern.