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

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Message-ID: <8373789b-929e-4ad9-ab0b-6ec620719a7e@linux.intel.com>
Date: Sun, 27 Apr 2025 13:10:24 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Dan Williams <dan.j.williams@...el.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
Subject: Re: [PATCH 3/3] iommu/vt-d: Simplify domain_attach_iommu()

On 4/26/25 02:49, Dan Williams wrote:
> 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.
> 

Yes. Perhaps adding a xa_store variant would be beneficial in all
places that require this pattern.

Something like this?

diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index 78eede109b1a..efbdff7ebda4 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -626,6 +626,35 @@ static inline void *xa_store_irq(struct xarray *xa, 
unsigned long index,
         return curr;
  }

+/**
+ * xa_store_or_kfree() - Store this entry in the XArray.
+ * @xa: XArray.
+ * @index: Index into array.
+ * @entry: New entry.
+ * @gfp: Memory allocation flags.
+ *
+ * This function is like calling xa_store() except it kfrees the new
+ * entry if an error happened.
+ *
+ * Context: Process context. Any context. Takes and releases the xa_lock.
+ * May sleep if the @gfp flags permit.
+ * Return: The old entry at this index or xa_err() if an error happened.
+ */
+static inline void *xa_store_or_kfree(struct xarray *xa, unsigned long 
index,
+               void *entry, gfp_t gfp)
+{
+       void *curr;
+
+       xa_lock(xa);
+       curr = __xa_store(xa, index, entry, gfp);
+       xa_unlock(xa);
+
+       if (xa_err(curr))
+               kfree(entry);
+
+       return curr;
+}
+
  /**
   * xa_erase_bh() - Erase this entry from the XArray.
   * @xa: XArray.

Thanks,
baolu