Re: [PATCH 3/3] iommu/vt-d: Simplify domain_attach_iommu()

[Baolu Lu <baolu.lu@linux.intel.com>]

On 4/24/2025 3:46 PM, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@linux.intel.com>
>> Sent: Wednesday, April 23, 2025 11:10 AM
>>
>>   	num = ida_alloc_range(&iommu->domain_ida, FLPT_DEFAULT_DID +
>> 1,
>>   			      cap_ndoms(iommu->cap) - 1, GFP_KERNEL);
>> -	if (num < 0) {
>> -		pr_err("%s: No free domain ids\n", iommu->name);
> 
> this error message could be kept.

Okay.

> 
>> -		goto err_unlock;
>> -	}
>> +	if (num < 0)
>> +		return num;
>>
>>   	info->refcnt	= 1;
>>   	info->did	= num;
>>   	info->iommu	= iommu;
>> -	curr = xa_cmpxchg(&domain->iommu_array, iommu->seq_id,
>> -			  NULL, info, GFP_KERNEL);
>> -	if (curr) {
>> -		ret = xa_err(curr) ? : -EBUSY;
>> -		goto err_clear;
>> -	}
>>
>> -	return 0;
>> -
>> -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));
>>   }
> 
> no_free_ptr() should be used before successful return. Here xa_store()
> could return error but at that point no auto free as no_free_ptr() already
> changes 'info' to NULL. then memory leak.
Hmm, I've considered this. My thought was that xa_store() failure only
occurs due to the system running out of memory, and the Linux kernel
can't recover from it. In that case, the system is already broken;
hence, handling the failure case here doesn't make things better.

Thanks,
baolu