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

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Message-ID: <42e8c668-e72d-490a-8a5e-8e94af90fda4@linux.intel.com>
Date: Thu, 24 Apr 2025 17:22:48 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "Tian, Kevin" <kevin.tian@...el.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Jason Gunthorpe <jgg@...pe.ca>
Cc: baolu.lu@...ux.intel.com, "iommu@...ts.linux.dev"
 <iommu@...ts.linux.dev>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] iommu/vt-d: Simplify domain_attach_iommu()

On 4/24/2025 3:46 PM, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@...ux.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