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

[Baolu Lu]

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