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

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Message-ID: <20250424133759.GA1213339@ziepe.ca>
Date: Thu, 24 Apr 2025 10:37:59 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Baolu Lu <baolu.lu@...ux.intel.com>
Cc: "Tian, Kevin" <kevin.tian@...el.com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....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 Thu, Apr 24, 2025 at 05:22:48PM +0800, Baolu Lu wrote:

> > > -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.

That's not the kernel pattern, you are supposed to unwind correctly in
those failures

I think you should not use cleanup.h for something complicated like
this..

Jason