linux-kernel - Re: WARNING: drivers/iommu/io-pgtable-arm.c:639

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Message-ID: <0eec3806-c002-54d5-95a9-7fa201c6b921@redhat.com>
Date: Wed, 10 Dec 2025 18:12:02 +0100 (CET)
From: Sebastian Ott <sebott@...hat.com>
To: Chaitanya Kulkarni <chaitanyak@...dia.com>
cc: Keith Busch <kbusch@...nel.org>, 
    "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>, 
    "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>, 
    Robin Murphy <robin.murphy@....com>, 
    "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>, 
    "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
    "linux-xfs@...r.kernel.org" <linux-xfs@...r.kernel.org>, 
    Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>, 
    Will Deacon <will@...nel.org>, Carlos Maiolino <cem@...nel.org>, 
    Leon Romanovsky <leon@...nel.org>
Subject: Re: WARNING: drivers/iommu/io-pgtable-arm.c:639

On Wed, 10 Dec 2025, Chaitanya Kulkarni wrote:
> (+ Leon Romanovsky)
>
> On 12/9/25 20:05, Keith Busch wrote:
>> On Wed, Dec 10, 2025 at 02:30:50AM +0000, Chaitanya Kulkarni wrote:
>>> @@ -126,17 +126,26 @@ static bool blk_rq_dma_map_iova(struct request *req, struct device *dma_dev,
>>>    		error = dma_iova_link(dma_dev, state, vec->paddr, mapped,
>>>    				vec->len, dir, attrs);
>>>    		if (error)
>>> -			break;
>>> +			goto out_unlink;
>>>    		mapped += vec->len;
>>>    	} while (blk_map_iter_next(req, &iter->iter, vec));
>>>
>>>    	error = dma_iova_sync(dma_dev, state, 0, mapped);
>>> -	if (error) {
>>> -		iter->status = errno_to_blk_status(error);
>>> -		return false;
>>> -	}
>>> +	if (error)
>>> +		goto out_unlink;
>>>
>>>    	return true;
>>> +
>>> +out_unlink:
>>> +	/*
>>> +	 * Unlink any partial mapping to avoid unmap mismatch later.
>>> +	 * If we mapped some bytes but not all, we must clean up now
>>> +	 * to prevent attempting to unmap more than was actually mapped.
>>> +	 */
>>> +	if (mapped)
>>> +		dma_iova_unlink(dma_dev, state, 0, mapped, dir, attrs);
>>> +	iter->status = errno_to_blk_status(error);
>>> +	return false;
>>>    }
>> It does look like a bug to continue on when dma_iova_link() fails as the
>> caller thinks the entire mapping was successful, but I think you also
>> need to call dma_iova_free() to undo the earlier dma_iova_try_alloc(),
>> otherwise iova space is leaked.
>
> Thanks for catching that, see updated version of this patch [1].
>
>> I'm a bit doubtful this error condition was hit though: this sequence
>> is largely the same as it was in v6.18 before the regression. The only
>> difference since then should just be for handling P2P DMA across a host
>> bridge, which I don't think applies to the reported bug since that's a
>> pretty unusual thing to do.
>
> That's why I've asked reporter to test it.
>
> Either way, IMO both of the patches are still needed.
>

The patch Keith posted fixes the issue for me. Should I do another run
with only these 2 applied?