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

[Sebastian Ott]

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?