linux-kernel - Re: [PATCH 13/16] nvme-pci: Convert to using dma_map_sg

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Message-ID: <92116e67-7388-aa31-cff3-71a7da82a731@nvidia.com>
Date:   Mon, 3 May 2021 17:26:57 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Logan Gunthorpe <logang@...tatee.com>,
        <linux-kernel@...r.kernel.org>, <linux-nvme@...ts.infradead.org>,
        <linux-block@...r.kernel.org>, <linux-pci@...r.kernel.org>,
        <linux-mm@...ck.org>, <iommu@...ts.linux-foundation.org>
CC:     Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian König <christian.koenig@....com>,
        Don Dutile <ddutile@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Jakowski Andrzej <andrzej.jakowski@...el.com>,
        Minturn Dave B <dave.b.minturn@...el.com>,
        Jason Ekstrand <jason@...kstrand.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Xiong Jianxin <jianxin.xiong@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 13/16] nvme-pci: Convert to using dma_map_sg_p2pdma for
 p2pdma pages

On 5/3/21 10:19 AM, Logan Gunthorpe wrote:
...
>>> +	nr_mapped = dma_map_sg_p2pdma_attrs(dev->dev, iod->sg, iod->nents,
>>> +				     rq_dma_dir(req), DMA_ATTR_NO_WARN);
>>> +	if (nr_mapped < 0) {
>>> +		if (nr_mapped != -ENOMEM)
>>> +			ret = BLK_STS_TARGET;
>>>    		goto out_free_sg;
>>> +	}
>>
>> But now the "nr_mapped == 0" case is no longer doing an early out_free_sg.
>> Is that OK?
> 
> dma_map_sg_p2pdma_attrs() never returns zero. It will return -ENOMEM in
> the same situation and results in the same goto out_free_sg.
> 

OK...that's true, it doesn't return zero. A comment or WARN or something
might be nice, to show that the zero case hasn't been overlooked. It's
true that the dma_map_sg_p2pdma_attrs() documentation sort of says
that (although not quite out loud).

thanks,
-- 
John Hubbard
NVIDIA