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Subject: Re: [PATCH v3 9/9] xen/gntdev: Implement dma-buf import functionality
To:     Oleksandr Andrushchenko <Oleksandr_Andrushchenko@epam.com>,
        Oleksandr Andrushchenko <andr2000@gmail.com>,
        xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org,
        dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org,
        jgross@suse.com, konrad.wilk@oracle.com
Cc:     daniel.vetter@intel.com, dongwon.kim@intel.com,
        matthew.d.roper@intel.com
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From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
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Message-ID: <0f1d87e5-823e-8b51-4ee5-029cc94eff99@oracle.com>
Date:   Wed, 13 Jun 2018 18:03:07 -0400
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Sender: linux-kernel-owner@vger.kernel.org
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On 06/13/2018 05:04 AM, Oleksandr Andrushchenko wrote:
> On 06/13/2018 06:14 AM, Boris Ostrovsky wrote:
>>
>>
>> On 06/12/2018 09:42 AM, Oleksandr Andrushchenko wrote:
>>
>>>   int gntdev_dmabuf_imp_release(struct gntdev_dmabuf_priv *priv, u32
>>> fd)
>>>   {
>>> -    return -EINVAL;
>>> +    struct gntdev_dmabuf *gntdev_dmabuf;
>>> +    struct dma_buf_attachment *attach;
>>> +    struct dma_buf *dma_buf;
>>> +
>>> +    gntdev_dmabuf = dmabuf_imp_find_unlink(priv, fd);
>>> +    if (IS_ERR(gntdev_dmabuf))
>>> +        return PTR_ERR(gntdev_dmabuf);
>>> +
>>> +    pr_debug("Releasing DMA buffer with fd %d\n", fd);
>>> +
>>> +    attach = gntdev_dmabuf->u.imp.attach;
>>> +
>>> +    if (gntdev_dmabuf->u.imp.sgt)
>>> +        dma_buf_unmap_attachment(attach, gntdev_dmabuf->u.imp.sgt,
>>> +                     DMA_BIDIRECTIONAL);
>>> +    dma_buf = attach->dmabuf;
>>> +    dma_buf_detach(attach->dmabuf, attach);
>>> +    dma_buf_put(dma_buf);
>>> +
>>> +    dmabuf_imp_end_foreign_access(gntdev_dmabuf->u.imp.refs,
>>> +                      gntdev_dmabuf->nr_pages);
>>
>>
>>
>> Should you first end foreign access, before doing anything?
>>
> I am rolling back in reverse order here, so I think we first need
> to finish local activities with the buffer and then end foreign
> access.

Looking at gntdev_dmabuf_imp_to_refs(), the order is
    dmabuf_imp_alloc_storage()
    dma_buf_attach()
    dma_buf_map_attachment()
    dmabuf_imp_grant_foreign_access()

Or was I looking at wrong place?

-boris