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SubjectRe: [RFC][PATCH 1/2] dma-buf: add importer private data to attachment
Hello Maarten,

On 2013년 06월 05일 22:23, Maarten Lankhorst wrote:
> Op 31-05-13 10:54, Seung-Woo Kim schreef:
>> dma-buf attachment has only exporter private data, but importer private data
>> can be useful for importer especially to re-import the same dma-buf.
>> To use importer private data in attachment of the device, the function to
>> search attachment in the attachment list of dma-buf is also added.
>>
>> Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
>> ---
>> drivers/base/dma-buf.c | 31 +++++++++++++++++++++++++++++++
>> include/linux/dma-buf.h | 4 ++++
>> 2 files changed, 35 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/base/dma-buf.c b/drivers/base/dma-buf.c
>> index 08fe897..a1eaaf2 100644
>> --- a/drivers/base/dma-buf.c
>> +++ b/drivers/base/dma-buf.c
>> @@ -259,6 +259,37 @@ err_attach:
>> EXPORT_SYMBOL_GPL(dma_buf_attach);
>>
>> /**
>> + * dma_buf_get_attachment - Get attachment with the device from dma_buf's
>> + * attachments list
>> + * @dmabuf: [in] buffer to find device from.
>> + * @dev: [in] device to be found.
>> + *
>> + * Returns struct dma_buf_attachment * attaching the device; may return
>> + * negative error codes.
>> + *
>> + */
>> +struct dma_buf_attachment *dma_buf_get_attachment(struct dma_buf *dmabuf,
>> + struct device *dev)
>> +{
>> + struct dma_buf_attachment *attach;
>> +
>> + if (WARN_ON(!dmabuf || !dev))
>> + return ERR_PTR(-EINVAL);
>> +
>> + mutex_lock(&dmabuf->lock);
>> + list_for_each_entry(attach, &dmabuf->attachments, node) {
>> + if (attach->dev == dev) {
>> + mutex_unlock(&dmabuf->lock);
>> + return attach;
>> + }
>> + }
>> + mutex_unlock(&dmabuf->lock);
>> +
>> + return ERR_PTR(-ENODEV);
>> +}
>> +EXPORT_SYMBOL_GPL(dma_buf_get_attachment);
> NAK in any form..
>
> Spot the race condition between dma_buf_get_attachment and dma_buf_attach....

Both dma_buf_get_attachment and dma_buf_attach has mutet with
dmabuf->lock, and dma_buf_get_attachment is used for get attachment from
same device before calling dma_buf_attach.

While, dma_buf_detach can removes attachment because it does not have
ref count. So importer should check ref count in its importer private
data before calling dma_buf_detach if the importer want to use
dma_buf_get_attachment.

And dma_buf_get_attachment is for the importer, so exporter attach and
detach callback operation should not call it as like exporter detach
callback operation should not call dma_buf_attach if you mean this kind
of race.

If you have other considerations here, please describe more specifically.

Thanks and Best Regards,
- Seung-Woo Kim

>
> ~Maarten
>
>

--
Seung-Woo Kim
Samsung Software R&D Center
--

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