On 2013년 06월 07일 20:24, Maarten Lankhorst wrote:
Op 07-06-13 04:32, 김승우 schreef:
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.
hint: what happens if 2 threads do this:
if (IS_ERR(attach = dma_buf_get_attachment(buf, dev))) attach = dma_buf_attach(buf, dev);
There really is no correct usecase for this kind of thing, so please don't do it.
Ok, dma_buf_get_attachment can not prevent attachments from one device.
Anyway, do you think that importer side private data, not to allow re-import one dma-buf to a device, has some advantage? If that, I'll add some check_and_attach function, otherwise, I'll find other way.
Thanks and Regards, - Seung-Woo Kim
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
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