On 01/27/2017 04:00 PM, Daniel Vetter wrote:
On Fri, Jan 27, 2017 at 09:04:25AM +0200, Oleksandr Andrushchenko wrote:
From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
From the description of the "DMA-BUF/GEM Object references
and lifetime overview" it is not clear when exactly
dma_buf gets destroyed and memory freed: only driver
.release function mentioned which makes confusion on the
real buffer's lifetime.
Add more description so all the paths are covered.
Cc: Rob Clark <robdclark@xxxxxxxxx>
Cc: Dave Airlie <airlied@xxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
---
drivers/gpu/drm/drm_prime.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 8d77b2462594..893a1a6311f0 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -40,8 +40,11 @@
* On the export the dma_buf holds a reference to the exporting GEM
* object. It takes this reference in handle_to_fd_ioctl, when it
* first calls .prime_export and stores the exporting GEM object in
- * the dma_buf priv. This reference is released when the dma_buf
- * object goes away in the driver .release function.
+ * the dma_buf priv. This refernce needs to be released when the
s/refernce/reference/
+ * final reference to the &dma_buf itself is dropped and its
+ * &dma_buf_ops.release function is called. For GEM-based drivers,
+ * the dma_buf should be exported using drm_gem_dmabuf_export() and
+ * then released by drm_gem_dmabuf_release().
*
* On the import the importing GEM object holds a reference to the
* dma_buf (which in turn holds a ref to the exporting GEM object).
@@ -51,6 +54,15 @@
* when the imported object is destroyed, we remove the attachment
* and drop the reference to the dma_buf.
*
+ * When all the references to the dma_buf are dropped, e.g. when
+ * userspace closes both handles to the imported (fd_to_handle_ioctl)
+ * and exported (handle_to_fd_ioctl) dma_buf and closes the corresponding
Usualla we call ioctls with uppercase, e.g. HANDLE_TO_FD IOCTL.
+ * file descriptor (handle_to_fd), then dma_buf gets destroyed.
+ * This can also happen as a part of the clean up procedure in the
+ * driver .release function if userspace fails to properly clean up.
Extended the references here to full file_ops one.
Since this is all tiny, I've done this while applying,
Thank you
thanks a lot for
your patch.
My pleasure
-Daniel
+ * Note that both the kernel and userspace (by keeeping the PRIME file
+ * descriptors open) can hold references onto a &dma_buf.
+ *
* Thus the chain of references always flows in one direction
* (avoiding loops): importing_gem -> dmabuf -> exporting_gem
*
--
2.7.4
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