[PATCH 1/2] drm/prime: keep a reference from the handle to exported dma-buf (v6)

[Daniel Vetter]

On Mon, Apr 22, 2013 at 09:54:36AM +1000, Dave Airlie wrote:
> Currently we have a problem with this:
> 1. i915: create gem object
> 2. i915: export gem object to prime
> 3. radeon: import gem object
> 4. close prime fd
> 5. radeon: unref object
> 6. i915: unref object
> 
> i915 has an imported object reference in its file priv, that isn't
> cleaned up properly until fd close. The reference gets added at step 2,
> but at step 6 we don't have enough info to clean it up.
> 
> The solution is to take a reference on the dma-buf when we export it,
> and drop the reference when the gem handle goes away.
> 
> So when we export a dma_buf from a gem object, we keep track of it
> with the handle, we take a reference to the dma_buf. When we close
> the handle (i.e. userspace is finished with the buffer), we drop
> the reference to the dma_buf, and it gets collected.
> 
> This patch isn't meant to fix any other problem or bikesheds, and it doesn't
> fix any races with other scenarios.
> 
> v1.1: move export symbol line back up.
> 
> v2: okay I had to do a bit more, as the first patch showed a leak
> on one of my tests, that I found using the dma-buf debugfs support,
> the problem case is exporting a buffer twice with the same handle,
> we'd add another export handle for it unnecessarily, however
> we now fail if we try to export the same object with a different gem handle,
> however I'm not sure if that is a case I want to support, and I've
> gotten the code to WARN_ON if we hit something like that.
> 
> v2.1: rebase this patch, write better commit msg.
> v3: cleanup error handling, track import vs export in linked list,
> these two patches were separate previously, but seem to work better
> like this.
> v4: danvet is correct, this code is no longer useful, since the buffer
> better exist, so remove it.
> v5: always take a reference to the dma buf object, import or export.
> (Imre Deak contributed this originally)
> v6: square the circle, remove import vs export tracking now
> that there is no difference
> 
> Signed-off-by: Dave Airlie <airlied at redhat.com>

Reviewing the right patch is apparently recommneded ;-)

Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch