[PATCH 2/2] dma-buf/fence-array: hold fences reference when creating an array

[Christian König]

Am 19.10.2016 um 20:35 schrieb Gustavo Padovan:
> 2016-10-19 Christian König <deathsimple at vodafone.de>:
>
>> Am 19.10.2016 um 19:48 schrieb Gustavo Padovan:
>>> From: Gustavo Padovan <gustavo.padovan at collabora.co.uk>
>>>
>>> When creating fence arrays we were not holding references to the fences
>>> in the array, however when destroy the array we were putting away a
>>> reference to these fences.
>>>
>>> This patch hold the ref for all fences in the array when creating the
>>> array.
>>>
>>> It then removes the code that was holding the fences on both amdgpu_vm and
>>> sync_file. For sync_file, specially, we worked on small referencing
>>> refactor for sync_file_merge().
>>>
>>> Signed-off-by: Gustavo Padovan <gustavo.padovan at collabora.co.uk>
>> I would prefer it to keep it like it is, cause this is a bit inconsistent.
>>
>> With this change the fence array takes the ownership of the array, but not
>> of the fences inside it.
> I was thinking more in to keep consistency between all fence users. Every
> user should hold a ref to the fence assigned to it. That is what patch
> 1 is doing for sync_file and think it is a good idea do the same here.

This might make the code easier to follow, but isn't necessary a good idea.

Usually with reference counted objects you increase the count every time 
the pointer to the object is assigned to a container. E.g. member of a 
larger structure or in this case an array of pointers.

>
> The array itself is not refcounted and the users calling
> fence_array_create() doesn't store the allocated array anywhere. The
> comment I errouneously removed already states that.

And exactly that's the point here. The array is the container for the 
pointers referencing the objects, since you give the ownership of this 
container to the fence_array object it is now responsible for releasing 
that reference before it releases the array.

This is good coding practice as far as I know.

Regards,
Christian.

>
> Gustavo
>