Re: [RFC PATCH 1/3] drm/virtio: .release ops for virtgpu fence release

["Kim, Dongwon" <dongwon.kim@intel.com>]

On 8/16/2023 10:05 PM, Dmitry Osipenko wrote:
> On 8/16/23 21:10, Kim, Dongwon wrote:
>> Hi,
>>
>> On 8/14/2023 9:18 PM, Dmitry Osipenko wrote:
>>> On 7/13/23 01:44, Dongwon Kim wrote:
>>>> virtio_gpu_fence_release is added to free virtio-gpu-fence
>>>> upon release of dma_fence.
>>>>
>>>> Cc: Gerd Hoffmann <kraxel@redhat.com>
>>>> Cc: Vivek Kasireddy <vivek.kasireddy@intel.com>
>>>> Signed-off-by: Dongwon Kim <dongwon.kim@intel.com>
>>>> ---
>>>>    drivers/gpu/drm/virtio/virtgpu_fence.c | 8 ++++++++
>>>>    1 file changed, 8 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/virtio/virtgpu_fence.c
>>>> b/drivers/gpu/drm/virtio/virtgpu_fence.c
>>>> index f28357dbde35..ba659ac2a51d 100644
>>>> --- a/drivers/gpu/drm/virtio/virtgpu_fence.c
>>>> +++ b/drivers/gpu/drm/virtio/virtgpu_fence.c
>>>> @@ -63,12 +63,20 @@ static void virtio_gpu_timeline_value_str(struct
>>>> dma_fence *f, char *str,
>>>>             (u64)atomic64_read(&fence->drv->last_fence_id));
>>>>    }
>>>>    +static void virtio_gpu_fence_release(struct dma_fence *f)
>>>> +{
>>>> +    struct virtio_gpu_fence *fence = to_virtio_gpu_fence(f);
>>>> +
>>>> +    kfree(fence);
>>>> +}
>>>> +
>>>>    static const struct dma_fence_ops virtio_gpu_fence_ops = {
>>>>        .get_driver_name     = virtio_gpu_get_driver_name,
>>>>        .get_timeline_name   = virtio_gpu_get_timeline_name,
>>>>        .signaled            = virtio_gpu_fence_signaled,
>>>>        .fence_value_str     = virtio_gpu_fence_value_str,
>>>>        .timeline_value_str  = virtio_gpu_timeline_value_str,
>>>> +    .release         = virtio_gpu_fence_release,
>>>>    };
>>>>      struct virtio_gpu_fence *virtio_gpu_fence_alloc(struct
>>>> virtio_gpu_device *vgdev,
>>> This change doesn't do anything practically useful, AFAICT.
>> The intention of this ".release" is to free virtio_gpu_fence when the
>> last dma_fence_put is done for the associated dma fence.
> What makes you think that fence won't be freed otherwise? Sounds like
> haven't tried to check what dma_fence_release() code does, have you?

I see it now. For some reason, I assumed virtio_gpu_fence holds the 
pointer of dma_fence. This release ops is indeed not needed as you 
mentioned. Thanks

>