On (22/06/01 16:38), Christian König wrote:
Well, you don't.
If you have a dynamic context structure you need to reference count that as well. In other words every time you create a fence in your context you need to increment the reference count and every time a fence is release you decrement it.
OK then fence release should be able to point back to its "context" structure. Either a "private" data in dma fence or we need to "embed" fence into another object (refcounted) that owns the lock and provide dma fence ops->release callback, which can container_of() to the object that dma fence is embedded into.
I think you are suggesting the latter. Thanks for clarifications.
Daniel might hurt me for this, but if you really only need a pointer to your context then we could say that using a pointer value for the context field is ok as well.
That should be fine as well as long as you can guarantee that it will be unique during the lifetime of all it's fences.
I think we can guarantee that. Object that creates fence is kmalloc-ed and it sticks around until dma_fence_release() calls ops->release() and kfree-s it. We *probably* can even do something like it now, by re-purposing dma_fence context member:
dma_fence_init(obj->fence, &fence_ops, &obj->fence_lock, (u64)obj, << :/ atomic64_inc_return(&obj->seqno));
I'd certainly refrain from being creative here and doing things that are not documented/common. DMA fence embedding should work for us.
The limiting factor of this approach is that now our ops->release() is under the same "pressure" as dma_fence_put()->dma_fence_release() are. dma_fence_put() and dma_fence_release() can be called from any context, as far as I understand, e.g. IRQ, however our normal object ->release can schedule, we do things like synchronize_rcu() and so on. Nothing is impossible, just saying that even this approach is not 100% perfect and may need additional workarounds.
Well just use a work item for release.
Yup, that's the plan.