Am 01.06.22 um 16:52 schrieb Sergey Senozhatsky:
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.
Yeah, exactly that's the idea. But if you are fine to create a subclass
of the dma_fence than that would indeed be cleaner.
Christian.
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.
