Am 31.05.22 um 04:51 schrieb Sergey Senozhatsky:
On (22/05/30 16:55), Christian König wrote:
Am 30.05.22 um 16:22 schrieb Sergey Senozhatsky:
[SNIP]
So the `lock` should have at least same lifespan as the DMA fence
that borrows it, which is impossible to guarantee in our case.
Nope, that's not correct. The lock should have at least same lifespan as the
context of the DMA fence.
How does one know when it's safe to release the context? DMA fence
objects are still transparently refcount-ed and "live their own lives",
how does one synchronize lifespans?
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.
If you have a static context structure like most drivers have then you
must make sure that all fences at least signal before you unload your
driver. We still somewhat have a race when you try to unload a driver
and the fence_ops structure suddenly disappear, but we currently live
with that.
Apart from that you are right, fences can live forever and we need to
deal with that.
Regards,
Christian.
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