Am 30.11.21 um 13:56 schrieb Thomas Hellström:
On 11/30/21 13:42, Christian König wrote:
Am 30.11.21 um 13:31 schrieb Thomas Hellström:
[SNIP]
Other than that, I didn't investigate the nesting fails enough to
say I can accurately review this. :)
Basically the problem is that within enable_signaling() which is
called with the dma_fence lock held, we take the dma_fence lock of
another fence. If that other fence is a dma_fence_array, or a
dma_fence_chain which in turn tries to lock a dma_fence_array we hit
a splat.
Yeah, I already thought that you constructed something like that.
You get the splat because what you do here is illegal, you can't mix
dma_fence_array and dma_fence_chain like this or you can end up in a
stack corruption.
Hmm. Ok, so what is the stack corruption, is it that the
enable_signaling() will end up with endless recursion? If so, wouldn't
it be more usable we break that recursion chain and allow a more
general use?
The problem is that this is not easily possible for dma_fence_array
containers. Just imagine that you drop the last reference to the
containing fences during dma_fence_array destruction if any of the
contained fences is another container you can easily run into recursion
and with that stack corruption.
That's one of the major reasons I came up with the dma_fence_chain
container. This one you can chain any number of elements together
without running into any recursion.
Also what are the mixing rules between these? Never use a
dma-fence-chain as one of the array fences and never use a
dma-fence-array as a dma-fence-chain fence?
You can't add any other container to a dma_fence_array, neither other
dma_fence_array instances nor dma_fence_chain instances.
IIRC at least technically a dma_fence_chain can contain a
dma_fence_array if you absolutely need that, but Daniel, Jason and I
already had the same discussion a while back and came to the conclusion
to avoid that as well if possible.
Regards,
Christian.
/Thomas
Regards,
Christian.
But I'll update the commit message with a typical splat.
/Thomas
