Rare crashes in RenderGraphBuilder / FRDGBuilder / TRDGHandle

Development Rendering
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1

Hello there,

We have some crashes concerning RenderGraphBuilder reported by Sentry on our Shipping build.

The 4 different callstack we have are pointing to:

  • TRDGHandle<T>::operator< (RenderGraphDefinitions.h:366)
  • FRDGBuilder::GetReservedCommitSize (RenderGraphBuilder.h:974)
  • FRDGBuilder::FlushCullStack (RenderGraphBuilder.cpp:1304)
  • FRDGBuilder::AddPassDependency (RenderGraphBuilder.cpp:1152)

No information found on EPS, nor on the Unreal Github.

I’m not sure how to tackle it, so I was wondering if maybe these crashes are known and a fix is on the way ?

Thank you,

Thomas

2

Steps to Reproduce
No repro steps yet.

3

Hello,

5.6.1 has some fixes in these areas. If you are already on 5.6.1, for the first callstack it’s possible there is a race condition in FRDGBuilder::ProcessAsyncSetupQueue and this changelist may be relevant or help as guides to how fixes have been made in this area

CL#43813963 Replaced FPipe with explicit task chain as a speculative fix to async setup queue race.

Also possibly related:

[CL#44451049 Fixed crash in RDG due to external access subresource being null at [0].](https://github.com/EpicGames/UnrealEngine/commit/38428fa1bdfc27ff893dc5cfd0603807454bb040)

CL#50784410 Make GRDGAllowRHIAccess atomic to silence TSAN. Also moved pass bit to other async setup queue union where it’s accessed instead.

For Callstack #2, #3 and #4 we don’t have any known issues, they’re likely related and possibly CL#43813963 above may address these too. If you ever get a repro you could test with r.RDG.ParallelSetup=0.

Hope this helps!

4

Thank you Alex, I will check that asap !