Summary
On a large-memory pod, the Moana Island render completes and writes its image, but the Cycles render process never exits. The main thread spins at 100% CPU with all worker threads parked, and the last renderer log line is a SyncAovBindings warning about an unknown pass elementId. The hang happens after a successful render, so it is distinct from both published failure modes: it is not the status-139 material-sync crash, and it is not a memory-limit result.
Configuration
- Cycles 5.2.0 (Hydra delegate), with the Blender cycles PR #75 material-sync change (the build validated for OpenChessSet on
test/cy2026-cycles-only)
- OpenUSD 26.03
- Container:
ghcr.io/nicolaspopravka/usd-render-benchmark-cycles@sha256:bad67a76cbfa5e342ee06049864555b8280630258a446a1db6d8f6fcba7c8d50
- NVIDIA RTX PRO 6000 Blackwell Server Edition, 96 GB VRAM, 188 GB system RAM
- NVIDIA driver 580.159.04
- Rocky Linux 8.10 (Green Obsidian), Linux 6.8.0-117
- Headless NVIDIA EGL through the release-matched
usdrecord wrapper
- Scene:
scenes/MoanaIsland/usd/island.usda, camera /island/cam/shotCam, --purposes render
Observed behavior
The render runs for roughly 14 minutes and writes island.jpg (960×402, 9,127 unique colors, mean RGB (218, 218, 250)). The process then does not terminate:
- About 19 minutes after the image was written, the process was still alive with the main thread spinning at exactly 100% CPU (201 ticks over a 2 s sample) and all 252 worker threads parked in
futex_wait_queue.
render.log is frozen. Its last line is:
Warning: in SyncAovBindings at line 154 of /opt/build/cycles/src/hydra/session.cpp -- Unknown pass elementId
- Peak resident memory was ~96.5 GiB of the 188 GiB available, so this is not memory pressure.
- gdb could not attach to the live process (the container lacks
CAP_SYS_PTRACE), so the spin site is not symbolized.
- A stock
usdrecord invocation would therefore never return. The pod was deleted after ~35 minutes of total runtime.
On the smaller pods this defect is never reached: the unpatched build segfaults during material sync (GH #25 class, fixed by PR #75), and the patched build on a ~29 GiB pod is killed by the cgroup OOM killer before completing (GH #9). Only a pod with enough memory to finish the render exposes the hang.
Logs and outputs
Follow-up
This is an hdCycles defect candidate: after the finished render, session work appears to wait on an unknown pass elementId while the main thread spins. When the next tagged Cycles release containing PR #75 lands and the full-scope rerun documented on GH #9 happens, capture a symbolized backtrace of the spin site (a debug build, or a runtime with CAP_SYS_PTRACE) and report upstream with this issue as the benchmark reference.
Summary
On a large-memory pod, the Moana Island render completes and writes its image, but the Cycles render process never exits. The main thread spins at 100% CPU with all worker threads parked, and the last renderer log line is a
SyncAovBindingswarning about an unknown pass elementId. The hang happens after a successful render, so it is distinct from both published failure modes: it is not the status-139 material-sync crash, and it is not a memory-limit result.Configuration
test/cy2026-cycles-only)ghcr.io/nicolaspopravka/usd-render-benchmark-cycles@sha256:bad67a76cbfa5e342ee06049864555b8280630258a446a1db6d8f6fcba7c8d50usdrecordwrapperscenes/MoanaIsland/usd/island.usda, camera/island/cam/shotCam,--purposes renderObserved behavior
The render runs for roughly 14 minutes and writes
island.jpg(960×402, 9,127 unique colors, mean RGB (218, 218, 250)). The process then does not terminate:futex_wait_queue.render.logis frozen. Its last line is:CAP_SYS_PTRACE), so the spin site is not symbolized.usdrecordinvocation would therefore never return. The pod was deleted after ~35 minutes of total runtime.On the smaller pods this defect is never reached: the unpatched build segfaults during material sync (GH #25 class, fixed by PR #75), and the patched build on a ~29 GiB pod is killed by the cgroup OOM killer before completing (GH #9). Only a pod with enough memory to finish the render exposes the hang.
Logs and outputs
docs/CY2026_CYCLES_MOANA_SEGV_DIAGNOSIS.mdon theopencode/runs/cycles-cy2026-moana-segv-diagnosisbranchmoana-segv-diagnosis-20260818T080451Z-bigpod/on the same branchFollow-up
This is an hdCycles defect candidate: after the finished render, session work appears to wait on an unknown pass elementId while the main thread spins. When the next tagged Cycles release containing PR #75 lands and the full-scope rerun documented on GH #9 happens, capture a symbolized backtrace of the spin site (a debug build, or a runtime with
CAP_SYS_PTRACE) and report upstream with this issue as the benchmark reference.