After CUDA Graph capture (which disables/re-enables event tracking),
CudaSlices modified during capture have stale write events. Any cudarc
API call (memcpy_dtoh, synchronize, launch_builder.arg) on these slices
fails with CUDA_ERROR_INVALID_VALUE because cuStreamWaitEvent gets an
invalid event handle.
Fix: use raw CUDA driver calls for ALL post-graph operations:
- cuStreamSynchronize instead of cudarc synchronize() (avoids bind_to_thread)
- cuMemcpyDtoH_v2 via raw_device_ptr for scalar readbacks (2 × 4 bytes)
- raw_device_ptr for EMA kernel args (bypasses device_ptr event wait)
Event tracking remains enabled globally — only the 3 post-graph call sites
use raw driver calls. All other cudarc operations (cat/stack, alloc, etc.)
work normally with event tracking.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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