[BUG]: [Unity 2021.3.18f1] Kernel-mode deadlock in NtGdiDdDDIDestroyAllocation2 during webrtc!UnityPluginUnload (Unkillable zombie process after 48h+ run)

[JhonJHUtd]

Package version

3.1.0-exp.8

Environment

* OS:Windows10
* Unity version:Unity 2021.3
* Graphics API:DirectX11
* Browser:Microsoft Edge 145.0.3800.70

Steps To Reproduce

Summary
Our Unity Windows build (LTS 2021.3.18f1) consistently becomes unresponsive after long-term execution (typically after 48+ hours). Once the program hangs, it enters a "zombie" state where the process cannot be terminated via Task Manager or taskkill /F. WinDbg analysis reveals a deadlock in the kernel-mode driver while unloading the WebRTC plugin and deallocating GPU resources.

Environment
Unity Version: 2021.3.18f1 (LTS)

Platform: Windows 10/11 (x64)

Graphics API: Direct3D 11

GPU: NVIDIA (tested with Game Ready and Studio Drivers)

Third-party Plugins: WebRTC (Unity Render Streaming or similar)

Technical Analysis (from Dump)
The attached .dmp file analysis shows that the hang occurs during the resource cleanup phase of the WebRTC plugin.

Key Stack Trace Observations:

Trigger: The hang is initiated by webrtc!VideoTrackRemoveSink, which leads to webrtc!UnityPluginUnload.

Driver Interaction: The WebRTC plugin attempts to release GPU/CUDA resources through NVIDIA's user-mode driver (nvwgf2umx.dll) and d3d11.dll.

The Deadlock: The thread enters the Windows kernel and gets stuck at win32u!NtGdiDdDDIDestroyAllocation2.

Because the thread is stuck in Kernel Mode waiting for a hardware resource deallocation that never completes, the OS prevents the process from being terminated to avoid potential system-wide instability or a BSOD.

Current Behavior

No response

Expected Behavior

No response

Anything else?

No response

[JhonJHUtd]