"Over release of MOW - COM" assert in COM wrappers

[stephentoub]

  Discovering: LibraryImportGenerator.Tests (method display = ClassAndMethod, method display options = None)
  Discovered:  LibraryImportGenerator.Tests (found 162 of 165 test cases)
  Starting:    LibraryImportGenerator.Tests (parallel test collections = on [2 threads], stop on fail = off)
Assertion failed: (!"Over release of MOW - COM") (/__w/1/s/src/coreclr/interop/comwrappers.cpp: Release: 519)

https://github.com/dotnet/runtime/pull/122407/checks?check_run_id=57752025260

Known Issue Error Message

Fill the error message using step by step known issues guidance.

{
  "ErrorMessage": "Over release of MOW - COM",
  "ErrorPattern": "",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Known issue validation

Build: 🔎
Result validation: ⚠️ Validation could not be done without an Azure DevOps build URL on the issue. Please add it to the "Build: 🔎" line.
Validation performed at: 12/11/2025 3:35:19 PM UTC

Report

Build	Definition	Test	Pull Request
1228887	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#121679
1228892	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122211
1228819	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122414
1228776	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122466
1228768	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#121513
1228677	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122463
1228706	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution
1228445	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#119352
1228658	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122460
1228403	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122023
1228505	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122441
1228500	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122425
1228442	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122430
1228180	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122453
1228338	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#119575
1228311	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#121305
1228190	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122454
1228146	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122381
1228140	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122407
1228125	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122450
1228102	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122448
1228170	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122414
1228130	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122451
1228078	dotnet/runtime	LibraryImportGenerator.Tests.WorkItemExecution	#122444

Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
24	24	24

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/interop-contrib
See info in area-owners.md if you want to be subscribed.

[AaronRobinsonMSFT]

/cc @jkoritzinsky

[jtschuster]

Likely caused by the test in this PR: #121643

update:

I think GetThis() with UniqueMarshalling on the receiving end is the culprit:

runtime/src/libraries/System.Runtime.InteropServices/tests/Common/ComInterfaces/IUniqueMarshalling.cs

Lines 22 to 29 in b500d44

	[GeneratedComClass]
	internal partial class UniqueMarshalling : IUniqueMarshalling
	{
	int _data = 0;
	public int GetValue() => _data;
	public void SetValue(int x) => _data = x;
	public IUniqueMarshalling GetThis() => this;
	}

[ericstj]

This is active in main right now, most builds hitting it. They don't always log the assertion, some just crash.

This build shows many failures - https://dev.azure.com/dnceng-public/public/_build/results?buildId=1227791&view=results

This mac failure has a dump report-- https://helixr1107v0xdeko0k025g8.blob.core.windows.net/dotnet-runtime-refs-heads-main-16db5125fb8a45fc8c/LibraryImportGenerator.Tests/1/coredump.50720.dmp.crashreport.json