[ci-scan] Known Build Error: NullReferenceException in AsyncHelpers.RuntimeAsyncTask.HandleSuspended on NativeAOT x86

[github-actions]

Build Information

Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1410188
Build error leg or test failing: windows-x86 Release NativeAOT_Libs-System.Threading.Channels.Tests

Error Message

{
  "ErrorMessage": "at System.Runtime.CompilerServices.AsyncHelpers.RuntimeAsyncTask`1.HandleSuspended(AsyncHelpers.RuntimeAsyncAwaitState&)",
  "ErrorPattern": "",
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

System.Threading.Channels.Tests crashes in runtime-nativeaot-outerloop (def 265) on windows-x86 Release with NativeAOT compilation. An unhandled NullReferenceException is thrown at AsyncHelpers.RuntimeAsyncTask<T>.HandleSuspended(AsyncHelpers.RuntimeAsyncAwaitState&) in AsyncHelpers.CoreCLR.cs:476. This is an x86-specific NativeAOT runtime-async issue — the async state machine helper dereferences a null pointer when suspending an async task on the 32-bit NativeAOT runtime.

Affected pipelines (3 confirmed failing builds):

• runtime-nativeaot-outerloop (def 265): windows-x86 Release NativeAOT_Libs — builds 1410188, 1408078, 1407254

Note: Build 1411078 (May 7, 2026) succeeded, indicating a possible recent fix. This KBE is filed to provide Build Analysis coverage for any recurrence.

Errors log:

Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Runtime.CompilerServices.AsyncHelpers.RuntimeAsyncTask`1.HandleSuspended(AsyncHelpers.RuntimeAsyncAwaitState&)
      in AsyncHelpers.CoreCLR.cs:line 476
exit code -1073740791

First build it occurred: Build 1407254 (May 4, 2026) is the earliest in the scanned window. Occurrence count in window: 3.

Recommended action:

• Owner: @dotnet/runtime-async (runtime-async area, @agocke, @stephentoub)
• Root cause: RuntimeAsyncTask<T>.HandleSuspended dereferences a null reference at line 476 of AsyncHelpers.CoreCLR.cs. Investigate whether the NativeAOT x86 async state machine sets up the RuntimeAsyncAwaitState correctly before calling HandleSuspended.
• File path: src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs
• If the failure is confirmed fixed by a recent PR, close this issue with a reference to that PR.

Note

🤖 This issue was generated by the CI Outer-Loop Failure Scanner.

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Generated by CI Outer-Loop Failure Scanner · ● 16.2M · ◷

Report

Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
0	0	0

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1410188
Error message validated: [AsyncHelpers.RuntimeAsyncTask1.HandleSuspended`]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 5/7/2026 3:30:21 AM UTC

Report

Build	Definition	Test	Pull Request
1410188	dotnet/runtime	System.Threading.Channels.Tests.WorkItemExecution

Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
0	1	1

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1410188
Error message validated: [AsyncHelpers.RuntimeAsyncTask1.HandleSuspended`]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 5/7/2026 3:30:21 AM UTC

Report

Build	Definition	Test	Pull Request
1424404	dotnet/runtime	System.Text.Json.SourceGeneration.Roslyn4.4.Tests.WorkItemExecution
1423942	dotnet/runtime	System.Text.Json.SourceGeneration.Roslyn4.4.Tests.WorkItemExecution
1423513	dotnet/runtime	System.Text.Json.SourceGeneration.Roslyn4.4.Tests.WorkItemExecution
1418798	dotnet/runtime	System.Threading.Channels.Tests.WorkItemExecution	#127762
1410188	dotnet/runtime	System.Threading.Channels.Tests.WorkItemExecution

Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
1	4	5

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1410188
Error message validated: [AsyncHelpers.RuntimeAsyncTask1.HandleSuspended`]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 5/7/2026 3:30:21 AM UTC

[dotnet-policy-service]

Tagging subscribers to this area: @agocke
See info in area-owners.md if you want to be subscribed.

[jakobbotsch]

Line 476 is in this code:

runtime/src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.CoreCLR.cs

Lines 471 to 479 in 9f657f0

	// Skip to a nontransparent/user continuation. Such continuaton must exist.
	// Since we see a VTS notifier, something was directly or indirectly
	// awaiting an async thunk for a ValueTask-returning method.
	// That can only happen in nontransparent/user code.
	Continuation nextUserContinuation = headContinuation.Next!;
	while ((nextUserContinuation.Flags & continueFlags) == 0 && nextUserContinuation.Next != null)
	{
	nextUserContinuation = nextUserContinuation.Next;
	}

@VSadov Do you want to take a look?