Test failure: System.Threading.Tests.BarrierTests.RunBarrierTest7a

[VincentBu]

Failed in: runtime-coreclr libraries-jitstressregs 20260419.1

Failed tests:

net11.0-windows-Release-x86-jitstressregs8-Windows.10.Amd64.Open
- System.Threading.Tests.BarrierTests.RunBarrierTest7a

Error message:

System.AggregateException : One or more errors occurred. (The participantCount argument must be less than or equal the number of participants. (Parameter 'participantCount'))
---- System.ArgumentOutOfRangeException : The participantCount argument must be less than or equal the number of participants. (Parameter 'participantCount')

Stack trace:

   at System.Threading.Tasks.Task.WaitAllCore(ReadOnlySpan`1 tasks, Int32 millisecondsTimeout, CancellationToken cancellationToken) in /_/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs:line 5207
   at System.Threading.Tasks.Task.WaitAll(Task[] tasks) in /_/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs:line 4879
   at System.Threading.Tests.BarrierTests.RunBarrierTest7a() in /_/src/libraries/System.Threading/tests/BarrierTests.cs:line 285
   at System.Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args) in /_/src/coreclr/System.Private.CoreLib/src/System/Reflection/MethodBaseInvoker.CoreCLR.cs:line 39
   at System.Reflection.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr) in /_/src/libraries/System.Private.CoreLib/src/System/Reflection/MethodBaseInvoker.cs:line 57
----- Inner Stack Trace -----
   at System.Threading.Barrier.RemoveParticipants(Int32 participantCount) in /_/src/libraries/System.Threading/src/System/Threading/Barrier.cs:line 444
   at System.Threading.Tests.BarrierTests.<>c__DisplayClass18_0.<RunBarrierTest7a>b__0() in /_/src/libraries/System.Threading/tests/BarrierTests.cs:line 277
   at System.Threading.Tests.BarrierTests.<>c__DisplayClass18_0.<RunBarrierTest7a>b__1(Object index) in /_/src/libraries/System.Threading/tests/BarrierTests.cs:line 284
   at System.Threading.Tasks.Task.InnerInvoke() in /_/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs:line 2562
   at System.Threading.Tasks.Task.<>c.<.cctor>b__301_0(Object obj) in /_/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs:line 2542
   at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state) in /_/src/libraries/System.Private.CoreLib/src/System/Threading/ExecutionContext.cs:line 279
--- End of stack trace from previous location ---
   at System.Threading.ExecutionContext.RunFromThreadPoolDispatchLoop(Thread threadPoolThread, ExecutionContext executionContext, ContextCallback callback, Object state) in /_/src/libraries/System.Private.CoreLib/src/System/Threading/ExecutionContext.cs:line 304
   at System.Threading.Tasks.Task.ExecuteWithThreadLocal(Task& currentTaskSlot, Thread threadPoolThread) in /_/src/libraries/System.Private.CoreLib/src/System/Threading/Tasks/Task.cs:line 2506

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[mangod9]

Most likely same root cause as #127131

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[dhartglassMSFT]

Windows-x86 regstress (same leg) also has failures in
System.Threading.Tasks.Tests.TaskRtTests_Core.RunTCSCompletionStateTests_SetCancel
System.Threading.Tasks.Tests.TaskRtTests_Core.RunTCSCompletionStateTests

putting here for posterity