[ci-scan] Known Build Error: StreamReader NegativeOneBufferSize test fails under PGO

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Build Information

Build: https://dev.azure.com/dnceng-public/public/_build/results?buildId=1414905
Pipeline: runtime-coreclr libraries-pgo (definition 145)
Affected leg: linux-x64 Release

Error Message

{
  "ErrorMessage": ["bufferSize ('-1') must be a non-negative and non-zero value"],
  "BuildRetry": false,
  "ExcludeConsoleLog": false
}

Summary

System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException fails under PGO (libraries-pgo pipeline). The test expects that new StreamReader(path, Encoding.UTF8, true, -1) does not throw, but under PGO it throws ArgumentOutOfRangeException: bufferSize ('-1') must be a non-negative and non-zero value.

The StreamReader(string, Encoding, bool, int) constructor calls ValidateArgsAndOpenPath(path, bufferSize) which skips validation for -1, then chains to the Stream-based constructor which converts -1 to DefaultBufferSize. Under normal execution this works; the PGO-compiled code path may be reordering or inlining in a way that hits validation before the -1 → default conversion.

Impact on platforms

• runtime-coreclr libraries-pgo (def 145) · linux-x64 Release · exit code 1

Console log

System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException [FAIL]
      System.ArgumentOutOfRangeException : bufferSize ('-1') must be a non-negative and non-zero value. (Parameter 'bufferSize')
      Stack Trace:
        at System.ArgumentOutOfRangeException.ThrowNegativeOrZero[T](T value, String paramName)
        at System.IO.StreamReader..ctor(String path, Encoding encoding, Boolean detectEncodingFromByteOrderMarks, Int32 bufferSize)
        at System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException()

Console log

First build it occurred

Present in builds 1414905 (May 10) and 1414533 (May 9). ≥2 occurrences.

Recommended action

Investigate whether PGO-guided inlining/optimization is changing the evaluation order of ValidateArgsAndOpenPath and the Stream ctor's bufferSize check. The -1 sentinel value should be converted to DefaultBufferSize before ThrowIfNegativeOrZero runs.

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Note

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Generated by CI Outer-Loop Failure Scanner · ● 56.5M · ◷

Report

Build	Definition	Test	Pull Request
1416672	dotnet/runtime	System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException	#126671

Summary

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

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1414905
Error message validated: [NegativeOneBufferSize_ShouldNotThrowException System.ArgumentOutOfRangeException]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 5/12/2026 11:31:36 AM UTC

Report

Build	Definition	Test	Pull Request
1416672	dotnet/runtime	System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException	#126671
1414905	dotnet/runtime	System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException

Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
0	2	2

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1414905
Error message validated: [NegativeOneBufferSize_ShouldNotThrowException System.ArgumentOutOfRangeException]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 5/12/2026 11:31:36 AM UTC

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1414905
Error message validated: [bufferSize ('-1') must be a non-negative and non-zero value]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 5/13/2026 8:12:07 AM UTC

Report

Build	Definition	Test	Pull Request
1419811	dotnet/runtime	System.IO.Tests.StreamWriter_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException	#126367
1419237	dotnet/runtime	System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException	#128148
1416672	dotnet/runtime	System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException	#126671
1414905	dotnet/runtime	System.IO.Tests.StreamReader_StringCtorTests.NegativeOneBufferSize_ShouldNotThrowException

Summary

24-Hour Hit Count	7-Day Hit Count	1-Month Count
0	4	4

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1414905
Error message validated: [NegativeOneBufferSize_ShouldNotThrowException System.ArgumentOutOfRangeException]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 5/12/2026 11:31:36 AM UTC

Known issue validation

Build: 🔎 https://dev.azure.com/dnceng-public/public/_build/results?buildId=1414905
Error message validated: [bufferSize ('-1') must be a non-negative and non-zero value]
Result validation: ✅ Known issue matched with the provided build.
Validation performed at: 5/13/2026 8:12:07 AM UTC

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