8336912: G1: Undefined behavior for G1ConfidencePercent=0

[tschatzl]

Hello,

please review this change to workaround an unintentional division by zero found by ubsan.

The global option G1ConfidencePercent allowed zero as confidence for predictions which this change simply disallows: not sure what the response of the VM would be if the user told it that it should have absolutely no confidence (i.e. confidence is zero) in the predictions (not "very low" confidence).

Testing: after this change, the ubsan failure goes away.

Thanks,
Thomas

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
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• Commit message must refer to an issue
• Change requires CSR request JDK-8337340 to be approved

Issues

• JDK-8336912: G1: Undefined behavior for G1ConfidencePercent=0 (Bug - P4)
• JDK-8337340: G1: Disallow a value of zero for G1ConfidencePercent (CSR)

Reviewers

• Albert Mingkun Yang (@albertnetymk - Reviewer)
• Sangheon Kim (@sangheon - Reviewer)

Reviewing

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$ git pull https://git.openjdk.org/jdk.git pull/20371/head

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[openjdk]

@tschatzl This change now passes all automated pre-integration checks.

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After integration, the commit message for the final commit will be:

8336912: G1: Undefined behavior for G1ConfidencePercent=0

Reviewed-by: ayang, sangheki

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At the time when this comment was updated there had been 94 new commits pushed to the master branch:

• a91f9ba: 8301403: Eliminate memory allocations in JVMFlag::printFlags during signal handling
• 2c9fd90: 8336315: tools/jpackage/windows/WinChildProcessTest.java Failed: Check is calculator process is alive
• 1cb27f7: 8334230: Optimize C2 classes layout
• 4148613: 8335907: JFR: Make SettingControls more robust
• 79bdd81: 8336763: Parallel: Merge PCMarkAndPushClosure and PCIterateMarkAndPushClosure
• 8162832: 8333354: ubsan: frame.inline.hpp:91:25: and src/hotspot/share/runtime/frame.inline.hpp:88:29: runtime error: member call on null pointer of type 'const struct SmallRegisterMap'
• 0325ab8: 8335610: DiagnosticFramework: CmdLine::is_executable() correction
• 7ac5311: 8331126: [s390x] secondary_super_cache does not scale well
• 156f0b4: 8337213: Shenandoah: Add verification for class mirrors
• 9e6e0a8: 8336343: Add more known sysroot library locations for ALSA
• ... and 84 more: https://git.openjdk.org/jdk/compare/92de2b2d5f21af38380b437af51e49c7ac142258...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

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[openjdk]

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[mlbridge]

Webrevs

• 00: Full (01781401)

[sangheon]

Looks good.

[tschatzl]

Thanks @albertnetymk @sangheon for your reviews
/integrate

[openjdk]

Going to push as commit de0b504.
Since your change was applied there have been 102 commits pushed to the master branch:

• e63d016: 8337031: Improvements to CompilationMemoryStatistic
• 1c6fef8: 8337515: JVM_DumpAllStacks is dead code
• 5b7bb40: 8325002: Exceptions::fthrow needs to ensure it truncates to a valid utf8 string
• d39e7af: 8320561: Inconsistency in monitorinflation logging
• 6c3ba5a: 8337415: Remove inappropriate Atomic access in FreeListAllocator
• f5c9e8f: 8334492: DiagnosticCommands (jcmd) should accept %p in output filenames and substitute PID
• 93c19ac: 8337219: AccessFlags factories do not require necessary arguments
• 6154a21: 8336032: Enforce immutability of Lists used by ClassFile API
• a91f9ba: 8301403: Eliminate memory allocations in JVMFlag::printFlags during signal handling
• 2c9fd90: 8336315: tools/jpackage/windows/WinChildProcessTest.java Failed: Check is calculator process is alive
• ... and 92 more: https://git.openjdk.org/jdk/compare/92de2b2d5f21af38380b437af51e49c7ac142258...master

Your commit was automatically rebased without conflicts.

[openjdk]

@tschatzl Pushed as commit de0b504.

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