8283555: G1: Concurrent mark accesses uninitialized BOT of closed archive regions

[tschatzl]

Hi all,

please review this change that fixes crashes occurring in the Loom repo because of missing initialization in the BOT of closed archive regions. This is a bug here too, just typically not occurring.

So during marking through the closed archive regions (for statistics mainly) it can happen that there are objects in these closed archive regions that are split into chunks. To get the start of the object that contains this chunk, we use the BOT.

Since it is not initialized for the closed archive regions G1 crashes as that call returns garbage.

The fix is to not only initialize open archive regions, but also closed archive regions.

The problem started with JDK-8264908 which means that there will be a JDK 18 backport.

Testing: failing test with Loom, GHA

Thanks,
Thomas

---

Progress

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Issue

• JDK-8283555: G1: Concurrent mark accesses uninitialized BOT of closed archive regions

Reviewers

• Albert Mingkun Yang (@albertnetymk - Reviewer) ⚠️ Review applies to ddc51e0
• Ivan Walulya (@walulyai - Reviewer)

Reviewing

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[tschatzl]

/label add hotspot-gc

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[mlbridge]

Webrevs

• 01: Full - Incremental (0645bec5)
• 00: Full (ddc51e03)

[albertnetymk]

It would be good to have a reference to the actual method/class name performing "object chunking" in the comment.

[openjdk]

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

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

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

8283555: G1: Concurrent mark accesses uninitialized BOT of closed archive regions

Reviewed-by: ayang, iwalulya

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At the time when this comment was updated there had been 1 new commit pushed to the master branch:

• 3e73a0b: 8283237: CallSite should be a sealed class

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[walulyai]

Lgtm!

[tschatzl]

Thanks @albertnetymk @walulyai for your reviews
/integrate

[openjdk]

Going to push as commit 19f01ab.
Since your change was applied there have been 21 commits pushed to the master branch:

• 929b6a3: 8282917: Remove InetAddressImplFactory from InetAddress
• 14c20bc: 8283187: C2: loop candidate for superword not always unrolled fully if superword fails
• 1c4f5fc: 8283575: Check for GNU time fails for version >1.7
• 2c43ecb: 8283323: libharfbuzz optimization level results in extreme build times
• 5905b02: 8276799: Implementation of JEP 422: Linux/RISC-V Port
• b05d4cc: 8283350: (tz) Update Timezone Data to 2022a
• a35afe8: 8283519: Hsdis with capstone should annotate output
• e6f707a: 8283437: Refactor imageio classes javadoc to use @throws instead of @exception
• af18b11: 8283574: Use Klass::_id for type checks in the C++ code
• 5cf580e: 8283587: [BACKOUT] Invalid generic signature for redefined classes
• ... and 11 more: https://git.openjdk.java.net/jdk/compare/a77160065bb6f62314711514f7694fe50f0dc35b...master

Your commit was automatically rebased without conflicts.

[openjdk]

@tschatzl Pushed as commit 19f01ab.

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