8372540: SerialGC: Remove race between allocation and expansion before is_init_completed

[xmas92]

JDK-8370943 added the ability to expand the heap for Serial and Parallel without having to GC during early startup (before is_init_completed). The expansion code was written with the assumption that it is performed in a safepoint.

We have currently observed one crash related to the fact that top is updated before we setup the card table. But we can also see that the synchronisation between expansion and allocation is not correct.

I propose that we create a critical section for the early expansion and any early allocation.

We might want to relax this critical section in the future, after we have fixed the expansion code and allocation interactions. But for now it seems safer to simply use a mutex.

We also looked at using a RW style lock, but deemed it a bit unnecessary (master...xmas92:jdk:pre-init-expansion-rw-lock). Any potential performance gain may be better achieved by simply resolving the synchronisation issues with expansion.

• Testing
  • GHA
  • Tier 1-3 on Oracle supported platforms
  • Stress-tested with reproducer while java -XX:-UseCompressedOops -XX:+UseSerialGC -XX:InitialHeapSize=1m -Xmx1002M -version; do date;

---

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Issue

• JDK-8372540: SerialGC: Remove race between allocation and expansion before is_init_completed (Bug - P4)

Reviewers

• Albert Mingkun Yang (@albertnetymk - Reviewer)
• Stefan Johansson (@kstefanj - Reviewer)
• Erik Österlund (@fisk - Reviewer)

Reviewing

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[bridgekeeper]

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[openjdk]

@xmas92 This change now passes all automated pre-integration checks.

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

8372540: SerialGC: Remove race between allocation and expansion before is_init_completed

Reviewed-by: ayang, sjohanss, eosterlund

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At the time when this comment was updated there had been 6 new commits pushed to the master branch:

• a1cc8f4: 8372444: Genshen: Optimize evacuation function
• d328e4e: 8372272: Hotspot shared lib loading - add load attempts to Events::log
• b98114f: 8365526: Crash with null Symbol passed to SystemDictionary::resolve_or_null
• ... and 3 more: https://git.openjdk.org/jdk/compare/5bd7db034aaf8aa6780945e02a7f9a35e16b036e...master

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[openjdk]

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• hotspot-gc

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[mlbridge]

Webrevs

• 00: Full (ba640c18)

[fisk]

Looks good.

[xmas92]

Thanks for the reviews.
/integrate

[openjdk]

Going to push as commit e27abe8.
Since your change was applied there have been 13 commits pushed to the master branch:

• f636fca: 8372645: ParallelGC: Remove race between allocation and expansion before is_init_completed
• 7278d2e: 8372258: Improve TypeVariable support
• 84ffe87: 8342175: MemoryEaterMT fails intermittently with ExceptionInInitializerError
• ... and 10 more: https://git.openjdk.org/jdk/compare/5bd7db034aaf8aa6780945e02a7f9a35e16b036e...master

Your commit was automatically rebased without conflicts.

[openjdk]

@xmas92 Pushed as commit e27abe8.

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