8385369: G1: Concurrent Cleanup For Next Mark accesses uncommitted bitmaps after region uncommit

[tschatzl]

Hi all,

please review this change that fixes a crash during concurrent bitmap clearing: regions and their associated bitmaps may be uncommitted after freeing them in a gc that runs during that time, while they are being cleared.

This obviously crashes the VM.

There is a test, but it is not very reliable (does not fail often without the patch) and I did not manage to further improve it - in one run it crashes in <1% of cases, in another in almost 10% of cases. Feel free to suggest to remove it.

Testing: new test, gha

Thanks,
Thomas

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• JDK-8385369: G1: Concurrent Cleanup For Next Mark accesses uncommitted bitmaps after region uncommit (Bug - P3)

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