8353849: [Lilliput] Avoid race in compact identity hashcode

[rkennke]

Multiple GC threads can concurrently update an object's mark-word (Parallel, G1 and Shenandoah). We need to be careful when doing object-size calculations and pass-through the pre-loaded, safe mark-word, instead of re-loading the mark-word from the object. In the latter case, we might read a forwarding pointer and interpret the bits as hash-bits which would lead to wrong size-calculation and crash.

Testing:

• hotspot_gc (+UCOH)

---

Progress

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Issue

• JDK-8353849: [Lilliput] Avoid race in compact identity hashcode (Bug - P2)

Reviewers

• Zhengyu Gu (@zhengyu123 - Reviewer) ⚠️ Review applies to 12804a55
• William Kemper (@earthling-amzn - Reviewer)

Reviewing

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[openjdk]

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

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8353849: [Lilliput] Avoid race in compact identity hashcode

Reviewed-by: zgu, wkemper

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[mlbridge]

Webrevs

• 03: Full - Incremental (c76ba87e)
• 02: Full - Incremental (47e1ea05)
• 01: Full - Incremental (08ce0ac7)
• 00: Full (12804a55)

[zhengyu123]

Seem reasonable.

[earthling-amzn]

LGTM

[rkennke]

Thanks @zhengyu123 and @earthling-amzn! I found more races in that code path and would need a re-review!

[earthling-amzn]

Latest revision passes internal testing pipelines on x86 and aarch64. Looks better to me!

[rkennke]

Thanks!

/integrate

[openjdk]

Going to push as commit e20e6c8.

[openjdk]

@rkennke Pushed as commit e20e6c8.

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