RFR: 8266963: Remove safepoint poll introduced in 8262443 due to reentrance issue [v2]

[David Holmes]

On Mon, 24 May 2021 06:18:56 GMT, Yude Lin <github.com+16811675+linade at openjdk.org> wrote:

>> Shenandoah hangs when running specjvm2008 derby. The reason is a Java Thread reenters safepoint/handshake and blocks on itself. Please checkout the bugid for more details. After discussion with @zhengyu123, we think this might not be Shenandoah-specific. I propose to add a check before processing the safepoint/handshake.
>> 
>> An alternative approach (also insight from @zhengyu123) is to move the check a little earlier to the specific place where the Java Thread do ThreadBlockInVM. To feel reassured that no more reentrance exists in other places, I still leave the check in safepoint/handshake as debug code. See https://github.com/openjdk/jdk/compare/master...linade:reentrancecond
>> 
>> I'd appreciate more of your thoughts on these as I understand it could be a rather critical part of the code.
>
> Yude Lin has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Revert "8262443: GenerateOopMap::do_interpretation can spin for a long time."
>    
>    This reverts commit 7988c1d9aa7e3b990c17fdf5e31195e66e7fc5f2.
>  - Revert "8266963: Reentrance condition for safepoint/handshake"
>    
>    This reverts commit aa1ba2353e28877217e23c00577427f4f2c001ca.

Okay by me.

Thanks,
David

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Marked as reviewed by dholmes (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/4028