RFR: 8350649: Class unloading accesses/resurrects dead Java mirror after JDK-8346567 [v5]

[Aleksey Shipilev]

On Wed, 26 Feb 2025 07:35:30 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> See bug for description of the bug. Shenandoah seems to be the only GC that runs into this problem so far.
>> 
>> Before [JDK-8346567](https://bugs.openjdk.org/browse/JDK-8346567), we pulled class modifiers from the native `Klass*`, and so we bypassed this trouble. But now we take modifiers out of Java mirror, and this happens during unloading, which accesses/resurrects potentially dead mirror.
>> 
>> Additional testing:
>>  - [x] Linux x86_64 server fastdebug, original reproducer now passes
>>  - [x] Linux x86_64 server fastdebug, `hotspot_gc_shenandoah`
>>  - [x] Linux x86_64 server fastdebug, `jdk_jfr`
>>  - [x] Linux x86_64 server fastdebug, `jdk_jfr` with `-XX:+UseShenandoahGC` now passes
>
> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Drop "is"

Thanks for reviews! Local testing passes fine, so I am integrating.

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PR Comment: https://git.openjdk.org/jdk/pull/23775#issuecomment-2685603297