RFR: 8339725: Concurrent GC crashed due to GetMethodDeclaringClass [v2]

[Erik Österlund]

On Mon, 9 Sep 2024 06:04:36 GMT, Liang Mao <lmao at openjdk.org> wrote:

>> Hi,
>> 
>> It's a fix for 8339725. I think getting the oop from Klass::java_mirror() should use a ON_PHANTOM_OOP_REF decorator here which could make sure the oop would be kept alive in concurrent marking and return nullptr while in concurrent reference processing and unloading.
>> 
>> test/hotspot/jtreg/runtime and gc are clean.
>> 
>> Thanks,
>> Liang
>
> Liang Mao has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix build error in windows/mac

Reading a strong reference such as OopHandle with ON_PHANTOM_OOP_REF is dangerous. The implication of using ON_PHANTOM_OOP_REF is that there are certain interactions with a reference processor. But it will not process OopHandle because they are strong references. So I really don't think we should be doing this.

I think a better solution is to do what existing code does today, which is to read klass->klass_holder() (which keeps the class alive) in the GetMethodDeclaringClass function.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/20907#issuecomment-2337829404