RFR: 8318109: Writing JFR records while a CHT has taken its lock asserts in rank checking

[Thomas Schatzl]

On Thu, 19 Oct 2023 17:06:16 GMT, Ivan Walulya <iwalulya at openjdk.org> wrote:

>> Hi all,
>> 
>>   please review this change to fix a lock rank issue after [JDK-8317440](https://bugs.openjdk.org/browse/JDK-8317440). The `JfrStacktrace_lock` rank needs to be adjusted because it may be used when gathering CHT statistics in generational ZGC (afaiu this operation may trigger a relocation which may trigger page allocation which may trigger a JFR event which may trigger JFR trace writing).
>> 
>> The `JfrStacktrace_lock` code seems to be a lock only guarding I/O too, so moving it to the lowest rank seems safe after code inspection, but also tier1-7 testing and around 100 runs of the failed application did not make it fail (reproduction is like 2/100 runs without this change).
>> 
>> Testing: tier1-7, ~100 runs of the failing application with no error
>> 
>> Hth,
>>   Thomas
>
> Marked as reviewed by iwalulya (Reviewer).

Thanks @walulyai @Hamlin-Li for your reviews

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PR Comment: https://git.openjdk.org/jdk/pull/16242#issuecomment-1775270782