RFR: 8358645: Access violation in ThreadsSMRSupport::print_info_on during thread dump

[David Holmes]

On Wed, 25 Jun 2025 08:39:41 GMT, Fredrik Bredberg <fbredberg at openjdk.org> wrote:

>> We started observing these occasional crashes involving the JfrSamplerThread (which is a NonJavaThread) during JFR's termination thread dump. Examination of the `print_info_on` code showed that it was making an invalid assumption that it is safe to walk the thread's thread-list at a safepoint, as that is not true when you are dealing with a NonJavaThread, as it is not held at the safepoint and so the list you are walking can disappear whilst you examine it. I added some test code to make this more likely and was able to trigger similar crashes - see JBS for details.
>> 
>> The simple fix is to only walk JavaThreads.
>> 
>> Testing
>>  - tier 5 JFR tests
>>  - selected tests with JFR explicitly enabled
>>  - tier 1-3 (sanity)
>> 
>> Thanks
>
> Looks good to me.

Thanks for the review @fbredber !

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PR Comment: https://git.openjdk.org/jdk/pull/25963#issuecomment-3004004507