RFR: 8347463: jdk/jfr/threading/TestManyVirtualThreads.java crashes with assert(oopDesc::is_oop_or_null(val)) [v5]

[Markus Grönlund]

On Mon, 27 Oct 2025 09:53:16 GMT, Anton Seoane Ampudia <aseoane at openjdk.org> wrote:

>> This PR introduces a fix for a intermittent assert crash due to a non-oop found in the stack when deoptimizing.
>> 
>> The `inline_native_GetEventWriter` JFR intrinsic performs a call into the runtime, which can safepoint, to write a checkpoint for the vthread. This call returns a global handle (`jobject`) that then gets resolved to a raw oop.
>> 
>> However, the corresponding `jfr_write_checkpoint_Type` does not set any return, modelling the call as `void`. If a safepoint hits in the small window after the stub returns but before the writer oop is used, and the GC moves the object in that window, the deoptimization path cannot resolve a handle that it never recorded, leading to the subsequent crash.
>> 
>> An IR Framework test is introduced to exercise the error explicitly. Additionally, related documentation in form of comments in the appropriate file (`runtime.hpp`) is added to hopefully prevent similar cases in the future.
>> 
>> **Testing:** passes tiers 1-5
>
> Anton Seoane Ampudia has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Apply review comments

Marked as reviewed by mgronlun (Reviewer).

Thanks for getting to the cause and fixing this.

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PR Review: https://git.openjdk.org/jdk/pull/27913#pullrequestreview-3382775048
PR Comment: https://git.openjdk.org/jdk/pull/27913#issuecomment-3450540758