RFR: 8324881: ObjectSynchronizer::inflate(Thread* current...) is invoked for non-current thread [v5]

[Axel Boldt-Christmas]

On Fri, 2 Feb 2024 04:40:16 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Axel Boldt-Christmas has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix enter_for LockingMode == LM_LEGACY and strengthen assert
>
> src/hotspot/share/runtime/synchronizer.cpp line 1372:
> 
>> 1370:       if (LockingMode == LM_LIGHTWEIGHT && inf->is_owner_anonymous() &&
>> 1371:           thread != nullptr && thread->lock_stack().contains(object)) {
>> 1372:         inf->set_owner_from_anonymous(thread);
> 
> I thought one of the invariants of lightweight locking was that a transition from anonymously owned to actual owner, can only be performed by the actual owner?
> 
> That said, can we actually reach here if not with the current thread? If we are re-locking for deopt then, IIUC, the object has not yet escaped, and has to be unlocked and not with an inflated monitor. In such a case we can't be racing with hashcode inflation either. But perhaps there are other circumstances where re-locking is needed?

Unsure if the `relock_objects` code only re-locks escaped and elided locks, or all elided locks. I believe it is the second. And if we re-lock nested elided locks then they can very well have escaped. (But the lock is guaranteed to be owned by the `deoptee_thread`)

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PR Review Comment: https://git.openjdk.org/jdk/pull/17626#discussion_r1475709904