RFR: 8324881: ObjectSynchronizer::inflate(Thread* current...) is invoked for non-current thread [v2]

[Coleen Phillimore]

On Tue, 30 Jan 2024 11:23:45 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

>> The `ObjectSynchronizer` has always assumed that the `current` parameters are both the current thread as well as the thread that is doing the locking. The only time that we are entering on behalf of another thread is when doing re-locking in deoptimization. This has worked because the deoptee thread is suspended. However ResourceMarks have been using the wrong thread when logging is enabled.
>> 
>> This change `ObjectSynchronizer` instruments the relevant methods with both a `JavaThread* locking_thread` as well as `[Java]Thread* current` to be able to use the correct thread for ResourceMarks. 
>> 
>> Having the `inflate` care about a `locking_thread` is a little unpleasant in my opinion. But it is required for LM_LIGHTWEIGHT. 
>> Would probably be cleaner if the inflate for LM_LIGHTWEIGHT was it's own thing, as it does not share the whole INFLATING protocol. But seems like a future RFE to refactor this code.
>> 
>> Can reproduce a crash by modifying `test/jdk/com/sun/jdi/EATests.java` and using `-XX:DiagnoseSyncOnValueBasedClasses=2` with LM_LEGACY or running `test/jdk/com/sun/jdi/EATests.java` with LM_LIGHTWEIGHT/LM_MONITOR and `-Xlog:monitorinflation=trace`. 
>> 
>> Could extend this test to capture this regression in the future (or creating a new test based on the same infrastructure). Will give it an attempt, so we have a regression test for this. But these tests get rather involved as the require a lot of jvmti setup.
>
> Axel Boldt-Christmas has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add regression test

src/hotspot/share/runtime/synchronizer.cpp line 1323:

> 1321:     locking_thread = JavaThread::cast(current);
> 1322:   }
> 1323:   return inflate(locking_thread, current, object, cause);

This looks strange passing locking_thread as nullptr.  Why not unconditionally make it current?  How can it ever be null?

edit: I see, it's guarded by is_lock_owned().  And you want "locking_thread" to be a JavaThread* not Thread* (another source of confusion).  This still looks odd.  Maybe locking_thread should be:

locking_thread = current->is_Java_thread() ? JavaThread::cast(current) : nullptr;

Then the LM_LEGACY path makes sense also?

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PR Review Comment: https://git.openjdk.org/jdk/pull/17626#discussion_r1471433890