RFR: 8307365: JvmtiStressModule hit SIGSEGV in JvmtiEventControllerPrivate::recompute_thread_enabled [v2]

[Leonid Mesnik]

On Tue, 16 May 2023 14:33:05 GMT, Patricio Chilano Mateo <pchilanomate at openjdk.org> wrote:

>> The following patch fixes a bug introduced while refactoring the VirtualThreadStart/End events. Specifically, the code to delete the JvmtiThreadState of a terminating vthread was moved before we start the VTMS transition. That allowed said code to run concurrently with recompute_enabled() leading to different crashing modes. I wrote the detailed sequence of events leading to the crash in the bug comments. 
>> 
>> To fix it I moved the cleanup code back after the call to VTMS_unmount_begin(). Now, since the rebinding of the JvmtiThreadState to that of the carrier has to be done after this cleanup code is executed, otherwise we would delete the wrong JvmtiThreadState state, I had to add a boolean argument to VTMS_unmount_begin() to differentiate the last unmount call from the other ones. This is unfortunate since ideally VTMS_unmount_begin() would be oblivious to these two cases as with VTMS_mount_end() where we don't need to check if this is the first mount.
>> I looked for other ways to solve it instead of the extra boolean argument but wasn't convinced. One way would be to have another JvmtiExport::cleanup_thread() that would handle this case. Another way which is very simple is to move the rebind_to_jvmti_thread_state_of() call to VTMS_unmount_end() instead. But that means during the transition the _jvmti_thread_state field of the carrier would be either null or that of the vthread, unlike today which is always that of the carrier during the transitions. I didn't want to change that behavior in this fix but I can also explore that route.
>> 
>> I tested the patch with the reproducer I attached to the bug, plus I also run tiers1-3 in mach5.
>> 
>> Thanks,
>> Patricio
>
> Patricio Chilano Mateo has updated the pull request incrementally with one additional commit since the last revision:
> 
>   remove extra assert

The changes looks good. Just small suggestion.
Any reasons why didn't add the test?

src/hotspot/share/prims/jvmtiThreadState.cpp line 584:

> 582:       JvmtiExport::post_vthread_unmount(vthread);
> 583:     }
> 584:     VTMS_unmount_begin(vthread, /* last_unmount */ false);

I think it would be better just to add 
thread->rebind_to_jvmti_thread_state_of(thread->threadObj());
after this call instead of adding a parameter to  VTMS_unmount_begin.
Just suggestion.

-------------

Marked as reviewed by lmesnik (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/13949#pullrequestreview-1429346892
PR Review Comment: https://git.openjdk.org/jdk/pull/13949#discussion_r1195657255