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

[Patricio Chilano Mateo]

On Tue, 16 May 2023 20:21:39 GMT, Patricio Chilano Mateo <pchilanomate at openjdk.org> wrote:

>> Summary: Thumbs up. This is most definitely NOT a trivial fix.
>> 
>> Normally the way I like to review these kinds of fixes is to map the failure
>> modes back to the fix just to make sure I understand how each of the
>> failure modes is covered by the changes. For this particular bug that has
>> NOT been an easy thing to do. I believe the failure modes are complicated
>> to follow because we "lost" the synchronization of being in the
>> `VTMS_unmount_begin` transition which allowed a thread calling
>> `recompute_enabled()` to race with our ending/exiting vthread/cthread
>> combo. Ouch.
>> 
>> The fix does restore the synchronization of being in the
>> `VTMS_unmount_begin` transition so I can see how we would no longer
>> be racing with the `recompute_enabled()` calling thread.
>
>> Summary: Thumbs up. This is most definitely NOT a trivial fix.
>> 
>> Normally the way I like to review these kinds of fixes is to map the failure modes back to the fix just to make sure I understand how each of the failure modes is covered by the changes. For this particular bug that has NOT been an easy thing to do. I believe the failure modes are complicated to follow because we "lost" the synchronization of being in the `VTMS_unmount_begin` transition which allowed a thread calling `recompute_enabled()` to race with our ending/exiting vthread/cthread combo. Ouch.
>> 
> Exactly. In the reproducer I aimed for the ThreadsListHandle crash, but while working on it I also hit the other ones.

> @pchilano - This bug has had reported sightings in Tier[34568] so Tier[1-3] testing is probably not enough. However, since you've been able to create a tight reproducer, your testing might be sufficient. Of course, as @dholmes-ora likes to say: only time will tell!
>
I actually also tested it in mach5 tiers 4-6 after the initial post.  : )

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PR Comment: https://git.openjdk.org/jdk/pull/13949#issuecomment-1550309385