RFR: 8264393: JDK-8258284 introduced dangling TLH race [v3]

[Daniel D.Daugherty]

On Thu, 1 Apr 2021 07:17:20 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> Daniel D. Daugherty has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   dholmes CR - fix nit in assert mesg.
>
> Marked as reviewed by rehn (Reviewer).

@robehn - Thanks for closing the loop on your review thread.

@dholmes-ora nutshell summary covers it:
when clearing a nested TLH you can't simply install the previous TLH as the threads_hazard_ptr, but instead set to NULL so that it is properly set by acquire_stable_list.

Another way to put it is that the `_threads_hazard_ptr` field must only be set to
a non-NULL value by the acquire_stable_list() protocol.

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PR: https://git.openjdk.java.net/jdk/pull/3272