RFR: 8264393: JDK-8258284 introduced dangling TLH race [v2]

[Daniel D.Daugherty]

On Wed, 31 Mar 2021 00:28:19 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Daniel D. Daugherty has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix two more ThreadsListHandle tests.
>
> Hi Dan,
> 
> So in a nutshell, 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.
> 
> This seems reasonable to me.
> 
> Thanks,
> David

@dholmes-ora - your nutshell summary is spot on. Thanks for the review.

> src/hotspot/share/runtime/threadSMR.cpp line 542:
> 
>> 540:     // And that protocol cannot be properly done with a ThreadsList that
>> 541:     // might not be the current system ThreadsList.
>> 542:     assert(_previous->_list->_nested_handle_cnt > 0, "must be > than zero");
> 
> Nit: "> than" reads "greater than than".

Fixed.

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