Integrated: 8264393: JDK-8258284 introduced dangling TLH race

[Daniel D.Daugherty]

On Tue, 30 Mar 2021 16:35:23 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

> I ported some 20 year old tests using JDK-8262881 in order to help
> test [~rehn]'s fix for JDK-8257831. These tests in combination with
> one piece of the fix from JDK-8257831 revealed a bug in my fix for
> JDK-8258284 from back in Dec 2020.
> 
> The race revealed by the ported tests from JDK-8262881 happens
> only with nested ThreadsListHandles. When TLH2 is destroyed, the
> thread updates its threads_hazard_ptr from the TLH2-list to the
> TLH1-list; I made this change back in 2020.12 using JDK-8258284.
> The threads_hazard_ptr can be observed by a thread calling
> ThreadsSMRSupport::free_list() as a stable ThreadsList at the same
> time as the TLH1 destructor is decrementing the nested_handle_cnt
> that permits the ThreadsList to be freed. So the thread calling
> ThreadsSMRSupport::free_list() thinks it has a stable hazard ptr
> (TLH1-list), but that hazard ptr can be freed and causes lots of
> confusion.
> 
> Update: This fix along with the fix from JDK-8264123 were stress
> tested with the new tests from JDK-8262881.

This pull request has now been integrated.

Changeset: f259eeaf
Author:    Daniel D. Daugherty <dcubed at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/f259eeaf
Stats:     65 lines in 4 files changed: 22 ins; 21 del; 22 mod

8264393: JDK-8258284 introduced dangling TLH race

Reviewed-by: dholmes, rehn, eosterlund

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