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

[Daniel D.Daugherty]

> 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.

Daniel D. Daugherty has updated the pull request incrementally with one additional commit since the last revision:

  dholmes CR - fix nit in assert mesg.

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3272/files
  - new: https://git.openjdk.java.net/jdk/pull/3272/files/98521a36..fa400b47

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3272&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3272&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3272.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3272/head:pull/3272

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