RFR: 8304738: UnregisteredClassesTable_lock never created [v2]

[Ioi Lam]

On Wed, 5 Apr 2023 21:20:08 GMT, Matias Saavedra Silva <matsaave at openjdk.org> wrote:

>> UnregisteredClassesTable_lock is never created in mutex_init() and is always nullptr. This lock is referenced in a few places and all of those are effectively thread unsafe. Some of the places `unregistered_classes_table` is accessed are under other locks, so the rank of this lock has to be adjusted appropriately. The lock will be initialized to enable the intended behavior. Verified with tier 1-4 tests.
>
> Matias Saavedra Silva has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Moved mutex up before read

Marked as reviewed by iklam (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/13358#pullrequestreview-1373708740