RFR: 8341544: Restore fence() in Mutex

[David Holmes]

On Mon, 12 May 2025 17:28:23 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> I agree with this point, addressed in the latest commit.
>
> Okay good, I liked those there even if they're covered by the mutex fence.

I'm conflicted. One the one hand we added the fence there because of the missing fence in the mutex, so if we fix mutex we should undo what we (only recently) did. On the other hand, the lack of a fence suggests to me we really don't need the SystemMemoryBarrier either.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25033#discussion_r2086442038