RFR: 8341544: Restore fence() in Mutex

[David Holmes]

On Tue, 13 May 2025 10:09:11 GMT, David Holmes <dholmes at openjdk.org> wrote:

> the lack of a fence suggests to me we really don't need the SystemMemoryBarrier either.

No that is my ignorance/forgetfulness about what SMB does. On the platforms that set UseSMB true, they elide barriers in other parts of the code and then use the SMB here to account for that. Thanks @pchilano for refreshing my memory here.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/25033#discussion_r2090079037