RFR: 8317600: VtableStubs::stub_containing() table load not ordered wrt to stores

[Dean Long]

On Thu, 5 Oct 2023 14:20:41 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> Hi all,
> 
>   please review this change that makes sure that `Vtablestubs::stub_containing()` (and `::vtable_stub_do()` I noticed while implementing this) use proper memory fences to correctly observe the next pointers in the hash table buckets.
> 
> I assume that this memory ordering issue never occurs in the wild, there is probably always some additional memory fencing between the addition of the element to the given bucket to the iteration. However it is still the more correct code (I believe) to explicitly enforce memory ordering.
> 
> Testing: gha, class unloading stress test
> 
> Thanks,
>   Thomas

Atomic acquire loads protected by VtableStubs_lock seem unnecessary if all stores are also protected by VtableStubs_lock.

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PR Comment: https://git.openjdk.org/jdk/pull/16056#issuecomment-1751825479