RFR: 8375541: G1: Race in G1BarrierSet::write_ref_field_post() [v3]

[Aleksey Shipilev]

On Wed, 21 Jan 2026 14:02:31 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> Hi all,
>> 
>>   during conversion of card table code to use `Atomic<T>` I think I found the following error: the code in `G1BarrierSet::write_ref_field_post` is wrong in that it allows reload of the `_card_table` value, which is exactly what the existing code imo wrongly fails to ensure. even if it does not, making the load explicit improves reading.
>> 
>> To not let this change get lost in that conversion, and potentially for backport to 26, I factored it out in this change.
>> 
>> There is no known issue caused by this code in particular, one other bug I'm working on that just looks like what could be caused by this is not fixed.
>> 
>> Testing: gha
>> 
>> Thanks,
>>   Thomas
>
> Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:
> 
>   * walulyai review

Not sure how much this actually saves us from C++ UB behavior wrt data races, but the fix does not hurt either.

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Marked as reviewed by shade (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/29311#pullrequestreview-3691778816