RFR: 8327647: Occasional SIGSEGV in markWord::displaced_mark_helper() for SPECjvm2008 sunflow [v4]

[Dean Long]

On Thu, 18 Apr 2024 17:19:30 GMT, Matias Saavedra Silva <matsaave at openjdk.org> wrote:

>> A misplaced memory barrier causes a very intermittent crash on on some aarch64 systems. This patch adds an appropriate LoadLoad barrier after a constant pool cache field entry is loaded. Verified with tier 1-5 tests.
>
> Matias Saavedra Silva has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fei comments

If I understand correctly, the order of writes must be:

1. ResolvedFieldEntry fields, except _get_code and _put_code
2. _get_code, _put_code
3. patch_bytecode(fast_bytecode)

so the order of reads must be reversed.  That's why there are load-acquires when reading _get_code and _put_code.
After [3] is done, after dispatching to fast_bytecode, we need to do a LoadLoad between the already read fast bytecode [3] and the "cache" fields [1].  The LoadLoad is not for the load of the next bytecode that will be done in dispatch_next().

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PR Comment: https://git.openjdk.org/jdk/pull/18477#issuecomment-2067373161