Integrated: 8338379: Accesses to class init state should be properly synchronized

[Aleksey Shipilev]

On Fri, 20 Sep 2024 14:02:51 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> See the bug for the discussion. We have not seen a clear evidence this is _the_ problem in the field, neither we were able to come up with a reproducer. We have found this gap by inspecting the code, while chasing a production bug.
> 
> In short, `InstanceKlass::_init_state` is used as the "witness" for initialized class state. When class initialization completes, it needs to publish the class state by writing `_init_state = _fully_initialized` with release semantics.
> 
> Various accessors that poll `IK::_init_state`, looking for class initialization to complete, need to read the field with acquire semantics. This is where the change fans out, touching VM, interpreter and compiler paths that e.g. implement clinit barriers. In some cases in assembler code, we can rely on hardware memory model to do what we need (i.e. acquire barriers/fences are nops).
> 
> I made the best _guess_ what ARM32, S390X, PPC64, RISC-V code should look like, based on what related code does for volatile loads. It would be good if port maintainers could sanity-check those.
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `all`
>  - [x] Linux AArch64 server fastdebug, `all`
>  - [x] GHA to test platform buildability + adhoc platform cross-compilation

This pull request has now been integrated.

Changeset: 6600161a
Author:    Aleksey Shipilev <shade at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/6600161ad46fe5b1e742409481bf225cd87f07c9
Stats:     32 lines in 17 files changed: 15 ins; 0 del; 17 mod

8338379: Accesses to class init state should be properly synchronized

Reviewed-by: mdoerr, dholmes, coleenp, fyang, amitkumar

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PR: https://git.openjdk.org/jdk/pull/21110