RFR: 8316694: Implement relocation of nmethod within CodeCache [v46]

[Chad Rakoczy]

On Sat, 30 Aug 2025 00:32:02 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> It failed on linux-x64 and linux-aarch64. I tried locally on linux-x64 but it passed.

Sorry for the late response I have been on vacation.

The test failed due to a race condition involving the de-optimization of a `not_installed` nmethod.

`CompiledICLocker` uses `CompiledICProtectionBehaviour::is_safe(nm)` to determine whether it needs to acquire the `CompiledIC_lock`. If the nmethod `not_installed` at the time of the check, the lock is not acquired. However, if the nmethod is de-optimized and its state transitions to `not_entrant`, the next evaluation of `is_safe(nm)` will return false because the nmethod is no longer `not_installed`.

The fix is to ensure that the `NMethodState_lock` is held when checking `nmethod::is_not_installed`, to prevent concurrent state changes that could lead to this race.

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PR Comment: https://git.openjdk.org/jdk/pull/23573#issuecomment-3272584418