RFR: 8276801: gc/stress/CriticalNativeStress.java fails intermittently with Shenandoah [v2]

[Aleksey Shipilev]

On Wed, 10 Nov 2021 13:08:23 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

> > I still do not understand about `ShenandoahCodeRoots::unregister_nmethod` here. You seem to have restored the assert in the nmethod-table ([0248f1e](https://github.com/openjdk/jdk/commit/0248f1e4cd6a8311f0532c637a31bd71c9041451)), but surely the assert `ShenandoahCodeRoots::unregister_nmethod` can also be called at safepoint without `CodeCache_lock` held?
> 
> It seems possible during [STW unloading](https://github.com/openjdk/jdk/blob/master/src/hotspot/share/gc/shared/parallelCleaning.cpp#L81)
> 
> I will take a further look in separate CR see if we can cleanup a bit.

Why further CR, though? I think current code is guaranteed to fail that new assert during STW unloading? If so, we need to keep `assert_locked_or_safepoint` intact.

-------------

PR: https://git.openjdk.java.net/jdk/pull/6316