Integrated: 8313202: MutexLocker should disallow null Mutexes

[Aleksey Shipilev]

On Wed, 26 Jul 2023 17:06:02 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> As seen in [JDK-8313081](https://bugs.openjdk.org/browse/JDK-8313081), it is fairly easy to pass nullptr `Mutex` to `MutexLocker` by accident, which would just silently avoid the lock.
> 
> There are a few places in Hotspot where we pass `nullptr` to simulate re-entrancy and/or conditionally take the lock. Those places can be more explicit, and the default `MutexLocker` can disallow nullptrs for extra safety.
> 
> More thorough testing with different GC/JIT combinations is running now, we might find more issues there. Meanwhile, please comment on the approach.
> 
> Additional testing:
>  - [x] `grep -R "MutexLocker " src/hotspot | grep -i null`, only new `ConditionalMutexLocker` hits
>  - [x] `grep -R "MutexLocker " src/hotspot | grep -i ?`, no hits
>  - [x] Linux AArch64 fastdebug, `tier1 tier2 tier3` x `Serial Parallel G1 Shenandoah`

This pull request has now been integrated.

Changeset: 2d168c57
Author:    Aleksey Shipilev <shade at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/2d168c573402c0fc3dfb6c1fe6f48ec46997fa67
Stats:     110 lines in 18 files changed: 46 ins; 13 del; 51 mod

8313202: MutexLocker should disallow null Mutexes

Reviewed-by: dholmes, coleenp, dcubed

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PR: https://git.openjdk.org/jdk/pull/15043