RFR: 8313202: MutexLocker should disallow null Mutexes [v7]

[Aleksey Shipilev]

On Mon, 4 Sep 2023 09:44:11 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`
>
> Aleksey Shipilev has updated the pull request incrementally with three additional commits since the last revision:
> 
>  - Touchup whitespace
>  - Rewrite jvmtiManageCapabilities lock usage
>  - Re-instate old asserts

@alexmenkov, I rewrote the `jvmtiCapabilities` lock usage introduced by #15219, want to take a look as well?

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PR Comment: https://git.openjdk.org/jdk/pull/15043#issuecomment-1711297469