RFR: 8300926: Several startup regressions ~6-70% in 21-b6 all platforms [v6]

[Robbin Ehn]

On Mon, 6 Mar 2023 07:05:00 GMT, Axel Boldt-Christmas <aboldtch at openjdk.org> wrote:

>> Robbin Ehn has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Comment fixes
>>  - Include/fwd fixes
>
> src/hotspot/share/prims/whitebox.cpp line 798:
> 
>> 796:       result += mh->method_holder()->mark_osr_nmethods(&deopt_scope, mh());
>> 797:     } else if (mh->code() != nullptr) {
>> 798:       deopt_scope.mark(mh->code());
> 
> I was working on a patch based on top of this one and had a crash here.
> 
> The second call to `mh->code()` returned a `nullptr`. It looks racy to me and seems like the only thing protecting `CompileMethod::code()` is the `CompiledMethod_lock` which is not held here. 
> 
> Regardless `mh->code()` should probably only be loaded once. (Or at least not re-loaded after the nullptr check)

Fixed, thanks!

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PR: https://git.openjdk.org/jdk/pull/12585