RFR 8234359: [JVMCI] invalidate_nmethod_mirror shouldn't use a phantom reference

[Vladimir Kozlov]

On other hand there is testing failure which seems 8234429.

May be we should hold this fix until 8234429 is resolved. And retest 
again after it fixed

Thanks,
Vladimir

On 11/21/19 10:15 AM, Vladimir Kozlov wrote:
> +1
> 
> Vladimir K
> 
> On 11/20/19 10:50 PM, Erik Österlund wrote:
>> Hi Tom,
>>
>> Looks good.
>>
>> Thanks,
>> /Erik
>>
>>> On 21 Nov 2019, at 06:22, Tom Rodriguez <tom.rodriguez at oracle.com> 
>>> wrote:
>>>
>>> http://cr.openjdk.java.net/~never/8234359/webrev
>>> https://bugs.openjdk.java.net/browse/JDK-8234359
>>>
>>> While testing the latest JVMCI in JDK11, crashes were occurring 
>>> during draining of the SATB buffers.  The problem was tracked down to 
>>> invalidate_nmethod_mirror being called on an nmethod whose 
>>> InstalledCode instance was also dead in the current GC. Reading this 
>>> oop using NativeAccess<ON_PHANTOM_OOP_REF> lead to that oop being 
>>> enqueued in the SATB buffer.  In JDK 14 it appears some other change 
>>> in G1 disables those barriers at the point this code is executed but 
>>> in JDK11 no such logic exists.  This code never resurrects that oop 
>>> so using the normal AS_NO_KEEPALIVE semantics is correct and avoids 
>>> attempting to enqueue the potentially dead object.
>>>
>>> tom
>>