RFR (S) 8215575: C2 crash: assert(get_instanceKlass()->is_loaded()) failed: must be at least loaded

[David Holmes]

On 8/01/2019 9:59 pm, Erik Österlund wrote:
> Hi David,
> 
> The required synchronization is that the _subklass link is read/written 
> with at least acquire/release semantics, correspondingly. And now they 
> are. (when appending, the link gets written with a conservative CAS, and 
> the link is loaded with load_acquire).

Okay. I took a look inside append_to_sibling_list and see there is lots 
of ordering control in there.

Aside: why do you need an Atomic::store in set_next_sibling ??

Thanks,
David

> Thanks,
> /Erik
> 
> On 2019-01-08 02:49, David Holmes wrote:
>> Hi Coleen,
>>
>> On 8/01/2019 5:50 am, coleen.phillimore at oracle.com wrote:
>>> Summary: Set InstanceKlass::loaded before adding classes to the 
>>> subklass list, which can be read concurrently by the compiler.
>>
>> I think you need a storestore barrier to ensure the new order is 
>> preserved.
>>
>> Cheers,
>> David
>>
>>> Thanks to Erik for the diagnosis and suggested fix.  See bug comments 
>>> for more details.
>>>
>>> Tested with hs-tier1-3, 6 and 8.
>>>
>>> open webrev at http://cr.openjdk.java.net/~coleenp/8215575.01/webrev
>>> bug link https://bugs.openjdk.java.net/browse/JDK-8215575
>>>
>>> Thanks,
>>> Coleen
>