RFR(S) 8176363: Incorrect lock order for G1 PtrQueue related locks

[Mikael Gerdin]

Hi Thomas,

On 2017-03-09 10:42, Thomas Schatzl wrote:
> Hi Mikael,
>
> On Wed, 2017-03-08 at 15:16 +0100, Mikael Gerdin wrote:
>> Hi all,
>>
>> Please review this change to the lock rank of the locks taken in the
>> G1 pre and post write barriers.
>>
>> The rank of these locks have long been a problem since even though
>> they are leaf locks semantically they have been ranked as "nonleaf"
>> locks in the lock rank system and this has caused several issues over
>> the years where a thread holding a VM mutex and attempting to write
>> an oop would in some rare cases hit a deadlock warning due to it
>> acquiring one of the CBL monitors.
>>
>> Now this problem has come up yet again with the weak JNI handles
>> bugfix where a lock rank assertion was hit yet again due to the fact
>> that some code was holding a leaf lock while resolving a weak JNI
>> handle.
>>
>> I suggest that the ranks of the involved locks are changed to "leaf -
>> 1", allowing them to be acquired by threads holding "leaf" locks.
>
> Looks good to me.

Thanks for the review.

/Mikael

>
> Thomas
>