RFR (S/M) JDK-8010196 NPG: Internal Error: Metaspace allocation lock -- possible deadlock

[Leonid Mesnik]

Great!

Leonid
On 04/09/2013 01:44 PM, Mikael Gerdin wrote:
> Good news!
> I managed to write a regression test by adding a bit more dependencies 
> every iteration:
>
> http://cr.openjdk.java.net/~mgerdin/8010196/webrev.0-regtest/webrev/
>
> /Mikael
>
>
> On 04/08/2013 06:34 PM, Mikael Gerdin wrote:
>> Leonid,
>>
>> On 04/08/2013 04:19 PM, Leonid Mesnik wrote:
>>> Mikael
>>>
>>> Is it possible to include regression test which reproduce problem?
>>> (based on BigArityTest.java)
>>
>> I can't say I understand what BigArityTest does that makes it introduce
>> cross-CLD dependencies.
>> I did write a test which does cause dependencies but I failed to make it
>> reproduce the problem, even though some of the dependencies were added
>> during a G1 concurrent mark cycle.
>>
>> /Mikael
>>
>>>
>>> Leonid
>>>
>>> On 04/08/2013 05:49 PM, Mikael Gerdin wrote:
>>>> Hi
>>>>
>>>> The problem is that when running the G1 garbage collector a call to
>>>> objArrayOopDesc::obj_at_put can in rare cases cause the G1 dirty card
>>>> queue buffer to fill up and this will cause G1 to take
>>>> DirtyCardQ_CBL_mon/16 to return the full buffer and get a new one.
>>>>
>>>> Adding dependencies to a ClassLoaderData is currently protected by the
>>>> per-metaspace "Metaspace allocation lock"/5 (which protects more than
>>>> just allocations).
>>>>
>>>> Because I want to avoid messing around with the lock ordering I
>>>> suggest that we use an ObjectLocker on the _dependencies oop in
>>>> ClassLoaderData.
>>>> _dependencies is a 2-element objArrayOop, in effect it's an ad-hoc
>>>> linked list of ClassLoaders/Classes which must be kept alive by this
>>>> CLD.
>>>>
>>>> Using an ObjectLocker on the head element of the linked list should be
>>>> at least as good as using the metaspace_lock(). There should not be
>>>> any new deadlock issues with VM mutexes since any application thread
>>>> could use a similar synchronized linked list construct.
>>>>
>>>> As a bonus I suggest that we factor out the dependency handling from
>>>> ClassLoaderData into a inner class: ClassLoaderData::Dependencies and
>>>> let Dependencies manage the head of the linked list by itself. This
>>>> should make it more clear that the dependency list is not guarded by
>>>> the metaspace lock anymore.
>>>>
>>>> Buglinks:
>>>> https://jbs.oracle.com/bugs/browse/JDK-8010196
>>>> http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8010196
>>>>
>>>> Testing:
>>>> default jprt run
>>>> jdk/test/java/lang/invoke/BigArityTest.java (which could reproduce the
>>>> issue with -XX:+UseG1GC -XX:G1UpdateBufferSize=1)
>>>>
>>>> Webrevs:
>>>> Incremental:
>>>> http://cr.openjdk.java.net/~mgerdin/8010196/webrev.0-fix/webrev
>>>> http://cr.openjdk.java.net/~mgerdin/8010196/webrev.0-factor-out/webrev
>>>> http://cr.openjdk.java.net/~mgerdin/8010196/webrev.0-rename/webrev
>>>> Everything:
>>>> http://cr.openjdk.java.net/~mgerdin/8010196/webrev.0/webrev
>>>>
>>>> Thanks
>>>> /Mikael
>>>
>>>
>>
>


-- 
Leonid Mesnik
JVM SQE