RFR (XS) 8047212: fix race between ObjectMonitor alloc and verification code

[Carsten Varming]

Dear Dan,

I thought acquire/release semantics mandated that the release should be
paired with an acquire. In this case, the first line in
verify_objmon_isinpool should be changed from "PaddedEnd<ObjectMonitor> *
block = (PaddedEnd<ObjectMonitor> *)gBlockList" to use a load_acquire.
Actually, it seems like there are a lot of reads of gBlockList that should
be replaced with a load_acquire in synchronizer.cpp.

Otherwise the change looks great.

Carsten
(not a reviewer).

On Mon, Oct 19, 2015 at 8:02 PM, Daniel D. Daugherty <
daniel.daugherty at oracle.com> wrote:

> Greetings,
>
> I have a fix for a long standing race between the lock-free ObjectMonitor
> verification code and the normal (locked) ObjectMonitor block allocation
> code path. For this fix, I would like at least a Runtime team reviewer
> and a Serviceability team reviewer. Thanks!
>
> JDK-8047212 runtime/ParallelClassLoading/bootstrap/random/inner-complex
>             assert(ObjectSynchronizer::verify_objmon_isinpool(inf)) failed:
>             monitor is invalid
> https://bugs.openjdk.java.net/browse/JDK-8047212
>
> Webrev URL:
> http://cr.openjdk.java.net/~dcubed/8047212-webrev/0-jdk9-hs-rt/
>
> Testing: Aurora Adhoc RT-SVC nightly batch
>          4 inner-complex fastdebug parallel runs for 4+ days and
>            600K iterations without seeing this failure; the experiment
>            is still running; final results to be reported at the end
>            of the review cycle
>          JPRT -testset hotspot
>
> This fix:
>
> - makes ObjectMonitor::gBlockList volatile
> - uses "OrderAccess::release_store_ptr(&gBlockList, temp)" to
>   make sure the new block updates _happen before_ gBlockList is
>   changed to refer to the new block
> - add SA support for a "static pointer volatile" field like:
>
>     static ObjectMonitor * volatile gBlockList;
>
> See the following link for a nice description of what "volatile"
> means in the different positions on a variable/parameter decl line:
>
>
> http://www.embedded.com/electronics-blogs/beginner-s-corner/4023801/Introduction-to-the-Volatile-Keyword
>
> Thanks, in advance, for any comments, questions or suggestions.
>
> Dan
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.openjdk.java.net/pipermail/serviceability-dev/attachments/20151019/44169596/attachment-0001.html>