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

[Daniel D. Daugherty]

Greetings,

I've updated the fix based on feedback from Carsten V and David H.

Webrev URL: http://cr.openjdk.java.net/~dcubed/8047212-webrev/1-jdk9-hs-rt/

Changes relative to round 0:

- only src/share/vm/runtime/synchronizer.cpp has changed
- reads of gBlockList now use OrderAccess::load_ptr_acquire()

code style cleanups:

- only cleaned up the functions that I touched to make the
   OrderAccess::load_ptr_acquire() changes
- changed implied booleans into real boolean expressions
- moved some locals to narrower context
- added/removed some blank lines
- made casts consistent with the majority style in this file

I'm repeating all of the same testing that I did for round 0. The
round 1 bits have not yet made it through JPRT-west, but the jobs
are mostly done.

Thanks, in advance, for any comments, questions or suggestions.

Dan





On 10/19/15, 9:02 PM, Daniel D. Daugherty 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
>
>