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

serguei.spitsyn at oracle.com serguei.spitsyn at oracle.com
Wed Oct 21 00:43:28 UTC 2015

Dan,

Nice finding!

The fixes look good to me. The changes in the oops_do() and deflate_idle_monitors() are not necessary as these functions are called in VM_Operation's. But some unification with OrderAccess::load_ptr_acquire() does not harm either.

Thanks, Serguei

On 10/20/15 14:15, Daniel D. Daugherty wrote:

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::loadptracquire() code style cleanups: - only cleaned up the functions that I touched to make the OrderAccess::loadptracquire() 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::verifyobjmonisinpool(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::releasestoreptr(&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

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