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

David Holmes david.holmes at oracle.com
Wed Oct 21 02:34:36 UTC 2015

On 21/10/2015 10:43 AM, serguei.spitsyn at oracle.com wrote:

Dan,

Nice finding! The fixes look good to me. The changes in the oopsdo() and deflateidlemonitors() are not necessary as these functions are called in VMOperation's. But some unification with OrderAccess::loadptracquire() does not harm either.

I was thinking on the same lines: that reading the variable at a safepoint should already be safe, but that consistently using load_acquire_ptr is harmless and stylistically a 'Good Thing".

The other thought I had was perhaps making the verification routines (which are non-product) use the lock as well. :)

Aside: did you check that all the other global monitor variables are accessed correctly - ie either always with the lock held or using OrderAccess operations if lock-free?

I have still have the query about the vmStructs changes but otherwise thumbs up.

Thanks, David

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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