RFR (S): CR6899058: G1: Internal error in ptrQueue.cpp:201 in nightly tests

[john cuthbertson - Sun Microsystems]

Hi Everyone,

Can I have a couple of volunteers to look over the code changes for this 
fix? The webrev can be found at 
http://cr.openjdk.java.net/~johnc/6899058/webrev.1/.

The problem here is a race between GC worker threads on the completed 
update buffer queue: one thread can be adding to the queue while 
processing a deferred store barrier (from the ReduceInitialCardMarks 
feature) under control of a lock, while another thread is removing 
completed update buffers (during remembered set updating) using a CAS. 
This can cause the consistency checks on the completed update buffer 
queue to fail. The fix is to remove elements from the queue under 
control of the same lock.

Testing: the failing test (gcl001), SPECjbb2005, refworkload, and jprt.

Thanks,

JohnC