RFR:8047290:Ensure consistent safepoint checking in MutexLockerEx

[Max Ockner]

Hi all,

I am a new member of the Hotspot runtime team in Burlington, MA.
Please review my first fix related to safepoint checking.

Summary: MutexLockerEx can either acquire a lock with or without a 
safepoint check.
In some cases, a particular lock must either safepoint check always or 
never to avoid deadlocking.
Some other locks have semantics which allow them to avoid deadlocks 
despite having a safepoint check only some of the time.
All locks that are OK having inconsistent safepoint checks have been 
marked. All locks that should never safepoint check and all locks that 
should always safepoint check have also been marked.
When a MutexLockerEx acquires a lock with or without a safepoint check, 
the lock's safepointAllowed marker is checked to ensure consistent 
safepoint checking.

Webrev: http://oklahoma.us.oracle.com/~mockner/webrev/8047290/
Bug: https://bugs.openjdk.java.net/browse/JDK-8047290

Tested with:
     jprt "-testset hotspot"
     jtreg hotspot
     vm.quick.testlist

Whitebox tests:
test/runtime/Safepoint/AssertSafepointCheckConsistency1.java: Test 
expects Assert ("This lock should always have a safepoint check")
test/runtime/Safepoint/AssertSafepointCheckConsistency2.java: Test 
expects Assert ("This lock should never have a safepoint check")
test/runtime/Safepoint/AssertSafepointCheckConsistency3.java: code 
should not assert. (Lock is properly acquired with no safepoint check)
test/runtime/Safepoint/AssertSafepointCheckConsistency4.java: code 
should not assert. (Lock is properly acquired with safepoint check)

Thanks,
Max