Review Request (S) 8028126: nsk/jvmti/scenarios/hotswap/HS101/hs101t006 Crashed the vm on Solaris-sparc64 fastdebug builds: only current thread can flush its registers

[serguei.spitsyn at oracle.com]

Please, review the fix for:
   https://bugs.openjdk.java.net/browse/JDK-8028126

Open webrev:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2013/hotspot/8028126-JVMTI-HS101.1/

Summary:
   This is a fix for a possible race condition between the 
VMOp_GetCurrentLocation
   reaching a safepoint and target debuggee thread exiting from Java 
execution.
   The fix is to recheck the existence of the last Java frame at a safepoint
   and clean the thread current location if the thread has been already 
exited from Java.

   I'm suggesting to fix this in hs25/JDK 8.
   It is important to fix as it is a P2 bug and the risk of fixing it is 
low.
   But need reviewers to share opinions on this.
   I'll add the 8-critical-request label if reviewers agree with the above.


Testing:
   The test nsk/jvmti/scenarios/hotswap/HS101/hs101t006 that was 
originally failed.
   In progress: nsk.jvmti, nsk.jdi, nsk.jdwp


Thanks,
Serguei