RFR: 8013214 BigApps fails due to 'fatal error: Illegal threadstate encountered: 6'

[Zhengyu Gu]

The fix of 8011218 caused this failure. When a JavaThread is in _thread_in_vm state, it is not a right state that it can call SafepointSynchronize::block(). 

The fix is base on Dan's comment, that grab and drop SR_lock to get the thread to honor the safepoint protocol.



Bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8013214
Webrev:  http://cr.openjdk.java.net/~zgu/8013214/webrev/

Test:
  Ran kitchensink stress test on Linux x86, compared before and after fix. The bug was reproducible without the fix and no longer reproducible after. 


Thanks,

-Zhengyu