Hi @pmathur,
From the JVM's error log we see that the segment violation occurred in a different stack frame. Previously it was Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord*), now it's nmethod::can_unload(BoolObjectClosure*, OopClosure*, oopDesc**, bool).
There is actually a related OpenJDK bug which refers to nmethod::can_unload but it is closed with "not an issue" there as it seems to be ok on Java 8. So I fear you are out of luck here.
I understand that you are reluctant to upgrade to Java 8 in your case. I assume you run Elasticsearch as a dedicated process, so although you are reluctant to upgrade your application stack to Java 8 (totally understandable), one option that you could consider is to run Elasticsearch on Java 8 and leave the rest of your application stack on Java 7.
Daniel