RFR: 8212184: Incorrect oop ref strength used for referents in FinalReference

[Kim Barrett]

> On Oct 15, 2018, at 10:42 AM, Per Liden <per.liden at oracle.com> wrote:
> 
> AccessBarrierSupport::resolve_unknown_oop_ref_strength() returns an incorrect oop ref strength for referents in FinalReference objects. It currently returns ON_WEAK_OOP_REF when it should return ON_STRONG_OOP_REF. This is not really an issue for any GC except ZGC when using the ZHeapIterator to walk the heap while resurrection is blocked.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8212184
> Webrev: http://cr.openjdk.java.net/~pliden/8212184/webrev.0
> 
> /Per

src/hotspot/share/gc/shared/accessBarrierSupport.cpp
  32   if (!java_lang_ref_Reference::is_referent_field(base, offset) ||
  33       java_lang_ref_Reference::is_final(base)) {
  34     ds |= ON_STRONG_OOP_REF;

This doesn't seem right.  Doesn't this give the wrong answer for G1?

I'm not even sure "strong" is the right answer for ZGC in the
described context.

What am I missing?