[lworld] RFR: 8306568: [lworld] Oop verification failure in InlineKlass::returned_inline_klass

[Tobias Hartmann]

Oop verification intermittently fails with ZGC when checking the oop return value of a method from `ThreadSafepointState::handle_polling_page_exception` -> `InlineKlass::returned_inline_klass`  at returns. The problem is that header verification in `oopDesc::is_oop` fails because the mark word is set. Given that this code is executed outside of a safepoint, it's not safe to assume that the mark word is zero. I changed the verification code accordingly.

Thanks,
Tobias

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Commit messages:
 - 8306568: [lworld] Oop verification failure in InlineKlass::returned_inline_klass

Changes: https://git.openjdk.org/valhalla/pull/840/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=840&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306568
  Stats: 7 lines in 1 file changed: 0 ins; 3 del; 4 mod
  Patch: https://git.openjdk.org/valhalla/pull/840.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/840/head:pull/840

PR: https://git.openjdk.org/valhalla/pull/840