[jdk21u] RFR: 8317262: LockStack::contains(oop) fails "assert(t->is_Java_thread()) failed: incorrect cast to JavaThread"

Tue Oct 17 09:10:10 UTC 2023

Clean backport to fix the trivial bug in new light-weight locking. This code path is disabled by default in JDK 21u, but the bug would manifest if any user experimentally enables it.

Additional testing:
 - [x] New regression test fails without the patch, passes with it (needs explicit `-XX:LockingMode=2` to reproduce)

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Commit messages:
 - Backport 4ea1b99c1a6efe144af381ea538f93718e9baf74

Changes: https://git.openjdk.org/jdk21u/pull/262/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=262&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317262
  Stats: 101 lines in 2 files changed: 97 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk21u/pull/262.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/262/head:pull/262

PR: https://git.openjdk.org/jdk21u/pull/262