[jdk21u] RFR: 8318757: VM_ThreadDump asserts in interleaved ObjectMonitor::deflate_monitor calls [v2]

[Aleksey Shipilev]

> Fixes an important race condition in monitor deflation code. Applies cleanly, but the test needs `-XX:+UnlockExperimentalVMOptions` to unlock `-XX:LockingMode=0`.
> 
> Additional testing:
>  - [x] MacOS AArch64 fastdebug, new regression test fails without the fix, passes with it
>  - [x] Linux AArch64 fastdebug `tier1 tier2 tier3 tier4`

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  Unlock LockingMode properly

-------------

Changes:
  - all: https://git.openjdk.org/jdk21u/pull/384/files
  - new: https://git.openjdk.org/jdk21u/pull/384/files/0b00053c..837837ff

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk21u&pr=384&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk21u&pr=384&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u/pull/384.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/384/head:pull/384

PR: https://git.openjdk.org/jdk21u/pull/384