[lworld] RFR: 8368002: [lworld] Crash in ThawBase::remove_top_compiled_frame_from_chunk [v2]

[Patricio Chilano Mateo]

> Please review this small fix. When thawing in the fast path, the top frame could be a runtime stub due to preempting on monitorenter. In the changes for JDK-8336845 I missed this, leading to a crash when dereferencing the nullptr returned by `f.cb()->as_nmethod_or_null()` in `ThawBase::remove_top_compiled_frame_from_chunk`.
> 
> I was able to reproduce the failure locally and verified it is now fixed. I did run into a pre-existing crash with Jetty (filed JDK-8368099). I also run all tests in java/lang/Thread/virtual stressing this path, tests Fuzz.java and TestVirtualThreads.java, plus extra mach5 tier testing.
> 
> Thanks,
> Patricio

Patricio Chilano Mateo has updated the pull request incrementally with one additional commit since the last revision:

  remove frames_size parameter and code duplication from remove_scalarized_frames

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/1603/files
  - new: https://git.openjdk.org/valhalla/pull/1603/files/69eb45da..4e2aed1f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1603&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1603&range=00-01

  Stats: 31 lines in 1 file changed: 0 ins; 26 del; 5 mod
  Patch: https://git.openjdk.org/valhalla/pull/1603.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1603/head:pull/1603

PR: https://git.openjdk.org/valhalla/pull/1603