Bug #21204: `TestEtc#test_ractor_parallel` is still flaky result with ModGC/MMTk

• Status: Assigned
• Assignee: eightbitraptor (Matt V-H)
• Target version: -
• Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN

[hsbt (Hiroshi SHIBATA)]

https://github.com/ruby/ruby/actions/runs/14121185441/job/39561623937?pr=13004

    1) Failure:
  TestEtc#test_ractor_parallel [/home/runner/work/ruby/ruby/src/test/etc/test_etc.rb:178]:
  pid 150540 killed by SIGABRT (signal 6) (core dumped)
  | [BUG] pthread_mutex_lock: Owner died (EOWNERDEAD)
  | ruby 3.5.0dev (2025-03-28T03:13:46Z pull/13004/merge 4cfbc634ea) +PRISM +GC[mmtk] [x86_64-linux]
  | 
  | -- Control frame information -----------------------------------------------
  | 
  | malloc_consolidate(): unaligned fastbin chunk detected
  | 
  | -- Threading information ---------------------------------------------------
  | Total ractor count: 1

[Eregon (Benoit Daloze)]

• Assignee set to eightbitraptor (Matt V-H)

This seems a ModGC bug as the failure seems to happen (from what I heard) only in the ModGC workflow, cc @eightbitraptor (Matt V-H) @peterzhu2118 (Peter Zhu)
The test has been omitted only for the ModGC workflow: https://github.com/ruby/etc/pull/55

[Eregon (Benoit Daloze)]

• Subject changed from `TestEtc#test_ractor_parallel` is still flaky result to `TestEtc#test_ractor_parallel` is still flaky result with ModGC/MMTk

[eightbitraptor (Matt V-H)]

• Status changed from Open to Assigned

[hsbt (Hiroshi SHIBATA)]

TestSocket#test_timestamp is failed sometimes on ModGC workflow.

    1) Failure:
  TestSocket#test_timestamp [/home/runner/work/ruby/ruby/src/test/socket/test_socket.rb:493]:
  <[[#<Socket:fd 7>], [], []]> expected but was
  <nil>.

https://github.com/ruby/ruby/actions/runs/14212913556/job/39823279828?pr=13037