"unreachable code: Block(0x20100ae8000) Marked" with Immix

[wks]

The following crash happened when running CI tests with release build and the Immix plan. Link: https://github.com/mmtk/mmtk-ruby/actions/runs/11549564269/job/32142824795?pr=113#step:9:7498

  TestZlibInflate#test_recursive_inflate = 0.64 s = .
  TestGemPackageTarHeader#test_empty = 0.01 s = .
  TestGemPackageTarHeader#test_equals2 = 0.01 s = .
  TestZlibInflate#test_finish_chunked = 0.00 s = .
  thread '<unnamed>' panicked at /home/runner/.cargo/git/checkouts/mmtk-core-3306bdeb8eb4322b/618fde4/src/policy/immix/immixspace.rs:551:26:
  internal error: entered unreachable code: Block(0x20100ae8000) Marked
  stack backtrace:
     0: rust_begin_unwind
     1: core::panicking::panic_fmt
     2: mmtk::policy::immix::immixspace::ImmixSpace<VM>::get_reusable_block
     3: mmtk::util::alloc::immix_allocator::ImmixAllocator<VM>::acquire_recyclable_lines
     4: <mmtk::util::alloc::immix_allocator::ImmixAllocator<VM> as mmtk::util::alloc::allocator::Allocator<VM>>::alloc
  TestCoverage#test_coverage_snapshot = 0.10 s = .
  TestGemPackageTarHeader#test_to_s = 0.02 s = .
     5: rb_mmtk_alloc
               at ./../mmtk_support.c:464:20
     6: rb_mmtk_alloc_obj
               at ./../mmtk_support.c:512:18
     7: rb_mmtk_newobj_of_inner
               at ./../gc/default.c:2620:17
     8: rb_gc_impl_new_obj
               at ./../gc/default.c:2667:15
     9: newobj_of
               at ./../gc.c:919:17
    10: rb_wb_protected_newobj_of
               at ./../gc.c:946:12
    11: rb_ary_tmp_new_from_values
               at ./../array.c:976:11
    12: rb_ary_new_from_values
               at ./../array.c:988:12
    13: iseq_location
               at ./../proc.c:1345:12
    14: rb_proc_location
               at ./../proc.c:1365:12
    15: threadptr_invoke_proc_location
               at ./../thread.c:976:16
    16: threadptr_invoke_proc_location
               at ./../thread.c:973:1
    17: native_set_thread_name
               at ./../thread_pthread.c:2693:21
    18: thread_do_start
               at ./../thread.c:640:5
    19: thread_start_func_2
               at ./../thread.c:708:18
    20: call_thread_start_func_2
               at ./../thread_pthread.c:2180:5
    21: nt_start
               at ./../thread_pthread.c:2225:13
    22: <unknown>
    23: <unknown>
  note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
  fatal runtime error: failed to initiate panic, error 5
  TestGemPackageTarHeader#test_update_checksum = 0.09 s = .
  TestGemPackageTarHeader#test_initialize_bad = 0.01 s = .
  TestGemPackageTarHeader#test_initialize = 0.01 s = .
  TestGemCommandsUnpackCommand#test_find_in_cache = 0.36 s = .
  TestCoverage#test_oneshot_line_coverage = 0.13 s = .
  running file: /home/runner/work/mmtk-ruby/mmtk-ruby/git/ruby/test/zlib/test_zlib.rb
  
  A test worker crashed. It might be an interpreter bug or
  a bug in test/unit/parallel.rb. Try again without the -j
  option.
  
  make: *** [uncommon.mk:965: yes-test-all] Error 1

In Immix, when a block is added into ImmixSpace::reusable_blocks during Block::sweep(), it is always set to BlockState::Reusable.

So far I have not been able to reproduce this bug locally. It may be related to the PR #113 I will try to restart the CI test to see if it can be reproduced on GitHub CI.

[wks]

The same thing can be reproduced in the current master revision without any change, as seen in https://github.com/mmtk/mmtk-ruby/actions/runs/11571460199/job/32209388461?pr=115 So the bug exists in the current code base, and is not introduced by #113.

2024-10-29T10:07:31.7410627Z thread '<unnamed>' panicked at /home/runner/.cargo/git/checkouts/mmtk-core-3306bdeb8eb4322b/618fde4/src/policy/immix/immixspace.rs:551:26:
2024-10-29T10:07:31.7412367Z internal error: entered unreachable code: Block(0x20101af0000) Marked
2024-10-29T10:07:31.7413613Z stack backtrace:
2024-10-29T10:07:31.7414070Z    0: rust_begin_unwind
2024-10-29T10:07:31.7414586Z    1: core::panicking::panic_fmt
2024-10-29T10:07:31.7415374Z    2: mmtk::policy::immix::immixspace::ImmixSpace<VM>::get_reusable_block
2024-10-29T10:07:31.7416471Z    3: mmtk::util::alloc::immix_allocator::ImmixAllocator<VM>::acquire_recyclable_lines
2024-10-29T10:07:31.7417842Z    4: <mmtk::util::alloc::immix_allocator::ImmixAllocator<VM> as mmtk::util::alloc::allocator::Allocator<VM>>::alloc
2024-10-29T10:07:31.7726449Z    5: rb_mmtk_alloc
2024-10-29T10:07:31.7731305Z              at ./../mmtk_support.c:464:20
2024-10-29T10:07:31.7735626Z    6: rb_mmtk_alloc_obj
2024-10-29T10:07:31.7740026Z              at ./../mmtk_support.c:512:18
2024-10-29T10:07:31.7772712Z    7: rb_mmtk_newobj_of_inner
2024-10-29T10:07:31.7777250Z              at ./../gc/default.c:2620:17
2024-10-29T10:07:31.7781457Z    8: rb_gc_impl_new_obj
2024-10-29T10:07:31.7785748Z              at ./../gc/default.c:2667:15
2024-10-29T10:07:31.7789953Z    9: newobj_of
2024-10-29T10:07:31.7794155Z              at ./../gc.c:912:17
2024-10-29T10:07:31.7798215Z   10: rb_wb_protected_newobj_of
2024-10-29T10:07:31.7802491Z              at ./../gc.c:939:12
2024-10-29T10:07:31.7829031Z   11: rb_ary_tmp_new_from_values
2024-10-29T10:07:31.7833454Z              at ./../array.c:976:11
2024-10-29T10:07:31.7837575Z   12: rb_ary_new_from_values
2024-10-29T10:07:31.7841881Z              at ./../array.c:988:12
2024-10-29T10:07:31.7897654Z   13: iseq_location
2024-10-29T10:07:31.7901993Z              at ./../proc.c:1345:12
2024-10-29T10:07:31.7906149Z   14: rb_proc_location
2024-10-29T10:07:31.7910444Z              at ./../proc.c:1365:12
2024-10-29T10:07:31.8056213Z   15: threadptr_invoke_proc_location
2024-10-29T10:07:31.8056886Z              at ./../thread.c:976:16
2024-10-29T10:07:31.8057424Z   16: threadptr_invoke_proc_location
2024-10-29T10:07:31.8058105Z              at ./../thread.c:973:1
2024-10-29T10:07:31.8058601Z   17: native_set_thread_name
2024-10-29T10:07:31.8059349Z              at ./../thread_pthread.c:2693:21
2024-10-29T10:07:31.8059903Z   18: thread_do_start
2024-10-29T10:07:31.8060633Z              at ./../thread.c:640:5
2024-10-29T10:07:31.8061129Z   19: thread_start_func_2
2024-10-29T10:07:31.8061858Z              at ./../thread.c:708:18
2024-10-29T10:07:31.8062862Z   20: call_thread_start_func_2
2024-10-29T10:07:31.8063579Z              at ./../thread_pthread.c:2180:5
2024-10-29T10:07:31.8064084Z   21: nt_start
2024-10-29T10:07:31.8064811Z              at ./../thread_pthread.c:2225:13
2024-10-29T10:07:31.8067840Z   22: <unknown>
2024-10-29T10:07:31.8068369Z   23: <unknown>
2024-10-29T10:07:31.8069091Z note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.