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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"GC crash _PyObject_AssertFailed with pdb","articleBody":"Reproducer:\r\n```py\r\ndef func():\r\n    print(\r\n      42\r\n    )\r\n\r\nimport pdb; pdb.set_trace()\r\nfunc()\r\n```\r\n\r\nCrash:\r\n```console\r\n@kumaraditya303 ➜ /workspaces/cpython (main ✗) $ ./python main.py \r\n\u003e /workspaces/cpython/main.py(7)\u003cmodule\u003e()\r\n-\u003e func()\r\n(Pdb) s\r\n--Call--\r\n\u003e /workspaces/cpython/main.py(1)func()\r\n-\u003e def func():\r\n(Pdb) n\r\n\u003e /workspaces/cpython/main.py(2)func()\r\n-\u003e print(\r\n(Pdb) n\r\n\u003e /workspaces/cpython/main.py(3)func()\r\n-\u003e 42\r\n(Pdb) j 1\r\n\u003e /workspaces/cpython/main.py(1)func()\r\n-\u003e def func():\r\n(Pdb) exit\r\nTraceback (most recent call last):\r\n  File \"/workspaces/cpython/main.py\", line 7, in \u003cmodule\u003e\r\n    func()\r\n    ^^^^^^\r\n  File \"/workspaces/cpython/main.py\", line 1, in func\r\n    def func():\r\n    \r\n  File \"/workspaces/cpython/main.py\", line 1, in func\r\n    def func():\r\n    \r\n  File \"/workspaces/cpython/Lib/bdb.py\", line 90, in trace_dispatch\r\n    return self.dispatch_line(frame)\r\n           ^^^^^^^^^^^^^^^^^^^^^^^^^\r\n  File \"/workspaces/cpython/Lib/bdb.py\", line 115, in dispatch_line\r\n    if self.quitting: raise BdbQuit\r\n                      ^^^^^^^^^^^^^\r\nbdb.BdbQuit\r\nModules/gcmodule.c:113: gc_decref: Assertion \"gc_get_refs(g) \u003e 0\" failed: refcount is too small\r\nEnable tracemalloc to get the memory block allocation traceback\r\n\r\nobject address  : 0x7f18ff3b81d0\r\nobject refcount : 2\r\nobject type     : 0x55cfef2a6460\r\nobject type name: builtin_function_or_method\r\nobject repr     : \u003cbuilt-in function print\u003e\r\n\r\nFatal Python error: _PyObject_AssertFailed: _PyObject_AssertFailed\r\nPython runtime state: finalizing (tstate=0x000055cfef3bca48)\r\n\r\nCurrent thread 0x00007f18ff707280 (most recent call first):\r\n  Garbage-collecting\r\n  \u003cno Python frame\u003e\r\nAborted (core dumped)\r\n```\r\n\r\n\u003cdetails\u003e\r\n\u003csummary\u003eGDB stack trace (main)\u003c/summary\u003e\r\n\r\n```console\r\n#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50\r\n#1  0x00007ffff7c71859 in __GI_abort () at abort.c:79\r\n#2  0x000055555585db52 in fatal_error_exit (status=-1) at Python/pylifecycle.c:2614\r\n#3  fatal_error (fd=2, header=header@entry=1, prefix=\u003coptimized out\u003e, \r\n    prefix@entry=0x55555594cd70 \u003c__func__.19026\u003e \"_PyObject_AssertFailed\", msg=\u003coptimized out\u003e, \r\n    msg@entry=0x55555594c575 \"_PyObject_AssertFailed\", status=status@entry=-1)\r\n    at Python/pylifecycle.c:2795\r\n#4  0x000055555585dbb4 in _Py_FatalErrorFunc (\r\n    func=func@entry=0x55555594cd70 \u003c__func__.19026\u003e \"_PyObject_AssertFailed\", \r\n    msg=msg@entry=0x55555594c575 \"_PyObject_AssertFailed\") at Python/pylifecycle.c:2811\r\n#5  0x00005555557431d2 in _PyObject_AssertFailed (\r\n    obj=obj@entry=\u003cbuilt-in method print of module object at remote 0x7ffff78f32f0\u003e, \r\n    expr=expr@entry=0x5555559ab18c \"gc_get_refs(g) \u003e 0\", \r\n    msg=msg@entry=0x55555594c5eb \"refcount is too small\", \r\n    file=file@entry=0x5555559ab11c \"Modules/gcmodule.c\", line=line@entry=113, \r\n    function=function@entry=0x5555559ab6c8 \u003c__func__.18373\u003e \"gc_decref\") at Objects/object.c:2360\r\n#6  0x000055555588ad50 in gc_decref (g=0x7ffff79001c0) at Modules/gcmodule.c:116\r\n#7  visit_decref (op=\u003cbuilt-in method print of module object at remote 0x7ffff78f32f0\u003e, \r\n    parent=0x7ffff7900ad0) at Modules/gcmodule.c:459\r\n#8  0x00005555557249a5 in dict_traverse (op=\u003coptimized out\u003e, visit=0x55555588ac96 \u003cvisit_decref\u003e, \r\n    arg=0x7ffff7900ad0) at Objects/dictobject.c:3547\r\n#9  0x000055555588a741 in subtract_refs (\r\n    containers=containers@entry=0x555555b869a8 \u003c_PyRuntime+53896\u003e) at Modules/gcmodule.c:478\r\n#10 0x000055555588be95 in deduce_unreachable (unreachable=0x7fffffffc1d0, \r\n    base=0x555555b869a8 \u003c_PyRuntime+53896\u003e) at Modules/gcmodule.c:1100\r\n#11 gc_collect_main (tstate=tstate@entry=0x555555ba0a48 \u003c_PyRuntime+160552\u003e, \r\n    generation=generation@entry=2, n_collected=n_collected@entry=0x7fffffffc258, \r\n    n_uncollectable=n_uncollectable@entry=0x7fffffffc260, nofail=nofail@entry=0)\r\n    at Modules/gcmodule.c:1226\r\n```\r\n\u003c/details\u003e\r\n\r\nPython versions tested:\r\n- Python 3.11.0b3+ 41e4b426ce (remotes/upstream/3.11:41e4b426ce, Jun 24 2022, 11:58:10) [GCC 9.4.0] on linux\r\n- Python 3.12.0a0 51fd4de101 (heads/main:51fd4de101, Jun 24 2022, 12:02:08) [GCC 9.4.0] on linux\r\n\r\ncc @markshannon @pablogsal \r\n","author":{"url":"https://github.com/kumaraditya303","@type":"Person","name":"kumaraditya303"},"datePublished":"2022-06-24T12:09:49.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":24},"url":"https://github.com/94215/cpython/issues/94215"}