JIT: assertion failure in `_Py_DECREF_NO_DEALLOC`

[devdanzin]

Crash report

What happened?

It's possible to make a debug JIT build abort by running the code below:

import gc
gc.set_threshold(1)

def f1():
    for i in range(5000):
        globals()[''] = i

f1()

Error message and backtrace:

Fatal Python error: _Py_DECREF_NO_DEALLOC: Expected a positive remaining refcount: bug likely caused by a refcount error in a C extension
Python runtime state: initialized

Current thread 0x00007ffff7e503c0 [python] (most recent call first):
  File "/home/danzin/crashers/reduced_crash_signal_SIGABRT_child_934_78_2.py", line 6 in f1
  File "/home/danzin/crashers/reduced_crash_signal_SIGABRT_child_934_78_2.py", line 8 in <module>

Program received signal SIGABRT, Aborted.

#0  __pthread_kill_implementation (threadid=<optimized out>, signo=6, no_tid=0) at ./nptl/pthread_kill.c:44
#1  __pthread_kill_internal (threadid=<optimized out>, signo=6) at ./nptl/pthread_kill.c:89
#2  __GI___pthread_kill (threadid=<optimized out>, signo=signo@entry=6) at ./nptl/pthread_kill.c:100
#3  0x00007ffff7c45e2e in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
#4  0x00007ffff7c28888 in __GI_abort () at ./stdlib/abort.c:77
#5  0x000055555609fbb4 in fatal_error_exit (status=status@entry=-1) at Python/pylifecycle.c:3284
#6  0x000055555609f7f6 in fatal_error (fd=<optimized out>, header=<optimized out>, prefix=<optimized out>, msg=<optimized out>, status=<optimized out>) at Python/pylifecycle.c:3493
#7  0x000055555609fb8e in _Py_FatalErrorFormat (func=<optimized out>, format=<optimized out>) at Python/pylifecycle.c:3546
#8  0x000055555609fbf6 in _Py_FatalRefcountErrorFunc (func=0x555556505200 <__func__._Py_DECREF_NO_DEALLOC> "_Py_DECREF_NO_DEALLOC",
    msg=0x555556505240 <str> "Expected a positive remaining refcount") at Python/pylifecycle.c:3553
#9  0x0000555556065d95 in _Py_DECREF_NO_DEALLOC (op=0x7d9ff6ff98a0) at ./Include/internal/pycore_object.h:269
#10 _Py_ClearExecutorDeletionList (interp=0x5555569764a0 <_PyRuntime+133952>) at Python/optimizer.c:313
#11 0x0000555555fedf1e in _Py_HandlePending (tstate=tstate@entry=0x5555569ad330 <_PyRuntime+358864>) at Python/ceval_gil.c:1401
#12 0x0000555555eedfa7 in check_periodics (tstate=<optimized out>) at Python/ceval_macros.h:494
#13 _PyTier2Interpreter (current_executor=<optimized out>, frame=<optimized out>, stack_pointer=<optimized out>, tstate=<optimized out>) at Python/executor_cases.c.h:59
#14 0x0000555555e7422e in _PyEval_EvalFrameDefault (tstate=<optimized out>, frame=<optimized out>, throwflag=<optimized out>) at Python/generated_cases.c.h:5348
#15 0x0000555555e4ef98 in _PyEval_EvalFrame (tstate=0x5555569ad330 <_PyRuntime+358864>, frame=0x7e8ff6fe5220, throwflag=0) at ./Include/internal/pycore_ceval.h:119
#16 _PyEval_Vector (tstate=<optimized out>, func=<optimized out>, locals=<optimized out>, args=<optimized out>, argcount=<optimized out>, kwnames=0x0) at Python/ceval.c:2483

Output from running with PYTHON_LLTRACE=4 PYTHON_OPT_DEBUG=4:
934_abort_lltrace_opt_debug.txt

Found using lafleur.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.15.0a3+ (heads/main:5989095dfd0, Dec 20 2025, 16:09:33) [Clang 21.1.2 (2ubuntu6)]

Linked PRs

• GH-143026: Fix assertion error in executor management. #143104