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Faulthandler segfaults when called from threads #131580
Description
Crash report
What happened?
In a GILfull build of main, it's rarely possible to get faulthandler to segfault when calling it from threads. Since it's a rare crash and I'm on mobile, no reduced test case is available at the moment.
Here's the traceback:
#0 _PyFrame_GetCode (f=0xfffff7fea1f0) at ./Include/internal/pycore_frame.h:94
#1 dump_frame (fd=fd@entry=2, frame=frame@entry=0xfffff7fea1f0)
at Python/traceback.c:914
#2 0x000000000076254c in dump_traceback (fd=fd@entry=2,
tstate=tstate@entry=0xaeb528 <_PyRuntime+329832>,
write_header=write_header@entry=0) at Python/traceback.c:1007
#3 0x0000000000762710 in _Py_DumpTracebackThreads (fd=2,
interp=<optimized out>, current_tstate=current_tstate@entry=0x0)
at Python/traceback.c:1114
#4 0x00000000007773b4 in faulthandler_thread (unused=unused@entry=0x0)
at ./Modules/faulthandler.c:631
#5 0x000000000075e77c in pythread_wrapper (arg=<optimized out>)
at Python/thread_pthread.h:242
#6 0x0000fffff7def188 in start_thread () from /lib64/libc.so.6
#7 0x0000fffff7e5971c in thread_start () from /lib64/libc.so.6Crash happened on ARM, if that's important.
Hmm, might be a duplicate of #128421.
Edit: reduced test case:
import faulthandler
from threading import Thread
for x in range(20):
Thread(target=faulthandler.dump_traceback_later, args=(1e-10,)).start()Found using fusil by @vstinner.
CPython versions tested on:
CPython main branch
Operating systems tested on:
Linux
Output from running 'python -VV' on the command line:
Python 3.14.0a6+ (heads/main:55815a6474c, Mar 15 2025, 14:05:03) [GCC 11.5.0 20240719 (Red Hat 11.5.0-5.0.1)]
Activity
ZeroIntensity commentedon Mar 24, 2025
Probably not, that seems to be FT only. From what I know, faulthandler is notoriously buggy in multithreaded programs, and there's not much we can do to fix it.
dgrisby commentedon Mar 24, 2025
I think this is a duplicate of #116008
tom-pytel commentedon Mar 25, 2025
Not EXACTLY same, but arises for the same reason yes, using python function
_Py_DumpTracebackThreads()in multithreaded scenario without holding the GIL.devdanzin commentedon Mar 25, 2025
Closing in favor of #116008.
vstinner commentedon Nov 5, 2025
faulthandler was made more resistant to crashes with commit a84181c. The problem is that writing the thread name in faulthandler is now more likely to crash if the thread completed.
Example of pthread_getname_np() crash in gdb: