Michael Goldish added the comment:
OK, I caught the crash with a debug build of Python 3.4.3.
I have a core dump and even the process itself still alive in memory. I can
provide any information you need. I can also explain how to debug a core dump
with Visual Studio, if necessary.
This time the crash was here:
static void
update_refs(PyGC_Head *containers)
{
PyGC_Head *gc = containers->gc.gc_next;
for (; gc != containers; gc = gc->gc.gc_next) {
assert(_PyGCHead_REFS(gc) == GC_REACHABLE);
_PyGCHead_SET_REFS(gc, Py_REFCNT(FROM_GC(gc)));
/* Python's cyclic gc should never see an incoming refcount
* of 0: if something decref'ed to 0, it should have been
* deallocated immediately at that time.
* Possible cause (if the assert triggers): a tp_dealloc
* routine left a gc-aware object tracked during its teardown
* phase, and did something-- or allowed something to happen --
* that called back into Python. gc can trigger then, and may
* see the still-tracked dying object. Before this assert
* was added, such mistakes went on to allow gc to try to
* delete the object again. In a debug build, that caused
* a mysterious segfault, when _Py_ForgetReference tried
* to remove the object from the doubly-linked list of all
* objects a second time. In a release build, an actual
* double deallocation occurred, which leads to corruption
* of the allocator's internal bookkeeping pointers. That's
* so serious that maybe this should be a release-build
* check instead of an assert?
*/
------> assert(_PyGCHead_REFS(gc) != 0); <------- crash
}
}
In the calling frame I can see that update_refs() is called with a PyGC_Head
object whose gc_refs is 0, and according to the paragraph above that shouldn't
happen. A screenshot is attached.
Stack trace:
msvcr100d.dll!_NMSG_WRITE(int rterrnum=10) Line 217
msvcr100d.dll!abort() Line 71
msvcr100d.dll!_wassert(const wchar_t * expr=0x0000000063220618, const wchar_t *
filename=0x00000000632205e0, unsigned int lineno=364) Line 153
python34_d.dll!update_refs(_gc_head * containers=0x000000006338cfc0) Line 364
+ 0x2b bytes
python34_d.dll!collect(int generation=0, __int64 *
n_collected=0x000000012beee530, __int64 * n_uncollectable=0x000000012beee520,
int nofail=0) Line 969
python34_d.dll!collect_with_callback(int generation=0) Line 1140 + 0x16 bytes
python34_d.dll!collect_generations() Line 1163 + 0x9 bytes
python34_d.dll!_PyObject_GC_Malloc(unsigned __int64 basicsize=56) Line 1739
python34_d.dll!_PyObject_GC_New(_typeobject * tp=0x00000000633ce280) Line 1748
+ 0xe bytes
python34_d.dll!PyList_New(__int64 size=0) Line 159 + 0xc bytes
python34_d.dll!PyEval_EvalFrameEx(_frame * f=0x000000010f387658, int
throwflag=3) Line 2347 + 0x8 bytes
python34_d.dll!fast_function(_object * func=0x0000000000000003, _object * * *
pp_stack=0x0000000129e69948, int n=737077536, int na=1661137695, int nk=0)
Line 4335
python34_d.dll!call_function(_object * * * pp_stack=0x000000012beee919, int
oparg=131) Line 4263
python34_d.dll!PyEval_EvalFrameEx(_frame * f=0x000000011c077528, int
throwflag=3) Line 2840
python34_d.dll!fast_function(_object * func=0x0000000000000003, _object * * *
pp_stack=0x0000000089a53190, int n=737078048, int na=1661137695, int nk=0)
Line 4335
python34_d.dll!call_function(_object * * * pp_stack=0x000000012beeeb19, int
oparg=131) Line 4263
python34_d.dll!PyEval_EvalFrameEx(_frame * f=0x000000010369f2a8, int
throwflag=0) Line 2840
python34_d.dll!PyEval_EvalCodeEx(_object * _co=0x0000000100000002, _object *
globals=0x0000000100000002, _object * locals=0x000000001fa5e218, _object * *
args=0x0000000000730088, int argcount=2, _object * * kws=0x0000000000730080,
int kwcount=0, _object * * defs=0x0000000000000000, int defcount=0, _object *
kwdefs=0x0000000000000000, _object * closure=0x0000000000000000) Line 3588 +
0xf bytes
python34_d.dll!function_call(_object * func=0x0000000003c10058, _object *
arg=0x000000001fa5e218, _object * kw=0x00000001296360c8) Line 638 + 0x8a bytes
python34_d.dll!PyObject_Call(_object * func=0x0000000003c10058, _object *
arg=0x000000001fa5e218, _object * kw=0x00000001296360c8) Line 2040 + 0x13 bytes
python34_d.dll!ext_do_call(_object * func=0x00000000c42c25a0, _object * * *
pp_stack=0x000000012beeee49, int flags=62980184, int na=1, int nk=0) Line 4561
+ 0xe bytes
python34_d.dll!PyEval_EvalFrameEx(_frame * f=0x00000000fa4eab18, int
throwflag=1) Line 2880
python34_d.dll!fast_function(_object * func=0x0000000000000001, _object * * *
pp_stack=0x000000003b42f398, int n=737079376, int na=1661137695, int nk=0)
Line 4335
python34_d.dll!call_function(_object * * * pp_stack=0x000000012beef049, int
oparg=131) Line 4263
python34_d.dll!PyEval_EvalFrameEx(_frame * f=0x000000010f38ec28, int
throwflag=0) Line 2840
python34_d.dll!PyEval_EvalCodeEx(_object * _co=0x0000000100000002, _object *
globals=0x0000000100000002, _object * locals=0x000000012a1e5d78, _object * *
args=0x0000000000730088, int argcount=2, _object * * kws=0x0000000000730080,
int kwcount=0, _object * * defs=0x0000000000000000, int defcount=0, _object *
kwdefs=0x0000000000000000, _object * closure=0x0000000000000000) Line 3588 +
0xf bytes
python34_d.dll!function_call(_object * func=0x00000000036d2d48, _object *
arg=0x000000012a1e5d78, _object * kw=0x000000012a1f1918) Line 638 + 0x8a bytes
python34_d.dll!PyObject_Call(_object * func=0x00000000036d2d48, _object *
arg=0x000000012a1e5d78, _object * kw=0x000000012a1f1918) Line 2040 + 0x13 bytes
python34_d.dll!ext_do_call(_object * func=0x00000000033f6040, _object * * *
pp_stack=0x000000012beef379, int flags=57486664, int na=0, int nk=0) Line 4561
+ 0xe bytes
python34_d.dll!PyEval_EvalFrameEx(_frame * f=0x000000010f80f118, int
throwflag=1) Line 2880
python34_d.dll!fast_function(_object * func=0x0000000000000001, _object * * *
pp_stack=0x000000012a1ee878, int n=737080704, int na=1661137695, int nk=0)
Line 4335
python34_d.dll!call_function(_object * * * pp_stack=0x000000012beef579, int
oparg=131) Line 4263
python34_d.dll!PyEval_EvalFrameEx(_frame * f=0x000000010f1c8b98, int
throwflag=1) Line 2840
python34_d.dll!fast_function(_object * func=0x0000000000000001, _object * * *
pp_stack=0x000000012a1ee878, int n=737081216, int na=1661137695, int nk=0)
Line 4335
python34_d.dll!call_function(_object * * * pp_stack=0x000000012beef779, int
oparg=131) Line 4263
python34_d.dll!PyEval_EvalFrameEx(_frame * f=0x000000010f80ee88, int
throwflag=0) Line 2840
python34_d.dll!PyEval_EvalCodeEx(_object * _co=0x0000000000000001, _object *
globals=0x0000000100000001, _object * locals=0x0000000000730058, _object * *
args=0x0000000000000000, int argcount=1, _object * * kws=0x0000000000000000,
int kwcount=0, _object * * defs=0x0000000000000000, int defcount=0, _object *
kwdefs=0x0000000000000000, _object * closure=0x0000000000000000) Line 3588 +
0xf bytes
python34_d.dll!function_call(_object * func=0x0000000003404058, _object *
arg=0x000000012a1ee058, _object * kw=0x0000000000000000) Line 638 + 0x8a bytes
python34_d.dll!PyObject_Call(_object * func=0x0000000003404058, _object *
arg=0x000000012a1ee058, _object * kw=0x0000000000000000) Line 2040 + 0x13 bytes
python34_d.dll!method_call(_object * func=0x0000000003404058, _object *
arg=0x000000012a1ee058, _object * kw=0x0000000000000000) Line 347 + 0x1d bytes
python34_d.dll!PyObject_Call(_object * func=0x0000000003826fa8, _object *
arg=0x0000000000730058, _object * kw=0x0000000000000000) Line 2040 + 0x13 bytes
python34_d.dll!PyEval_CallObjectWithKeywords(_object * func=0x0000000000000000,
_object * arg=0x0000000000000000, _object * kw=0x0000000000000000) Line 4115
python34_d.dll!t_bootstrap(void * boot_raw=0x00000000e2e0df70) Line 1000 +
0x20 bytes
python34_d.dll!bootstrap(void * call=0x000000000070ef20) Line 176
msvcr100d.dll!_callthreadstartex() Line 314 + 0x17 bytes
msvcr100d.dll!_threadstartex(void * ptd=0x000000007be2d110) Line 297
kernel32.dll!0000000076eb5a4d()
[Frames below may be incorrect and/or missing, no symbols loaded for
kernel32.dll]
ntdll.dll!00000000775aba01()
----------
Added file: http://bugs.python.org/file38498/gc_refs.png
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<http://bugs.python.org/issue23187>
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