[issue6763] Crash on mac os x leopard in mimetypes.guess_type (or PyObject_Malloc)

[Leonardo Santagada]

New submission from Leonardo Santagada <santagada at gmail.com>:

Python 2.6.2 (and the maint branch if using old mimetypes.py) crash
(with a bus error) on mac os x (10.5.7 & 10.5.8) with the file I posted.
The problem appears to be in the allocation of memory by the GC.

What I do is I call mimetypes.guess_type in more than one thread at the
same time, then I guess what is happening is this:

1. The first thread to run notices mimetypes.inited is false so it call
its init funtion.
2. Somehow the first thread loses the gil while still executing the init
3. Another thread tries to execute guess_type as it is already inited it
calls itself, in vain as the init still hasn't exchanged it value for
the new function so it goes into recursion
4. Somehow the allocator fails during the recursion

here is the final pieces of my stack trace (its a very long sequence of
recursions into guess_type):

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_PROTECTION_FAILURE at address: 0xb0000ffc
[Switching to process 61544 thread 0x117]
0x96912122 in szone_malloc ()

#0  0x96912122 in szone_malloc ()
#1  0x969120d8 in malloc_zone_malloc ()
#2  0x9691206c in malloc ()
#3  0x0006f32c in PyObject_Malloc (nbytes=376) at Objects/obmalloc.c:913
913             return (void *)malloc(nbytes);
#4  0x0006fe61 in _PyObject_DebugMalloc (nbytes=360) at
Objects/obmalloc.c:1347
1347            p = (uchar *)PyObject_Malloc(total);
#5  0x00149b13 in _PyObject_GC_Malloc (basicsize=344) at
Modules/gcmodule.c:1351
1351            g = (PyGC_Head *)PyObject_MALLOC(
#6  0x00149c24 in _PyObject_GC_NewVar (tp=0x193500, nitems=5) at
Modules/gcmodule.c:1383
1383            PyVarObject *op = (PyVarObject *) _PyObject_GC_Malloc(size);
#7  0x00048a06 in PyFrame_New (tstate=0x33df30, code=0x473148,
globals=0x48e380, locals=0x0) at Objects/frameobject.c:642
642                         f = PyObject_GC_NewVar(PyFrameObject,
&PyFrame_Type,
#8  0x00100816 in PyEval_EvalCodeEx (co=0x473148, globals=0x48e380,
locals=0x0, args=0x374fb4, argcount=2, kws=0x374fbc, kwcount=0,
defs=0x4a6f9c, defcount=1, closure=0x0) at Python/ceval.c:2755
2755            f = PyFrame_New(tstate, co, globals, locals);

----------
components: Interpreter Core
messages: 91876
nosy: santagada
severity: normal
status: open
title: Crash on mac os x leopard in mimetypes.guess_type (or PyObject_Malloc)
type: crash
versions: Python 2.6

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue6763>
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