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gh-135106: [crash repro] Randomly deposit objects in _Py_Dealloc #135589

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gh-135106: [crash repro] Randomly deposit objects in _Py_Dealloc #135589

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030abcd
gh-135106: Randomly return `1` in _Py_RecursionLimit_GetMargin
colesbury Jun 16, 2025
92e82ac
Update Include/internal/pycore_pystate.h
colesbury Jun 16, 2025
7c86a25
Update test so that RNG is in _Py_Dealloc
colesbury Jun 17, 2025
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3 changes: 3 additions & 0 deletions Include/cpython/pystate.h
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Original file line number Diff line number Diff line change
Expand Up @@ -208,6 +208,9 @@ struct _ts {
*/
PyObject *threading_local_sentinel;
_PyRemoteDebuggerSupport remote_debugger_support;

uint64_t prng;
Py_ssize_t ob_dealloc_depth;
};

/* other API */
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14 changes: 13 additions & 1 deletion Objects/object.c
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Expand Up @@ -3155,6 +3155,16 @@ _PyObject_AssertFailed(PyObject *obj, const char *expr, const char *msg,
Py_FatalError("_PyObject_AssertFailed");
}

static int
should_randomly_deposit_object(PyThreadState *tstate)
{
// splitmix64 from https://prng.di.unimi.it/splitmix64.c
uint64_t z = (tstate->prng += 0x9e3779b97f4a7c15);
z = (z ^ (z >> 30)) * 0xbf58476d1ce4e5b9;
z = (z ^ (z >> 27)) * 0x94d049bb133111eb;
uint64_t r = z ^ (z >> 31);
return (r & 0xFF) < 2;
}

/*
When deallocating a container object, it's possible to trigger an unbounded
Expand All @@ -3170,7 +3180,7 @@ _Py_Dealloc(PyObject *op)
destructor dealloc = type->tp_dealloc;
PyThreadState *tstate = _PyThreadState_GET();
intptr_t margin = _Py_RecursionLimit_GetMargin(tstate);
if (margin < 2) {
if (margin < 2 || (tstate->ob_dealloc_depth > 0 && should_randomly_deposit_object(tstate))) {
_PyTrash_thread_deposit_object(tstate, (PyObject *)op);
return;
}
Expand All @@ -3192,7 +3202,9 @@ _Py_Dealloc(PyObject *op)
_Py_ForgetReference(op);
#endif
_PyReftracerTrack(op, PyRefTracer_DESTROY);
tstate->ob_dealloc_depth++;
(*dealloc)(op);
tstate->ob_dealloc_depth--;

#ifdef Py_DEBUG
// gh-89373: The tp_dealloc function must leave the current exception
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4 changes: 4 additions & 0 deletions Python/pystate.c
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Expand Up @@ -1486,6 +1486,10 @@ init_threadstate(_PyThreadStateImpl *_tstate,
tstate->state = _Py_THREAD_SUSPENDED;
}

PyTime_t now;
PyTime_MonotonicRaw(&now);
tstate->prng = (uint64_t)now;

tstate->_status.initialized = 1;
}

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