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gh-117657: Fix some races in tracebacks #121748

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gh-117657: Fix some races in tracebacks #121748

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6cb8897
Fix races in tracebacks
Fidget-Spinner Jul 14, 2024
5bc855c
use atomics in new_reference
Fidget-Spinner Jul 14, 2024
da8415d
Add more atomics
Fidget-Spinner Jul 14, 2024
ef99cb9
Update Include/cpython/pyatomic_msc.h
Fidget-Spinner Jul 22, 2024
951a34d
revert atomics
Fidget-Spinner Jul 24, 2024
6e0e176
Use argumentclinic
Fidget-Spinner Jul 24, 2024
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4 changes: 4 additions & 0 deletions Include/cpython/pyatomic_gcc.h
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Original file line number Diff line number Diff line change
Expand Up @@ -516,6 +516,10 @@ static inline int
_Py_atomic_load_int_acquire(const int *obj)
{ return __atomic_load_n(obj, __ATOMIC_ACQUIRE); }

static inline void
_Py_atomic_store_uint8_release(uint8_t *obj, uint8_t value)
{ __atomic_store_n(obj, value, __ATOMIC_RELEASE); }

static inline void
_Py_atomic_store_uint32_release(uint32_t *obj, uint32_t value)
{ __atomic_store_n(obj, value, __ATOMIC_RELEASE); }
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13 changes: 13 additions & 0 deletions Include/cpython/pyatomic_msc.h
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Expand Up @@ -989,6 +989,19 @@ _Py_atomic_load_int_acquire(const int *obj)
#endif
}

static inline void
_Py_atomic_store_uint8_release(uint8_t *obj, uint8_t value)
{
#if defined(_M_X64) || defined(_M_IX86)
*(uint8_t volatile *)obj = value;
#elif defined(_M_ARM64)
_Py_atomic_ASSERT_ARG_TYPE(unsigned __int8);
__stlr8((unsigned __int8 volatile *)obj, (unsigned __int8)value);
#else
# error "no implementation of _Py_atomic_store_uint32_release"
#endif
}

static inline void
_Py_atomic_store_uint32_release(uint32_t *obj, uint32_t value)
{
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8 changes: 8 additions & 0 deletions Include/cpython/pyatomic_std.h
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Expand Up @@ -911,6 +911,14 @@ _Py_atomic_load_int_acquire(const int *obj)
memory_order_acquire);
}

static inline void
_Py_atomic_store_uint8_release(uint8_t *obj, uint8_t value)
{
_Py_USING_STD;
atomic_store_explicit((_Atomic(uint8_t)*)obj, value,
memory_order_release);
}

static inline void
_Py_atomic_store_uint32_release(uint32_t *obj, uint32_t value)
{
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24 changes: 22 additions & 2 deletions Objects/exceptions.c
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Expand Up @@ -308,16 +308,26 @@ BaseException_set_args(PyBaseExceptionObject *self, PyObject *val, void *Py_UNUS
}

static PyObject *
BaseException_get_tb(PyBaseExceptionObject *self, void *Py_UNUSED(ignored))
BaseException_get_tb_lock_held(PyBaseExceptionObject *self, void *Py_UNUSED(ignored))
{
if (self->traceback == NULL) {
Py_RETURN_NONE;
}
return Py_NewRef(self->traceback);
}

static PyObject *
BaseException_get_tb(PyBaseExceptionObject *self, void *Py_UNUSED(ignored))
{
PyObject *res;
Py_BEGIN_CRITICAL_SECTION(self);
res = BaseException_get_tb_lock_held(self, NULL);
Py_END_CRITICAL_SECTION();
return res;
}

static int
BaseException_set_tb(PyBaseExceptionObject *self, PyObject *tb, void *Py_UNUSED(ignored))
BaseException_set_tb_lock_held(PyBaseExceptionObject *self, PyObject *tb, void *Py_UNUSED(ignored))
{
if (tb == NULL) {
PyErr_SetString(PyExc_TypeError, "__traceback__ may not be deleted");
Expand All @@ -337,6 +347,16 @@ BaseException_set_tb(PyBaseExceptionObject *self, PyObject *tb, void *Py_UNUSED(
return 0;
}

static int
BaseException_set_tb(PyBaseExceptionObject *self, PyObject *tb, void *Py_UNUSED(ignored))
{
int res;
Py_BEGIN_CRITICAL_SECTION(self);
res = BaseException_set_tb_lock_held(self, tb, NULL);
Py_END_CRITICAL_SECTION();
return res;
}

static PyObject *
BaseException_get_context(PyObject *self, void *Py_UNUSED(ignored))
{
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8 changes: 4 additions & 4 deletions Objects/object.c
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Expand Up @@ -2360,12 +2360,12 @@ new_reference(PyObject *op)
#if !defined(Py_GIL_DISABLED)
op->ob_refcnt = 1;
#else
op->ob_tid = _Py_ThreadId();
_Py_atomic_store_uintptr_release(&op->ob_tid, _Py_ThreadId());
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I don't think we want to do this, at least not for now. I want to wait until we fix all the other races before we address new_reference because there are perf implications and the race is in practice benign.

The "release" memory order is also stronger (and more expensive on arm64) than necessary.

op->_padding = 0;
op->ob_mutex = (PyMutex){ 0 };
op->ob_gc_bits = 0;
op->ob_ref_local = 1;
op->ob_ref_shared = 0;
_Py_atomic_store_uint8_release(&op->ob_gc_bits, 0);
_Py_atomic_store_uint32_release(&op->ob_ref_local, 1);
_Py_atomic_store_ssize_release(&op->ob_ref_shared, 0);
#endif
#ifdef Py_TRACE_REFS
_Py_AddToAllObjects(op);
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