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gh-127716: Fix data race in memoryview.release() #154770

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gh-127716: Fix data race in memoryview.release() #154770

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30 changes: 23 additions & 7 deletions Objects/memoryobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -103,14 +103,25 @@ _PyManagedBuffer_FromObject(PyObject *base, int flags)
return (PyObject *)mbuf;
}

static inline int
atomic_or(int *flags, int bit)
{
#ifdef Py_GIL_DISABLED
return (int)_Py_atomic_or_uint32((uint32_t *)flags, (uint32_t)bit);
#else
int prev = *flags;
*flags = prev | bit;
return prev;
#endif
}

static void
mbuf_release(_PyManagedBufferObject *self)
{
if (self->flags&_Py_MANAGED_BUFFER_RELEASED)
int prev_flags = atomic_or(&self->flags, _Py_MANAGED_BUFFER_RELEASED);
if (prev_flags & _Py_MANAGED_BUFFER_RELEASED)
return;

self->flags |= _Py_MANAGED_BUFFER_RELEASED;

/* PyBuffer_Release() decrements master->obj and sets it to NULL. */
_PyObject_GC_UNTRACK(self);
PyBuffer_Release(&self->master);
Expand Down Expand Up @@ -1109,12 +1120,17 @@ static void
_memory_release(PyMemoryViewObject *self)
{
assert(get_exports(self) == 0);
if (self->flags & _Py_MEMORYVIEW_RELEASED)
int prev_flags = atomic_or(&self->flags, _Py_MEMORYVIEW_RELEASED);
if (prev_flags & _Py_MEMORYVIEW_RELEASED)
return;

self->flags |= _Py_MEMORYVIEW_RELEASED;
assert(self->mbuf->exports > 0);
if (--self->mbuf->exports == 0) {
#ifdef Py_GIL_DISABLED
Py_ssize_t prev_exports = _Py_atomic_add_ssize(&self->mbuf->exports, -1);
#else
Py_ssize_t prev_exports = self->mbuf->exports--;
#endif
assert(prev_exports > 0);
if (prev_exports == 1) {
mbuf_release(self->mbuf);
}
}
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