[clip]
> This is a different issue.

It is the issue relevant for this discussion. As written in my comment: "So, `bf_releasebuffer` cannot rely on (i) the data in Py_buffer being what `bf_getbuffer` put there, and (ii) getting the same Py_buffer data only once."

> PyObject_GetBuffer() is called twice too: once when creating the
> memoryview, once when calling memory_getbuf.
> So again, bf_getbuffer is called the same number of times as
> bf_releasebuffer.

Yes, it is called twice, but with exactly the same data in Py_buffer.
So I would rather say that bf_releasebuffer is called twice on the Py_buffer returned by the first Getbuffer, and zero times for the buffer returned by the second one.

> > Note that the view.internal pointer is also clobbered above.
> 
> Are you sure? memoryobject.c doesn't touch that pointer at all.

dup_buffer does *dst = *src, which overwrites the view.internal pointer obtained from one GetBuffer call with a pointer obtained from a previous one.