https://github.com/python/cpython/commit/77195cd44b2506cda88a3cfc98918526068... commit: 77195cd44b2506cda88a3cfc98918526068b1d46 branch: main author: Brandt Bucher <brandt@python.org> committer: brandtbucher <brandtbucher@gmail.com> date: 2021-12-28T09:49:48-08:00 summary: bpo-46090: Allow PyThreadState.datastack_* members to be NULL (GH-30234) files: M Include/internal/pycore_frame.h M Python/pystate.c diff --git a/Include/internal/pycore_frame.h b/Include/internal/pycore_frame.h index 883bef199ba59..8eca39d1ab250 100644 --- a/Include/internal/pycore_frame.h +++ b/Include/internal/pycore_frame.h @@ -174,10 +174,13 @@ static inline InterpreterFrame * _PyThreadState_BumpFramePointer(PyThreadState *tstate, size_t size) { PyObject **base = tstate->datastack_top; - PyObject **top = base + size; - if (top < tstate->datastack_limit) { - tstate->datastack_top = top; - return (InterpreterFrame *)base; + if (base) { + PyObject **top = base + size; + assert(tstate->datastack_limit); + if (top < tstate->datastack_limit) { + tstate->datastack_top = top; + return (InterpreterFrame *)base; + } } return _PyThreadState_BumpFramePointerSlow(tstate, size); } diff --git a/Python/pystate.c b/Python/pystate.c index 0301ce676950b..68fae8d283091 100644 --- a/Python/pystate.c +++ b/Python/pystate.c @@ -749,8 +749,7 @@ free_threadstate(PyThreadState *tstate) static void init_threadstate(PyThreadState *tstate, PyInterpreterState *interp, uint64_t id, - PyThreadState *next, - _PyStackChunk *datastack_chunk) + PyThreadState *next) { if (tstate->_initialized) { Py_FatalError("thread state already initialized"); @@ -784,11 +783,9 @@ init_threadstate(PyThreadState *tstate, tstate->exc_info = &tstate->exc_state; tstate->cframe = &tstate->root_cframe; - assert(datastack_chunk != NULL); - tstate->datastack_chunk = datastack_chunk; - /* If top points to entry 0, then _PyThreadState_PopFrame will try to pop this chunk */ - tstate->datastack_top = &tstate->datastack_chunk->data[1]; - tstate->datastack_limit = (PyObject **)(((char *)tstate->datastack_chunk) + DATA_STACK_CHUNK_SIZE); + tstate->datastack_chunk = NULL; + tstate->datastack_top = NULL; + tstate->datastack_limit = NULL; tstate->_initialized = 1; } @@ -799,11 +796,6 @@ new_threadstate(PyInterpreterState *interp) PyThreadState *tstate; _PyRuntimeState *runtime = interp->runtime; - _PyStackChunk *datastack_chunk = allocate_chunk(DATA_STACK_CHUNK_SIZE, NULL); - if (datastack_chunk == NULL) { - return NULL; - } - /* We serialize concurrent creation to protect global state. */ HEAD_LOCK(runtime); @@ -833,14 +825,13 @@ new_threadstate(PyInterpreterState *interp) } interp->threads.head = tstate; - init_threadstate(tstate, interp, id, old_head, datastack_chunk); + init_threadstate(tstate, interp, id, old_head); HEAD_UNLOCK(runtime); return tstate; error: HEAD_UNLOCK(runtime); - _PyObject_VirtualFree(datastack_chunk, datastack_chunk->size); return NULL; } @@ -2186,8 +2177,6 @@ _Py_GetConfig(void) static PyObject ** push_chunk(PyThreadState *tstate, int size) { - assert(tstate->datastack_top + size >= tstate->datastack_limit); - int allocate_size = DATA_STACK_CHUNK_SIZE; while (allocate_size < (int)sizeof(PyObject*)*(size + MINIMUM_OVERHEAD)) { allocate_size *= 2; @@ -2196,10 +2185,16 @@ push_chunk(PyThreadState *tstate, int size) if (new == NULL) { return NULL; } - tstate->datastack_chunk->top = tstate->datastack_top - &tstate->datastack_chunk->data[0]; + if (tstate->datastack_chunk) { + tstate->datastack_chunk->top = tstate->datastack_top - + &tstate->datastack_chunk->data[0]; + } tstate->datastack_chunk = new; tstate->datastack_limit = (PyObject **)(((char *)new) + allocate_size); - PyObject **res = &new->data[0]; + // When new is the "root" chunk (i.e. new->previous == NULL), we can keep + // _PyThreadState_PopFrame from freeing it later by "skipping" over the + // first element: + PyObject **res = &new->data[new->previous == NULL]; tstate->datastack_top = res + size; return res; } @@ -2212,9 +2207,6 @@ _PyThreadState_BumpFramePointerSlow(PyThreadState *tstate, size_t size) PyObject **top = base + size; if (top >= tstate->datastack_limit) { base = push_chunk(tstate, (int)size); - if (base == NULL) { - return NULL; - } } else { tstate->datastack_top = top; @@ -2244,16 +2236,20 @@ _PyThreadState_PushFrame(PyThreadState *tstate, PyFunctionObject *func, PyObject void _PyThreadState_PopFrame(PyThreadState *tstate, InterpreterFrame * frame) { + assert(tstate->datastack_chunk); PyObject **base = (PyObject **)frame; if (base == &tstate->datastack_chunk->data[0]) { _PyStackChunk *chunk = tstate->datastack_chunk; _PyStackChunk *previous = chunk->previous; + // push_chunk ensures that the root chunk is never popped: + assert(previous); tstate->datastack_top = &previous->data[previous->top]; tstate->datastack_chunk = previous; _PyObject_VirtualFree(chunk, chunk->size); tstate->datastack_limit = (PyObject **)(((char *)previous) + previous->size); } else { + assert(tstate->datastack_top); assert(tstate->datastack_top >= base); tstate->datastack_top = base; }