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gh-128002: fix asyncio.all_tasks against concurrent deallocations of tasks #128541

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merged 4 commits into from
Jan 9, 2025
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gh-128002: fix asyncio.all_tasks against concurrent deallocations of tasks #128541

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6873433
stop the world in all tasks
kumaraditya303 Jan 4, 2025
078f2d4
add comment
kumaraditya303 Jan 6, 2025
58ea4ee
use _Py_TryIncref to protect against concurrent deallocations
kumaraditya303 Jan 7, 2025
0b6922e
fix comment
kumaraditya303 Jan 7, 2025
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2 changes: 1 addition & 1 deletion Include/internal/pycore_object.h
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Original file line number Diff line number Diff line change
Expand Up @@ -120,7 +120,7 @@ PyAPI_FUNC(void) _Py_NO_RETURN _Py_FatalRefcountErrorFunc(
PyAPI_DATA(Py_ssize_t) _Py_RefTotal;

extern void _Py_AddRefTotal(PyThreadState *, Py_ssize_t);
extern void _Py_IncRefTotal(PyThreadState *);
extern PyAPI_FUNC(void) _Py_IncRefTotal(PyThreadState *);
extern void _Py_DecRefTotal(PyThreadState *);

# define _Py_DEC_REFTOTAL(interp) \
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19 changes: 14 additions & 5 deletions Modules/_asynciomodule.c
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Expand Up @@ -3772,11 +3772,20 @@ _asyncio_all_tasks_impl(PyObject *module, PyObject *loop)

llist_for_each_safe(node, &state->asyncio_tasks_head) {
TaskObj *task = llist_data(node, TaskObj, task_node);
if (PyList_Append(tasks, (PyObject *)task) < 0) {
Py_DECREF(tasks);
Py_DECREF(loop);
err = 1;
break;
// The linked list holds borrowed references to task
// as such it is possible that the task is concurrently
// deallocated while added to this list.
// To protect against concurrent deallocations,
// we first try to incref the task which would fail
// if it is concurrently getting deallocated in another thread,
// otherwise it gets added to the list.
if (_Py_TryIncref((PyObject *)task)) {
if (_PyList_AppendTakeRef((PyListObject *)tasks, (PyObject *)task) < 0) {
Py_DECREF(tasks);
Py_DECREF(loop);
err = 1;
break;
}
}
}
ASYNCIO_STATE_UNLOCK(state);
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