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bpo-40696: Fix a hang that can arise after gen.throw() (GH-20287)

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This updates _PyErr_ChainStackItem() to use _PyErr_SetObject()
instead of _PyErr_ChainExceptions(). This prevents a hang in
certain circumstances because _PyErr_SetObject() performs checks
to prevent cycles in the exception context chain while
_PyErr_ChainExceptions() doesn't.
This commit is contained in:
Chris Jerdonek 2020-05-22 13:33:27 -07:00 • committed by GitHub
parent 909b5714e1
commit 7c30d12bd5
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7 changed files with 130 additions and 23 deletions
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62
Python/errors.c
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@ -477,7 +477,9 @@ PyErr_SetExcInfo(PyObject *p_type, PyObject *p_value, PyObject *p_traceback)
/* Like PyErr_Restore(), but if an exception is already set,
set the context associated with it.
*/
The caller is responsible for ensuring that this call won't create
any cycles in the exception context chain. */
void
_PyErr_ChainExceptions(PyObject *exc, PyObject *val, PyObject *tb)
{
@ -512,18 +514,60 @@ _PyErr_ChainExceptions(PyObject *exc, PyObject *val, PyObject *tb)
}
}
/* Set the currently set exception's context to the given exception.
If the provided exc_info is NULL, then the current Python thread state's
exc_info will be used for the context instead.
This function can only be called when _PyErr_Occurred() is true.
Also, this function won't create any cycles in the exception context
chain to the extent that _PyErr_SetObject ensures this. */
void
_PyErr_ChainStackItem(_PyErr_StackItem *exc_state)
_PyErr_ChainStackItem(_PyErr_StackItem *exc_info)
{
if (exc_state->exc_type == NULL || exc_state->exc_type == Py_None) {
PyThreadState *tstate = _PyThreadState_GET();
assert(_PyErr_Occurred(tstate));
int exc_info_given;
if (exc_info == NULL) {
exc_info_given = 0;
exc_info = tstate->exc_info;
} else {
exc_info_given = 1;
}
if (exc_info->exc_type == NULL || exc_info->exc_type == Py_None) {
return;
}
Py_INCREF(exc_state->exc_type);
Py_XINCREF(exc_state->exc_value);
Py_XINCREF(exc_state->exc_traceback);
_PyErr_ChainExceptions(exc_state->exc_type,
exc_state->exc_value,
exc_state->exc_traceback);
_PyErr_StackItem *saved_exc_info;
if (exc_info_given) {
/* Temporarily set the thread state's exc_info since this is what
_PyErr_SetObject uses for implicit exception chaining. */
saved_exc_info = tstate->exc_info;
tstate->exc_info = exc_info;
}
PyObject *exc, *val, *tb;
_PyErr_Fetch(tstate, &exc, &val, &tb);
PyObject *exc2, *val2, *tb2;
exc2 = exc_info->exc_type;
val2 = exc_info->exc_value;
tb2 = exc_info->exc_traceback;
_PyErr_NormalizeException(tstate, &exc2, &val2, &tb2);
if (tb2 != NULL) {
PyException_SetTraceback(val2, tb2);
}
/* _PyErr_SetObject sets the context from PyThreadState. */
_PyErr_SetObject(tstate, exc, val);
Py_DECREF(exc); // since _PyErr_Occurred was true
Py_XDECREF(val);
Py_XDECREF(tb);
if (exc_info_given) {
tstate->exc_info = saved_exc_info;
}
}
static PyObject *