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[3.8] bpo-20526: Fix PyThreadState_Clear(): don't decref frame (GH-19120) #19136

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Merged
merged 1 commit into from
Mar 24, 2020
Merged

[3.8] bpo-20526: Fix PyThreadState_Clear(): don't decref frame (GH-19120) #19136

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1 change: 1 addition & 0 deletions Include/cpython/pystate.h
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Original file line number Diff line number Diff line change
Expand Up @@ -55,6 +55,7 @@ struct _ts {
struct _ts *next;
PyInterpreterState *interp;

/* Borrowed reference to the current frame (it can be NULL) */
struct _frame *frame;
int recursion_depth;
char overflowed; /* The stack has overflowed. Allow 50 more calls
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2020-03-23-18-08-34.bpo-20526.NHNZIv.rst
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@@ -0,0 +1,3 @@
Fix :c:func:`PyThreadState_Clear()`. ``PyThreadState.frame`` is a borrowed
reference, not a strong reference: ``PyThreadState_Clear()`` must not call
``Py_CLEAR(tstate->frame)``.
12 changes: 10 additions & 2 deletions Python/pystate.c
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Expand Up @@ -762,11 +762,19 @@ PyThreadState_Clear(PyThreadState *tstate)
{
int verbose = tstate->interp->config.verbose;

if (verbose && tstate->frame != NULL)
if (verbose && tstate->frame != NULL) {
/* bpo-20526: After the main thread calls
_PyRuntimeState_SetFinalizing() in Py_FinalizeEx(), threads must
exit when trying to take the GIL. If a thread exit in the middle of
_PyEval_EvalFrameDefault(), tstate->frame is not reset to its
previous value. It is more likely with daemon threads, but it can
happen with regular threads if threading._shutdown() fails
(ex: interrupted by CTRL+C). */
fprintf(stderr,
"PyThreadState_Clear: warning: thread still has a frame\n");
}

Py_CLEAR(tstate->frame);
/* Don't clear tstate->frame: it is a borrowed reference */

Py_CLEAR(tstate->dict);
Py_CLEAR(tstate->async_exc);
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