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bpo-39877: Fix PyEval_RestoreThread() for daemon threads #18808

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bpo-39877: Fix PyEval_RestoreThread() for daemon threads #18808

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4 changes: 4 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2020-03-06-17-08-53.bpo-39877.e32GOe.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
Fix the :c:func:`PyEval_RestoreThread` function for daemon threads. It does no
longer crash randomly at Python exit: access directly ``_PyRuntime`` variable
rather than using ``tstate->interp->runtime``, since tstate can be dangling
pointer.
22 changes: 14 additions & 8 deletions Python/ceval.c
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Original file line number Diff line number Diff line change
Expand Up @@ -236,9 +236,8 @@ _PyEval_FiniThreads(struct _ceval_runtime_state *ceval)
}

static inline void
exit_thread_if_finalizing(PyThreadState *tstate)
exit_thread_if_finalizing(_PyRuntimeState *runtime, PyThreadState *tstate)
{
_PyRuntimeState *runtime = tstate->interp->runtime;
/* _Py_Finalizing is protected by the GIL */
if (runtime->finalizing != NULL && !_Py_CURRENTLY_FINALIZING(runtime, tstate)) {
drop_gil(&runtime->ceval, tstate);
Expand Down Expand Up @@ -285,7 +284,7 @@ PyEval_AcquireLock(void)
Py_FatalError("PyEval_AcquireLock: current thread state is NULL");
}
take_gil(ceval, tstate);
exit_thread_if_finalizing(tstate);
exit_thread_if_finalizing(runtime, tstate);
}

void
Expand All @@ -305,13 +304,16 @@ PyEval_AcquireThread(PyThreadState *tstate)
{
assert(tstate != NULL);

_PyRuntimeState *runtime = tstate->interp->runtime;
/* bpo-39877: Access directly _PyRuntime rather than using
tstate->interp->runtime: see PyEval_RestoreThread()
for the rationale. */
_PyRuntimeState *runtime = &_PyRuntime;
struct _ceval_runtime_state *ceval = &runtime->ceval;

/* Check someone has called PyEval_InitThreads() to create the lock */
assert(gil_created(&ceval->gil));
take_gil(ceval, tstate);
exit_thread_if_finalizing(tstate);
exit_thread_if_finalizing(runtime, tstate);
if (_PyThreadState_Swap(&runtime->gilstate, tstate) != NULL) {
Py_FatalError("PyEval_AcquireThread: non-NULL old thread state");
}
Expand Down Expand Up @@ -384,13 +386,17 @@ PyEval_RestoreThread(PyThreadState *tstate)
{
assert(tstate != NULL);

_PyRuntimeState *runtime = tstate->interp->runtime;
/* bpo-39877: Access directly _PyRuntime rather than using
tstate->interp->runtime to support calls from Python daemon threads
after Py_Finalize() has been called. tstate can be a dangling pointer:
point to freed memory (PyThreadState). */
_PyRuntimeState *runtime = &_PyRuntime;
struct _ceval_runtime_state *ceval = &runtime->ceval;
assert(gil_created(&ceval->gil));

int err = errno;
take_gil(ceval, tstate);
exit_thread_if_finalizing(tstate);
exit_thread_if_finalizing(runtime, tstate);
errno = err;

_PyThreadState_Swap(&runtime->gilstate, tstate);
Expand Down Expand Up @@ -1244,7 +1250,7 @@ _PyEval_EvalFrameDefault(PyFrameObject *f, int throwflag)
take_gil(ceval, tstate);

/* Check if we should make a quick exit. */
exit_thread_if_finalizing(tstate);
exit_thread_if_finalizing(runtime, tstate);

if (_PyThreadState_Swap(&runtime->gilstate, tstate) != NULL) {
Py_FatalError("ceval: orphan tstate");
Expand Down