bpo-31857: Make the behavior of USE_STACKCHECK deterministic (#4098)

1 files changed, 7 insertions, 9 deletions

diff --git a/Include/ceval.h b/Include/ceval.h
index c5ccf47..70306b8 100644
--- a/Include/ceval.h
+++ b/Include/ceval.h
@@ -93,21 +93,19 @@ PyAPI_FUNC(int) Py_GetRecursionLimit(void);
       PyThreadState_GET()->overflowed = 0;  \
     } while(0)
 PyAPI_FUNC(int) _Py_CheckRecursiveCall(const char *where);
-/* XXX _Py_CheckRecursionLimit should be changed to
-   _PyRuntime.ceval.check_recursion_limit.  However, due to the macros
-   in which it's used, _Py_CheckRecursionLimit is stuck in the stable
-   ABI.  It should be removed therefrom when possible.
+
+/* Due to the macros in which it's used, _Py_CheckRecursionLimit is in
+   the stable ABI.  It should be removed therefrom when possible.
 */
 PyAPI_DATA(int) _Py_CheckRecursionLimit;
 
 #ifdef USE_STACKCHECK
-/* With USE_STACKCHECK, we artificially decrement the recursion limit in order
-   to trigger regular stack checks in _Py_CheckRecursiveCall(), except if
-   the "overflowed" flag is set, in which case we need the true value
-   of _Py_CheckRecursionLimit for _Py_MakeEndRecCheck() to function properly.
+/* With USE_STACKCHECK, trigger stack checks in _Py_CheckRecursiveCall()
+   on every 64th call to Py_EnterRecursiveCall.
 */
 #  define _Py_MakeRecCheck(x)  \
-    (++(x) > (_Py_CheckRecursionLimit += PyThreadState_GET()->overflowed - 1))
+    (++(x) > _Py_CheckRecursionLimit || \
+     ++(PyThreadState_GET()->stackcheck_counter) > 64)
 #else
 #  define _Py_MakeRecCheck(x)  (++(x) > _Py_CheckRecursionLimit)
 #endif