GH-91079: Decouple C stack overflow checks from Python recursion checks. (GH-96510)

Author: markshannon

Include/cpython/pystate.h

@@ -95,8 +95,10 @@ struct _ts {
     /* Was this thread state statically allocated? */
     int _static;
 
-    int recursion_remaining;
-    int recursion_limit;
+    int py_recursion_remaining;
+    int py_recursion_limit;
+
+    int c_recursion_remaining;
     int recursion_headroom; /* Allow 50 more calls to handle any errors. */
 
     /* 'tracing' keeps track of the execution depth when tracing/profiling.
@@ -202,6 +204,16 @@ struct _ts {
     _PyCFrame root_cframe;
 };
 
+/* WASI has limited call stack. Python's recursion limit depends on code
+   layout, optimization, and WASI runtime. Wasmtime can handle about 700
+   recursions, sometimes less. 500 is a more conservative limit. */
+#ifndef C_RECURSION_LIMIT
+#  ifdef __wasi__
+#    define C_RECURSION_LIMIT 500
+#  else
+#    define C_RECURSION_LIMIT 800
+#  endif
+#endif
 
 /* other API */
 

Include/internal/pycore_ceval.h

@@ -12,15 +12,8 @@ extern "C" {
 struct pyruntimestate;
 struct _ceval_runtime_state;
 
-/* WASI has limited call stack. Python's recursion limit depends on code
-   layout, optimization, and WASI runtime. Wasmtime can handle about 700-750
-   recursions, sometimes less. 600 is a more conservative limit. */
 #ifndef Py_DEFAULT_RECURSION_LIMIT
-#  ifdef __wasi__
-#    define Py_DEFAULT_RECURSION_LIMIT 600
-#  else
-#    define Py_DEFAULT_RECURSION_LIMIT 1000
-#  endif
+#  define Py_DEFAULT_RECURSION_LIMIT 1000
 #endif
 
 #include "pycore_interp.h"        // PyInterpreterState.eval_frame
@@ -118,19 +111,22 @@ extern void _PyEval_DeactivateOpCache(void);
 /* With USE_STACKCHECK macro defined, trigger stack checks in
    _Py_CheckRecursiveCall() on every 64th call to _Py_EnterRecursiveCall. */
 static inline int _Py_MakeRecCheck(PyThreadState *tstate)  {
-    return (tstate->recursion_remaining-- <= 0
-            || (tstate->recursion_remaining & 63) == 0);
+    return (tstate->c_recursion_remaining-- <= 0
+            || (tstate->c_recursion_remaining & 63) == 0);
 }
 #else
 static inline int _Py_MakeRecCheck(PyThreadState *tstate) {
-    return tstate->recursion_remaining-- <= 0;
+    return tstate->c_recursion_remaining-- <= 0;
 }
 #endif
 
 PyAPI_FUNC(int) _Py_CheckRecursiveCall(
     PyThreadState *tstate,
     const char *where);
 
+int _Py_CheckRecursiveCallPy(
+    PyThreadState *tstate);
+
 static inline int _Py_EnterRecursiveCallTstate(PyThreadState *tstate,
                                                const char *where) {
     return (_Py_MakeRecCheck(tstate) && _Py_CheckRecursiveCall(tstate, where));
@@ -142,7 +138,7 @@ static inline int _Py_EnterRecursiveCall(const char *where) {
 }
 
 static inline void _Py_LeaveRecursiveCallTstate(PyThreadState *tstate)  {
-    tstate->recursion_remaining++;
+    tstate->c_recursion_remaining++;
 }
 
 static inline void _Py_LeaveRecursiveCall(void)  {
@@ -157,6 +153,7 @@ extern PyObject* _Py_MakeCoro(PyFunctionObject *func);
 extern int _Py_HandlePending(PyThreadState *tstate);
 
 
+
 #ifdef __cplusplus
 }
 #endif

Include/internal/pycore_runtime_init.h

@@ -68,7 +68,7 @@ extern "C" {
 #define _PyThreadState_INIT \
     { \
         ._static = 1, \
-        .recursion_limit = Py_DEFAULT_RECURSION_LIMIT, \
+        .py_recursion_limit = Py_DEFAULT_RECURSION_LIMIT, \
         .context_ver = 1, \
     }
 

Lib/test/support/__init__.py

@@ -60,7 +60,7 @@
     "run_with_tz", "PGO", "missing_compiler_executable",
     "ALWAYS_EQ", "NEVER_EQ", "LARGEST", "SMALLEST",
     "LOOPBACK_TIMEOUT", "INTERNET_TIMEOUT", "SHORT_TIMEOUT", "LONG_TIMEOUT",
-    "Py_DEBUG",
+    "Py_DEBUG", "EXCEEDS_RECURSION_LIMIT",
     ]
 
 
@@ -2352,3 +2352,6 @@ def adjust_int_max_str_digits(max_digits):
         yield
     finally:
         sys.set_int_max_str_digits(current)
+
+#For recursion tests, easily exceeds default recursion limit
+EXCEEDS_RECURSION_LIMIT = 5000

Lib/test/test_ast.py

@@ -825,9 +825,9 @@ def next(self):
 
     @support.cpython_only
     def test_ast_recursion_limit(self):
-        fail_depth = sys.getrecursionlimit() * 3
-        crash_depth = sys.getrecursionlimit() * 300
-        success_depth = int(fail_depth * 0.75)
+        fail_depth = support.EXCEEDS_RECURSION_LIMIT
+        crash_depth = 100_000
+        success_depth = 1200
 
         def check_limit(prefix, repeated):
             expect_ok = prefix + repeated * success_depth

Lib/test/test_call.py

@@ -864,6 +864,44 @@ def test_multiple_values(self):
         with self.check_raises_type_error(msg):
             A().method_two_args("x", "y", x="oops")
 
+@cpython_only
+class TestRecursion(unittest.TestCase):
+
+    def test_super_deep(self):
+
+        def recurse(n):
+            if n:
+                recurse(n-1)
+
+        def py_recurse(n, m):
+            if n:
+                py_recurse(n-1, m)
+            else:
+                c_py_recurse(m-1)
+
+        def c_recurse(n):
+            if n:
+                _testcapi.pyobject_fastcall(c_recurse, (n-1,))
+
+        def c_py_recurse(m):
+            if m:
+                _testcapi.pyobject_fastcall(py_recurse, (1000, m))
+
+        depth = sys.getrecursionlimit()
+        sys.setrecursionlimit(100_000)
+        try:
+            recurse(90_000)
+            with self.assertRaises(RecursionError):
+                recurse(101_000)
+            c_recurse(100)
+            with self.assertRaises(RecursionError):
+                c_recurse(90_000)
+            c_py_recurse(90)
+            with self.assertRaises(RecursionError):
+                c_py_recurse(100_000)
+        finally:
+            sys.setrecursionlimit(depth)
+
 
 if __name__ == "__main__":
     unittest.main()

Lib/test/test_collections.py

@@ -545,7 +545,7 @@ def test_odd_sizes(self):
         self.assertEqual(Dot(1)._replace(d=999), (999,))
         self.assertEqual(Dot(1)._fields, ('d',))
 
-        n = 5000
+        n = support.EXCEEDS_RECURSION_LIMIT
         names = list(set(''.join([choice(string.ascii_letters)
                                   for j in range(10)]) for i in range(n)))
         n = len(names)

Lib/test/test_compile.py

@@ -111,8 +111,7 @@ def __getitem__(self, key):
 
     @unittest.skipIf(support.is_wasi, "exhausts limited stack on WASI")
     def test_extended_arg(self):
-        # default: 1000 * 2.5 = 2500 repetitions
-        repeat = int(sys.getrecursionlimit() * 2.5)
+        repeat = 2000
         longexpr = 'x = x or ' + '-x' * repeat
         g = {}
         code = '''

Lib/test/test_dynamic.py

@@ -140,11 +140,11 @@ class MyGlobals(dict):
             def __missing__(self, key):
                 return int(key.removeprefix("_number_"))
 
-        # 1,000 on most systems
-        limit = sys.getrecursionlimit()
-        code = "lambda: " + "+".join(f"_number_{i}" for i in range(limit))
+        # Need more than 256 variables to use EXTENDED_ARGS
+        variables = 400
+        code = "lambda: " + "+".join(f"_number_{i}" for i in range(variables))
         sum_func = eval(code, MyGlobals())
-        expected = sum(range(limit))
+        expected = sum(range(variables))
         # Warm up the the function for quickening (PEP 659)
         for _ in range(30):
             self.assertEqual(sum_func(), expected)

Lib/test/test_exceptions.py

@@ -1372,6 +1372,7 @@ def test_recursion_normalizing_exception(self):
         code = """if 1:
             import sys
             from _testinternalcapi import get_recursion_depth
+            from test import support
 
             class MyException(Exception): pass
 
@@ -1399,13 +1400,8 @@ def gen():
             generator = gen()
             next(generator)
             recursionlimit = sys.getrecursionlimit()
-            depth = get_recursion_depth()
             try:
-                # Upon the last recursive invocation of recurse(),
-                # tstate->recursion_depth is equal to (recursion_limit - 1)
-                # and is equal to recursion_limit when _gen_throw() calls
-                # PyErr_NormalizeException().
-                recurse(setrecursionlimit(depth + 2) - depth)
+                recurse(support.EXCEEDS_RECURSION_LIMIT)
             finally:
                 sys.setrecursionlimit(recursionlimit)
                 print('Done.')

Lib/test/test_isinstance.py

@@ -8,7 +8,7 @@
 from test import support
 
 
-
+
 class TestIsInstanceExceptions(unittest.TestCase):
     # Test to make sure that an AttributeError when accessing the instance's
     # class's bases is masked.  This was actually a bug in Python 2.2 and
@@ -97,7 +97,7 @@ def getclass(self):
         class D: pass
         self.assertRaises(RuntimeError, isinstance, c, D)
 
-
+
 # These tests are similar to above, but tickle certain code paths in
 # issubclass() instead of isinstance() -- really PyObject_IsSubclass()
 # vs. PyObject_IsInstance().
@@ -147,7 +147,7 @@ def getbases(self):
         self.assertRaises(TypeError, issubclass, B, C())
 
 
-
+
 # meta classes for creating abstract classes and instances
 class AbstractClass(object):
     def __init__(self, bases):
@@ -179,7 +179,7 @@ class Super:
 
 class Child(Super):
     pass
-
+
 class TestIsInstanceIsSubclass(unittest.TestCase):
     # Tests to ensure that isinstance and issubclass work on abstract
     # classes and instances.  Before the 2.2 release, TypeErrors were
@@ -353,10 +353,10 @@ def blowstack(fxn, arg, compare_to):
     # Make sure that calling isinstance with a deeply nested tuple for its
     # argument will raise RecursionError eventually.
     tuple_arg = (compare_to,)
-    for cnt in range(sys.getrecursionlimit()+5):
+    for cnt in range(support.EXCEEDS_RECURSION_LIMIT):
         tuple_arg = (tuple_arg,)
         fxn(arg, tuple_arg)
 
-
+
 if __name__ == '__main__':
     unittest.main()

Lib/test/test_marshal.py

@@ -117,7 +117,8 @@ def test_code(self):
 
     def test_many_codeobjects(self):
         # Issue2957: bad recursion count on code objects
-        count = 5000    # more than MAX_MARSHAL_STACK_DEPTH
+        # more than MAX_MARSHAL_STACK_DEPTH
+        count = support.EXCEEDS_RECURSION_LIMIT
         codes = (ExceptionTestCase.test_exceptions.__code__,) * count
         marshal.loads(marshal.dumps(codes))
 

Misc/NEWS.d/next/Core and Builtins/2022-09-05-09-56-32.gh-issue-91079.H4-DdU.rst

@@ -0,0 +1,3 @@
+Separate Python recursion checking from C recursion checking which reduces
+the chance of C stack overflow and allows the recursion limit to be
+increased safely.

Modules/_testinternalcapi.c

@@ -44,9 +44,7 @@ get_recursion_depth(PyObject *self, PyObject *Py_UNUSED(args))
 {
     PyThreadState *tstate = _PyThreadState_GET();
 
-    /* subtract one to ignore the frame of the get_recursion_depth() call */
-
-    return PyLong_FromLong(tstate->recursion_limit - tstate->recursion_remaining - 1);
+    return PyLong_FromLong(tstate->py_recursion_limit - tstate->py_recursion_remaining);
 }
 
 

Parser/asdl_c.py

@@ -1380,19 +1380,16 @@ class PartingShots(StaticVisitor):
         return NULL;
     }
 
-    int recursion_limit = Py_GetRecursionLimit();
     int starting_recursion_depth;
     /* Be careful here to prevent overflow. */
     int COMPILER_STACK_FRAME_SCALE = 3;
     PyThreadState *tstate = _PyThreadState_GET();
     if (!tstate) {
         return 0;
     }
-    state->recursion_limit = (recursion_limit < INT_MAX / COMPILER_STACK_FRAME_SCALE) ?
-        recursion_limit * COMPILER_STACK_FRAME_SCALE : recursion_limit;
-    int recursion_depth = tstate->recursion_limit - tstate->recursion_remaining;
-    starting_recursion_depth = (recursion_depth < INT_MAX / COMPILER_STACK_FRAME_SCALE) ?
-        recursion_depth * COMPILER_STACK_FRAME_SCALE : recursion_depth;
+    state->recursion_limit = C_RECURSION_LIMIT * COMPILER_STACK_FRAME_SCALE;
+    int recursion_depth = C_RECURSION_LIMIT - tstate->c_recursion_remaining;
+    starting_recursion_depth = recursion_depth * COMPILER_STACK_FRAME_SCALE;
     state->recursion_depth = starting_recursion_depth;
 
     PyObject *result = ast2obj_mod(state, t);

Python/Python-ast.c

@@ -975,7 +975,6 @@ _PyAST_Validate(mod_ty mod)
     int res = -1;
     struct validator state;
     PyThreadState *tstate;
-    int recursion_limit = Py_GetRecursionLimit();
     int starting_recursion_depth;
 
     /* Setup recursion depth check counters */
@@ -984,12 +983,10 @@ _PyAST_Validate(mod_ty mod)
         return 0;
     }
     /* Be careful here to prevent overflow. */
-    int recursion_depth = tstate->recursion_limit - tstate->recursion_remaining;
-    starting_recursion_depth = (recursion_depth< INT_MAX / COMPILER_STACK_FRAME_SCALE) ?
-        recursion_depth * COMPILER_STACK_FRAME_SCALE : recursion_depth;
+    int recursion_depth = C_RECURSION_LIMIT - tstate->c_recursion_remaining;
+    starting_recursion_depth = recursion_depth * COMPILER_STACK_FRAME_SCALE;
     state.recursion_depth = starting_recursion_depth;
-    state.recursion_limit = (recursion_limit < INT_MAX / COMPILER_STACK_FRAME_SCALE) ?
-        recursion_limit * COMPILER_STACK_FRAME_SCALE : recursion_limit;
+    state.recursion_limit = C_RECURSION_LIMIT * COMPILER_STACK_FRAME_SCALE;
 
     switch (mod->kind) {
     case Module_kind:

Python/ast.c

@@ -1080,7 +1080,6 @@ int
 _PyAST_Optimize(mod_ty mod, PyArena *arena, _PyASTOptimizeState *state)
 {
     PyThreadState *tstate;
-    int recursion_limit = Py_GetRecursionLimit();
     int starting_recursion_depth;
 
     /* Setup recursion depth check counters */
@@ -1089,12 +1088,10 @@ _PyAST_Optimize(mod_ty mod, PyArena *arena, _PyASTOptimizeState *state)
         return 0;
     }
     /* Be careful here to prevent overflow. */
-    int recursion_depth = tstate->recursion_limit - tstate->recursion_remaining;
-    starting_recursion_depth = (recursion_depth < INT_MAX / COMPILER_STACK_FRAME_SCALE) ?
-        recursion_depth * COMPILER_STACK_FRAME_SCALE : recursion_depth;
+    int recursion_depth = C_RECURSION_LIMIT - tstate->c_recursion_remaining;
+    starting_recursion_depth = recursion_depth * COMPILER_STACK_FRAME_SCALE;
     state->recursion_depth = starting_recursion_depth;
-    state->recursion_limit = (recursion_limit < INT_MAX / COMPILER_STACK_FRAME_SCALE) ?
-        recursion_limit * COMPILER_STACK_FRAME_SCALE : recursion_limit;
+    state->recursion_limit = C_RECURSION_LIMIT * COMPILER_STACK_FRAME_SCALE;
 
     int ret = astfold_mod(mod, arena, state);
     assert(ret || PyErr_Occurred());