https://github.com/python/cpython/commit/0e2ed4b0e1ae36bd7dbbcb210f686deffc10f14e
commit: 0e2ed4b0e1ae36bd7dbbcb210f686deffc10f14e
branch: 3.14
author: Miss Islington (bot) <[email protected]>
committer: vstinner <[email protected]>
date: 2026-01-09T15:34:39Z
summary:

[3.14] gh-143191: Use _PyOS_MIN_STACK_SIZE in _thread.stack_size() (GH-143601) 
(#143611)

gh-143191: Use _PyOS_MIN_STACK_SIZE in _thread.stack_size() (GH-143601)

The stack size must be at least _PyOS_MIN_STACK_SIZE+SYSTEM_PAGE_SIZE
bytes.
(cherry picked from commit ba10100c3931b18812b82d7124e2238f01927910)

Co-authored-by: Victor Stinner <[email protected]>

files:
A Misc/NEWS.d/next/Library/2026-01-09-13-07-22.gh-issue-143191.PPR_vW.rst
M Lib/test/test_thread.py
M Modules/_threadmodule.c

diff --git a/Lib/test/test_thread.py b/Lib/test/test_thread.py
index d94e04250c9307..ac924728febc99 100644
--- a/Lib/test/test_thread.py
+++ b/Lib/test/test_thread.py
@@ -76,6 +76,14 @@ def test_stack_size(self):
         thread.stack_size(0)
         self.assertEqual(thread.stack_size(), 0, "stack_size not reset to 
default")
 
+        with self.assertRaises(ValueError):
+            # 123 bytes is too small
+            thread.stack_size(123)
+
+        with self.assertRaises(ValueError):
+            # size must be positive
+            thread.stack_size(-4096)
+
     @unittest.skipIf(os.name not in ("nt", "posix"), 'test meant for nt and 
posix')
     def test_nt_and_posix_stack_size(self):
         try:
diff --git 
a/Misc/NEWS.d/next/Library/2026-01-09-13-07-22.gh-issue-143191.PPR_vW.rst 
b/Misc/NEWS.d/next/Library/2026-01-09-13-07-22.gh-issue-143191.PPR_vW.rst
new file mode 100644
index 00000000000000..507b58362bec97
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2026-01-09-13-07-22.gh-issue-143191.PPR_vW.rst
@@ -0,0 +1,2 @@
+:func:`_thread.stack_size` now raises :exc:`ValueError` if the stack size is
+too small. Patch by Victor Stinner.
diff --git a/Modules/_threadmodule.c b/Modules/_threadmodule.c
index 1389a1ef2c1b23..32110090feb21e 100644
--- a/Modules/_threadmodule.c
+++ b/Modules/_threadmodule.c
@@ -2147,9 +2147,10 @@ thread_stack_size(PyObject *self, PyObject *args)
     if (!PyArg_ParseTuple(args, "|n:stack_size", &new_size))
         return NULL;
 
-    if (new_size < 0) {
-        PyErr_SetString(PyExc_ValueError,
-                        "size must be 0 or a positive value");
+    Py_ssize_t min_size = _PyOS_MIN_STACK_SIZE + SYSTEM_PAGE_SIZE;
+    if (new_size != 0 && new_size < min_size) {
+        PyErr_Format(PyExc_ValueError,
+                     "size must be at least %zi bytes", min_size);
         return NULL;
     }
 

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