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Py_C_STACK_SIZE causes test_max_level failure on musl/s390x #139467
Description
Bug report
Bug description:
Hello,
I am updating Python in Alpine to 3.14 and encountered the following test failure on s390x:
======================================================================
ERROR: test_max_level (test.test_grammar.TokenTests.test_max_level)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/builds/lotheac/aports/main/python3/src/Python-3.14.0rc3/Lib/test/test_grammar.py", line 257, in test_max_level
result = eval("(" * MAXLEVEL + ")" * MAXLEVEL)
MemoryError: Parser stack overflowed - Python source too complex to parse
----------------------------------------------------------------------
the root cause seems to be the following define in Python/ceval.c, added in commit 0142236:
#if defined(__s390x__)
# define Py_C_STACK_SIZE 320000
I was able to make the tests pass by removing this stack size limitation for s390x with the following patch, making it use the default size 4000000 as other architectures do:
diff --git a/Python/ceval.c b/Python/ceval.c
index e5b1b82e45e..fe8c4a7d092 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -352,7 +352,7 @@ _Py_EnterRecursiveCallUnchecked(PyThreadState *tstate)
}
}
-#if defined(__s390x__)
+#if 0
# define Py_C_STACK_SIZE 320000
#elif defined(_WIN32)
// Don't define Py_C_STACK_SIZE, ask the O/S
Because this dumb patch appears to work, I would like to ask you for some insight on why this Py_C_STACK_SIZE override on s390x exists. I'm not very familiar with s390x myself.
CPython versions tested on:
3.14
Operating systems tested on:
Linux
Activity
picnixz commentedon Oct 2, 2025
cc @markshannon (this was #130396)
[-][3.14] s390x Py_C_STACK_SIZE causes test_max_level failure on musl[/-][+][3.14] s390x Py_C_STACK_SIZE causes `test_max_level` failure on musl[/+][-][3.14] s390x Py_C_STACK_SIZE causes `test_max_level` failure on musl[/-][+]Py_C_STACK_SIZE causes `test_max_level` failure on musl/s390x[/+]vstinner commentedon Jun 18, 2026
Hi. I modified Python build system to increase the default stack size from 128 kiB to 1 MiB and update Py_C_STACK_SIZE. Can you please check if you can still reproduce the issue on s390x?
lotheac commentedon Jun 18, 2026
could you tell me which commit you did it in? it would be easier for me to test that way.
vstinner commentedon Jun 19, 2026
The latest musl fix is 9a61d1c.
lotheac commentedon Jun 19, 2026
@vstinner I applied df6c157 and 9a61d1c on top of 3.14.5, and can no longer reproduce the issue. Thanks!
vstinner commentedon Jun 19, 2026
That's great! Thanks for testing.