Thanks, Serhiy.

test_recursionlimit_recovery in test_sys passed, but now I'm getting the following failure:

FAIL: test_recursionlimit_fatalerror (test.test_sys.SysModuleTest)

I modified test_recursionlimit_fatalerror to use subTest() and it looks like the test passed when sys.setrecursionlimit(50). See i=1000 in the following output:

======================================================================
FAIL: test_recursionlimit_fatalerror (test.test_sys.SysModuleTest) (i=1000)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/berker/hacking/cpython/default/Lib/test/test_sys.py", line 283, in test_recursionlimit_fatalerror
    err)
AssertionError: b'Fatal Python error: Cannot recover from stack overflow' not found in b''

----------------------------------------------------------------------

test_runpy still segfaults:

test_main_recursion_error (test.test_runpy.RunPathTestCase) ... Fatal Python error: Segmentation fault

I wrote a quick and dirty reproducer for this. I can attach here if you think it would be useful for debugging.