From 9deb41af0393eb99d518994fab65a962542fa8cd Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Wed, 10 Jun 2026 21:39:03 +0200
Subject: [PATCH] gh-151278: Fix test_faulthandler on UBSan (#151279)

* Py_FatalError() no longer calls _PyFaulthandler_Fini() if it
  doesn't hold the GIL.
* Skip test_faulthandler tests raising signals if run with UBSan.
* Enable test_faulthandler in GitHub Action "Reusable Sanitizer".

(cherry picked from commit e60c42dc3f5a8dd9b10bc9a8a028ef2765469650)
---
 Lib/test/test_faulthandler.py | 13 +++++++++----
 Python/pylifecycle.c          |  4 +++-
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/Lib/test/test_faulthandler.py b/Lib/test/test_faulthandler.py
index 371c63adce9412..9f4dbe7f866347 100644
--- a/Lib/test/test_faulthandler.py
+++ b/Lib/test/test_faulthandler.py
@@ -33,6 +33,11 @@
 CURRENT_THREAD_HEADER = fr'{CURRENT_THREAD_ID} \(most recent call first\):'
 
 
+def skip_if_sanitizer_signal(signame):
+    return support.skip_if_sanitizer(f"TSAN/UBSan itercepts {signame}",
+                                     thread=True, ub=True)
+
+
 def expected_traceback(lineno1, lineno2, header, min_count=1):
     regex = header
     regex += '  File "<string>", line %s in func\n' % lineno1
@@ -247,7 +252,7 @@ def test_fatal_error_c_thread(self):
             func='faulthandler_fatal_error_thread',
             py_fatal_error=True)
 
-    @support.skip_if_sanitizer("TSAN itercepts SIGABRT", thread=True)
+    @skip_if_sanitizer_signal("SIGABRT")
     def test_sigabrt(self):
         self.check_fatal_error("""
             import faulthandler
@@ -259,7 +264,7 @@ def test_sigabrt(self):
 
     @unittest.skipIf(sys.platform == 'win32',
                      "SIGFPE cannot be caught on Windows")
-    @support.skip_if_sanitizer("TSAN itercepts SIGFPE", thread=True)
+    @skip_if_sanitizer_signal("SIGFPE")
     def test_sigfpe(self):
         self.check_fatal_error("""
             import faulthandler
@@ -271,7 +276,7 @@ def test_sigfpe(self):
 
     @unittest.skipIf(_testcapi is None, 'need _testcapi')
     @unittest.skipUnless(hasattr(signal, 'SIGBUS'), 'need signal.SIGBUS')
-    @support.skip_if_sanitizer("TSAN itercepts SIGBUS", thread=True)
+    @skip_if_sanitizer_signal("SIGBUS")
     @skip_segfault_on_android
     def test_sigbus(self):
         self.check_fatal_error("""
@@ -286,7 +291,7 @@ def test_sigbus(self):
 
     @unittest.skipIf(_testcapi is None, 'need _testcapi')
     @unittest.skipUnless(hasattr(signal, 'SIGILL'), 'need signal.SIGILL')
-    @support.skip_if_sanitizer("TSAN itercepts SIGILL", thread=True)
+    @skip_if_sanitizer_signal("SIGILL")
     @skip_segfault_on_android
     def test_sigill(self):
         self.check_fatal_error("""
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 6241d6ddca19cf..27f80cc4f614cd 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -3362,7 +3362,9 @@ fatal_error(int fd, int header, const char *prefix, const char *msg,
        This function already did its best to display a traceback.
        Disable faulthandler to prevent writing a second traceback
        on abort(). */
-    _PyFaulthandler_Fini();
+    if (has_tstate_and_gil) {
+        _PyFaulthandler_Fini();
+    }
 
     /* Check if the current Python thread hold the GIL */
     if (has_tstate_and_gil) {