From 9ab96964e78f67859acd66088d7b72e9539712df Mon Sep 17 00:00:00 2001
From: Sam Gross <colesbury@gmail.com>
Date: Thu, 6 Jan 2022 15:08:40 -0500
Subject: [PATCH] faulthandler: don't dump all threads when running without the
 GIL

It's not safe to access other threads stacks when running without the GIL.
---
 Lib/test/support/script_helper.py |  2 +-
 Lib/test/test_capi/test_misc.py   |  2 +-
 Lib/test/test_faulthandler.py     | 14 ++++++++++----
 Modules/faulthandler.c            |  5 +++++
 Python/pylifecycle.c              |  9 ++++++++-
 5 files changed, 25 insertions(+), 7 deletions(-)

diff --git a/Lib/test/support/script_helper.py b/Lib/test/support/script_helper.py
index c2b43f4060e..5c66261edd4 100644
--- a/Lib/test/support/script_helper.py
+++ b/Lib/test/support/script_helper.py
@@ -39,7 +39,7 @@ def interpreter_requires_environment():
     global __cached_interp_requires_environment
     if __cached_interp_requires_environment is None:
         # If PYTHONHOME is set, assume that we need it
-        if 'PYTHONHOME' in os.environ:
+        if 'PYTHONHOME' in os.environ or 'PYTHONGIL' in os.environ:
             __cached_interp_requires_environment = True
             return True
         # cannot run subprocess, assume we don't need it
diff --git a/Lib/test/test_capi/test_misc.py b/Lib/test/test_capi/test_misc.py
index 5c966e54b69..b317f7883cd 100644
--- a/Lib/test/test_capi/test_misc.py
+++ b/Lib/test/test_capi/test_misc.py
@@ -311,7 +311,7 @@ def test_getitem_with_error(self):
                     r'Python runtime state: initialized\n'
                     r'ValueError: bug\n'
                     r'\n'
-                    r'Current thread .* \(most recent call first\):\n'
+                    r'(Current thread|Stack).* \(most recent call first\):\n'
                     r'  File .*, line 6 in <module>\n'
                     r'\n'
                     r'Extension modules: _testcapi \(total: 1\)\n')
diff --git a/Lib/test/test_faulthandler.py b/Lib/test/test_faulthandler.py
index 8d106daaf65..f816573d301 100644
--- a/Lib/test/test_faulthandler.py
+++ b/Lib/test/test_faulthandler.py
@@ -95,21 +95,25 @@ def check_error(self, code, lineno, fatal_error, *,
 
         Raise an error if the output doesn't match the expected format.
         """
+        if sys.flags.nogil:
+            all_threads = False
         if all_threads:
             if know_current_thread:
                 header = 'Current thread 0x[0-9a-f]+'
             else:
                 header = 'Thread 0x[0-9a-f]+'
-        else:
+        elif know_current_thread:
             header = 'Stack'
         regex = [f'^{fatal_error}']
         if py_fatal_error:
             regex.append("Python runtime state: initialized")
         regex.append('')
-        regex.append(fr'{header} \(most recent call first\):')
-        if garbage_collecting:
+        if all_threads or know_current_thread:
+            regex.append(fr'{header} \(most recent call first\):')
+        if garbage_collecting and all_threads:
             regex.append('  Garbage-collecting')
-        regex.append(fr'  File "<string>", line {lineno} in {function}')
+        if all_threads or know_current_thread:
+            regex.append(fr'  File "<string>", line {lineno} in {function}')
         regex = '\n'.join(regex)
 
         if other_regex:
@@ -691,6 +695,8 @@ def check_register(self, filename=False, all_threads=False,
 
         Raise an error if the output doesn't match the expected format.
         """
+        if sys.flags.nogil:
+            all_threads = False
         signum = signal.SIGUSR1
         code = """
             import faulthandler
diff --git a/Modules/faulthandler.c b/Modules/faulthandler.c
index 5309a3728c5..c06f1d3d705 100644
--- a/Modules/faulthandler.c
+++ b/Modules/faulthandler.c
@@ -183,6 +183,11 @@ faulthandler_dump_traceback(int fd, int all_threads,
 
     reentrant = 1;
 
+    if (_PyRuntime.preconfig.disable_gil) {
+        // It's not safe to dump all threads when running without the GIL.
+        all_threads = 0;
+    }
+
     /* SIGSEGV, SIGFPE, SIGABRT, SIGBUS and SIGILL are synchronous signals and
        are thus delivered to the thread that caused the fault. Get the Python
        thread state of the current thread.
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 8ca94d66811..3809aa62ef5 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -2559,7 +2559,14 @@ _Py_FatalError_DumpTracebacks(int fd, PyInterpreterState *interp,
     PUTS(fd, "\n");
 
     /* display the current Python stack */
-    _Py_DumpTracebackThreads(fd, interp, tstate);
+    if (_PyRuntime.preconfig.disable_gil) {
+        if (tstate != NULL) {
+            _Py_DumpTraceback(fd, tstate);
+        }
+    }
+    else {
+        _Py_DumpTracebackThreads(fd, interp, tstate);
+    }
 }
 
 /* Print the current exception (if an exception is set) with its traceback,