From 7ed2b6b5876f82d4658eb7601c32b0910b5926b6 Mon Sep 17 00:00:00 2001
From: Sergey Miryanov <sergey.miryanov@gmail.com>
Date: Sat, 8 Nov 2025 16:02:43 +0500
Subject: [PATCH 1/2] Acquire tstate and stop the world in faulthandler_user

---
 Include/internal/pycore_faulthandler.h |  1 +
 Modules/faulthandler.c                 | 28 ++++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/Include/internal/pycore_faulthandler.h b/Include/internal/pycore_faulthandler.h
index 78cd657e6ae5ae..c968a1a2a0e58b 100644
--- a/Include/internal/pycore_faulthandler.h
+++ b/Include/internal/pycore_faulthandler.h
@@ -42,6 +42,7 @@ struct faulthandler_user_signal {
     int chain;
     _Py_sighandler_t previous;
     PyInterpreterState *interp;
+    PyThreadState *tstate;
 };
 #endif /* FAULTHANDLER_USER */
 
diff --git a/Modules/faulthandler.c b/Modules/faulthandler.c
index 9b8c77e2b0401f..04ad4f5198369a 100644
--- a/Modules/faulthandler.c
+++ b/Modules/faulthandler.c
@@ -945,8 +945,26 @@ faulthandler_user(int signum)
     if (!user->enabled)
         return;
 
+    PyThreadState *tstate = PyGILState_GetThisThreadState();
+    if (!tstate) {
+        tstate = user->tstate;
+    }
+
+    if (tstate) {
+        assert (user->interp);
+
+        _PyThreadState_Attach(tstate);
+        _PyEval_StopTheWorld(user->interp);
+    }
+
     faulthandler_dump_traceback(user->fd, user->all_threads, user->interp);
 
+    if (tstate) {
+        assert (user->interp);
+        _PyEval_StartTheWorld(user->interp);
+        _PyThreadState_Detach(tstate);
+    }
+
 #ifdef HAVE_SIGACTION
     if (user->chain) {
         (void)sigaction(signum, &user->previous, NULL);
@@ -1056,8 +1074,14 @@ faulthandler_register_py_impl(PyObject *module, int signum, PyObject *file,
     user->all_threads = all_threads;
     user->chain = chain;
     user->interp = PyThreadState_GetInterpreter(tstate);
+    user->tstate = PyThreadState_New(user->interp);
     user->enabled = 1;
 
+    if (!user->tstate) {
+        Py_XDECREF(file);
+        return NULL;
+    }
+
     Py_RETURN_NONE;
 }
 
@@ -1073,6 +1097,10 @@ faulthandler_unregister(user_signal_t *user, int signum)
     (void)signal(signum, user->previous);
 #endif
     Py_CLEAR(user->file);
+    if (user->tstate) {
+        PyThreadState_Clear(user->tstate);
+        user->tstate = NULL;
+    }
     user->fd = -1;
     return 1;
 }

From c8e89f0659642e1b96098212a7d6b90c4d5ddf11 Mon Sep 17 00:00:00 2001
From: Sergey Miryanov <sergey.miryanov@gmail.com>
Date: Sat, 8 Nov 2025 23:26:48 +0500
Subject: [PATCH 2/2] Fix

---
 Include/internal/pycore_faulthandler.h |  1 -
 Modules/faulthandler.c                 | 33 ++++++++++++--------------
 2 files changed, 15 insertions(+), 19 deletions(-)

diff --git a/Include/internal/pycore_faulthandler.h b/Include/internal/pycore_faulthandler.h
index c968a1a2a0e58b..78cd657e6ae5ae 100644
--- a/Include/internal/pycore_faulthandler.h
+++ b/Include/internal/pycore_faulthandler.h
@@ -42,7 +42,6 @@ struct faulthandler_user_signal {
     int chain;
     _Py_sighandler_t previous;
     PyInterpreterState *interp;
-    PyThreadState *tstate;
 };
 #endif /* FAULTHANDLER_USER */
 
diff --git a/Modules/faulthandler.c b/Modules/faulthandler.c
index 04ad4f5198369a..93ae9b16766df5 100644
--- a/Modules/faulthandler.c
+++ b/Modules/faulthandler.c
@@ -945,23 +945,30 @@ faulthandler_user(int signum)
     if (!user->enabled)
         return;
 
-    PyThreadState *tstate = PyGILState_GetThisThreadState();
+    int attach = 0;
+    PyThreadState *tstate = PyThreadState_GetUnchecked();
     if (!tstate) {
-        tstate = user->tstate;
+        tstate = PyGILState_GetThisThreadState();
+        if (tstate) {
+            attach = 1;
+        }
     }
 
-    if (tstate) {
-        assert (user->interp);
-
+    if (attach) {
         _PyThreadState_Attach(tstate);
-        _PyEval_StopTheWorld(user->interp);
     }
 
+    if (user->all_threads) {
+        assert (user->interp);
+        _PyEval_StopTheWorld(user->interp);
+    }
     faulthandler_dump_traceback(user->fd, user->all_threads, user->interp);
-
-    if (tstate) {
+    if (user->all_threads) {
         assert (user->interp);
         _PyEval_StartTheWorld(user->interp);
+    }
+
+    if (attach) {
         _PyThreadState_Detach(tstate);
     }
 
@@ -1074,14 +1081,8 @@ faulthandler_register_py_impl(PyObject *module, int signum, PyObject *file,
     user->all_threads = all_threads;
     user->chain = chain;
     user->interp = PyThreadState_GetInterpreter(tstate);
-    user->tstate = PyThreadState_New(user->interp);
     user->enabled = 1;
 
-    if (!user->tstate) {
-        Py_XDECREF(file);
-        return NULL;
-    }
-
     Py_RETURN_NONE;
 }
 
@@ -1097,10 +1098,6 @@ faulthandler_unregister(user_signal_t *user, int signum)
     (void)signal(signum, user->previous);
 #endif
     Py_CLEAR(user->file);
-    if (user->tstate) {
-        PyThreadState_Clear(user->tstate);
-        user->tstate = NULL;
-    }
     user->fd = -1;
     return 1;
 }