[3.11] gh-108987: Fix _thread.start_new_thread() race condition (#109135) (#109272)

gh-108987: Fix _thread.start_new_thread() race condition (#109135)

Fix _thread.start_new_thread() race condition. If a thread is created
during Python finalization, the newly spawned thread now exits
immediately instead of trying to access freed memory and lead to a
crash.

thread_run() calls PyEval_AcquireThread() which checks if the thread
must exit. The problem was that tstate was dereferenced earlier in
_PyThreadState_Bind() which leads to a crash most of the time.

Move _PyThreadState_CheckConsistency() from thread_run() to
_PyThreadState_Bind().

(cherry picked from commit 517cd82ea7d01b344804413ef05610934a43a241)

2 files changed, 29 insertions, 22 deletions

diff --git a/Python/ceval_gil.h b/Python/ceval_gil.h
index d20af26..94e2df0 100644
--- a/Python/ceval_gil.h
+++ b/Python/ceval_gil.h
@@ -185,25 +185,6 @@ drop_gil(struct _ceval_runtime_state *ceval, struct _ceval_state *ceval2,
 }
 
 
-/* Check if a Python thread must exit immediately, rather than taking the GIL
-   if Py_Finalize() has been called.
-
-   When this function is called by a daemon thread after Py_Finalize() has been
-   called, the GIL does no longer exist.
-
-   tstate must be non-NULL. */
-static inline int
-tstate_must_exit(PyThreadState *tstate)
-{
-    /* bpo-39877: Access _PyRuntime directly rather than using
-       tstate->interp->runtime to support calls from Python daemon threads.
-       After Py_Finalize() has been called, tstate can be a dangling pointer:
-       point to PyThreadState freed memory. */
-    PyThreadState *finalizing = _PyRuntimeState_GetFinalizing(&_PyRuntime);
-    return (finalizing != NULL && finalizing != tstate);
-}
-
-
 /* Take the GIL.
 
    The function saves errno at entry and restores its value at exit.
@@ -216,7 +197,7 @@ take_gil(PyThreadState *tstate)
 
     assert(tstate != NULL);
 
-    if (tstate_must_exit(tstate)) {
+    if (_PyThreadState_MustExit(tstate)) {
         /* bpo-39877: If Py_Finalize() has been called and tstate is not the
            thread which called Py_Finalize(), exit immediately the thread.
 
@@ -255,7 +236,7 @@ take_gil(PyThreadState *tstate)
             _Py_atomic_load_relaxed(&gil->locked) &&
             gil->switch_number == saved_switchnum)
         {
-            if (tstate_must_exit(tstate)) {
+            if (_PyThreadState_MustExit(tstate)) {
                 MUTEX_UNLOCK(gil->mutex);
                 // gh-96387: If the loop requested a drop request in a previous
                 // iteration, reset the request. Otherwise, drop_gil() can
@@ -295,7 +276,7 @@ _ready:
     MUTEX_UNLOCK(gil->switch_mutex);
 #endif
 
-    if (tstate_must_exit(tstate)) {
+    if (_PyThreadState_MustExit(tstate)) {
         /* bpo-36475: If Py_Finalize() has been called and tstate is not
            the thread which called Py_Finalize(), exit immediately the
            thread.
diff --git a/Python/pystate.c b/Python/pystate.c
index ec278ee..db2ce87 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -882,6 +882,10 @@ _PyThreadState_Init(PyThreadState *tstate)
 void
 _PyThreadState_SetCurrent(PyThreadState *tstate)
 {
+    // gh-104690: If Python is being finalized and PyInterpreterState_Delete()
+    // was called, tstate becomes a dangling pointer.
+    assert(_PyThreadState_CheckConsistency(tstate));
+
     _PyGILState_NoteThreadState(&tstate->interp->runtime->gilstate, tstate);
 }
 
@@ -2255,6 +2259,28 @@ _PyThreadState_CheckConsistency(PyThreadState *tstate)
 #endif
 
 
+// Check if a Python thread must exit immediately, rather than taking the GIL
+// if Py_Finalize() has been called.
+//
+// When this function is called by a daemon thread after Py_Finalize() has been
+// called, the GIL does no longer exist.
+//
+// tstate can be a dangling pointer (point to freed memory): only tstate value
+// is used, the pointer is not deferenced.
+//
+// tstate must be non-NULL.
+int
+_PyThreadState_MustExit(PyThreadState *tstate)
+{
+    /* bpo-39877: Access _PyRuntime directly rather than using
+       tstate->interp->runtime to support calls from Python daemon threads.
+       After Py_Finalize() has been called, tstate can be a dangling pointer:
+       point to PyThreadState freed memory. */
+    PyThreadState *finalizing = _PyRuntimeState_GetFinalizing(&_PyRuntime);
+    return (finalizing != NULL && finalizing != tstate);
+}
+
+
 #ifdef __cplusplus
 }
 #endif