gh-112723: Call `PyThreadState_Clear()` from the correct interpreter (#112776)

The `PyThreadState_Clear()` function must only be called with the GIL
held and must be called from the same interpreter as the passed in
thread state. Otherwise, any Python objects on the thread state may be
destroyed using the wrong interpreter, leading to memory corruption.

This is also important for `Py_GIL_DISABLED` builds because free lists
will be associated with PyThreadStates and cleared in
`PyThreadState_Clear()`.

This fixes two places that called `PyThreadState_Clear()` from the wrong
interpreter and adds an assertion to `PyThreadState_Clear()`.

1 files changed, 3 insertions, 4 deletions

diff --git a/Python/pystate.c b/Python/pystate.c
index f0c5259..e18eb01 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -1454,6 +1454,7 @@ void
 PyThreadState_Clear(PyThreadState *tstate)
 {
     assert(tstate->_status.initialized && !tstate->_status.cleared);
+    assert(current_fast_get(&_PyRuntime)->interp == tstate->interp);
     // XXX assert(!tstate->_status.bound || tstate->_status.unbound);
     tstate->_status.finalizing = 1;  // just in case
 
@@ -2150,7 +2151,7 @@ _PyGILState_Fini(PyInterpreterState *interp)
 
 
 // XXX Drop this.
-PyStatus
+void
 _PyGILState_SetTstate(PyThreadState *tstate)
 {
     /* must init with valid states */
@@ -2160,7 +2161,7 @@ _PyGILState_SetTstate(PyThreadState *tstate)
     if (!_Py_IsMainInterpreter(tstate->interp)) {
         /* Currently, PyGILState is shared by all interpreters. The main
          * interpreter is responsible to initialize it. */
-        return _PyStatus_OK();
+        return;
     }
 
 #ifndef NDEBUG
@@ -2170,8 +2171,6 @@ _PyGILState_SetTstate(PyThreadState *tstate)
     assert(gilstate_tss_get(runtime) == tstate);
     assert(tstate->gilstate_counter == 1);
 #endif
-
-    return _PyStatus_OK();
 }
 
 PyInterpreterState *