[3.13] gh-117657: Fix TSAN race involving import lock (GH-118523) (#120169)

This adds a `_PyRecursiveMutex` type based on `PyMutex` and uses that
for the import lock. This fixes some data races in the free-threaded
build and generally simplifies the import lock code.
(cherry picked from commit e21057b99967eb5323320e6d1121955e0cd2985e)

Co-authored-by: Sam Gross <colesbury@gmail.com>

2 files changed, 27 insertions, 9 deletions

diff --git a/Modules/_testinternalcapi/test_lock.c b/Modules/_testinternalcapi/test_lock.c
index 4900459..1544fe1 100644
--- a/Modules/_testinternalcapi/test_lock.c
+++ b/Modules/_testinternalcapi/test_lock.c
@@ -2,6 +2,7 @@
 
 #include "parts.h"
 #include "pycore_lock.h"
+#include "pycore_pythread.h"      // PyThread_get_thread_ident_ex()
 
 #include "clinic/test_lock.c.h"
 
@@ -476,6 +477,29 @@ test_lock_rwlock(PyObject *self, PyObject *obj)
     Py_RETURN_NONE;
 }
 
+static PyObject *
+test_lock_recursive(PyObject *self, PyObject *obj)
+{
+    _PyRecursiveMutex m = (_PyRecursiveMutex){0};
+    assert(!_PyRecursiveMutex_IsLockedByCurrentThread(&m));
+
+    _PyRecursiveMutex_Lock(&m);
+    assert(m.thread == PyThread_get_thread_ident_ex());
+    assert(PyMutex_IsLocked(&m.mutex));
+    assert(m.level == 0);
+
+    _PyRecursiveMutex_Lock(&m);
+    assert(m.level == 1);
+    _PyRecursiveMutex_Unlock(&m);
+
+    _PyRecursiveMutex_Unlock(&m);
+    assert(m.thread == 0);
+    assert(!PyMutex_IsLocked(&m.mutex));
+    assert(m.level == 0);
+
+    Py_RETURN_NONE;
+}
+
 static PyMethodDef test_methods[] = {
     {"test_lock_basic", test_lock_basic, METH_NOARGS},
     {"test_lock_two_threads", test_lock_two_threads, METH_NOARGS},
@@ -485,6 +509,7 @@ static PyMethodDef test_methods[] = {
     {"test_lock_benchmark", test_lock_benchmark, METH_NOARGS},
     {"test_lock_once", test_lock_once, METH_NOARGS},
     {"test_lock_rwlock", test_lock_rwlock, METH_NOARGS},
+    {"test_lock_recursive", test_lock_recursive, METH_NOARGS},
     {NULL, NULL} /* sentinel */
 };
 
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 386e942..5f943d4 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -16,7 +16,6 @@
 #include "pycore_call.h"          // _PyObject_CallNoArgs()
 #include "pycore_ceval.h"         // _PyEval_ReInitThreads()
 #include "pycore_fileutils.h"     // _Py_closerange()
-#include "pycore_import.h"        // _PyImport_ReInitLock()
 #include "pycore_initconfig.h"    // _PyStatus_EXCEPTION()
 #include "pycore_long.h"          // _PyLong_IsNegative()
 #include "pycore_moduleobject.h"  // _PyModule_GetState()
@@ -627,10 +626,7 @@ PyOS_AfterFork_Parent(void)
     _PyEval_StartTheWorldAll(&_PyRuntime);
 
     PyInterpreterState *interp = _PyInterpreterState_GET();
-    if (_PyImport_ReleaseLock(interp) <= 0) {
-        Py_FatalError("failed releasing import lock after fork");
-    }
-
+    _PyImport_ReleaseLock(interp);
     run_at_forkers(interp->after_forkers_parent, 0);
 }
 
@@ -675,10 +671,7 @@ PyOS_AfterFork_Child(void)
     _PyEval_StartTheWorldAll(&_PyRuntime);
     _PyThreadState_DeleteList(list);
 
-    status = _PyImport_ReInitLock(tstate->interp);
-    if (_PyStatus_EXCEPTION(status)) {
-        goto fatal_error;
-    }
+    _PyImport_ReleaseLock(tstate->interp);
 
     _PySignal_AfterFork();