Memory leak in test__interpchannels: _PyXIData_New not freed in channel_send

[ashm-dev]

Bug report

Bug description:

LeakSanitizer detects memory leaks in the test__interpchannels test module. The leaks occur in _PyXIData_New() function called from channel_send() in Modules/_interpchannelsmodule.c.

Affected versions:

• Python 3.13
• Python 3.14
• Python main branch

Steps to reproduce:

1. Build Python with address sanitizer:

CC=clang CXX=clang++ ./configure --with-address-sanitizer --with-pydebug --with-undefined-behavior-sanitizer --disable-optimizations && make -j$(nproc)

2. Run the test:

./python -X dev -X showrefcount -m test test__interpchannels -j$(nproc)

Expected behavior:
No memory leaks detected.

Actual behavior:
LeakSanitizer reports multiple direct memory leaks. The exact number of leaked bytes and allocations varies between Python versions.

Problematic code locations:

All leaks originate from _PyXIData_New():

cpython/Python/crossinterp.c

Lines 306 to 314 in d86ad87

	_PyXIData_t *
	_PyXIData_New(void)
	{
	_PyXIData_t *xid = PyMem_RawCalloc(1, sizeof(_PyXIData_t));
	if (xid == NULL) {
	PyErr_NoMemory();
	}
	return xid;
	}

Called through:

1. channel_send():
   

   cpython/Modules/_interpchannelsmodule.c

   Lines 1773 to 1819 in d86ad87

   	static int
   	channel_send(_channels *channels, int64_t cid, PyObject *obj,
   	_waiting_t *waiting, unboundop_t unboundop, xidata_fallback_t fallback)
   	{
   	PyThreadState *tstate = _PyThreadState_GET();
   	PyInterpreterState *interp = tstate->interp;
   	int64_t interpid = PyInterpreterState_GetID(interp);
   	// Look up the channel.
   	PyThread_type_lock mutex = NULL;
   	_channel_state *chan = NULL;
   	int err = _channels_lookup(channels, cid, &mutex, &chan);
   	if (err != 0) {
   	return err;
   	}
   	assert(chan != NULL);
   	// Past this point we are responsible for releasing the mutex.
   	if (chan->closing != NULL) {
   	PyThread_release_lock(mutex);
   	return ERR_CHANNEL_CLOSED;
   	}
   	// Convert the object to cross-interpreter data.
   	_PyXIData_t *data = _PyXIData_New();
   	if (data == NULL) {
   	PyThread_release_lock(mutex);
   	return -1;
   	}
   	if (_PyObject_GetXIData(tstate, obj, fallback, data) != 0) {
   	PyThread_release_lock(mutex);
   	GLOBAL_FREE(data);
   	return -1;
   	}
   	// Add the data to the channel.
   	int res = _channel_add(chan, interpid, data, waiting, unboundop);
   	PyThread_release_lock(mutex);
   	if (res != 0) {
   	// We may chain an exception here:
   	(void)_release_xid_data(data, 0);
   	GLOBAL_FREE(data);
   	return res;
   	}
   	return 0;
   	}

2. channel_send_wait():
   

   cpython/Modules/_interpchannelsmodule.c

   Lines 1843 to 1894 in d86ad87

   	// Like channel_send(), but strictly wait for the object to be received.
   	static int
   	channel_send_wait(_channels *channels, int64_t cid, PyObject *obj,
   	unboundop_t unboundop, PY_TIMEOUT_T timeout,
   	xidata_fallback_t fallback)
   	{
   	// We use a stack variable here, so we must ensure that &waiting
   	// is not held by any channel item at the point this function exits.
   	_waiting_t waiting;
   	if (_waiting_init(&waiting) < 0) {
   	assert(PyErr_Occurred());
   	return -1;
   	}
   	/* Queue up the object. */
   	int res = channel_send(channels, cid, obj, &waiting, unboundop, fallback);
   	if (res < 0) {
   	assert(waiting.status == WAITING_NO_STATUS);
   	goto finally;
   	}
   	/* Wait until the object is received. */
   	if (wait_for_lock(waiting.mutex, timeout) < 0) {
   	assert(PyErr_Occurred());
   	_waiting_finish_releasing(&waiting);
   	/* The send() call is failing now, so make sure the item
   	won't be received. */
   	channel_clear_sent(channels, cid, &waiting);
   	assert(waiting.status == WAITING_RELEASED);
   	if (!waiting.received) {
   	res = -1;
   	goto finally;
   	}
   	// XXX Emit a warning if not a TimeoutError?
   	PyErr_Clear();
   	}
   	else {
   	_waiting_finish_releasing(&waiting);
   	assert(waiting.status == WAITING_RELEASED);
   	if (!waiting.received) {
   	res = ERR_CHANNEL_CLOSED_WAITING;
   	goto finally;
   	}
   	}
   	/* success! */
   	res = 0;
   	finally:
   	_waiting_clear(&waiting);
   	return res;
   	}

3. _sharednsitem_set_value():
   

   cpython/Python/crossinterp.c

   Lines 2065 to 2084 in d86ad87

   	static int
   	_sharednsitem_set_value(_PyXI_namespace_item *item, PyObject *value,
   	xidata_fallback_t fallback)
   	{
   	assert(_sharednsitem_is_initialized(item));
   	assert(item->xidata == NULL);
   	item->xidata = _PyXIData_New();
   	if (item->xidata == NULL) {
   	return -1;
   	}
   	PyThreadState *tstate = PyThreadState_Get();
   	if (_PyObject_GetXIData(tstate, value, fallback, item->xidata) < 0) {
   	PyMem_RawFree(item->xidata);
   	item->xidata = NULL;
   	// The caller may want to propagate PyExc_NotShareableError
   	// if currently switched between interpreters.
   	return -1;
   	}
   	return 0;
   	}

4. _copy_string_obj_raw() via _PyXI_InitFailure():
   

   cpython/Python/crossinterp.c

   Lines 1041 to 1065 in d86ad87

   	static const char *
   	_copy_string_obj_raw(PyObject *strobj, Py_ssize_t *p_size)
   	{
   	Py_ssize_t size = -1;
   	const char *str = PyUnicode_AsUTF8AndSize(strobj, &size);
   	if (str == NULL) {
   	return NULL;
   	}
   	if (size != (Py_ssize_t)strlen(str)) {
   	PyErr_SetString(PyExc_ValueError, "found embedded NULL character");
   	return NULL;
   	}
   	char *copied = PyMem_RawMalloc(size+1);
   	if (copied == NULL) {
   	PyErr_NoMemory();
   	return NULL;
   	}
   	strcpy(copied, str);
   	if (p_size != NULL) {
   	*p_size = size;
   	}
   	return copied;
   	}

   
   

   cpython/Python/crossinterp.c

   Lines 1805 to 1825 in d86ad87

   	int
   	_PyXI_InitFailure(_PyXI_failure *failure, _PyXI_errcode code, PyObject *obj)
   	{
   	PyObject *msgobj = PyObject_Str(obj);
   	if (msgobj == NULL) {
   	return -1;
   	}
   	// This will leak if not paired with clear_xi_failure().
   	// That happens automatically in _capture_current_exception().
   	const char *msg = _copy_string_obj_raw(msgobj, NULL);
   	Py_DECREF(msgobj);
   	if (PyErr_Occurred()) {
   	return -1;
   	}
   	*failure = (_PyXI_failure){
   	.code = code,
   	.msg = msg,
   	.msg_owned = 1,
   	};
   	return 0;
   	}

Analysis:

The allocated memory in _PyXIData_New() is not being properly freed. The function allocates memory using _PyMem_DebugRawAlloc() but the corresponding cleanup appears to be missing in error paths or normal execution flow.

Full leak reports:
See attached log files for detailed stack traces on Python 3.13, 3.14, and main branch.

313.log
314.log
main.log

CPython versions tested on:

3.13, 3.14, CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-140306: Fix memory leaks in cross-interpreter data handling #140307
• [3.14] gh-140306: Fix memory leaks in cross-interpreter data handling (GH-140307) #140338
• [3.13] gh-140306: Fix memory leaks in cross-interpreter data handling (GH-140307) #140357
• [3.13] gh-140306: Fix memory leaks in cross-interpreter data handling #140397