https://github.com/python/cpython/commit/dcfbd3be9f1e0ba7aa32214e8f5f7f2ea4375a28 commit: dcfbd3be9f1e0ba7aa32214e8f5f7f2ea4375a28 branch: 3.13 author: Miss Islington (bot) <[email protected]> committer: colesbury <[email protected]> date: 2024-05-29T19:47:47Z summary:
[3.13] gh-119525: Fix deadlock with `_PyType_Lookup` and the GIL (GH-119527) (#119746) The deadlock only affected the free-threaded build and only occurred when the GIL was enabled at runtime. The `Py_DECREF(old_name)` call might temporarily release the GIL while holding the type seqlock. Another thread may spin trying to acquire the seqlock while holding the GIL. The deadlock occurred roughly 1 in ~1,000 runs of `pool_in_threads.py` from `test_multiprocessing_pool_circular_import`. (cherry picked from commit c22323cd1c200ca1b22c47af95f67c4b2d661fe7) Co-authored-by: Sam Gross <[email protected]> files: A Misc/NEWS.d/next/Core and Builtins/2024-05-24-21-04-00.gh-issue-119525.zLFLf1.rst M Objects/typeobject.c diff --git a/Misc/NEWS.d/next/Core and Builtins/2024-05-24-21-04-00.gh-issue-119525.zLFLf1.rst b/Misc/NEWS.d/next/Core and Builtins/2024-05-24-21-04-00.gh-issue-119525.zLFLf1.rst new file mode 100644 index 00000000000000..83c29a16e572d7 --- /dev/null +++ b/Misc/NEWS.d/next/Core and Builtins/2024-05-24-21-04-00.gh-issue-119525.zLFLf1.rst @@ -0,0 +1,2 @@ +Fix deadlock involving ``_PyType_Lookup()`` cache in the free-threaded build +when the GIL is dynamically enabled at runtime. diff --git a/Objects/typeobject.c b/Objects/typeobject.c index f588992216447d..14c43a7f0664da 100644 --- a/Objects/typeobject.c +++ b/Objects/typeobject.c @@ -5062,7 +5062,7 @@ is_dunder_name(PyObject *name) return 0; } -static void +static PyObject * update_cache(struct type_cache_entry *entry, PyObject *name, unsigned int version_tag, PyObject *value) { _Py_atomic_store_uint32_relaxed(&entry->version, version_tag); @@ -5073,7 +5073,7 @@ update_cache(struct type_cache_entry *entry, PyObject *name, unsigned int versio // exact unicode object or Py_None so it's safe to do so. PyObject *old_name = entry->name; _Py_atomic_store_ptr_relaxed(&entry->name, Py_NewRef(name)); - Py_DECREF(old_name); + return old_name; } #if Py_GIL_DISABLED @@ -5093,10 +5093,12 @@ update_cache_gil_disabled(struct type_cache_entry *entry, PyObject *name, return; } - update_cache(entry, name, version_tag, value); + PyObject *old_value = update_cache(entry, name, version_tag, value); // Then update sequence to the next valid value _PySeqLock_UnlockWrite(&entry->sequence); + + Py_DECREF(old_value); } #endif @@ -5208,7 +5210,8 @@ _PyType_LookupRef(PyTypeObject *type, PyObject *name) #if Py_GIL_DISABLED update_cache_gil_disabled(entry, name, version, res); #else - update_cache(entry, name, version, res); + PyObject *old_value = update_cache(entry, name, version, res); + Py_DECREF(old_value); #endif } return res; _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3/lists/python-checkins.python.org/ Member address: [email protected]
