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gh-117657: Fix data races in the method cache in free-threaded builds (#117954) 

Fix data races in the method cache in free-threaded builds

These are technically data races, but I think they're benign (to
the extent that that is actually possible). We update cache entries
non-atomically but read them atomically from another thread, and there's
nothing that establishes a happens-before relationship between the
reads and writes that I can see.
This commit is contained in:
mpage 2024-04-17 09:42:56 -07:00 committed by GitHub
parent deaecb88fa
commit b6c62c79e7
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2 changed files with 5 additions and 4 deletions
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8
Objects/typeobject.c
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@ -4974,13 +4974,15 @@ is_dunder_name(PyObject *name)
static void static void
update_cache(struct type_cache_entry *entry, PyObject *name, unsigned int version_tag, PyObject *value) update_cache(struct type_cache_entry *entry, PyObject *name, unsigned int version_tag, PyObject *value)
{ {
entry->version = version_tag; _Py_atomic_store_uint32_relaxed(&entry->version, version_tag);
entry->value = value; /* borrowed */ _Py_atomic_store_ptr_relaxed(&entry->value, value); /* borrowed */
assert(_PyASCIIObject_CAST(name)->hash != -1); assert(_PyASCIIObject_CAST(name)->hash != -1);
OBJECT_STAT_INC_COND(type_cache_collisions, entry->name != Py_None && entry->name != name); OBJECT_STAT_INC_COND(type_cache_collisions, entry->name != Py_None && entry->name != name);
// We're releasing this under the lock for simplicity sake because it's always a // We're releasing this under the lock for simplicity sake because it's always a
// exact unicode object or Py_None so it's safe to do so. // exact unicode object or Py_None so it's safe to do so.
Py_SETREF(entry->name, Py_NewRef(name)); PyObject *old_name = entry->name;
_Py_atomic_store_ptr_relaxed(&entry->name, Py_NewRef(name));
Py_DECREF(old_name);
} }
#if Py_GIL_DISABLED #if Py_GIL_DISABLED

1
Tools/tsan/suppressions_free_threading.txt
View File

@ -47,5 +47,4 @@ race:set_inheritable
race:start_the_world race:start_the_world
race:tstate_set_detached race:tstate_set_detached
race:unicode_hash race:unicode_hash
race:update_cache
race:update_cache_gil_disabled race:update_cache_gil_disabled