https://github.com/python/cpython/commit/54c6fcbefd33a8d8bf8c004cf1aad3be3d37b933
commit: 54c6fcbefd33a8d8bf8c004cf1aad3be3d37b933
branch: main
author: Sam Gross <[email protected]>
committer: colesbury <[email protected]>
date: 2024-10-15T16:09:35Z
summary:
gh-124375: Avoid calling `_PyMem_ProcessDelayed` on other thread states
(#124459)
This fixes a crash when running the PyO3 test suite on the free-threaded
build. The `qsbr` field is initialized after the `PyThreadState` is
added to the interpreter's linked list -- it might still be NULL.
Instead, we "steal" the queue of to-be-freed memory blocks. This is
always initialized (possibly empty) and protected by the stop the world
pause.
files:
A
Misc/NEWS.d/next/Core_and_Builtins/2024-10-15-15-29-41.gh-issue-124375.wNrWVa.rst
M Python/gc_free_threading.c
diff --git
a/Misc/NEWS.d/next/Core_and_Builtins/2024-10-15-15-29-41.gh-issue-124375.wNrWVa.rst
b/Misc/NEWS.d/next/Core_and_Builtins/2024-10-15-15-29-41.gh-issue-124375.wNrWVa.rst
new file mode 100644
index 00000000000000..4bd17a6e683bc7
--- /dev/null
+++
b/Misc/NEWS.d/next/Core_and_Builtins/2024-10-15-15-29-41.gh-issue-124375.wNrWVa.rst
@@ -0,0 +1 @@
+Fix a crash in the free threading build when the GC runs concurrently with a
new thread starting.
diff --git a/Python/gc_free_threading.c b/Python/gc_free_threading.c
index 38564d9d9b0058..3814cd46e2b440 100644
--- a/Python/gc_free_threading.c
+++ b/Python/gc_free_threading.c
@@ -420,18 +420,24 @@ merge_queued_objects(_PyThreadStateImpl *tstate, struct
collection_state *state)
static void
process_delayed_frees(PyInterpreterState *interp)
{
- // In STW status, we can observe the latest write sequence by
- // advancing the write sequence immediately.
+ // While we are in a "stop the world" pause, we can observe the latest
+ // write sequence by advancing the write sequence immediately.
_Py_qsbr_advance(&interp->qsbr);
_PyThreadStateImpl *current_tstate = (_PyThreadStateImpl
*)_PyThreadState_GET();
_Py_qsbr_quiescent_state(current_tstate->qsbr);
+
+ // Merge the queues from other threads into our own queue so that we can
+ // process all of the pending delayed free requests at once.
HEAD_LOCK(&_PyRuntime);
- PyThreadState *tstate = interp->threads.head;
- while (tstate != NULL) {
- _PyMem_ProcessDelayed(tstate);
- tstate = (PyThreadState *)tstate->next;
+ for (PyThreadState *p = interp->threads.head; p != NULL; p = p->next) {
+ _PyThreadStateImpl *other = (_PyThreadStateImpl *)p;
+ if (other != current_tstate) {
+ llist_concat(¤t_tstate->mem_free_queue,
&other->mem_free_queue);
+ }
}
HEAD_UNLOCK(&_PyRuntime);
+
+ _PyMem_ProcessDelayed((PyThreadState *)current_tstate);
}
// Subtract an incoming reference from the computed "gc_refs" refcount.
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