https://github.com/python/cpython/commit/cca30230d992c46dfb607dcc24b3dc2e6d05f536
commit: cca30230d992c46dfb607dcc24b3dc2e6d05f536
branch: main
author: Sam Gross <[email protected]>
committer: colesbury <[email protected]>
date: 2024-03-08T12:39:53-05:00
summary:
gh-115103: Fix unregistering of QSBR state (#116480)
If a thread blocks while waiting on the `shared->mutex` lock, the array
of QSBR states may be reallocated. The `tstate->qsbr` values before the
lock is acquired may not be the same as the value after the lock is acquired.
files:
M Python/qsbr.c
diff --git a/Python/qsbr.c b/Python/qsbr.c
index 69f77f49082819..d7ac8f479cda1b 100644
--- a/Python/qsbr.c
+++ b/Python/qsbr.c
@@ -233,13 +233,17 @@ _Py_qsbr_register(_PyThreadStateImpl *tstate,
PyInterpreterState *interp,
void
_Py_qsbr_unregister(_PyThreadStateImpl *tstate)
{
+ struct _qsbr_shared *shared = tstate->qsbr->shared;
+
+ PyMutex_Lock(&shared->mutex);
+ // NOTE: we must load (or reload) the thread state's qbsr inside the mutex
+ // because the array may have been resized (changing tstate->qsbr) while
+ // we waited to acquire the mutex.
struct _qsbr_thread_state *qsbr = tstate->qsbr;
- struct _qsbr_shared *shared = qsbr->shared;
assert(qsbr->seq == 0 && "thread state must be detached");
-
- PyMutex_Lock(&shared->mutex);
assert(qsbr->allocated && qsbr->tstate == (PyThreadState *)tstate);
+
tstate->qsbr = NULL;
qsbr->tstate = NULL;
qsbr->allocated = false;
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