Sync branches 260626-1120

1 files changed, 10 insertions, 1 deletions

diff --git a/contrib/tools/python3/Python/lock.c b/contrib/tools/python3/Python/lock.c
index 24c404a1246..6def8567b11 100644
--- a/contrib/tools/python3/Python/lock.c
+++ b/contrib/tools/python3/Python/lock.c
@@ -210,7 +210,16 @@ _PyRawMutex_LockSlow(_PyRawMutex *m)
 
         // Wait for us to be woken up. Note that we still have to lock the
         // mutex ourselves: it is NOT handed off to us.
-        _PySemaphore_Wait(&waiter.sema, -1, /*detach=*/0);
+        //
+        // Loop until we observe an actual wakeup. A return of Py_PARK_INTR
+        // could otherwise let us exit _PySemaphore_Wait and destroy
+        // `waiter.sema` while _PyRawMutex_UnlockSlow's matching
+        // _PySemaphore_Wakeup is still pending, since the unlocker has
+        // already CAS-removed us from the waiter list without any handshake.
+        int res;
+        do {
+            res = _PySemaphore_Wait(&waiter.sema, -1, /*detach=*/0);
+        } while (res != Py_PARK_OK);
     }
 
     _PySemaphore_Destroy(&waiter.sema);