misc: add news entry

KowalskiThomas · KowalskiThomas · commit 39aa50fbfd6f · 2026-04-27T14:53:16.000+02:00
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-04-23-08-36-47.gh-issue-148891.AMMHow.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-04-23-08-36-47.gh-issue-148891.AMMHow.rst
@@ -0,0 +1,6 @@
+Fix a crash in :func:`contextvars.Context.run` where a re-entrant GC
+invocation (triggered by ``_PyHamt_Assoc`` or ``_PyHamt_Without``
+allocating nodes) could free the current HAMT while it was still being
+traversed.  The fix holds a strong reference to the old ``ctx_vars``
+across the hazardous call in ``contextvar_set`` and ``contextvar_del``.
+
