From 6f9525dd3f0ef5809106ca0923a7512d666a04bb Mon Sep 17 00:00:00 2001 From: Neil Schemenauer Date: Thu, 26 Sep 2024 19:33:07 -0700 Subject: [PATCH] gh-116510: Fix crash during sub-interpreter shutdown (gh-124645) Fix a bug that can cause a crash when sub-interpreters use "basic" single-phase extension modules. Shared objects could refer to PyGC_Head nodes that had been freed as part of interpreter shutdown. --- ...-09-26-17-55-34.gh-issue-116510.dhn8w8.rst | 3 ++ Python/gc.c | 29 +++++++++++++++++-- 2 files changed, 29 insertions(+), 3 deletions(-) create mode 100644 Misc/NEWS.d/next/Core_and_Builtins/2024-09-26-17-55-34.gh-issue-116510.dhn8w8.rst diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2024-09-26-17-55-34.gh-issue-116510.dhn8w8.rst b/Misc/NEWS.d/next/Core_and_Builtins/2024-09-26-17-55-34.gh-issue-116510.dhn8w8.rst new file mode 100644 index 00000000000000..fc3f8af72d87bf --- /dev/null +++ b/Misc/NEWS.d/next/Core_and_Builtins/2024-09-26-17-55-34.gh-issue-116510.dhn8w8.rst @@ -0,0 +1,3 @@ +Fix a bug that can cause a crash when sub-interpreters use "basic" +single-phase extension modules. Shared objects could refer to PyGC_Head +nodes that had been freed as part of interpreter cleanup. diff --git a/Python/gc.c b/Python/gc.c index 024d041437be4a..028657eb8999c1 100644 --- a/Python/gc.c +++ b/Python/gc.c @@ -1944,6 +1944,13 @@ _PyGC_DumpShutdownStats(PyInterpreterState *interp) } } +static void +finalize_unlink_gc_head(PyGC_Head *gc) { + PyGC_Head *prev = GC_PREV(gc); + PyGC_Head *next = GC_NEXT(gc); + _PyGCHead_SET_NEXT(prev, next); + _PyGCHead_SET_PREV(next, prev); +} void _PyGC_Fini(PyInterpreterState *interp) @@ -1952,9 +1959,25 @@ _PyGC_Fini(PyInterpreterState *interp) Py_CLEAR(gcstate->garbage); Py_CLEAR(gcstate->callbacks); - /* We expect that none of this interpreters objects are shared - with other interpreters. - See https://github.com/python/cpython/issues/90228. */ + /* Prevent a subtle bug that affects sub-interpreters that use basic + * single-phase init extensions (m_size == -1). Those extensions cause objects + * to be shared between interpreters, via the PyDict_Update(mdict, m_copy) call + * in import_find_extension(). + * + * If they are GC objects, their GC head next or prev links could refer to + * the interpreter _gc_runtime_state PyGC_Head nodes. Those nodes go away + * when the interpreter structure is freed and so pointers to them become + * invalid. If those objects are still used by another interpreter and + * UNTRACK is called on them, a crash will happen. We untrack the nodes + * here to avoid that. + * + * This bug was originally fixed when reported as gh-90228. The bug was + * re-introduced in gh-94673. + */ + finalize_unlink_gc_head(&gcstate->young.head); + finalize_unlink_gc_head(&gcstate->old[0].head); + finalize_unlink_gc_head(&gcstate->old[1].head); + finalize_unlink_gc_head(&gcstate->permanent_generation.head); } /* for debugging */