[Python-checkins] [3.9] gh-112275: Fix HEAD_LOCK deadlock in child process after fork (GH-112336) (#123688)

[ambv]

https://github.com/python/cpython/commit/0152431f179e85f582a4c393aa3b99d3918a1109
commit: 0152431f179e85f582a4c393aa3b99d3918a1109
branch: 3.9
author: Łukasz Langa <luk...@langa.pl>
committer: ambv <luk...@langa.pl>
date: 2024-09-04T22:41:03+02:00
summary:

[3.9] gh-112275: Fix HEAD_LOCK deadlock in child process after fork (GH-112336) 
(#123688)

HEAD_LOCK is called from _PyEval_ReInitThreads->_PyThreadState_DeleteExcept 
before _PyRuntimeState_ReInitThreads reinit runtime->interpreters.mutex which 
might be locked before fork.

(cherry picked from commit 522799a05e3e820339718151ac055af6d864d463)

Co-authored-by: ChuBoning <102216855+chubon...@users.noreply.github.com>

files:
A 
Misc/NEWS.d/next/Core_and_Builtins/2024-09-04-18-20-11.gh-issue-112275.W_iMiB.rst
M Modules/posixmodule.c

diff --git 
a/Misc/NEWS.d/next/Core_and_Builtins/2024-09-04-18-20-11.gh-issue-112275.W_iMiB.rst
 
b/Misc/NEWS.d/next/Core_and_Builtins/2024-09-04-18-20-11.gh-issue-112275.W_iMiB.rst
new file mode 100644
index 00000000000000..d663be1867ed3d
--- /dev/null
+++ 
b/Misc/NEWS.d/next/Core_and_Builtins/2024-09-04-18-20-11.gh-issue-112275.W_iMiB.rst
@@ -0,0 +1,3 @@
+A deadlock involving ``pystate.c``'s ``HEAD_LOCK`` in ``posixmodule.c``
+at fork is now fixed. Patch by ChuBoning based on previous Python 3.12
+fix by Victor Stinner.
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 7645bcfea97b4f..f498d40e34c3cf 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -589,10 +589,10 @@ PyOS_AfterFork_Child(void)
 {
     _PyRuntimeState *runtime = &_PyRuntime;
     _PyGILState_Reinit(runtime);
+    _PyRuntimeState_ReInitThreads(runtime);
     _PyEval_ReInitThreads(runtime);
     _PyImport_ReInitLock();
     _PySignal_AfterFork();
-    _PyRuntimeState_ReInitThreads(runtime);
     _PyInterpreterState_DeleteExceptMain(runtime);
 
     run_at_forkers(_PyInterpreterState_GET()->after_forkers_child, 0);

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