[Python-checkins] [3.11]GH-112275: Fix HEAD_LOCK deadlock in child process after fork (#112336)

[ambv]

https://github.com/python/cpython/commit/522799a05e3e820339718151ac055af6d864d463
commit: 522799a05e3e820339718151ac055af6d864d463
branch: 3.11
author: ChuBoning <102216855+chubon...@users.noreply.github.com>
committer: ambv <luk...@langa.pl>
date: 2024-09-04T19:14:59+02:00
summary:

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

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

Co-authored-by: Łukasz Langa <luk...@langa.pl>

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 46859dab35c500..6fb2fc8ce250c1 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -603,6 +603,11 @@ PyOS_AfterFork_Child(void)
         goto fatal_error;
     }
 
+    status = _PyRuntimeState_ReInitThreads(runtime);
+    if (_PyStatus_EXCEPTION(status)) {
+        goto fatal_error;
+    }
+
     PyThreadState *tstate = _PyThreadState_GET();
     _Py_EnsureTstateNotNULL(tstate);
 
@@ -622,11 +627,6 @@ PyOS_AfterFork_Child(void)
 
     _PySignal_AfterFork();
 
-    status = _PyRuntimeState_ReInitThreads(runtime);
-    if (_PyStatus_EXCEPTION(status)) {
-        goto fatal_error;
-    }
-
     status = _PyInterpreterState_DeleteExceptMain(runtime);
     if (_PyStatus_EXCEPTION(status)) {
         goto fatal_error;

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