From 0d03a185ac784ffb057885022aa3000b294e66f3 Mon Sep 17 00:00:00 2001
From: Daniele Parmeggiani <daniele.parmeggiani@arm.com>
Date: Mon, 8 Jun 2026 14:11:17 +0100
Subject: [PATCH 1/2] gh-150902: Optimize `PyCriticalSection2` to skip locking
 the same locks as the ones held by the current CS2

---
 Python/critical_section.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/Python/critical_section.c b/Python/critical_section.c
index 98e23eda7cdd77e..a2673f51fe73180 100644
--- a/Python/critical_section.c
+++ b/Python/critical_section.c
@@ -72,6 +72,21 @@ _PyCriticalSection2_BeginSlow(PyThreadState *tstate, PyCriticalSection2 *c, PyMu
         c->_cs_base._cs_prev = 0;
         return;
     }
+    // Same optimization as in _PyCriticalSection_BeginSlow: skip locking when
+    // recursively acquiring the same locks.
+    if (tstate->critical_section &&
+        tstate->critical_section & _Py_CRITICAL_SECTION_TWO_MUTEXES) {
+        PyCriticalSection2 *prev2 = (PyCriticalSection2 *)
+            untag_critical_section(tstate->critical_section);
+        assert(m1 < m2);
+        assert(prev2->_cs_base._cs_mutex < prev2->_cs_mutex2);
+        if (prev2->_cs_base._cs_mutex == m1 && prev2->_cs_mutex2 == m2) {
+            c->_cs_base._cs_mutex = NULL;
+            c->_cs_mutex2 = NULL;
+            c->_cs_base._cs_prev = 0;
+            return;
+        }
+    }
     c->_cs_base._cs_mutex = NULL;
     c->_cs_mutex2 = NULL;
     c->_cs_base._cs_prev = tstate->critical_section;

From b61696ed0d137d2cd4ac40bf59a0bf48af9a2764 Mon Sep 17 00:00:00 2001
From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com>
Date: Mon, 8 Jun 2026 13:14:46 +0000
Subject: [PATCH 2/2] =?UTF-8?q?=F0=9F=93=9C=F0=9F=A4=96=20Added=20by=20blu?=
 =?UTF-8?q?rb=5Fit.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../2026-06-08-13-14-42.gh-issue-150902.-CWZ66.rst               | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 Misc/NEWS.d/next/Core_and_Builtins/2026-06-08-13-14-42.gh-issue-150902.-CWZ66.rst

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-06-08-13-14-42.gh-issue-150902.-CWZ66.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-06-08-13-14-42.gh-issue-150902.-CWZ66.rst
new file mode 100644
index 000000000000000..e3b7cd387b439fe
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-06-08-13-14-42.gh-issue-150902.-CWZ66.rst
@@ -0,0 +1 @@
+Apply an existing optimization of PyCriticalSection (single mutex) to PyCriticalSection2: avoid acquiring the same locks that the current CS has already acquired.