From 0e349ea5541104c76cafc173bfcfef8de872f96f Mon Sep 17 00:00:00 2001
From: Mark Shannon <mark@hotpy.org>
Date: Fri, 16 Jul 2021 11:48:46 +0100
Subject: [3.10] bpo-44645: Check for interrupts on any potentially backwards
 edge. (GH-27167) (GH-27183)

(cherry picked from commit 000e70ad5246732fcbd27cf59268185cbd5ad734)

Co-authored-by: Mark Shannon <mark@hotpy.org>
---
 Lib/test/test_threading.py | 25 +++++++++++++++++++++++++
 Python/ceval.c             |  7 ++++++-
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
index f648a8b..3b5bc42 100644
--- a/Lib/test/test_threading.py
+++ b/Lib/test/test_threading.py
@@ -1604,6 +1604,31 @@ class InterruptMainTests(unittest.TestCase):
         self.assertRaises(ValueError, _thread.interrupt_main, signal.NSIG)
         self.assertRaises(ValueError, _thread.interrupt_main, 1000000)
 
+    @threading_helper.reap_threads
+    def test_can_interrupt_tight_loops(self):
+        cont = True
+        started = False
+        iterations = 100_000_000
+
+        def worker():
+            nonlocal iterations
+            nonlocal started
+            started = True
+            while cont:
+                if iterations:
+                    iterations -= 1
+                else:
+                    return
+                pass
+
+        t = threading.Thread(target=worker)
+        t.start()
+        while not started:
+            pass
+        cont = False
+        t.join()
+        self.assertNotEqual(iterations, 0)
+
 
 class AtexitTests(unittest.TestCase):
 
diff --git a/Python/ceval.c b/Python/ceval.c
index 6482c88..429ddb8 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -3759,14 +3759,17 @@ main_loop:
             if (Py_IsFalse(cond)) {
                 Py_DECREF(cond);
                 JUMPTO(oparg);
+                CHECK_EVAL_BREAKER();
                 DISPATCH();
             }
             err = PyObject_IsTrue(cond);
             Py_DECREF(cond);
             if (err > 0)
                 ;
-            else if (err == 0)
+            else if (err == 0) {
                 JUMPTO(oparg);
+                CHECK_EVAL_BREAKER();
+            }
             else
                 goto error;
             DISPATCH();
@@ -3783,12 +3786,14 @@ main_loop:
             if (Py_IsTrue(cond)) {
                 Py_DECREF(cond);
                 JUMPTO(oparg);
+                CHECK_EVAL_BREAKER();
                 DISPATCH();
             }
             err = PyObject_IsTrue(cond);
             Py_DECREF(cond);
             if (err > 0) {
                 JUMPTO(oparg);
+                CHECK_EVAL_BREAKER();
             }
             else if (err == 0)
                 ;
-- 
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