From acb1522671591d978c5f6936f7d6c7c8ef5534d9 Mon Sep 17 00:00:00 2001
From: Denis Otkidach <denis.otkidach@gmail.com>
Date: Wed, 12 May 2021 14:44:39 +0300
Subject: [PATCH 1/3] bpo-42130: Add test for swallowed cancellation

---
 Lib/test/test_asyncio/test_asyncio_waitfor.py | 33 +++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/Lib/test/test_asyncio/test_asyncio_waitfor.py b/Lib/test/test_asyncio/test_asyncio_waitfor.py
index 2ca64abbeb527c..fc5a4218ac6999 100644
--- a/Lib/test/test_asyncio/test_asyncio_waitfor.py
+++ b/Lib/test/test_asyncio/test_asyncio_waitfor.py
@@ -28,6 +28,7 @@ async def run(self):
 
         self.exited = True
 
+
 class AsyncioWaitForTest(unittest.TestCase):
 
     async def atest_asyncio_wait_for_cancelled(self):
@@ -56,6 +57,38 @@ async def atest_asyncio_wait_for_timeout(self):
     def test_asyncio_wait_for_timeout(self):
         asyncio.run(self.atest_asyncio_wait_for_timeout())
 
+    async def atest_asyncio_wait_for_hang(self, inner_steps, outer_steps):
+        # bpo-42130: wait_for can swallow cancellation causing task to hang
+        async def inner(steps):
+            for _ in range(steps):
+                await asyncio.sleep(0)
+
+        finished = False
+
+        async def wait_for_coro(steps):
+            nonlocal finished
+            await asyncio.wait_for(inner(steps), timeout=1)
+            await asyncio.sleep(0.1)
+            finished = True
+
+        task = asyncio.create_task(wait_for_coro(inner_steps))
+        for _ in range(outer_steps):
+            await asyncio.sleep(0)
+        assert not task.done()
+
+        task.cancel()
+        with self.assertRaises(asyncio.CancelledError):
+            await task
+        self.assertFalse(finished)
+
+    def test_asyncio_wait_for_hang(self):
+        # Test with different number of inner/outer steps to weaken dependence
+        # on implementation details
+        for inner_steps in range(3):
+            for outer_steps in range(3):
+                with self.subTest(inner_steps=inner_steps, outer_steps=outer_steps):
+                    asyncio.run(self.atest_asyncio_wait_for_hang(inner_steps, outer_steps))
+
 
 if __name__ == '__main__':
     unittest.main()

From 053f426f9f6bb1247580e8f9765e810b26ac4c67 Mon Sep 17 00:00:00 2001
From: Denis Otkidach <denis.otkidach@gmail.com>
Date: Thu, 13 May 2021 13:26:57 +0300
Subject: [PATCH 2/3] Revert GH-21894 as not valid solution for bpo-37658

---
 Lib/asyncio/tasks.py                | 15 ++++++---------
 Lib/test/test_asyncio/test_tasks.py | 16 ----------------
 2 files changed, 6 insertions(+), 25 deletions(-)

diff --git a/Lib/asyncio/tasks.py b/Lib/asyncio/tasks.py
index 9a9d0d6e3cc269..6e5c0eec12b5df 100644
--- a/Lib/asyncio/tasks.py
+++ b/Lib/asyncio/tasks.py
@@ -433,15 +433,12 @@ async def wait_for(fut, timeout):
         try:
             await waiter
         except exceptions.CancelledError:
-            if fut.done():
-                return fut.result()
-            else:
-                fut.remove_done_callback(cb)
-                # We must ensure that the task is not running
-                # after wait_for() returns.
-                # See https://bugs.python.org/issue32751
-                await _cancel_and_wait(fut, loop=loop)
-                raise
+            fut.remove_done_callback(cb)
+            # We must ensure that the task is not running
+            # after wait_for() returns.
+            # See https://bugs.python.org/issue32751
+            await _cancel_and_wait(fut, loop=loop)
+            raise
 
         if fut.done():
             return fut.result()
diff --git a/Lib/test/test_asyncio/test_tasks.py b/Lib/test/test_asyncio/test_tasks.py
index a9e4cf53566ca9..f84b9c97a559ea 100644
--- a/Lib/test/test_asyncio/test_tasks.py
+++ b/Lib/test/test_asyncio/test_tasks.py
@@ -1147,22 +1147,6 @@ def gen():
         res = loop.run_until_complete(task)
         self.assertEqual(res, "ok")
 
-    def test_wait_for_cancellation_race_condition(self):
-        def gen():
-            yield 0.1
-            yield 0.1
-            yield 0.1
-            yield 0.1
-
-        loop = self.new_test_loop(gen)
-
-        fut = self.new_future(loop)
-        loop.call_later(0.1, fut.set_result, "ok")
-        task = loop.create_task(asyncio.wait_for(fut, timeout=1))
-        loop.call_later(0.1, task.cancel)
-        res = loop.run_until_complete(task)
-        self.assertEqual(res, "ok")
-
     def test_wait_for_waits_for_task_cancellation(self):
         loop = asyncio.new_event_loop()
         self.addCleanup(loop.close)

From fd4ea70bbd418c9d247a2a1d3169c8889171337c Mon Sep 17 00:00:00 2001
From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com>
Date: Thu, 13 May 2021 11:16:06 +0000
Subject: [PATCH 3/3] =?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

---
 .../NEWS.d/next/Library/2021-05-13-11-16-06.bpo-42130.ez0TO5.rst | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 Misc/NEWS.d/next/Library/2021-05-13-11-16-06.bpo-42130.ez0TO5.rst

diff --git a/Misc/NEWS.d/next/Library/2021-05-13-11-16-06.bpo-42130.ez0TO5.rst b/Misc/NEWS.d/next/Library/2021-05-13-11-16-06.bpo-42130.ez0TO5.rst
new file mode 100644
index 00000000000000..f632aa99b923d2
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-05-13-11-16-06.bpo-42130.ez0TO5.rst
@@ -0,0 +1 @@
+:meth:`asyncio.wait_for` fix swallowing of cancellation
\ No newline at end of file