diff --git a/distributed/process.py b/distributed/process.py
index c73c9bfe17b..0f0a6a50720 100644
--- a/distributed/process.py
+++ b/distributed/process.py
@@ -232,9 +232,11 @@ def _start():
     def _watch_process(cls, selfref, process, state, q):
         r = repr(selfref())
         process.join()
-        exitcode = process.exitcode
-        assert exitcode is not None
-        logger.debug("[%s] process %r exited with code %r", r, state.pid, exitcode)
+        exitcode = original_exit_code = process.exitcode
+        if exitcode is None:
+            # The child process is already reaped
+            # (may happen if waitpid() is called elsewhere).
+            exitcode = 255
         state.is_alive = False
         state.exitcode = exitcode
         # Make sure the process is removed from the global list
@@ -247,6 +249,16 @@ def _watch_process(cls, selfref, process, state, q):
         finally:
             self = None  # lose reference
 
+        # logging may fail - defer calls to after the callback is added
+        if original_exit_code is None:
+            logger.warning(
+                "[%s] process %r exit status was already read will report exitcode 255",
+                r,
+                state.pid,
+            )
+        else:
+            logger.debug("[%s] process %r exited with code %r", r, state.pid, exitcode)
+
     def start(self):
         """
         Start the child process.
diff --git a/distributed/tests/test_asyncprocess.py b/distributed/tests/test_asyncprocess.py
index 65aa0e303cc..fb4906e4c55 100644
--- a/distributed/tests/test_asyncprocess.py
+++ b/distributed/tests/test_asyncprocess.py
@@ -7,14 +7,11 @@
 import sys
 import threading
 import weakref
-from datetime import timedelta
 from time import sleep
 
 import psutil
 import pytest
-from tornado import gen
 from tornado.ioloop import IOLoop
-from tornado.locks import Event
 
 from distributed.compatibility import LINUX, MACOS, WINDOWS
 from distributed.metrics import time
@@ -238,13 +235,9 @@ async def test_close():
 async def test_exit_callback():
     to_child = get_mp_context().Queue()
     from_child = get_mp_context().Queue()
-    evt = Event()
+    evt = asyncio.Event()
 
-    # FIXME: this breaks if changed to async def...
-    @gen.coroutine
     def on_stop(_proc):
-        assert _proc is proc
-        yield gen.moment
         evt.set()
 
     # Normal process exit
@@ -259,7 +252,7 @@ def on_stop(_proc):
     assert not evt.is_set()
 
     to_child.put(None)
-    await evt.wait(timedelta(seconds=5))
+    await asyncio.wait_for(evt.wait(), 5)
     assert evt.is_set()
     assert not proc.is_alive()
 
@@ -275,7 +268,7 @@ def on_stop(_proc):
     assert not evt.is_set()
 
     await proc.terminate()
-    await evt.wait(timedelta(seconds=5))
+    await asyncio.wait_for(evt.wait(), 5)
     assert evt.is_set()
 
 
diff --git a/setup.cfg b/setup.cfg
index bc76731dde2..08e404fbddc 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -79,8 +79,6 @@ filterwarnings =
     ignore:Scheduler already contains a plugin with name nonidempotentplugin. overwriting:UserWarning
     ignore:Increasing number of chunks by factor of 20:dask.array.core.PerformanceWarning
     ignore::distributed.versions.VersionMismatchWarning
-    ignore:(?s)Exception in thread AsyncProcess Dask Worker process \(from Nanny\) watch process join.*assert exitcode is not None:pytest.PytestUnhandledThreadExceptionWarning
-    ignore:(?s)Exception in thread AsyncProcess SpawnProcess-\d+ watch process join.*assert exitcode is not None:pytest.PytestUnhandledThreadExceptionWarning
     ignore:(?s)Exception in thread.*old_ssh.*channel\.send\(b"\\x03"\).*Socket is closed:pytest.PytestUnhandledThreadExceptionWarning
     ignore:(?s)Exception in thread.*paramiko\.ssh_exception\.NoValidConnectionsError:pytest.PytestUnhandledThreadExceptionWarning
     ignore:(?s)Exception ignored in. <Finalize object, dead>.*sem_unlink.*FileNotFoundError:pytest.PytestUnraisableExceptionWarning