fix #2418 / Linux: fix race condition

HISTORY.rst

@@ -11,6 +11,8 @@ XXXX-XX-XX
 
 **Bug fixes**
 
+- 2418_, [Linux]: fix race condition in case /proc/PID/stat does not exist, but
+  /proc/PID does, resulting in FileNotFoundError.
 - 2470_, [Linux]: `users()`_ may return "localhost" instead of the actual IP
   address of the user logged in.
 

psutil/_pslinux.py

@@ -1722,7 +1722,12 @@ def wrapper(self, *args, **kwargs):
             raise NoSuchProcess(self.pid, self._name)
         except FileNotFoundError:
             self._raise_if_zombie()
-            if not os.path.exists("%s/%s" % (self._procfs_path, self.pid)):
+            # /proc/PID directory may still exist, but the files within
+            # it may not, indicating the process is gone, see:
+            # https://github.com/giampaolo/psutil/issues/2418
+            if not os.path.exists(
+                "%s/%s/stat" % (self._procfs_path, self.pid)
+            ):
                 raise NoSuchProcess(self.pid, self._name)
             raise
 

psutil/tests/test_linux.py

@@ -2133,6 +2133,15 @@ def test_issue_1014(self):
                 p.memory_maps()
             assert m.called
 
+    def test_issue_2418(self):
+        p = psutil.Process()
+        with mock_open_exception(
+            '/proc/%s/statm' % os.getpid(), FileNotFoundError
+        ):
+            with mock.patch("os.path.exists", return_value=False):
+                with pytest.raises(psutil.NoSuchProcess):
+                    p.memory_info()
+
     @pytest.mark.skipif(not HAS_RLIMIT, reason="not supported")
     def test_rlimit_zombie(self):
         # Emulate a case where rlimit() raises ENOSYS, which may