From cbc46afa59dcc43c2c8c90ae7a0a0dc404325a89 Mon Sep 17 00:00:00 2001
From: Mariatta <Mariatta@users.noreply.github.com>
Date: Thu, 13 Apr 2017 19:26:16 -0700
Subject: [PATCH] [3.6] bpo-29694: race condition in pathlib mkdir with flags
 parents=True (GH-1089). (GH-1126)

(cherry picked from commit 22a594a0047d7706537ff2ac676cdc0f1dcb329c)
---
 Lib/pathlib.py           |  4 ++--
 Lib/test/test_pathlib.py | 30 ++++++++++++++++++++++++++++++
 Misc/NEWS                |  4 ++++
 3 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/Lib/pathlib.py b/Lib/pathlib.py
index 8c1cb96bad..70f5cba76f 100644
--- a/Lib/pathlib.py
+++ b/Lib/pathlib.py
@@ -1230,8 +1230,8 @@ class Path(PurePath):
         except FileNotFoundError:
             if not parents or self.parent == self:
                 raise
-            self.parent.mkdir(parents=True)
-            self._accessor.mkdir(self, mode)
+            self.parent.mkdir(parents=True, exist_ok=True)
+            self.mkdir(mode, parents=False, exist_ok=exist_ok)
         except OSError:
             # Cannot rely on checking for EEXIST, since the operating system
             # could give priority to other errors like EACCES or EROFS
diff --git a/Lib/test/test_pathlib.py b/Lib/test/test_pathlib.py
index 3ff9726d43..846f721e8d 100644
--- a/Lib/test/test_pathlib.py
+++ b/Lib/test/test_pathlib.py
@@ -8,6 +8,7 @@ import socket
 import stat
 import tempfile
 import unittest
+from unittest import mock
 
 from test import support
 android_not_root = support.android_not_root
@@ -1816,6 +1817,35 @@ class _BasePathTest(object):
             p.mkdir(exist_ok=True)
         self.assertEqual(cm.exception.errno, errno.EEXIST)
 
+    def test_mkdir_concurrent_parent_creation(self):
+        for pattern_num in range(32):
+            p = self.cls(BASE, 'dirCPC%d' % pattern_num)
+            self.assertFalse(p.exists())
+
+            def my_mkdir(path, mode=0o777):
+                path = str(path)
+                # Emulate another process that would create the directory
+                # just before we try to create it ourselves.  We do it
+                # in all possible pattern combinations, assuming that this
+                # function is called at most 5 times (dirCPC/dir1/dir2,
+                # dirCPC/dir1, dirCPC, dirCPC/dir1, dirCPC/dir1/dir2).
+                if pattern.pop():
+                    os.mkdir(path, mode)      # from another process
+                    concurrently_created.add(path)
+                os.mkdir(path, mode)          # our real call
+
+            pattern = [bool(pattern_num & (1 << n)) for n in range(5)]
+            concurrently_created = set()
+            p12 = p / 'dir1' / 'dir2'
+            try:
+                with mock.patch("pathlib._normal_accessor.mkdir", my_mkdir):
+                    p12.mkdir(parents=True, exist_ok=False)
+            except FileExistsError:
+                self.assertIn(str(p12), concurrently_created)
+            else:
+                self.assertNotIn(str(p12), concurrently_created)
+            self.assertTrue(p.exists())
+
     @with_symlinks
     def test_symlink_to(self):
         P = self.cls(BASE)
diff --git a/Misc/NEWS b/Misc/NEWS
index 6e2db58a92..e623457cdd 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -31,6 +31,10 @@ Core and Builtins
 
 Library
 -------
+
+- bpo-29694: Fixed race condition in pathlib mkdir with flags
+  parents=True.  Patch by Armin Rigo.
+
 - bpo-29692: Fixed arbitrary unchaining of RuntimeError exceptions in 
   contextlib.contextmanager.
   Patch by Siddharth Velankar.
-- 
2.40.0