From: Mariatta <Mariatta@users.noreply.github.com>
Date: Fri, 14 Apr 2017 02:26:24 +0000 (-0700)
Subject: [3.5] bpo-29694: race condition in pathlib mkdir with flags parents=True (GH-1089... 
X-Git-Tag: v3.5.4rc1~212
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=d7abeb7024b9755c291c29bdc8c4494246e975ad;p=python

[3.5] bpo-29694: race condition in pathlib mkdir with flags parents=True (GH-1089). (GH-1127)

(cherry picked from commit 22a594a0047d7706537ff2ac676cdc0f1dcb329c)
---

diff --git a/Lib/pathlib.py b/Lib/pathlib.py
index 16b99cddbc..29914b97e7 100644
--- a/Lib/pathlib.py
+++ b/Lib/pathlib.py
@@ -1217,8 +1217,8 @@ 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 86d3077d5c..5e0708ae73 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
 TESTFN = support.TESTFN
@@ -1767,6 +1768,35 @@ 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 0caeefdfff..c6df1b8609 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -48,6 +48,10 @@ Extension Modules
 
 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.