Issue #25583: Merge makedirs fix from 3.4 into 3.5

2 files changed, 8 insertions, 3 deletions

diff --git a/Lib/os.py b/Lib/os.py
index 3d2c6d3..2b89b93 100644
--- a/Lib/os.py
+++ b/Lib/os.py
@@ -230,7 +230,7 @@ def makedirs(name, mode=0o777, exist_ok=False):
         try:
             makedirs(head, mode, exist_ok)
         except FileExistsError:
-            # be happy if someone already created the path
+            # Defeats race condition when another thread created the path
             pass
         cdir = curdir
         if isinstance(tail, bytes):
@@ -239,8 +239,10 @@ def makedirs(name, mode=0o777, exist_ok=False):
             return
     try:
         mkdir(name, mode)
-    except OSError as e:
-        if not exist_ok or e.errno != errno.EEXIST or not path.isdir(name):
+    except OSError:
+        # Cannot rely on checking for EEXIST, since the operating system
+        # could give priority to other errors like EACCES or EROFS
+        if not exist_ok or not path.isdir(name):
             raise
 
 def removedirs(name):
diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
index 1e67e7a..618c18a 100644
--- a/Lib/test/test_os.py
+++ b/Lib/test/test_os.py
@@ -1040,6 +1040,9 @@ class MakedirTests(unittest.TestCase):
         os.makedirs(path, mode=mode, exist_ok=True)
         os.umask(old_mask)
 
+        # Issue #25583: A drive root could raise PermissionError on Windows
+        os.makedirs(os.path.abspath('/'), exist_ok=True)
+
     def test_exist_ok_s_isgid_directory(self):
         path = os.path.join(support.TESTFN, 'dir1')
         S_ISGID = stat.S_ISGID