Merge "Fixes race condition with privsep utime"

nova/privsep/path.py

@@ -70,12 +70,10 @@ def chmod(path, mode):
 def utime(path):
     if not os.path.exists(path):
         raise exception.FileNotFound(file_path=path)
-
-    # NOTE(mikal): the old version of this used execute(touch, ...), which
-    # would apparently fail on shared storage when multiple instances were
-    # being launched at the same time. If we see failures here, we might need
-    # to wrap this in a try / except.
-    os.utime(path, None)
+    # context wrapper ensures the file exists before trying to modify time
+    # which fixes a race condition with NFS image caching (see LP#1809123)
+    with open(path, 'a'):
+        os.utime(path, None)
 
 
 @nova.privsep.sys_admin_pctxt.entrypoint

releasenotes/notes/fix-image-utime-race-condition-3c404e272ea91b34.yaml

@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    Fixes a race condition when multiple instances are launched at the same
+    time, which leads to a failure when modifying the modified time of the
+    instance base image. This issue was noticed when using an NFS backend. For
+    more information see https://bugs.launchpad.net/nova/+bug/1809123
+