exception when attempting obejct relink during part power increase

[Alistair Coles]

Exception seen during relinking phase of a partition power increase:

err Relinking <path> to <path> failed: [Errno 17] File exists:
 Traceback (most recent call last):
   File "/opt/ss/lib/python2.7/site-packages/swift/obj/diskfile.py", line 1845, in _finalize_put
     relink_paths(target_path, new_target_path)
   File "/opt/ss/lib/python2.7/site-packages/swift/obj/diskfile.py", line 474, in relink_paths
     os.link(target_path, new_target_path)
 OSError: [Errno 17] File exists

This could be due to the relinker relinking an object concurrent with the object being PUT, so that both the relinker and object server are concurrently attempting to create a link from the next part power dir to the old part power dir. The look-before-you-leap check in diskfile.relink_paths is insufficient to prevent the exception when the relink and PUT are concurrent.

[Alistair Coles (alistair-coles)]

https://review.opendev.org/c/openstack/swift/+/778530

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/swift 2.27.0 release.