Description of problem:

A 'docker pull' command will hang intermittently (meaning occasionally when docker pulls are run, not that one docker pull is occasionally hanging) with the following for example:

[root@sd-e6ec-7fc8 ~]# docker pull tomcat:7.0
Trying to pull repository docker.io/library/tomcat ... 7.0: Pulling from library/tomcat
6d1ae97ee388: Verifying Checksum
8b9a99209d5c: Pulling fs layer
2e05a52ffd47: Pulling fs layer
9fdaeae348bb: Pulling fs layer
67d05086af43: Pulling fs layer
2e9d1ec89d66: Pulling fs layer
1afb0d51eee0: Pulling fs layer
5cb24a57fa37: Pulling fs layer
110c2f290b04: Pulling fs layer
966dcd51a14f: Pulling fs layer
8a57ce404f1b: Pulling fs layer
e1b97b980d07: Pulling fs layer
0e74df9853d7: Pulling fs layer
20d94860039d: Verifying Checksum
ad4e266e1bd1: Pulling fs layer
13091c61ed8d: Pulling fs layer
6c6bae9ca483: Pulling fs layer
068fc2e47624: Pulling fs layer
373f6ee029ce: Layer already being pulled by another client. Waiting.


Version-Release number of selected component (if applicable):
 docker-1.8.2-10.el7.x86_64

How reproducible:
Reliably for customer

Steps to Reproduce:
1. Try pulling from either docker.io or registry.access.redhat.com
2.
3.

Actual results:
Intermittently, the pull will hang with the above output

Expected results:
Image should be pulled, or an error should be given.

Additional info:


Restarting the docker daemon sometimes has an effect. The customer reports that after restarting the daemon, they can either pull the image normally or the pull will hang again with the same "already being pulled" message - no indication yet of any reason why this sometimes works and sometimes doesn't.