Comment 4 for bug 1251425

Reviewed: https://review.openstack.org/57943
Committed: http://github.com/openstack/cinder/commit/009b0544a2be24779192b11d159032f27d83e272
Submitter: Jenkins
Branch: stable/havana

commit 009b0544a2be24779192b11d159032f27d83e272
Author: Eric Harney <email address hidden>
Date: Thu Nov 14 15:51:15 2013 -0500

    GlusterFS: Synchronize operations that manipulate qcow2 data

    Operations that modify qcow2 chains or the GlusterFS driver's
    snapshot info file should use locking so that more than one thread
    cannot run these operations at the same time.

    Without this it is possible for multiple threads to concurrently
    modify snapshot information resulting in an incomplete snapshot
    chain.

    Closes-Bug: #1251425

    (cherry picked from commit 8a1fd8889170c289910944db016a4206fe5e1e32)
    Change-Id: I93c6ffecd9aec38560cb19085243390b9120b363