NewDreamNetwork/ceph-client — comment on commit 971d9728082a09868963bbc043bce36947c1d10a
File:  line 0
By alexelder:

Are you talking about the ceph_mdsc_put_request() call? Why would you
need to hold a lock for that? It is just the request that would be released,
and it has already been disassociated from the ceph inode's unsafe list.

And I believe it's the inode mutex that would protect concurrent calls,
blocking the second while the first does its processing.