Ceph » Linux kernel client

While reviewing a change to the xattr code, Sage noticed that some
calls to __build_xattrs() were being made after having completed
a capability check. Since __build_xattrs() drops i_ceph_lock,
the earlier capability checks may no longer be valid. (At least
I think that's the problem--Sage, please correct me if I'm wrong.)

So these checks need to be moved so they're done in a safe way.

In his review, Sage said he thought the proposed change could go
in and this fix be done separately, so I'm documenting this here.