Potential double mutex_lock bug in net/ceph/auth.c

Hi,

I'm testing a static bug finder (EBA) on Linux 4.7 release candidates
and I may have found a potential double lock:

  Double lock in net/ceph/auth.c
  second lock at 108: mutex_lock(& ac->mutex); [ceph_auth_build_hello]
  after calling from 263: ret = ceph_auth_build_hello(ac, msg_buf, msg_len);
  if ! ac->protocol -> true at 262
  first lock at 261: mutex_lock(& ac->mutex); [ceph_build_auth]

This seems to have been introduced by commit e9966076cdd9 ("libceph:
wrap auth methods in a mutex").

I hope it helps!

Thanks,

-- iago