ceph: just call get_session in __ceph_lookup_mds_session

I originally thought there was a potential race here, but the fact
that this is called with the mdsc->mutex held, ensures that the
last reference to the session can't be put here.

Still, it's clearer to just return the value from get_session here,
and may prevent a bug later if we ever rework this code to be less
reliant on mutexes.
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/mds_client.c

@@ -550,15 +550,9 @@ void ceph_put_mds_session(struct ceph_mds_session *s)
 struct ceph_mds_session *__ceph_lookup_mds_session(struct ceph_mds_client *mdsc,
 						   int mds)
 {
-	struct ceph_mds_session *session;
-
 	if (mds >= mdsc->max_sessions || !mdsc->sessions[mds])
 		return NULL;
-	session = mdsc->sessions[mds];
-	dout("lookup_mds_session %p %d\n", session,
-	     refcount_read(&session->s_ref));
-	get_session(session);
-	return session;
+	return get_session(mdsc->sessions[mds]);
 }
 
 static bool __have_session(struct ceph_mds_client *mdsc, int mds)