ceph: fix possible long time wait during umount

During umount, if there has no any unsafe request in the mdsc and
some requests still in-flight and not got reply yet, and if the
rest requets are all safe ones, after that even all of them in mdsc
are unregistered, the umount must wait until after mount_timeout
seconds anyway.
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/mds_client.c

@@ -2884,6 +2884,10 @@ static void handle_reply(struct ceph_mds_session *session, struct ceph_msg *msg)
 		set_bit(CEPH_MDS_R_GOT_SAFE, &req->r_req_flags);
 		__unregister_request(mdsc, req);
 
+		/* last request during umount? */
+		if (mdsc->stopping && !__get_oldest_req(mdsc))
+			complete_all(&mdsc->safe_umount_waiters);
+
 		if (test_bit(CEPH_MDS_R_GOT_UNSAFE, &req->r_req_flags)) {
 			/*
 			 * We already handled the unsafe response, now do the
@@ -2894,9 +2898,6 @@ static void handle_reply(struct ceph_mds_session *session, struct ceph_msg *msg)
 			 */
 			dout("got safe reply %llu, mds%d\n", tid, mds);
 
-			/* last unsafe request during umount? */
-			if (mdsc->stopping && !__get_oldest_req(mdsc))
-				complete_all(&mdsc->safe_umount_waiters);
 			mutex_unlock(&mdsc->mutex);
 			goto out;
 		}