libceph: drop mutex on error in handle_reply()

The osd client mutex is acquired just before getting a reference to
a request in handle_reply().  However the error paths after that
don't drop the mutex before returning as they should.

Drop the mutex after dropping the request reference.  Also add a
bad_mutex label at that point and use it so the failed request
lookup case can be handled with the rest.

This resolves:
    http://tracker.ceph.com/issues/4615

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>

net/ceph/osd_client.c

@@ -1337,8 +1337,7 @@ static void handle_reply(struct ceph_osd_client *osdc, struct ceph_msg *msg,
 	req = __lookup_request(osdc, tid);
 	if (req == NULL) {
 		dout("handle_reply tid %llu dne\n", tid);
-		mutex_unlock(&osdc->request_mutex);
-		return;
+		goto bad_mutex;
 	}
 	ceph_osdc_get_request(req);
 
@@ -1437,6 +1436,8 @@ done:
 
 bad_put:
 	ceph_osdc_put_request(req);
+bad_mutex:
+	mutex_unlock(&osdc->request_mutex);
 bad:
 	pr_err("corrupt osd_op_reply got %d %d\n",
 	       (int)msg->front.iov_len, le32_to_cpu(msg->hdr.front_len));