nbd: Fix hung on disconnect request if socket is closed before

When userspace closes the socket before sending a disconnect
request, the following I/O requests will be blocked in
wait_for_reconnect() until dead timeout. This will cause the
following disconnect request also hung on blk_mq_quiesce_queue().
That means we have no way to disconnect a nbd device if there
are some I/O requests waiting for reconnecting until dead timeout.
It's not expected. So let's wake up the thread waiting for
reconnecting directly when a disconnect request is sent.
Reported-by: Xu Jianhai <zero.xu@bytedance.com>
Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/20220322080639.142-1-xieyongji@bytedance.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/nbd.c

@@ -946,11 +946,15 @@ static int wait_for_reconnect(struct nbd_device *nbd)
 	struct nbd_config *config = nbd->config;
 	if (!config->dead_conn_timeout)
 		return 0;
-	if (test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags))
-		return 0;
-	return wait_event_timeout(config->conn_wait,
+
+	if (!wait_event_timeout(config->conn_wait,
+				test_bit(NBD_RT_DISCONNECTED,
+					 &config->runtime_flags) ||
 				atomic_read(&config->live_connections) > 0,
-				  config->dead_conn_timeout) > 0;
+				config->dead_conn_timeout))
+		return 0;
+
+	return !test_bit(NBD_RT_DISCONNECTED, &config->runtime_flags);
 }
 
 static int nbd_handle_cmd(struct nbd_cmd *cmd, int index)
@@ -2076,6 +2080,7 @@ static void nbd_disconnect_and_put(struct nbd_device *nbd)
 	mutex_lock(&nbd->config_lock);
 	nbd_disconnect(nbd);
 	sock_shutdown(nbd);
+	wake_up(&nbd->config->conn_wait);
 	/*
 	 * Make sure recv thread has finished, we can safely call nbd_clear_que()
 	 * to cancel the inflight I/Os.