nbd: requeue command if the soecket is changed

In commit 2da22da5 (nbd: fix zero cmd timeout handling v2),
it is allowed to reset timer when it fires if tag_set.timeout
is set to zero. If the server is shutdown and a new socket
is reconfigured, the request should be requeued to be processed by
new server instead of waiting for response from the old one.
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Hou Pu <houpu@bytedance.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/nbd.c

@@ -434,12 +434,22 @@ static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req,
 		 * Userspace sets timeout=0 to disable socket disconnection,
 		 * so just warn and reset the timer.
 		 */
+		struct nbd_sock *nsock = config->socks[cmd->index];
 		cmd->retries++;
 		dev_info(nbd_to_dev(nbd), "Possible stuck request %p: control (%s@%llu,%uB). Runtime %u seconds\n",
 			req, nbdcmd_to_ascii(req_to_nbd_cmd_type(req)),
 			(unsigned long long)blk_rq_pos(req) << 9,
 			blk_rq_bytes(req), (req->timeout / HZ) * cmd->retries);
 
+		mutex_lock(&nsock->tx_lock);
+		if (cmd->cookie != nsock->cookie) {
+			nbd_requeue_cmd(cmd);
+			mutex_unlock(&nsock->tx_lock);
+			mutex_unlock(&cmd->lock);
+			nbd_config_put(nbd);
+			return BLK_EH_DONE;
+		}
+		mutex_unlock(&nsock->tx_lock);
 		mutex_unlock(&cmd->lock);
 		nbd_config_put(nbd);
 		return BLK_EH_RESET_TIMER;