[PATCH v3 3/5] nbd: don't handle response without a corresponding request message

[Yu Kuai]

While handling a response message from server, nbd_read_stat() will
try to get request by tag, and then complete the request. However,
this is problematic if nbd haven't sent a corresponding request
message:

t1                      t2
                        submit_bio
                         nbd_queue_rq
                          blk_mq_start_request
recv_work
 nbd_read_stat
  blk_mq_get_rq_by_tag
 blk_mq_complete_request
                          nbd_send_cmd

Thus add a new cmd flag 'NBD_CMD_INFLIGHT', it will be set in
nbd_send_cmd() and checked in nbd_read_stat().

Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 drivers/block/nbd.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index ca54a0736090..7b9e19675224 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -127,6 +127,11 @@ struct nbd_device {
 };
 
 #define NBD_CMD_REQUEUED	1
+/*
+ * This flag will be set if nbd_send_cmd() succeed, and will be checked in
+ * normal completion.
+ */
+#define NBD_CMD_INFLIGHT	2
 
 struct nbd_cmd {
 	struct nbd_device *nbd;
@@ -743,6 +748,12 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
 	cmd = blk_mq_rq_to_pdu(req);
 
 	mutex_lock(&cmd->lock);
+	if (!test_bit(NBD_CMD_INFLIGHT, &cmd->flags)) {
+		dev_err(disk_to_dev(nbd->disk), "NBD_CMD_INFLIGHT is not set %d\n",
+			tag);
+		ret = -ENOENT;
+		goto out;
+	}
 	if (cmd->cmd_cookie != nbd_handle_to_cookie(handle)) {
 		dev_err(disk_to_dev(nbd->disk), "Double reply on req %p, cmd_cookie %u, handle cookie %u\n",
 			req, cmd->cmd_cookie, nbd_handle_to_cookie(handle));
@@ -980,6 +991,8 @@ static int nbd_handle_cmd(struct nbd_cmd *cmd, int index)
 	 * returns EAGAIN can be retried on a different socket.
 	 */
 	ret = nbd_send_cmd(nbd, cmd, index);
+	if (!ret)
+		set_bit(NBD_CMD_INFLIGHT, &cmd->flags);
 	if (ret == -EAGAIN) {
 		dev_err_ratelimited(disk_to_dev(nbd->disk),
 				    "Request send failed, requeueing\n");
-- 
2.31.1