nbd: handle unexpected replies better

If the server or network is misbehaving and we get an unexpected reply
we can sometimes miss the request not being started and wait on a
request and never get a response, or even double complete the same
request.  Fix this by replacing the send_complete completion with just a
per command lock.  Add a per command cookie as well so that we can know
if we're getting a double completion for a previous event.  Also check
to make sure we dont have REQUEUED set as that means we raced with the
timeout handler and need to just let the retry occur.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/nbd.c

@@ -116,11 +116,12 @@ struct nbd_device {
 
 struct nbd_cmd {
 	struct nbd_device *nbd;
+	struct mutex lock;
 	int index;
 	int cookie;
-	struct completion send_complete;
 	blk_status_t status;
 	unsigned long flags;
+	u32 cmd_cookie;
 };
 
 #if IS_ENABLED(CONFIG_DEBUG_FS)
@@ -157,6 +158,27 @@ static void nbd_requeue_cmd(struct nbd_cmd *cmd)
 		blk_mq_requeue_request(req, true);
 }
 
+#define NBD_COOKIE_BITS 32
+
+static u64 nbd_cmd_handle(struct nbd_cmd *cmd)
+{
+	struct request *req = blk_mq_rq_from_pdu(cmd);
+	u32 tag = blk_mq_unique_tag(req);
+	u64 cookie = cmd->cmd_cookie;
+
+	return (cookie << NBD_COOKIE_BITS) | tag;
+}
+
+static u32 nbd_handle_to_tag(u64 handle)
+{
+	return (u32)handle;
+}
+
+static u32 nbd_handle_to_cookie(u64 handle)
+{
+	return (u32)(handle >> NBD_COOKIE_BITS);
+}
+
 static const char *nbdcmd_to_ascii(int cmd)
 {
 	switch (cmd) {
@@ -330,6 +352,9 @@ static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req,
 	}
 	config = nbd->config;
 
+	if (!mutex_trylock(&cmd->lock))
+		return BLK_EH_RESET_TIMER;
+
 	if (config->num_connections > 1) {
 		dev_err_ratelimited(nbd_to_dev(nbd),
 				    "Connection timed out, retrying (%d/%d alive)\n",
@@ -354,6 +379,7 @@ static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req,
 					nbd_mark_nsock_dead(nbd, nsock, 1);
 				mutex_unlock(&nsock->tx_lock);
 			}
+			mutex_unlock(&cmd->lock);
 			nbd_requeue_cmd(cmd);
 			nbd_config_put(nbd);
 			return BLK_EH_DONE;
@@ -364,6 +390,7 @@ static enum blk_eh_timer_return nbd_xmit_timeout(struct request *req,
 	}
 	set_bit(NBD_TIMEDOUT, &config->runtime_flags);
 	cmd->status = BLK_STS_IOERR;
+	mutex_unlock(&cmd->lock);
 	sock_shutdown(nbd);
 	nbd_config_put(nbd);
 done:
@@ -441,9 +468,9 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
 	struct iov_iter from;
 	unsigned long size = blk_rq_bytes(req);
 	struct bio *bio;
+	u64 handle;
 	u32 type;
 	u32 nbd_cmd_flags = 0;
-	u32 tag = blk_mq_unique_tag(req);
 	int sent = nsock->sent, skip = 0;
 
 	iov_iter_kvec(&from, WRITE | ITER_KVEC, &iov, 1, sizeof(request));
@@ -485,6 +512,8 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
 			goto send_pages;
 		}
 		iov_iter_advance(&from, sent);
+	} else {
+		cmd->cmd_cookie++;
 	}
 	cmd->index = index;
 	cmd->cookie = nsock->cookie;
@@ -493,7 +522,8 @@ static int nbd_send_cmd(struct nbd_device *nbd, struct nbd_cmd *cmd, int index)
 		request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
 		request.len = htonl(size);
 	}
-	memcpy(request.handle, &tag, sizeof(tag));
+	handle = nbd_cmd_handle(cmd);
+	memcpy(request.handle, &handle, sizeof(handle));
 
 	dev_dbg(nbd_to_dev(nbd), "request %p: sending control (%s@%llu,%uB)\n",
 		req, nbdcmd_to_ascii(type),
@@ -586,10 +616,12 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
 	struct nbd_reply reply;
 	struct nbd_cmd *cmd;
 	struct request *req = NULL;
+	u64 handle;
 	u16 hwq;
 	u32 tag;
 	struct kvec iov = {.iov_base = &reply, .iov_len = sizeof(reply)};
 	struct iov_iter to;
+	int ret = 0;
 
 	reply.magic = 0;
 	iov_iter_kvec(&to, READ | ITER_KVEC, &iov, 1, sizeof(reply));
@@ -607,8 +639,8 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
 		return ERR_PTR(-EPROTO);
 	}
 
-	memcpy(&tag, reply.handle, sizeof(u32));
-
+	memcpy(&handle, reply.handle, sizeof(handle));
+	tag = nbd_handle_to_tag(handle);
 	hwq = blk_mq_unique_tag_to_hwq(tag);
 	if (hwq < nbd->tag_set.nr_hw_queues)
 		req = blk_mq_tag_to_rq(nbd->tag_set.tags[hwq],
@@ -619,11 +651,25 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
 		return ERR_PTR(-ENOENT);
 	}
 	cmd = blk_mq_rq_to_pdu(req);
+
+	mutex_lock(&cmd->lock);
+	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));
+		ret = -ENOENT;
+		goto out;
+	}
+	if (test_bit(NBD_CMD_REQUEUED, &cmd->flags)) {
+		dev_err(disk_to_dev(nbd->disk), "Raced with timeout on req %p\n",
+			req);
+		ret = -ENOENT;
+		goto out;
+	}
 	if (ntohl(reply.error)) {
 		dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)\n",
 			ntohl(reply.error));
 		cmd->status = BLK_STS_IOERR;
-		return cmd;
+		goto out;
 	}
 
 	dev_dbg(nbd_to_dev(nbd), "request %p: got reply\n", req);
@@ -648,18 +694,18 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
 				if (nbd_disconnected(config) ||
 				    config->num_connections <= 1) {
 					cmd->status = BLK_STS_IOERR;
-					return cmd;
+					goto out;
 				}
-				return ERR_PTR(-EIO);
+				ret = -EIO;
+				goto out;
 			}
 			dev_dbg(nbd_to_dev(nbd), "request %p: got %d bytes data\n",
 				req, bvec.bv_len);
 		}
-	} else {
-		/* See the comment in nbd_queue_rq. */
-		wait_for_completion(&cmd->send_complete);
 	}
-	return cmd;
+out:
+	mutex_unlock(&cmd->lock);
+	return ret ? ERR_PTR(ret) : cmd;
 }
 
 static void recv_work(struct work_struct *work)
@@ -855,7 +901,7 @@ static blk_status_t nbd_queue_rq(struct blk_mq_hw_ctx *hctx,
 	 * that the server is misbehaving (or there was an error) before we're
 	 * done sending everything over the wire.
 	 */
-	init_completion(&cmd->send_complete);
+	mutex_lock(&cmd->lock);
 	clear_bit(NBD_CMD_REQUEUED, &cmd->flags);
 
 	/* We can be called directly from the user space process, which means we
@@ -868,7 +914,7 @@ static blk_status_t nbd_queue_rq(struct blk_mq_hw_ctx *hctx,
 		ret = BLK_STS_IOERR;
 	else if (!ret)
 		ret = BLK_STS_OK;
-	complete(&cmd->send_complete);
+	mutex_unlock(&cmd->lock);
 
 	return ret;
 }
@@ -1475,6 +1521,7 @@ static int nbd_init_request(struct blk_mq_tag_set *set, struct request *rq,
 	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(rq);
 	cmd->nbd = set->driver_data;
 	cmd->flags = 0;
+	mutex_init(&cmd->lock);
 	return 0;
 }