[PATCH v3 2/6] nbd: disallow NBD_SET_SOCK on an active device

[Yang Erkun <yangerkun@huawei.com>]

We cannot add a socket to an already running nbd device, the reconfigure
for netlink can only active dead socket. But for ioctl path, we can call
NBD_SET_SOCK after NBD_DO_IT, reject this using nbd->pid which has been
setted when NBD_DO_IT. Besides, it is the root cause for commit
b98e762e3d71 ("nbd: freeze the queue while we're adding connections").

Signed-off-by: Yang Erkun <yangerkun@huawei.com>
---
 drivers/block/nbd.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index b1a5acd57426..a15553ab4b97 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1302,6 +1302,13 @@ static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
 		goto put_socket;
 	}
 
+	if (nbd->pid) {
+		dev_err(disk_to_dev(nbd->disk),
+			"Cannot add socket to a running device\n");
+		err = -EBUSY;
+		goto put_socket;
+	}
+
 	nsock = kzalloc_obj(*nsock);
 	if (!nsock) {
 		err = -ENOMEM;
-- 
2.52.0