nbd: freeze the queue for queue limits updates

nbd currently updates the logical and physical block sizes as well
as the discard_sectors on a live queue.  Freeze the queue first to
make sure there are not commands in flight that can see torn or
inconsistent limits.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20240229143846.1047223-3-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/nbd.c

@@ -316,7 +316,7 @@ static void nbd_mark_nsock_dead(struct nbd_device *nbd, struct nbd_sock *nsock,
 	nsock->sent = 0;
 }
 
-static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize,
+static int __nbd_set_size(struct nbd_device *nbd, loff_t bytesize,
 		loff_t blksize)
 {
 	if (!blksize)
@@ -348,6 +348,18 @@ static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize,
 	return 0;
 }
 
+static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize,
+		loff_t blksize)
+{
+	int error;
+
+	blk_mq_freeze_queue(nbd->disk->queue);
+	error = __nbd_set_size(nbd, bytesize, blksize);
+	blk_mq_unfreeze_queue(nbd->disk->queue);
+
+	return error;
+}
+
 static void nbd_complete_rq(struct request *req)
 {
 	struct nbd_cmd *cmd = blk_mq_rq_to_pdu(req);