[PATCH v6 5/8] nbd: skip queue freeze when setting size at device startup

Commit 242a49e5c878 ("nbd: freeze the queue for queue limits updates")
added the freeze to keep in-flight commands from seeing
torn queue_limits.  But at startup the capacity is still 0
(invalidate_disk cleared it) and the write cache is off (the previous
patch cleared it on disconnect, and nbd_set_size sets it back only after
the commit), so submit_bio_noacct() rejects any bio before it reaches
the driver and no I/O is in flight.  Drop the freeze by checking
capacity and write cache state in nbd_set_size.

Signed-off-by: Yang Erkun <[email protected]>
---
 drivers/block/nbd.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 8aeffc0eaaa1..66f1b3263b94 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -375,7 +375,11 @@ static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize, loff_t blksize)
 	nbd_apply_limits(&lim, nbd->config->flags);
 	lim.logical_block_size = blksize;
 	lim.physical_block_size = blksize;
-	error = queue_limits_commit_update_frozen(nbd->disk->queue, &lim);
+	/* No need freeze with 0 capacity and write cache disabled */
+	if (!get_capacity(nbd->disk) && !blk_queue_write_cache(nbd->disk->queue))
+		error = queue_limits_commit_update(nbd->disk->queue, &lim);
+	else
+		error = queue_limits_commit_update_frozen(nbd->disk->queue, &lim);
 	if (error)
 		return error;
 
-- 
2.52.0