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Re: [PATCH v3 5/6] nbd: skip queue freeze when setting size at device startup



在 2026/7/22 11:49, yu kuai 写道:

Hi,

在 2026/7/13 14:56, Yang Erkun 写道:

Commit 242a49e5c878 ("nbd: freeze the queue for queue limits updates")
introduce queue freeze/unfreeze in nbd_set_size to avoid inflight
commands see this inconsistent limits. However, this cannot be happened
when device setup since the capacity is still 0.


Same reason above, 0 capacity disk will only reject non-zero sized bio from
bio_check_eod().
Mabye we have reached an agreement on this issue? Flush bio will be reject since not enable write cache. 





time nbd-client --name myexport --connections 96 127.0.0.1 1234

Before this patchset:
real    0m2.195s
user    0m0.005s
sys     0m0.022s

After this patchset:
real    0m0.090s
user    0m0.004s
sys     0m0.018s

Signed-off-by: Yang Erkun <yangerkun@huawei.com>
---
   drivers/block/nbd.c | 21 ++++++++++++++-------
   1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 400f638e832e..2c7b09c70da2 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -331,7 +331,8 @@ 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, loff_t blksize) 
+static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize, loff_t blksize,
+			bool freeze)
   {
   	struct queue_limits lim;
   	int error;
@@ -371,7 +372,13 @@ static int nbd_set_size(struct nbd_device *nbd, loff_t bytesize, loff_t blksize)
lim.logical_block_size = blksize; 
   	lim.physical_block_size = blksize;
-	error = queue_limits_commit_update_frozen(nbd->disk->queue, &lim);
+
+	if (freeze)
+		error = queue_limits_commit_update_frozen(nbd->disk->queue,
+				&lim);
+	else
+		error = queue_limits_commit_update(nbd->disk->queue, &lim);
+
   	if (error)
   		return error;
@@ -1563,7 +1570,7 @@ static int nbd_start_device(struct nbd_device *nbd) 
   		args->index = i;
   		queue_work(nbd->recv_workq, &args->work);
   	}
-	return nbd_set_size(nbd, config->bytesize, nbd_blksize(config));
+	return nbd_set_size(nbd, config->bytesize, nbd_blksize(config), false);
   }
static int nbd_start_device_ioctl(struct nbd_device *nbd) 
@@ -1631,13 +1638,13 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
   	case NBD_SET_SOCK:
   		return nbd_add_socket(nbd, arg, false);
   	case NBD_SET_BLKSIZE:
-		return nbd_set_size(nbd, config->bytesize, arg);
+		return nbd_set_size(nbd, config->bytesize, arg, true);
   	case NBD_SET_SIZE:
-		return nbd_set_size(nbd, arg, nbd_blksize(config));
+		return nbd_set_size(nbd, arg, nbd_blksize(config), true);
   	case NBD_SET_SIZE_BLOCKS:
   		if (check_shl_overflow(arg, config->blksize_bits, &bytesize))
   			return -EINVAL;
-		return nbd_set_size(nbd, bytesize, nbd_blksize(config));
+		return nbd_set_size(nbd, bytesize, nbd_blksize(config), true);
   	case NBD_SET_TIMEOUT:
   		nbd_set_cmd_timeout(nbd, arg);
   		return 0;
@@ -2122,7 +2129,7 @@ static int nbd_genl_size_set(struct genl_info *info, struct nbd_device *nbd)
   		bsize = nla_get_u64(info->attrs[NBD_ATTR_BLOCK_SIZE_BYTES]);
if (bytes != config->bytesize || bsize != nbd_blksize(config)) 
-		return nbd_set_size(nbd, bytes, bsize);
+		return nbd_set_size(nbd, bytes, bsize, true);


This is still called from nbd_genl_connect().
nbd->pid check exist in nbd_set_size, and nbd_genl_connect call nbd_genl_size_set before nbd_start_device, which has not set nbd->pid, so path from nbd_genl_connect won't work. But for path from nbd_genl_reconnect, we need this protect... 



Will it be much simpler to just check pid in nbd_set_size()?


   	return 0;
   }
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