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

["yu kuai" <yukuai@fygo.io>]

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().

>
> 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().

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

>   	return 0;
>   }
>   

-- 
Thanks,
Kuai