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

[yangerkun <yangerkun@huawei.com>]

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;
>>    }
>>    
>