Re: [PATCH v3 3/6] nbd: remove queue freeze in nbd_add_socket

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

Hi,

在 2026/7/13 14:56, Yang Erkun 写道:
> nbd_add_socket can never run concurrently with inflight I/O:
>
>   - netlink path: nbd_genl_connect calls nbd_add_socket before
>     nbd_start_device, so no I/O can happened when invoking nbd_add_socket,
>     nbd_genl_reconfigure cannot too since it won't call nbd_add_socket
>
>   - ioctl path: NBD_SET_SOCK cannot be called after NBD_DO_IT with
>     the previous commit, so capability of nbd will keep 0 while
>     invoking NBD_SET_SOCK
>
> Removing the freeze in nbd_add_socket to speed up nbd device startup.

Check nbd_open(), the pid is not checked there, which means the nbd device
can be opened after add_disk() succeed. Normally read/write IO will not pass
bio_check_eod() checking, however, there can be special zero sized bio that
might still be issued to nbd device. So I think there should be a pid checking
in nbd_open() for this patch, and I'm not aware of any special IO mush be handled
before nbd_start_device(). Otherwise, the freeze is still necessary since
nbd_handle_cmd() will deference config->socks[] directly.

>
> Signed-off-by: Yang Erkun <yangerkun@huawei.com>
> ---
>   drivers/block/nbd.c | 9 ---------
>   1 file changed, 9 deletions(-)
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index a15553ab4b97..0755b7046ed4 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -1272,7 +1272,6 @@ static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
>   	struct socket *sock;
>   	struct nbd_sock **socks;
>   	struct nbd_sock *nsock;
> -	unsigned int memflags;
>   	int err;
>   
>   	/* Arg will be cast to int, check it to avoid overflow */
> @@ -1283,12 +1282,6 @@ static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
>   		return err;
>   	nbd_reclassify_socket(sock);
>   
> -	/*
> -	 * We need to make sure we don't get any errant requests while we're
> -	 * reallocating the ->socks array.
> -	 */
> -	memflags = blk_mq_freeze_queue(nbd->disk->queue);
> -
>   	if (!netlink && !nbd->task_setup &&
>   	    !test_bit(NBD_RT_BOUND, &config->runtime_flags))
>   		nbd->task_setup = current;
> @@ -1335,12 +1328,10 @@ static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
>   	INIT_WORK(&nsock->work, nbd_pending_cmd_work);
>   	socks[config->num_connections++] = nsock;
>   	atomic_inc(&config->live_connections);
> -	blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
>   
>   	return 0;
>   
>   put_socket:
> -	blk_mq_unfreeze_queue(nbd->disk->queue, memflags);
>   	sockfd_put(sock);
>   	return err;
>   }

-- 
Thanks,
Kuai