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

在 2026/7/22 14:35, yu kuai 写道:
> Hi,
> 
> 在 2026/7/22 11:17, yu kuai 写道:
>> 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.
> 
> Sorry this is a mistake, nbd_open() must succeed before pid is set, because of ioctl
> like NBD_SET_SOCK and NED_DO_IT :( I just forgot this simple case.

nbd can only accept request from bio, so bio_check_eod will reject them all?

> 
>>
>>> Signed-off-by: Yang Erkun <[email protected]>
>>> ---
>>>     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;
>>>     }
>