Re: [PATCH net-next 2/2] net: reorder dev_addr_sem lock

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From: Stanislav Fomichev <sdf@fomichev.me>
Date: Tue, 11 Mar 2025 01:45:07 -0700
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index 9355058bf996..c9d44dad203d 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -3080,21 +3080,32 @@ static int do_setlink(const struct sk_buff *skb, struct net_device *dev,
>  		struct sockaddr *sa;
>  		int len;
>  
> +		netdev_unlock_ops(dev);
> +
> +		/* dev_addr_sem is an outer lock, enforce proper ordering */
> +		down_write(&dev_addr_sem);
> +		netdev_lock_ops(dev);
> +
>  		len = sizeof(sa_family_t) + max_t(size_t, dev->addr_len,
>  						  sizeof(*sa));
>  		sa = kmalloc(len, GFP_KERNEL);
>  		if (!sa) {
> +			up_write(&dev_addr_sem);
>  			err = -ENOMEM;
>  			goto errout;
>  		}
>  		sa->sa_family = dev->type;
>  		memcpy(sa->sa_data, nla_data(tb[IFLA_ADDRESS]),
>  		       dev->addr_len);

Can we move down_write() and netdev_lock_ops() here ?


> -		err = netif_set_mac_address_user(dev, sa, extack);
> +		err = netif_set_mac_address(dev, sa, extack);
>  		kfree(sa);
> -		if (err)
> +		if (err) {
> +			up_write(&dev_addr_sem);
>  			goto errout;
> +		}
>  		status |= DO_SETLINK_MODIFIED;
> +
> +		up_write(&dev_addr_sem);
>  	}
>  
>  	if (tb[IFLA_MTU]) {
> -- 
> 2.48.1