Re: [PATCH net-next 3/4] netdev: avoid skipping objects on race with device disappearance

[Bobby Eshleman <bobbyeshleman@gmail.com>]

On Tue, Jun 09, 2026 at 12:08:03PM -0700, Jakub Kicinski wrote:
> If the currently dumped device disappears while we were mid-dump
> we will get the next device without resetting the sub-object ID.
> This is quite unlikely, it was reported by an AI tool not a real
> user. Let's fix it for better dump consistency.
> 
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> ---
>  net/core/netdev-genl.c | 22 +++++++++++++++++-----
>  1 file changed, 17 insertions(+), 5 deletions(-)
> 
> diff --git a/net/core/netdev-genl.c b/net/core/netdev-genl.c
> index d35af460e886..18046ad0f883 100644
> --- a/net/core/netdev-genl.c
> +++ b/net/core/netdev-genl.c
> @@ -310,11 +310,14 @@ int netdev_nl_napi_get_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
>  			err = -ENODEV;
>  		}
>  	} else {
> +		unsigned long start_ifindex = ctx->ifindex;
> +
>  		for_each_netdev_lock_scoped(net, netdev, ctx->ifindex) {
> +			if (ctx->ifindex != start_ifindex)
> +				ctx->napi_id = 0;
>  			err = netdev_nl_napi_dump_one(netdev, skb, info, ctx);
>  			if (err < 0)
>  				break;
> -			ctx->napi_id = 0;
>  		}
>  	}
>  
> @@ -634,13 +637,17 @@ int netdev_nl_queue_get_dumpit(struct sk_buff *skb, struct netlink_callback *cb)
>  			err = -ENODEV;
>  		}
>  	} else {
> +		unsigned long start_ifindex = ctx->ifindex;
> +
>  		for_each_netdev_lock_ops_compat_scoped(net, netdev,
>  						       ctx->ifindex) {
> +			if (ctx->ifindex != start_ifindex) {
> +				ctx->rxq_idx = 0;
> +				ctx->txq_idx = 0;
> +			}
>  			err = netdev_nl_queue_dump_one(netdev, skb, info, ctx);
>  			if (err < 0)
>  				break;
> -			ctx->rxq_idx = 0;
> -			ctx->txq_idx = 0;
>  		}
>  	}
>  
> @@ -786,8 +793,6 @@ netdev_nl_stats_by_queue(struct net_device *netdev, struct sk_buff *rsp,
>  		ctx->txq_idx = ++i;
>  	}
>  
> -	ctx->rxq_idx = 0;
> -	ctx->txq_idx = 0;
>  	return 0;
>  }
>  
> @@ -902,6 +907,7 @@ int netdev_nl_qstats_get_dumpit(struct sk_buff *skb,
>  	struct netdev_nl_dump_ctx *ctx = netdev_dump_ctx(cb);
>  	const struct genl_info *info = genl_info_dump(cb);
>  	struct net *net = sock_net(skb->sk);
> +	unsigned long start_ifindex;
>  	struct net_device *netdev;
>  	unsigned int ifindex;
>  	unsigned int scope;
> @@ -934,7 +940,13 @@ int netdev_nl_qstats_get_dumpit(struct sk_buff *skb,
>  		return err;
>  	}
>  
> +	start_ifindex = ctx->ifindex;
> +
>  	for_each_netdev_lock_ops_compat_scoped(net, netdev, ctx->ifindex) {
> +		if (ctx->ifindex != start_ifindex) {
> +			ctx->rxq_idx = 0;
> +			ctx->txq_idx = 0;
> +		}
>  		err = netdev_nl_qstats_get_dump_one(netdev, scope, skb,
>  						    info, ctx);
>  		if (err < 0)
> -- 
> 2.54.0
> 
> 

Reviewed-by: Bobby Eshleman <bobbyeshleman@meta.com>