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 12:59:16PM -0700, Bobby Eshleman wrote:
> 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>

I just noticed we handle this differently in rtnetlink with
cb->seq/dev_base_seq/nl_dump_check_consistent(), but it seems like
netdev-genl.c intentionally does not use NLM_F_DUMP_INTR?

Best,
Bobby