Re: [PATCH net-next v7 2/5] net: add a generation counter for dev->mc changes

[Nicolas Dichtel <nicolas.dichtel@6wind.com>]

Le 24/09/2026 à 03:15, Yuyang Huang a écrit :
> A multi-part RTM_GETMULTICAST dump of dev->mc resumes by position, so
> entries added or removed between two dump rounds can be skipped or
> repeated. The IPv4 and IPv6 dumps report that with NLM_F_DUMP_INTR by
> stamping cb->seq from a per netns generation counter combined with
> dev_base_seq, see inet_base_seq().
> 
> Add the equivalent for the device multicast lists: a per netns counter
> bumped whenever an entry is added to or removed from any dev->mc. The
> list helpers do not know which device a list belongs to, so give
> netdev_hw_addr_list an owner set for dev->mc only and bump the counter
> of dev_net(owner) where entries are created and freed. That covers the
> dev_mc_* helpers, both lists of a sync, the hardware sync helpers
> drivers call from their rx mode callbacks or their own workers and the
> reconciliation after an asynchronous rx mode update, while snapshot
> and other lists have no owner and are not tracked. It is atomic since
> the writers only hold the address lock of their own device.
> 
> Used by the following patch for the AF_PACKET multicast dump.
> 
> Signed-off-by: Yuyang Huang <sigefriedhyy@gmail.com>
> ---
>  include/linux/netdevice.h   |  3 +++
>  include/net/net_namespace.h |  1 +
>  net/core/dev_addr_lists.c   | 21 +++++++++++++++++++++
>  3 files changed, 25 insertions(+)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 5d16737167ee..be3804cdbb2d 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -256,6 +256,9 @@ struct netdev_hw_addr_list {
>  
>  	/* Auxiliary tree for faster lookup on addition and deletion */
>  	struct rb_root		tree;
> +
> +	/* Set for dev->mc, the owning device of a tracked list */
> +	struct net_device	*owner;
There are several lists owned by a device (dev->dev_addrs, dev->uc, dev->mc,
dev->rx_mode_addr_cache), the name 'owner' does not reflect that it is set only
when the list is dev->mc.
I wonder if the name should be changed or if __hw_addr_init() should be updated
to always set owner when the list is owned by a device.

>  };
>  
>  #define netdev_hw_addr_list_count(l) ((l)->count)
> diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
> index 46b4c67e2966..d8c681ab5c74 100644
> --- a/include/net/net_namespace.h
> +++ b/include/net/net_namespace.h
> @@ -71,6 +71,7 @@ struct net {
>  	spinlock_t		rules_mod_lock;
>  
>  	unsigned int		dev_base_seq;	/* protected by rtnl_mutex */
> +	atomic_t		dev_mc_genid;	/* bumped on dev->mc changes */
>  	u32			ifindex;
>  
>  	spinlock_t		nsid_lock;
> diff --git a/net/core/dev_addr_lists.c b/net/core/dev_addr_lists.c
> index 08528ca0a8b3..18acd874fdbd 100644
> --- a/net/core/dev_addr_lists.c
> +++ b/net/core/dev_addr_lists.c
> @@ -16,6 +16,19 @@
>  
>  #include "dev.h"
>  
> +/**
> + * __hw_addr_changed - account a change of a tracked address list
> + * @list: the address list an entry was added to or removed from
> + *
> + * Bumps the netns generation counter RTM_GETMULTICAST dumps use to detect
> + * changes of dev->mc between dump rounds. Untracked lists have no owner.
> + */
> +static void __hw_addr_changed(struct netdev_hw_addr_list *list)
> +{
> +	if (list->owner)
> +		atomic_inc(&dev_net(list->owner)->dev_mc_genid);
> +}
> +
>  /*
>   * General list handling functions
>   */
> @@ -126,6 +139,7 @@ static int __hw_addr_add_ex(struct netdev_hw_addr_list *list,
>  
>  	list_add_tail_rcu(&ha->list, &list->list);
>  	list->count++;
> +	__hw_addr_changed(list);
list->count and dev_mc_genid evolves together. Perhaps some helpers would be
less error-prone for future patches?

__hw_addr_count_inc()
__hw_addr_count_dec()
__hw_addr_count_reset()

?

>  
>  	return 0;
>  }
> @@ -162,6 +176,7 @@ static int __hw_addr_del_entry(struct netdev_hw_addr_list *list,
>  	list_del_rcu(&ha->list);
>  	kfree_rcu(ha, rcu_head);
>  	list->count--;
> +	__hw_addr_changed(list);
>  	return 0;
>  }
>  
> @@ -487,6 +502,8 @@ void __hw_addr_flush(struct netdev_hw_addr_list *list)
>  {
>  	struct netdev_hw_addr *ha, *tmp;
>  
> +	if (list->count)
> +		__hw_addr_changed(list);
>  	list->tree = RB_ROOT;
>  	list_for_each_entry_safe(ha, tmp, &list->list, list) {
>  		list_del_rcu(&ha->list);
> @@ -501,6 +518,7 @@ void __hw_addr_init(struct netdev_hw_addr_list *list)
>  	INIT_LIST_HEAD(&list->list);
>  	list->count = 0;
>  	list->tree = RB_ROOT;
> +	list->owner = NULL;
>  }
>  EXPORT_SYMBOL(__hw_addr_init);
>  
> @@ -612,6 +630,7 @@ void __hw_addr_list_reconcile(struct netdev_hw_addr_list *real_list,
>  				__hw_addr_insert(real_list, ref_ha,
>  						 addr_len);
>  				real_list->count++;
> +				__hw_addr_changed(real_list);
>  			}
>  			continue;
>  		}
> @@ -623,6 +642,7 @@ void __hw_addr_list_reconcile(struct netdev_hw_addr_list *real_list,
>  			list_del_rcu(&real_ha->list);
>  			kfree_rcu(real_ha, rcu_head);
>  			real_list->count--;
> +			__hw_addr_changed(real_list);
>  		}
>  	}
>  
> @@ -1177,6 +1197,7 @@ EXPORT_SYMBOL(dev_mc_flush);
>  void dev_mc_init(struct net_device *dev)
>  {
>  	__hw_addr_init(&dev->mc);
> +	dev->mc.owner = dev;
>  }
>  EXPORT_SYMBOL(dev_mc_init);
>