Re: [PATCH net-next v8 2/5] net: add a generation counter for dev->mc changes

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

Le 27/09/2026 à 02:24, 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 the lists of a device and NULL
> for snapshots and other standalone lists, and change list->count
> through helpers that bump the counter of dev_net(owner) when the list
> is dev->mc. 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. 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>


If another version is needed, you can rename counter to _counter to highlight
that the helpers should be used.
> ---
>  include/linux/netdevice.h   |  5 ++++
>  include/net/net_namespace.h |  1 +
>  net/core/dev_addr_lists.c   | 52 +++++++++++++++++++++++++++++++------
>  3 files changed, 50 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index d037faff7c44..69d1cde0a38a 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -256,6 +256,11 @@ struct netdev_hw_addr_list {
>  
>  	/* Auxiliary tree for faster lookup on addition and deletion */
>  	struct rb_root		tree;
> +
> +	/* The device a list belongs to, NULL for snapshots and other
> +	 * standalone lists
> +	 */
> +	struct net_device	*owner;
>  };
>  
>  #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..c941c3ec1007 100644
> --- a/net/core/dev_addr_lists.c
> +++ b/net/core/dev_addr_lists.c
> @@ -16,6 +16,37 @@
>  
>  #include "dev.h"
>  
> +/* Only dev->mc is tracked, RTM_GETMULTICAST dumps use the netns generation
> + * counter to detect changes between dump rounds.
> + */
> +static void __hw_addr_changed(struct netdev_hw_addr_list *list)
> +{
> +	struct net_device *dev = list->owner;
> +
> +	if (dev && list == &dev->mc)
> +		atomic_inc(&dev_net(dev)->dev_mc_genid);
> +}
> +
> +static void __hw_addr_count_inc(struct netdev_hw_addr_list *list)
static void __hw_addr_count_add(struct netdev_hw_addr_list *list, int value)
> +{
> +	list->count++;
list->count += value;> +	__hw_addr_changed(list);
> +}
#define __hw_addr_count_inc(l) __hw_addr_count_add(l, 1)

> +
> +static void __hw_addr_count_dec(struct netdev_hw_addr_list *list)
> +{
> +	list->count--;
> +	__hw_addr_changed(list);
> +}
> +
> +static void __hw_addr_count_reset(struct netdev_hw_addr_list *list)
> +{
> +	if (!list->count)
> +		return;
> +	list->count = 0;
> +	__hw_addr_changed(list);
> +}
> +
>  /*
>   * General list handling functions
>   */
> @@ -125,7 +156,7 @@ static int __hw_addr_add_ex(struct netdev_hw_addr_list *list,
>  	rb_insert_color(&ha->node, &list->tree);
>  
>  	list_add_tail_rcu(&ha->list, &list->list);
> -	list->count++;
> +	__hw_addr_count_inc(list);
>  
>  	return 0;
>  }
> @@ -161,7 +192,7 @@ 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_count_dec(list);
>  	return 0;
>  }
>  
> @@ -492,7 +523,7 @@ void __hw_addr_flush(struct netdev_hw_addr_list *list)
>  		list_del_rcu(&ha->list);
>  		kfree_rcu(ha, rcu_head);
>  	}
> -	list->count = 0;
> +	__hw_addr_count_reset(list);
>  }
>  EXPORT_SYMBOL_IF_KUNIT(__hw_addr_flush);
>  
> @@ -501,6 +532,7 @@ 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);

For correctness, __hw_addr_splice() should use helper:

@@ -509,8 +509,8 @@ static void __hw_addr_splice(struct netdev_hw_addr_list *dst,
 {
         src->tree = RB_ROOT;
         list_splice_init(&src->list, &dst->list);
-        dst->count += src->count;
-        src->count = 0;
+        __hw_addr_count_add(dst, src->count);
+        __hw_addr_count_reset(src);
 }

Renaming  struct netdev_hw_addr_list->count to _count would help to check all
users and highlight that modifying _count should be done with helpers.

>  
> @@ -536,7 +568,7 @@ int __hw_addr_list_snapshot(struct netdev_hw_addr_list *snap,
>  			entry = list_first_entry(&cache->list,
>  						 struct netdev_hw_addr, list);
>  			list_del(&entry->list);
> -			cache->count--;
> +			__hw_addr_count_dec(cache);
>  			memcpy(entry->addr, ha->addr, addr_len);
>  			entry->type = ha->type;
>  			entry->global_use = false;
> @@ -554,7 +586,7 @@ int __hw_addr_list_snapshot(struct netdev_hw_addr_list *snap,
>  
>  		list_add_tail(&entry->list, &snap->list);
>  		__hw_addr_insert(snap, entry, addr_len);
> -		snap->count++;
> +		__hw_addr_count_inc(snap);
>  	}
>  
>  	return 0;
> @@ -604,14 +636,14 @@ void __hw_addr_list_reconcile(struct netdev_hw_addr_list *real_list,
>  			if (delta > 0) {
>  				rb_erase(&ref_ha->node, &ref->tree);
>  				list_del(&ref_ha->list);
> -				ref->count--;
> +				__hw_addr_count_dec(ref);
>  				ref_ha->sync_cnt = delta;
>  				ref_ha->refcount = delta;
>  				list_add_tail_rcu(&ref_ha->list,
>  						  &real_list->list);
>  				__hw_addr_insert(real_list, ref_ha,
>  						 addr_len);
> -				real_list->count++;
> +				__hw_addr_count_inc(real_list);
>  			}
>  			continue;
>  		}
> @@ -622,7 +654,7 @@ void __hw_addr_list_reconcile(struct netdev_hw_addr_list *real_list,
>  			rb_erase(&real_ha->node, &real_list->tree);
>  			list_del_rcu(&real_ha->list);
>  			kfree_rcu(real_ha, rcu_head);
> -			real_list->count--;
> +			__hw_addr_count_dec(real_list);
>  		}
>  	}
>  
> @@ -685,6 +717,7 @@ int dev_addr_init(struct net_device *dev)
>  	/* rtnl_mutex must be held here */
>  
>  	__hw_addr_init(&dev->dev_addrs);
> +	dev->dev_addrs.owner = dev;
>  	memset(addr, 0, sizeof(addr));
>  	err = __hw_addr_add(&dev->dev_addrs, addr, sizeof(addr),
>  			    NETDEV_HW_ADDR_T_LAN);
> @@ -962,6 +995,7 @@ EXPORT_SYMBOL(dev_uc_flush);
>  void dev_uc_init(struct net_device *dev)
>  {
>  	__hw_addr_init(&dev->uc);
> +	dev->uc.owner = dev;
>  }
>  EXPORT_SYMBOL(dev_uc_init);
>  
> @@ -1177,6 +1211,7 @@ 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);
>  
> @@ -1348,6 +1383,7 @@ static void netif_rx_mode_retry(struct timer_list *t)
>  void netif_rx_mode_init(struct net_device *dev)
>  {
>  	__hw_addr_init(&dev->rx_mode_addr_cache);
> +	dev->rx_mode_addr_cache.owner = dev;
>  	timer_setup(&dev->rx_mode_retry_timer, netif_rx_mode_retry, 0);
>  }
>