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

[Yuyang Huang <sigefriedhyy@gmail.com>]

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;
 };
 
 #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);
 
 	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);
 
-- 
2.43.0