[PATCH v2 1/1] igmp: call ip_mc_clear_src() only when we have no users of ip_mc_list

[Veaceslav Falico <vfalico@redhat.com>]

In igmp_group_dropped() we call ip_mc_clear_src(), which resets the number
of source filters per mulitcast. However, igmp_group_dropped() is also
called on NETDEV_DOWN, NETDEV_PRE_TYPE_CHANGE and NETDEV_UNREGISTER, which
means that the group might get added back on NETDEV_UP, NETDEV_REGISTER and
NETDEV_POST_TYPE_CHANGE respectively, leaving us with broken source
filters.

To fix that, we must clear the source filters only when there are no users
in the ip_mc_list, i.e. in ip_mc_dec_group().

Signed-off-by: Veaceslav Falico <vfalico@redhat.com>

---
diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 1fd3d9c..732e30b 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -1182,7 +1182,6 @@ static void igmp_group_dropped(struct ip_mc_list *im)
 	}
 done:
 #endif
-	ip_mc_clear_src(im);
 }
 
 static void igmp_group_added(struct ip_mc_list *im)
@@ -1319,6 +1318,7 @@ void ip_mc_dec_group(struct in_device *in_dev, __be32 addr)
 				*ip = i->next_rcu;
 				in_dev->mc_count--;
 				igmp_group_dropped(i);
+				ip_mc_clear_src(i);
 
 				if (!in_dev->dead)
 					ip_rt_multicast_event(in_dev);