[NET]: Set a separate lockdep class for neighbour table's proxy_queue

Otherwise the following calltrace will lead to a wrong
lockdep warning:

  neigh_proxy_process()
    `- lock(neigh_table->proxy_queue.lock);
  arp_redo /* via tbl->proxy_redo */
  arp_process
  neigh_event_ns
  neigh_update
  skb_queue_purge
    `- lock(neighbor->arp_queue.lock);

This is not a deadlock actually, as neighbor table's proxy_queue
and the neighbor's arp_queue are different queues.

Lockdep thinks there is a deadlock as both queues are initialized
with skb_queue_head_init() and thus have a common class.

Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 11 insertions, 1 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 0e86b6007a0a..5992f65b4184 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -619,6 +619,13 @@ static inline void skb_queue_head_init(struct sk_buff_head *list)
         list->qlen = 0;
 }
 
+static inline void skb_queue_head_init_class(struct sk_buff_head *list,
+                struct lock_class_key *class)
+{
+        skb_queue_head_init(list);
+        lockdep_set_class(&list->lock, class);
+}
+
 /*
  *      Insert an sk_buff at the start of a list.
  *
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index cfc60019cf92..841e3f32cab1 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1331,6 +1331,8 @@ void neigh_parms_destroy(struct neigh_parms *parms)
         kfree(parms);
 }
 
+static struct lock_class_key neigh_table_proxy_queue_class;
+
 void neigh_table_init_no_netlink(struct neigh_table *tbl)
 {
         unsigned long now = jiffies;
@@ -1379,7 +1381,8 @@ void neigh_table_init_no_netlink(struct neigh_table *tbl)
         init_timer(&tbl->proxy_timer);
         tbl->proxy_timer.data     = (unsigned long)tbl;
         tbl->proxy_timer.function = neigh_proxy_process;
-        skb_queue_head_init(&tbl->proxy_queue);
+        skb_queue_head_init_class(&tbl->proxy_queue,
+                        &neigh_table_proxy_queue_class);
 
         tbl->last_flush = now;
         tbl->last_rand  = now + tbl->parms.reachable_time * 20;