[PATCH 3.16 010/305] ipv6: Fix another sparse warning on rt6i_node

[Ben Hutchings]

3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ben Hutchings <b...@decadent.org.uk>

Commit 0933273ce750 "ipv6: fix sparse warning on rt6i_node" fixed some
sparse warnings in ip6_fib.c, but introduced a new one in
fib6_update_sernum() (which was removed before the corresponding
upstream commit).

fib6_update_sernum() is called in a RCU read-side section, so use
rcu_dereference() to read rt6_info::rt6i_node.

Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -1681,10 +1681,10 @@ static void fib6_prune_clones(struct net
 static int fib6_update_sernum(struct rt6_info *rt, void *arg)
 {
        __u32 sernum = *(__u32 *)arg;
+       struct fib6_node *fn = rcu_dereference(rt->rt6i_node);
 
-       if (rt->rt6i_node &&
-           rt->rt6i_node->fn_sernum != sernum)
-               rt->rt6i_node->fn_sernum = sernum;
+       if (fn && fn->fn_sernum != sernum)
+               fn->fn_sernum = sernum;
 
        return 0;
 }