[PATCH 3.16 163/294] ipv6: fix sparse warning on rt6i_node

[Ben Hutchings]

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

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

From: Wei Wang <wei...@google.com>

commit 4e587ea71bf924f7dac621f1351653bd41e446cb upstream.

Commit c5cff8561d2d adds rcu grace period before freeing fib6_node. This
generates a new sparse warning on rt->rt6i_node related code:
  net/ipv6/route.c:1394:30: error: incompatible types in comparison
  expression (different address spaces)
  ./include/net/ip6_fib.h:187:14: error: incompatible types in comparison
  expression (different address spaces)

This commit adds "__rcu" tag for rt6i_node and makes sure corresponding
rcu API is used for it.
After this fix, sparse no longer generates the above warning.

Fixes: c5cff8561d2d ("ipv6: add rcu grace period before freeing fib6_node")
Signed-off-by: Wei Wang <wei...@google.com>
Acked-by: Eric Dumazet <eduma...@google.com>
Acked-by: Martin KaFai Lau <ka...@fb.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
[bwh: Backported to 3.16: drop changes in rt6_cache_allowed_for_pmtu()]
Signed-off-by: Ben Hutchings <b...@decadent.org.uk>
---
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -96,7 +96,7 @@ struct rt6_info {
         * the same cache line.
         */
        struct fib6_table               *rt6i_table;
-       struct fib6_node                *rt6i_node;
+       struct fib6_node __rcu          *rt6i_node;
 
        struct in6_addr                 rt6i_gateway;
 
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -4737,7 +4737,7 @@ static void __ipv6_ifa_notify(int event,
                 * our DAD process, so we don't need
                 * to do it again
                 */
-               if (!(ifp->rt->rt6i_node))
+               if (!rcu_access_pointer(ifp->rt->rt6i_node))
                        ip6_ins_rt(ifp->rt);
                if (ifp->idev->cnf.forwarding)
                        addrconf_join_anycast(ifp);
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -836,7 +836,7 @@ add:
                }
                rt->dst.rt6_next = iter;
                *ins = rt;
-               rt->rt6i_node = fn;
+               rcu_assign_pointer(rt->rt6i_node, fn);
                atomic_inc(&rt->rt6i_ref);
                inet6_rt_notify(RTM_NEWROUTE, rt, info);
                info->nl_net->ipv6.rt6_stats->fib_rt_entries++;
@@ -861,7 +861,7 @@ add:
                                return err;
                }
                *ins = rt;
-               rt->rt6i_node = fn;
+               rcu_assign_pointer(rt->rt6i_node, fn);
                rt->dst.rt6_next = iter->dst.rt6_next;
                atomic_inc(&rt->rt6i_ref);
                inet6_rt_notify(RTM_NEWROUTE, rt, info);
@@ -1413,8 +1413,9 @@ static void fib6_del_route(struct fib6_n
 
 int fib6_del(struct rt6_info *rt, struct nl_info *info)
 {
+       struct fib6_node *fn = rcu_dereference_protected(rt->rt6i_node,
+                                   lockdep_is_held(&rt->rt6i_table->tb6_lock));
        struct net *net = info->nl_net;
-       struct fib6_node *fn = rt->rt6i_node;
        struct rt6_info **rtp;
 
 #if RT6_DEBUG >= 2
@@ -1593,7 +1594,9 @@ static int fib6_clean_node(struct fib6_w
                        if (res) {
 #if RT6_DEBUG >= 2
                                pr_debug("%s: del failed: rt=%p@%p err=%d\n",
-                                        __func__, rt, rt->rt6i_node, res);
+                                        __func__, rt,
+                                        rcu_access_pointer(rt->rt6i_node),
+                                        res);
 #endif
                                continue;
                        }