commit a431b4d969f617c5ef8711b6bf493199eecec759
Author: Cong Wang <xiyou.wangcong@gmail.com>
Date:   Tue May 9 14:35:10 2017 -0700

    ipv4: restore rt->fi for reference counting, try #2
    
    Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>

diff --git a/include/net/route.h b/include/net/route.h
index 2cc0e14..4335eb7 100644
--- a/include/net/route.h
+++ b/include/net/route.h
@@ -69,6 +69,7 @@ struct rtable {
 
 	struct list_head	rt_uncached;
 	struct uncached_list	*rt_uncached_list;
+	struct fib_info		*fi; /* for refcnt to shared metrics */
 };
 
 static inline bool rt_is_input_route(const struct rtable *rt)
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index da449dd..d77c453 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -1429,8 +1429,15 @@ int fib_sync_down_dev(struct net_device *dev, unsigned long event, bool force)
 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 			if (event == NETDEV_UNREGISTER &&
 			    nexthop_nh->nh_dev == dev) {
+				/* This should be fine, we are on unregister
+				 * path so synchronize_net() already waits for
+				 * existing readers. We have to release the
+				 * dev here because dst could still hold this
+				 * fib_info via rt->fi, we can't wait for GC.
+				 */
+				RCU_INIT_POINTER(nexthop_nh->nh_dev, NULL);
+				dev_put(dev);
 				dead = fi->fib_nhs;
-				break;
 			}
 #endif
 		} endfor_nexthops(fi)
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 655d9ee..f647310 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1387,6 +1387,11 @@ static void ipv4_dst_destroy(struct dst_entry *dst)
 {
 	struct rtable *rt = (struct rtable *) dst;
 
+	if (rt->fi) {
+		fib_info_put(rt->fi);
+		rt->fi = NULL;
+	}
+
 	if (!list_empty(&rt->rt_uncached)) {
 		struct uncached_list *ul = rt->rt_uncached_list;
 
@@ -1424,6 +1429,16 @@ static bool rt_cache_valid(const struct rtable *rt)
 		!rt_is_expired(rt);
 }
 
+static void rt_init_metrics(struct rtable *rt, struct fib_info *fi)
+{
+	if (fi->fib_metrics != (u32 *)dst_default_metrics) {
+		fib_info_hold(fi);
+		rt->fi = fi;
+	}
+
+	dst_init_metrics(&rt->dst, fi->fib_metrics, true);
+}
+
 static void rt_set_nexthop(struct rtable *rt, __be32 daddr,
 			   const struct fib_result *res,
 			   struct fib_nh_exception *fnhe,
@@ -1438,7 +1453,7 @@ static void rt_set_nexthop(struct rtable *rt, __be32 daddr,
 			rt->rt_gateway = nh->nh_gw;
 			rt->rt_uses_gateway = 1;
 		}
-		dst_init_metrics(&rt->dst, fi->fib_metrics, true);
+		rt_init_metrics(rt, fi);
 #ifdef CONFIG_IP_ROUTE_CLASSID
 		rt->dst.tclassid = nh->nh_tclassid;
 #endif
@@ -1490,6 +1505,7 @@ struct rtable *rt_dst_alloc(struct net_device *dev,
 		rt->rt_gateway = 0;
 		rt->rt_uses_gateway = 0;
 		rt->rt_table_id = 0;
+		rt->fi = NULL;
 		INIT_LIST_HEAD(&rt->rt_uncached);
 
 		rt->dst.output = ip_output;