net/ipv6: Move rcu locking to callers of fib6_get_cookie_safe

A later patch protects 'from' in rt6_info and this simplifies the
locking needed by it.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index f8b2218..810a37ac 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2159,9 +2159,12 @@ static struct dst_entry *rt6_dst_from_check(struct rt6_info *rt, u32 cookie)
 
 static struct dst_entry *ip6_dst_check(struct dst_entry *dst, u32 cookie)
 {
+	struct dst_entry *dst_ret;
 	struct rt6_info *rt;
 
-	rt = (struct rt6_info *) dst;
+	rt = container_of(dst, struct rt6_info, dst);
+
+	rcu_read_lock();
 
 	/* All IPV6 dsts are created with ->obsolete set to the value
 	 * DST_OBSOLETE_FORCE_CHK which forces validation calls down
@@ -2170,9 +2173,13 @@ static struct dst_entry *ip6_dst_check(struct dst_entry *dst, u32 cookie)
 
 	if (rt->rt6i_flags & RTF_PCPU ||
 	    (unlikely(!list_empty(&rt->rt6i_uncached)) && rt->from))
-		return rt6_dst_from_check(rt, cookie);
+		dst_ret = rt6_dst_from_check(rt, cookie);
 	else
-		return rt6_check(rt, cookie);
+		dst_ret = rt6_check(rt, cookie);
+
+	rcu_read_unlock();
+
+	return dst_ret;
 }
 
 static struct dst_entry *ip6_negative_advice(struct dst_entry *dst)