net/ipv6: prefer rcu_access_pointer() over rcu_dereference()

rt6_cache_allowed_for_pmtu() checks for rt->from presence, but
it does not access the RCU protected pointer. We can use
rcu_access_pointer() and clean-up the code a bit. No functional
changes intended.
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -2277,14 +2277,8 @@ static void rt6_do_update_pmtu(struct rt6_info *rt, u32 mtu)
 
 static bool rt6_cache_allowed_for_pmtu(const struct rt6_info *rt)
 {
-	bool from_set;
-
-	rcu_read_lock();
-	from_set = !!rcu_dereference(rt->from);
-	rcu_read_unlock();
-
 	return !(rt->rt6i_flags & RTF_CACHE) &&
-		(rt->rt6i_flags & RTF_PCPU || from_set);
+		(rt->rt6i_flags & RTF_PCPU || rcu_access_pointer(rt->from));
 }
 
 static void __ip6_rt_update_pmtu(struct dst_entry *dst, const struct sock *sk,