ipv4: avoid a test in ip_rt_put()

We can save a test in ip_rt_put(), considering dst_release() accepts
a NULL parameter, and dst is first element in rtable.

Add a BUILD_BUG_ON() to catch any change that could break this
assertion.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Cong Wang <amwang@redhat.com>
Acked-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 3 deletions

diff --git a/include/net/route.h b/include/net/route.h
index bc40b633a5c4..2ea40c1b5e00 100644
--- a/include/net/route.h
+++ b/include/net/route.h
@@ -198,10 +198,13 @@ struct in_ifaddr;
 extern void fib_add_ifaddr(struct in_ifaddr *);
 extern void fib_del_ifaddr(struct in_ifaddr *, struct in_ifaddr *);
 
-static inline void ip_rt_put(struct rtable * rt)
+static inline void ip_rt_put(struct rtable *rt)
 {
-        if (rt)
-                dst_release(&rt->dst);
+        /* dst_release() accepts a NULL parameter.
+         * We rely on dst being first structure in struct rtable
+         */
+        BUILD_BUG_ON(offsetof(struct rtable, dst) != 0);
+        dst_release(&rt->dst);
 }
 
 #define IPTOS_RT_MASK   (IPTOS_TOS_MASK & ~3)