[PATCH net-next] tcp: md5: only call tp->af_specific->md5_lookup() for md5 sockets

[Eric Dumazet]

RETPOLINE made calls to tp->af_specific->md5_lookup() quite expensive,
given they have no result.
We can omit the calls for sockets that have no md5 keys.

Signed-off-by: Eric Dumazet <eduma...@google.com>
---
 net/ipv4/tcp_output.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 
383cac0ff0ec059ca7dbc1a6304cc7f8183e008d..95feffb6d53f8a9eadfb15a2fffeec498d6e993a
 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -585,14 +585,15 @@ static unsigned int tcp_syn_options(struct sock *sk, 
struct sk_buff *skb,
        unsigned int remaining = MAX_TCP_OPTION_SPACE;
        struct tcp_fastopen_request *fastopen = tp->fastopen_req;
 
+       *md5 = NULL;
 #ifdef CONFIG_TCP_MD5SIG
-       *md5 = tp->af_specific->md5_lookup(sk, sk);
-       if (*md5) {
-               opts->options |= OPTION_MD5;
-               remaining -= TCPOLEN_MD5SIG_ALIGNED;
+       if (unlikely(rcu_access_pointer(tp->md5sig_info))) {
+               *md5 = tp->af_specific->md5_lookup(sk, sk);
+               if (*md5) {
+                       opts->options |= OPTION_MD5;
+                       remaining -= TCPOLEN_MD5SIG_ALIGNED;
+               }
        }
-#else
-       *md5 = NULL;
 #endif
 
        /* We always get an MSS option.  The option bytes which will be seen in
@@ -720,14 +721,15 @@ static unsigned int tcp_established_options(struct sock 
*sk, struct sk_buff *skb
 
        opts->options = 0;
 
+       *md5 = NULL;
 #ifdef CONFIG_TCP_MD5SIG
-       *md5 = tp->af_specific->md5_lookup(sk, sk);
-       if (unlikely(*md5)) {
-               opts->options |= OPTION_MD5;
-               size += TCPOLEN_MD5SIG_ALIGNED;
+       if (unlikely(rcu_access_pointer(tp->md5sig_info))) {
+               *md5 = tp->af_specific->md5_lookup(sk, sk);
+               if (*md5) {
+                       opts->options |= OPTION_MD5;
+                       size += TCPOLEN_MD5SIG_ALIGNED;
+               }
        }
-#else
-       *md5 = NULL;
 #endif
 
        if (likely(tp->rx_opt.tstamp_ok)) {
-- 
2.17.0.484.g0c8726318c-goog