tcp: add TCP_INFO status for failed client TFO

The TCPI_OPT_SYN_DATA bit as part of tcpi_options currently reports whether
or not data-in-SYN was ack'd on both the client and server side. We'd like
to gather more information on the client-side in the failure case in order
to indicate the reason for the failure. This can be useful for not only
debugging TFO, but also for creating TFO socket policies. For example, if
a middle box removes the TFO option or drops a data-in-SYN, we can
can detect this case, and turn off TFO for these connections saving the
extra retransmits.

The newly added tcpi_fastopen_client_fail status is 2 bits and has the
following 4 states:

1) TFO_STATUS_UNSPEC

Catch-all state which includes when TFO is disabled via black hole
detection, which is indicated via LINUX_MIB_TCPFASTOPENBLACKHOLE.

2) TFO_COOKIE_UNAVAILABLE

If TFO_CLIENT_NO_COOKIE mode is off, this state indicates that no cookie
is available in the cache.

3) TFO_DATA_NOT_ACKED

Data was sent with SYN, we received a SYN/ACK but it did not cover the data
portion. Cookie is not accepted by server because the cookie may be invalid
or the server may be overloaded.

4) TFO_SYN_RETRANSMITTED

Data was sent with SYN, we received a SYN/ACK which did not cover the data
after at least 1 additional SYN was sent (without data). It may be the case
that a middle-box is dropping data-in-SYN packets. Thus, it would be more
efficient to not use TFO on this connection to avoid extra retransmits
during connection establishment.

These new fields do not cover all the cases where TFO may fail, but other
failures, such as SYN/ACK + data being dropped, will result in the
connection not becoming established. And a connection blackhole after
session establishment shows up as a stalled connection.

Signed-off-by: Jason Baron <jbaron@akamai.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Christoph Paasch <cpaasch@apple.com>
Cc: Yuchung Cheng <ycheng@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 668e25a76d69809b5ade30f5774a4c62833b8b9b..ca6f01531e64acd689db559e10239dd21ee9209a 100644 (file)
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -223,7 +223,7 @@ struct tcp_sock {
                fastopen_connect:1, /* FASTOPEN_CONNECT sockopt */
                fastopen_no_cookie:1, /* Allow send/recv SYN+data without a cookie */
                is_sack_reneg:1,    /* in recovery from loss with SACK reneg? */
-               unused:2;
+               fastopen_client_fail:2; /* reason why fastopen failed */
        u8      nonagle     : 4,/* Disable Nagle algorithm?             */
                thin_lto    : 1,/* Use linear timeouts for thin streams */
                recvmsg_inq : 1,/* Indicate # of bytes in queue upon recvmsg */

diff --git a/include/uapi/linux/tcp.h b/include/uapi/linux/tcp.h
index 81e697978e8b5d1d2f6861dba8dd59ce669ede0d..74af1f759cee4148ba2459f92201cb92e787ee85 100644 (file)
--- a/include/uapi/linux/tcp.h
+++ b/include/uapi/linux/tcp.h
@@ -155,6 +155,14 @@ enum {
        TCP_QUEUES_NR,
 };
 
+/* why fastopen failed from client perspective */
+enum tcp_fastopen_client_fail {
+       TFO_STATUS_UNSPEC, /* catch-all */
+       TFO_COOKIE_UNAVAILABLE, /* if not in TFO_CLIENT_NO_COOKIE mode */
+       TFO_DATA_NOT_ACKED, /* SYN-ACK did not ack SYN data */
+       TFO_SYN_RETRANSMITTED, /* SYN-ACK did not ack SYN data after timeout */
+};
+
 /* for TCP_INFO socket option */
 #define TCPI_OPT_TIMESTAMPS    1
 #define TCPI_OPT_SACK          2
@@ -211,7 +219,7 @@ struct tcp_info {
        __u8    tcpi_backoff;
        __u8    tcpi_options;
        __u8    tcpi_snd_wscale : 4, tcpi_rcv_wscale : 4;
-       __u8    tcpi_delivery_rate_app_limited:1;
+       __u8    tcpi_delivery_rate_app_limited:1, tcpi_fastopen_client_fail:2;
 
        __u32   tcpi_rto;
        __u32   tcpi_ato;

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 9d69e1da93f2740523c2a8464f03319705a107a7..8fc1e8b6d4082f02f66955c63fef962571ceb083 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2666,6 +2666,7 @@ int tcp_disconnect(struct sock *sk, int flags)
        /* Clean up fastopen related fields */
        tcp_free_fastopen_req(tp);
        inet->defer_connect = 0;
+       tp->fastopen_client_fail = 0;
 
        WARN_ON(inet->inet_num && !icsk->icsk_bind_hash);
 
@@ -3305,6 +3306,7 @@ void tcp_get_info(struct sock *sk, struct tcp_info *info)
        info->tcpi_reord_seen = tp->reord_seen;
        info->tcpi_rcv_ooopack = tp->rcv_ooopack;
        info->tcpi_snd_wnd = tp->snd_wnd;
+       info->tcpi_fastopen_client_fail = tp->fastopen_client_fail;
        unlock_sock_fast(sk, slow);
 }
 EXPORT_SYMBOL_GPL(tcp_get_info);

diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index a915ade0c81803a3b190e8c0513220b4e67c35e4..19ad9586c7201135777c190e6851587acce14033 100644 (file)
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -422,7 +422,10 @@ bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
                cookie->len = -1;
                return true;
        }
-       return cookie->len > 0;
+       if (cookie->len > 0)
+               return true;
+       tcp_sk(sk)->fastopen_client_fail = TFO_COOKIE_UNAVAILABLE;
+       return false;
 }
 
 /* This function checks if we want to defer sending SYN until the first

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a2e52ad7cdab3e66a469a8ca850848988b3888d7..88b987ca9ebbbbf0f28ea4560e3731837aea7fb3 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5814,6 +5814,10 @@ static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
        tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);
 
        if (data) { /* Retransmit unacked data in SYN */
+               if (tp->total_retrans)
+                       tp->fastopen_client_fail = TFO_SYN_RETRANSMITTED;
+               else
+                       tp->fastopen_client_fail = TFO_DATA_NOT_ACKED;
                skb_rbtree_walk_from(data) {
                        if (__tcp_retransmit_skb(sk, data, 1))
                                break;