5.4-stable review patch. If anyone has any objections, please let me know.
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From: Jason Baron jbaron@akamai.com
[ Upstream commit 480274787d7e3458bc5a7cfbbbe07033984ad711 ]
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 Stable-dep-of: 0ec986ed7bab ("tcp: fix incorrect undo caused by DSACK of TLP retransmit") Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/tcp.h | 2 +- include/uapi/linux/tcp.h | 10 +++++++++- net/ipv4/tcp.c | 2 ++ net/ipv4/tcp_fastopen.c | 5 ++++- net/ipv4/tcp_input.c | 4 ++++ 5 files changed, 20 insertions(+), 3 deletions(-)
diff --git a/include/linux/tcp.h b/include/linux/tcp.h index 68dacc1994376..0c1255a9d3068 100644 --- a/include/linux/tcp.h +++ b/include/linux/tcp.h @@ -225,7 +225,7 @@ 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 81e697978e8b5..74af1f759cee4 100644 --- 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 a878b8b6e0b96..54399256a4380 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -2713,6 +2713,7 @@ 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);
@@ -3360,6 +3361,7 @@ 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 35088cd30840d..38752bdedee39 100644 --- a/net/ipv4/tcp_fastopen.c +++ b/net/ipv4/tcp_fastopen.c @@ -446,7 +446,10 @@ 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 702f46d2f9fea..57907fe94b238 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -5896,6 +5896,10 @@ 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;