tcp: better retrans tracking for defer-accept

For passive TCP connections using TCP_DEFER_ACCEPT facility,
we incorrectly increment req->retrans each time timeout triggers
while no SYNACK is sent.

SYNACK are not sent for TCP_DEFER_ACCEPT that were established (for
which we received the ACK from client). Only the last SYNACK is sent
so that we can receive again an ACK from client, to move the req into
accept queue. We plan to change this later to avoid the useless
retransmit (and potential problem as this SYNACK could be lost)

TCP_INFO later gives wrong information to user, claiming imaginary
retransmits.

Decouple req->retrans field into two independent fields :

num_retrans : number of retransmit
num_timeout : number of timeouts

num_timeout is the counter that is incremented at each timeout,
regardless of actual SYNACK being sent or not, and used to
compute the exponential timeout.

Introduce inet_rtx_syn_ack() helper to increment num_retrans
only if ->rtx_syn_ack() succeeded.

Use inet_rtx_syn_ack() from tcp_check_req() to increment num_retrans
when we re-send a SYNACK in answer to a (retransmitted) SYN.
Prior to this patch, we were not counting these retransmits.

Change tcp_v[46]_rtx_synack() to increment TCP_MIB_RETRANSSEGS
only if a synack packet was successfully queued.

Reported-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Julian Anastasov <ja@ssi.bg>
Cc: Vijay Subramanian <subramanian.vijay@gmail.com>
Cc: Elliott Hughes <enh@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/request_sock.h b/include/net/request_sock.h
index b01d8dd9ee7ce99eb1bf702f00007ae456f28c16..a51dbd17c2de0cede7d134667e641477030519b0 100644 (file)
--- a/include/net/request_sock.h
+++ b/include/net/request_sock.h
@@ -49,13 +49,16 @@ struct request_sock_ops {
                                           struct request_sock *req);
 };
 
+extern int inet_rtx_syn_ack(struct sock *parent, struct request_sock *req);
+
 /* struct request_sock - mini sock to represent a connection request
  */
 struct request_sock {
        struct request_sock             *dl_next; /* Must be first member! */
        u16                             mss;
-       u8                              retrans;
-       u8                              cookie_ts; /* syncookie: encode tcpopts in timestamp */
+       u8                              num_retrans; /* number of retransmits */
+       u8                              cookie_ts:1; /* syncookie: encode tcpopts in timestamp */
+       u8                              num_timeout:7; /* number of timeouts */
        /* The following two fields can be easily recomputed I think -AK */
        u32                             window_clamp; /* window clamp at creation time */
        u32                             rcv_wnd;          /* rcv_wnd offered first time */
@@ -231,7 +234,7 @@ static inline int reqsk_queue_removed(struct request_sock_queue *queue,
 {
        struct listen_sock *lopt = queue->listen_opt;
 
-       if (req->retrans == 0)
+       if (req->num_timeout == 0)
                --lopt->qlen_young;
 
        return --lopt->qlen;
@@ -269,7 +272,8 @@ static inline void reqsk_queue_hash_req(struct request_sock_queue *queue,
        struct listen_sock *lopt = queue->listen_opt;
 
        req->expires = jiffies + timeout;
-       req->retrans = 0;
+       req->num_retrans = 0;
+       req->num_timeout = 0;
        req->sk = NULL;
        req->dl_next = lopt->syn_table[hash];
 

diff --git a/net/dccp/minisocks.c b/net/dccp/minisocks.c
index ea850ce35d4acef9ef80cf342a55cbe5e44dae56..662071b249cc627130cf90eeaa8e5b7bcd8b829d 100644 (file)
--- a/net/dccp/minisocks.c
+++ b/net/dccp/minisocks.c
@@ -174,8 +174,7 @@ struct sock *dccp_check_req(struct sock *sk, struct sk_buff *skb,
                         * To protect against Request floods, increment retrans
                         * counter (backoff, monitored by dccp_response_timer).
                         */
-                       req->retrans++;
-                       req->rsk_ops->rtx_syn_ack(sk, req, NULL);
+                       inet_rtx_syn_ack(sk, req);
                }
                /* Network Duplicate, discard packet */
                return NULL;

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index d34ce2972c8f90bca6809342aab5451c9138241e..2026542d683647b1199c02a8d634d3e0d11f7ff4 100644 (file)
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -521,21 +521,31 @@ static inline void syn_ack_recalc(struct request_sock *req, const int thresh,
                                  int *expire, int *resend)
 {
        if (!rskq_defer_accept) {
-               *expire = req->retrans >= thresh;
+               *expire = req->num_timeout >= thresh;
                *resend = 1;
                return;
        }
-       *expire = req->retrans >= thresh &&
-                 (!inet_rsk(req)->acked || req->retrans >= max_retries);
+       *expire = req->num_timeout >= thresh &&
+                 (!inet_rsk(req)->acked || req->num_timeout >= max_retries);
        /*
         * Do not resend while waiting for data after ACK,
         * start to resend on end of deferring period to give
         * last chance for data or ACK to create established socket.
         */
        *resend = !inet_rsk(req)->acked ||
-                 req->retrans >= rskq_defer_accept - 1;
+                 req->num_timeout >= rskq_defer_accept - 1;
 }
 
+int inet_rtx_syn_ack(struct sock *parent, struct request_sock *req)
+{
+       int err = req->rsk_ops->rtx_syn_ack(parent, req, NULL);
+
+       if (!err)
+               req->num_retrans++;
+       return err;
+}
+EXPORT_SYMBOL(inet_rtx_syn_ack);
+
 void inet_csk_reqsk_queue_prune(struct sock *parent,
                                const unsigned long interval,
                                const unsigned long timeout,
@@ -599,13 +609,14 @@ void inet_csk_reqsk_queue_prune(struct sock *parent,
                                req->rsk_ops->syn_ack_timeout(parent, req);
                                if (!expire &&
                                    (!resend ||
-                                    !req->rsk_ops->rtx_syn_ack(parent, req, NULL) ||
+                                    !inet_rtx_syn_ack(parent, req) ||
                                     inet_rsk(req)->acked)) {
                                        unsigned long timeo;
 
-                                       if (req->retrans++ == 0)
+                                       if (req->num_timeout++ == 0)
                                                lopt->qlen_young--;
-                                       timeo = min((timeout << req->retrans), max_rto);
+                                       timeo = min(timeout << req->num_timeout,
+                                                   max_rto);
                                        req->expires = now + timeo;
                                        reqp = &req->dl_next;
                                        continue;

diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index e5bad82d35842036b2a71bfb5c017c16b055d36b..b5e781b529aa965d412d4463baf013230ec8793f 100644 (file)
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -620,7 +620,7 @@ static int inet_diag_fill_req(struct sk_buff *skb, struct sock *sk,
        r->idiag_family = sk->sk_family;
        r->idiag_state = TCP_SYN_RECV;
        r->idiag_timer = 1;
-       r->idiag_retrans = req->retrans;
+       r->idiag_retrans = req->num_retrans;
 
        r->id.idiag_if = sk->sk_bound_dev_if;
        sock_diag_save_cookie(req, r->id.idiag_cookie);

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index ba48e799b031b3a45c902dff2f8690a8ce2627fa..b236ef04914f99585455269fe2c9a18241088461 100644 (file)
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -340,7 +340,7 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
        }
 
        req->expires    = 0UL;
-       req->retrans    = 0;
+       req->num_retrans = 0;
 
        /*
         * We need to lookup the route here to get at the correct

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 60cf836120a1a9094eadce9be6337f9c7fb16197..e95b4e508afed4a52fb03b9c7e44bdaa755bf5ae 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5991,7 +5991,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
                                 */
                                if (req) {
                                        tcp_synack_rtt_meas(sk, req);
-                                       tp->total_retrans = req->retrans;
+                                       tp->total_retrans = req->num_retrans;
 
                                        reqsk_fastopen_remove(sk, req, false);
                                } else {

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 60e2e5d3ce29360b73fa693104b8cff7ad71dbdf..e3607669064ef9d4f9a5b1ba3f6f79c6d74244ed 100644 (file)
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -877,10 +877,13 @@ static int tcp_v4_send_synack(struct sock *sk, struct dst_entry *dst,
 }
 
 static int tcp_v4_rtx_synack(struct sock *sk, struct request_sock *req,
-                             struct request_values *rvp)
+                            struct request_values *rvp)
 {
-       TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
-       return tcp_v4_send_synack(sk, NULL, req, rvp, 0, false);
+       int res = tcp_v4_send_synack(sk, NULL, req, rvp, 0, false);
+
+       if (!res)
+               TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
+       return res;
 }
 
 /*
@@ -1386,7 +1389,8 @@ static int tcp_v4_conn_req_fastopen(struct sock *sk,
        struct sock *child;
        int err;
 
-       req->retrans = 0;
+       req->num_retrans = 0;
+       req->num_timeout = 0;
        req->sk = NULL;
 
        child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);
@@ -1740,7 +1744,7 @@ struct sock *tcp_v4_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
 
        tcp_initialize_rcv_mss(newsk);
        tcp_synack_rtt_meas(newsk, req);
-       newtp->total_retrans = req->retrans;
+       newtp->total_retrans = req->num_retrans;
 
 #ifdef CONFIG_TCP_MD5SIG
        /* Copy over the MD5 key from the original socket */
@@ -2638,7 +2642,7 @@ static void get_openreq4(const struct sock *sk, const struct request_sock *req,
                0, 0, /* could print option size, but that is af dependent. */
                1,    /* timers active (only the expire timer) */
                jiffies_delta_to_clock_t(delta),
-               req->retrans,
+               req->num_timeout,
                from_kuid_munged(seq_user_ns(f), uid),
                0,  /* non standard timer */
                0, /* open_requests have no inode */

diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 27536ba16c9da7b89d5385073c7ae4d4f9e27f3c..0404b3f4c959fea5728b0c12eaf9d6db1ca331cf 100644 (file)
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -552,7 +552,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
                         * it can be estimated (approximately)
                         * from another data.
                         */
-                       tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans);
+                       tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->num_timeout);
                        paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
                }
        }
@@ -581,7 +581,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
                 * Note that even if there is new data in the SYN packet
                 * they will be thrown away too.
                 */
-               req->rsk_ops->rtx_syn_ack(sk, req, NULL);
+               inet_rtx_syn_ack(sk, req);
                return NULL;
        }
 
@@ -695,7 +695,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
        /* Got ACK for our SYNACK, so update baseline for SYNACK RTT sample. */
        if (tmp_opt.saw_tstamp && tmp_opt.rcv_tsecr)
                tcp_rsk(req)->snt_synack = tmp_opt.rcv_tsecr;
-       else if (req->retrans) /* don't take RTT sample if retrans && ~TS */
+       else if (req->num_retrans) /* don't take RTT sample if retrans && ~TS */
                tcp_rsk(req)->snt_synack = 0;
 
        /* For Fast Open no more processing is needed (sk is the
@@ -705,7 +705,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
                return sk;
 
        /* While TCP_DEFER_ACCEPT is active, drop bare ACK. */
-       if (req->retrans < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
+       if (req->num_timeout < inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
            TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
                inet_rsk(req)->acked = 1;
                NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDEFERACCEPTDROP);

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index fc04711e80c89dd0dc92ff1027efaa7324b218c3..62c69ab19fdfe414ec1cdf58682bbfc6134dd5e3 100644 (file)
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -318,7 +318,7 @@ static void tcp_fastopen_synack_timer(struct sock *sk)
        req = tcp_sk(sk)->fastopen_rsk;
        req->rsk_ops->syn_ack_timeout(sk, req);
 
-       if (req->retrans >= max_retries) {
+       if (req->num_timeout >= max_retries) {
                tcp_write_err(sk);
                return;
        }
@@ -327,10 +327,10 @@ static void tcp_fastopen_synack_timer(struct sock *sk)
         * regular retransmit because if the child socket has been accepted
         * it's not good to give up too easily.
         */
-       req->rsk_ops->rtx_syn_ack(sk, req, NULL);
-       req->retrans++;
+       inet_rtx_syn_ack(sk, req);
+       req->num_timeout++;
        inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
-                         TCP_TIMEOUT_INIT << req->retrans, TCP_RTO_MAX);
+                         TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
 }
 
 /*

diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index 182ab9a85d6cb5c0ad88e89bab6f5c0d22c380e8..40161977f7cf0b69ecc488d87427e03c88d61598 100644 (file)
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -214,7 +214,7 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb)
                ireq6->iif = inet6_iif(skb);
 
        req->expires = 0UL;
-       req->retrans = 0;
+       req->num_retrans = 0;
        ireq->ecn_ok            = ecn_ok;
        ireq->snd_wscale        = tcp_opt.snd_wscale;
        ireq->sack_ok           = tcp_opt.sack_ok;

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index bb6782e849960e9aa2ea5063fdaea3b2484d1a3f..c73d0ebde9c8eee55e35204dad161f6dd320e2ed 100644 (file)
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -495,9 +495,12 @@ static int tcp_v6_rtx_synack(struct sock *sk, struct request_sock *req,
                             struct request_values *rvp)
 {
        struct flowi6 fl6;
+       int res;
 
-       TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
-       return tcp_v6_send_synack(sk, NULL, &fl6, req, rvp, 0);
+       res = tcp_v6_send_synack(sk, NULL, &fl6, req, rvp, 0);
+       if (!res)
+               TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_RETRANSSEGS);
+       return res;
 }
 
 static void tcp_v6_reqsk_destructor(struct request_sock *req)
@@ -1364,7 +1367,7 @@ static struct sock * tcp_v6_syn_recv_sock(struct sock *sk, struct sk_buff *skb,
 
        tcp_initialize_rcv_mss(newsk);
        tcp_synack_rtt_meas(newsk, req);
-       newtp->total_retrans = req->retrans;
+       newtp->total_retrans = req->num_retrans;
 
        newinet->inet_daddr = newinet->inet_saddr = LOOPBACK4_IPV6;
        newinet->inet_rcv_saddr = LOOPBACK4_IPV6;
@@ -1866,7 +1869,7 @@ static void get_openreq6(struct seq_file *seq,
                   0,0, /* could print option size, but that is af dependent. */
                   1,   /* timers active (only the expire timer) */
                   jiffies_to_clock_t(ttd),
-                  req->retrans,
+                  req->num_timeout,
                   from_kuid_munged(seq_user_ns(seq), uid),
                   0,  /* non standard timer */
                   0, /* open_requests have no inode */