tcp: invalidate rate samples during SACK reneging

[ Upstream commit d4761754b4fb2ef8d9a1e9d121c4bec84e1fe292 ]

Mark tcp_sock during a SACK reneging event and invalidate rate samples
while marked. Such rate samples may overestimate bw by including packets
that were SACKed before reneging.

< ack 6001 win 10000 sack 7001:38001
< ack 7001 win 0 sack 8001:38001 // Reneg detected
> seq 7001:8001 // RTO, SACK cleared.
< ack 38001 win 10000

In above example the rate sample taken after the last ack will count
7001-38001 as delivered while the actual delivery rate likely could
be much lower i.e. 7001-8001.

This patch adds a new field tcp_sock.sack_reneg and marks it when we
declare SACK reneging and entering TCP_CA_Loss, and unmarks it after
the last rate sample was taken before moving back to TCP_CA_Open. This
patch also invalidates rate samples taken while tcp_sock.is_sack_reneg
is set.

Fixes: b9f64820fb22 ("tcp: track data delivery rate for a TCP connection")
Signed-off-by: Yousuk Seung <ysseung@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Priyaranjan Jha <priyarjha@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 647532b0eb0314217260ca8b3e43992fe9c066d0..f50b717ce6448a21cced3eae6f40d93fab3b4f76 100644 (file)
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -219,7 +219,8 @@ struct tcp_sock {
        } rack;
        u16     advmss;         /* Advertised MSS                       */
        u8      rate_app_limited:1,  /* rate_{delivered,interval_us} limited? */
-               unused:7;
+               is_sack_reneg:1,    /* in recovery from loss with SACK reneg? */
+               unused:6;
        u8      nonagle     : 4,/* Disable Nagle algorithm?             */
                thin_lto    : 1,/* Use linear timeouts for thin streams */
                thin_dupack : 1,/* Fast retransmit on first dupack      */

diff --git a/include/net/tcp.h b/include/net/tcp.h
index fba4fc46871d20eaf3444ff0d703ea644c203970..caf35e062639945a6af7578e2817b67ddbae11e7 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1001,7 +1001,7 @@ void tcp_rate_skb_sent(struct sock *sk, struct sk_buff *skb);
 void tcp_rate_skb_delivered(struct sock *sk, struct sk_buff *skb,
                            struct rate_sample *rs);
 void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost,
-                 struct skb_mstamp *now, struct rate_sample *rs);
+                 bool is_sack_reneg, struct skb_mstamp *now, struct rate_sample *rs);
 void tcp_rate_check_app_limited(struct sock *sk);
 
 /* These functions determine how the current flow behaves in respect of SACK

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index dd33c785ce16f0577fe90438857d1c83f30e2cd7..05d2bde008646be4b06d2783e2f1e3ad64ad1e00 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2297,6 +2297,7 @@ int tcp_disconnect(struct sock *sk, int flags)
        tp->snd_cwnd_cnt = 0;
        tp->window_clamp = 0;
        tcp_set_ca_state(sk, TCP_CA_Open);
+       tp->is_sack_reneg = 0;
        tcp_clear_retrans(tp);
        inet_csk_delack_init(sk);
        /* Initialize rcv_mss to TCP_MIN_MSS to avoid division by 0

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 05255a2868888f8f04b32847a4e40183a60db0c9..2f107e46355cbfe3fbf9a2bcc1baafc2bb50070d 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1966,6 +1966,8 @@ void tcp_enter_loss(struct sock *sk)
                NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
                tp->sacked_out = 0;
                tp->fackets_out = 0;
+               /* Mark SACK reneging until we recover from this loss event. */
+               tp->is_sack_reneg = 1;
        }
        tcp_clear_all_retrans_hints(tp);
 
@@ -2463,6 +2465,7 @@ static bool tcp_try_undo_recovery(struct sock *sk)
                return true;
        }
        tcp_set_ca_state(sk, TCP_CA_Open);
+       tp->is_sack_reneg = 0;
        return false;
 }
 
@@ -2494,8 +2497,10 @@ static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
                        NET_INC_STATS(sock_net(sk),
                                        LINUX_MIB_TCPSPURIOUSRTOS);
                inet_csk(sk)->icsk_retransmits = 0;
-               if (frto_undo || tcp_is_sack(tp))
+               if (frto_undo || tcp_is_sack(tp)) {
                        tcp_set_ca_state(sk, TCP_CA_Open);
+                       tp->is_sack_reneg = 0;
+               }
                return true;
        }
        return false;
@@ -3589,6 +3594,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
        struct tcp_sacktag_state sack_state;
        struct rate_sample rs = { .prior_delivered = 0 };
        u32 prior_snd_una = tp->snd_una;
+       bool is_sack_reneg = tp->is_sack_reneg;
        u32 ack_seq = TCP_SKB_CB(skb)->seq;
        u32 ack = TCP_SKB_CB(skb)->ack_seq;
        bool is_dupack = false;
@@ -3711,7 +3717,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
                tcp_schedule_loss_probe(sk);
        delivered = tp->delivered - delivered;  /* freshly ACKed or SACKed */
        lost = tp->lost - lost;                 /* freshly marked lost */
-       tcp_rate_gen(sk, delivered, lost, &now, &rs);
+       tcp_rate_gen(sk, delivered, lost, is_sack_reneg, &now, &rs);
        tcp_cong_control(sk, ack, delivered, flag, &rs);
        tcp_xmit_recovery(sk, rexmit);
        return 1;

diff --git a/net/ipv4/tcp_rate.c b/net/ipv4/tcp_rate.c
index 9be1581a5a08c36f4544fbdabedd9741fb266a1e..18309f58ab8d8056fec9d732006a6f1af281a60f 100644 (file)
--- a/net/ipv4/tcp_rate.c
+++ b/net/ipv4/tcp_rate.c
@@ -106,7 +106,7 @@ void tcp_rate_skb_delivered(struct sock *sk, struct sk_buff *skb,
 
 /* Update the connection delivery information and generate a rate sample. */
 void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost,
-                 struct skb_mstamp *now, struct rate_sample *rs)
+                 bool is_sack_reneg, struct skb_mstamp *now, struct rate_sample *rs)
 {
        struct tcp_sock *tp = tcp_sk(sk);
        u32 snd_us, ack_us;
@@ -124,8 +124,12 @@ void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost,
 
        rs->acked_sacked = delivered;   /* freshly ACKed or SACKed */
        rs->losses = lost;              /* freshly marked lost */
-       /* Return an invalid sample if no timing information is available. */
-       if (!rs->prior_mstamp.v64) {
+       /* Return an invalid sample if no timing information is available or
+        * in recovery from loss with SACK reneging. Rate samples taken during
+        * a SACK reneging event may overestimate bw by including packets that
+        * were SACKed before the reneg.
+        */
+       if (!rs->prior_mstamp.v64 || is_sack_reneg) {
                rs->delivered = -1;
                rs->interval_us = -1;
                return;